Reclaiming Cooling: Wastewater Reuse as a Strategic Resource for Data Center Water Management

Abstract

As data center developers turn to arid regions of the US for new projects, water for cooling becomes an ever more pressing concern. Water-driven cooling is one of the most efficient ways to cool data centers, lowering power usage effectiveness (PUE). Cooling towers account for 20 – 30% of water demand at power plants, and the potential substitution of reclaimed municipal wastewater has been projected to save up to 300 million gallons per day of freshwater withdrawals across power plants in Texas  (Stillwell & Webber, 2014). Although the current literature on this substitution is growing, the full environmental cost of using wastewater has not been compared with that of freshwater in a single life cycle assessment that accounts for tertiary-treatment energy, a dual-pipe distribution system, chemical use, and blowdown. This research fills that gap through a comparative life cycle analysis (LCA).

This study builds on Akhoundi et al.'s (2020) work and uses depth filtration, granular activated carbon (GAC), and chlorination as the primary treatment train, quantifying impacts across three main categories: global warming potential (GWP), cumulative energy demand, and freshwater displacement. Isolating these categories within an impact assessment and sensitivity analysis allows us to identify tradeoffs between energy use, carbon emissions, and water consumption. A wastewater scenario has about twice the GWP of the freshwater case, with treatment energy accounting for roughly 80% of the difference. This research analyzes different treatment trains. Looking at the UF+RO scenario, wastewater energy usage grows to over five times that of freshwater, but is balanced out by improvements in cycles of concentration (COC) that would reduce blowdown and chemical consumption. Running the GWP sensitivity analysis under a fully decarbonized grid scenario shows a significant reduction in carbon-equivalent emissions, with chemical production remaining as the main contributor. A cooling system commissioned today and operated through 2050 would spend the majority of its service life under grid conditions where the GWP penalty of reuse is negligible, while its water savings accrue at full value.

While the substitution of reuse water for freshwater is one-to-one, an indirect water penalty of approximately 0.93 L/m³ results from the higher upstream electricity and chemical inputs in the reuse train. This number however, is nearly negligible, accounting for less than 0.1 percent of the direct displacement benefit. Because water treatment falls on the utility, municipal-data-center water partnerships could offer significant benefits that cannot be captured by an operational LCA alone. These findings provide a decision framework for data center developers, utilities, and regulators evaluating reclaimed water infrastructure.