Characteristics During Thermal Hydrolysis Or Combined Pretreatment And Anaerobic Digestion Of High-solid Sludge

The performence of thermal hydrolysis pretreatment（165℃,50 min）, anaerobic digestion（mesophilic and thermophilic, HRT=15d） in 10% solid content dewatering sludge from municipal wastewater treatment plant（WWTP） was investigated by using thermal hydrolysis reactor, completely mixed anaerobic digestion reactor. At the same time, the H₂O₂ with thermal was used for 14% solid content dewatering sludge. After pretreatment, using mesophilic Biochemical Methane Potential（BMP） test to carried out the biogas dose in anaerobic digestion and the performance of the pretreated sewage sludge to get the best condition of thermal hydrolysis. The analysis results are valuable for the application thermal hydrolysis pretreatment and anaerobic digestion of high-solid sludge and the other treatment schemes of pretreated high-solid sludge. Main conclusions are as follows:（1） Thermal hydrolysis pretreatment could release and hydrolysis the organics as the cell was crashed. The VSS reduction is 42.92%. The main content of dissolved organic matter in hydrolysate was dissolved protein（50%） and carbohydrate（21%） after thermal hydrolysis pretreatment at 165℃ for 50 min.（2） Comparison on mesophilic and thermophilic anaerobic digestion performance of sludge with high solid content by thermal hydrolysis pretreatment was carried out: The biogas production could reach as high as 25.95m3·（kg VSS·d）-1 under the mesophilic condition with HRT for 15 d, the concentration of methane reached 68.6%, the hydrolysis efficiency of VSS could reach as high as 52.22%; While the removal efficiency of VS was below 30% and the biogas production was only 1.65m3·（kg VSS·d）-1 under the thermophilic condition, the VFA was accumulated largely and the concentration of methane was only 24.42%. At the same time, comparison on mesophilic and thermophilic anaerobic digestion performance of sludge with high solid content was carried out: the hydrolysis efficiency of VSS could respectively reach 38.58% and 40.85%, and the hydrolysis efficiency of VS could respectively reach 20.67% and 18.48%, the biogas production could respectively reach 17.64m3·（kg VSS·d）-1 and 20.07m3·（kg VSS·d）-1. The FISH results evidenced the actual operation conditions of reactors.（3） H₂O₂ with low temperature thermal hydrolysis combined pretreatment works well. When the pretreatment temperature 115℃, 15 min and oxidation pretreatment time coefficient n is 0.2, SS, VSS hydrolysis rate was best. The VSS hydrolysis rate was 42.17%, the dissolubility SCOD reached 64.13g/L, dissolution rate increased from 1.12% to 1.12%.（4） ATH pretreatment can effectively improve the sludge anaerobic digestion gas production and the gas production rate is significantly higher than TH pretreatment. When the pretreatment temperature 115℃, 15 min and oxidation pretreatment time coefficient n is 0.2, BMP cumulative gas production was increased by 51%, at the same time the VS removal rate of 41.38%. ATH pretreatment achieved at low temperatures close to high temperature thermal hydrolysis on hydrolysis effect and digestion efficiency.