Short chain fatty acids accumulation and microbial community succession during ultrasonic-pretreated sludge anaerobic fermentation process: Effect of alkaline adjustment

• Alkaline adjustment was used to enhance SCFAs accumulation in anaerobic fermentation of ultrasonic sludge.
• The optimum conditions for SCFAs production were determined.
• Mechanisms for SCFAs accumulation were analyzed.

Short chain fatty acids (SCFAs) are value-added products from waste activated sludge (WAS) anaerobic fermentation. The effects of alkaline adjustment, in the range of pH 7–10, on SCFAs accumulation and microbial community of ultrasonic-pretreated WAS at 20 ± 2 °C were investigated in this study. Experimental results indicated that optimum conditions for SCFAs accumulation were pH 9 and fermentation time of 7 days. The changes of protease activity showed that on the initial phase, ultrasonic pretreatment and alkaline adjustment rather than biotic effect was the leading cause of SCFAs improvement at high pHs. DGGE analysis revealed that alkaline adjustment had a strong impact on microbial community. Some bacteria belonged to Firmicutes, Proteobacteria and Bacteroidetes could adapt to high alkaline environments and contribute to proteins and carbohydrates degradation and SCFAs production in the later phase of anaerobic fermentation.