Effects of microwave irradiation at various temperatures on biosludge disintegration

The waste biological sludge disintegration by using microwave irradiation was investigated at a ramping rate of 2°C/min and 5 min holding time at various target temperatures. Significant disintegration of biosludge was observed and the highest disintegration degree was determined about 82% at the temperature of 110°C. Increase of target temperature elevated the energy needs to 98, 123 and 148 kWh/kg TS at the temperatures of 75°C, 90°C and 110°C, respectively. The gradual increase of sugar and protein in the sludge slurry with increasing temperatures indicates successful degradation. The microwave pretreatment increased the specific surface area of the sludge by particle size reduction. The specific surface area of raw sludge was 70 m²/kg and rose to approximately 253.7 m²/kg at 110°C with an increment ratio of 260%. Although a significant NH₄-N release was not observed, PO₄-P concentrations increased from 11.0 mg/L to 16.3, 20.7 and 29.2 mg/L at the temperatures of 75°C, 90°C, 110°C, respectively. While the specific filter resistance of waste biological sludge was about 1.0 × 10¹³, increasing the microwave target temperature, the ability of dewatering decreased and the highest SFR value of 5.1 × 10¹⁴ was observed at the temperature of 110°C.