Charting a Path for Innovative Toilet Technology ... - ACS Publications

Feb 8, 2008 - Eawag, Swiss Federal Institute of Aquatic Science and. Technology, 8600 ... and sustainable urban water management system. Introduction...
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Policy Analysis Charting a Path for Innovative Toilet Technology Using Multicriteria Decision Analysis M A R K E . B O R S U K , * ,†,‡ M A X M A U R E R , † JUDIT LIENERT,† AND TOVE A. LARSEN† Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland

Received August 30, 2007. Revised manuscript received January 03, 2008. Accepted January 04, 2008.

Practical and theoretically sound methods for analyzing innovative environmental technologies are needed to inform public and private decisions regarding research and development, risk management, and stakeholder communication. By integrating scientific assessments with a characterization of values, multicriteria decision analysis (MCDA) supports the ranking of alternative technology pathways on the basis of technical, financial, and social concerns. We applied MCDA to evaluate the use of NoMix urine separating toilets for managing environmental risk and postponing expensive upgrades to a large wastewater treatment plant near Zürich, Switzerland. Results indicate that, given current priorities, no single, fixed course of action (including the status quo) will be desirable to all stakeholders over the considered time horizon. However, a path forward is suggested that is not significantly disadvantageous to any stakeholder now and leaves open future options, allowing society to achieve overall greater benefits if priorities change, new environmental risks are revealed, or technology improves. While our analysis focuses on a particular catchment in Switzerland, many communities worldwide are faced with an aging and inefficient wastewater treatment infrastructure while also experiencing growth and development. Our framework can help these communities balance the conflicting objectives of diverse stakeholders and gain insight into the role that urine separation can play in transitioning to a more comprehensive and sustainable urban water management system.

Introduction Emerging environmental concerns often generate technological innovation (1). However, if conventional technologies are deeply entrenched, innovative substitutes may not be adopted, despite their superiority. This technological “lockin” may occur for any number of reasons, including institutional, political, and economic commitments (2) or habits of behavior, learning, and culture (3). It may also be that those stakeholders in the best position to affect adoption of the new technology do not have a view of the long-term advantages nor a clear path for implementation. The sanitary system of the modern Western world provides a case in point. The conventional methods of wastewater * Corresponding author phone: 1-603-646-9944; fax: 1-603-6462277; e-mail: [email protected]. † Eawag. ‡ Current address: Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire. 10.1021/es702184p CCC: $40.75

Published on Web 02/08/2008

 2008 American Chemical Society

collection, transport, and treatment are extremely wasteful of nutrients, which could otherwise be recycled for agricultural use. They are also very water inefficient, using large amounts of water for transport. In combined sewer systems, this leads to overflow problems during storm events and associated water pollution. Finally, micropollutants, those compounds, such as pharmaceuticals, which may have significant health effects at low concentration, go largely untreated in the current system (4). All of these problems are especially grievous when this Western technology is exported to developing countries with the promise that it will solve existing water pollution problems. Recently, the NoMix (or urine separating) toilet has been developed as an innovative approach to sustainable wastewater management (5–7). The NoMix approach is an example of both a source separation and waste design strategy (8, 9). The technology consists of a specially designed toilet in which urine is collected separately (Figure 1), a urine storage tank in or near the household, a treatment unit located either locally or centrally that processes the urine, possibly recovering nutrients in the process, and a means for transporting the urine from the storage tanks to the treatment unit. Urine is the targeted waste type of the NoMix technology because it contains most of the nutrients (5) and 60–70% of micropollutants, including natural and synthetic hormones, antibiotics, and other pharmaceuticals (10, 11). Thus, separating urine at the source, rather than handling it as part of a mixed waste stream at the treatment plant, can be an elegant and efficient way of dealing with micropollutants and facilitating nutrient recycling (12). Furthermore, wastewater that does not contain urine has a biologically balanced C/P/N ratio, making it possible to achieve excellent treatment results with compact treatment plants focused on COD removal (5, 13, 14). While conceptually simple, the NoMix technology concept has proven significantly more difficult to implement (15). As with other innovations, this may be because successful adoption depends not only on the priorities of users, but on those of developers and suppliers as well. Surveys have shown household users to be receptive to the NoMix concept, so long as the current standards of bathroom convenience and hygiene are maintained and no additional costs are incurred (16, 17). However, while toilet manufacturers believe they can develop NoMix units that meet these requirements, they do not see an immediate market for their product (18). The wastewater treatment industry sees the potential to use the NoMix technology to help them meet environmental standards at lower cost but is unsure of the appropriate implementation strategy (19). Finally, scientists recognize an interesting research opportunity but would like to know what projects would most likely make the emerging technology practical before investing significant time and effort. Clearly, all these stakeholders have a role in the successful realization of the NoMix concept. In addition to differing stakeholder concerns, there are differing types and levels of NoMix technology implementation. For example, urine storage can be either short- or longterm at either a local or a centralized location. This choice affects the type and cost of treatment options that are available. Furthermore, it is unlikely to be cost-effective to replace all existing toilets in an area at one time. Thus, various transition scenarios are possible, some of which may have benefits that are quite different from those that will ultimately accrue. For example, even before nutrient recycling or micropollutant removal begin to take place on a large scale, VOL. 42, NO. 6, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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time and that there will always be some uncertainty that can never be fully resolved. Thus, rather than expend undue effort to gather more information, we make use of sensitivity analysis to learn what information could make the most difference for the decision. Collecting this information will then provide the basis for future work.

Problem Description

FIGURE 1. Various types of NoMix toilets are available on the market today. This is a model by Roediger (photo: Yvonne Lehnhard). separately collected and stored urine can be used to smooth out the daily fluctuations in nutrients that occur in the present treatment systems. The peaks of these fluctuations, which arise from society’s daily cycle of sleeping, eating, drinking, and using the toilet, largely determine the size, cost, and efficiency of treatment plants. “Shaving” these peaks can lead to significant near-term savings by decreasing the required design capacity of new plants or prolonging the lifetime of existing plants (5, 20). Another consideration is that some of the issues involved in deciding whether to implement NoMix technology are not yet resolvable. For example, there are many uncertainties surrounding the level and consequences of micropollutants in wastewater emissions (4). Without knowing the present risks, it is impossible to accurately assess the future potential benefits of pollutant reduction. Thus, later stages of implementation may need to be decided adaptively, as we learn from initial stages. However, decisions made now may limit available options in the future. This aspect of path dependence is a widely recognized challenge for technology futures analysis (21). We believe that an application of multicriteria decision analysis (MCDA) with an emphasis on value-focused thinking (22) can help to structure the NoMix evaluation process and possibly clarify the important issues of implementation. MCDA has been proposed previously for analyzing such emerging technologies and their implications (23, 24). However, it has been pointed out that multicriteria models are usually static in their temporal structure, making it difficult to address issues that pertain to different or varying time horizons (23). Another difficulty is that decision alternatives of an MCDA are often assumed to be mutually exclusive, an assumption that may not be reasonable for technologies that evolve with time in unknown ways. Implementing a less than optimal technology now, for example, may allow society to achieve greater benefits in the future by leaving open more options. This was explicitly recognized by Keeney and McDaniels (25) in the context of climate change policy. We hope to build upon their methodological development. One of the goals of our analysis is to exemplify the assessment of a particular technology using the information that is currently available. We acknowledge that there are gaps in our knowledge and many uncertainties that are both aleatory and epistemic. However, we are fortunate enough to be conducting this analysis near the end of a six-year interdisciplinary research project on the social and technical aspects of the NoMix system (www.novaquatis.eawag.ch). Therefore, we can expect that our project team knows about as much as there is to know about this technology at this 1856

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Study Location. Although the NoMix toilet technology is potentially promising for a wide variety of conditions and settings, to make our analysis concrete, we will focus on a situation concerning a proposed mixed use development near Zürich, Switzerland, called Glattpark (http://www.glattpark.ch). Glattpark is being developed on a 67 ha site and includes multifamily housing for 7000 inhabitants as well as office space for another 7000 workers. The wastewater of Glattpark is to be handled by the treatment plant in nearby Kloten/Opfikon, which is already operating near full capacity. Thus, there is hope that urine source separation in Glattpark can be used to postpone or avoid an expensive expansion of the Kloten/Opfikon plant. Additionally, the developers and city government have committed to environmentally sustainable management of the site, thus making it attractive to pursue efforts that will help close the nutrient cycle. Stakeholders. Certainly, to be successful, NoMix toilets must be acceptable to household users. However, the full pathway to implementation still requires significant research and development effort. Therefore, in addition to households, we consider wastewater treatment plant managers, sanitary equipment manufacturers, engineering consultants, and research scientists to all be key stakeholders in the NoMix technology. While the government at various levels might also be considered a stakeholder, because of the public nature of the wastewater treatment industry in Switzerland, we consider the views of the treatment plant managers to reflect the requirements imposed by the government. A previous study of NoMix (26) also considered farmers as stakeholders because the nutrients potentially recovered from urine can be used to produce agricultural fertilizer. The results of the study revealed that farmers would use the urinebased fertilizer so long as it did not cost more than their current fertilizer product nor present any risks to human health. Therefore, rather than include the farmers as stakeholders, we decided to make their requirements a precondition to the rest of the analysis. If a urine-based fertilizer can be produced that is as cheap, safe, and convenient as the current product, then the details of the urine collection and recycling process will be immaterial to the farmers. Decision Alternatives. Unfortunately, the decision regarding NoMix technology for the Glattpark development is not independent of how the rest of the catchment of the Kloten/Opfikon treatment plant is handled. This is because separate urine treatment with subsequent nutrient recycling is only economically practical in the long term if most of the catchment implements urine source separation. This would allow substantial downsizing and simplification of the treatment plant with attendant long-term cost savings. Therefore, we conceive of the NoMix decision for our case study as a hierarchy of decisions, stated as follows: (1) Is urine collection and conversion to fertilizer an appropriate long-term goal for the entire Kloten/Opfikon catchment? (2) If the answer to question 1 is “No,” then can urine separation in Glattpark alone be used as a peak-shaving strategy to postpone expansion of the Kloten/Opfikon plant? (3) If the answer to question 1 is “Yes,” then how should urine from Glattpark be handled during the transition period? In particular, should peak shaving be implemented as an intermediate step? (4) If peak shaving is an appropriate part of either the long-term or transition strategy, then how exactly should it be implemented?

FIGURE 2. Schematic of alternatives considered. To address the questions above, we originally formulated 12 strategic alternatives, which we narrowed down to the eight most attractive or interesting for the present analysis: a status quo (or “business as usual”) alternative, five peakshaving alternatives for Glattpark that contain various combinations of some key options, and two nutrient recycling alternatives for the full Kloten/Opfikon catchment (Figure 2). The details of these alternatives follow: 0. Status Quo. This alternative assumes that Glattpark will be built and the wastewater will be handled in the traditional manner at the Kloten/Opfikon wastewater treatment plant (WWTP). This implies that the plant will need to be upgraded in 2011. 1. Peak Shaving. In this alternative, NoMix toilets (such as those available from the German firm, Roediger, www. roevac.com) are installed in all Glattpark residences. These will each be connected to a 5 L storage tank located in the WC, which is sufficient for two to three days of urine. Delivery to the WWTP will occur via the existing sewer line using timers that release the stored urine at appropriate intervals to level out the delivery rate. 2.A. Peak Shaving with Limited CSO Control. Alternative 1 will not address the significant problem of combined sewer overflow (CSO) during storm events. Therefore, alternative 2.A employs a larger 10 L storage tank in each WC that will allow sewer managers to delay urine release for up to five days during storms. This will involve the installation of a more sophisticated release system that can be centrally controlled via communication lines (e.g., telephone or cable). 2.B. Peak Shaving with Conservative CSO Control. Alternative 2.A may still be a problem during extended rainy periods. Therefore, this alternative expands the storage tank to 30 L/WC and locates it in the cellar of multifamily apartment buildings. Releases would be centrally controlled. 2.C.i. Peak Shaving with No CSO Risk 1. To completely eliminate the risk of CSO events, all urine could be directed through dedicated lines to an intermediate storage tank located in Glattpark. Trucks would be used to pick up stored urine and deliver it to a storage tank at the WWTP to be used for peak shaving. This would further increase the operator’s control over the process. To allow for truck transport, tanks would need to be sized large enough for a five day storage time at both Glattpark and the WWTP.

2.C.ii. Peak Shaving with No CSO Risk 2. This alternative is similar to the previous one but has urine stored onsite in tanks in the basements of multifamily buildings rather than at a central Glattpark location. Smaller and more evenly spaced truck deliveries of urine would allow a smaller storage tank at the WWTP. 3.A. Nutrient Recycling 1. Of the alternatives described above, only the last one (2.C.ii) can be reliably implemented throughout the entire Kloten/Opfikon catchment for nutrient recycling. This is because, although it has been suggested (5) that the centralized release mechanism of alternatives 1-2.B might be used to transport pure urine through existing sewers at night, this is still highly speculative. Additionally, although Glattpark could be constructed to have separate local lines for urine (alt. 2.C.i), this would not be the case throughout the entire catchment. Therefore, alternative 3.A extends the building storage and truck transport of alternative 2.C.ii to the rest of the catchment. Urine would then be stored in a large tank at the WWTP and recycled into a fertilizer product. For example, a combination of electrodialysis and ozonation is currently being tested for this purpose in a pilot plant project (27). The remaining wastewater would continue to be transported in the existing sewers and treated at the WWTP. Because this wastewater would have a biologically balanced C/P/N ratio, the process of treatment would be much simpler and only require removal of organics (COD) (5, 13, 14). 3.B. Nutrient Recycling 2. Another option is to recover the nutrients in urine onsite. This would involve small treatment units designed to process the urine of one or two multifamily buildings. We assume that the responsibility and cost of operating the urine treatment units would be borne by the existing treatment plant managers or their contractors. They would also continue to handle the wastewater arriving at the WWTP in existing sewers, as described for alternative 3.A, above.

Multicriteria Decision Analysis To evaluate the alternatives described in the previous section, we performed an MCDA with an emphasis on value-focused thinking (22). This means involving stakeholders in the process of structuring the decision by carefully discussing the values that matter to them regarding the decision at hand. The process started with the construction of hierarchies to establish and structure the decision objectives of each stakeholder (22). Quantitative attributes were then defined for measuring the achievement of each detailed objective. An assessment was then made of the expected outcome of each alternative in terms of the defined attributes. Next, a multiattribute value function was derived for each stakeholder to describe the relative importance of the various attributes and the levels of those attributes (28). Finally, the multiattribute value of each alternative was calculated for each stakeholder to determine how well each of the alternatives satisfies the stakeholders’ objectives, and sensitivity and uncertainty analyses were performed on these results. Utility functions are often used instead of value functions in situations involving uncertainty because they incorporate stakeholders’ attitudes toward risk (29). Decision alternatives are then ranked according to calculations of expected utility. However, we decided that the nature of uncertainties in the NoMix decision was too vague to properly formulate risk attitudes or outcome probabilities. Therefore, we generated ranges of multiattribute values that attempt to represent the range of possible outcomes of the various alternatives. These ranges can then be considered informally in the decision-making process and revised as new knowledge becomes available. VOL. 42, NO. 6, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. Objective hierarchies for the five stakeholder groups followed by detailed attributes for the Environmental Quality objective, as elicited from research scientists. Attribute weights, which were assessed at a later stage of the analysis, are shown in the right column. When any of the higher level objectives consist of two or more subobjectives, the total weight on the subobjectives is given in parentheses. Because of the sensitivity of profit estimates, weights were not assessed for the Sanitary Equipment Manufacturers. Objective Hierarchies. An objectives hierarchy was developed for each stakeholder (Figure 3; Detailed definitions and methods can be found in the Supporting Information). Outcome Assessment. Each of the identified alternatives was evaluated with respect to its predicted ability to meet each of the stakeholder objectives identified in the previous section. This was done by assessing the levels of quantitative attributes characterizing the detailed subobjectives. For the attributes associated with WWTP operation, sanitary equipment manufacture, and engineering consultancy, the quantitative outcome assessment was performed by the professional stakeholder representatives. The outcomes on all other attributes were assessed by the authors using the combined results of the Novaquatis research projects as well as the background literature that these projects assembled. Much uncertainty remained, thus requiring the adoption of various assumptions and estimations. However, as mentioned in the Introduction, we believe that our estimations represent the current state of the science (see Supporting Information for assumptions and a table of outcomes.) Some of the critical issues in our outcome assessment were the following: (1) The currently available NoMix toilet has some drawbacks, as revealed in surveys of users. These include the requirement that men sit when urinating, the awkward sitting position for some women and all children, difficulty with cleaning the two separate bowls, the need for several flushes to remove wastes, occasional problems with toilet paper blockage, the need for regular flushing with citric acid to prevent pipe scaling, and some dislike of the toilet appearance. (2) Some users of NoMix toilets have the sense that it smells more than conventional toilets. This smell could come from the toilet itself or the storage tank. Therefore, 1858

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onsite smell was scored according to the presence of a NoMix toilet and the size and location of the storage tanks. (3) It is hypothesized that NoMix toilets might be further improved to overcome the drawbacks of the current design. Therefore, we also considered a scenario in which a “high-tech” toilet is developed that eliminates all problems of aesthetics, hygiene, cleaning, convenience, and toilet smell. We assumed that this toilet would have a cost that is 50% higher and a reduced lifetime. Of course, because such a toilet does not yet exist, these assumptions are particularly uncertain. (4) Economically, the largest advantage of the peak-shaving alternatives is in postponing the need to upgrade the Kloten/ Opfikon WWTP. It is estimated that an investment of 10 million Swiss Francs (CHF) can be delayed for up to seven years (from 2011 to 2018) (30). Once built, the new WWTP can be expected to last for 35 years. Therefore, we chose a 48 year time horizon (2005 to 2053) for all economic calculations and annualized all costs and savings with a 3% interest rate. The upgraded WWTP is expected to have higher running costs, which are also delayed by seven years. For the nutrient recycling alternatives, it is assumed that the WWTP will be downsized in 2023 when the life of the current plant expires, resulting in significant long-term cost savings. Of course, some of the savings at the WWTP will be offset by the cost of the equipment and operations of the NoMix system, which we assume will be borne by the WWTP budget. The production of fertilizer is assumed to be cost neutral. Value Function Assessment. The next step was to develop the value function that allows us to rank the alternatives according to how well they achieve the multiple objectives of each stakeholder group. We used an additive functional form: v(x1,... ,xn) ) w1v(x1) + wnv(xn) , where ν(x1,. . ., xn) is

FIGURE 6. Overall value of each of the alternatives to WWTP managers. Also shown are bar graphs depicting the contributions of each of the three upper-level objectives to total value.

FIGURE 4. (a) Overall value of each of the alternatives to private households and bar graphs depicting the contributions of each of the four upper-level objectives to total value. (b) Results for households after assuming that a high-tech toilet can be developed to eliminate problems of aesthetics, hygiene, cleaning, convenience, and smell and that additional costs of the NoMix technology are offset by subsidies or reduced taxes.

FIGURE 5. Sensitivity of the households’ ranking of alternatives to the weight on Environmental Quality. For clarity, not all alternatives are shown. Those that are not shown have a trend similar to the Peak Shave alternative. Vertical line indicates current weight. the multidimensional value function for a particular stakeholder group, the ν(x1) are linear, one-dimensional value functions that convert each of the n attributes x1 to a common scale, and the w1 are the tradeoff weights for each attribute (see Supporting Information for a justification of assumptions and stakeholder elicitation details). Weights for each attribute for each stakeholder are given in Figure 3.

Model Results and Sensitivity Analysis Households are overwhelmingly expected to prefer the Status Quo to the implementation of any peak-shaving or nutrient recycling alternatives (Figure 4a). This is because the installation of a NoMix toilet introduces personal bathroom quality concerns, health risk potential, and significant costs that are not outweighed by the environmental benefits. Even if a “high-tech” toilet could be developed that overcomes all the problems of aesthetics, hygiene, cleaning, convenience, and smell, the rankings of households would not change (not shown). However, if, in addition, the higher costs to the households were subsidized by the government

FIGURE 7. Overall value of each of the alternatives to WWTP managers after incurring the cost of subsidies to households. Because of the high costs involved, the values were rescaled relative to those in Figure 6. Therefore, only the relative rankings and not the actual numbers can be compared between figures. Error bars indicate uncertainty in the cost of “high-tech” toilets. or offset by reduced taxes, the Nutrient Recycling 1 alternative would be very nearly preferable (Figure 4b). In fact, sensitivity analysis shows that if the weight on the Environmental Quality attribute were to increase beyond 0.25, this alternative would actually be the most preferred (Figure 5). Because the Environmental Quality attribute has a much greater weight to the WWTP manager than to households and because of the potential for significant cost savings at the plant, WWTP managers are likely to be motivated to pursue the NoMix alternatives over the Status Quo (Figure 6). The Nutrient Recycling 1 alternative ranks the highest, primarily because of its environmental benefit. There are not large differences in the ability of the various alternatives to meet the Plant Operation objectives, suggesting that the potential problems involved with the new technology are expected to be outweighed by the interesting new challenges and benefits to employee motivation. Unfortunately, if the WWTP must subsidize households to gain their acceptance of NoMix, then much of the cost savings at the plant will be negated. As mentioned in the previous section, these costs, which include the price of a hypothetical “high-tech” toilet, are particularly uncertain. We used a price ranging from that of the existing NoMix toilet to a price 1.5 times greater and a lifetime that is half as long. Even with this significant uncertainty, it seems that, because of the large number of households that would need to be subsidized, the Nutrient Recycling alternatives are no longer desirable (Figure 7). Only some of the more modest peak shaving alternatives might be preferred to the Status Quo. However, if the weight on the Environmental Quality attribute were to be greater than 0.45, then either Nutrient Recycling alternative would be preferred to the Status Quo (Figure 8). The sanitary equipment manufacturers would be most motivated by either of the Nutrient Recycling alternatives implemented using the “high-tech” toilets (Figure 9), even though they expect that this would require a five million franc research investment to develop. This preference arises because many more toilets can be sold throughout the entire catchment than for the peak-shaving alternatives, and apparently, they expect the profit margin to be higher for VOL. 42, NO. 6, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 8. Sensitivity of the WWTP manager’s ranking of alternatives to the weight on Environmental Quality. For clarity, not all alternatives are shown. Those that are not shown have a trend similar to the Peak Shave alternative. Vertical line indicates current weight.

FIGURE 9. Overall value of each of the alternatives to sanitary equipment manufacturers.

FIGURE 10. Overall value of each of the alternatives to engineering consultants. Also shown are bar graphs depicting the contributions of each of the three upper-level objectives to total value. high-tech toilets than for the current design. However, it seems that they do not expect this higher profit to outweigh the investment cost if toilets were sold to Glattpark alone. Still, any of the alternatives would be more profitable than the Status Quo for this stakeholder group. Similarly, both the engineering consultants (Figure 10) and the research scientists (not shown) should like to pursue any alternative over the Status Quo, and the Nutrient Recycling alternatives would be most preferred. This is because these last two dominate the others on all objectives for both stakeholders.

Synthesis and Path Construction The present stakeholder situation presents quite a dilemma. WWTP managers can expect to benefit greatly from separately collecting and processing urine into fertilizer. These benefits will accrue to financial, environmental, and operational objectives (Figure 6). However, they can only expect public acceptance of urine separation if they are willing to fully subsidize the additional costs to households, including the currently uncertain costs of a hypothetical “high-tech” toilet (Figure 4b). Unfortunately, these subsidies are likely to overwhelm the value of the benefits for all alternatives but the most moderate of peak-shaving options (Figure 7). Even in these cases, peak-shaving would only be justifiable if the high-tech toilet were to not cost any more than the currently available NoMix model. According to the assessments of the equipment manufacturers, this seems unlikely, as they expect 1860

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to obtain a higher profit from a high-tech toilet than from the current model to cover the significant expenses required to develop it. Further, if urine source separation is implemented only in Glattpark, the manufacturers would prefer to sell the existing model rather than spend the money to develop a more advanced design (Figure 9). This occurs, in part, because the manufacturers did not declare having any nonmonetary objectives for their decision, unlike the WWTP managers or engineering consultants, for example. Overall, this troublesome situation suggests that, given the present priorities, separate urine collection for use in peak-shaving or nutrient recycling does not appear to be a tenable long-term goal for the Kloten/Opfikon catchment. However, the emerging risks of micropollutants and other water quality impairments hint that the weight stakeholders place on the Environmental Quality objective could significantly change in the future. Sensitivity analyses show that if heightened concerns lead to a doubling of the relative importance of this objective for households and WWTP managers, the Nutrient Recycling 1 alternative would become most preferred (Figures 5 and 8). Because of the significant uncertainty surrounding the risk of micropollutants and the need to make a decision for Glattpark now, it might be argued that a precautionary approach should be adopted. A review of our results shows that such a path can be identified. Alternative 2.B., Peak Shaving with Conservative CSO Control, is currently the most acceptable of the peak-shaving alternatives for households (Figure 4b). This is because the location of a large storage tank in the cellar reduces the smell, health risk, and space requirements of the NoMix technology while providing effective protection against CSO events and associated micropollutant releases. The lack of additional intermediate or central storage tanks has practical benefits for WWTP operations, which make it desirable for plant managers, even when the costs of subsidies are included (Figure 7). This alternative is also relatively easily converted to either of the Nutrient Recycling options without wasted expenditures because it channels urine to an onsite storage tank without the need for WC storage, intermediate storage, or separate sewer lines beyond the building. Therefore, alternative 2.B. makes for a desirable transition scenario that leaves open future options should increased health risks or resource shortages force society to place more weight on environmental protection relative to cost or convenience objectives. To actually forge this path will require some careful communication and negotiation among the stakeholder groups. The equipment manufacturers will first need to be urged to pursue development of a high-tech toilet that meets consumers’ needs and then sell it at a reasonable price to the developers of Glattpark. This will not necessarily be the most desirable alternative for the manufacturers, but should still be preferable to the Status Quo (Figure 9). It will also be more desirable if it comes with an agreement that, if determined to be appropriate in the future, a larger contract for the entire Kloten/Opfikon catchment will be forthcoming. Households in Glattpark will only accept the high-tech urine separating toilet if they are reimbursed for their expenses. This will likely be an amount between 50 and 120 CHF per WC per year, depending on the selling price and anticipated lifetime of the toilet. We suggest that this amount actually be paid to the residents, and not to the developer, to help compensate them for any minor inconveniences. It would also be useful to remind residents that, while the environmental benefits may not be great now, the technology provides insurance against currently unforeseen risks or resource shortages. The WWTP managers will likely be just barely breaking even with this alternative, both in terms of expenses and effort. However, we anticipate that there will be additional

benefits not accounted for in our analysis related to the gaining of experience and momentum. Having a high-tech toilet available as a result of the Glattpark experience should facilitate future technology transfer to other catchments. While the selection of alternative 2.B. may not be ideal from the perspective of engineering consultants and research scientists, it will have significant benefits relative to the Status Quo and comes with little risk for these groups. Therefore, it would be worth their while to invest some time and energy into activities that will facilitate the NoMix decision and implementation process. Appropriate tasks might be to (1) conduct tests and surveys related to the newly developed high-tech toilet to ensure that it meets user requirements, (2) aid in the development and testing of signaling devices to coordinate the release of urine from the onsite storage tanks, (3) perform detailed cost studies to determine the appropriate amount and timing of household subsidies, (4) investigate the human and ecological risks associated with CSOs to determine if further control measures are necessary, and (5) work on developing a urine-based fertilizer product that is cheap, safe, and convenient to use. These activities will both encourage implementation and provide interesting research opportunities.

Discussion While our analysis focuses on a particular development in a particular catchment in Switzerland, we believe that the results can be applied more broadly. Many communities in Western Europe and the United States are faced with an aging wastewater treatment infrastructure, while also experiencing growth and development. This situation makes long-term planning and the definition of priorities much more demanding than in the past (16). Despite some remaining uncertainties in our analysis (see Supporting Information), we believe the application of MCDA helps to clarify the role that peak-shaving can play in allowing these communities to postpone or avoid expensive WWTP expansions. It can also give them a head start in testing urine separation technology and transitioning to a more comprehensive, decentralized, and sustainable wastewater treatment system (31). MCDA also gives insight into the possible barriers to technology adoption. In this case, it seems that manufacturers do not want to make the investment necessary to solve remaining consumer problems with NoMix toilets because they are waiting for action by the wastewater treatment community to generate a market. Meanwhile, although our analysis suggests that based on current priorities and cost accounting WWTP managers should promote the NoMix technology, the problem comes when they must consider paying for the household installations. Then the NoMix alternatives are only preferable over the Status Quo at the lower end of the possible range in installation costs. This means that if the WWTP managers are at all risk averse, then they should logically maintain the existing technology rather than pursue NoMix. This seems to be the sticking point of the whole situation. This source of technological “lock-in”, excess inertia caused by an unbalanced distribution of benefits or a shortterm period of lower payoffs for some stakeholders, has been recognized as a common barrier to innovative technologies (32). However, as we learned in a previous analysis (33) and applied to the present case, using MCDA to analyze the preferences of each stakeholder group separately rather than combining results across all groups can be especially instructive. In particular, it can suggest a path for implementation that suffices for all groups, even if it is not necessarily optimal for all. We believe that the precautionary path we laid out above will do this given adequate coordination among stakeholders.

Even when the specific results of our analysis are not directly applicable to a particular community, whether for financial, cultural, or practical reasons, the decision analytic approach to quantitatively balancing conflicting objectives among a diversity of stakeholders should still be appropriate. In fact, the objectives hierarchy shown in Figure 4 may be comprehensive enough to apply to most situations. Only the weights and outcome assessments will then need to be revised.

Acknowledgments We thank the stakeholder representatives and the scientists of the Novaquatis project for contributing their time and expertise to our analysis. We also thank Peter Reichert and two anonymous reviewers for their constructive comments on an earlier version of this manuscript. Funding was provided by Eawag, the Swiss Federal Institute of Aquatic Science and Technology.

Supporting Information Available Details on the creation of objectives hierarchies; considerations and assumptions used in assessing outcomes; table of assessed outcomes (Table S-1); method and assumptions used in value function construction; and discussion of remaining uncertainties. This material is available free of charge via the Internet at http://pubs.acs.org.

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