Codigestion and combined heat and power systems energize wastewater treatment plants – Analysis and case studies

Abstract

Wastewater treatment industry aims to transform from being an energy consumer to an energy producer by recovering energy embedded in wastewater. There are several ways to achieve energy self-sufficiency or energy-positive status in wastewater treatment plants. This paper presents an energy performance analysis of wastewater treatment considering both energy efficiency and energy recovery mechanisms. Various treatment scenarios based on wastewater characteristics, plant capacity, primary treatment efficiency, and supplemental feedstock are considered to evaluate the potential for energy recovery in wastewater treatment. Energy efficiency (process equipment upgrades), carbon capture enhancement through sludge removal in primary treatment unit and biogas production through the addition of supplemental feedstock are considered in the analysis. Codigestion and combined heat and power system integration is considered to enhance biogas production and in turn electricity and heat production from wastewater treatment. Case studies highlighting the progress of codigestion and CHP integration are discussed in detail to understand the impact of various feedstock and technology combinations. The study confirms that carbon capture in the primary treatment unit can contribute to downstream energy conservation as well as enhanced biogas production. The energy recovery potential in wastewater treatment also increased with organic strength of the wastewater and the treatment capacity. Further, the type of CHP unit, number and size are critical factors in optimizing the energy losses in the conversion process. Despite the codigestion challenges and the capital costs required for both CHP and codigestion systems, their integration still leads the way forward for energy-positive and cost-effective wastewater treatment plants.