Diss. ETH No. 10832
Behavior and Fate of Detergent-derived Fluorescent Whitening Agents in Sewage Treatment
A dissertation submitted to the
SWISS FEDERAL INSTITUTE OF TECHNOLOGY
for the degree of
Doctor of Natural Sciences
presented by THOMAS POIGER Dipl. Chem. ETH born on September 11, 1964 Citizen of DObendorf {ZH)
accepted on the recommendation of Prof. Dr. R. Schwarzenbach, examiner Prof. Dr. W. Giger, co-examiner Dr. J. Kaschig, co-examiner
Zurich 1994 Meinen Eltem danke ich tor lhre Liebe und lhre Sorge um mich, ihre jahrelange Unterstutzung und den langen Atem den es braucht, bis lhr Sohn auf seinen eigenen Seinen stehen kann.
Walter Giger und Hansruedi Siegrist haben diese Doktorarbeit geleitet und dafOr gesorgt dass ich nicht bloss Wissenschaftler, sondem auch Vater sein konnte. Ihnen gilt mein besonderer Dank.
Rene Schwarzenbach danke ich tor die Obemahme des Referates, Jurgen Kaschig tor die Obemahme des zweiten Korreferates, die vielen Anregungen wahrend meiner Arbeit und die unermOdliche Sereitschaft, neue Substanzproben heranzuschaffen.
Durch ihre direkte Mitarbeit haben Tom Field, Jean-Claude Soderegger, Ivonne Oliveiras und Dia Kabioti einen grossen Anteil an dieser Arbeit geleistet. Von Jennifer Field, Stefan Haderlein, Marijan Ahel und Stefan MOiier habe ich in entscheidenden Momenten wertvolle Anregungen und ldeen bekommen, ohne die es wohl nur sehr harzig weiter gegangen ware.
Meine Kolleglnnen Alfredo Alder, Marc Suter, Eva Molnar, Rene Reiser, Heidi Tolijander, Franz-Gunther Kari, David Scheidegger, Beat Altenbach, Pilar Fernandez, Christian Schaffner und Sonja Riediker haben dafOr gesorgt, dass ich mich in der Arbeitsgruppe wohl gefOhlt habe. Ebenso meine Mit- Doktorandlnnen Seate Escher, Andre Weidenhaupt, Hans Kramer, Urs Lendenmann und Jorg Klausen. Viele der so lieblos 11 Kolleglnnen 11 genannten waren aber auch gute Freunde von denen ich mich nur sehr ungem trenne. lch hoffe, dass sich unsere Lebenswege noch oft kreuzen werden.
Den Mitarbeitem der Klaranlage Glatt, sowie der Klaranlagen Opfikon, SOlach und Niederglatt danke ich tor lhre Hilfe und ihre Bereitschaft, beinahe jeden Spezialwunsch zu erfOllen, den ich mir ausgedacht habe.
Neben Walter Giger, Hansruedi Siegrist und Rene Schwarzenbach haben sich auch Seate Escher und Hans Kramer redlich darum bemOht, diese Arbeit lesbar und verstandlich zu machen. Fur die geopferte Zeit bedanke ich mich recht herzlich.
Meiner Frau Anke mochte ich dafOr danken dass sie Ober weite Strecken ihre eigene Ausbildung zurOckgestellt hat, um sich um unsere Kinder zu kOmmern, wahrend ich meine Krafte auf die Gewinnung neuer Erkenntnisse gelenkt habe. Diese Arbeit wurde im Rahmen des Rhine Basin Programms durchgefOhrt und von diesem grosszOgig unterstOtzt.
Bedanken mochte ich mich ausserdem bei der Ciba-Geigy AG, welche alle Referenzsubstanzen kostenlos zur VerfOgung gestellt hat. Table of Contents
Zusammenfassung
Abstract
1. Synopsis 1.1. Introduction and Motivation ...... 1 1.2. Specific Objectives ...... 2 1.3. Main Results ...... 3
2. General Introduction 2.1. What are FWAs? ...... 5 2.2. Types, Production, and Usage of FWAs ...... 7 2.3. Some Important Properties of FWAs ...... 9 2.4. Occurrence and Behavior of FWAs in the Environment ...... 1 O
3. Analytical Methods 3.1. Introduction ...... 13 3.2. Experimental...... 1 5 3.2.1 . Materials ...... 15 3.2.2. Extraction of FWAs from Sludges ...... 15 3.2.3. Enrichment of FWAs from Aqueous Samples ...... 16 3.2.4. Extraction of FWA from Lake Sediments ...... 17 3.2.5. High-Performance Liquid Chromatography (HPLC) ...... 18 3.2.6. Post-Column UV-Irradiation and Fluorescence Detection ...... 1 8 3.3. Results and Discussion ...... 1 9 3.3.1. Extraction of FWA from Sludges ...... 19 3.3.2. Enrichment of FWAs from Aqueous Samples ...... 25 3.3.3. Extraction of FWAs from Lake Sediments ...... 27 3.3.4. Chromatographic Separation and Detection ...... 27
4. Partitioning of FWAs 4.1. Introduction ...... 35 4.2. Experimental ...... 36 4.2.1. Determination of Octanol-Water Partition Coefficients ...... 36 4.2.2. Adsorption-Desorption Experiments ...... 36 4.3. Results and Discussion ...... 37 ·4.3.1. Octanol-Water Partitioning ...... 37 4.3.2. Sorption to River Sediment...... 41 4.3.3. Photoisomerization and Partitioning in Sewage ...... 44
5. Occurrence and Behavior of FWAs in Sewage Treatment Plants 5.1. Sampling ...... 51 5.2. Sewage In- and Effluents ...... 51 5.3. Sludges ...... 52 5.4. Mass Flows of FWAs During Sewage Treatment ...... 54 5.4.1. General Informations on the Field Study ...... 54 5.4.2. Diurnal and Daily Variations ...... 56 5.4.3. Elimination of FWAs During Activated Sludge Treatment ...... 5 7 5.4.4. Mass Flows ...... 59 5.5. Discharge of FWAs to Surface Water and Farmland ...... 62
6. Occurrence of FWAs in Natural Waters and Lake Sediments 6.1. River Water ...... 65 6.2. Sediments ...... 68
7. Conclusions ...... 71
References ...... 73
Appendix ...... 79 Zusammenfassung
Optische Aufheller (OA) sind organisch-synthetische Verbindungen, die in Waschmitteln sowie bei der Papier- und Textilherstellung eingesetzt warden. Bedingt durch ihre physikalisch-chemischen Eigenschaften adsorbieren OA stark an Materialien wie Baumwolle, Zellulose und Polymerfasern. Absorbiertes ultraviolettes Licht wird als blaues Fluoreszenz- Licht abgestrahlt und verandert damit die Farbe des von Natur aus leicht gelblichen Materials so, dass es strahlend weiss erscheint.
Waschmittel gehoren zu den am haufigsten verwendeten Chemikalien. Die lnhaltsstoffe von Waschmitteln gelangen nach dem Gebrauch bestimmungsgemass ins Abwasser und damit in Klaranlagen. Vom Schicksal der Stoffe in der Klaranlage hangt schliesslich ab, wieviel davon in Oberflachengewasser gelangt, respektive wieviel allenfalls zusammen mit Klarschlamm auf landwirtschaftliche Flachen ausgebracht wird.
Um das Verhalten von ausgesuchten OA in Klaranlagen untersuchen zu konnen, mussten zuerst geeignete spurenanalytische Methoden entwickelt werden. Aus Klarschlamm wurden OA mittels FIOssigextraktion oder mittels Oberkritischer Fluid-Extraktion extrahiert. Die Anreicherung aus rohem und behandeltem Abwasser erfolgte mittels Festphasenextraktion. Die Extrakte aus Schlamm und Wasser wurden dann mit Hochdruck-FIOssigkeits- Chromatographie und Fluoreszenz-Detektion analysiert. Die Methode ermoglicht die Bestimmung sowohl der OA selbst, als auch der lsomeren, die bei der Bestrahlung mit Sonnenlicht entstehen.
In einer einwochigen Feldstudie wurden die MassenflOsse von OA in der kommunalen Klaranlage Zurich-Glatt (Schweiz) bestimmt. Daraus ergab sich folgendes Bild tor das Verhalten von OA in Klaranlagen:
Die OA werden in unterschiedlichem Mass aus dem Abwasser eliminiert.
Die Elimination geschieht durch Anlagerung an Klarschlamm und das
Mass der Elimination ist bestimmt durch das individuelle
Sorptionsverhalten. Biologischer Abbau der OA findet weder in der (aeroben) biologischen Stufe, noch wahrend der (anaeroben) Stabilisierung des Klarschlammes statt.
Der durchschnittliche Gehalt an OA in Klarschlammen aus Klaranlagen in der Region Zurich betragt 118 mg/kg Trocknsubstanz (Bereich 85-170 mg/kg TS).
Aus diesen Oaten lasst sich der Eintrag von OA in die Umwelt abschatzen. Danach werden jahrlich ca. 10.8 t oder 7.5 % der verbrauchten Menge an QA in Schweizer Oberflachengewasser eingetragen, wahrend etwa 12 t pro Jahr, respektive 8.3 % der verbrauchten Menge mit dem Klarschlamm auf landwirtschaftliche Flachen gelangen. Der restliche Anteil an OA wurde entweder wahrend dem Waschen von der Wasche aufgenommen (73 %) oder mit dem Klarschlamm deponiert oder verbrannt (14 %). Die Resultate dieser Arbeit sollen als Basis fUr weitere Untersuchungen an OA in natUrlichen Systemen dienen.
Abstract
Fluorescent whitening agents (FWAs) are organic-synthetic chemicals which are used in detergents and in the manufacturing of textiles and paper. Due to their physico-chemical properties FWAs adsorb on substrates such as cotton, cellulose and polymers. FWAs absorb ultraviolet light and re-emit blue fluorescent light whereby the color of the substrate is changed from yellowish to bluish white.
Detergents belong to the most heavily used chemicals. After use detergent components are discharged to sewers for treatment in sewage treatment plants. How much of the detergent chemicals is finally discharged to surface waters or farmland is dependent on their individual behavior and fate during sewage treatment. In contrast to major detergent components such as surfactants and builders, data on the fate of FWAs during sewage treatment is very scarce. For the field investigations on the behavior of selected detergent-derived FWAs during sewage treatment, suitable analytical methods had to be developed. FWAs were extracted from sewage sludge by liquid extraction or supercritical fluid extraction. Solid phase extraction using C1 a Empore disks was applied for the enrichment of FWAs from raw and treated wastewater. The extracts were analyzed by reversed-phase high-performance liquid chromatography and fluorescence detection. The method allowed the equally sensitive determination of the parent FWAs as well as the isomers which are formed upon exposure to sunlight.
The mass flows of FWAs were determined in a field study at the municipal sewage treatment plant Zurich-Glatt, Switzerland. From this data the following conclusions concerning the fate of FWAs can be derived:
(i) Elimination rates vary significantly between different FWAs
(ii) Elimination is due to adsorption to primary and activated sewage sludge and the observed elimination rates are consistent with the individual sorption behavior of FWAs as investigated in laboratory experiments.
(iii) No evidence for biodegradation of FWAs was found during the (aerobic) biological treatment of wastewater with activated sludge and during anaerobic-mesophilic digestion of raw sewage sludge.
(iv) FWAs removed during wastewater treatment are thus quantitatively recovered in anaerobically digested sewage sludge. The average residual level of FWAs in sludges from nine sewage treatment plants around Zurich, Switzerland was 118 mg/kg dry matter (range 85-170 mg/kg).
The discharge of FWAs was estimated based on the results of these field investigations. Average annual discharge of FWAs to Swiss surface water is approximately 11 t /year (7.5 % of the consumed FWAs) while FWA discharge to farmland associated with sewage sludge is 13 t/year (8.3 %). These results will be the basis for further investigations on the fate of FWAs in the environment. 1
1. SYNOPSIS
1 . 1 . Introduction and Motivation
Detergents and cleaning agents are used in very large quantities. Worldwide consumption of detergent products was estimated at 31 million tons/year in 1984 (Jakobi et al. 1987). Modern laundry detergents are complex mixtures of synthetic chemicals. The most important components, on a weight basis, are surfactants, builders, and bleaching agents. Other components are, for example, enzymes, foam regulators, dyes, and perfumes. Fluorescent whitening agents (FWAs) are added to laundry detergents in relatively small amounts of ca. 0.15 % (w/w) to improve the whiteness of textiles.
Laundry wastewaters are discharged to surface water, usually after treatment in a sewage treatment plant. Because of their direct discharge and because of the large quantities in which detergent chemicals are used, it is especially important to understand their behavior and fate in sewage treatment plants as well as in natural waters in order to minimize the risk for the aquatic environment.
Efficient removal of pollutants from wastewater reduces their potential hazard for the environment. Studies on the removal are therefore of primary importance. Several processes may be important for the removal of a chemical from wastewater, for example biodegradation or adsorption to sewage sludge. Biodegradation may lead to persistent metabolites which might even be more toxic to aquatic life than the parent compounds. An example for this is the bio-transformation of the nonionic surfactants alkylphenolpolyethoxylates (APEO) to alkylphenol and alkylphenol mono- and diethoxylates (Ahel et al. 1994).
The aqueous effluent is not the only point of discharge in a sewage treatment plant. Anaerobically digested sewage sludge is still frequently disposed of on farmland despite the ongoing debate on the usefulness of this practice (Hahn 1990, Lahl and Zeschmar-Lahl 1990). Consequently, pollution of sewage sludge with persistent chemicals should be minimized. Special 2 SYNOPSIS attention should be given to chemicals which are removed from wastewater by adsorption to sludge. If these chemicals are persistent under anaerobic conditions, the potential problem for the environment may be simply transfered from water to land.
The environmental behavior of heavily used detergent components such as the surfactant linear alkybenzene sulfonate (LAS) or the complexing agent nitrilotriacetate (NTA) was investigated thoroughly (Bernhardt 1984, Painter 1992). In contrast to this, data on the environmental behavior of FWAs is very limited (for a recent review see Kramer 1992). According to present knowledge, FWAs are not readily biodegradable. During sewage treatment, FWAs are partly removed from wastewater by adsorption to sewage sludge. Although adsorption is believed to be the most important process for FWA removal, no investigations are reported on the further fate of FWAs during anaerobic sludge treatment. Correspondingly, it is impossible to quantify the amount of FWAs discharged to agricultural land associated with sewage sludge. Although FWAs were sporadically determined in effluents of sewage treatment plants, no quantitative information of FWA discharge to surface water is available. This lack of knowledge is best illustrated by the fact that FWA discharge was estimated recently by a worst-case assumption (Ciba- Geigy AG, cited by Kramer 1992).
1.2. Specific Objectives
The major objective of this study was to determine the behavior and fate of detergent-derived FWAs during sewage treatment. For this purpose, compound-specific analytical procedures had to be developed that allow the quantitative determination FWAs in sewage and sludges. Based on these analytical methods, mass flows of FWAs should be determined in a full-scale mechanical-biological sewage treatment plant. In order to achieve a better understanding of the processes involved in the fate of FWAs during sewage treatment (e.g. adsorbtion to sludge, biodegradation and others), the field studies should be supported by laboratory investigations.
Based on the results of the mass flow studies, the discharge of FWAs to surface water and to agricultural land should be estimated and compared to residual levels of FWAs determined in natural waters and sediments. The 3 results of this study should finally provide a basis for the assessment of the environmental acceptability of FWAs.
1.3. Main Results
The analytical methods that were developed for this study based on reversed-phase high-performance liquid chromatography. Post-column irradiation in combination with fluorescence detection provided an excellent tool for the sensitive and selective determination of the (highly fluorescent) parent compounds as well as the (non-fluorescent) isomers which are formed in solution upon short exposure to sunlight. FWAs were extracted from freeze- dried sewage sludges using either liquid extraction (LE) or supercritical fluid extraction (SFE). Recovery of the detergent-derived FWAs 2-4 from sewage sludges was 77-81 % and 84-93 % for SFE and LE, respectively. Enrichment of FWAs from water samples was done by solid phase extraction (SPE) using
C18-Empore disks. Sample pretreatment was minimized by the use of disks instead of cartridges, because of simultaneous filtration and enrichment even of highly particle-loaded samples. Recovery of FWAs from aqueous samples ranged from 76-96 %.
The mass flows of three stilbene fluorescent whitening agents (FWAs) typically added to laundry detergents in Switzerland were determined in field investigations at a municipal sewage treatment plant in Zurich, Switzerland. From this data the following conclusions concerning the behavior and fate of FWAs in a mechanichical sewage treatment plant can be drawn:
(i) Elimination of FWAs from wastewater occurs during both mechanical and biological treatment.
(ii) Overall removal rates of 53-98 % were observed depending on FWA. The average residual level of FWAs in effluents of several sewage treatment plants was 9.6 µg/L.
(iii) Elimination is due to adsorption to primary and activated sewage sludge and the observed elimination rates are consistent with the individual sorption behavior of FWAs as investigated in laboratory experiments. 4 SYNOPSIS
(iv) No evidence for biodegradation of FWAs was found during the (aerobic) biological treatment of wastewater with activated sludge and during anaerobic-mesophilic digestion of raw sewage sludge.
(v) FWAs removed during wastewater treatment are thus quantitatively recovered in anaerobically digested sewage sludge. The average residual level of FWAs in sludges from nine sewage treatment plants around Zurich, Switzerland was 118 mg/kg.
From the residual levels of FWAs in sewage sludges the average annual FWA discharge on Swiss farmland was estimated at 13 tons/year. Given current Swiss sludge disposal legislation, a maximum of 20 mg m·2 y·1 FWAs associated with sludge may be applied to farmland. Estimated discharge of detergent-derived FWAs to surface water is 11 tons/year. The concentrations of FWAs determined in river water from 6 different rivers in Switzerland ranged from 70-1000 ng/L. 5
2. GENERAL INTRODUCTION
2.1. What are FWAs ?
White, the "colorless color", is regarded as symbol of purity and cleanliness. The imitation of the perfect white found in fresh snow or in white flowers has long been a challenge to human beings. However, many inventions were necessary before man made goods could be produced in the brilliant white that has almost become normal in modern life (Anliker 1975).
Most of the industrial white products, such as textiles, paper, and plastics, exhibit an undesirable yellowish cast, caused by colored impurities. These impurities absorb light in the UV and blue visible spectral range of daylight, thus reducing the intensity and the spectrum of the reflected light relative to the incident light. Some of the impurities can be removed by bleaching with oxidants, such as sodium hypochlorite or hydrogen peroxide. However, the extent to which bleaching can improve the whiteness of a substrate is limited, because excessive bleaching also leads to damage of the substrate itself (Anliker 1975).
Fluorescent whitening agents (FWAs), also called optical brighteners, are synthetic organic chemicals closely related to dyes. Applied to a substrate, FWAs absorb ultraviolet (UV) light and reemit most of the absorbed energy as blue fluorescent light. Figure 2.1 illustrates, how the reflectance spectrum of yellowish white substrate (A) is modified by the blue fluorescence of a FWA (8), yielding the reflectance spectrum (C).
Most of the white materials in use nowadays contain FWAs. As the FWAs used in textiles are subject to degradation by sunlight and are also continuously washed out during laudering, the whitening effect is gradually lost (Bode 1975, Leaver 1977). FWAs therefore, are also added to laundry detergents in small amounts of 0.1-0.3 % (w/w), to compensate for this loss. During the washing process these FWAs partly adsorb to fabrics. Between 5 and 80% of the FWAs, however, remain in the washing liquor, depending on the type of FWA, the washing temperature, the composition of the detergent, 6 GENERAL INTRODUCTION and the type of fabric (Bode 1975). Residual FWAs in laundry wastewater are discharged to sewers for treatment in municipal wastewater treatment plants.
reflectance(%) 140 ultraviolet light visible light c 120
100
80
60
B
300 400 500 nm 600 wavelength A.
Figure 2. 1: Reflectance spectra of a white substrate after bleaching (AJ and after treatment with FWA (CJ, and the fluorescence spectrum of the FWA (BJ (Anders 1975).
In 1971, Jensen and Petterson reported high levels of a hydrophobic FWA in fish (Jensen and Pettersson 1971 ). The levels of the FWA in fish liver were 100-300 times higher than in the corresponding river water, indicating a certain degree of bio-accumulation. These findings attracted the attention of scientists and the public in general, who were already alerted by the controversy over the bio-accumulation of DDT, PCBs, and the heavy metals mercury and cadmium, and foresaw another potential problem for the environment (Zinkernagel 1975).
The sudden public concern induced the manufacturers to publish data on the environmental behavior of FWAs in 1975 (Anliker and MOiier 1975, Ganz 7 et al. 1975, Ganz et al. 1975). The reported data on toxicology, biodegradation, photodegradation and bioaccumulation led to the general concusion: "FWAs no hazard" (Zinkernagel 1975). Since then, only few investigations on the environmental behavior of FWAs were reported in the literature.
2.2. Types, Production, and Usage of FWAs
Numerous FWAs for all types of substrates (cellulose, wool, and synthetic polymers) and application forms (batch or continuous processes, simultaneous bleaching etc.) are available, including anionic, neutral, and cationic compounds. For a complete and comprehensive overview on the principle of whitening, the types of FWAs in use their synthesis and application see Ullmanns (Siegrist et al. 1991 ).
Only very few of the available FWAs are used as detergent additives. Detergents sold in Switzerland, almost exclusively contain FWAs 2 and 3 (figure 2.2). FWA 4 was added to detergents used in large-scale laundry facilities until recently. FWA 6 was used as detergent additive before other FWAs (2-4) were developed and are of little importance in modern detergents. FWA 1 and 7 are used in textile and paper whitening applications. FWA 5 is a research compound and was used as an internal standard, because it does not occur in environmental samples (Ciba-Geigy AG 1992).
The most recent estimate of the worldwide production of FWAs is given by Kramer (Kramer 1992), based on informations from Ciba-Geigy AG, one of the main manufacturers of FWAs. According to Kramer, the. worldwide production of FWAs 2 and 3 in 1989 was 3000 and 14 000 tons/year, respectively. On average, Swiss household laundry detergents contain approximately 0.15 % (w/w) FWAs 2 or 3 in a ratio of 1 :3. Total FWA consumption in Switzerland was estimated at 144 t/year in 1992 (Ciba-Geigy AG 1992). 8 GENERAL INTRODUCTION
Rz-ONH Gn.s - rN - """ ~ N -N~NH ~ /) ~ N--{ SO~ N~ "N Rr N=(NH-0-R;, Triazinylaminostilbenes R1 R2
FWA1 - N(CH2CHpH)2 H I\ FWA3 -N 0 H \_/
FWA6 -Ntt-Q H
FWA7 - N(CH2CHPHh -S~
R2 R1 Ra Ra
R1 R2 Distyrylbiphenyls R1 R2 Ra
FWA2 -$03e H H
FWA4 H -S~ Cl
FWA5 Bis(benzo[b]furan-2-yl)biphenyls
Figure 2.2: Structures of the FWAs included In this study. 9
2.3. Some Important Properties of FWAs
Stilbene-based FWAs are light-sensitive chemicals, especially when present in dilute solution. Exposure of dissolved FWAs to sunlight causes reversible (E)-(Z) (or trans-cis) isomerization of the stilbene moiety, as illustrated in Figure 2.3. FWAs containing one stilbene moiety (e.g. FWAs 1, 3, 6 and 7) occur in two isomeric forms, herein called (E)-FWA x and {Z)-FWA x. With two stilbene moieties present in FWAs (2 and 4) three isomeric forms are possible, which will be called {E,E)-, (E,Z)- and (Z,Z)-FWA x. FWAs are produced and added to laundry detergents in their fluorescent {E)- or {E,E)- isomeric forms. Photoisomerization to the corresponding (Z)- or (E,Z)- and (Z,Z)-isomers leads to a complete loss of fluorescence {Smit and Ghiggino 1987). The constant ratio of {E)- and (Z)-isomers in solution, the so-called photostationary state, is achieved within a few minutes of exposure to direct sunlight. Because different isomers have different UV spectra {Figure 2.4), the isomer ratio is dependent on the spectrum of the irradiating light.
R
H H hv
A
(E) - Stilbene (Z) • Stilbene
Figure 2.3: (E)-(Z) isomerizatlon of stilbene-type FWAs
FWAs in their {E)-form absorb UV light with an absorbance maximum in the range of 340-360 nm with a molar extinction coefficient of over 50 000 M-1cm·1. The absorbed light is partly re-emitted as blue fluorescence with a maximum at a wavelength of ca. 430 nm. The quantum yield, e.g. the ratio of emitted to absorbed photons, is generally very high {0.2-0.9) {Smit and Ghiggino 1987). Figure 2.4 shows the absorbance spectra of (E)- and (Z)-FWA 3 and the fluorescence spectrum of (E)-FWA 3.
As FWAs strongly adsorb to cellulosic surfaces, adsorption to sewage sludge, as well as natural particulate matter, is likely to occur. Disulfonated 1 0 GENERAL INTRODUCTION
FWAs are moderately, tetra- and hexasulfonates are well water-soluble. All FWAs studied here are non-volatile.
c I '\ I \ I GI u c GI u UI f! 0 :J \ ;:: I GI -u I c ca \ -e \ .c51 \ ca \ \ ' ' - 300 400 500
wavelength (nm)
Figure 2.4: UV absorption spectra of (E)-FWA 3 (A) and (Z)-FWA 3 (8), and fluorescence spectrum of (E)-FWA 3 (CJ.
2.4. Occurrence and Behavior of FWAs in the Environment
FWAs may enter the aquatic environment via several different paths:
(i) as a component of production and application wastewater, (ii) released from textiles during washing, or (iii) as residual detergent FWAs in laundry washing liquor.
How much of the FWAs reach the surface waters is determined by the fraction of households connected to STPs and the efficiency of the removal of FWAs during the sewage treatment process. Investigations on the removal of FWAs were done in several sewage treatment plants in the United States (Ganz et al. 1975). Depending on the design of the STPs, removal rates of 55- 1 1
99 %, based on the influent concentrations, were reported. Levels of FWAs were also determined in primary, activated, and digested sludges. However, all data were based on grab samples rather than composite samples and the sampling concept obviously did not allow an interpretation of the data in terms of mass flows. Therefore no clear anwer could be given on whether FWAs were biodegraded during sewage treatment and what fraction of the FWAs was transfered to sludge.
The biological degradation of several FWAs has been tested in laboratory experiments. No evidence of biodegradability was found in tests whereby the oxygen demand of bacterial cultures fed with FWAs was measured over a period of 5 days (BOD5) (Zinkernagel 1975, Dojlido 1979). In cultures with activated sludge, two FWAs were shown to be slowly biodegraded after an adaptation period of 10-15 days (Guglielmetti 1975). This relatively long adaptation period may be the reason why FWAs were not biodegraded in tests using laboratory-scale activated sludge treatment facilities. In these tests FWAs were partially removed from wastewater by adsorption to sludge (Dojlido 1979).
In contrast to their resistance towards biodegradation, FWAs are readily degraded photochemically (Guglielmetti 1975, Dojlido 1979, lkuno et al. 1985). In natural water systems photochemical degradation, therefore, is expected to be one of the major removal processes of FWAs, along with adsorption and sedimentation.
Levels of FWAs in river water have been reported by several authors. Anders analyzed samples from nine European rivers in 1973, but only in one sample the level was above the detection limit (10 ng/L) (Anders 1975). The situation in Japan seems to be different. Between 1979 and 1988, FWA levels of a few ng/L up to 45 µg/L were reported (Abe and Yoshimi 1979, Uchiyama 1979, Kato et al. 1982, Komaki and Yabe 1982, Abe et al. 1983, Hirayama et al. 1983, Tsuji et al. 1988). Analysis of river sediments yielded FWA concentrations of 0.1-10.7 and 0.1-3.4 mg/kg dry matter FWAs 2 and 3, respectively (Abe et al. 1983). FWA levels in rivers in the United States of 16 ng/L above and 1.5 µg/L below sewage outfalls were reported in 1977 (Burg et al. 1977). 1 2 GENERAL INTRODUCTION
2.5. Goals of this Work
The objectives of this study can be divided into the following categories:
Analytical methods
Compound-specific analytical procedures should be developed that allow the quantitative determination FWAs in sewage and sludges as well as in natural water. In contrast to earlier work, these methods should allow the determination of all, not only the fluorescent isomers of FWAs which are used in laundry detergents.
Behavior and fate of FWAs during Sewage Treatment
The mass flows of FWAs should be determined in a field study at a real- scale mechanical-biological sewage treatment plant. The processes which are involved in the fate of FWAs during sewage treatment should be identified and characterized in laboratory investigations
Discharge of FWAs to the environment
Based on the results of the field studies (e.g. rates of removal of FWAs from wastewater, residual levels of FWAs in sludge and effluents from sewage treatment plants) the discharge of FWAs to surface water and to agricultural land in Switzerland should be estimated to provide a basis for further research and the assessment of the ecological acceptability of FWAs.
Occurrence of FWAs in natural water systems
No data is available on the occurrence of FWAs in Swiss rivers, data for European rivers pre-dates 1975 (Anders 1975) and most data was below the detection limit of the analytical methods used at that time. The estimated FWA discharge should therefore be compared to residual FWA levels in river water and sediment. 13
3. ANAL VTICAL METHODS
3.1. Introduction
Most of the available analytical procedures focus on the identification and determination of a large variety of structurally related FWAs in detergents, textiles, and paper. All steps, including extraction, preconcentration, and chromatographic separation, are performed in rooms equipped with special light sources, emitting no UV or blue light. Under these conditions, no isomerization of stilbene FWAs occurs and thus only the fluorescent (E)- and (E,E)-isomers have to be determined.
Numerous methods based on thin layer chromatography (TLC) were reported in the literature (Theidel and Schmitz 1967, Werthmann and Borowski 1974, Lehmann and Becker-Klose 1976, Bloching et al. 1979, Lepri et al. 1985). Quantitative determination was done by fluorimetric or absorbance detection of the spots on the TLC plates (Anders 1975). Theidel developed a method combining several paper chromatographic and TLC systems (Theidel and Schmitz 1967, Theidel 1975). Newer analytical methods for the determination of FWAs in detergents usually base on high- performance liguid chromatography (HPLC) with fluorescence detection (Kirkpatrick 1977, McPherson and Omelczenko 1980, Nakae et al. 1980, Tsuji et al. 1981, Micali et al. 1984, Jasperse and Steiger 1992). In all of the above mentioned methods, instrumental sensitivity is rarely ever a problem because of the high FWA concentrations in the samples and because of their intense fluorescence.
In environmental analyses the situation is completely different. Typically, only few different FWAs are present in environmental samples in relatively low concentrations. As these FWAs were exposed to sunlight, not only the fluorescent (E)- and (E,E)-isomers but also their photoisomerization products, the (Z)- and (E,Z)-isomers are present in environmental systems. Therefore, in environmental analysis all isomers and not only the fluorescent isomers of FWAs must be analyzed in order to obtain a complete picture Ganz and co- workers (1975 a) used TLC for the determination of FWAs in sewage and 1 4 ANALYTICAL METHODS sludge. Several Japanese autors regularly published work on the determination of FWAs in river water, using ion-pair liquid-liquid extraction or solid phase extraction for preconcentration and TLC or HPLC for separation (Abe and Yoshimi 1979, Uchiyama 1979, Katayama et al. 1982, Kato et al. 1982, Abe et al. 1983, Hirayama et al. 1983, Tsuji et al. 1988). Komaki and Yabe reported the direct determination of FWAs in river water using fluorescence spectroscopy (Komaki and Yabe 1982).
Until now the problem of the determination of non-fluorescent FWA isomers has not been adequately solved. While fluorescence detection was used for the determination of (E)-isomers of FWAs in environmental matrices, the non-fluorescent (Z)-isomers had to be determined by absorption detection (Anders 1975, Abe et al. 1983, Tsuji et al. 1988). This change of detection method was accompanied by a loss in both selectivity and sensitivity, and increased the need for more effective preconcentration and clean-up steps. In the method which is presented here, this problem has been solved by the use of post-column UV irradiation combined with fluorescence detection. By this combination, all isomers of an FWA can be detected equally senstive by fluorescence detection.
Solid phase extraction (SPE) was frequently applied for the enrichment of FWAs from river water samples (Abe et al. 1983, Tsuji et al. 1988). These methods, however, can not directly be used for the analysis of raw sewage and primary effluent samples, as these samples contain a large amount of suspended particulate matter which rapidly blocks the pores of the SPE material. Filtration of samples prior to SPE is therefore required in combination with conventional SPE cartridges. Filtration of sewage samples, however, is time-consuming and produces two kinds of samples, the filtrate and a particle- loaded filter, which have to be processed separately. In the method presented here, sample pretreatment has been minimized by using membrane C18 SPE disks for simultaneous filtration and solid phase extraction. 1 5
3.2. Experimental
3.2.1. Materials
Reference compounds of (E)- and (E,E)-FWAs 1-7 (technical grade with 30-90 % active substance content) as well as (E,Z)- and (Z,Z)-2, (Z)-FWA 3, and FWA 5, all as sodium salts, were provided by Ciba-Geigy AG. FWA 5 was used as an internal standard for this project, because it does not occur in the environment and does not interfere with the chromatographic separation of the other FWAs.
Reagent grade extraction solvents, N,N-Dimethyl formamid (DMF), ammonium acetate and tetrabutyl-ammonium hydrogen sulfate (TBA), were purchased from Fluka AG (Buchs, Switzerland). Solvents for HPLC were purchased from Riedel-de Haen (Seelze, Germany) and were used as received. The C18 bonded-phase Empore disks were a gift from the 3M Co. (Minneapolis MN).
3.2.2. Extraction of FWAs from Sludges
Liquid Extraction (LE)
Samples of 200-500 mg dry sludge were mixed with 3 x 1O ml of 0.03 M TBA in methanol in screw-cap test tubes and briefly shaken, followed by sonication for 30 min. The sample was centrifuged at 1500 rpm for 5 min and decanted into a 50 ml measuring flask. The extraction was repeated twice The extracts were combined and diluted to volume (50 ml) with 0.1 M ammonium acetate in water. An injection volume of up to 100 µL was used for HPLC analysis of the LE sewage sludge extracts.
For comparison of extraction efficiencies, also extraction solvents other than TBA in methanol were used. These extracts were evaporated to dryness, redissolved in 0.1 M TBA in DMF/water (1:1) and spiked with 25 µL of 0.1 µg/µL FWA 5 in methanol for HPLC analysis. 1 6 ANALYTICAL METHODS
Supercritical Fluid Extraction (SFE)
All extractions were performed using an ISCO 2600 pump and SFX-21 O extractor {Lincoln, NE) and SFC grade C02 (Scott Specialty Gases, Plumsteadville, PA). Fused-silica capillaries (30-32 µm i.d. x 10 cm, Polymicro Technologies, Phoenix, AZ) were connected to the extractor outlet to restrict dynamic flow rates to 0.7-0.9 mUmin measured as liquid C02 flow at the pump. Extracts were collected in 3-4 ml of chloroform.
Unless otherwise noted, the following procedure was used to extract FWAs from sewage sludge. A glass fiber filter with a nominal pore size of 1µm (Gelman Sciences, Ann Arbor, Ml) was first placed over the outlet frit of a 2.5 ml extraction cell. Samples of 100 mg dry sludge were then weighed directly into the cell. Approximately 1 ml of 0.25 M TBA in methanol was added directly to the cell. The cell was then assembled and placed into the extraction unit operated at 80 °C. With the exit valve closed, the cell was pressurized to 400 atm for a 20 min static extraction. The exit valve was then opened and a 5 min dynamic extraction was performed.
Anaerobically-digested sludge samples required only one extraction. As FWAs were less easily extracted from activated sludge and raw sludge the extraction procedure was repeated one more time, after allowing the cell to cool. The extracts were combined and concentrated to ca. 1 ml under a nitrogen stream. The extracts were spiked with 25 µl of 0. 1 µg/µl FWA 5 in methanol and transfered to autosampler vials. Injection volumes of 5-1 O µl were used to analyze the SFE sludge extracts by HPlC .
. 3.2.3. Enrichment of FWAs from Aqueous Samples
Polypropylene filter assemblies (Millipore, Bedford, MA) attached to a
vacuum manifold (Supelco, Bellafonte, PA) were used to support the C1a Empore disks. The disks were preconditioned using 5 ml methanol followed by 20 ml of distilled water and were not allowed to go to dryness prior to sample application. 17
Water samples were homogenized for 4 min using a stainless steel auger. Except where noted, water samples were not filtered prior to extraction so that the total concentration of FWAs could be determined. Samples of homogenized raw sewage (10 ml), primary effluent (10 ml), secondary effluent (50 ml), and river water (200 ml) were passed through a 25 mm C18 disk by vacuum. Air was pulled through the disk for 2 min after the enrichment to remove excess water in the disk.
Elution of the disk was performed by adding 1 ml of 0.05 M TBA in methanol to the disk and allowing it to soak for 2 min after which the vacuum was applied. The procedure was repeated five additional times and all six extracts were collected in a single vial. The solvent was evaporated to dryness under a stream of nitrogen and mild heating (T=50 °C). Approximately 1 ml of a mixture of water and DMF ( 1: 1) was added back and spiked with 10 µL of the internal standard. Injection volumes of 25-100 µL were used to analyze the SPE extracts by HPLC.
To determine the fraction of FWAs in particulate and dissolved phases, a glass fiber filter with a nominal pore size of 0.45 µm (Gelman Sciences, Ann Arbor, Ml) was stacked on top of a C18 disk. Water samples were extracted through the filter and disk as described above. After sample application, disk and filter were separated and processed individually according to the procedures outlined above. The particulate bound FWA fraction was operationally defined as the fraction of FWAs eluted from the glass fiber filter. The dissolved FWA fraction was operationally defined as the fraction of FWAs eluted from the C1 8 disk.
To test the possibility of FWA breakthrough during sample isolation, experiments were conducted by stacking two C1s disks together. Breakthrough was investigated with primary effluent (20 ml), secondary effluent (50 ml), and river water (200 ml). After sample concentration, the two disks were separated and processed individually.
3.2.4. Extraction of FWA from Lake Sediments
Samples of 1 g dry sediment were extracted subsequently 3 times with methanol containing 0.03 M TBA according to the procedure for sewage 1 8 ANALYTICAL METHODS sludges (LE). The methanolic extracts were evaporated to dryness under vacuum and re-dissolved in 2.5 ml of a mixture of water and DMF (1 :1). After addition of 10 µL of internal standard (1 µgll FWA 5 in methanol) the extract was transfered to autosampler vials. Injection volumes of 100 µL were used to analyze the sediment extracts by HPLC.
3.2.5. High-Performance Liquid Chromatography (HPLC)
All analyses were performed using a Hewlett-Packard model 1090L Series II HPLC equipped with an autosampler, a ternary solvent delivery system and a heated column compartment. Two different reversed-pase systems were used including:
(i) A micro-bore column (Hypersil ODS, 5 µm, 200 x 2.1 mm i. d. with pre- column, Hewlett Packard) operated at 80°C with an eluent flow rate of 1mUmin. The mobile phase solvents were methanol (eluent A) and 0.1 M aqueous ammonium acetate buffer of pH 6.5 (eluent 8). A 15 min linear gradient from 35% A/65% 8 to 70% A/30% 8 was used for analysis. Initial eluent composition was re-established by a 2 min linear gradient, followed by an equilibration time of 3 min.
{ii) A narrow-bore column (Hypersil ODS, 5 µm, 200 x 4.6 mm i. d. with pre- column, Hewlett Packard) operated at room temperature with an eluent flow rate of 1mllmin. The mobile phase solvents were a 1: 1 mixture of acetonitrile and methanol {eluent A) and 0.1 M aqueous ammonium acetate buffer of pH 6.5 {eluent 8). A 25 min linear gradient from 30% A/70% 8 to 70% A/30% 8 was used for analysis. Initial eluent composition was re-established by a 2 min linear gradient, followed by an equilibration time of 5 min.
3.2.6. Post-Column UV-Irradiation and Fluorescence Detection
The outlet of the HPLC column was connected to a post-column UV irradiation apparatus {8eam8oost™, ict AG, Basel, Switzerland) equipped with a UV lamp with a maximum intensity at 254 nm and a 0.3 mm i. d. x 1m Teflon capillary for an irradiation time of 5 seconds. This irradiation time was 19 sufficient to achieve photostationary conditions {see Chapter 4.3.3). The irradiated eluate was then monitored with a Hewlett Packard model 1046A fluorescence detector at an excitation wavelength of 350 nm and an emission wavelength of 430 nm.
Standard solutions of FWAs were prepared either in DMF/water 1:1 (LE and solid phase extracts) or in chloroform containing 0.3 M TBA {SFE extracts). Due to the limited solubility of FWAs, the maximum concentration of FWAs tor standards was 0.5 mg/mL in DMF/water { 1: 1) and 0.25 mg/mL in chloroform. Standard solutions of {E)- and {E,E)-FWAs were exposed to direct sunlight for 1 min to allow for a partial isomerization of FWAs and to get mixtures of (E)- or {E,E)- and (Z)- or {E,Z)-isomers, respectively. Concentration series for external calibration curves were prepared by dilution of the standard solutions in the appropriate solvent (0.01 M TBA in methanol/0.1 M aqueous ammonium acetate {3:2) for LE extracts, 0.3 M TBA in chloroform for SFE extracts and 0.3 M TBA in DMF/water (1 :1) for solid phase extracts).
3.3. Results and Discussion
3. 3. 1 . Extraction of FWA from Sludges
Liquid Extraction (LE):
Several methods tor the extraction of FWAs from textiles and paper (Theidel and Schmitz 1967, Werthmann and Borowski 1974, Lehmann and Becker-Klose 1976), sewage sludge and soil samples (Ganz et al. 1975) have been reported in the literature. The most favored extractants were mixtures of pyridine/water (1 :1 ), acetone/water/ammonia {90:10:5) and ethylene glycol monomethylester/ammonia (7:3). Although the above extractants do extract FWAs quantitatively, as was confirmed in preliminary experiments (Table 3.1 ), the combination with HPLC analysis requires evaporation of these solvents and re-dissolution in solvents suitable for HPLC determinations.
On the other hand, solvents like methanol, ethanol, acetone or chloroform do not extract FWAs efficiently. In initial experiments using 2 0 ANALYTICAL METHODS methanol or acetone/water (9:1) only 20-40% of the total extractable FWAs were extracted in a single step. Addition of bases like ammonium hydroxide or sodium hydroxide, or ion-pairing agents like tetraalkyl ammonium salts to methanol and acetone/water improved the extraction efficiency, Table 3.1. Bases are believed to promote extraction by increasing the negative surface charge of the sludge matrix. With ion-pairing reagents, FWAs form strong lipophilic ion-pairs that partition more readily into organic solvents.
Table 3. 1: Comparison of the extraction efficiencies of different solvents and additives on the extraction of FWAs from anaerobically digested sewage sludge. Additives: tetrabutylammonium hydrogensulfate (TBA), sodium hydroxide (NaOH), aqueous ammonia solution (NH3, 25 %), ammonium acetate (NH4Ac), N,N'-dimetyl forrnamide (DMF).
Extractant Additive Extraction yield relative to highest yield(%)
PNA2 PNA3 PNA4
Pyridine:water (1 :1) 100 100 100
Ethylene glycol:NH3 (7:3) - 89 91 83
DMF:water (1 :1) 66 63 60
Chloroform 1 1 0 TBA (0.03 M) 19 56 19 TBA (0.3 M) 13 42 13
Acetone:water (9:1) 25 38 19 NaOH (0.01 M) 39 46 29 NH3 (5 %) 82 81 70 NH4Ac (0.1 M) 67 73 45 TBA (0.03 M) 78 84 78
Methanol 28 22 20 NaOH (0.01 M) 60 62 50 NH3(5%) 72 75 62 NH4Ac (0.1 M) 44 35 29 TBA (0.03 M) 64 76 60 21
The influence of increasing TBA concentration on the extraction efficiency was investigated using methanol as a solvent, (Figure 3.1 ). A TBA concentration of 0.03 M was selected for subsequent experiments since no further increase in extraction efficiency was observed at higher concentrations. The use of TBA in methanol is less laborious as only dilution prior to HPLC analysis is necessary, rather than the evaporation and re-dissolution required when using basic extractants.
100
0 80 ::!! -0 --0-- FWA1 .5 "C "C ·;;."ii 60 "ii e FWA2 ·->- ....tn G1 c: .s::. .9 C> (J 40 • FWA3 -e :.2 x -G1 --O--FWA4 20
0 0 0.02 0.04 0.06
[TBA] in methanol (mol/I)
Figure 3.1: Effect of TBA concentration on the extraction efficiency of FWAs from sewage sludge (liquid extraction with methanol).
Supercritical Fluid Extraction (SFE):
The advantages of SFE over conventional liquid extraction methods include reduction in analysis time, solvent expenditure, and disposal costs. Recently, SFE has been extended to the extraction of organic acids by introducing ion-pair reagents (Field et al. 1992). Ion- pairing reagents with SFE have been shown to quantitatively extract organic sulfonates including linear alkylbenzene sulfonates (LAS) and secondary alkane sulfonates (SAS} from sewage sludges. While sulfonic acids are not intrinsically soluble in supercritical C02, ion- pairing reagents, such as TBA, interact with the sulfonic acid functional groups to form ion-pairs that are soluble in supercritical fluids. Ion-pair 2 2 ANALYTICAL METHODS reagents also potentially interact with matrix sites to promote the extraction of organic acids.
Initial conditions for evaluating the extraction efficiency of FWAs from sewage sludge, described by Field et al. (Field et al. 1992) , include an extraction temperature of 80 °C and 400 atm C02 with a 5 min static and a 1 O min dynamic extraction period. For the purpose of determining extraction profiles and optimal extraction conditions, samples were extracted consecutively 3 times and the sum of extracted FWAs was defined as 100 %. Under the initial conditions, only 60 to 80 % of totally extractable FWAs were obtained in the first extraction step. By changing the extraction temperature from 80 to 100 °c and extending the static extraction time from 5 to 20 min, FWA recovery was increased to approximately 85-95 % of totally extractable FWAs.
The effect of TBA concentration in the methanol modifier is illustrated in Figure 3.2. FWA recovery from sewage sludge samples was about 10-fold higher with added TBA than in extractions without TBA. The TBA concentration required for optimal extraction was found to be 0.25 M.
100
80
e FWA2
• FWA3
--O-FWA4
0 0.1 0.2 0.3 0.4 0.5 [TBA] in methanol modifier (mol/I)
Figure 3.2: Effect of TBA concentration on the extraction efficiency of FWAs from sewage sludge (supercritical fluid extraction with methanol modified C02). 23
FWA recovery in SFE, as well as in LE, largely depends on the type of sludge sample. Extraction profiles obtained with raw and anaerobically digested sewage sludge are compared in Figure 3.3. Extraction of FWAs is less efficient from raw than from anaerobically digested sludge probably due to the much higher content of organic matter in raw sludge (Table 5.2). Thus, the number of extractions required for quantitative recovery depends on the sludge type. Two consecutive SFE extractions were required to quantitatively extract FWAs from raw sludge samples while only a single extraction was required for digested sludge.
LE raw sludge digested sludge 100 100 .!! .a ! 80 80 Ill
::)C GI 60 60 ~ 0 40 40 '(/!. .5 3! .!! 20 20 >- 0 2 3 2 3 extraction number extraction number
FWA: 02 l:;f 3
SFE raw sludge digested sludge 100 100 .!! .Cl Ill 80 Ci 80 Ill ~ )C GI 60 60 i 0 40 'if. 40 .5 "O 'i 20 20 >. 0 0 2 3 2 3 extraction number extraction number
Figure 3.3: Extraction profiles of multiple extraction experiments: Influence of the type of sludge on the extraction efficiency. 2 4 ANALYTICAL METHODS
Table 3.2: Precision of FWA determination and comparison of FWA concentrations obtained by liquid extraction and supercritical fluid extraction.
LE SFE
concentrationc) RSOd) concentrationc) RSQd)
Sludge type FWA mg/kg dry sludge % mg/kg dry sludge %
Raw8) 1 8.8 12.2 7.5 8.6 2 27.3 1.5 29.7 4.1 3 49.5 1.8 51.4 5.2 4 3.3 1.2 3.4 5.4
Anaerobically 1 9.0 5.7 9.3 21.8 digestedb) 2 58.1 3.2 57.0 8.6 3 95.5 1.8 95.5 9.2 4 5.7 3.0 6.0 10.2 a), b) Samples taken at the sewage treatment plant •Glatt", Zurich: (a) mixture of 3 grab samples taken at 3 different days, (b) taken directly from the reactor. c) Four samples, duplicate determinations. d) Relative standard deviation
Table 3.3: Recovery of FWAs from raw and anaerobically digested sewage sludge using liquid extraction and supercritical fluid extraction.
LE SFE
Sludge type FWA Recoverya> (%) RecoveryC) (%)
Raw 1 61 ±5 67 ±9 2 92 ±3 77 ±5 3 86 ±4 80 ±7 4 84 ±3 77 ±6
Anaerobically 1 92 ±3 84 ±7
digested 2 90 ±2 81 ±8 3 93 ±2 81 ±6 4 93 ±3 81 ±7 a) Four samples, duplicate extractions, duplicate determinations. 25
In order to validate ion-pair/SFE for FWA determination in sewage sludge, the levels of FWAs measured by SFE were compared to that obtained by LE. Table 3.2 summarizes the FWA concentrations obtained by the two independent extraction methods. Results obtained by SFE and LE extraction procedures are in good agreement, the differences of FWA concentrations being well within the relative standard deviation (RSD) of each method. The higher RSD's obtained by SFE may, in part, be due to the smaller sample sizes (100 mg} used in SFE compared to 500 mg used in LE.
3.3.2. Enrichment of FWAs from Aqueous Samples
Membrane extraction disks offer a convenient alternative to solid phase extraction columns. The greater diameter of the membranes compared to conventional SPE cartridges allows simultaneous filtration and solid phase extraction. With a glass fiber filter stacked on top of the SPE disk, even 50 ml of unfiltered raw sewage could be extracted within 20 min. If information on the fraction of particle bound FWAs was needed, the glass fiber filter and the SPE disk were separated after the enrichment step and eluted separately.
Retention of disulfonated FWAs by the C10 SPE disks was excellent even without addition of salt or ion-pair reagent to the water samples. Experiments to determine FWA breakthrough indicated, that FWAs were quantitatively isolated from at least 10 ml of raw sewage and primary effluent and from 50 and 200 ml of secondary effluent and river water respectively, by the first of two stacked C1a disks. No FWAs were detected in the extract of the second disk. Although FWAs are negatively charged at environmental pH, the hydrophobic interaction between the C1a SPE disk and the FWAs seems to be strong enough for an efficient isolation.
A variety of solvents was evaluated for elution of FWAs from the C10 SPE disks. Acetonitrile and especially methanol were suitable elution solvents. However, large volumes (10-15 ml) were required to elute FWAs from the disks and recovery rates of less than 70 % were achieved for the determination of FWAs in primary effluent samples. By the addition of 0.05 M TBA to the elution solvent, FWAs could be recovered from the C10 SPE disk in only 6 ml and recovery rates were improved by approximately 25 %. This may be explained, in part, by a more efficient extraction of TBA-FWA ion-pairs from 2 6 ANALYTICAL METHODS the suspended particulate matter, as was already shown for the methanolic extraction of FWAs from sewage sludge (Figure 3.1 ).
Table 3.4: Reproducibility of FWA determination and recovery from water samples.
Matrix FWA Present RS02} Added3) Recovery4) (µg/l) (%) (µg/l) ( o/o)
Raw sewage1) 2 18 5 25-100 89 (10 ml) 3 23 6 25-100 86 4 1.2 8 2.5-10 77
Primary effluent1) 2 14 3 . 11-44 88 (10 ml) 3 12 2 11-44 89 4 0.4 4 1-4 76
Secondary effluent1) 2 6 1 5-15 93 (50 ml) 3 3 5 5-15 91 4 0.05 10 0.5-1.5 82
River water1) 2 0.8 2 1-5 96 (200 ml) 3 0.4 3 1-5 84 4 0.01 11 0.1-0.5 88
1) Samples from Zurich-Glatt municipal sewage treatment plant and from Glatt river 1 km downstream of the plant. 2) Relative standard deviation of 4 replicate determinations. 3) Spiked with 5-15 µL of standard solution and equilibrated for 15 h. 4) Average of six determinations.
To determine the precision of the method, replicate sample extractions were performed using samples of raw sewage, primary effluent, secondary effluent and river water from the Zurich-Glatt sewage treatment plant and from Glatt river 1 km dqwnstream of the plant (Table 3.4). For the determination of FWA recovery, the samples were spiked with different amounts of FWAs. Recovery rates were determined after an equilibration time of 15 h, to allow for partitioning of FWAs between water and suspended particles. Recovery rates were good for FWAs 2 and 3 (84-96 o/o) and acceptable for FWA 4 (76-88 o/o) (Table 3.4). 27
3.3.3. Extraction of FWAs from Lake Sediments
Lake sediments were extracted in the same way as sludge samples using LE with methanol containing 0.03 M TBA. As for sludge samples, extraction of sediment samples was exhaustive, e.g. no FWAs were found upon re-extraction and analysis of pre-extracted samples. In order to lower the detection limit compared to sludge analysis, the extracts were evaporated and the residue was redissolved in DMF:H20 (1 :1 ). Assuming similar behavior of FWAs in sediment extracts as in eluates from Empore disks, evaporation of solvent and re-dissolution should not affect the recovery values. However, no detailed study of recovery and reproducibility of FWA determination in • sediment samples was done. Assuming that recovery values will be less than 100 %, the reported FWA levels in sediments from lake Biel should be treated as lower limit-values.
3.3.4. Chromatographic Separation and Detection
Several different reversed-phase chromatographic systems were tested during this study in order to separate all isomers of FWAs typically contained in extracts of sewage wastewaters and sludges, river water, and sediments.
Very short separation times were obtained when the HPLC column was operated at elevated temperatures. The influence of temperature on the separation efficiency is best illustrated by a Van Deemter plot, Figure 3.4. The height of a theoretical plate which is often used to describe the performance of a chromatographic system is plotted against the flow velocity of the mobile phase for various temperatures. As is obvious from Figure 3.4, smaller plate heights are obtained at higher temperatures and the influence of the flow velocity on the plate height becomes less distinct with increasing temperature. The reason for the improved separation efficiency at elevated temperature is a better mass transfer of analytes between the stationary and the mobile phase. As a result, higher flow rates can be applied without any loss in separation efficiency when the temperature is increased and shorter separation times are obtained. I 28 ANALYTICAL METHODS
0.1 -o- 40°C e -0- 60°C E 0.08 ---6--- 80 °C -(I> cu -i5.. "B 0.06 i.... 0 Q) 0.04 =cu 0 -.r:::. .21- 0.02 Q) J:
0 0 0.5 1 1.5 2
Eluent flow rate (mllmin)
Figure 3.4: Van Deemter plots as a function of temperature. Column: Hypersil ODS, 5µm, 200x2. 1 mm i.d., mobile phase: binary mixtures of methanol and ammonium acetate buffer (capacity factor k'=5), sample: (E,E)-FWA 2.
Examples of chromatograms of wastewater and sludge extracts obtained with the system operated at 80 °C are given in Figure 3.5. All photoisomers of FWAs 1-3 are baseline-separated, which allows the determination of isomer ratios and response factors for individual isomers. It must be noted, however, that under the applied rigid conditions (high flow rate at high temperature) the columns had to be replaced after approximately 200 analyses.
Polymer based reversed-phase are known to be more stable towards hydrolytic degradation by the mobile phase than silca-based columns. Such a polymer column was used as an alternative (Poiger et al. 1993). The stability of this column was excellent and separations similar to the ones described for the silica-based columns could be achieved. However, the costs for this polymer column were much higher than for comparable silica-based columns and the higher price almost compensated the cost savings from longer column lifetime. 29
80
70
60
Q) (.) ~ 50 ,... C\I c ,...-• • ti- ' 30 20 B 10 c 0 0 5 10 15 Time (min) Figure 3.5: Examples of HPLC chromatograms of a sewage sludge extract obtained by liquid extraction of raw sludge (A) and extracts of primary effluent (B) and secondary effluent (C). HPLC conditions: column Hypersil ODS, 5µm, 200x2. 1 mm i.d., flow 1 mUmin, temperature 80°C, linear eluent gradient from 65 % aqueous ammonium acetate buffer (eluent A) and 35 % methanol (eluent 8) to 30 % A/70 %8 within 15 min. 3 0 ANALYTICAL METHODS Finally, a system was applied, which consisted of a narrow bore reversed- phase column (Hypersil ODS, 5µm, 200x4.6 mm i.d.) operated at room temperature with a binary gradient of aqueous ammonium acetate buffer and a 1: 1 mixture of methanol and acetonitrile. Elution gradients with methanol or acetonitrile alone did not yield satisfactory separations. Examples of separations of FWAs in river water and sediment extracts performed with this system are given in Figure 3.6. Separation of FWAs 2-4 is comparable with the separations obtained by the microbore system described above, with a slightly different elution order of isomers of FWA 3 and FWA 4 and longer separation times. Another advantage besides the slower column degradation as compared to separation at 80 °C is that this system does not require a thermostated column compartment. Besides the signals for the typical detergent-derived FWAs 2-4, which were known to be present also in river water, signals for more hydrophilic FWAs were obtained in chromatograms of some river water extacts, Figure 3.6 (A}. Two of these signals were identified as the two isomers of FWA 7. The other signals probably originate from other tetrasulfonated stilbene FWAs, but were not identified so far. In extracts of older sections of a sediment core from lake Biel, two signals in the more hydrophobic range of the chromatograms were identified as the two isomers of FWA 6, Figure 3.6 (B,C). Peak identification was performed by coinjection of standards and extracts. As FWAs were always present in two isomeric forms after exposure of standard solutions or extracts to sunlight, two peaks in the chromatograms could serve for identification of a FWA, whereby fluorescent and non- fluorescent isomers were easily distinguished, Figure 3. 7. As UV detection is less sensitive than fluorescence detection, comparison of UV absorption spectra was only possible in extracts of sewage sludge and (if large samples were processed) in extracts of raw sewage and secondary effluent. The selected approach for the detection of FWAs takes advantage of the fact, that photoisomerization is a reversible process. The separated FWA isomers are irradiated through a transparent capillary wrapped around a UV lamp connected in-line between the HPLC column outlet and the fluorescence detector. By this irradiation, non-fluorescent (Z)- and (E,Z)-isomers are partially reconverted into fluorescent (E)- and (E,E)-isomers and can thus be detected by fluorescence detection. Irradiation is applied after HPLC separation in 31 60 C\I I -w -u.i ...... I 50 -t::!. LO (") (") ...... I I 40 I wf:i w C\I - I - Q) -N 0 u.i c: Q) - 0 A UJ 30 ~ 0 :::> LL 20 c 0 5 10 15 20 25 30 Time (min) Figure 3.6: Examples of HPLC chromatograms of a river water extract (A) and extracts of two sections of a sediment core from lake Biel (8, CJ. HPLC conditions: column Hypersil ODS, Sµm, 200x4.6 mm i.d., flow 1 mUmin, temperature ambient, linear eluent gradient from 70 % aqueous ammonium acetate buffer (e/uent A) and 30 % methanoVacetonitrile 1:1 (eluent 8) to 30 % A/70 %8 within 25 min. 3 2 ANALYTICAL METHODS order to minimize matrix effects. The length of the capillary was optimized so that the separated FWAs are irradiated long enough to achive a constant ratio of (E)- and (Z)-isomers (photostationary conditions). This isomeric ratio is constant for a given light source and also independent from the initial isomeric composition (Chapter 4.3.3) Under these conditions, signals are obtained for every isomer that is separated by HPLC. The response factors are different for every FWA, but are identical for their (E)- and (Z)-isomers. How the UV-fluorescence detection of FWAs is affected by irradiadion before and after separation, is illustrated in Figure 3.7. A standard of four (E)- or (E,E)-FWAs was prepared in the absence of UV light. The resulting chromatogram, acquired without post-column irradiation, contained four signals, Figure 3. 7 (A). By exposing the standard sample to sunlight for 1 min, (E)- and (E,E)-FWAs were partially converted into the corresponding (Z)- and {E,Z)-isomers. The chromatogram, again acquired without post-column irradiation, still contains only the four signals, but the peak areas are smaller, Figure 5 (8). When the same irradiated standard was then analyzed after post- column irradiation, Figure 5 (C), additional signals, representing (Z)- FWAs 1 and 3 and (E,Z)-FWA 2, appeared due to partial reconversion into the corresponding (E)- and (E,E)-isomers. The retention time of (Z,Z)-FWA 2 was determined from separate injections of a reference compound, because this isomer was not formed upon sunlight irradiation. The (E,Z)- and (E,E)- isomers of FWA 4 co-eluted under the chosen HPLC conditions. Humic substances were present in extracts of river water, sediments, sewage wastewater and sludges. A.ltough these substances are fluorescening at 430 nm (Komaki and Yabe 1982), they did not interfere with FWA determinations. No interferences were found with co-eluting substances having absorbance bands at the emission wavelength of FWAs (430 nm). The detection limit for an absolute amount of a single isomer of FWAs 1 and 3 was 50 pg, and 5 pg for FWAs 2 and 4 injected to into the HPLC (signal to noise (S/N) ~10). The lower detection limit for FWAs 2 and 4 is due to the higher extinction coefficient and the higher fluorescence quantum yield of these FWAs. Instrumental sensitivity, however, was not the determining factor for the detection limits. In samples with low FWA concentrations, as river water and lake sediment extracts, the blank levels for FWAs 2-4 rather than 33 so- 40· 30. 20· 10- ,___-A..___, ---- '-' "-- _____....;;_; A 0 50 CJ) 40 c:0 ~ ((} 30 Q).... 0 :l LL 20 10 8 0 50 Cl' .., w ~ !!:!: !:!. 40 'O cac:. 30 CJ( w -. 8: ~ 20 8: C'( g"-; g 10 c 0 0 2 4 6 8 10 Time (min) Figure 3.7: Detection of isomers by post-column irradiation. HPLC chromatograms of a reference mixture of four (E)-FWAs. (A) prepared and injected without prior irradiation with UV or visible blue light and detected without post-column irradiation (PCI). The same standard mixture injected after to min of daylight irradiation yields chromatograms (8) without PC/ and (C) with PC/. Chromatographic conditions are given in the experimental section. Peak numbers refer to numbers of FWAs given in Rgure 2.2, the conformation of the stilbene groups is given in brackets. 3 4 ANALYTICAL METHODS instrumental sensitivity limited their detectability. This was not unexpected, because these FWAs are contained in laundry detergents and are therefore also present in clothing and in dust particles. The detections limits, where relevant, are given together with the experimental data (Chapter 6.1, 6.2). With the chromatographic methods described above, all isomers of FWAs 2 and 3 could be separated. The combination of post-column irradiation and fluorescence detection provides the possibility to determine not only the total concentration of FWAs in environmental matrices but also their isomeric composition. This is necessary to assess the environmental behavior of FWAs, since different isomers behave differently (Chapter 4.3.3). The sensitivity and selectivity of the method are adequate for the determination of FWAs In extracts of sewage wastewaters and sludges as well as in extracts of river water and lake sediment. 35 4. SOLID/WATER PARTITIONING OF FWAs 4.1. Introduction For the discussion of the partitioning behavior of FWAs it is useful to recall some of the physico-chemical properties of FWAs outlined in Chapter 2.2. Aromatic sulfonates such as FWAs are strong acids. Therefore, FWAs are negatively charged in aqueous solutions at environmental pH's. Despite this negative charge, some FWAs are still only moderately water-soluble. Thus, several types of interactions between FWAs and natural suspended solids are likely to occur: (i) anion exchange interactions of sulfonate groups with positively charged surface sites, (ii) hydrophobic interactions with natural organic matter, and (iii) specific interactions with cellulosic material. These interactions are comparable to those of the structurally related, so-called direct dyes. The binding mechanism of direct dyes to cellulose is, however, not very well understood. Hydrogen bonding to large conjugated aromatic systems has been proposed as a model for this type of binding (Giles 1983). All of these interactions may be operative at the same time. Furthermore, FWAs in aqueous solutions isomerize upon exposure to sunlight and different isomers may exhibit different partitioning behavior. Adsorption to suspended particles presumably is a key factor in the elimination of FWAs from wastewater and surface water (Ganz et al. 1975, Dojlido 1979, Komaki et al. 1981). Despite the relative importance of liquid- solid partitioning in comparison to other processes that may be involved in the fate of FWAs in the aquatic environment, no studies dealing specifically with the mechanisms of partitioning and the factors influencing it have been carried out. Consequently, no quantitative information on the partitioning of FWAs is available. The goal of the work described in this Chapter was to characterize 3 6 PARTITIONING OF FWAs the partitioning behavior of FWAs into suspended matter, taking into account their photoisomerization. The results of the partitioning studies should provide a basis for the interpretation of the results of the field investigations on the behavior of FW As in sewage treatment. 4.2. Experimental 4.2.1. Determination of Octanol-Water Distribution Ratios Octanol-water distribution ratios were determined at 25 °C for all photoisomers of FWAs 1-3 and for (E)-FWA 4 at pH=5, at which the sulfonate groups are deprotonated. All experiments were carried out in a dark room to prevent isomerization. Before use, the 1-octanol and the water containing 0, 10-4, 10-3, or 10-2 M calcium chloride were saturated with each other. FWA isomers were added to the aqueous phase by a 1: 100 dilution of a stock solution (50 mg/L). The aqueous phase contaning FWAs and the octanol phase (phase ratio 1: 1) were equilibrated for 10 min by vigorous shaking, and then centrifuged (1000 rpm, 5 min) to accelerate the phase separation. Analysis of the octanol phase was not possible because even small volumes of octanol distorted the chromatographic separation of FWAs. Instead, an aliquot of the octanol phase was back-extracted with water containing the same amount of calcium as in the first partitioning step (phase ratio 1: 1) in the same manner, and FWA concentrations were determined in both water phases. 4.2.2. Adsorption-Desorption Experiments In order to imitate natural conditions as well as possible, sorption experiments were performed using freeze-dried, sieved Glatt river sediment {< 200 µm) and filtered Glatt river water. The initial concentration of FWAs in the sediment were determined according to the procedure for sewage sludges {LE). Glatt river water from the outflow of Lake Greifen was filtered through a cellulose membrane filter with a nominal pore size of 0.45 µm (Millipore, Bedford, MA) in order to remove both, particles and most of the FWAs present at concentrations of 20-40 ng/L. No detectable amounts of FWAs were found 37 after filtration, because FWAs readily adsorb to cellulose membrane filters. All subsequent experiments were carried out in a dark room in order to prevent (E)/(Z)-isomerization. Adsorption experiments were carried out by suspension of 1 g of dry sediment in 200 ml of river water, where previously 30 to 300 µg/l of all isomers of FWAs 2 and 3 and (E,E)-FWA 4 were added. The Erlenmeyer flasks with the suspensions were placed on a shaker. Samples were taken in time intervals of 5 min to 10 h, filtered with glass fiber filters with a nominal pore size of 0.45 µm (Gelman Sciences, Ann Arbor, Ml), and analysed by HPlC. The concentration of adsorbed FWAs was calculated from the initial FWA concentration in the sediment and the concentration difference of FWAs in solution before and after sorption took place. Desorption experiments were performed with unspiked (but polluted) Glatt river sediment containing 5.2, 3.3, and 0.7 mg/kg FWAs 2, 3, and 4, respectively. Dry sediment (5 g) was suspended in 200 ml of filtered river water. The suspensions were shaken and samples were taken and analysed in the same manner as for the adsorption experiments. 4.3. Results and Discussion 4.3.1. Octanol-Water Partitioning Hydrophobic interactions between natural organic matter and FWAs were expected to be a significant contribution to the binding of FWAs to suspended solids. Partitioning between octanol and water is frequently used as a model for the partitioning of hydrophobic compounds between water and natural organic matter (Schwarzenbach et al. 1993). The octanol-water partition coefficient, Kow. is defined as the ratio of the concentration of a species in octanol and in water. If more than one species contributes to the overall partitioning of a compound, as is the case with organic acids and bases, an octanol-water distribution ratio, Dow, is used instead of Kaw. Hydrophobic organic acids may partition into octanol in their protonated or deprotonated form. The partition coefficients of the anions are usually more 3 8 PARTITIONING OF FWAs than 2 orders of magnitude smaller than of the neutral species. In addition, formation of ion-pairs of anions with cations such as Na+, K+, Mg2+, and Ca2+ has been found to promote partitioning into oc~anol (Westall et al. 1985, Jafvert et al. 1990). Thus, partitioning of organic acids (and bases) is strongly dependent on pH and ionic strength. Sulfonic acids usually have pKa values below 2 (King 1991 ). Therefore, only anions have to be considered at pH 6-8. Ion-pair formation, however, might influence the partitioning behavior of sulfonates, as was shown for linear alkyl benzene sulfonates (LAS) (Brownawell et al. 1991). Octanol-water distribution ratios for all photoisomers of FWAs 2-3 and of (E,E) 4 were determined with aqueous phases containing different Ca2+ concentrations in large excess compared to FWA concentrations. Very low Dow values for FWAs were obtained in the absence of calcium ions in the aqueous phase (Table 4.1 ), indicating that the sulfonated FWAs are too hydrophilic to partition readily into octanol. The large increase of Dow in the presence of calcium ions indeed strongly supported the assumed ion-pair formation. Table 4.1: Octanol-water distribution ratios of FWA Isomers at different calcium concentrations ((Ca2+ }} In the aqueous phase. FWA Isomer log Dow [Lwaterfloctanoil [Ca2+]1mM -> 0 0.1 1 10 2 (Z,Z) -3.9 -2.6 -1.6 -1.8 (E,Z) -2.9 -1.8 -0.8 -1.0 (E,E) -2.4 -1.1 -0.1 0.0 3 (Z) -1.9 -0.6 0.2 0.6 (E) -1.1 0.0 0.9 1.6 4 (E,E) -1.3 0.3 1.0 1.7 In order to evaluate the experimental data, a simple model was used, based on a set of 3 possible reactions. Formation of a 1 :1 complex of FWAs 39 and calcium ions in water is assumed to yield a net uncharged ion-pair (eqn. 1). The FWAs may partition into oetanol directly (2) or as their ion-pairs (3). 2 (1) "" K = [CaFWA]w Ca + FWA!- = Ca - FWJ\v 2 2 [ Ca "" lw [FWA -lw 2 [FWA -] (2) FW~ = FW~- K - o ow - [FWA2-Jw Kea _ [CaFWA] (3) Ca - FWJ\v =Ca - FWA:, 0 ow - [CaFWA]w The observed octanol-water distribution ratio for the sum of ion-paired and non-ion-paired FWA, Dow, is expressed by equation (4): 2 D _ [FWA -] +[CaFWA] (4) 0 0 ow - [FWA2-]w +[CaFWAJw Substitution of the variables for the concentration of FWAs and their ion- pairs by the use of equations (1)-(3) yields Dow as a function of the calcium concentration, the stability constant of the calcium-FWA complex, and of the octanol-water partition constant of ion-paired and non-ion paired FWA: 2 D _ K w +K ·Kg~ ·[Ca ""] (5) 0 ow - 1+K ·[Ca2-1-] The partition coefficients for the non-ion-paired FWAs, K0 w, were determined from the experimental data at [Ca2+]=0, Table 4.1. Values for K and Kg8w were determined by a least-square fit of Dow versus calcium concentration according to eqn. (5), Figure 4.1 and Table 4.2. For a given FWA, Kow of (E)-isomers is greater than of (Z)-isomers. This is in agreement with the general finding, that hydrophobic molecules are more compatible with the aqueous phase, when their volume is smaller (Schwarzenbach et al. 1993). {Z)-Stilbenes are more flexible than the corresponding {E)-stilbenes with its rigid conjugated tt-system and may fold to yield smaller molecular volumes in aqueous solution. 4 0 PARTITIONING OF FWAs 2 Ca ------log Kow = 1.8 1 ~ 0 0 0) 2 0 0 D _K0 w+K·K8:v·[Ca 1 - ow- 1+K·[Ca2•] 1 (log K=2. 1 [M · ], R=0.99) -1 log Kaw =-1.1 -5 -4 -3 -2 -1 log [Ca 2+] (mol/L) Figure 4.1: Influence of calcium on the octsnol•wster partitioning of (E)-FWA 3. Table 4.2: Octanol-wster partitioning coefficients for FWA Isomers and their ion-pairs with cslclum. Numbers in brackets indicate the relative standard deviations (%), R is the correlation coefficient of the calculation. FWA isomer log K0 w log Keaow log K[M-1] R 2 (Z,Z) -3.9 (15) -1. 7 (43) 3.7 (230) 0.77 (E,Z) -2.9 (21) -0.83 (40) 3.6 (210) 0.81 (E,E) -2.4 (17) o.o (16) 3.4 (73) 0.98 3 (Z) -1. 9 (17) 0.7 (<1) 2.7 (<1) 0.99 (E) -1.1 (7) 1.8 (<1) 2.1 (<1) 0.99 4 (E,E) -1.3 (36) 2.0 (12) 2.0 (23) 0.99 41 Good agreement of experimental data and model calculation was found for both isomers of FWA 3. The Kow of the FWA ion-pairs obtained by the model is more than 2 orders of magnitude higher than Kow for the native FWAs. The two sulfonate moieties of FWA 3 are close together and FWA 3 could even serve as a bidentate ligand. This might explain the relatively high conditional stability constant for the formation of ion-pairs obtained by the model calculation. Unfortunately, to the best of my knowledge, no stability constants for complexes of aromatic sulfonates with calcium (or any other metal except Ag+) are available in the literature. Thus, comparison of the obtained values for the stability constants to other data is not possible. e..,...... @: S03 so;A R ~ ;/ ~ R Figure 4.2: Suggested bidentate coordination of calcium by FWA 3. For isomers of FWA 2 a poor fit of model calculation and experimental data is obtained. The stability constants for assumed 1: 1 complexes derived from the model are even one order of magnitude higher than for FWA 3. This indicates that a more sophisticated model would be required in order to interpret the partitioning behavior of FWA 2 in the presence of calcium and other cations. For example the FWAs might form clusters with calcium ions. Depending on calcium (and FWA) concentrations these clusters might have different sizes and might exhibit different partitioning behavior. 4.3.2. Sorption to River Sediment Sorption equilibria were achieved within 20 h (Figure 4.3). Initially, both adsorption and desorption processes are fast, followed by a considerably slower step. In the desorption experiments, even a slight decrease in the amount of dissolved FWAs was found after 6 h. This decrease was attributed to the fact that dry sediment was added to the river water in the beginning of the experiment and that some swelling of the particles might have occured. 4 2 PARTITIONING OF FWAs A 8 100 0 0 l 0 c: -o- (Z,Z)·FWA 2 .2 00 -o- (E,Z)·FWA 2 -e- (E,E)·FWA 2 i.5 c: --(E)·FWA3 40 -o- (Z)·FWA 3 iLL. 20 o. 0 400 800 1200 400 BOO 1200 Time (min) Time (min) Figure 4.3: Examples far the kinetics of adsorption (A) and desorption (8) of FWAs in the system Glatt river water-Glatt river sediment (5 g/L (A) and 25 g/L (8)). No adsorption isotherms were determined. However, initial concentrations of FWAs in the aqueous phase were very low(< 1µM). At such low concentrations the adsorbed fraction of a solute can be considered to be linearly dependent on the concentration in solution. In such cases, a distribution coefficient, Kd, is defined according to equation (1 ), where [FWA]s and [FWA]w are the concentrations of an adsorbed and dissolved FWA isomer. (1) K - [FWA]s d - [FWA]w If all interaction between the solid phase and the solute is attributed to the organic matter contained in the solid, a distribution coefficient between organic matter and water, KoM. can be defined (eqn. (2)). The fraction of organic matter, foM. in Glatt river sediment was 0.11, determined as volatile solids. Table 4.3 lists Kd and KoM values for all isomers of FWAs 2 and 3. In analogy to the Kow data, different distribution coefficients 43 were obtained for different isomers. Distribution coefficients of (Z)- or (Z,Z)- isomers were generally higher than of (E)- or (E,Z)- and (E,E)- isomers. Table 4.3: Distribution coefficients for FWAs 2 and 3 (Glatt river water and Glatt river sediment). FWA Isomer ~ KOM [Ukg] [Ukg om) 2 (Z,Z) 12 117 (E,Z) 32 302 (E,E) 218 2059 3 (Z) 109 1025 (E) 444 4186 Linear free-energy relationships (LFER) between octanol-water partition coefficients (Kow) and organic matter-water partition constants (KoM) have been derived for a number of compound classes (Schwarzenbach et al. 1993). (3) logK0 M = a·logK0 w +b Values for coefficient a range between 0.37 and 1. 12 and for b between -0.72 and 1.15. An attempt to establish such a LFER for isomers of FWAs 2 and 3 is shown in Figure 4.4. Dow values for a Ca2+ concentration of 1 mM (Table 4.1) were used for the correlation in order to simulate the natural conditions as well as possible. However, as was outlined in the previous Chapter, other cations such as Na+, K+, Mg2+, and NH4+ may further increase Dow- The rather large value obtained for coefficient b in the LFER here indicates that hydrophobic partitioning is not the only interaction between FWAs and natural suspended matter. Specific interactions and ion-exchange interactions between FW As and suspended solids may contribute strongly to the observed partitioning. 4 4 PARTITIONING OF FWAs 4 -E 0 ~ 3 -~ 0 ~ O') .Q log K M = 0.63 log Dow + 3.06 2 0 r2 = 0.95, N = 5, f OM= 0.11 -2 - 1 0 1 log Dow Figure 4.4: Linear free-energy relationship of the organic matter-water distribution coefficient, KoM, and the octanol-water distribution ratio, Dow· ([Ca2+]= 1 mM) 4.3.3. Photoisomerization and Partitioning in Sewage lsomerization of dissolved FWAs upon exposure to light was mentioned several times in the previous Chapters. While adsorbed FWAs are relatively stable, dissolved FWAs readily isomerize in the presence of light (Milligan and Holt 1974). The constant ratio of (E)- and (Z)-isomers, the so-called photostationary state, is achieved within a few minutes of exposure to direct sunlight. Because different isomers have different UV spectra (Figure 2.4), the isomer ratio is dependent on the spectrum of the irradiating light. The spectrum of the light which actually reaches the dissolved FWAs is altered by UV absorbing co-solutes, as well as, in concentrated solutions by the FWAs 45 themselves. Therefore, the isomer ratios are dependent also on the concentration of FWAs {except for dilute solutions as sewage and river water samples) and the kind and concentration of co-solutes. Table 4.4 lists the ratios of the isomers of FWAs1-4 after irradiation of dilute solutions with sunlight and with a UV lamp. Table 4.4: EIZ-ratios of FWAs in the photostationary state after sunlight and UV irradiation. FWA isomer isomer ratio after irradiation with - sunlighta) UV 254nmb) 1 (Z) 79% 33% (E) 21 % 67% 2 (Z,Z) n.d.c) n.d.c) (E,Z) 8% 14 % 2% (E,E) 92% 86 % 98% 3 (Z) 78% 75 % 34% (E) 22% 25 % 66% 4 (E,Z),(Z,Z)d) 27% (E,E) 73% a) Left column: aqueous sample was exposed to sunlight in a glass vial. Right column: isomer ratio in the aqueous phase of primary and secondary effluent samples taken after sunlight irradiation. b) Ratio of peaks for (E)· and (E,E)-isomers in HPLC chromatograms with and without post· column UV-irradiation. c) (Z,Z)-isomer was not formed in detectable amounts. d) This row represents the sum of non-fluorescent isomers, because isomers were not separated in HPLC Although it is evident from the results reported in the previous Chapters, that the different isomers exhibit different partitioning characteristics, in a first step it is useful! to treat the FWAs as a sum of isomers and examine their average partitioning behavior. This picture is then refined in a second step by looking at the isomeric compositions and the partitioning behavior of individual isomers. 4 6 PARTITIONING OF FWAs The fraction of adsorbed FWAs 2-4 as a function of the amount of suspended solids is shown in Figure 4.5. Clearly, the preference of FWAs for suspended solids increases in the order 2<3<4, which is in good agreement with the findings reported in the previous Chapters. If sorption of FWAs to suspended solids is the dominating process for their removal during sewage treatment, the extent to which FWAs are removed from wastewater is determined by their individual partitioning behavior. As a consequence, the extent to which FWAs are removed from wastewater should increase in the order 2<3<4. As is shown in Chapter 5.4.4 this is indeed the case. 5.1 30 63 3800 28,500 80 i::J ii.i 60 I ~ 40 I -.c.-FWA4 20 -o-FWA3 -o-FWA2 0-+---.-.,....J=-r---..,._.+~...... ~~...-...... -~--..-1._,...,...,..,...,-~..1,-..,..,...,..,..,.rl 1 10 100 1000 10,000 100,000 Suspended solids (mg/L) Figure 4.5: Partitioning of FWAs to suspended solids in raw sewage, primary effluent, secondary effluent, activated sludge and anaerobically digested sludge of the sewage treatment plant Glatt, Zurich. lsomerization of FWAs in sewage was found to be very fast. Even samples of raw influent which were exposed to sunlight for less than 30 sec contained significant amounts of (Z)- and (E,Z) isomers (Figure 4.6). The isomeric composition of FWAs as shown in Figure 4.6 varies between raw influent, and in primary and secondary effluent, respectively. As will be explained below, this is not simply the result of different irradiation times. 47 Rather, it is a combination of isomerization and the different partitioning behavior of the individual isomers. 100 (15) ~adsorbed (3) ~dissolved ;g-o -Q) ( Z) ( £) (Z) ( £) (Z) ( £) FWA3 Figure 4.6: Partitioning of FWA Isomers to suspended solids in raw sewage, primary effluent and secondary effluent of the sewage treatment plant Glatt, Zurich. Numbers in brackets indicate the percentage of adsorbed isomer. A simple model was used to simulate the partitioning of FWAs under the influence of sunlight. Irradiation yields and maintains a a constant ratio of (E)- and (Z)-isomers in solution, KEZ (eqn. 4). The isomers adsorb to the solid phase with their individual distribution coeffitions K: and K:, (5) and (6): (4) (E)- FWA,.., = (Z)- FWA,.., K - [Z]w EZ - [E]w 4 8 PARTITIONING OF FWAs KE= [EJs (5) (E)-FWAw = {E)-FWA5 d [EJw Kz - [Z]s {6) (Z)-FWAw =(Z)-FWA 5 d - [ZJw [Z]5 , [E]5 , [ZJw, and [Elw are the concentrations of adsorbed and dissolved (Z)- and (E)-isomers. With equations (4)-(6) the fractions of adsorbed and total (Z)- and {E)-isomers were calculated as a function of the particle concentration and the constants KEZ, K;, and K;, which were determined from the field data. As shown in Figure 4.7 for FWA 3, the isomer ratio is dependent on the amount of suspended particulate matter. In solutions with low particle content, the ratio is dominated by the photochemically favoured (Z)-isomer and the isomer ratio is expressed by K EZ alone. With increasing particle content, the more strongly adsorbing {E)-isomer is favoured and becomes the dominant species. 100 Secondary effluent Primary effluent total (E) 80 Raw influent -e....~ adsorbed (E) c: 0 60 ;; (J ~ - 40 Suspended solids {mg/L) Figure 4.7: Model prediction of the ratios of (E}- and (Z}-lsomers of FWA 3 in solutions of different particle content under photostationary conditions (e.g. after sufficient irradiation time). Parameters: K EZ =3, K; =2000 Ukg, K; =30 000 Ukg. 49 For comparison of this model calculation with data obtained from the real samples, the particle contents of raw influent, and of primary and secondary effluent are indicated also in Figure 4.7 {vertical lines).Very good agreement between model calculation and field data is obtained for primary and secondary effluent {Table 4.5). For raw influent the model overestimates the fraction of the {Z)-isomer, most likely because the sample was not exposed to sunlight long enough to achieve photostationary conditions {one of the model assumptions). The same is also true for sludges, where the {E)- and {E,E)- isomers are the absolutely dominant {>90 %) species. Primary sludge is settled before isomerization can take place. Activated sludge is loaded with {Z)- and {E,Z)-isomers only during the day when isomerization takes place. During the night, these isomers are washed out due to their smaller affinity for suspended solids. Table 4.5: Comparison of measured and predicted Isomer ratios. Fraction of isomer[%] measured (predicteda)) (E,Z)-FWA2 (Z)-FWA3 Anaerobically digested 1.1 ( 4.0 ) 4.5 (17) sludge Activated sludge 2.6 ( 4.8 ) 9.5 (18) Raw influent 7.4 (13 41 ( 54) Primary effluent 12 (13 60 ( 63) Secondary effluent 14 (14 70 (72) a) Model parameters: FWA2: Kcz=0.16, K:=750 Ukg, K: =3 ooo Ukg. FWA3: Kcz=3, K: =2 ooo Ukg, K: =30 ooo Ukg. 51 5. OCCURRENCE AND BEHAVIOR OF FWAs IN SEWAGE TREATMENT PLANTS 5.1. Sampling Raw, anaerobic-mesophilic-digested, and activated sewage sludges were collected from several municipal sewage treatment plants in the region of Zurich, Switzerland in 1992. Sediment from the Glatt River was collected near Rumlang, Switzerland in 1991. Sludge and sediment samples were frozen within a few hours of collection and freeze-dried in aliquots of ca. 50 ml. Dried sludges were homogenized in an electric coffee grinder and stored at 4°C. Volatile solids were determined in the samples in order to assess the total organic matter in the dried sludges. Samples of raw sewage, primary effluent, and secondary effluent were collected as 24-h composites over a ten day sampling period in July and August 1992 at the Zurich-Glatt municipal sewage treatment plant, as well as, on single days in August 1992 from several other municipal sewage treatment plants in the region of Zurich. Brown glass sample bottles containing 1 % formalin (37 % formaldehyde) were used to collect and preserve samples. 5.2. Sewage In- and Effluents Concentrations of FWAs 2-4 in 24 h composite samples of primary and secondary sewage effluent from various treatment plants in the region of Zurich, Switzerland are reported in Table 5.1. As these concentrations may vary considerably from day to day (Chapter 5.4.2), the data presented in Table 5.1 should only be seen as first insight into the approximate range of concentrations at which FWAs occur in wastewaters. Note that sand filtration does not reduce FWA concentrations significantly, because secondary effluent contains only little suspended solids and most of the FW As are present in the dissolved phase (Chapter 4.3.3). 5 2 OCCURRENCE AND BEHAVIOR OF FWAs IN SEWAGE TREATMENT Table 5.1: FWA concentrations in wastewater8). FWA 2 3 4 ratio 2 / 3 primary effluent (µg/L) (µg/L) (µg/L) Zurich Glatt 14.0 11.4 0.38 1.2 Opfikon 21.3 9.8 2.40 2.2 BOlach 9.0 11.3 0.37 0.80 Niederglattb) 6.9 7.1 0.27 0.97 secondary effluent Zurich Glatt 5.6 2.6 0.05 2.2 Opfikon 8.9 2.8 0.15 3.2 Bulach 6.6 4.5 0.03 1.5 Niederglatt 3.3 3.5 0.01 0.94 tertiary effluent cJ Opfikon 8.7 2.5 0.01 3.5 a) 24 h composite samples b) raw influent c) sand filter 5.3. Sludges In anaerobically stabilized sludges collected from municipal wastewater treatment plants in the region of Zurich, Switzerland, the total FWA concentrations ranged from 85-170 mg/kg dry matter (Table 5.2). The FWA concentrations in raw sludge were lower than those in anaerobically digested sludges, indicating that FWAs become relatively enriched in sludge due to solids reduction during anaerobic sludge digestion. The concentration ratios of FWAs 2 and 3 in sewage (Table 5.1) and sludge (Table 5.2) varied significantly between different sewage treatment plants. While FWA 3 was more abundant than FWA 2 in sewage and sludge from Bulach, FWA 2 was the dominating FWA in Opfikon. Usage of different 53 Table 5.2: FWA concentrations In sewage sludges (mg/kg) Sample type FWA 1 FWA 2 FWA 3 FWA 4 total ratio Volatile Sampling location 2 I 3 solids(%) Anaerobically digested sludges Opfikon n.d. a) 53 55 11 119 0.96 n.d. Bau ma n.d. 30 68 4 102 0.44 51 Niederglatt n.d. 27 55 3 85 0.49 48 FAllanden n.d. 30 75 4 109 0.40 48 Bassersdorf n.d. 29 69 11 109 0.42 54 Uster n.d. 42 57 3 102 0.74 48 Seuzach 11 28 65 5 109 0.43 44 BOlach 8 33 105 5 151 0.31 57 Zurich-Glatt 9 58 96 6 169 0.60 48 Average 9 37 72 . 6 118 0.53 50 Range 8·11 27-58 55- 3·11 85- 0.3-1 44-57 105 169 Raw sludges Herisau 4 18 39 2 63 0.46 73 Zurich-Glatt 9 27 50 3 89 0.54 70 Activated sludge Zurich-Glatt n.d. 30 38 2 70 0.79 n.d. a) n.d. =not determined detergents is not a good explanation for this finding, because all sewage treatment plants are located close to each other in a small area. Large laundry facilities as the airport laundry facility in Opfikon, however, are using specialized detergents that are different from household detergents also in their FWA content. Their contribution to the total discharge of FWAs is significant, as is illustrated by the relatively high concentration of FWA 4 (used almost exclusively in detergents for large scale laundry facilities) in primary effluent samples from Opfikon. This contribution is therefore likely to be the reason for the variation of the FWA composition in sewage sludges. 5 4 OCCURRENCE ANO BEHAVIOR OF FWAs IN SEWAGE TREATMENT 5.4. Mass Flows of FWAs During Sewage Treatment 5.4.1. General Informations on the Field Study 55 The complete data-set of FWA concentrations, hydraulic flows, and mass flows at the sampling points indicated in Figure 5.1 is given in the appendix (Table A 1). The data derived from the analysis of raw sewage and excess sludge was only used for control purposes. Sampling of raw sewage did not yield a representative amount of the suspended particulate matter, and the levels of FWAs determined in raw sewage therefore underestimated the true levels. Excess sludge was not accessible for sampling and return sludge was sampled instead at one of four separate streams. However, amount of FWAs in these particular return sludge samples were markedly higher than the corresponding difference of primary and secondary effluent fluxes. 500 FW A 2 ~ Primary effluent 400 ~ Secondary effluent 300 200 100 0 '>: :g,"' 300 FWA3 en 200 -~ 0 ;;::: 100 en en C'O :e 0 12 FWA4 10 8 6 4 2 0 26 27 28 29 30 31 2 3 date Sun Mon Tue Wed Thu Fri Sat Sun Mon weekday July August Figure 5.2: Dally variations of FWA mass flows in primary and secondary effluents of the sewage treatment plant Glatt, Zurich. 5 6 OCCURRENCE AND BEHAVIOR OF FWAs IN SEWAGE TREATMENT 5.4.2. Diurnal and Daily Variations The daily variations of the mass flows of FWAs 2-4 associated with primary and secondary effluent during the sampling period is shown in Figure 5.2. From this overview it is already apparent that the efficiency of removal during the activated sludge treatment increases in the order 2<3<4. Surprisinglyt on August 3, the concentration of FWA 2 in secondary effluent is higher than in primary effluent. This can be explained by the observation that FWAs are enriched on activated sludge by adsorption to suspended solids (Chapter 5.4.3). When the FWA levels in primary effluent are high, the activated sludge is charged with FWAs. Conversely, when FWA levels in primary effluent are low, FWAs may be released from the sludge. 50 40 FWA2 30 20 -ca, 10 :i. ------c 0 0 ;:: «S '- c raw influent --- secondary effluent GJ -CJ c 0 0 15 FWA3 10 5 0 ------0 0 0 0 0 0 0 0 0 0 0 0 (") 0 (") 0 M 0 C") '::? C") 0 M 0 .;,;. r.:. 6) N 0 Cr> iii co a c.? a:> ,.- T- ,.- C\I T- ,.- .,- T- Time "' Figure 5.3: Diurnal variation of FWA concentrations in raw influent and secondary effluent of the sewage treatment plant at Opfikon . 57 The role of the activated sludge as a reservoir for FWAs is also illustrated in Figure 5.3. Levels of FWAs 2 and 3 were determined in raw influent and secondary effluent of the STP in Opfikon. The levels of FWAs in raw influent varied significantly during the day. The effluent levels, however, remained almost constant and were sometimes higher than the influent levels. 5.4.3. Elimination of FWAs During Activated Sludge Treatment With the determination of the mass flows of FWAs at the main sampling points alone (Figure 5.1 ), it is difficult to distinguish between different elimination processes that occur during the activated sludge treatment. Particularly, if several processes may affect the elimination of a chemical during this stage of sewage treatment, namely adsorption to sewage sludge and biodegradation, it is important to obtain informations on the relative significance of these processes. Therefore, in addition to the main study, experiments were carried out that should allow a distinction between adsorption and degradation processes. primary effluent returned sludge effluent to 0 secondary clarifier Figure 5.4: Scheme of the activated sludge system at the sewage treatment plant Glatt, ZDrich, with sampling points (only one of four streams shown). The activated sludge facility at the sewage treatment plant Glatt (Figure 5.4) is especially suitable for this kind of experiments, because the water passes through the aeration tanks without much longitudinal mixing (Plug flow mode) (Siegrist et al. 1989). Specified water packages can be sampled several times during the residence time in the activated sludge system at different locations along the flow path. Informations on the rates of overall 5 8 OCCURRENCE ANO BEHAVIOR OF FWAs IN SEWAGE TREATMENT removal processes including sorption and biodegradation of target chemicals can be derived directly without the use of computer models. The results of FWA determinations at the sampling points indicated in Figure 5.4 are given in Figure 5.5. Sample "0 11 is a hypothetical sample, representing the dissolved FWA fraction at the moment when returned sludge and primary effluent are mixed. This point is not directly accessible and the value is therefore calculated from the dissoved FWA fractions in returned sludge and primary effluent before mixing. The water package was sampled in time intervals of approximately 30 min, the average total residence time in the activated sludge was 90 min. c 120 :c0 µg/L ...tel A c -ID 80 () c 0 (,) ~ 40 'ii 0 - 0 µg/L c a. 30min 0 ~ FWA2 0 15 t: ' ~ FWA3 tel c ' • ID -C,) c 0 10 B (,) ~ --o LL. "C ID ...... > 5 0fl) fl) :s 0 ---- 0 1 2 3 4 RS sludge sample Figure 5.5: Levels of dissolved and total FWAs 2 and 3 In the activated sludge samples. Samples were taken in time intewals of 30 min at the sampling points indicated in Figure 5.4, RS is retum sludge. 59 Biological degradation of FWAs would gradually reduce their concentration in activated sludge. The total concentration (sum of dissoved and adsorbed fraction) of FWAs 2 and 3 (Figure 5.5 A), however, remained constant throughout the residence time of the wastewater in the activated sludge system, indicating that no detectable biochemical transformation processes occurred. To verify this result, samples of activated sludge were taken to the laboratory and aerated for another 48 h. Again no change in FWA concentrations occurred. In contrast to the constant total FWA concentrations, the fraction of FWAs in the dissolved phase (Figure 5.5 B) gradually decreased during the activated sludge treatment, and finally reached a value close to the one found in returned sludge. This nicely illustrates that FWAs are indeed removed from wastewater by adsorption to activated sludge. The differences in mass flows between primary and secondary effluent (e.g. the amount of FWAs eliminated in the activated sludge treatment) may therefore be attributed to sorption processes and not to biodegradation. 5.4.4. Mass Flows The average FWA mass flows during the field investigation are listed in Table 5.3. The amounts of FWAs entering the sewage treatment plant associated with raw influent were relatively small in comparison with the amount of 30 kg/day of the anionic surfactant secondary alkane sulfonates (SAS) that was determined in the same field study (Field et al., submitted for publication). During primary clarification, approximately 23, 69, and 92 % of the FWAs 2, 3 and 4 in raw sewage, respectively were removed associated with primary sludge (Figure 5.6). Of the residual FWAs in primary effluent, another 39, 65 and 89 % were removed during activated sludge treatment and secondary clarification. Residual masses of FWAs 2, 3, and 4 in secondary effluent were 216, 18 and 0.8 g/day, or 47, 11, and 2 % of the corresponding influent levels, respectively. As no biodegradation of FWAs was observed during activated sludge treatment (Chapter 5.4.3), FWAs removed during activated sludge treatment were quantitatively recovered in excess sludge. 6 0 OCCURRENCE ANO BEHAVIOR OF FWAs IN SEWAGE TREATMENT Table 5.3: Average FWA mass flows (glday). FWA 2 3 4 Raw influent 461 744 32.8 Primary effluent 349 230 5.4 Secondary effluent 216 80 0.8 Excess sludge 133 156 4.6 Raw sludge 245 664 32 Anaerobic sludge 259 635 35 Comparison of the mass flows of FWAs 2, 3 and 4 associated with raw sludge (e.g. the sum of primary and excess sludge) and with anaerobically- digested .sludge yielded very good agreement (53, 89, and 98 %, and 56, 85, and 107 %, respectively). Good agreement was obtained despite the fact that the anaerobically-digested sludges sampled in this study do not correlate with the influents and effluents sampled, because of the long residence time of sludge in the digestors. This finding strongly indicates that FW As are also not biodegraded during anaerobic sludge treatment. FWA2 Excess sludge 30% Raw influent Anaerobically digested sludge 61 FWA3 21 % 11 % WA adsorbed ~ dissolved FWA4 16% 2% Figure 5.6: Mass flows of FWAs 2,3, and 4 In the sewage treatment plant Glatt, Zurich. The fraction of adsorbed FWAs was determined in grab samples rather than composite samples and does not necessarily reflect the average situation. (PC primary clarifier, AS activated sludge treatment, SC secondary clarifier, AD anaerobic digestor). Removal rates vary considerably between FWAs 2, 3, and 4, respectively. The extent to which these FWAs (relative to each other) are eliminated from wastewater is consistent with their liquid-solid partitioning behavior (Chapter 4.3.3). The more readily FWAs adsorb to suspended solids, the more readily they are removed from wastewater. As was shown in Chapter 4.3.3, not only different FWAs but also different FWA isomers exhibit different partitiong behavior. lsomerization of FWAs in wastewater was found to be a fast process and photostationary conditions are achieved within a few minutes of exposure to sunlight. This raises the question, what impact sunlight has on the elimination of FWAs during sewage treatment. 6 2 OCCURRENCE AND BEHAVIOR OF FWAs IN SEWAGE TREATMENT A qualitative answer may easily be given. Sunlight will generally reduce the removal rates of FWAs, because photoisomerization leads to isomers which are less sorptive than the parent isomers. A quantification of this reduction in removal rates, however, is more difficult since several factors are limiting the impact of sunlight: • Intense sunlight is only available during few hours a day. • Sunlight only penetrates the top layer of the water in the settling tanks and in the activated sludge basin. • Only in the case of FWA 3 isomerization leads to a significant fraction of the less sorptive (Z)-isomer (Table 4.4). As a result, the fractions of (E,Z)-FWA 2 and (Z)-FWA 3 in activated sludge and anaerobically digested sludge were far below the fractions calculated for photostationary conditions (Table 4.5). While the impact of sunlight on the removal rate of FWA 2 seems to be almost negligible (fraction of (E,Z)-isomer only 1 % in anaerobically digested sludge), a closer look should be given to FWA 3. A rough estimate can be made by the content of the (Z)-isomer in sludge (4.5 %) and its adsorption constant for sludge particles (2 000 lJkg). The adsorption constant of (Z)-FWA 3 is very close to the adsorption constant of (E,E)-FWA 2 and a similar elimination rate (50 %) may therefore be assumed. This means that the amount of (Z)-FWA 3 released to the secondary clarifier is approximately equal to the amount in sludge. Thus the contribution of the (Z)-isomer (or the impact of sunlight) is in the range of only 10 %. 5.5. Discharge of FWAs to Surface Water and Farmland Estimates of the fractions of FWAs entering the Swiss STPs associated with raw sewage and leaving the STPs associated with anaerobically- digested sewage sludge and sewage effluents can be made based on the levels of FWAs in anaerobically-digested sludges and the elimination rates of FWAs during sewage treatment, Table 5.4. Since sludge is stored in the anaerobic digesters for several weeks, the FWA levels determined in anaerobically-digested sludge represent an average value of FWAs removed from wastewater during this time period. Calculation of FWA discharge to surface water based on FWA levels in sludge and elimination rated as 63 determined in the mass flow study are therefore more reliable than estimates based on effluent concentrations. Table 5.4: Estimation of the amounts of FWAs 2 and 3 in raw sewage, secondary effluents and anaeroblcally·digested sludge. Numbers in brackets indicate the fraction in each compartment relative to the consumption. FWA 2 FWA 3 Annual consumptions) [t/y] 36 (=100 108 (=100 % ) % ) Elimination in STPb) [%] 53 89 Level in anaerobically ·digested sludgec) [mg/kg] 37 72 Amount in: raw sewaged) [t/y] 18.2 (50 %) 21.0 (19 %) secondary effluente) [tly] 8.5 (23 %) 2.3 (2 %) sludge'> [t/y] 9.6 (27 %) 18.7 (17 %) a) Data from Ciba-Geigy AG. b) Chapter 5.4.4, Figure 5.6. c) Chapter 5.3, Table 5.2. d) Amount in sludge divided by elimination rate in STP e) Amount in raw sewage multiplied by (100% ·elimination rate) f) Level in sludge multiplied by annual sludge production of 260 000 t dry mass/y (Gujer 1989). As is shown in Table 5.4, a considerable fraction (72 %) of the consumed FWAs 2 and 3 is lost before the sewage treatment facility. This may be expected because FWAs are produced and added to detergents in order to adsorb to the textiles. Approximately 20 % are bound to sewage sludge and another 8 % are discharged to surface water. Approximately 110 000 of the total 260 000 tons/year (dry weight) of anaerobically-digested sludge are applied to Swiss farmland (Snozzi 1989). This corresponds to a FWA disposal associated with sewage sludge of ca. 13 tons/year. According to current Swiss legislation, sludge application is limited_ to 5 tons ha-1 (dry weight) within 3 years. The corresponding maximum annual FWA loading is therefore 20 mg m·2 y·1. 65 6. OCCURRENCE OF FWAs IN NATURAL WATERS AND LAKE SEDIMENTS 6.1. River Water Levels of FWAs 2 and 3 were determined in 2-week composite samples of river water (Table 6.1). The samples were obtained from automatic sampling stations of the NADUF-program, a monitoring program for the survey of several chemical and physical parameters of important rivers in Switzerland (Jakob et al. 1994). Some of the characteristics of the rivers are given in Table 6.2. From the FWA levels given in Table 6.1, mass flows and per-capita flows were calculated (Table 6.3). Although these values represent a very limited time window, they might serve as a rough estimate for the amount of FWAs in Swiss rivers. Comparison with a per-capita consumption of FWAs shows that approximately 5 % of FWA 2 and 1.5 % of FWA 3 are finally found in river water. Chancy I I I ~ Olan 25km 50km ~~ Figure 6. 1: Map of Switzerland with selected sampling locations of the NADUF-program 6 6 OCCURRENCE OF FWAs IN NATURAL WATERS AND LAKE SEDIMENTS Table 6.1: Levels of FWAs 2 and 3 in river water samples. River Sampling FWA2 FWA3 locationa> [ng/L] [ng/L] Limmat Gebenstorf 155 ±10 67 ±29 Rhein Rekingen 41 ±6 36 ±8 Village-Neut 142 ±8 372 ±48 Aare Brugg 107 ±13 94 ±6 Rhone Chancy 59 ±2 63 ±10 Glatt Rheinsfelden 574 ±23 439 ±24 Blank 4 ±3 12 ±2 LOQb) 29 22 a) 2-week composite samples (November 29 to December 13, 1993) from automatic sampling stations of the NAOUF-program. Samples were stored at 4°0, no preservatives were added. b) Limit of quantification (LOO= Blank + 1O cs) Table 6.2: Characteristics of the investigated rivers. (Jakob et al. 1994). River Sampling Catchment Average Population/a location area hydraulic flow [km2] (Q) [persons/(m3/s)] [m3/s] Lim mat Gebenstorf 2415 102 8260 Rhein Rekingen 14718 440 5570 Village-Neut 36472 1067 6470 Aare Brugg 11750 314 6180 Rhone Chancy 10294 327 4360 Glatt Rheinsfelden 416 8.5 39970 67 Table 6.3: Mass flows and per capita flows of FWAs calculated from data in Table 6.1. River Sampling Hydraulic Mass flow Per capita mass flow location flow [kg/d] [mgld person] [m3/s]a> FWA2 FWA3 FWA2 FWA3 Limmat Gebenstorf 68 0.91 0.39 1.08 0.47 Rhein Rekingen 352 1.25 1.09 0.51 0.45 Village-Neut 699 8.58 22.47 1.24 3.25b) Aare Brugg 191 1.77 1.55 0.91 0.80 Rhone Chancy 248 1.26 1.35 0.89 0.95 Glatt Rheinsfelden 6.3 0.31 0.24 0.91 0.70 Average 0.92 0.67C) Total usage 16.4 49.3 a) Data supplied by Landeshydrologie und -geologie, Bern, Switzerland. b) Chromatographic signals for FWA 3 overlapped with signals from an unknown compound. c) Value for Village-Neut not included. While FWA levels in river water samples varied considerably for different rivers (36-574 ng/L, Table 6.1), the per capita mass flows of FWAs 2 and 3 were surprisingly similar. The average mass flows relative to the consumption were 5.6 and 1.4 % for FWAs 2 and 3, respectively. The discharge of FWAs to surface waters via sewage effluents was estimated to be approximately 23 and 2 % of the consumed FWAs 2 and 3, respectively (Chapter 5.5). This indicates that at least FWA 2 is further eliminated in surface water, most probably due to photodegradation and due to adsorption to suspended particulate matter, followed by sedimentation. However, more detailed information on the photochemical behavior of FWAs is needed in order to assess the fate of FWAs in natural water systems. Investigations on the kinetics and products of photodegradation of FWAs are currently going on in this institute (Kramer, doctoral work in progress). 6 8 OCCURRENCE OF FWAs IN NATURAL WATERS AND LAKE SEDIMENTS 6.2. Sediments Since FWAs are removed from wastewater by adsorption to suspended solids and since they proved to be persistent under aerobic and anaerobic conditions found in sewag~ treatment plants, their enrichment in sediments seemed to be very likely. Lake Biel was chosen to test this hypothesis not by theoretical but rather by practical considerations, because other studies were carried out at the same time (Albrecht and Luck, 1994; Toljander, 1994). Lake Biel is a small lake in the east of Switzerland (Figure 6.2). It receives water from a relatively large drainage area of 8 000 km2 {21 % of Switzerland) with a population of 1 million inhabitants. Due to the large drainage area in comparison to the size of the lake, the average residence time of the water is only 70 days (Lake Geneva: 12 years, Lake Constance: 6 years) (Santschi and Schindler 1977). ..___..., SchOss river ~ .... 1okm ... 1 1 Lake Wohlen ~ Lake Murten Figure 6.2: Map of lake Biel with the sampling location Indicated ( e ). A sediment core was taken at the sampling location indicated in Figure 6.2. Radioisotope dating of this core was done by the Environmental Physics Department at EAWAG (Albrecht and Luck, 1994). The dating is exceptionally 69 2-4, and 6 in Figure 6.3: Concentration profiles of radioisotopes, and FWAs 38, 109, and 6 a sediment core from lake Biel. The limits of quantification (LOO) were µglkg for FWAs 2, 3, and 4, respectively. ('I') 0 CJ) co ...... LO ..q- CJ) co co co I I I I I I ~ 0 CJ) co co co LO ..q- ('I') co co ...... CJ) CJ) CJ) CJ) CJ) CJ) ~ ~ ~ ~ ~ ~ ' I ' ' 0 0 ('I') 0 C> 0 .::.:.. C\I Ch :::i. 0 0 ~ 0 0 0 ('I') ~ 0 0 0 L... 0 ························t·········1 ...... L······················j························('I') C> 0 ~ 0 C> C\I :::i. 0 0 ·1--~:~r~~= ~~: l ~ -- ~ -- 0 0 0 ('I') N 0 C> co i N co i ct> co 0 0 C\I C> 0 ~ 0 CD ~ E -u .r. -a. 0 0 0 0 0 0 0 ('I') ..q- LO -c! ~ C\I 7 0 OCCURRENCE OF FWAs IN NATURAL WATERS AND LAKE SEDIMENTS detailed, because a nuclear power plant upstream of the sampling locaton accidentally released radionuclides in 1976 and 1982. The other two maxima of 137Cs reflect the commonly found maxima for the atmospheric atom bomb tests (1963) and the Tschernobyf accident (1986). Sharp peaks for all radioisotopes indicate, that no bio-turbation (no mixing of sediment layers due to biological activity) occured in the sedimentation period studied. The average sedimentation rate was 90 mm/year. Visual inspection of the freshly cut core indicated that the sediment was anoxic at least part of the year (grey to black color). The sediment contained some clay but no sand. The history of the application FWAs as detergent ingredients and along with it the history of FWA inputs into lake Biel is recorded in the concentration profile of FWAs in the sediment core (Figure 6.3). Besides the nowadays mainly used FW As 2-3, the more hydrophobic FWA 6 is found in deeper sections of this core with a concentration maximum corresponding to the time period from 1959-69. FWA 6 has lost its significance as a detergent additive with the introduction of FWAs 2-3. This change in detergent formulation is recorded in the sediment core. The fact that the levels of FWAs 2 and 3 in the sediment are almost constant on a depth corresponding to a time period of more than 30 years strongly indicates their persistence under the environmental conditions of this sediment. 71 7. CONCLUSIONS By the combination of field investigations (mass balance study, survey of FWA levels in sewage sludges) and laboratory studies (liquid-solid partitioning), it was not only possible to determine elimination rates of FWAs from wastewater but also to identify the processes involved and the amounts of FWAs which are finally discharged to surface water and sediment. Among the different processes which may affect the fate of pollutants in sewage treatment (e.g. biodegradation, chemical transformation, and adsorption), only adsorption to sewage sludge was found to be important for the elimination of FWAs from wastewater. No evidence for biodegradation was found during (aerobic) activated sludge treatment and anaerobic digestion of sewage sludge (Chapter 5.4). Lack of ready biodegradability both aerobically. and anaerobically and an enrichment of FWAs in sewage sludge, however, immediately raise the question of what the consequences for the environment are. According to present knowledge (Burg et al., 1977) FWAs exhibit a very low toxicity. Therfore, FWAs should not be put into the same category with chlorinated hydrocarbons and pesticides and probably not even surfactants. at least as long as FWAs are used in such small quantities compared to surfactants. However, research on the toxicology of FWAs so far mainly focused on toxiclogic, not ecotoxicologic aspects. Relatively little is known about the fate of FWAs applied to farmland with sewage sludge. Focus of studies on this subject was always on the question of human, not environmental health. Therefore only uptake of FWAs by plants and infiltration of FWAs to groundwater were investigated so far (Ganz et al. 1975, Muecke et al. 1975). Since a major portion of the consumed FWAs finally end up on farmland, the further fate of these FWAs and their effects on soil microorganisms should definitely be investigated. Comparison of FWA discharge and FWA mass flows determined in several rivers (Chapter 6.1) indicates that at least FWA 2 is further eliminated in surface water. Photodegradation and adsorption to suspended particulate matter, followed by sedimentation are processes likely to be involved in the 7 2 CONCLUSIONS fate of FWAs in the aquatic environment. 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Anliker A. and MOiier G.), Georg Thieme Publishers, 129-142. 79 APPENDIX Raw influent: ~ Ill co Date Hydraulic flow Concentrations (µg/L} Mass flows (g/day) C::: Qi '01 ... tJ" 0 FWA2 FWA3 FWA4 FWA2 FWA3 FWA4 (') .g Cl) (m3/day) ::r-· I iii' - C) Ill :ti. )> July 26 28270 ""4 ""O iii' ""O 17.9 16 .... a; .. m 27 33030 ±2.0 12.0 ±0.7 0.49 ±0.15 591 398 ...... z 28 31090 ::::i 0 ""4 .,, 29 30880 15.8 ±0.4 10.6 ±0.6 0.50 ±0.07 486 327 15 co Q. x co c:: ~ 30 31520 ~ ... 5· (') 31 32520 CQ 0 :::i August 1 46410 6.1 ±0.3 6.6 ±0.4 0.33 ±0.15 264 284 14 (') sCl) Cl) 2 31280 :::i 3 ::::- 3 37650 17.2 12.9 0.62 648 486 23 lb Qi Ill 4 38040 Ill g. :::i ~ ..111 Average 33759 14.2 ±5.5 10.5 ±2.8 0.49 ±0.12 497 374 17 0 ~ ::r '-!:: ....Ill c:: ~ Primary effluent: c:: ~ (:)• Date Hydraulic flow Concentrations (µg/L} Mass flows (g/day) ID - .... ~ 0 (m3/day} FWA2 FWA3 FWA4 FWA2 FWA3 FWA4 ~ Ill ~ July 26 28270 7.3 ±0.3 5.6 ±0.6 206 158 Cl) ID 14.2 ±0.1 9.0 ±2.0 0.31 469 298 10.2 :::i 27 33030 ~ Q. CQ 28 31090 15.0 ±0.2 9.0 ±0.4 0.19 ±0.00 467 280 6.0 Cl) Q. 29 30880 15.2 ±1.0 7.8 ±1.1 0.21 ±0.04 468 241 6.5 ~ ~ 30 31520 14.7 ±0.5 9.5 ±0.6 0.28 ±0.13 462 301 8.9 ID 3 31 32520 13.0 ±0.0 8.7 ±0.1 0.16 ±0.01 422 284 5.2 3 ....ID Cl) Cl).... August 1 43310 7.9 ±0.2 6.5 ±0.5 0.19 ±0.03 343 280 8.1 ....:::i ... 7.0 ±2.6 5.0 ±1.9 0.11 ±0.06 218 158 3.4 (') 2 31280 'ts 0 3 37650 5.4 ±0.1 3.8 ±0.3 0.07 ±0.00 201 145 2.7 ii;" :::i...... :::i Cl) 4 38040 6.2 ±0.2 4.1 ±0.4 0.07 ±0.01 235 156 2.7 :::i.... 0 Average 33759 10.6 ±4.1 6.9 ±2.2 0.18 ±0.08 349 230 6.0 .... Secondarx effluent: Date Hydraulic flow Concentrations (µg/L) Mass flows (g/day) ';;} tr (m3/day) FWA2 FWA3 FWA4 FWA2 FWA3 FWA4 CD' ). July 26 28270 5.7 ±0.3 2.3 ±0.3 0.045 ±0.004 160 64 1.27 ..... 27 33030 5.4 ±0.0 1.8 ±0.2 0.021 ±0.010 177 61 0.69 '()" 6.1 ±0.1 2.3 ±0.1 0.015 ±0.010 73 0.47 0 28 31090 190 ::i 29 30880 7.0 ±0.3 2.5 ±0.0 0.015 ±0.008 215 78 0.46 c:-s· 30 31520 6.8 ±0.4 2.4 ±0.0 0.018 ±0.006 216 77 0.57 31 32520 7.2 ±0.4 2.2 ±0.1 0.012 ±0.006 233 71 0.39 .a" August 1 43310 7.5 2.7 0.029 326 118 1.26 2 31280 6.0 ±0.2 2.5 ±0.0 0.024 ±0.016 187 78 0.75 3 37650 6.4 ±0.0 2.8 ±0.2 0.040 ±0.019 241 105 1.51 4 38040 n.d. n.d. n.d. Average 33759 6.4 ±0.7 2.4 ±0.3 0.024 ±0.012 216 80 0.82 Excess sludse: Date Hydraulic flow dry content Concentrations (mg/kg) Mass flows (g/day) {m3/day) (kg/m3) FWA2 FWA3 FWA4 FWA2 FWA3 FWA4 July 26 759 27 762 6.0 50.1 78.5 3.89 229 359 18 28 751 29 742 7.0 53.8 ±1.7 78.3 ±3.2 3.68 ±0.15 280 407 19 30 742 31 768 August 1 768 6.1 61.8 97.3 4.07 290 456 19 2 776 3 887 6.3 50.4 ±0.6 83.9 ±2.0 3.77 ±0.09 282 469 21 4 994 Average 795 6.4 54.0 ±5.5 84.5 ±8.9 3.85 ±0.17 270 423 19 -CCI Raw sludse: Date Hydraulic flow dry content Concentrations (mg/kg} Mass flows (g/day) ~ <» tJ" N (m3/day) (kg/m3) FWA2 FWA3 FWA4 FWA2 FWA3 FWA4 Ci" )I. .,,)> July 26 ... .,, 27 m n-0 z 28 300 37.3 25.5 ±2.7 70.6 ±4.0 3.47 ±0.12 285 790 39 ::::i c 29 280 ~ x t: 30 250 36.0 28.8 ±0.9 74.9 ±2.7 3.81 ±0.06 259 674 34 Cll 31 260 ~ August 1 240 2 220 26.0 36.5 ±3.4 102.2 ±7.8 4.88 ±0.34 209 585 28 3 220 4 250 35.0 25.9 69.6 3.24 226 609 28 Average 253 33.6 29.2 ±5.1 79.3 ±15.4 3.85 ±0.72 245 664 32 AnaerobicallI disested sludse: Date Hydraulic flow dry content Concentrations (mg/kg) Mass flows (g/day) (m3/day) (kg/m3) FWA2 FWA3 FWA4 FWA2 FWA3 FWA4 July 26 27 28 300 29 280 30 250 28.5 31.4 ±2.5 85.7 ±8.2 5.43 ±0.24 224 61 (). 39 31 260 August 1 240 2 220 26.7 50.0 112.3 5.49 294 660 32 3 220 4 250 Average 253 27.6 40.7 ±13 99.0 ±18 5.46 ±0.04 259 635 35 ,, Matrix Suspended FWA Concentration Dissolved fraction (o/o)a) Adsorbed fraction (o/o)a) Total Total ID ';J ~ tr ii""' i'. solids (mg/l) (µg/l) (E) or (E,E) (Z) or (E,Z) (E) or (E,E} (Z) or(E,Z) adsorbed (Z) or(E,Z) c:: iii' l:i. Anaerobically 28500 2 868 99 1.1 ii' ~ 4.5 ~ digested sludgeb) 3 2370 100 Qj () 4c) 117 100 g: ()~ :J ~ Activated sludge 3800 2 113 7.5 0.7 90 1.9 92 2.6 0 0 0 :J 3 115 0.7 1.0 90 8.5 98 9.5 .... Ill 0 0 4 1.0 99.5 Ill .... "'11 (QI Raw influent 63.3 2 42 79 7.0 14 0.4 14 7.4 CD ~ 3 26 19 37 39 4.5 44 41 ID ;- :J 4 0.44 89 Q. ~ Ill CD ~ 8.9 12 c: Primary effluent 29.7 2 26 79 12 8.6 0.3 ~ 19 2.8 24 60 CD fi- 3 23 57 21 !II Cit 4 0.31 77 9 Ills- Secondary effluent 5.1 2 5.9 83 14 3.0 0.2 3.2 14 Q. 3 2.0 23 69 6.4 2.0 8.3 70 s- 4 0.02 n.d. c;;·Q. Cl) 0 a) Sum of dissolved and adsorbed (E)- and (Z)-isomers is 100 % :;;- b) Centrifuged and filtered sample still contained particulate matter, therefore results for the dissolved fraction give only a rough estimate. l c) (E,E)- and (E,Z)-FWA 4 are not separated In HPLC. n.d. Not determined, because value was close to blanc level. •:J Q. Curriculum Vitae Name: Thomas Frank Poiger Date of birth: September 11, 1964 Bom in: Vienna, Austria Citizenship: Switzerland 1971-1977 Primary school in Tagelswangen and Dubendorf 1977-1979 Sekundary school in Dubendorf 1979-1983 Gymnasium in Oerlikon, Matura Type C 1983-1984 Practical Work 1984-1989 Undergraduate and graduate studies at the Swiss Federal Institute of Technology, Zurich, Switzerland 1987-1988 Exchange visitor at the University of Marburg, Germany 1990 Diploma in Chemistry at the Swiss Federal Institute of Technology, Zurich, Switzerland 1990 Marriage and birth of first child 1992 Birth of second child 1990-1994 Doktoral studies at the Swiss Federal Institute for Environmental Science and Technology and the Swiss Federal Institute of Technology, Zurich