Biodiesel production from urban and suburban municipal sewage sludges in Tokyo, Japan

The world's population, energy demands and waste generation are increasing year by year. In many countries, sewage sludge is disposed of in landfills, but 96.5% of the total sludge produced in Tokyo, Japan, is incinerated. GHG emissions from the Bureau of Sewerage accounted for approximately 37% of the Tokyo Metropolitan Government's activities and more than half of CO2 emissions are from sludge incineration. Therefore, a process is needed to replace or reduce the incineration of sewage sludge in Tokyo. This study proposes how to mitigate sludge handling, reduce greenhouse gas emissions, and produce sustainable energy based on initial fieldwork. Samples were collected to measure sewage sludge's potential for biodiesel production from urban and suburban wastewater treatment plants in Tokyo. Results showed the average 30 wt. % dry basis organics in sludge with high concentrations of free fatty acids and triglycerides in urban sludge and high ester content in suburban sludge and 97 % - 99% biodiesel yield was achieved through acid/base transesterification. Scale-up of the organics extraction and biodiesel production from sewage sludge can reduce fossil fuel dependency, and greenhouse gas emissions (approximately 19% from the incineration process) and contribute to achieving carbon neutrality in wastewater treatment.