Thermochemical liquidization and anaerobic treatment of dewatered sewage sludge

Dewatered sewage sludge was thermochemically liquidized at 175°C and the liquidized sludge was separated by centrifugation to 57.7% (w/w) supernatant moisture, 92.3%; volatile solid (VS), 7.0%] and 42.3% precipitate (moisture, 71.6%; VS, 18.9%). The supernatant was successfully anaerobically digested. Biogas yield from the supernatant at organic loading concentrations of 1.9–2.2 g VS/l during 9 days' incubation was 440 ml/g-added VS and digestion ratio was 66% (w/w). Biogas yield in the case of dewatered sewage sludge was 257% ml/g-added VS and digestion ratio was 45%. Digestion of the supernatant resulted in high biogas productivity and a high digestion ratio compared with that of the dewatered sewage sludge. Moreover, it was suggested that the precipitate can be incinerated without the need for any supplemental fuel.