TONY FERNANDEZ
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© 2001 American Chemical Society
ROEDIGER VAKUUM + HAUSTECHNIK, GMBH
Could one answer be a new toilet that separates urine from wastewater streams? The RoedigerNoM ix toilet
TOVE A. LARSEN, IRENE PETERS, ALFREDO ALDER, RIK EGGEN, MAX MAURER, AND JANE MUNCKE
unicipal wastewater treatment needs rethinking. It is burdened with a pollutant load that it was never intended to manage. Problems with the existing management system are manifold. The current system— waterborne transport and centralized treatment—consumes large amounts of freshwater. It discharges nutrients to water bodies, where they cause pollution and are lost for further use at a time when scarce raw materials are being depleted to produce synthetic mineral fertilizers. Concern is also growing about human excretion of micropollutants such as pharmaceuticals, synthetic and natural hormones, and their metabolites. Many of these substances
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Using existing collection and treatment infrastructure, urine source separation is well suited to aid the transition to decentralized wastewater management. (suspected to be largely excreted in urine) are not removed by biological wastewater treatment (1–3) and often are very potent, especially hormonally active agents, which have caused changes in the morphology and behavior of some species (4). Moreover, the spread of antibiotics to the environment could lead to increased resistance of microorganisms to these substances. Fortunately, a promising alternative to centralized wastewater management may soon be available that addresses many of these problems. It involves separation of urine from feces in a special “NoMix” toilet with in-house storage of the collected liquid followed by its subsequent transport and treatment (Figures 1 and 3). Such urine source separation is technologically easy to accomplish, and at pilot scale, the technology is already in place in several countries. At the Swiss Federal Institute for Environmental Science and Technology (EAWAG) FIGURE 1
Urine source separation technology In the variant of the urine source separation technology being explored in the NOVAQUATIS project at EAWAG, urine stored in-house is released into the sewers at controlled times and is transported to the wastewater treatment plant, where it can be diverted for separate treatment. Fertilizer application in agriculture No-mix toilet
System control and processing of urine Control of release
Existing sewers
Treatment plant Receiving water
Source: Adapted from Reference (12).
in Dübendorf, the NOVAQUATIS project (www. novaquatis.eawag.ch) is exploring the engineering, microbiological, exotoxicological, economic, and social science aspects of this novel approach. Source-separating urine provides a range of benefits. A urine-separating NoMix toilet saves 80% of the water used for toilet flushing, accounting for 30% of the average Western European’s direct daily water use and 10% of the total freshwater use in Switzerland. Because urine accounts for a large fraction of the wastewater nutrient load, this approach can also reduce emissions from fertilizer production and halt the contamination of agricultural soils by the heavy metals found in the raw materials used to produce synthetic fertilizers. It also reduces micropollutant discharges to water bodies. Using existing collection and treatment infra194 A
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structure, urine source separation is well suited to aid the transition to decentralized wastewater management. For the approach to succeed, however, many stakeholders—consumers, public agencies, industry, and agriculture—must aid in the dissemination of NoMix technology.
Problem synthesis Thousands of xenobiotic substances that have been brought into use in the past few decades are finding their way into municipal wastewater. Centralized treatment technology cannot deal with this new pollutant load and offers no incentive to polluters to seek better alternatives. Current urban water management practice contains strong elements of what economists call a natural monopoly, in which a single supplier can service the market at lower cost than two or more suppliers. This situation stifles innovation and locks in a technology that is inferior in many respects. Therefore, municipal wastewater treatment systems should be moving toward source separation schemes, but it is not clear how to make this happen. What are the right technologies? How can they be implemented? Addressing the latter question may be the more challenging issue because of the current system’s built-in inertia—it is well established, longlived, seems to adequately serve public needs, and has large amounts of capital invested in the present infrastructure, in which several complementary technologies work together to make the system function. It may be feasible to unbundle wastewater management and introduce competition in treatment, for example, but it is hard to see how this can be done for transport. The sewer system is too extensive to sustain several independent providers. In fact, for most deregulated public utilities—power, rail transport, and water supply—network operation has remained a monopoly, and establishing competition in unbundled services has proven harder to accomplish than anticipated. Ultimately, household on-site technology would make today’s centralized wastewater collection and treatment infrastructure redundant. Important issues to be addressed include how the transition to a decentralized technology regime can be accomplished, what it would cost, and who is going to pay for it.
Why urine source separation? Human excrements are the greatest source of nutrients in wastewater, and the major fraction of excreted nutrients is found in urine (Figure 2). Although the numbers can vary, urine typically contributes around 80% of the nitrogen, 50% of the phosphorus, and 90% of the potassium in the total nutrient load arriving at a treatment plant. This input can have a pronounced effect on the maximum daily load of ammonia with which the plant has to cope, and the urine peak early in the morning when most people get up is an important factor for planning plant capacity.
System mechanics The NoMix toilet has one compartment for feces and one for urine. The urine flows through separate pipes to a storage tank that is emptied periodically. An alternative currently being explored is storing a day’s worth of urine within the toilet for later controlled release through the existing pipes in the building. NoMix toilets (Figure 3) already exist in Scandinavia, notably Sweden. There, a low-tech approach has been chosen for urine transport and treatment. Storage is decentralized and uses large tanks that are periodically emptied by local farmers who spread the urine directly on their fields (6). The technology variant being researched at EAWAG is adapted to a municipal setting and relies on smaller, on-site storage tanks and use of the existing sewer network for transport to a treatment facility. Depending on the intended use, urine transport could occur at different times of the day. If urine is to be entirely removed from the wastewater stream for
FIGURE 2
Nutrient distribution in urine and feces Human excrement is the main source for nutrients in municipal wastewater. 100 80
Feces
Iron
Magnesium
Calcium
Boron
0
Sulfur
20
Potassium
40
Phosphorus
60 Nitrogen
Percent
Absent urine, plant influent carbon and nitrogen levels would be almost balanced; that is, the plant’s bacteria feeding on the organic matter in the wastewater could absorb all the nitrogen content. Excess phosphorus remaining after biological treatment can easily be reduced. Production of inert sludge is thereby reduced, enabling savings in sludge handling and especially in ash disposal from sludge incineration, which is on the way to becoming the primary sludge disposal option, at least in Europe. Urine is also the main culprit for the acute toxicity effect that occurs when there are combined sewer overflows. Most industrialized countries transport municipal wastewater and rainwater in the same (combined) sewers. During heavy rains, the total amount of sewage arriving at a treatment plant can exceed its capacity, and raw sewage, diluted by rainwater, is released directly into rivers and lakes. The discharge contains ammonia, a byproduct of urine decomposition, which is acutely toxic to fish. Although a problem when released unintentionally to the environment, under other circumstances, urine provides definite benefits. Nitrogen, phosphorus, potassium, and sulfur are basic constituents of synthetic mineral fertilizers used in agriculture. Substituting urine components for these fertilizers eliminates environmental impacts associated with production and use of the latter and slows resource depletion (see box on page 197A (5)). Other resource demand problems can also be avoided. For example, nitrogen is in plentiful supply in the atmosphere, but its industrial fixation is energy-intensive. As an alternative, urine provides a ready source of fixed nitrogen. In summary, the economic and environmental advantages of adopting urine source separation are manifold: smaller, simpler treatment plants; lower nutrient emissions to rivers, lakes, and oceans; reduced sludge production; reduced use of flocculation chemicals, which saves money and reduces environmental impacts; natural resource conservation; lower fertilizer impacts; and greatly reduced toxic impacts of combined sewer overflows.
Urine
Source: EAWAG.
nutrient recycling, it could be released at night when the sewers are empty (Figure 1). This would require using storage tanks large enough to bridge a series of rainy nights. The Swiss urine-to-fertilizer strategy emphasizes processing of the urine solution. Sterilization, pH stabilization, removal of potentially harmful micropollutants, and the elimination of the characteristic odor are important treatment steps. An alternative, low-cost approach for reducing the early-morning urine peak, involves temporarily separating urine using small storage tanks that are fully integrated into the toilet. The stored urine is released later during the day to ensure that a smooth, even load arrives at the treatment plant. Release could also be controlled to withhold urine when combined sewer overflows are likely to occur, thus reducing the adverse effects of raw sewage emissions to rivers and lakes. Modeling of this option shows that it could successfully compete with the more traditional approach of enlarging treatment plants and rainwater storage capacity (7). This strategy enables technological learning, especially in the area of real-time control, beginning with simple strategies like peak-shaving, followed by more advanced strategies for better response to rain events.
Stakeholders Implementation of NoMix technology is not cost-free, even though it can use existing infrastructure. Investment is necessary at the household level, in particular, when the nutrient recycling option is pursued. NoMix toilets could be installed in the course of natural appliance turnover, but piping and storage are bigger items to consider, and additional treatment facilities would have to be built. To accomplish all this, multiple parties have to realize a stake in the new technology. Although its marketability has not yet been tested, producers of sanitary appliances and equipment are already investing in NoMix technology (8, 9). The first generation of NoMix toilets was produced by small Scandinavian companies; the type shown in the photo on page 193A and Figure 3 was produced by Roediger Vakuum + Haustechnik (www.roevac.de), a German manufacturer. Several Swiss firms have shown interest in a toilet with integrated storage. Consumers who participate in pilot projects have responded favorably to the NoMix technology, despite some minor technical difficulties (10, 11). The technology saves them money by conserving water—flushMAY 1, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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ing urine in the NoMix toilet requires 0.0–0.2 L, whereas a modern water-saving toilet uses 2–3 L for a small flush. On a daily basis, a family of four could save around 80 L of water. Given typical Swiss water prices, annual savings of $100 (USD) can be realized—double that amount, if the toilet to be replaced is not of the modern, water-saving kind. Household investment in NoMix technology could be amortized over 5–10 years. FIGURE 3
The mechanisms of source separation The front compartment of the Roediger NoMix toilet is used for the urine, and the back is used for feces. When the back compartment is flushed, the front compartment outlet is closed by a valve.
AG, urine stored in-house is released
Source: Roediger Vakuum + Haustechnik GmbH.
Public authorities will have to act if urine separation technology is to grow more rapidly. Consumers can install NoMix toilets but still need the involvement of regulatory agencies and wastewater service providers. If existing sewers are used for transport, storage tank opening should be coordinated with treatment plant operations. Moreover, urine storage and treatment require new infrastructure, particularly if the nutrient-recycling option is pursued. Public authorities should have an interest in pursuing NoMix technology, because it can significantly improve treatment plant effluent quality. Using NoMix technology to level the ammonia peaks produces the same effect as expanding treatment capacity, either reducing the ammonia and nitrite content of the effluent, or allowing for additional nitrogen elimination (12). In some countries, denitrification to reduce nitrogen in plant effluent has been mandated to prevent further ocean eutrophication. This expensive end-of-pipe measure would be redundant, and its effect easily surpassed, if urine were removed at the source. The attraction of urine-based fertilizer for farmers is more tenuous, since they are not yet affected by
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shortcomings of the present system. Containment of heavy metals might be the most relevant issue for them. Organic farmers could find the urine-based fertilizer a welcome source of nutrients, since the organic certification requirements they have to meet often prohibit using synthetic mineral fertilizers (13). Any use of urine-based fertilizer on the farm should be preceded by an assessment of associated ecotoxicological risks; for example, microresidues in urine (pharmaceuticals and hormones) may have to be removed from the fertilizer product. Such a risk assessment is being carried out by the EAWAG NOVAQUATIS project. For several years, the phosphate industry has been exploring alternative sources for raw phosphate, for example, phosphate reclamation from wastewater and chicken manure. Although the industry has not yet shown an interest in phosphates reclaimed from source-separated urine, it might soon begin to do so. The industry’s interest in alternative raw material sources is driven by increasing difficulties with disposing of hazardous wastes generated during phosphate rock refining. Although EAWAG scientists and associated institutions do not have a direct commercial interest in the NoMix technology, they are stakeholders nevertheless, exploring alternatives to current materials policy. In the NOVAQUATIS project, engineers are developing treatment methods for separated urine solutions to make its constituent nutrients available for agriculture. Microbiologists and agricultural ecologists are studying the ecotoxicological risks that a urine-derived fertilizer could bring to soils and plants. Environmental scientists are assessing material flows associated with conventional and nutrient-separated waste management regimes. Economists and social scientists are exploring the acceptance of the technology, taking into account cost and consumer attitudes.
Next steps Urine source separation is but one step toward a more comprehensive source separation strategy that makes it easier to treat and recycle wastewater stream components. Because individually they are more homogeneous, wastewater components can be better controlled if they have not been mixed. Ecological engineering approaches that use ecosystems for engineering tasks and exploit their self-organizing capacity (14, 15) likewise benefit from, and increasingly rely on, source separation. For example, separation of urine and feces leaves “gray water” that can be more easily treated in constructed wetlands. In the future, source separation may permit the use of completely decentralized wastewater treatment systems that avoid transport altogether. Already, the relative ease of accomplishing urine source separation in an existing, inert system permits implementation to occur, though gradually, and positive effects are being realized from the start. To move toward really intelligent wastewater management, however, change has to be more radical. The principle of source separation could be extended to other household wastewater sources. The major water-
using appliances in the raw materials long distances to where they are needAdvantages of nutrient recycling household—toilet, washed, as well as after their consumption, when nutrients ing machine, and dishare discharged into lakes, rivers, and oceans, where Current fertilizer production and use consume limited they cause pollution and are largely unavailable for washer—are responsible resources and harm the environment. At current use in agriculture. extraction rates, reserves of phosphate rock that are for at least 85% of the orClearly, a closed nutrient cycle is desirable (7), economically recoverable with today’s technology will ganic pollutant load in and some nutrient recycling is already happening. last less than 100 years, and the reserve base will last residential wastewater. For instance, in many places, sewage sludge is being less than 300 years (http://minerals.usgs.gov/minerals/ Equipping these applispread on agricultural fields. The sludge acts as a pubs/commodity). ances with a device for fertilizer, but the practice primarily serves as a cheap In addition to resource limits, phosphate rock has a internal waste reclamadisposal option. Given the increasing contamination high heavy metal content, giving rise to hazardous tion would be a logical of sewage sludge with pollutants from municipal wastes when processed. The cadmium content of way of reducing pollutant wastewater, its application to fields is increasingly phosphate rock, for example, ranges from 0.1 to 850 emissions from wasteless viable (Environ. Sci. Technol. 2000,34 (19), mg cadmium per kilogram phosphorus. Because these water. Recent develop430A–435A). Source separating urine could reopen impurities are not entirely removed from the final ments in membrane this pathway for agricultural application of nutrients product, phosphate fertilizer application introduces technology and other recovered from municipal wastewater treatment and heavy metals, such as cadmium, which is very toxic, physical–chemical treatavoid the current problem of effluents from treatment into the soil. This problem will worsen if rock of lesser ment methods hint that plants contributing significantly to nutrient pollution quality is used in the future as the resource is expendsuch solutions may be reof water bodies. ed. There are also impacts associated with hauling alistic in the not-too-distant future (16). Use of (10) Burström, A.; Jönsson, H. Double Flushed Urine technologically sophisticated appliances such as these Separating Toilets—User Experiences and a Follow-Up of would leave households with small remaining Problems; Report 229, ISSN 00283-0086; Swedish University of Agricultural Sciences, Department of amounts of wastewater that could be treated on-site Agricultural Engineering: Uppsala, Sweden, 1998. to a quality comparable with rainwater. In this sce(11) Hanäus, J.; Hellström, D.; Johansson, E. Water Sci. nario, public responsibility for wastewater transport Technol. 1997, 35 (9), 153–160. and treatment would be largely delegated to house(12) Larsen, T. A.; Gujer, W. Water Sci. Technol. 1996, 34 (3–4), 87–94. holds, opening up a mass market for in-house water (13) Haller, M. Düngeverhalten von Bio- und IP-Landwirten treatment technology that could provide greater (Fertilizer Use by Farmers in Switzerland); Department of rewards for innovation than the large-scale infraEnvironmental Sciences, Swiss Federal Institute of structure of today. Such radical source separation Technology: Zürich, 2000. could also alleviate the burden of dealing with cont(14) Ecological Engineering: An Introduction to Ecotechnology; Mitsch, W. J., Jorgensen, S. E., Eds.; Wiley and Sons: New aminated biosolids, because with separated waste York, 1989. streams, the resulting separate fractions of biosolids (15) Ecological Engineering for Wastewater Treatment; Etnier, would be of higher quality and could be directed toC., Guterstam, B., Eds.; Lewis Publishers: Boca Raton, FL, 1997. ward their most suitable destination. (16) Larsen, T. A.; Gujer, W. In Water Resources and Waste Taking source separation seriously, handling all Management. Conference Preprint of the 1st World wastewater components individually, and reducing Congress of the International Water Association, July 3–7, the associated water use pose a real challenge. At 2000, Paris; 2000, 5, 293–300. some point, we may want to downsize the entire All authors are at the Swiss Federal Institute for urban water infrastructure or do away with it altogether. This cannot happen overnight, but if we don’t Environmental Science and Technology (EAWAG), start the journey now, we will never get there. Dübendorf, Switzerland, and are part of the NOVAQUATIS management team. Tove A. Larsen References (
[email protected]) is an environmental engineer in (1) Ternes, T. A. Water Res. 1998, 32 (11), 3245–3260. the Urban Hydrology Division of EAWAG and leader of (2) Stumpf, M.; Ternes, T. A. Vom Wasser. 1996, 87, 251–261. the entire NOVAQUATIS project; Irene Peters is an (3) Pharmaceuticals and Personal Care Products in the economist in the Systems Analysis, Integrated AssessEnvironment: Scientific and Regulatory Issues. ment, and Modelling Division and heads a project Daughton, C. G., Jones-Lepp, T., Eds.; American conducting a comprehensive evaluation of all aspects of Chemical Society: Washington, DC, 2001. the NoMix technology, Alfredo Alder is an analytical (4) Ashfield, L. A.; Pottinger, T. G.; Sumpter, J. P. Environ. Toxicol. Chem. 1998, 17 (3), 679–685. chemist in the Chemical Pollutants Division and (5) Beck, M. B.; Cummings, R. G. Habitat Intl. 1996, 20 (3), coordinates a project analyzing the fate of various phar405–420. maceuticals in urine; Rik Eggen is a molecular biologist (6) Höglund, C.; Stenström, T. A.; Jönsson, H.; Sundin, A. heading the Environmental Microbiology and MolecWater Sci. Technol. 1998, 38 (6), 17–25. ular Ecotoxicology Division and coordinates the projects (7) Larsen, T. A.; Rauch, W.; Gujer, W. Waste design paves the way for sustainable urban wastewater management, subon the potential ecotoxicological effects of substances in mitted to the UNESCO Symposium Frontiers in Urban urine; Max Maurer is a process engineer in the Water Management: Deadlock or Hope?, Marseille, Environmental Engineering Division and coordinates France, June 18–20, 2001. (8) Fussler, C. Driving Eco-Innovation; Pitman Publishing: the projects exploring methods to process the urine London, 1996. solution; and Jane Muncke, an environmental scientist, (9) Moore, C.; Miller, A. Green Gold: Japan, Germany, the is working on the effects of conventional versus urineUnited States, and the Race for Environmental Techbased fertilizers and is also assistant to the project leader. nology; Beacon Press: Boston, 1995.
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