The effects of pH(5-12)on primary sludge(PS)fermentation and volatile fatty acids(VFAs)accumulation were studied in batch experiments.The results showed that strong alkaline conditions(pH 10-12)could speed up hydrolysis to produce large amount of SCOD but inhabit acidification resulting in less VFAs production;While weak bases(pH 8,9)led more VFAs accumulation though less SCOD production.The optimal condition for primary sludge to accumulate VFAs in this study was pH at 9 and fermentation time of 10 d.Analysis also found protein degradation played an important role in VFAs production.More protein hydrolyzed and acidified at pH 9 than that at pH 10 systems though protein content at pH 10 was larger.Acetic and propionic acids were the dominant acid species.Furthermore,the comparison of VFAs,NH4+and pH relationship at pH 9 and uncontrolled systems further showed that weak bases condition could largely enhance the processes of sludge solubilization,protein and carbohydrate degradation,and reduce VFAs consumption,eventually,resulted in large VFAs accumulation in fermentation systems.