Influence of deflocculation on microwave disintegration and anaerobic biodegradability of waste activated sludge

• Sludge deflocculation by 0.1 g/g SS sodium citrate, enhanced floc disruption.
• Floc disruption facilitated an increase in disintegration efficiency of microwave.
• The irradiation energy of microwave reduced by 1.4 times for deflocculated sludge.
• Cost reduction in pretreatment can be achieved through deflocculation.
• Kinetic parameters demonstrate an efficient sludge degradation rate during hydrolysis.

In the present study, the potential benefits of deflocculation on microwave pretreatment of waste activated sludge were investigated. Deflocculation in the absence of cell lysis was achieved through the removal of extra polymeric substances (EPS) by sodium citrate (0.1 g sodium citrate/g suspended solids), and DNA was used as a marker for monitoring cell lysis. Subsequent microwave pretreatment yielded a chemical oxygen demand (COD) solubilisation of 31% and 21%, suspended solids (SS) reduction of 37% and 22%, for deflocculated and flocculated sludge, respectively, with energy input of 14,000 kJ/kg TS. When microwave pretreated sludge was subjected to anaerobic fermentation, greater accumulation of volatile fatty acid (860 mg/L) was noticed in deflocculated sludge, indicating better hydrolysis. Among the samples subjected to BMP (Biochemical methane potential test), deflocculated microwave pretreated sludge showed better amenability towards anaerobic digestion with high methane production potential of 0.615 L (g VS)−1.

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