Carbon Source Recovery from Waste Activated Sludge by Low-Temperature Thermal Hydrolysis Process

Abstract

To recover a preferred carbon source from waste activated sludge (WAS), this study systematically investigated the effects of a low-temperature thermal hydrolysis process (THP) on WAS solubilization and dewaterability at 25°C–120°C for 60 min. Experimental results indicated that organics [soluble chemical oxygen demand (SCOD), proteins, carbohydrates, and lipids] and nutrients (N and P) were efficiently released into the sludge supernatant after THP. Deoxyribonucleic acid (DNA) tests identified 60°C as the threshold of sludge cell disintegration, which increased DNA from nearly 0–166.64 mg/L. Sludge dewaterability deteriorated after THP, as evidenced by longer filtration times and higher water contents of sludge cake, particularly at 120°C, which was due to the release of abundant soluble extracellular polymeric substances. The optimal heating temperature for carbon source recovery was 80°C, which achieved the highest biodegradability (5-day biochemical oxygen demand/SCOD 0.62), satisfied SCOD/total nitrogen (18.6), and had acceptable dewaterability.