Microwave thermal hydrolysis of sewage sludge as a pretreatment stage for anaerobic digestion

This article focuses on the effects of microwave thermal hydrolysis on sewage sludge anaerobic digestion. Volatile suspended solid (VSS) and COD solubilization of treated sludge were investigated. It was found that the microwave hydrolysis provided a rapid and efficient process to release organics from sludge. The increase of organic dissolution ratio was not obvious when holding time was over 5min. The effect of the VSS solubilization was mainly dependent on temperature. The highest value of VSS dissolving ratio, 36.4 %, was obtained at 170 degrees C for 30 min. COD dissolving ratio was about 25 % at 170 degrees C. BMP test of excess sludge and mixture of primary and excess sludge proved the increase of methane production. Total biogas production of microwave treated mixture sludge increased by 12.9 % to 20.2 % over control after 30 days digestion. For excess sludge, biogas production was 11.1 % to 25.9 % higher than untreated sludge.