[Characteristic of sludge thermal hydrolysis using microwave heating with alkali addition]

NaOH was added into sludge to improve thermal hydrolysis when heated with microwave irradiation. Volatile suspended solid (VSS) rapidly dissolved into aqueous phase when adding 0.1 g NaOH per gram into suspended solid (SS) of sludge. More than 60% of VSS solubilized at 170 degrees C, and VSS to SS ratio of treated sludge reduced to 25%. For 5 min treatment, soluble COD (SCOD) in treated sludge liquid phase was 9.8, 12.8, 15.1, and 14.5 g/L respectively at 80, 120, 150 and 170 degrees C. Accordingly, the SCOD to TCOD (total COD) ratio was 24.0%, 31.3%, 36.9% and 35.6%. The pH of the microwave heated sludge decreased with higher temperature and longer hydrolysis time, while the finale pH of different testes were still higher than 10.5. Alkali dose effect on organic matters dissolving was analyzed at the range of 0-0.2 g NaOH into per gram SS. Results showed that when alkali dose was above 0.05 g, the rapid dissolving trend became level for VSS and SS. BMP (biochemical methane potential) test was used to investigate treated sludge digestibility at NaOH dose of 0.05 g with 5 min microwave heating at set temperature and 0.1 g with 1 min heating. Results showed that adding 0.05 g NaOH improved sludge anaerobic digestion, the biogas production was 28.5% higher than control at 150 degrees 2, while adding 0.1 g NaOH would inhibit treated sludge digestion process.