Co-digestion of sewage sludge and crude glycerol from biodiesel production

Biodiesel has become one of the most attractive fuels since it was globally understood the renewability of its nature. Glycerol is a major byproduct of biodiesel production which is often regarded as a waste stream which is accompanied by a significant disposal cost. The effect of glycerol on the performance of a cascade of two anaerobic continuous stirred tank (CSTR) reactors treating thickened sludge at mesophilic conditions was investigated. The objective of this study was to evaluate the use of glycerol as a co-substrate during the anaerobic treatment of sewage sludge. For this purpose, feed mixtures of sewage sludge supplemented with 0%, 2%, 3% and 4% (v/v) glycerol were tested at hydraulic retention times between 12.3 d and 19.7 d. By adding 4% of glycerol, the system failed due to overloading. In all other cases, biodegradability of mixtures estimated to be higher than 88%, while the methane yield coefficient was 0.8 Lbiogas/g TVSremoved. Moreover, co-digestion improved biogas production by 3.8-4.7 times.