THE APPLICATIOD NAN EFFICIENC "MIXEF YO D OXIDANTS" FOR THE TREATMEN DRINKINF TO G WATER

JC Geldenhuys

WRC Repor 832/1/0o tN 0

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Vrywaring Hierdie verslag sprui t n navorsingsproje' voor t ui t t deu e Waternavorsingskommissiwa kdi r e (WNK) gefinansie goedgekeun e s i r r publikasievi s i r . Goedkeuring beteke noodwendie nni t gda die inhoud die siening en beleid van die WNK of die lede van die projek-loodskomitee weerspieél t meldinda nie f handelsnamo n , gva gebruir vi f -war eo K ke goedgekeuWN deu e rdi f aanbeveeo r l word nie. THEÍ APPLICATION AND EFFICIENCY OF "MIXED OXIDANTS" FOR THE TREATMENT OF DRINKING WATER

Final report to the W ATER RESEARCH COMMISSION

by J.C. Geldenhuys

LIBRARC YIR 93190x PO Bo HAGUE , 250TH FD 9A S9 O68 0 3 0 7 Tel. 1 :+3 Fax: +31 70 35 899 64 BARCODE 7/ : 3 , - LO: ' 6 WRC Repor . 832/1/0tNo 0 ISBN No. 1 86845 691 9 Executive Summary

Ongoing research into new technologies is required to develop less expensive water treatment processes without sacrificing water quality.

The proces area e disinfectiof sth o f so tha e ton need s examinene i b o st d continuousl fino yt d more efficient against presently known micro-organisms and the potentially harmful ones that are discovered.

In addition, growing concern chlorinf o se abouus e wittth potentialls hit y harmful by-products place greater emphasis on the need for water utilities to investigate water disinfection alternatives to chlorination. A seemingly advanced technology, new to Western practice but utilised for some time Eastermane n i th f w yo nno bloc states receives ha , d much acclai generalatee mf o Th . l conceps ti that of an electrolytic cell and used to generate amounts of anolyte and catholyte, said to contai varietna oxidantsf yo mixture ,th whicf eo referrehs i "mixes a o dt d oxidants" oxidante .Th s include amongst others, , , peroxide, ozon hydroxyd ean l radicals. This technolog purporteys i presendo t followine tth g advantages over present disinfection methods:

• The efficiency of the oxidants produced is, by mass, higher than that of chlorine; • Oxidant mixture producee b n sca d on-site using only electricit sodiud yan m ; • Oxidant concentratio compositiod nan adjustee b y nma d accordin specifigo t c needsd an ; residuaA • l ma maintainee yb producn di t water.

Although there is no record of the large-scale application of this technique in water disinfection, it could be considered as a means of primary disinfection on small water treatment plants and to augment depleted concentration distribution si n systems. Chlorinatio varioun i s forms si regarded as a reliable, cost-effective method for disinfecting water for drinking purposes. It is used on small, remote plants and on large-scale sophisticated drinking water treatment plants. However in remote areas the application of chlorine presents problems where difficulties such as the following, may exist. These and other reasons may give impetus into investigating other disinfectants.

• Distance from the place of chlorine manufacture • Transport and delivery schedules are unreliable or non-existent; • Lac f sufficienko t expertis propee th n eo r dosin chlorinf go e (especiall f gaseouyo s chlorine); qualite Th chlorinf yo • obtaines ega d causes problem poine th dosingf t o ts a .

Definitive research is required into the evaluation of the application of mixed oxidant technology for treatmene th drinkinf o t g water, especiallremotn i e us er areay fo primara s sa y disinfectant.

The objectives of this research project were as follows:

evaluato T • relativelea concepw yne t that coul usee disinfectiodr b dfo watef no r supplied to small and rural communities; and • To make recommendations on the application of mixed oxidants and the possible benefits and shortcomings of such a system.

Conclusions

The results obtained in this study confirm that there are aspects of the production of mixed oxidants that are not well understood and therefore not well defined either. There also seems to be an overlap between the new emerging science of electrochemical activation of water (EGA) and the electrochemical formation of mixed oxidant solutions by electrolytic means. The results and affects claime achievee b applicatioe o dth t y db f EGno A technology sometimes border metae th n -so physica enougt no d hlan conclusive evidenc availables i eitheeo t r suppor discarr to claime dth s made. Since only two different Electrochemical Activation (EGA) devices were examined, and both posed developer o d operational problems durin testse gth woult ,i d unfai mako rt e comment othey an rn so EGA device available sb thay tma e commerciall functionine th n o r yo improve f go d model thoss sa e Ill

that were tested. Results obtained however indicate that despit e operationath e l problems experienced thapossibles i t ti , redobasee th n xdo potentia solutione th f lo produco ,t anolytn ea f eo consistent quality. Reproducibility of the results was good and it can be expected that this aspect of the performance of the mixed oxidant generators could be equaled or improved in devices which are of better design and construction. This aspect was not only important for the execution of the tests which were done woult ,bu d significanf also e ob t importanc commerciaf ei mixea f o de oxidanlus t generator had to be considered. Redox potential of the anolyte taken over a period of time showed tha decaoxidative e tth th yn i teste poweth coult sn i i slos kepd e dwrwa b an t constant long enough exposo t bacterie eth solutioo at n wit knowha n redox value.

The possible applicatio mixef no d oxidant disinfectanta s sa investigateds wa , . Although cars ewa experimente taketh n ni preservo st mixee eth d oxidant (anolyte) solutio harveso nt totae th t l potential oxidative power, and the possible synergistic effects of all the oxidants present, its effect did not significantly exceed that of chlorine. This was in spite of the fact that the anolyte vapours, and presumably the anolyte solution as well, contained other strong oxidants such as and . It was also confirmed that the catholyte solution did not contain chlorine at concentrations that would have significant microbiocidal properties. This fact is also supported by the low or negative redox potential measure catholytee th n di .

Results from batch experiments show that the greatest reduction in the bacterial numbers took place within the first minute. In most cases both the anolyte and chlorine killed more than 99% of the present durin firse gth t minut f exposureeo . Increased contac t significantlt no tim d edi y reduc numbere e th bacteri e batcth e f furthersth y o l haan al test n averagI e . sth e percentage reduction in bacterial numbers were 99,5 anolyt97,8e d th 5 an r chlorind 4fo ean e solution respectively after five minutes contact time. The overall percentage reduction in the continuous flow tests were 99,85 for the anolyte and 99,61 for the chlorine.

It can therefore be concluded that under the test conditions that prevailed that the mixed oxidant generators examine product no d ddi e anolyte solution spropertiee witth l hal claimes sa literaturedn i . unite Th s product testeno d ddi eproduca t that behaved significantly differently from chlorine either. IV

Although it seems as though mixed oxidant solutions of consistent quality can be produced from Electrochemical Activation (EGA) devices improvementd an , functionine th n s i equipmen e th f go t ca expectee nb sucf o e hfuturen d i disinfectanus e th , t generator rurae th ln s i area s would probably no practicale tb wits .A h other electrolytic chlorine generator reliablsa e electricity sourc essentiaes i l whilst, in most rural areas this cannot be guaranteed. The availability of high purity mixee th n di e oxidanus o t t generato alsy orma presen problema t furtheA . r problem e coulth e db disposal of the alkaline catholyte solution of which a volume equal to about one sixth of the volume of the anolyte, is produced.

Recommendations for future research

The following aspecte generatioth f o s d applicatioan n f mixeo n d oxidants warrant further investigation: • Examine and understand the principle of operation of the mixed oxidant generator. • Develop methods to analyse for the different oxidative compounds present in the anolyte. • Develop methods to analyse for the different compounds present in the catholyte. • Design of a system in which the mixed oxidant solution can be applied such that full oxidative compoundpotentiae th l al f o l s presen fluivapoure e utilisedwels e th th d a b n s ti a ln sca . • Examine potential non-conventional applications and benefits of mixed oxidants.

A membe previousla f ro y disadvantaged population group participate researce th n di thi r hfo s project. ACKNOWLEDGEMENTS

researce Th thihn i s report emanated fro mprojeca t fundeWatee th y drb Research Commission entitled:

THE APPLICATION AND EFFICCffiNCY OF " MIXED OXIDANTS" FOR THE TREATMEN DRINKINF TO G WATER

Steerine Th g Committee responsibl thir efo s project, consiste followine th f do g persons: Dr IM Msibi Water Research Commission (Chairman) GrabK Prof oWO . w Universit Pretorif yo a Prof. J Haarhoff Rand Afrikaans University Mrs S D Freese Umgeni Water GeldenhuyC J r M s Rand Water PietersMA rS e Cape Metropolitan Council Mr J W D Pietersen Midvaal Water Company Ms U Wium Water Research Commission (Secretary)

financine projec Th e Watee th th f gy o b rt Research Commissio contributioe th d nan e th f no member Steerine th f so g Committe gratefulle ear y acknowledged.

This project was only made possible with the co-operation of many individuals and institutions. The author therefore wishe recoro st sincers dhi e thank followinge th o st :

Department of Biological Sciences of Rand Water for performing the microbiological analyses. Mes. Hanna Enslin, Suzette van Wyk, Marike Hinze, Derdre Gerber and Surendri Chetty for performing the experimental work. SaaymaA s M typinr nfo manuscripte gth . VI

TABLE OF CONTENTS Pag. eNo Executive Summary...... i Acknowledgements...... ^ Tabl Contentf eo s ...... vi List of tables...... viii List of figures ...... x .i Glossary...... x

1. INTRODUCTION...... 1

2. LITERATURE REVIEW...... 3

1 2. Disinfectants produce ...... y db .3

2.1.1 Chlorine...... 4 2.1.2 ...... 4 2.1.3 Ozone ...... 5 . 2.1.4 Percompounds...... 6 2.1.5 Mixed Oxidants...... 6

2.2 Aspects of Oxidation ...... 11

2.2.1 Oxidation-reduction potential...... 11 2.2.2 Oxidant Demand/Requirement...... 2 1 . 2.2.3 Redox Control for Pathogen Management...... 13

3. MATERIAL AND METHODS ...... 17

3.1 Methods used for chemical and physical determinants...... 17

3.1.1 Redox Potential...... 7 1 . 3.1...... H p 2 . 17- 3.1.3 Chlorine and oxidant concentration...... 7 1 . 3.1.4 Ozone, chlorine and hydrogen peroxide concentration in the gas phase ...... 17

3.2 Methods used to determine microbiological determinants...... 18

3 . 3 Description of equipment used...... 8 1 .

3.3.1 Mixed oxidant generator...... 8 1 .

3.3.2 Apparatus use exposo dt e bacterial culture mixeo st d oxidants...... 1 .2 Vil

4. RESULTS AND DISCUSSION...... 24

4.1 Reliability of the equipment and consistency of the product...... 24

4.1.1 Relationship between redo anolyte th x catholyte...... n d potentiai ean H p d lan 4 .2 4.1.2 Relationship between flow rate throug generatoe hth redod ran x potential...... 5 .2 4.1.3 Reproducibilit results...... f yo 6 .2 4.1.4 Consistency of the anolyte quality ...... 27

4.2 Chemical composition anolyte...... e ofth 0 .3 4.3 Microbiocidal effects of the anolyte...... 31

5. CONCLUSION...... 36

6. RECOMMENDATIONS FOR FUTURE RESEARCH...... 38

7. REFERENCES...... 39 VIH

LIST OF TABLES

TABLE 1,1 Propertie anolytf so catholytd ean e solutions producee th y db STEL apparatus fro m300a 0 mg// sodium chloride solution as electrolyte ...... 9

TABLE 4.1 The concentration of various determinants in the anolyte and catholyte fluid and vapours ...... 30

TABLE 4.2 Comparison betwee bactericidae nth l effect anolytf so d ean chlorine solutions in batch experiments ...... 32

TABLE 4.3 Comparison between the percentage reduction of bacterial numbers expose anolyto dt chlorind ean e solution batcn si h experiments ...... 3 .3

TABLE 4.4 Comparison between the bactericidal effects of anolyte and chlorine solution continuoun si s flow experiments ...... 4 3 .

TABLE 4.5 Comparison between percentage reduction in bacterial numbers exposed to anolyte and chlorine solutions in continuous flow experiments ...... 34 IX

LIST OF FIGURES

FIGUR 1 DiagraE1. Flomf o w Electrolytic Module ...... 7

FIGURE 3.1 Diagra Electrochemicamf o l Activation Equipment (EGA) ...... 0 .2

FIGURE 3.2 Diagra equipmenmf o t use batcr dfo h experiment teso st t bactericidal effectanolyte th hypochloritf d o s ean e ...... 2 2 .

FIGURE 3.3 Diagram of the flow-through system used to test the bactericidal effect of the anolyte and ...... 23

FIGURE 4.1 Relationship between redo xanolytn i potentia catholytH d p ean d an l e ...... 5 2 .

FIGURE 4.2 Relationship between flow rate through the generator and redox potential in the anolyte ...... 26

FIGURE 4.3 Reproducibility of anolyte and catholyte quality in successive operations ...... 27

FIGUR 4 ERedo4. x potentia measurs la anolytf eo e activit stirrea yn i d batch volume against time ...... 28

FIGURE 4.5 Redox potential as measure of chlorine activity in a stirred batch volume against time...... 28

FIGURE 4.6 Redox potential as measure of anolyte activity in a continuously flowing stream against time ...... 29

FIGURE 4.7 Redox potential as measure of chlorine activity in a continuously flowing stream against time ...... 29 GLOSSARY

CT Produc oxidanf o t t concentratio contacd nan t time.(mg// *minutes)

DPD N,N- di-diethyl-p-phenylenediamine

EGA Electrochemical Activation

EH Hydrogen electrode potential

FAS Ferrous ammonium sulphate

HOC1

ORP Oxidation Reduction Potential

Redox Oxidation Reduction potential

THM Trihalomethane 1. INTRODUCTION

Statisticians estimate that more than 12 million South Africans hav acceso en potablo st e water (i.e. water whic bees hha n treate qualita do t y acceptabl drinkinr efo g purposes). Rural communities lack bot infrastructure hth finance th d eean require ensurdo t e potable water locat ,bu l authorities arw eno obliged to provide all sectors of the community with access thereto. Research into new technologies is therefore being sought develoo t , p less expensive water treatment processes without sacrificing water quality.

Producing readily available potable water is a challenge as water utility companies are unable to guarante qualit e treatee eth th f yo d wate t intrpu o supply onc t leaveei purificatioe sth n pland an t enter sdistributioa n network. Water quality deteriorates with time chlorind ,an e levels which should prevent recontamination by micro-organisms are often so low that the desired effect is not achieved. As a result the water at the end of a distribution network is often not of the quality expected by the consumer or specified by quality standards.

In addition, growing concerns about the use of chlorine with its potentially harmful by-products place greater emphasis on the need for water utilities to investigate alternative water disinfection to chlorine. The production and application of solutions containing various strong oxidants, collectively called "Mixed Oxidants thesf o e e on alternatives s "i . Mixed oxidants generally refemixtura o rt f eo hydroxyl radicals, ozone, chlorine dioxide, hydrogen peroxide, chlorine and other strong oxidising species. This mixture is produced electrochemically on site as required from a sodium chloride solutio unia n i t comprise anodef do cathoded san speciallf so y selected alloys. Research conducted Russiae atth n Scientists' Centr Electrochemicar efo l Activation Techniques (RSCEAT), suggests that efficience th oxidante masth y f b y o e s shighear r than tha chlorinef to producd ,an e residuals than tca be maintained in treated water. Although there is no record of the large scale application of this techniqu waten ei r disinfection, instances have been recorded wher e mixeeth d oxidants have apparently been used successfully for disinfecting water in refugee camps. It is at this stage not suggested that mixed oxidants should be used as the sole means of water disinfection. However becaus purportee th f eo d eas efficiencd ean generatiof yo applicatiod nan coulnt i consideree db a s da means to augment depleted disinfectant concentrations in a distribution system. Motivation Chlorinatio varioun i s form regardes si reliablea s da , cost-effective metho disinfectinr dfo g water for drinking purposes. It is used on small, remote plants and on large-scale sophisticated drinking water treatment plants, howeve remotn ri e area applicatioe sth chlorinf no e presents problems where difficultie se following sucth s ha existy ma , . Thes othed ean r reason givy ema s impetus into investigating other disinfectants. • Distance fro place m th chlorinf eo e manufacture • Transport and delivery schedules are unreliable or non-existent; • Users lack sufficient expertise on the proper dosing of chlorine (especially gaseous chlorine); qualite Th chlorinf yo • obtaines ega d causes problem poine th dosingf t o ts a .

The presence of chlorine disinfection by-products like trihalomethanes, organic halogens, and mutagenic substances, is still a cause for concern. The only way in which the formation of potentially dangerous compound avoidee b y removo t s ma di precursore eth thesf so e compoundsa e us r o , mean disinfectiof so n alternat chlorineeo t . Disinfectio electrochemically-producey nb d oxidanty sma be an option, but this method also has its limitations: oxidants that do not produce harmful by- products, in general, do not produce a residual either.

A seemingly advanced technology, new to Western practice but utilised for some time now by many of the Eastern block states, has received much acclaim of late. The general concept is that of an electrolytic electrolytceld lan e use generatdo t e amount anolytf so catholyted ean , sai contaio dt na variety of oxidants, the mixture of which is referred to as "mixed oxidants" (MIOX). The oxidants include amongst others, chlorine, chlorine dioxide, hydrogen peroxide, ozone and hydroxyl radicals. This technology is purported to present the following advantages over present disinfection methods: efficience oxidante Th th f • yo s produce massy b , d,is higher than tha chlorinef o t ; • Oxidant mixtures can be produced on-site using only electricity and sodium chloride; • Oxidant concentratio compositiod nan adjustee b y nma d accordin specifigo t c needsd an ; • A residual may be maintained in product water. Definitive research is required into the evaluation of the application of mixed oxidant technology for the treatment of drinking water, especially for use in remote areas as a primary disinfectant or to augment disinfectant residual t outlyina s g area f wateso r distribution networks, where chlorine residual may be low or lacking. objectivee Th thif so s research project wer followss ea : • To evaluate a relatively new concept that could be used for disinfection of water supplied smalo t rurad an l l communitiesd ;an • To make recommendations on the application of mixed oxidants and the possible benefits and shortcomings of such a system.

2. LITERATURE REVIEW

2.1 Disinfectants produced by electrolysis Disinfection with chlorine and chlorine products is an established process in the provision of safe drinking waterdevelopinn i t bu , g countrie regulasa r suppl chemicalf yo serioua s si s problem. With special attention being focusse ruran do l programmes, on-site productiof no disinfectants could fil needa l , provided operatio maintenancd nan e coul simplifiede db . Electrolytic production of gaseous chlorine is a well-known process in the chemical industry, although small production cells have still to prove their reliability and low maintenance requirements (Wabner and Fleischmann, 1986). Small electrolytic production units using sodium chlorid feea s eda stock have been marketed successfullr yfo some time. These units are typically used to chlorinate small drinking water supplies or swimming pools.

Strong oxidants have amon effective gth e disinfectants prominena , t position. Oxidants like chlorine, hypochlorite and ozone are today the most important chemicals for drinking-water disinfection produco T . e these chemicals (which possess high positive redox potentials), electrochemical methods are preferred as they provide in a simple elegant manner, the strong oxidation conditions required. The technology of mixed oxidant production claims simple process control, separated oxidation and reduction zones and no need for storage of oxidising chemicals (Wabne Fleischmand ran , 1986).

2.1.1 Chlorine Chlorine mose ,th t widely used disinfectan waten i t r purification bees ha ,n produced electrochemicall grean yi t quantitie morr sfo e thayears0 e n10 Th . products of brine electrolysis are chlorine, and hydrogen accordin followine th o gt g reaction :

2NaCl+2H2O •* Cl 2NaO2+ HH+ 2 ...... (i> With an anodic reversible discharge potential of+1.247V for the reaction

2C1" •* Cl2 + 2e", ...... (2) Possible side-reactions at the are:

2H2O •* O2 + 4FT+4e'

CIO6 H3 2"O+ -» 2C1C Cl'+6F4 V+ f +1,5 O 6e'...... 2+ (3) The quantitatively more important reaction is the generation according to reaction 3. For direct drinking water disinfection the chlorate formation should be closely monitored becaus it'f eo s high toxicity. Other side reactions reducing chlorine yield also occu chlorinn ri e solutions, viz:

20F T2C1+ 2 •* CIO C + 'H r+ 20 ci2 + H2o -» HOCI + FT + cr

2HOC1 + NaCIO -» 1 NaClOHC 2 3+

The products are hypochlorite and chlorate; the latter can thus be formed at the anod solutioweln s i e a s a l n (Wabne Fleichmand ran , 1986).

2.1.2 Hypochlorites Hypochlorite e mosth f t o importan e ar s t disinfectants producee . ar The o yto d electrochemicall by-produca s ya chlorinf o t e production. Therefore this methos di well investigated and documented. The generated hypochlorite can decompose on both the cathode and the anode: Anode:12ClO~+6H2O 4 C1O3" + 8 Cr+12lT+3 O2+12e'

Cathode: ClO'+H2O+2e' Cl' + 2Oif

The rate of chlorate generation is proportional to the concentration of HOC1 + CIO" minimizee b solutioe n inth ca reduced y db nan d retention electrolyttimee th f so en i the cell. The chemical chlorate generation from hypochlorite is negligible if the electrolyte is kept at temperatures under 30°C and pH values outside the range 4 to 6. The reaction, cío- -> cr+o.soz, is slower than the chlorate reaction, but is catalyzed by impurities like cobalt, nickel and copper. Hypochlorite solutions decompose according to these two reactions and canno storee tb extender dfo d periods. Bot sodiue hth calciud man m hypochlorites are produced and used for disinfection purposes.

2.1.3 Ozone Ozone is one of the strongest oxidants known (redox potential of 2.07 V). It has become increasingly importan water-disinfectionr fo t whicr firss fo , wa t t husei n di 1 893 in the Netherlands, on Rhine River water. Though ozone was discovered in the electrolysi watef so 1839n ri mose th , t importan economid an t c metho produco dt e ozon stil s ei sileny b l t corona discharge from r oxygedrieo r d ai generator n i f so different designs. In recent years the electrochemical generation of ozone has been reinvestigated intensively using new materials as . This has increased the efficiency of the generators and ozone yields of up to 1 8% by volume of the anodically-generate obtainablee saie b ar o d t s dga .

Ozone production is in proportion to the energy applied to the ozone generator as demonstrate followine th dn i g reactions oxonee Th . - generation reactio initiatens i d when free electrons in the corona dissociate oxygen molecules:

e" + O2 •» 2O + e" This is followed by ozone formation from a three-body collision reaction:

OOM •+ *2+ O3+M Where M is any other molecule in the gas. (White, 1992)

2.1.4 Percompounds Inorganic peroxocompounds like peroxides, perborates, perphoshatesd an , percarbonate strone sar g oxidant havd san e been use disinfectionr dfo instancr fo , en i oral hygiene, cosmetics and the food industry. They play a significant role in water purification as well; hydrogen peroxide has to date been used for that purpose in the United State Americf formeso e th d raan United Soviet Socialist Republic. Solid peroxides are commercially available for swimming pool-disinfection. In this application the combinee yar d with metal salt activator increaso st reactioe eth n rate. All these compounds can be electrochemically prepared (Wabner and Fleischman, 1986).

2.1.5 Mixed Oxidants Research into various aspects of a phenomena referred to as "Electrochemical Activation EGr "o A whic defines hi : "decomposindas g water with electricita s yi physical-chemical modificatio watef no r composition with fT, OH", metal oxide hydrates, acids, peroxide compounds and radicals, free chlorine, ozone, hydrogen peroxide, hypochlorite anión, etc. appearing in it;" led to the development of two related designs for generators, employing the same principles, but used for different purposes. Both design e commerciallar s y availabl r producinefo g anolyted an s catholytes from either purified slightly mineralised water containing about 100-200 mg/ dissolvef /o d salt r sodiuso m chloride brine solution g/l).7 - 5 s( EGA unite sar sold unde trade rth e names suc Emeralds ha , Sapphir Crystald ean . These devices utilis same eth e basic Flow Electrolytic Module (FEMoptione th t r o )bu sx exismi o tt recirculat anolyte eth catholytd ean e stream obtaio st n specific effects anolyte Th . e produced has a lower pH and positive redox potential. The catholyte displays a high negativa d an H ep redox unipotential M comprises ti FE e .Th titanium-rutheniuf do m oxide anodes and cathodes that operate under a potential of "several million volt/cm2 The electrodes are separated by a ceramic diaphragm. Any number of FEM units can be incorporated int osingla e unit calle Floda w Electrochemical Reactor (FERo t ) increas capacite e th productio e th f yo n unit Figure Se . eschematia 1.r 1fo c diagram ounitf M th.eFE

Diaphragm Anolyte Catholyte Outlet Outlet

Anode athode

Brine Inlet Brine Inlet to Anode to Catode Direction of flow

Figure 1.1 Diagram of Flow Electrolytic Module

According to the literature sited and information supplied by manufacturers, when using slightly mineralised water as the electrolyte the two product streams produced have many economic applications in the medical, agricultural and general health and 8

biology fields. Somobservatione th f eo s mad resultd ean s achieved when applyine gth products fro EGAe mth , borde metaphysicae th n ro difficule ar d explaino lt an . Some of the observations include:

• Apparent change wettine th n si g propertie waterf so . • Softening of rock that improves the milling efficiency.

• Improved germination of seed that had been watered with the catholyte. • More rapid mass gai pulletn i s that received catholyt thein ei r drinking water. • Reductio salmonellf no a infectio improven a egg n ni d san d percentag chicf eo k hatchlings after receiving intermitted dose anolytef so .

The devices use produco dt e anolyt catholytd ean e streams from sodium chloride brine is commercially available as the "STEL" and "REDO" units. The redox potential and pH values of the anolyte and catholyte streams produced from brine span a much wider rang thoss ea e produced from slightly mineralized water.

Simplified, the main processes that take place in an electrolyser can be expressed in the following way:

1. Oxidation of the water at the anode: 2H2O - 4e~ •* 4H* +O2

2. Reductio watecathodef e no th t ra : 2H2 O2e+ ' •» H 2Of2+ f

3. Formatio gaseouf no s chlorin chloridn ei e solution anodee th t sa : 2C1 "2e- ~ -> C12 4. Formatio highlf no y active oxidant anodie th n si c chamber: i.e.

C12O, C1O2, CIO", HOC1, cr, 02', 03, H02, OIT, H202 5. Formation of highly active reductants in the cathodic chamber:

Off, H3-, O/, H2, FKV, H02', 02'

Presence of enough strong oxidants and free radicals in the anolyte turns it into a solution with marked biocidal properties. Catholyte solutions saturated with reductants exhibit improved adsorption and chemical ability as well as good cleaning properties ORd an P leve(OxidatioH e p f Th .lo n Reduction Potential anolyte th n )i e and catholyte produced from solutions with different salinity are characterized by changes that are related to the initial values: in the anolyte the pH value is reduced elevateP extreme OR anth e do dt th e positive (oxidant) value catholyte th n ;i e thH ep reduceP i sextreme increaseOR th e o dt th ed negativdan e (reductant) value.

Table 1. Propertie anolytf so catholytd ean e solutions produce STEe th y Ldb apparatus usin 300ga 0 mg/i sodium chloride solution as electrolyte

Anolyte pH (mVP OR ) Active ingredients Concentration of active ingredients, mg// <4.5 1100 to 1200 C102,C102-,C1,HOC1, If concentration of o2,o- active chlorines < 200 mg/7, O2 and O" concentration is 1 to 3 mg/7 6± 1 800 to 950 HOC1, C10\ C102-, 03, f I concentratiof o n 02, H202, H02- active chlorine0 <20 mg/7, O3 ,H d O2O2an 2 concentration is 1 to 3 mg/7. ...8.5 7. 5 0 6580 o 0t HOC1, CIO", 03, 02, If concentration of H202, H02- active chlorine0 <20 mg//, O3 ,H d 02O2an 2 concentration is up to 10 mg//

Catholvte pH ) ORmV P( Active ingredients + 11. 5 ±0.5 -80 -90o 0t 0 Na , Off, OH-, H202, HO2", O2", H2 OR POxidatio= n Reduction Potential (Table from Strand, 1994) 10

The STEL unit is used to produce anolyte streams with potentially high disinfecting power that could be attributed to the high positive redox potential.

Examples of such applications are: • Sterilisatio surgicaf no l instruments use hospitalsn di casen I .interna e sth l structurf eo Pseudomonas aemginosa, as observed by electron microscope was found to be irreversibly damage applyiny db anolyt n ORgn a a f Pd o ean solutio7 3, f no witH p ha 950 mV. • Decontaminatio pipelinef no equipmend san foon i t d processing plant. • Decontamination of slaughtered animal carcasses in abattoirs. • Contro microbiologicaf o l l contaminatio fruif ncolo n i t d storage. • Productio emulsionf no pesr sfo t contro plantsn lo . • Disinfection of swimming pool water. • Water treatment.

The Centre for Applied and Research in Salisbury, United Kingdom (1995) reporte e preliminarth n o d y evaluatio e Enigmth f o na Electrochemical System. This equipment is comparable to the STEL and REDO apparatus. The anode is made of titanium coated with ruthenium oxide, iridium and platinum, while the cathode is titanium polished or coated with pyrocarbo glasd nan s carbon membrane .Th e separatin anolyte gth catholytd ean e consist ultrafiltratiof so n electrocatalyti zirconiumcf o ceramic d be a n s,o yttrium, aluminum and niobium oxides. Depending on the chemical and mineral composition of the original electrolyt redod an xeH potentiausep e anolytde th th catholytf d lo ean e produce withie dar n the limits of -2 to 8,400 to 200 mV and 7 to 12, -80 to -900 mV, respectively. It is claimed that water flowing through the Enigma system is altered by the electric field of several million volt r squarspe e centimeter causin imbalancn ga watee th n ei r structure enrichin t witgi h electrochemical product sC1: whicbe 2 , y HOC1hma , CIO*, Cl*, HO2, HO/, O2, HO*, O3,O2., O", H 0 , H*, H O , C1 0, C10 ", HC1, C1 O , S O -, C O ', H SO , HSO C 1anolyte inth e 3 + 2 2 2 2 2 7 2 88 2 62 2 4 3 and HO", H3O2", O2~, HO2" H2O2, H2, HO, H2', NaOH, KOH, Ca(OH)2, Mg(OH)2 in the catholyte weaA . k anolyte solutio prepares nwa d using electrochemical activatio volt2 3 t nsa 11

an dcurrena amp2 f o t s from water, whil estrona g anolyte solution required 16a vold an t current of 10-13 amp in an electrolyte containing 7500 mg// of sodium chloride. The strong anolyte had a pH 5,9 and a redox potential of 978 mV.

Pathogens like Vibrio cholera, Shigella dysenteriae, Salmonella enteritidis, Legionella pneumophila and were exposed to the undiluted anolyte to determine how efficien solutioe th t n woul killinn i e micro-organismse db g th r comparativFo . e purposes these organisms were also expose mg/0 5 chlorine f /do o t . Fresh undiluted anolyte killel dal micro-organisme th seconds0 3 n si . Concentration mg/0 5 f /s o chlorin e gave similar results.

Dilution 1:80anolytf e so th f 0o e prove ineffective b do t unreliabld ean achieveo t killine eth g of the bacteria in 30 seconds and the contact time had to be increased to 10 minutes. Similar results were obtained when diluting the 50 mg// chlorine solution. A 1:300 dilution of the chlorine solution, which is equivalent to about 0,16 mg// of chlorine, was more effective in killing the bacteria than similar applications of the diluted anolyte. (Strand, 1994)

2.2 Aspects of Oxidation Reduction Potential

2.2.1 Oxidation-reduction potential Oxidation and reduction (redox) reactions mediate the behavior of many chemical constituent n drinking-i s , process- d wastan , e wate s wel a rs mos a l t aquatic compartment e environmentth f o s reactivitiee Th . mobilitied san f importano s t elements in biological systems (e.g. Fe, S, N and C), as well as those of a number of metallic elements, depend strongl redon yo x conditions. Reactions involving both electronEh-dependentd an - protond san pH e sar ; (Hydrogen Electrode Potential) therefore, chemical reaction aqueoun si s medi characterizeae ofteb n d nca an H p y db Eh together wit activite hth dissolvef yo d chemical species. Like pH, EH representn sa intensity factor. It does not characterize the capacity of the system for oxidation or reduction. 12

The potential difference measured in a solution between an inert indicator electrode anstandare dth d hydrogen electrode shoulequatee b t d no EH o dt thermodynami a , c property, of the solution. The assumption of a reversible chemical equilibrium, fast electrode kinetics, and the lack of interfering reactions at the electrode surface are essentia r suc fo interpretationln ha . These condition rarele sar n f ever)i y (i t me , natural water.

Thus, although measuremen Ef wateHn to i relativels ri y straightforward, many factors limit the interpretation of these values. These factors include irreversible reactions, electrode poisoning, the presence of multiple redox couples, very small

exchange currents, and inert redox couples. The measurement of redox potential, when properly performed and interpreted, is useful in developing a more complete understanding of water chemistry.

2.2.2 Oxidant Demand/Requirement Oxidants are added to water supplies and wastewater primarily for disinfection, although their beneficial uses include slime removal, oxidatio f undesirablo n e inorganic species (e.g. ferrous , reduced manganese, ammonia), and oxidation of organic constituents (e.g. taste odour-producind -an g compounds). Oxidant demand refers to the difference between the added oxidant dose and the residual oxidant concentration measured afte a prescriber d contacd t an a givetim t H a ep n temperature.

The fate of oxidants in water and wastewater is complex. For example, chlorine reacts with sample constituents along three general pathways: oxidation, addition and substitution. First, chlorine can oxidize reduced species, such as Fe , Mn , and 2+ 2+ sulfide thesn I . e reactions, chlorin reduces ei inorganio dt c chloride (Cl~). Second, chlorine can add to olefins and other double-bond-containing organic compounds to produce chlorinated organic compounds. Third, chlorine can substitute onto 13

chemical substrates additioe Th . substitutio d nan n reactions produce organochlorine species (e.g. chlorination of phenol to chlorophenols), or active chlorine species (e.g. chlorinatio ammonif no producao t e monochloramine). Chlorine reacts with naturally occurring organic compounds via a combination of these mechanisms to generate such products as trihalomethanes (THMs).

Oxidant deman oxidand dan t requirement significantle sar y affecte chemicae th y db l and physical characteristics of the sample and the manner in which the oxidant consumptio s measuredi n n particularI . , oxidant reactivit s influencei y y b d temperature, pH, contact time, and oxidant dose. Sample temperature strongly affects reaction kinetics, and thus affects also the demand exerted in a given contact time. Sample pH affects reaction kinetics and thus the nature and extent of the demand r exampleFo . , ozon unstabls ei t hig ea value H h p ozon d san e demans di especially sensitive to sample pH. Oxidant demand increases with time and therefore the demand must be defined for a given contact time. Oxidant demand also is very dependen oxidann o t t dose. Increasing oxidant dose usually will increase demand, but it is incorrect to assume that doubling the oxidant dose will double the oxidant demand thesr Fo .e reasons difficuls i t i , extrapolato t t e oxidant demand data from one set of conditions to another.

2.2.3 Redox Control for Pathogen Management The control of pathogenic bacteria and in potable water has evolved into a complicated set of checks and procedures. It is no longer sufficient to simply add chlorin specifiea o et d leve leav d greatesthatt e a an l t eTh i . t concern these days i levee th disinfectiof lo n byproducts possible ,th e dissolutio metalf no s like copped ran lead potentiae ,th l los disinfectanf so t alon distributioe gth n hos a line othef d to san r consequences.

It is becoming very clear that the less chlorine is added and still ensure the disinfection required, the better. This however, is made difficult by the chemical 14

characteristics of chlorine; a portion of the added chemical will almost certainly combine with constituents in the water to form less germicidal compounds. In addition, changes in water conditions such as pH impact strongly on chlorine's ability disinfecto t . valueT C e , whicTh produce disinfectane th s th hi f o t t concentratio mg//n n(i d )an contact tim minutes)n e(i , give indication sa totae th lf n o oxidativ e power availableo t kill micro-organisms in a specific configuration. The CT values for different oxidants and micro-organisms vary. Stronger oxidants like ozone would requir loweea r concentratio shorted nan r contact time thereford ,an smalleea valueT rC achievo ,t e the same resul weakea s a t r oxidant suc monochloramines ha valueT C . s coule db use controo dt l disinfectio t ther legitimatne bu ear e concerns about whethee th r approach accomplishes effective disinfection. For one thing it fails to recognize the failin residuaf go l measuremen indicato t e disinfecting powe worr ro k value.

Redox is an analytical technique that measures the potential for oxidation to take plac treatmena n ei t system. Since disinfectio oxidanty nb s like chlorine, chlorine dioxide, bromin ozonr eo e result fro oxidatioe mth micro-organismsf no standt ,i o st reason that measuring the potential for oxidation to occur should give a clear picture disinfectioe th f o n powe treatmena f ro t system. Several studies would indicate that redox potential accurately predicts disinfection rate. Indeed, oxidative effects are known to be responsible for the disinfection phenomenon.

In the 1960s, Ebba Lund was studying inactivation rates resulting from the addition of various oxidants to test samples. Her studies revealed a direct correlation between redox potentia inactivatiod an l n r studierateHe . s found too, thae th t correlation between chlorine concentration (residual inactivatiod )an n ratepoors ,wa . It was discovered that in addition to pH and temperature, the quality of water had a direct impact on chlorine's ability to disinfect. Any material in water that has the 15

ability to lower the redox potential reduces the ability of a given residual of chlorine to kill micro-organisms.

Oxidatio lose electronf th so s n i s from some species specieorganie e b Th y . r scma o inorganic, livin deadr speciege o Th . s which gains electrons oxidizee s th i s i ,d ran sai havdo t e been reduced. Whe nspeciea oxidizes i reducer do changedt i s chemical characteristics due to the electron transfer. For instance, the conversion of metallic iron to iron oxide (rust) is caused by oxidation. Even though the substance still exists after oxidation took place s chemicait , l structur beed eha n altered. Experiments demonstrated that a given redox potential maintained for a period of time would produc a repeatable e inactivation curv r micro-organismsfo e . Residual oxidant concentratio s tracke e samnwa th en di experiment produced an s d very different results. Holding a constant residual showed no consistent relationship to inactivation rate.

Harriett efirse Chicth t s researchekwa applo rt principale yth reactiof so n kinetico st disinfectioe th n process establishmene studier th o t He . d sle whaf to t became known Chick's a s Law, which states:

——<** dt Where: Nquantit= reactantf yo , k - reaction constant, time= t .

Lund's work led to the development of a third and more practical equation. Lund's Law states that:

dt c

E-EC represent redoe sth x potential maintaine excesn di minimua f so m threshold. Using calculu rearrango st equatioe eth simplifiee nth d final form results: 16

n = Calculated constant

Lund' statew decreasesLa g s lo tha e tth micro-organism n i activity proportionals i o t the product redox e oth f maintained contacte th d an time. purpose Th Lund'f eo s Law is to provide a practical equation that can be reliably used in actual water treatment situation predico st t inactivation time, base parametea n do r tha easils ti y measured and controlled. Unlike the current CT rules, Eh values are independent of chlorine species, pH, temperature and water quality. (Stand, 1994)

The formatio disinfectiof no n by-product majoa w rno concers si potabln i e water treatment, especiall theis ya r regulated limit continuousle sar y being lowered. THMs take three day morr so fulleo t y develo lowee th chlorin e d rth pan e dosage lowee ,th r the ultimate THM level. Redox technology can help minimize levels in both of these areas, by reducing the over dosage of chlorine.

Chlorine residua s alwayha l s serve s basia d f controo s t displaybu l s several shortcomings. Redox monitoring however, shows promise in overcoming these. By continuously reportin e actuagth l disinfecting powechlorinatee th f o r d process, redox-based control scheme regulatn sca e chlorine feed rat exactlo et y matce hth requirement. This chlorine minimization will in turn reduce the exposure to THM formation (Strand, 1994). 17

. 3 METHOD EQUIPMEND SAN T USED

3.1 Methods use chemicar dfo physicad an l l determinations

3.1.1 Redox Potential

A redox potential electrode from Swiss Laboratories with platinum titrode part no. 6.0431.10 uses 0dwa throughou tese tth t progracalibrates wa d man df o ever y yda recommendee th n i e us d solution.

3.1.2 pH sleevA e diaphragm Metroh electrodmH p calibration e th use s d edwa an s done every day of use at pH 4 and 7. The accuracy of the electrode was tested by measuring the pH o buffefa r at . pH10

3.1.3 Chlorin oxidand ean t concentration N, N- di-diethyl-p-phenylenediamine (DPD) was used as indicator in the titrimetic procedure with ferrous ammonium sulphate (FAS s titrana ) o measurt t e th e concentratio f chlorinno othed ean r oxidant e solutionsth n i s . Where applicable distinctio mads nwa e betwee varioue nth s chlorine species, i.e. monochloramind ean di-chloramine that could be present by the addition of small amounts of iodine to the solution same Th .e reagent methodd san s were use determino dt concentratioe eth n mixee th f do oxidants, specificall anolytee resulte yth th d s an ,expresse mg/s da i chlorine. The minimum detection limit with these methods is 0.018 mg/i of chlorine. Method #45566 American Public Health Association (APHA), American Water Works Association (AWWA) and Water Pollution Control Federation (WPCF), "Standard Methods Examinationthe for Waterof Wastewater".and

3.1.4 Ozone, chlorine and hydrogen peroxide concentrations in the gas phase. Drager reaction tubes were use measurdo t concentratioe eth ozonef no , chlorind ean hydrogen peroxide wher don e coult ei b conventionae t eb dno l mean anolyte th n si e 18

and catholyte vapours. The following tubes were used:

Tube number Measuring range

Ozone (O3) CH21001 20 to 300 parts per million (ppm) 3 Og 3 m /m 2 = ) m (1pp part0 millior 50 s pe o t n0 5 (ppm) 1 70 0 2 H C Chlorine (C12) 3 (lppmCl2 = 2,95mg C12/m )

part3 millior o t s pe 1 Hydroge0, n (ppm) n peroxid 1 30 e0 (H3 2H OC 2) 3 (Ippm H2O2 = 1,4 mg H2O2 /m ) (Dragerwerk Aktiengesellschaft Liibeck, 1997)

3.2 Methods used for microbiological determinations Standard Plate Count Escherichia bacteria e usecolis th n wa di l suspension expose oxidantse th o dt e Th . original culture was isolated from water with the membrane filter technique on M-FC agar incubate 44,5°t da 1r 8C fo hour s accordin accreditego t d metho 1.2.2.03.o dN 1 of Rand Water.

Standard plate count hour8 t 37°4 a s r sCfo were performe o determint d e eth efficienc mixee th f dyo oxidant chlorinr so e agains exampln colia tE s a typicaf eo l heterotrophic bacteria. Pour plates with dilutions as required were made with yeast extract agar according to the accredited laboratory method No 1.2.2.01.1 of Rand Water. Results were expressed as the number of colony forming units per ml. (cfu/m/).

3.3 Description of equipment used.

3.3.1 Mixed oxidant generator. The number of different mixed oxidant generators available on the local market is limited with the result that only two different mixed oxidant generators could be 19

tested. Flow throug devicee hth s were more than significantly influence levee th ly db reservoie heighsale anolyte th e n th th t i th f catholytd f d o to ran e an e discharge tubes in relatio mixee th no dt oxidant generator floe w.Th resistanc thesen i e tubes alsd oha a significant affect. A locally assembled unit, using Russian made components, proved to be particularly difficult to operate as the flow through the unit fluctuated and precise t possiblecontrono s fulle wa lTh y. imported Electrochemical Activation (EGA) unit, REDO Diaphragmalyser produced by the Russian firm NPO Perspektiva base Dubnan di , Russia prove more b o det reliable. Howeve founs wa dt ri thae tth qualit produce th f yo t alsvers oywa sensitiv adjustmento et eitheo st electricae rth l current applied or restricted discharge of the products. To avoid this problem calibrated peristaltic pumps were used to dispense the anolyte and catholyte solutions in the correct proportions as required. A calibrated peristaltic pump was used to dispens volumee eth bacteriaf so l suspensions when required Figure Se . ea 3.r 1fo schematic diagram of the EGA equipment, REDO Diaphramalyser, as used in the experiments. 20

Anolyte Discharge Catholyte Discharge

Brine Inlet

o: Catholyte inlet H

Anolyte inlet

Reactor A: Reactor in which anolyte is produced. Reactor C: Reactor in which catholyte is produced Figur1 e3. Diagram of Electrochemical Activation Equipment (EGA)

Of the emphasized and promoted attractions of the mixed oxidant generators are the economical running costs based on the low electrical consumption and the use of cheap freely available table salt. It was found that the brine produced with this salt tended to clog the tubes and damage the membranes very quickly, requiring frequent descaling of the systems. lodinated salt was not used to avoid the possibility of 21

forming undesirable iodine based by-products durin electrolytie gth c processo T . circumvent these problems, laboratory grade sodium chloride was used.

Changes in the ambient temperature also affected the performance of the generators anqualit e anolyte dth th catholytf d yo ean e negatively. Throughou experimente tth s brinwatee p uses th ta r er dwa preparationfo . Manuals supplied wit generatore hth s advised tha sale tth t concentrations electrolyt e useth dn i e coul betweee db 1d 0 an n3 percent cleas wa r t tha.I t this concentratio strona d nha g influenc currene th n eo t that coul e qualitappliee db th d f catholytee anolytyo dan th d eadvican n e O th . f eo supplier of the equipment a 3% sodium chloride solution was used to feed the generator thit A .s concentratio frequence nth cleaninf yo membranee gth reduces i d as well as the possibility of damage as a result of build up of scale. This sodium chloride concentratio lowese th s whict nta wa electrin ha c curren suitablf to e strength produced high concentrations of oxidants at low pH in the anolyte and the catholyte was strong alkali.

3.3.2 Apparatus used to expose bacterial cultures to mixed oxidants During the course of the test programme it became clear that the way in which the anolyte e solutioth s a , n that contain e stronsth g disinfectant mixes i s d wite hth bacterial suspension woul importante db . Sinc possibls i et i e tha anolyte tth e contains oxidants with a very short half-life, experiments were designed such that the oxidative powe solutioe th n ri n coul preservee db d until whild micro-organism,an e eth s were exposed to anolyte. To dilute the anolyte to a concentration equivalent to that of a chlorine solution used for the disinfection of drinking water and apply it in small bench scale experiments, was difficult and did not produce the desired results. Experiments were then designe whicn di bacteriae hth l suspensions were exposedo t anolyte desiree th th f eo d concentratio eithen i r batc flowr ho - through mode.

experimente th l Inal s wher oxidative eth microbiocidar eo l powe anolyte th f s ro ewa testecompares wa t di d wit equivalenn ha t concentratio chlorinef no e Th . 22

concentrations (activity botf )anolyto e hth chlorind ean e solutions were determined with DPD titrations using FAS as a titrant and the results expressed in terms of mg// chlorine. The aim normally was to use chlorine concentrations similar to those used for disinfectio f drinkinno g water. Thi mg/4 ordee s 2- fref th woul o /f n eo ri e db available chlorine.

The batch experiments were done in a 200 litre plastic container with a stirrer. The bacteria were suspende litr0 f unchlorinate10 eo n di d clarifie damoune wateth d f oxidanan o rt t (anolyte) added was equal to the chlorine concentration applied in a duplicate experiment. Anolyte was added through a submerged tube at the bottom of the drum to avoid any loss of the anolyte to the atmosphere and to ensure good mixing. Addition of the anolyte continued unti desiree lth d oxidant concentratio watee obtaineds th n ri wa . Samples for bacteriological and chlorine determinations were taken after respectively 1,5,10 and 30 minutes contact time from the containers. See Figure 3.2 for a schematic diagram of the equipment used for the batch experiments.

-Water with bacteria -Stirrer

_Addition poinf to Anolyte

Figure 3.2 Diagram of equipment used for batch experiments to test bactericidal effects of the anolyte and hypochlorite

possibilitAe sth y existed that volatil reactivd ean e oxidants presen anolyte th n o te could escape fro solutioe mth reacr no t with constituents other tha bacterie nth n ai 23

watee th flora w through syste closemn i d vessel designeds swa .

The flow-through system comprised of five identical glass vessels of 50 cm3 each connected in series. Anolyte and hypochlorite solutions and suspensions of the bacteri testee b o adt were metered with calibrated peristaltic pump mixed e sth an n di desired proportions in the glass vessels. Flows through the reaction vessels were adjusted to achieve the required contact time of one minute in each vessel. Samples coul e systestag y takee th d b an n ei t m na wit maximuha m contact tim f fiveo e minutes. See Figure 3.3 for a schematic diagram of the flow-through system.

Bacterial Suspension

r~7 n r~7 n

Peristaltic Pumps

\J \J \J V V V pH Redox

Measurement Anolyte/ Sample Points Hypochlorite

Figure 3.3 Diagram of the flow-through system used to test the bactericidal effect of the anolyte and hypochlorite 24

4 RESULTS AND DISCUSSION

4.1 Reliabilit equipmene th f yo consistencd tan produce th f yo t

The two mixed oxidant generators available were tested for reliability, ease of operation, the consistenc e producth f yo t produce e repeatabilitth d an d f resulto y s unde e samth r e conditions. After selectin bringa e concentratio currene th d ntan settin qualite e gth th f yo anolyt catholytd ean e solutions were measured ove periodra performance Th . botf eo e hth mixed oxidant generators were influence operatiny db g factors brin e liklevee th eth f e o l containin gproduce vesseth d an tl discharge tube relation si generatoe e th th o nt d an r electrical potential ove electrodese rth . Electrical control generatore th n so s were corroded by the anolyte and catholyte vapours resulting in failure, poor control and difficulty in setting the current s appliethawa t d accurately. Although similar operational problems were experienced with both the generators, the EGA (REDO Diaphragmalyser) unit was used predominantly as it was more reliable, was relatively easy to operate and the reproducibility of the products were high.

4.1.1 Relationship between redox potential and pH in the anolyte and catholyte

Figure 4.1 depict relationshie sth p between redox potentia. FropH m d this i an l t si clear that higher redox potentia anolyte l th wer n i e H whilobtainep e w eth lo t da inverse, producin glowea r redox potentia t higa l catholytee h th trupHs r ewa ,fo . keepinn Thii s si g wit face hth t thaanolyte th t e containe strone dth g oxidising compounds responsible for the biocidal effects. Redox potential values as high as + 1200mV were recorded.

The low pH can be attributed to the high chlorine concentration, up to 1500 mg//, present in the anolyte while the hydroxide anión concentration present in the catholyte is responsible for the high pH. 25

1500

1000 - Anolyte

500 H

tu Catholyte o - oX a atSJ -500 -

-1000 6 8 10 12 14 PH

Figur 1 e4. Relationship between redo xanolyt n potentiai catholytH d p ean d lan e

4.1.2 Relationship between flow rate through the generator and redox potential As can be seen from Figure 4.2, flow rate through the generator influenced the redox potential of the anolyte. Higher redox potential values were recorded at lower flow rates with longer detention time in the reactor. 26

1400

1200 -

¿ 1000 < - 0 80 H tú O 600 - X S 400 -

200 -

O 0 60 0 50 0 40 0 30 0 20 100 700 800 FLOW ( ¡al minI )

Figure 4.2 Relationship between flow rate through the generator and redox potential in the anolyte.

4.1.3 Reproducibility of results

The ability of the anolyte and cathloyte generator to repeatedly produce a product of consistent quality was tested by running the generator under the same operating conditions using the same instrument settings a number of times in succession. From cleas i Figur t i r 3 thae4. produca t consistenf o t t quality measures a , redoe th y xdb potential, coul producee db d unde same th r e operating condition f repeatesi n di different test runs. The results of nine such tests are shown in Figure 4.3. 27

1000 - 800 - 600 400 -

TEST RUNS

• anolyte ~*~ catholyte |

Figure 4.3 Reproducibility of anolyte and catholyte quality in successive operations

4.1.4 Consistenc anolyte th f yo e quality The potentia anolyte th f lo achiev o et especifia c redox potential valu waten ei s rwa compare sodiuthaa do t f o t m hypochlorite solution. Redox potential measurements for both oxidants were taken in stirred batch as well as continuously flowing solutions while the data was recorded electronically. The aim of the experiments was two fold: determino T . 1 what ea t rat redoe eth x potentia respective th f lo e solutions would change due to decay in the batch process. Based on the results it would then be possible to see if there is a cut off point before the bacteria had to be introduced withou oxidative th t f losino y eg an power . Whethe2 . redoe rth x potential would remain constan continuousle th n i t y flow experimen sho5 t4. e wFigured th an 4 s4. result respectivelr sfo anolytsodiue e yth th d mean hypochlorit stirree th n ei d batch experiments and Figures 4.6 and 4.7 in the continuously flowing experiments. From thes eseee graphb nn tha qualitca e oxidantt se i t th th f yo s remained consistent during 28

the recording period. This gave the assurance that the redox potential in the solutions would remain constan periodr tfo s long enoug introducho t exposd ean bacterie eth a knowa o t n redox potential.

yuu - ^ 800 -

£. 700 -

J 60°

g 500 a O 400 • 0. X O 300 aQ - 0 20 01

100 o - () 200 400 600 800 1000 1200 1400 1600 1800 2000 TIME IN SECONDS

Figur 4 e4. Redox potentia measurs la anolytf eo e activit stirrea yn i d batch volume against time.

1000 -

900 • ^ •«•"•""•"••'•"'•••''•^ """""^ 800 -

- 0 70 -§

g$ 600-

| 500- x 40°- O Q 300-

200

100 o - 0 80 100 0 060 0 12040 0 0 20 140() 0 1600 1800 2000 TIM SECONDN EI S

Figure 4.5 Redox potential as measure of chlorine activity in a stirred batch volume against time. 29

900 -

800

700 -

600-

500 - g 400 ' Q 300 - a.fid 200-

100 -

0 0 90 0 80 0 70 0 60 0 50 0 40 0 30 0 20 0 10 0

TIME IN SECONDS Figure 4.6 Redox potential as measure of anolyte activity in a continuously flowing steam against time.

1200

1000 > I J 800 H i 600 BU

200 -

0 90 100 0 080 0 70 0 60 0 50 0 40 0 30 0 20 0 10 0

TIME IN SECONDS Figur 7 4. eRedo x potentia measurs la chlorinf eo e activit continuousla yn i y flowing steam against time. 30

4.2 Chemical composition of the anolyte At all times during the operation of the mixed oxidant generator relatively large volume f gaso s proportion ,i n wit e volumhth f anolyto e r catholyteo e , were produced. The anolyte contained about 15% by volume of gas and the catholyte some 30%. Analyses of the gas in the product streams confirmed that oxygen was present in the anolyte and hydrogen in the catholyte. The gas is most likely due to the electrolysi waterf so .

It was not possible to analyse the product streams for all the possible oxidants that, according to literature and the information on the generators, could be present. The following compounds that could be detected more easily in the fluid or the gas phase were analysed for: chlorine, monochloramine, di-chloramine, ozone and hydrogen peroxide.

Table 4.1 The concentration of the various determinants in the anolyte and catholyte fluivapourd dan s

Concentration Concentration in the fluid (mg//) in the vapour (mg/m3) Anolyte fluid Chlorine 1200 Mono-chloramine < 1 Di-chloramine < 1 Anolyte vapour Ozone 600 Chlorine 1475 0 2 Hydrogen peroxide Catholyte flui1 d Chlorine Mono-chloramin1 < e 1 Di-chloramin< e 0 20 Catholyte vapour Ozone Chlorine <1 Hydrogen peroxide 80

The concentratio oxidative th f no e specie vapoure th n si s were determined wit commerciae hth l Dráger Tube apparatus. Tubes sensitive for the various compounds that were suspected of being presen vapoure th n ti s wer readinge e th use d dan s obtained, converte expreso dt concentratioe sth n 31 f vapouro 3 /m .g Determinatiom s a f oxidanno t concentrations other than tha f chlorino t e th n ei anolyte and catholyte fluid presented many problems and no reliable results were obtained. This was combinee th possibl o t e d variouy e du effec th f o t s oxidative species analyticae presenth d an t l methods that were used methodpotassiue e th Th . d an s m includeD indigDP e odth trisulphonate colorimetric methods of determination for chlorine and ozone respectively. Disadvantages of these method thae sspecit ar t theno compoune r eyo ar d specifi falsd can e positive resultobtainee b n sca d in mixtures of strong oxidants. The masking of possible interfering compounds present in the solution t attempteno s swa d

suitablo N e method coul foune db determino dt presence eth concentratioe th r eo fref no e radical species that are purported to be present in the product streams.

Microbiocida3 4. l effectanolyte th f so e

The results of the microbiological tests are summarised in Tables 4.2 and 4.4 and the percentage reduction of the bacteria on exposure to the two oxidants in the batch and continuous flow experiments are given in Tables 4.3 and 4.5 respectively. 32

Tabl 2 e4. Comparison betwee bactericidae nth l effec anolytf to chlorind ean e solutionn si batch experiments. Test Oxidant Standard Plate Count (cfu/m/d an ) Concentration [oxidant concentration] (mg//) Before Aftex e r posure for: exposure 1 Minute Minute5 s 10 Minutes 30 Minutes to oxidant Anolyte 29000 71 40 34 37 1 Eqv. Chlorine cone. [4.6] [4.4] [4.0] [3.8] [3.5] HOC1 19800 62 100 1500 38 Chlorine cone. [3.2] [2.7] [2.0] [1.8] [1-5] Anolyte 1900 30 20 24 11 2 Eqv. Chlorine cone. [4.4] [4.0] [3.9] [3.7] [3] HOC1 2800 300 40 12 16 Chlorine cone. [3] [3] [3] [3] [2] Anolyte 89000 30 120 60 500 3 Eqv. Chlorine cone. [4.0] [4.0] [3.7] [3.5] [3.0] HOC1 97000 38 90 32 15 Chlorine cone. [4.0] [3.8] [3.3] [3.1] [2-5] Anolyte 181000 No result 2100 520 15000 4 Eqv. Chlorine cone. [3-0] [3.9] [3.7] [3-6] [3-4] HOC1 103000 930 4700 460 3100 Chlorine cone. [4.0] [2.8] [2.5] [2.2] [1.9] Anolyte 21600 47 60 40 10 5 Eqv. Chlorine cone. [2.0] [1.8] [1-9] [1-7] [1-2] HOC1 1600 5 70 40 80 Chlorine cone. [3.0] [2.4] [2.0] [2.0] [1.6] HOCL = Hypochlorite solution Eqv chlorine concentration = Equivalent oxidant activity measured as "chlorine" concentration in anloyte. Chlorine con Chlorine= e concentratio measures na hypochlorite th n di e solution. CF UColon= y forming units Test conditions: pH of water 7,9 Temperature of water: 15°C 33

Tabl Compariso3 e4. n betwee percentage nth e reductio f bacteriano l numbers exposeo dt anolyte and chlorine solutions in batch experiments

Test Oxidant Reductio% Standarn i d Plate count after Overall exposure for % 1 5 10 30 reduction in test Minute Minutes Minutes Minutes Anolyte 99,75 99,86 99,88 99,87 99,84 1 Eqv. Chlorine cone. [4,4] [4,0] [3,8] [3,5] HOC1 99,68 99,49 92,42 99,80 97,84 Chlorine cone. [3,2] [2,7] [2,0] [1,8] [1,5] Anolyte 98,42 98,94 98,73 99,42 98,87 2 Eqv. Chlorine cone. [4,0] [3,9] [3,7] [3] HOC1 89,28 98,57 99,57 99,42 96,71 Chlorine cone. [3] [3] [3] [3] [2] Anolyte 99,96 99,86 99,93 99,43 99,79 3 Eqv. Chlorine cone. [4,0] [3,7] [3,5] [3,0] HOC1 99,96 99,90 99,96 99,98 99,95 Chlorine cone. [3,8] [3,3] [3,1] [2,5] Anolyte resulo N t 98,84 99,71 89,91 99,48 4 Eqv. Chlorine cone. [3,9] [3,7] [3,6] 3,4] HOC1 99,09 95,43 99,55 96,99 97,76 Chlorine cone. [2,8] [2,5] [2,2] [1,9] Anolyte 99,78 99,72 99,81 99,95 99,81 5 Eqv. Chlorine cone. [1,8] [1,9] [1,7] [1,2] HOC1 99,68 95,62 97,5 95,00 96,95 Chlorine cone. [2,4] [2,0] [2,0] [1,6] HOC LHypochlorit= e solution Eqv chlorine concentratio Equivalenn= t oxidant activity measure "chlorines da " concentration i anloyte. Chlorine con Chlorine= e concentratio measures na hypochlorite th n di e solution. Test conditions: pH of water 7,9 Temperature of water: 15°C

Overall % reduction in test: Results calculated from the percentage reduction obtained after respectivel minute5 o t y1 s contact time. 34

Tabl 4 e4. Comparison betwee bactericidae nth l effec anolytf to chlorind ean e solutionn si continuous flow experiments.

Test Effect of Anolyte (Oxidant) Effect of Hypochlorite Eqv. Initial Eqv. Standard Chlorine Initial Chlorine Standard Chlorine Standard Chlorine Plate Cone. Standard cone, Plate cone. Plate cone, Count (mg//) Plate after 5 Count (mg/0 Count after5 after 5 Count min. after 5 (cfu/m/) min. min. (cfu/m/) (mg/0 min. (mg//) (cfu/mO (cf/mO 1 3.3 13200 2.3 30 3.8 12500 3.3 7 2 4.2 54800 3.4 6 4.1 21100 0.2 230 3 6.2 89000 3.5 25 5.4 42000 4.1 180 4 5.4 8300 4.5 29 6.1 8300 5.1 26 5 7.2 42000 5.1 20 6.1 48000 5.1 11 chlorinv Eq e concentratio Equivalenn= t oxidant activity measure "chlorines da " concentration i anloyte. Chlorine con Chlorine= e concentratio measures na hypochlorite th n di e solution. cfu = Colony forming units Test conditions watef o 9 H r7, p : Temperatur waterf eo : 15°C

TABLE 4.5 Comparison between percentage reduction in bacterial numbers exposed to anolyte and chlorine solutions in continuous flow experiments.

Test Effect of Anolyte (Oxidant) Effect of Hypochlorite Eqv. Eqv. % Chlorine Chlorine % Chlorine Chlorine Reduction Cone. cone. Reduction Cone. cone. after 5 (mg/0 After5 after 5 (mg/0 After 5 min. min. mm. min. (mg/0 (mg/0 1 3,3 2,3 99,72 3,8 3,3 99,94 2 4,2 3,4 99,98 4,1 0,2 98,91 3 6,2 3,5 99,97 5,4 4,1 99,57 4 5,4 4,5 99,65 6,1 5,1 99,68 5 7,2 5,1 99,95 6,1 5,1 99,97 Eqv. Chlorine concentration = Equivalent oxidant activity measured as "chlorine" concentration in anolyte. Chlorine cone. = Chlorine concentration as measured in the hypochlorite solution. Test conditions: pH of water 7,9 Temperature of water: 15°C 35

above Inth e experiment s endeavourewa t i s applo dt closs ya possibls ea e similar oxidant concentrations measured as mg/7 of chlorine in the form of anolyte and chlorine solution to the bacterial suspensions. From the results it can be seen that both the oxidants were efficient in reducing the number of bacteria present by a large margin. In case of the batch experiments it cleas wa r tha largese th t t reductio bacteriae th n i l numbers took place withi firse nth t minute after the oxidant had been added for both the anolyte and the chlorine solution. The percentage reduction after five minutes contact time in this case varied between 99,87 and 99,89 for the anolyt betweed ean n 96,7 99,9d 1chlorine an cas5n th i f eo e solution, whil overale eth l average reduction was 99,56 and 97,84 for the anolyte and chlorine respectively after five minutes contact time apparene .Th t poorer results obtaine experimentae th de wit chlorindu e he th b y l erroema n ri Standare th d Plate Count determination wher somn ei e instance increasn sa counte th n ei s were noticed after five minutes contact time. If these figures are excluded from the calculations the overall percentage reduction by the chlorine will be slightly higher at 98,92 percent. Similar results were obtained in the flow through experiments. Bacterial numbers exposed to the anolyte was reduced by between 99,65 and 99,98 percent and between 99,57 and 99,97 percen chlorinee th y tb thesn .I e case overale sth l average reductio 99,8s 99,6ne d wa 5th an r 1fo anolyte and the chlorine respectively.

From the above it can be seen that little difference could be detected between the effect of the anolyte and chlorine solutions on the number of bacterial present in either the batch or the continuous flow experiments at approximately the same oxidant concentration as expressed in term f chlorinso e concentration. Althoug percentage t hseemth i f i s sa e reductio bacterian i l numbers causeanolyte th y d b highe s ei r than cause chloriney db difference ,th absolutels ei y marginal. 36 5. CONCLUSION

The results obtained in this study confirm that there are aspects of the production of mixed oxidants welt no tha l e understootar thereford dan welt eno l defined either. There als ooverlan seema e b po st emerginbetweew ne e th ng scienc f electrochemicao e l activatio f wateo n re (EGAth d an ) electrochemical formation of mixed oxidant solutions by electrolytic means. The results and affects claime achievee b applicatioe o th dt y db f EGno A technology sometimes border metae th n -so physica enougt no d hlan conclusive evidenc availabls ei eitheeo t r suppor discarr to claime dth s made. Since only two different Electrochemical Activation (EGA) devices were examined, and both posed or developed operational problems during the tests, it would unfair to make comments on any other EGA devices that may be available commercially or on the functioning of improved models as those that were tested. Results obtained however indicate that despite the operational problems experienced that it is possible, based on the redox potential of the solution, to produce an anolyte of consistent quality. Reproducibilit resulte th f y o expectes e werb n eca t goodi d thadan t this aspecf to the performance of the mixed oxidant generators could be equaled or improved in devices which are of better design and construction. This aspect was not only important for the execution of the tests, which were don woult ebu d significanf also e ob t importanc commerciaf ei mixea f o de oxidanlus t generator had to be considered. Redox potential of the anolyte taken over a period of time showed that the decay in the oxidative power was slow and in the tests it could be kept constant long enough to expose the bacteria to solution with a known redox value.

The possible applicatio mixef no d oxidant disinfectanta s sa investigateds wa , . Although cars ewa experimente taketh n ni preservo st mixee eth d oxidant (anolyte) solutio harveso nt totae th t l potential oxidative power, and the possible synergistic effects of all the oxidants present, its effect did not significantly exceeded tha chlorinef to fac e spit.n i th Thi t f s thae o anolyt e swa tth e vapoursd ,an presumably the anolyte solution as well, contained other strong oxidants such as ozone and hydrogen peroxide alss owa confirmet .I d tha catholyte tth e solutio contait no d nndi chlorin concentrationt ea s that would have significant microbiocidal properties. This fact is also supported by the low or negative redox potential measure catholytee th n di . 37

Results from batch experiments show that the greatest reduction in the bacterial numbers took place withi firse nth t minute mosn I . t cases bot anolyte hth chlorind ean e killed e morth f o e tha% n99 bacteria present during the first minute of exposure. Increased contact time did not significantly reduce the numbers of the bacteria any further. In all the batch tests the average percentage reduction in bacterial numbers were respectively anolyt 97,8e 99,d th an r chlorin5d 45 fo ean e solution after five minutes contact time. The over all percentage reduction in the continuous flow tests were 99,85 for anolyte th chlorinee 99,6d th ean r 1fo .

thereforn ca t I concludee eb d that unde tese rth t conditions that prevailed thamixee th t d oxidant generators examine product no d ddi e anolyte solution spropertiee witth l hal claimes sa literaturedn i . unite Th sproduct testeno d ddi producea t that behaved significantly differently from chlorine either. Although it seems as though mixed oxidant solutions of consistent quality can be produced from Electrochemical Activation (EGA) devices, and improvements in the functioning of the equipment can be expected in future, the use of such disinfectant generator in the rural areas would probably not be practical. As with other electrolytic chlorine generators a reliable electricity source is essential whilst mosn ,i t rural areas this canno guaranteede tb availabilite .Th higf yo h purity sodium chloride mixee th n di e oxidanus o t t generato alsy orma presen problemta furtheA . r problem e coulth e db disposal of the alkaline catholyte solution of which a volume equal to about one sixth of the volume the anolyte, is produced. 38

. 6 RECOMMENDATION FUTURR SFO E RESEARCH

The following aspects of the generation and application of mixed oxidants warrant further investigation:

• Examin understand ean principle dth operatiof eo mixee th f ndo oxidant generator. • Develop methods to analyse for the different oxidative compounds present in the anolyte. • Develop method analys o differense t th r efo t compounds presen catholytee th n i t . • Desig systea f no whicmn i mixee hth d oxidant solutio appliee b n ndca such that full oxidative potential of all the compounds present in the fluid as well as the vapours can utilised . • Examine potential non-conventional applications and benefits of mixed oxidants. 39 7. REFERENCES

Adham, S.S., R.R. Trussell, P.F. Gagliardo A.Wd ,an . Olivieri. 1997. Membranes barrie:a o rt micro-organisms. Blackwell Science Ltd, World Congress 1997. SS1-2 4SS1-28- .

American Public Health Association (APHA), American Water Works Association (AWWA Wated )an r Pollution Control Federation (WPCF), "Standard Methodse th r fo Examination of Water and Wastewater", 18th ed., Washington, 1992, American Public Health Association, p 294 - 319

Bakhir, V.M. 1990. Electrochemical Activation: The Chemical Compound and Properties of Electrochemically Activated Solutions. Moscow, Russia, pp. 1-11.

Dragerwerk Altiengesellschaft Lübeck, 1997. Drager-Tube Handbook. Soil, water and air investigation wels s a technica s a l analysiss ga l . 11th Edition.

Los Alamos Technical Associates. 1993. MIOX Operations User's Guide. Albuquerque, N.M. pp.i 22.

Strand, R.L. 1994. Redox Automation for Pathogen Management. Stranco Incorporated, Bradley, Illinois, . 1-7pp . Srand,R.L. 1994. Istumental Methods for Meeting Rechlorination Requirements.

Wabner, D.W. W.Dd an , . Fleischmann. 1986. Electrolytic Disinfection Productio Smalr nfo l Water Supplies. Munich, Germany, pp. 1-37.

White, G.C. 1992. Handboo f Chlorinatioko Alternativd nan e Disinfectants Norstrann Va . d Reinhold .New York. 1308 p. Water Research Com m i s s i o n PO Box 824, Pretoria, 0001, South Africa 0340 0 Tel17 233 +2 : , Fax: +27 12 331 2565

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