Comparison of biodiesel production from sewage sludge obtained from the A2/O and MBR processes by in situ transesterification

The potential of two types of sludge obtained from the anaerobic-anoxic-oxic (A2/O) and membrane bioreactor (MBR) processes as lipid feedstock for biodiesel production via in situ transesterification was investigated. Experiments were conducted to determine the optimum conditions for biodiesel yield using three-factor and four-level orthogonal and single-factor tests. Several factors, namely, methanol-to-sludge mass ratio, acid concentration, and temperature, were examined. The optimum yield of biodiesel (16.6% with a fatty acid methyl ester purity of 96.7%) from A2/O sludge was obtained at a methanol-to-sludge mass ratio of 10:1, a temperature of 60 °C, and a H2SO4 concentration of 5% (v/v). Meanwhile, the optimum yield of biodiesel (4.2% with a fatty acid methyl ester purity of 92.7%) from MBR sludge was obtained at a methanol-to-sludge mass ratio of 8:1, a temperature of 50 °C, and a H2SO4 concentration of 5% (v/v). In this research, A2/O technology with a primary sedimentation tank is more favorable for obtaining energy from wastewater than MBR technology.