Journal of Environmental Management 90 (2009) 1909–1917
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Journal of Environmental Management
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Real-life efficiency of urine source separation
L. Rossi a,*, J. Lienert b, T.A. Larsen b a Swiss Federal Institute of Technology (EPFL), ENAC ISTE ECOL, Station 2, 1015 Lausanne, Switzerland b Eawag, Swiss Federal Institute of Aquatic Science and Technology, U¨berlandstrasse 133, 8600 Du¨bendorf, Switzerland article info abstract
Article history: Urine source separation (NoMix technology) is a promising innovation in wastewater management. To Received 3 July 2008 improve and further develop NoMix technology, it has been implemented in four Swiss households and Received in revised form at our research institute (Eawag). We conducted measurements during one year on frequency of toilet 9 December 2008 usage (in households 5.2/person/day for weekdays, and 6.3/person/day for weekends), flushing behavior Accepted 8 January 2009 (30–85% small flushes), and recovered urine. We calculate the amount of urine effectively recovered per Available online 5 February 2009 voiding in NoMix toilets (138 ml/flush in households; 309 ml/flush in women’s toilets at Eawag), and waterfree urinals (225 ml/usage). We estimate urine recovery in the households to be maximally 70–75% Keywords: Flushing pattern of the expected quantity, leaving room for technical and behavioral improvements. Based on sampling of Nitrogen loading N and P concentrations, we suspect nitrogen losses in the extended urine piping system. For households NoMix technology and workplaces, the daily and weekly flushing pattern is recorded. Our results are in accordance with Toilet use literature data from a shorter period but with more people. These results represent a good dimensioning Urine recovery basis for future urine source separation applications. An example of extrapolation to an entire watershed is presented. The flushing pattern corresponds well with the typical nitrogen loading of a treatment plant. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction per capita for the investment in NoMix installations, assuming a life expectancy of 15 years for these installations. CSO control is also Urine source separation has the potential to become an integral relatively expensive due to the high price of CSO tanks (in part of mainstream wastewater treatment where high nutrient Switzerland about 1000 US$/m3). In one example, a CSO tank of elimination rates are required (Larsen et al., 2007). Although the 2000 m3 was necessary to avoid ammonia risks in the environ- potential is of course larger in areas with no existing wastewater ment, which corresponds to a total investment of about 2 M US$. management infrastructure, there is still room for improvements of Rossi et al. (2004) calculated that with the same money invested in the existing European wastewater treatment plants with NoMix at-source control of urine, about 2100 US$/NoMix installation could technology (Lienert and Larsen, 2007a) – especially if one wants to be invested, however assuming a life expectancy of these installa- obtain high nutrient removal and recycling rates and at the same tions equal to that of CSO tanks. Of course, NoMix technology does time optimize the total energy demand (Maurer et al., 2003; Wil- not allow for the control of suspended solids that play an important senach and van Loosdrecht, 2006). Urine source separation is role during rain events in urban areas. However, if urine in CSOs promising with respect to nutrient removal optimization, because was avoided, one could concentrate on particulate matter without ca. 80% of N and 50% of P from domestic wastewater at treatment the trade off experienced today between suspended matter and plants is contained in urine (Larsen and Gujer, 1996). Furthermore, soluble pollutants (urine also contains about 30% of dissolved NoMix technology may rapidly prove economically interesting, not organic carbon (DOC) and a large part of the soluble phosphorus in only for savings on the treatment plant, but also where combined raw wastewater). sewer overflow (CSO) tanks are primarily necessary due to high One may also want to extend the life time of an existing, over- ammonia loadings. Based on the savings at treatment plants, loaded treatment plant, either by peak shaving (Rauch et al., 2003) Maurer et al. (2005) set approximate benchmarks of 260–440 US$ or by separating advanced nutrient elimination from removal of organic matter (Wilsenach and van Loosdrecht, 2004). If NoMix technology shall rely on local storage and subsequent transport of urine in combined sewers as first suggested by Larsen and Gujer * Corresponding author. Tel.: þ41 21 693 57 80; fax: þ41 21 693 56 70. E-mail addresses: luca.rossi@epfl.ch (L. Rossi), [email protected] (J. Lie- (1996) (for explanations see below), avoiding urine in CSOs is of nert), [email protected] (T.A. Larsen). special importance, and storage capacity must be optimized in
0301-4797/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2009.01.006 1910 L. Rossi et al. / Journal of Environmental Management 90 (2009) 1909–1917 order to avoid transport during rain. Transport of locally stored Faeces etc. urine in combined sewers makes sense in two fundamentally different situations: ‘wave transport’ or ‘peak shaving’. In both versions, urine is stored in the household during daytime and NoMix toilets transported through combined sewers at night. For ‘wave trans- Urine port’, the idea is to obtain as concentrated a urine solution as possible at the treatment plant for further processing, and the Urine tank Sewer release of urine from the storage has to be synchronized accord- with valve Waterfree ingly, taking transport times into account (Huisman et al., 2000). operated by urinals For ‘peak shaving’, one aims at the opposite effect: to level out the remote control nitrogen loading of the treatment plant over 24 h in order to optimize nitrification (Rauch et al., 2003). There are other (combinations of) transport possibilities, but the most difficult optimization of storage capacity follows from the transport in Fig. 1. Principle of urine source separation technology (NoMix toilets) with controlled combined sewers. A stakeholder perspective on different urine release of urine to the sewer system. storage and transport options is presented in Borsuk et al. (2008). For ‘wave transport’, high safety levels would have to be set because overflows would be severe with concentrated urine in the sewer. To study in detail the storage of urine at source in detail, data For this reason we have focused on the peak shaving option, which were collected over one year in four apartments equipped with would have immediate advantages at the treatment plant (opti- NoMix toilets in a Swiss city. The residents were only little informed mizing nitrification) and at the same time would allow for learning about the reason for the NoMix toilets before they moved into the whether real-time control of urine storage tanks is reliable enough apartments. During the study, information and coaching were to assure safe transport also of concentrated urine in combined intensified in order to secure continuation of the study that had sewers. For peak shaving, however, the optimization problem has some negative consequences for the residents (frequent visits of two parameters. Leveling out the nitrogen load of the treatment researchers, practical problems, etc.). A total of ten persons lived in plant and holding back urine in household storage tanks when it the four apartments, including one child of around six years, which rains are opposed strategies, which call for integrated manage- we counted as half a person as approximation in order to account ment. Rauch et al. (2003) demonstrated that in a typical catchment for the smaller amount of urine produced by children of that age around Zu¨ rich in Switzerland, a storage capacity of 10 l per toilet and less toilet use per day (Laak, 1974; Friedler et al., 1996b; and the simplest possible real-time control strategy could produce Almeida et al., 1999; Nijman et al., 2002). The characteristics of a 30% reduction in the peak loading of nitrogen (corresponding to inhabitants (age, occupational activities, socio-economics, etc) are a 30% increase of capacity of the treatment plant) and at the same described elsewhere (Thiemann, 2006). The German company time could reduce the amount of raw urine discharged during rain Roediger produced the NoMix toilets (www.roevac.com), and the events by 50%. A real-time control strategy may be implemented, Swiss company Geberit the water cistern, equipped with two using the electrical network or wireless technology to give a signal flushing modes (www.geberit.com). A small flush corresponds to to empty the recipient. ca. 3 l of water, a big one to ca. 6 l. A closing mechanism opens when In all cases, a necessary pre-condition for a successful integra- people sit on the toilet, allowing urine to be collected separately in tion of NoMix technology into the existing sewer system is a proper the front of the toilet. When people rise to flush, the urine outlet is functioning and understanding of the household sanitary devices: closed, and the entire toilet bowl is cleaned with a normal flush, the NoMix toilet and storage tank. To this end, we must look at the without diluting the urine. To estimate the frequency of toilet uses, technology where it is actually implemented, i.e. in the bathroom. an electrical signal was generated when people pushed the full or For a systematic discussion of the difficulties associated with pilot the small toilet flush button, and it was stored on a logger (Eltek projects in bathrooms, see Lienert and Larsen (2007b). 1000 Squirrel) that recorded the date and time of each flush. In Hence, the aim of this study was to better understand urine order to avoid registering multiple flushes (if people press the same collection and storage in order to optimize the NoMix technology. button several times), the registration of the next flush event was Rather than relying on sociological data (questionnaire surveys, blocked during an interval of about 17 s. This time corresponds to diaries) as others, we used technical measurements to collect data. the filling of the toilet reservoir. The urine from the NoMix toilets We also discuss some of the advantages and shortcomings of this was stored in a 200-litre recipient in the cellar of the house. An approach. The comparison of our results with other literature ultrasonic probe (Milltronics PL-372 probe) measured the urine information will help to define a dimensioning basis for future level every 10 min (acquisition of data in a Microdaq VC-301 implementation of urine separation at source. In this paper, we will process recorder) and converted it to liters according to a linear extrapolate our results to an entire watershed in order to validate rating curve. our approach. The same type of data were collected at a working place, at Eawag, the Swiss Federal Institute of Aquatic Science and Tech- 2. Material and methods nology, during one year. We registered the time of toilet use on a logger in the men’s and in the women’s bathrooms, each equip- 2.1. In house experimental set-up ped with one NoMix toilet (www.dubbletten.nu). In this NoMix toilet, urine is flushed with a small amount of water, and feces with The basic idea of NoMix technology is the separation of urine a normal flush. The amount of flush water for the urine outlet is and feces by means of NoMix toilets and in some cases waterfree supposed to be about 0.1–0.2 l, but in this case it was actually only urinals at the household or institutional level. Urine is stored in 8 ml (6 direct measurements in the toilet itself). The men’s bath- a tank located in or near the households/institutions and if inte- room was further equipped with one conventional toilet and three grated in conventional sewer-based wastewater treatment, feces different waterfree urinals: Ernst (www.system-ernst.de), Uridan are evacuated through the existing sewer system to the wastewater (www.uridan.ch), and Urimat (www.urimat.com). The frequency of treatment plant (WWTP; Fig. 1). urinal use was estimated using a motion detector. The urine from L. Rossi et al. / Journal of Environmental Management 90 (2009) 1909–1917 1911 the waterfree urinals and NoMix toilets was stored in two 500 l 12 tanks situated one floor below, separately for men and women. An ultrasonic probe (Milltronics PL-372 probe) was installed on the 10 urine tanks, during one year for the men’s tank and three months for the women’s tank. All information about toilet use or urine 8 levels in tanks was stored in a database (CODEAU, 1996), allowing a validation of the time dependent variables over long periods. Statistical analysis was performed with the Data Desk software 6 (www.datadesk.com). Social enquiry has been conducted in households through personal interviews and through question- 4 naires at the working place (Lienert and Larsen, 2006). 2 2.2. Validation of the results at the level of a watershed and per day (all apartments) Amount of toilet use per habitant 0 In order to extrapolate the results from at-source control to Mon Tue Wed Thu Fri Sat Sun a watershed level, a measuring campaign was performed during 6 weeks in 2002/2003 on the wastewater treatment plant (WWTP) Extreme value (>95%) Adjacent value Ergolz1 situated in Canton Baselland, Switzerland. The watershed 75% comprises 23,500 habitants (no age distinction). For flow o Extreme value (95%) Median 25% measurements, an ultrasonic probe (Milltronics PL-372 probe) was installed at the entry of the WWTP on a platform, upstream of a combined sewer overflow (CSO). Information was collected every o minute on a Milltronic Logger. The relation between level measurements and flow was established through flow measure- Fig. 2. Pattern of average daily use of toilet per habitant in households over an average ment from a Venturi channel installed downstream of the CSO at week. the entry of the WWTP. This Venturi channel was inspected and calibrated three months before our measuring campaign. During 3. Results rain events, the amount of water discharged to the CSO tank was recorded in order to be able to calibrate also at high water flows. 3.1. Pattern of toilet use in households Ammonia was measured in-line with a WTW selective membrane device (AmmoLyt 700 IQ ammonium sensor, in Fig. 2 shows the pattern of toilet use during an average week conjunction with the AmmoLyt ammonium combination elec- (Monday–Sunday) for all the 9.5 residents in the four private trode). Data were collected each minute on the IQ Sensor-Net households investigated. This figure summarizes more than one system from WTW. The system was maintained by automatic, in- year of measurements. During weekends, the average number of situ air cleaning using compressed air. The probe was installed on toilet uses was significantly larger than during weekdays (week- a swimming mounting device at the entry of the WWTP, allowing days: 5.2 flushes/person/day; weekends: 6.3 flushes/person/day; T- for measurement in a turbulent flow regime, without perturbations test, p 0.0001 < a ¼ 0.05; Table 1). The variations are relatively due to toilet paper or sanitary wastes. The probe was calibrated high, as we consider one year of measurements, including holiday before use and also on a weekly basis during the measuring periods. campaign. Ammonia analyses in the laboratory were performed on In Fig. 3, the hourly flush frequency per apartment is shown. We manual samples of 1 l, 5–10 min after sampling (Dr. Lange chose percentage of usage in order to be able to compare the four #LCK303). The same sample was analyzed 24 h later, after complete apartments directly without taking into account the differences in decomposition of urea present in the effluent. On the basis of these number of flushes per day. The patterns represent the use of toilets manual measurements, the on-line ammonia measurements were over 24 h for an average weekday or weekend. In order to facilitate converted to total urea and ammonia N (a linear correlation was the presentation, the standard deviation is not illustrated. found with R2 ¼ 0.92). Since flow and concentration were both There are of course differences between the four apartments, measured every minute, the resulting load of ammonia/urea-N was but in general the pattern is easily recognizable, especially on obtained with the same high resolution. weekends where the results are less influenced by the resident’s
Table 1 Average number of toilet uses and average urine collected in households and a working place (standard deviations in parentheses).
Number of toilet uses (¼flushes) per person Amount urine collected per toilet use Amount urine collected per day (ml/ and daya (ml/use) person/day)a Households average (Roediger NoMix 5.6 ( 1.4) 138 ( 45) 804 ( 265) toilet) Households weekdays (Roediger NoMix 5.2 ( 1.2) 144 ( 43) 671 ( 232) toilet) Households weekend (Roediger NoMix 6.3 ( 1.3) 135 ( 43) 970 ( 340) toilet) Eawag women (Dubbletten NoMix 309 ( 292) toilet) Eawag men (Dubbletten toilet plus 225( 87) urinals)b
a Because it was not possible to identify the number of individuals using the Eawag NoMix toilets, we cannot identify the number of flushes per person and the urine collected per person. Values in this column cannot be estimated multiplying column 2 and 3, as the distributions are not similar. b Note that 88% were uses of the waterfree urinals, only 12% were NoMix toilets uses. 1912 L. Rossi et al. / Journal of Environmental Management 90 (2009) 1909–1917
12% Apart. 1 Weekdays Apart. 2 10% Apart. 3 8% Apart. 4
6%
4%
2% % of toilet use per hour 0% 4-5h 5-6h 6-7h 7-8h 8-9h 00-1h 1h-2h 2h-3h 3h-4h 9-10h 10-11h 11-12h 12-13h 13-14h 14-15h 15-16h 16-17h 17-18h 18-19h 19-20h 20-21h 21-22h 22-23h 23-24h
Apart. 1 12% Weekend Apart. 2 10% Apart. 3
8% Apart. 4
6%
4%
2% % of toilet use per hour 0% 4-5h 5-6h 6-7h 7-8h 8-9h 00-1h 1h-2h 2h-3h 3h-4h 9-10h 10-11h 11-12h 12-13h 13-14h 14-15h 15-16h 16-17h 17-18h 18-19h 19-20h 20-21h 21-22h 22-23h 23-24h
Fig. 3. Toilet use profile for the four different apartments during weekdays (above) and weekends (below). The vertical axis represents the percentage of toilet use during discrete one-hour intervals (sum over 24 h ¼ 100%).
different working situations. Not surprisingly, people tend to go to Fig. 4 (left). In the same figure, the distribution of the amount of the toilet a few hours later in the morning during weekends. urine per toilet flush (Roediger NoMix toilet) is presented on the right. An average value of about 138 ml/per flush ( 45 ml) is esti- 3.2. Urine production in households mated (Table 1).
The total daily amount of urine collected in the tank was 3.3. Pattern of toilet use at working place evaluated considering 174 days of measurements (results not illustrated). The average amount of urine collection per day The NoMix toilets at Eawag are situated in the public area differed significantly (T-test, p 0.0001 < a ¼ 0.05) between bathrooms in order to ensure access also to visitors who took part weekdays (6.37 ( 2.20) l/day) and weekends (9.22 ( 3.23) l/day; in different acceptance studies (Pahl-Wostl et al., 2003; Lienert and Table 1). Larsen, 2006). The total number of toilet uses per day is presented The correlation between the total number of flushes per day in Fig. 7, for a period of 13 months. Extreme values are mainly with the amount of urine collected in the urine tank is presented in linked with social events. The toilets are located in a public area
25 25
20 20 y = 0.137x R2= 0.3227 15 15
10 10 the tank (l) 5 5
0 Number of data in each category
0 0 Daily amount of urine collected in 30 60 90
02040 60 80 100 120 150 180 210 240 270 300 Daily number of toilet use (-) Volume of urine per toilet use (ml/flush)
Fig. 4. Correlation between total number of toilet uses and amount of urine collected in households (left) and distribution of urine volume per toilet use (ml/flush) in households (right). L. Rossi et al. / Journal of Environmental Management 90 (2009) 1909–1917 1913
200 Even if the average number of flushes per day stayed relatively constant during the measurement period in the households * (5.8 1.4 average total toilet uses per day), we observed a devel- 160 opment in the use of the small flush button (Fig. 7). In apartment 4, * the initial high proper usage stabilized at about the same level (about 50–65% use of the small button) as in the apartments 1 and 120 3, where initial proper usage was low. In apartment 2, there was * a general low proper usage, stabilizing at the very low level of 10% * use of the small button towards the end of the period with a short 80 intermittent phase where some improvement had been observed. For the working place, the frequency of small flushes varied 40 considerably over time for the women’s NoMix toilet (Fig. 7
Total amount of toilet use at bottom; mean values: 49.5% 18.0 small flushes for women, and working place per day (n/day) 29.7% 10.7 for men). This very low frequency of small flushes of 0 * * the women’s NoMix toilet can be linked to the presence of students Mon Tue Wed Thu Fri Sat Sun during a few weeks at the beginning of 2005, as illustrated by the increase of toilet uses during the same period. The very high Fig. 5. Number of toilet uses per day at a working place (Eawag; only men’s toilets i.e. three waterfree urinals and one NoMix toilet). frequencies of small flushes during the period April–June 2004 (80–88%) are difficult to explain, but occur during a period of less near restaurant, auditorium and meeting room facilities. It is thus frequent use of the toilet. A general positive trend over the entire not possible to evaluate the average use of toilet per person. measurement period was observed between the proportion of We correlate the amount of urine stored in the two tanks with small flush uses and the total number of toilet uses, but this the number of usages recorded in the men’s (Figs. 5 and 6 left) and correlation is weak (R2 ¼ 0.54, results not illustrated). For the men’s women’s bathroom (Fig. 6 right). The correlation is high for the NoMix toilets, the percentage of small flush was low, as expected: men’s (R2 ¼ 0.82), but low for the women’s (R2 ¼ 0.29) bathroom. Due to the presence of urinals nearby, this toilet is mainly used for The totality of urine collected in waterfree urinals reaches the defecation. Nevertheless, a constant decrease of small flush urine tank (i.e. no losses). As more than 88% of the toilet visits are frequencies of the men’s toilet was observed, independently from related with urinal use, the correlation between daily number of the number of total toilet uses (R2 ¼ 0.4). toilet use and volume of urine collected daily is thus higher for the men’s toilets (Fig. 6, left) than for women (Fig. 6, right). The weak 3.6. Extrapolation to an entire watershed correlation for the women’s NoMix toilet use could be explained with physiological differences. Moreover, the duration of the The urine production estimated for the four households (average investigated period is longer for the men’s toilets (392 days) than values, from Fig. 3) can be compared with on-line measurements of for women (52 days). The volume of urine per usage had an average the WWTP Ergolz1 conducted during weekdays and weekends. In value of 225 ml/usage for men (i.e., including urinals) and 309 ml/ this specific case, the average load for weekdays estimated by our flush for women (only Dubbletten NoMix toilets; Table 1). own on-line measurement system (176 kg N/day) was comparable (T-test, p ¼ 0.0407 < a ¼ 0.05) with the average daily load measured 3.4. Concentrations of nutrients in urine tanks by the WWTP itself over one year (183 kg/day). Results of daily profile of NH4–N are presented in Fig. 8 for weekdays (top) and for Concentrations of nutrients (NH4,Ptot,PO4, and Ptot) in the weekends (bottom). The results have been normalized by dividing different urine tanks are presented in Table 2. the average hourly amount of N by the average daily load. The two curves agree very well. In view of the small number of 3.5. Frequency of small and large flushes in the households and at apartments, this is rather surprising. Although it cannot be the working place excluded that this is partially due to chance, the results indicate that already on the level of an apartment house one may observe In Fig. 7, the mean daily use of the small button is compared to more or less the same time pattern as in a small catchment, at least the percentage of total flushes for households (top) and for the when averaged over time. In this catchment, two thirds of the working place (bottom). population is situated near the WWTP so that there is only a small
50 20
y = 0.247x y = 0.2862x 2 40 R = 0.8199 16 R2 = 0.2919
30 12
20 8
10 4 Daily amount of urine Daily amount of urine collected in the tank (l) collected in the tank (l)
0 0 04080120160 010203040 Daily number of toilet use (-) Daily number of toilet use (-)
Fig. 6. Urine collected in the tank and number of toilet uses per day at Eawag (Left: men’s bathroom, n ¼ 392; Right: women’s bathroom, n ¼ 52). 1914 L. Rossi et al. / Journal of Environmental Management 90 (2009) 1909–1917
Table 2 Measured nutrient concentrations in urine and literature values (interval of measurements in brackets).