Comparison of degradation properties of carbohydrate and protein during anaerobic digestion of activated sludge at mesophilic temperature

The degradation of carbohydrate and protein is vital to the sludge anaerobic digestion process. This study investigated the degradation properties of carbohydrate and protein to gain an insight into organic matter removal during anaerobic digestion. Results show that carbohydrate was more efficiently degraded than protein, and also degraded before it. The final removal efficiencies of volatile solids, carbohydrate, and protein were 36.18%, 52.04%, 31.2%, respectively. The first four days of digestion represented a lag phase for protein degradation because the rapid degradation of carbohydrate during this phase led to suppression of protease formation. Kinetic results for protein degradation demonstrated that, after the initial lag phase, it followed first-order kinetics, with rate constants of 0.016 d^-1 and 0.002 d^-1 during the rapid degradation phase (four to 24 days), and slow degradation phase (24-52 days), respectively. Carbohydrate degradation followed first order kinetics at a constant rate of 0.007 d^-1 following the initial rapid degradation phase. Cumulative biogas production increased linearly with protein degradation, and exponentially with carbohydrate degradation.