The purpose of this research was to examine energy recovery potentials and utilization of sewage heat, digestion gas, and sewage sludge from municipal wastewater treatment plants. This study analyzed the effects of greenhouse gas reduction, improvement of energy self-efficiency, and economic benefits upon the recovery of unutilized energy sources from the plants.

Based on the results of this study, energy self-efficiency can be improved from 51.6% (as of 2015) to 115%. It was found that the energy recovery of unutilized energy would help municipal wastewater treatment plants achieve over 100% of energy self-efficiency.

Estimated reduction potentials of greenhouse gas by the recovery showed annually approximately 422,762 tCO2eq, 18,984 tCO2eq, and 73,693 tCO2eq by sewage heat, digestion gas, and sewage sludge, respectively. These account for 25% of greenhouse gas emissions from the wastewater treatment plant in 2015. Potential economic benefits by the recovery revealed that the total savings were found to be KRW 120.5 billion won per year: sewage heat (KRW 116 billion won), digestion gas (KRW 3.2 billion won), and sewage sludge (KRW 900 million won).

By considering the recovery of the energy from unutilized energy sources from municipal wastewater treatment plants, the improvement of energy self-efficiency and the reduction of greenhouse gas as well as economic savings can be achieved.

Based on this study, we proposed several ways to recover unused energy resources from municipal wastewater treatment plants. It is necessary to include sewage heat as a renewable energy source, to expand the utilization rate of dry heat for sewage sludge, and to establish standards and guidelines for calculating energy self-efficiency rate at the plants.