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 Fresh water withdrawn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.