| The traditional sludge anaerobic treatment process has the problems of low organic loading,long hydraulic retention time,and high investment cost.Therefore,the development of high efficiency sludge anaerobic process has become a breakthrough point for researchers.At present,the anaerobic digestion reactor basically uses the continuous stirred-tank reactor(CSTR),which cannot achieve solid-liquid separation compared to high-efficiency anaerobic reactors such as UASB,EGSB,and IC.The anaerobic sequencing batch reactor(ASBR),which repeats a cycle including feeding,reaction,thickening,and withdrawal steps in a single reactor.The ASBR process can maintain a high concentration of methanogenic bacteria and high solid-liquid separation properties in the system.In this study,the two-phase "CSTR-ASBR" anaerobic digestion system was used to treat waste activated sludge.The feasibility of solid-liquid separation in ASBR and the effect of solid-liquid separation on the anaerobic digestion were investigated by improving the internal structure of ASBR and optimizing the operation conditions.At the same time,under different HRT conditions,the effect of low-temperature hydrolysis on the separation of two-phase anaerobic digestion system and solid-liquid separation of ASBR was analyzed.The main results are as follows:(1)In order to determine the optimal thermal hydrolysis parameters,the changes of SCOD and soluble protein of sludge in the thermal hydrolysis process were investigated under the conditions of 60 ?,70 ?,80 ? and 90 ?.After the test sludge was hydrolyzed at 60 ?,70 ?,80 ?,and 90 ? for 60 min,the SCOD of the supernatant increased to 2150 mg/L,3318 mg/L,4036 mg/L,and 4216 mg/L,respectively.The results showed that the organic matter in the hydrolyzed sludge was basically proportional to the temperature and time.However,as the heat treatment time was prolonged(>45 min),the dissolution rate of organic matter became slower.Therefore,from the aspects of energy saving and treatment effects,the time and temperature of low-temperature thermal hydrolysis are selected to be 45 min and80°C,respectively.(2)The effects of low-temperature hydrolysis and organic loading on the digestion performance of the two-phase "CSTR-ASBR" anaerobic digestion system were investigated.The results show that the solid-liquid separation can be achieved in the ASBR reactor,and the low-temperature hydrolysis pretreatment can enhance the solid-liquid separation capability.Under different organic load conditions,two-phase anaerobic digestion system has better digestion performance and solid-liquid separation characteristics.In addition,due to the solid-liquid separation,the SRT of the methanogenic reactor increased from the 16 d,10.7d,and 8d of the design to 29.1d,17.8d,and 11.4d,respectively.Higher microbial activity and higher organic matter concentrations in the reactor increase the anaerobic digestion performance of the methanogenic phase.(3)The characteristics of the solid-liquid separation in the methanogenic reactor were analyzed from three aspects: the water quality of the effluent,the TS concentration and the organic matter distribution.The results showed that the organic concentration and TS concentration in the methanogenic reactor were significantly different in height.The bottom of the reactor formed a high solids and low organic precipitation area,while the upper part of the reactor formed a clear water area.During the operation of the system,the TS concentration of the sludge discharged from the reactor is up to 74 mg/L,which ensures that the organics have a longer residence time in the reactor.The ammonia nitrogen concentration and SCOD concentration of the effluent from the methanogenic reactor were maintained between 311 and 689 mg/L and between 497 and 793 mg/L,respectively.The SS concentration in the reactor clear water zone was maintained at 359 to 534 mg/L.The solid-liquid separation effect was obtained inside the methane phase(ASBR)reactor. |
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