Decentralized Water Treatment

To explore ways to lower costs and technology hurdles to distributed water treatment systems, National Alliance for Water Innovation (NAWI) and Stanford’s Water in the West convened a meeting of experts in February 2023 at Stanford University. Their  report was recently released and cited below summarizes the findings of the workshop that brought together researchers, industry experts, practitioners, policymakers and other stakeholders to discuss the current state of knowledge in extreme decentralized water treatment systems, and to identify the areas where further research and development are needed to allow the spread of this practice. All the comments of this blog entry are derived from the report of the workshop cited below.

Fairhart, A., Sedlak, D.L., Fiske, P., Kehoe, P., and Mauter, M. (2023). Extreme Decentralized Water Treatment. Exploring the Future of Premise-scale Water Treatment and Reuse: A Water in the West Series. Available at: https://purl.stanford.edu/kh912mb9452

Access to an adequate quantity of treated and piped potable water and management of wastewater produced in homes and businesses is expected by all city dwellers and most suburban dwellers in wealthy countries like ours. Readily available safe drinking water and treatment of sewage is also crucial to public health and protection of the environment. For well over a century, municipal drinking water provision and wastewater management have been made possible by large investments in centralized systems. Fresh water withdrawn from rivers, reservoirs, and groundwater passes through drinking water treatment plants and is distributed through a vast underground pipe network to buildings throughout our urban and suburban communities.

After it is used, wastewater is collected in underground sewers that carry it to wastewater treatment plants to be cleaned to regulatory requirements prior to its discharge to the environment. In some water-stressed cities and locations like Northern Virginia some of the treated wastewater undergoes additional treatment to be directly or indirectly reused. This recycled water often is returned to users through another dedicated water distribution system recycling of the purple pipe water (non-potable by convention) in Loudoun County for data centers or in Fairfax for golf courses and ball fields. Alternatively, treated wastewater may be subjected to advanced treatment prior to being returned to the drinking water supply like delivering treated UOSA wastewater to the Occoquan Reservoir via release into the Occoquan River.

Although water reuse via the purple pipe system solves problems, the costs associated with the construction of a dedicated water distribution system for non-potable water throughout an entire area has high relative costs, regulatory complexities, and risks of unintentional cross-connections between recycled water and potable water pipes have limited the spread of such systems. The second approach, direct recycling is hindered in many places by the “ick” factor, but in locations like Northern Virginia, utilizing the Occoquan River to deliver the treated wastewater to the Occoquan Reservoir overcomes that. Another alternative, a relatively new approach to water recycling called decentralized water reuse may have promising advantages for utilities, developers, data centers and entrepreneurs.

Distributed water recycling systems have made considerable progress in cities where there is a recognition of the need to address water scarcity due to climate and growth and where partnerships have been built between utilities, building operators and regulatory authorities. The current generation of treatment technologies for distributed treatment typically recycle less than half of the wastewater produced within the building. In part, this is due to concerns about costs, but it is also determined by constraints put upon uses of recycled water in buildings. Although it is technically feasible to treat wastewater to a point at which it can be used for drinking, cooking and bathing, or to employ rooftop rainwater collection for potable purposes, such projects have rarely been built due to concerns about safety or the acceptability of the water.

With data centers, the bulk of the on-site water demand is for non-potable uses- cooling and watering of landscape. In a water-cooled system, water-cooled chillers and cooling towers located on top of the data center roofs produce chilled water, which is delivered to computer room air conditioners for cooling the entire building. In 2021, when Prince William County looked at water consumption for its 25 operational data centers at the time it found that water use varied by season and ranged from about 0.2 to 0.5 gallons per square foot per day. Prince William County Board of County Supervisors have recently approved rezonings that will ultimately result in tens of millions of square feet of data centers. Utilizing on-site water treatment could reduce the need for expansions of the UOSA plant, address part of the growing salinity problem, and reduce the cost of treatment for Fairfax Water.  

The workgroup at Stanford found that although existing technologies have proven to be adequate for the current generation of distributed water recycling systems, there is considerable room for improvement. NAWI was founded to conduct research research to lower costs and improve the feasibility of technologies that could help make non-traditional water sources a larger part of our nation’s water portfolio. In Japan more than 2,500 individual buildings in the country utilize in-building wastewater reclamation and rainwater harvesting systems, an alternative approach to centralized treatment that creates sustainable, resilient structures (Kimura et al. 2013). These systems treat different types of wastewaters within each building, including domestic sewage and graywater. The treated water is then used for various purposes like toilet flushing, cooling, garden watering, car cleaning and even fire protection. The emphasis in Japan  is on reusing water within the building where it was generated.

The shift towards building-scale water management has been facilitated by various factors, such as supportive local regulations, favorable tax policies, and technological expertise in designing and operating these systems. Further, the availability of a design manual and clearly defined water quality requirements for reclaimed water have further bolstered the adoption of on-site wastewater reclamation.

This approach has not worked as well in Bengalaru, India. The adoption of building-scale water treatment has not been as successful, the city’s journey features a blend of policy directives, innovative industry response and consumer-centric approaches (Miörner et al. 2023). Small-scale sewage treatment plants (SSTPs) are mandated to be included in all new construction and certain existing buildings. These systems are often contained within the building complex, treating wastewater for reuse in non-potable applications, like gardening and toilet flushing, contributing to a circular water economy at the community level.

Bengalaru, India lacks governance structures and regulatory standards, and the city grapples with ensuring accountability and quality in the rapidly growing ONWS market. Furthermore, concerns surrounding the health and safety of workers interacting with these systems underline the urgency for comprehensive regulation. Bengaluru’s story is one of policy-induced innovation and adaptation in the face of necessity. It serves as a reminder that while solutions can be replicated, execution of the solution will vary based on a variety of factors.

The factors for success identified in the report, would favor a distributed reuse for data centers. The bulk of water used on site is for non-potable purposes, the waste water tends to be fairly uniform in characteristics and there is a localized tremendous volume. The conversion of natural landscapes to impervious surfaces creates a stormwater problem whose solution could provide makeup water to the recycled on-site water. Virginia needs to work with NAWI and the data center industry to address this opportunity for sustainable water use.   Amazon Web Services (AWS) and Goggle have  commited “to be water positive by 2030.” Let’s see if we can do something to make all the data centers in Northern Virginia sustainable.