| Anaerobic digestion(AD)is a common approach to treat waste activated sludge(WAS)in wastewater treatment plants.In that the water content of WAS is at high level,basic problems in operating of conventional AD are presented as low efficiency,large volume and high operating costs.Compared with conventional AD of WAS,the high solid AD(HSAD)has advantages to improve digestion efficiency,digester volume,improve and gas production performance,but,HSAD is more susceptible to various factors,which effects on the stability of process.Concerning on inhibition of the high-level concentrations of ammonia nitrogen and phosphate in sludge liquor during HSAD,the feasibility of recirculated anaerobic digestion-alkaline thermal treatment(AD-TAP)process was evaluated by using WAS.The process operation,anaerobic digestion efficiency and population structure distribution was analyzed,and the feasibility of recirculated AD-TAP process was also discussed.Simultaneously,THP batch tests were conducted by using waste activated sludge from a wastewater treatment plant.The effect of thermal hydrolysis pretreatment conditions on the hydrolysis efficiency of different solids-containing sludge was investigated;Fourier transform infrared spectroscopy was used to analyze the change of organic groups and the chemical reactions occurring in each stage during the thermal hydrolysis pretreatment of high solid sludge.The purpose of this study is to study the distribution and structural changes of thermally-hydrolysed organic matter in high solids-containing sludge,and provide theoretical basis for further analysis of thermal hydrolysis mechanism and optimization conditions.The main conclusions are as follows:(1)Through the analysis of the “Recirculated Anaerobic Digestion-Alkaline ThermalTreatment” process system and the conventional indicators of the anaerobic digestion reactor with intermediate temperature and high temperature,we can know that the removal rate of VSS after anaerobic digestion are 31.16% and 41.05%,respectively.The efficiency is similar to the high solid sludge "thermal hydrolysis-anaerobic digestion" process,the process has the feasibility of application.(2)The ammonia nitrogen concentration in the digester decreased obviously due to the ammonia evaporation in the alkali heat treatment process of the anaerobic digestion alkali heat treatment reflux process.The highest free ammonia concentration in the intermediate and high temperature reactors were 0.045 g/L and 0.592 g/L,respectively,both are lower than the ammonia inhibition concentration threshold of anaerobic microorganisms.This process has the potential to reduce the inhibition of high solids and anaerobic digestion of ammonia.At the same time,due to the addition of Ca O in the process,it also has a certain function of phosphorus removal.(3)The results of high-throughput sequencing technology for detection of microrganismms in anaerobic digestion systems at medium and high temperatures shows that there are significant differences in the species composition of the bacteria and the archaea in the mild and high temperature system of the "Recirculated Anaerobic Digestion-Alkaline Thermal Treatment" process.The relative abundance of Methanothermobacter and Hydrogenispora are higher in the high temperature digested sludge.The relative abundance of Methanobacterium is higher under the medium temperature condition.(4)The result of thermal hydrolysis pretreatment batch test of the high solid sludge under different solid content(10% and 15%),temperature(100,120,140,160,180,200°C)and time(15,30,60,90,120 min)conditions shows that the temperature is the main factor to affecting the thermal hydrolysis efficiency.The best hydrolysis temperature of sludge with solids content of 10% and 15% was 160~180°C,and the optimal hydrolysis time was 60 min and 30 min,respectively.(5)The result of infrared spectroscopy analysis of organic substances after thermal hydrolysis pretreatment showed that the organic functional groups in the sludge under different pretreatment conditions are similar(mainly are COO,NH3+,NH2+,O-H,CH3,CH2,etc.).The area peak area of the wavering vibration region of theamino acid COO is reduced to the lowest,and the protein in the sludge can be fully hydrolyzed after the thermal hydrolysis pretreatment of high solid sludge(10% solid content)at 160~180? and 60~90min.The area peak area of the CH3,CH2 and CH,saturated alkyl CH3 antisymmetric expansion,and long chain alkyl CH2 are at a lower level under the condition of 140~170 C and 30~60min,and the macromolecular organic matter in the sludge is hydrolyzed to small molecular organic matter. |
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