Overburdened Centralized Wastewater Facilities. Interviews identified the lack of wastewater capacity at centralized facilities as a key driver on the US East Coast. Overburdened municipal facilities cause envi-ronmental discharge issues if they cannot fully treat flows entering the facility. This is particularly challenging during storm events in cities that have combined stormwater and municipal sewers. Several locations have incentivized the development of OWR to help prevent combined sewer overflows (CSOs) and to improve the quality of receiving waters. One key project in New York City is the Domino Sugar Factory Redevelopment Project, described Zach Gallagher. It includes a 400,000 gpd (~1.5 million liters per day) district-scale reuse project that collects wastewaters from five new buildings to produce non-potable water for toilet flushing, irrigation, and cooling towers. Any excess water that is not used is discharged to the East River. By providing a high level of onsite treatment, the project simultaneously diverts wastewater from downstream treatment facilities while reducing potable demands. Aaron Tartakovsky cited OWR projects in Connecticut that help protect sensitive environmental zones by reusing significant amounts of wastewater and discharging only a fraction of the highly treated effluent to the environment.
Economic Advantage. OWR can only be sustainable if the communities implementing it see that its benefits outweigh its costs. In many locations, OWR may notbe more cost-effective than centralized treatment. However, interviewees cited several factors that can help tip the scale towards economic viability including (1) high costs of centralized water/wastewater services, (2) infeasible expansion costs for centralized facilities (i.e., treatment and collection/distribution systems), and (3) incentives to address constraints like limited wastewater capacity. Jay Garland cited life-cycle assessments that have identified cases where OWR makes more economic sense because it avoids the costs of constructing an extensive distribution system and pumping water over long distances. Sedlak noted that his initial skepticism of the economic viability of OWR was turned around by techno-economic analyses that demonstrated its lower cost compared to centralized non-potable reuse, particularly when multiple benefits could be achieved. For example, Eawag’s Circular Sanitation Toolbox helps identify opportunities to couple OWR with the recovery of other resources.
Challenges for OWR Implementation
Any new water paradigm faces challenges as it goes through initial implementation and wider adoption. In the interviews, the most cited challenges were: (1) cost, (2) lack of public health requirements and program organization, and (3) the need to step out of the “municipal mindset.”
Cost. The cost of OWR was the primary challenge cited by interviewees. As Michael Jahne explained, “Economies of scale are real!” In practice, an onsite water system can have a higher cost for a developer than a sewer connection to a centralized facility. Both he and Page noted that these calculations, however, should also factor in the added resilience that OWR can bring to a community. One of the biggest challenges is therefore to help potential developers and communities understand when and where OWR can offer significant benefits. One new tool that is helpful for evaluating this trade-off is the EPA’s Non-Potable Environmental and Economic Water Reuse calculator (NEWR), which allows users to evaluate the full cost of both centralized and decentralized reuse including the costs of pumping and distributing water. Gallagher also referenced a combined cost of water and wastewater of $12 per 1000 gallons ($3.20 per 1000 L) as a rule-of-thumb for identifying areas where OWR makes more financial sense. Morgenroth suggested that it’s not appropriate to only look at the cost of water reuse against today’s prices; they should also be compared against future prices: “If you have plenty of water, you may not consider water reuse…until the day you run out of water.”
Lack of Program Organization and Public Health Requirements. Getting OWR off the ground in a new location is often impeded by the absence of a clear and simple permitting pathway. Without a well-structured OWR program, a developer may need permission from multiple, independent city departments, who in turn may have no mechanisms to coordinate with each other. Regulatory reform is often required to break down the bureaucratic obstacles and streamline OWR implementation.
Furthermore, one unique challenge with OWR is that different LRTs are needed to address the wide range of potential source waters and end uses (Figure 1). This leads to a more complex matrix of requirements compared to municipal reuse. This complexity may present challenges for regulators, particularly in regions with insufficient staffing, experience, or internal support to implement a new paradigm.
Stepping Out of the Municipal Mindset. One broader question that came up during multiple interviews was whether the mindset used in municipal settings should carry over into OWR (i.e., design principles, monitoring strategies, etc.). In some cases, this may be beneficial, expressed Garland, such as the application of risk-based LRT frameworks used in municipal settings. But there is not consensus on whether OWR should use the same technologies, design philosophy, and operations approach. Morgenroth questioned whether onsite water systems should look like miniature versions of centralized facilities or if design approaches should be adapted for OWR’s unique constraints. Instead of pushing technologies to their limits while relying on significant operational oversight, he suggested that keeping operations simple (e.g., operating at lower membrane flux rates to extend maintenance intervals) might be favorable for onsite water systems. Griggs agreed, saying that if an onsite water system does not have the same level of operational oversight as municipal-scale systems, then it should be designed to operate with more autonomy and greater robustness against failures. Jahne asked if it made sense to require municipal-scale monitoring technologies at smaller scales, such as in single-family homes. Given the increasing challenges of oversight at decreasing scales, it may be preferred to reduce the monitoring burden and rely on greater levels of treatment to protect public health.
Solutions to Expand OWR Implementation
Several solutions were identified to expand OWR implementation. The most cited solutions were: (1) legislation and regulations, (2) mandates and incentives, and (3) experience.
Legislation and Regulations. Streamlining the permitting process is one of the most critical steps to expand OWR implementation. To do this, San Francisco passed regulatory reform legislation that helped organize the relevant permitting agencies under a single OWR program umbrella. This created clear, cohesive permitting pathways and eliminated the need for developers to coordinate with multiple, independent agencies. San Francisco’s ordinance provided the necessary scaffolding to do OWR more efficiently by improving communication and consistency between the regulators, city officials, trades, and developers, stated Tartakovsky. The NBRC developed model legislation that has facilitated the development of programs across the country, including one for Austin Water.
Beyond legislative reform, the development of uniform public health requirements creates consistency in project implementation by setting the bar for success. The establishment of pathogen LRTs (described above) was cited by multiple interviewees as a key effort by the NBRC to help regulators define public health requirements and create consistency across the nation. While regulations set the bar, they should also include oversight to make sure that the bar is met. Jashinski emphasized the importance of ongoing monitoring to ensure treatment systems function as they were designed. For example, requiring flow meters can ensure that projects comply with their recycled water production goals and allow regulators to identify facilities that are using excess potable water. This oversight motivates projects to maintain their systems and ensure proper operation.
Mandates and Incentives. Several interviewees cited mandates that require the development of OWR as the most effective tool for advancing implementation. Mandates have been used to spur the advancement of OWR in multiple locations across the US including: Austin, TX, which requires condensate and rain water reuse for all buildings over 250,000 square feet; the City of Los Angeles, which requires buildings over 25 stories tall to use recycled water for cooling towers; and the City and County of San Francisco, which requires recycling wastewater in new commercial and graywater in new multi-family buildings over 100,000 square feet.
Financial incentives were also important to kick-start early adopters. Sedlak noted that new paradigms always include a period of experim-entation where the successful ideas are separated from the dead-ends. State and federal funding incentives can be important mechanisms to de-risk projects and convince early adopters to pursue an unproven approach. One such example is New York City’s $4 million investment in Domino Sugar’s $12-16 million redevelopment project, noted Gallagher.
