Enhanced short-chain fatty acids production from waste activated sludge by combining calcium peroxide with free ammonia pretreatment

This study reported a new low-cost and high-efficient combined method of CaO2+ free ammonia (FA) pretreatment for sludge anaerobic fermentation. Experimental results showed that the optimal short-chain fatty acids (SCFA) yield of 338.6 mg COD/g VSS was achieved when waste activated sludge (WAS) was pretreated with 0.05 g/g VSS of CaO2+ 180 mg/L of FA for 3 d, which was 2.5-fold of that from CaO2 pretreatment and 1.5-fold of that from FA pretreatment. The mechanism investigations exhibited that the CaO2+ FA could provided more biodegradable substrates, this combination accelerated the disintegration of sludge cells, which thereby providing more organics for subsequent SCFA production. It was also found that the combination of CaO2 and FA inhibited the specific activities of hydrolytic microbes, SCFA producers, and methanogens to some extents, but its inhibition to methanogens was much severer than that to the other two types of microbes.