Employing Energy Management Planning to Achieve Net Zero Energy in Wastewater Operations

This paper outlines how energy management planning can accomplish dual goals of energy self-sufficiency and optimum treatment processing, and how this provides robust performance and acceptable payback on investment, leading to net zero energy wastewater operations. The energy content of wastewater surpasses the energy required by treatment, reportedly be a factor of up to 10 times. Nevertheless, conventional activated sludge plants with advanced treatment consume typically 1,800 kWh/MG of electricity, but facilities vary from 1,000 to 3,000 kWh/MG. Energy efficiency studies conclude that the potential for energy use reductions through efficient pumps and aerators are on the order of 30 to 50 percent, which is a range of about 400 to 700 kWh/MG. For plants with anaerobic digestion, a rule-of-thumb for electrical production from biogasfueled generators is 500 kWh/MG. Supplementation of anaerobic digesters with high strength organic waste and fats, oils and grease is possible where utilities have excess digester capacity. The experience with supplementation is that facilities have increased biogas by a factor of two or three times pre-existing conditions, and are able to have a corresponding increases in electricity production, where generators have been adequately sized. When thermal heat can be returned for plant processes, overall plant efficiencies rise even higher. Energy planning studies have also shown that innovative technologies that build upon anaerobic processes reduce energy usage from typical values, and, further, energy plans have demonstrated some unexpected results, such as the economic and environmental justification of anaerobic digestion combined with thermal processing, such as dryers and incinerators. While local conditions, particularly energy pricing and government subsidies, likely shape the specific planning objectives and outcomes of any individual plant, the variety of energy efficiency and production technologies that are becoming proven can result in a similar endpoint, and specifically net zero energy wastewater treatment.