Energy Content of Organics in Municipal Wastewater Treatment Streams at Tsumori Wastewater Treatment Plant

Abstract

This study elucidated the energy budget in wastewater treatment streams at Tsumori, Ichioka, and Chishima wastewater treatment plants (WWTPs) in Osaka. At Tsumori WWTP, the primary sludge produced in primary settling tanks and excess sludge produced in secondary settling tanks of the three WWTPs were collected and then digested anaerobically to biogas for cogeneration. The energy content of raw sewage at Tsumori WWTP was 4.3 kJ/L. Those at Ichioka and Chishima WWTPs were 2.1 kJ/L. The respective energy contents of primary sludge of Tsumori, Ichioka, and Chishima WWTPs were 16.3, 7.6, and 10.2 kJ/g. Those of excess sludge were 14.6, 8.3, and 9.8 kJ/g, respectively. The total calorific inflow to the three WWTPs was 1.1 × 10 9 kJ/d. About 40% and 30% of the total calorific energy respectively becomes primary sludge and excess sludge. The remaining 30% is consumed in the aeration tanks. About 30-40% the total calorific energy is recovered as biogas by anaerobic digestion, which produces electricity at 1.6 × 10 8 kJ/d, corresponding respectively to 47% and 33% of the electricity consumption of Tsumori WWTP and the three WWTPs. INTRODUCTION Wastewater treatment plants (WWTPs) for municipal sewage are implemented to reduce emissions of pollutants such as biochemical oxygen demand (BOD) and chemical oxygen demand (COD) to receiving water bodies. Various advanced treatment processes have been developed to improve water quality (e.g. nutrient removal), but they necessitate higher energy consumption than conventional processes. Little attention has been devoted to energy consumption at WWTPs because the benefits from improved water quality are believed to be greater than the environmental impact derived from energy consumption (Lazarova et al., 2012; Soda et al., 2013).