Energy Efficiency for Biosolids Treatment: An Update of Best Practices and Case Studies

After manpower, energy is the highest cost item on the balance sheet of most wastewater treatment plants (WWTPs). Over the last decade, energy consumption by this sector has been on the upswing as additional treatment demands and regulatory requirements have increased. In many cases, mass and volume reduction, which is a universal goal of solids treatment processes, can result in additional processing and increased energy use. High energy consumption affects the water industry world-wide and is inextricably linked to the issue of climate change. In the United States, there are more than 16,000 WWTPs, which are together responsible for consumption of 1 percent of the country's total electric power. This corresponds to an annual cost of approximately 4 billion and results in greenhouse gas (GHG) emissions of more than 45 million tons (41 million tonnes).The Global Water Research Coalition (GWRC), which is an international group of 14 government, not-for-profit, and private research organizations, including the Water Environment Research Foundation (WERF), is leading a research project to develop a compendium of Best Practices in energy efficient design and operation of water and wastewater plants. The goal of this research is to provide tools to treatment facilities to reduce energy consumption through optimization, with an overarching goal of becoming energy and carbon neutral by 2030. When considering energy efficiency objectives, both incremental improvements in energy efficiency through optimization of existing processes and operations and/or implementation of new processes and technologies are being evaluated. The Best Practice compendium is being developed based on surveys of existing treatment plants in Europe, North America, Australia, and South Africa.Based on the best practices for energy recovery from biosolids in North America, the WERF research team collected data on OpenCEL Focused Pulsed technology, on Linear Motion Mixers for Anaerobic Digesters and on Stirling external combustion engines for biogas. Best practices from the GWRC compendium are referenced, including an overview of the CAMBI thermal hydrolysis technology.