Enhanced water reduction by turning during sewage sludge composting

BACKGROUND Turning can supply oxygen and increase dewatering efficiency during composting. This study was conducted to investigate the influence of turning on water removal and the interactive influence of turning during different phases. Dewatered sewage sludge was composted using control technology for bio-composting, during which the temperature, free airspace, pile settlement and water reduction were measured and calculated. During the temperature-increasing and thermophilic phase, turning once and without turning were performed and compared. During the cooling phase, higher (every 2 days) and lower (every 4 days) turning frequencies were used and compared. RESULTS The results showed that there was a significant difference in water removal between the different turning modes during three phases (P value of temperature increasing, thermophilic and cooling phase, respectively, 0.0122, 0.0092 and 0.0056). Furthermore, the water removal was significantly related to the interaction between different turning modes during the thermophilic phase and cooling phase (P = 0.0092). CONCLUSION No turning in the temperature-increasing phase, turning once in the thermophilic phase, and turning every 4 days in the cooling phase was the most efficient turning strategy for water removal, for which the water reduction was 591.63 kg ton(-1) matrix, significantly higher than those in other treatments. (c) 2013 Society of Chemical Industry