Journal of Environmental Management 90 (2009) 1909–1917 Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman 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.