The impact of intermediate thermal hydrolysis on the degradation kinetics of carbohydrates in sewage sludge

•Carbohydrates degradation is a complex multi-step mechanistic process.•Thermal hydrolysis enhanced carbohydrates degradation for both process configurations.•Degradation rate was fast then slowed down due to nature of remaining compounds.•Carbohydrate degradation rate impacts on sludge digester HRT and the loading rate.

The purpose of this paper is to report the results, from laboratory-scale investigations, on the impact of intermediate thermal hydrolysis process (ITHP) on already digested sludge in general, and sludge carbohydrate content degradation process efficiency in particular. The ITHP performance data were compared with the performance of established conventional thermal hydrolysis process (THP). The degradation of sludge carbohydrates as a result of thermal pre-treatment and anaerobic digestion followed the first order kinetics. The overall sludge organic matter degradation kinetics rate constants indicated that the use of THP as an intermediate digestion step can enhance the already digested sludge organic matter degradation; further reducing the sludge mass and increasing its conversion to biogas.