Disintegration and acidification of MBR sludge under alkaline conditions

• Alkaline pH values greatly enhanced disintegration and VFA production of MBR sludge.
• The optimal condition for VFA production was under pH 11.0 and digestion time 4 d.
• High pH stimulated organic matter transfer from the inner to the outer of microbes.
• Bound EPS were involved in organic matter transformation and VFA production.

The effects of alkaline treatment on sludge disintegration and acidification under anaerobic conditions were investigated in order to explore potential use of waste activated sludge (WAS) discharged from membrane bioreactors (MBRs). During the 12-day anaerobic digestion process, it was observed that volatile fatty acids (VFAs) production was greatly improved by alkaline treatment. The optimal conditions for VFA production of MBR sludge were under pH 11.0 and digestion time 4 d, and specific VFA production could reach about 219.7 mg COD/g VSS. Compositions of VFAs at pH 11.0 showed that acetic acid was the most prevalent product. Meanwhile, test results indicated that sludge hydrolysis and nutrient release were enhanced at alkaline pH values. Alkaline treatment stimulated organic matter (e.g., proteins and carbohydrates) to penetrate through cell membranes, transferring from the inner to the outer of microbes. It was also found that bound extracellular polymeric substances (EPS) played an important role in mass transfer and VFA production during sludge disintegration and acidification.