NGUYEN VIET THANH Enhancement of Biogas Production From Concentrated Waste Activated Sludge by Alkaline Pretreatment rƁ@PCi Anaerobic digestion (methane fermentation) is widely used for energy and reduction of sewage sludge. Of the sludge generated from the sewage treatment plant, waste activated sludge is generated in the final settling tank of the activated sludge method and the concentration of easily decomposable organic substances is low, and the efficiency of methane fermentation is low because the cells are mainly microbial cells. For that reason, there is a simple and low-cost method of decomposing and solubilizing sludge and promoting digestion by alkali pretreatment with NaOH. Therefore, the purpose of this study is to increase the amount of biogas generated by treating solid sludge with waste activated sludge, which is hardly degradable by treating with alkali (NaOH). For both TS2% sludge and high-concentration excess sludge (TS about 4.0%), the effective solubilization conditions were an alkali concentration of 0.1N and a solubilization time of 6h from the increasing behavior of soluble COD. In batch experiments, the most effective effect was observed in the neutralized 0.1N system. The effect of alkali pretreatment was also confirmed in continuous experiments. Furthermore, stable operation was possible even under high pH conditions without neutralization due to long-term operation, and the VS removal rate was higher in the alkaline treatment system. Therefore, alkali pretreatment is considered to be a useful method for increasing methane production, although it is necessary to add an acid as a neutralizing agent for stable operation from the beginning of operation.