“Wastewater treatment plants are not waste disposal facilities but are water resource recovery facilities that produce clean water, recover nutrients (such as phosphorus and nitrogen), and have the potential to reduce the nation’s dependence on fossil fuels through the production and use of renewable energy and the implementation of energy conservation.” This quote from the 2011 WEF Renewable Energy Position Statement clearly calls attention to the role of wastewater management through Water Resource Recovery Facilities (WRRF) to address the needs of the Utility of the Future.
The water resources utility of the future will integrate these three major concepts of Nutrients, Energy and Water, and many cutting edge utilities are already implementing this management goal of resource recovery. This focus may initially have been internal to the water or wastewater utility, investigating sustainable energy management through energy conservation, increased renewable energy production (where feasible), and focus on overall energy management. The overall societal benefit of the resilience improvement through distributed generation is starting to be realized. The fact that a water resource recovery facility (wastewater plant) that generates its own energy can operate when the power is out is an asset during extreme events. In addition, this capacity can be coordinated with electric utilities to address peak loads and other system needs. Valuable energy products generated on-site at wastewater plants can also supply a portion of energy demand within their respective service areas.
On average, the energy content of wastewater (chemical, hydraulic and thermal) is five times greater than the energy required for treatment. The most common opportunity for on-site power generation is through biogas created through anaerobic digestion. However, technologies such as gasification, pyrolysis, and incineration may be used to generate electricity or fuel. District energy systems, facilities to generate renewable diesel or aviation fuel, hydrogen fuel cells, and in-line hydropower are all being installed today.
However, becoming net energy positive is not the only goal. Optimizing overall sustainability may actually require using more energy or producing less energy onsite. Treating water to higher standards is often more energy intensive. Similarly, using biogas as a transportation fuel reduces onsite power production and increased energy use is required to further process biosolids to maximize reuse potential and to recover nutrients and minerals (e.g., nitrogen, phosphorous, magnesium).
A number of utilities worldwide have already taken the leap and begun this transformation towards resource recovery. While it is not practical for all water resource recovery facilities to become energy positive or neutral, all can take steps towards increasing sustainability while also improving resilience in the energy sector.