Mesophilic two-phase anaerobic digestion of waste activated sludge with different VS contents

Two types of waste activated sludge (WAS) and kitchen garbage were used to prepare the WAS samples with different volatile solid (VS) contents, and the digestion efficiencies of prepared samples were investigated by mesophilic two-phase anaerobic digestion (TPAD) process. The experimental results showed that the ratio of volatile fatted acids and bicarbonate alkalinity (VFA/BA) in acidogenic phase was 0.05 for the system with the addition of kitchen garbage, and those of WAS samples were both lower than 0.02, indicating better stabilization of the two-phase systems. The VS and total COD removal efficiencies increased with increasing hydraulic retention time (HRT). The maximum removal efficiencies of VS and total COD were achieved when the HRT was 20d, and the maximum VS and total COD removal efficiencies were 47.9% and 49.2%, respectively. The specific methanogenic activity (SMA) and methane content of biogas both increased with increasing HRT. The addition of kitchen garbage into the low organic WAS sample could improve both organic removal efficiency and biogas yield.