Influence of Thermal Hydrolysis Pretreatment on Mesophilic and Thermophilic Anaerobic Digestion of Sludge

Aiming at the influence of sludge thermal hydrolysis pretreatment(THP)on anaerobic digestion,a series of experiments involved in sludge mesophilic anaerobic digestion (MAD) and thermophilic anaerobic digestion(TAD) with or without THP were designed and compared in this study to acquire the optimal treatment of sludge based on the balanced budget of energy in different systems.Results showed that the cumulative methane production per unit VS in THP followed by MAD(THP-MAD)reached the highest value of 276.9mLCH 4 /gVS added, which was 1.32 times of direct MAD of sludge.Meanwhile,the initial concentrations of soluble chemical oxygen demand and total volatile fatty acid in THP-MAD system were up to 34.71 times and 6.77 times of those in MAD, respectively.Moreover,the pH value and total alkalinity as well as the concentration of total ammonia nitrogen and free ammonia were increased in THP-MAD system compared with MAD system.In addition,the dominant archaea was changed from acetoclastic methanogen Methanothrix (52.47%) in MAD to hydrogenotrophic methanogen Methanomassiliicoccus (52.99%) in THP-MAD.However,there was no lag phase for direct TAD but 5.47 days lag phase for THP-MAD,and a higher maximum methane yield rate and a shorter effective methane production time in direct TAD than THP-MAD,which led to a higher net energy for direct TAD than THP-MAD.