Biodiesel production from wet sewage sludge and reduced CO2 emissions compared to incineration in Tokyo, Japan

Sewage sludge has potential use as a feedstock source for biodiesel production, but pretreatment such as drying it before the conversion has made it an uneconomical process. In this study, sewage sludge samples were collected from two different wastewater treatment facilities in Tokyo to develop an efficient process for extracting the saponifiable lipids and preparing biodiesel. A direct extraction method was chosen and performed in multi-stages by mixing hexane with sewage sludge in a jar at room temperature using various process conditions. Results showed the saponifiable lipids' extraction in the range of 19-21.5 wet wt. % (38-41 wt% DM), and it was possible to extract saponifiable lipids in an energy-efficient and economical manner. Furthermore, these extracted saponifiable lipids were converted into biodiesel through acid/base transesterification, resulting in an approximately 98 % and 99 % biodiesel yield using 1 wt% NaOH and 2 wt% H2SO4, respectively with a 94% lipid conversion efficiency. The biodiesel's high heating value, low cost, and low sulfur content make it a candidate for a carbon-neutral fuel and its production can reduce CO2 emissions in comparison to sludge incineration.