Wastewater treatment facilities can be viewed as widely unheralded sources of energy, nutrients and water resources. Methane emitted by sewage sludge can be captured and exploited to produce renewable natural gas (RNG) or generate renewable electricity on-site. Nitrogen and other nutrients can also be tapped and recycled as fertilizer, while the water itself can be treated and reused as fresh water.

Most treatment plants do not act on the potential for realizing these benefits, which could provide revenue to offset their own production costs and advance sustainability goals. Prospects for recovering these resources from the roughly 15,000 U.S. municipal wastewater plants were analyzed by U.S. Argonne National Laboratory researchers.

The assessment was based on a comprehensive data set of all wastewater treatment facilities in the U.S. to weigh the resource recovery potential for each. The likely contributions of three resource recovery technologies were explored: anaerobic digestion to convert methane in biogas to carbon dioxide, anaerobic digestion to produce RNG and hydrothermal liquefaction to yield renewable diesel.

Most wastewater resources are produced by large treatment plants processing more than 5 million gallons a day. These make up only 8% of total treatment plants but produce 77% of the total energy, water and nutrients in wastewater flow. The 10% of treatment facilities that use anaerobic digestion can exploit this existing technology to produce RNG or electricity.

More than 50% of U.S. counties could meet 75% or more of their irrigation demands using reclaimed wastewater. These counties are concentrated east of the Mississippi, where demand is lower. Nitrogen production via anaerobic digestion could exceed demand in the northeastern region, while hydrothermal liquefaction can be deployed to recover 60% to 90% of total phosphorus contained in wastewater influent.