| Anaerobic digestion is the most commonly applied technique for stabilization of waste activated sludge. But the hydrolysis of sludge organic matter is the key step for sludge anaerobic digestion, which results in the slow degradation, long residence time, large fermenter volume and low methane yield. To improve the efficiency of anaerobic digestion, there is a pretreatment process to disintegrate the sludge flocs, disrupt bacterial cell wall and make the hydrolysis faster significantly. Thermal hydrolysis is an effective method in various pretreatment techniques.Thermal hydrolysis was applied at a temperature of 170? for 30 min on the Beijing sewage sludge, and analyze the effect of thermal hydrolysis on sludge internal material structure. Anaerobic biodegradation of treated and untreated sludge from three different sludge sewage plant were tested by Biochemical Methane Potential(BMP), respectively. Dealing with sludge by applying the traditional sludge anaerobic digestion and thermal hydrolysis-anaerobic digestion technique Under the condition of different hydraulic retention time(HRT) and sludge concentration, respectively.and then this study discussed the effect of thermal hydrolysis technology on sludge anaerobic digestion and the feasibility of the engineering practice.The results show that thermal hydrolysis could destroy the sludge flocs and microbial cell structure, the material inside the cell dissolved and hydrolyzed, the ratio of Soluble organic matter increased, Such as suspended solid(SS), volatile suspended solid(VSS) and soluble chemical oxygen demand(SCOD). The amount of volatile fatty acid(VFA) increased 2.5 times, acetic acid is the main components.Methane production of different sludge increased in different degree with thermal hydrolysis especially for surplus sludge. Methane yield reach 0.388m3CH4/kgVSadded and the highest increased by 65%. Compared with other literature, it was found that the methane production capability of Beijing sludge was stronger.The research resulted that biogas production and degradation of organic matter fall in traditional anaerobic digestion process as the HRT shortened, and the concentration of VFA accumulated, the activity of methanogens was inhibited by a certain degree.But in thermal hydrolysis-anaerobic digestion process, methane yield and the removal rate of organic matter increased by 30% ~ 40% and 25%, respectively. When HRT was 4 days, this two indicators was in a higher level and reach 0.292 m3CH4/kgVSadded and 33.8%, respectively. It was found that pH value is keep stable, alkalinity is higher, and VFA stay at lower levels in this system, which suggests that the system has better stability. The maximum biogas production in traditional sludge anaerobic digestion was discovered under the condition of TS=8%, as well as thermal hydrolysis-anaerobic digestion process. Methane yield of sludge with thermal hydrolysis reach 0.391 m3CH4/kgVSaddedand1.113 m3CH4/kgVSrem, respectively. This two indicators was increased by 26.9% and 43.7% than that of TS=6% sludge, increased by 26.9% and 43.7% than that of TS=9% sludge. The removal rateof 6%, 8% and 9% sludge with thermal hydrolysis were all more than 35%,and were 34%,26%,24% higher than that of untreated sludge.Kinetics evaluation of anaerobic digestion was also conducted in this study.The performance of anaerobic digestion reactor at steady-state operation had been describedwith various models. It was found that the first-order kinetic rate constant, methane yield and biggest substrate utilization of sludge with thermal hydrolysis were all higher than that of untreated sludge.The optimal technical parameters of beijing sludge anaerobic digestion process are: thermal hydrolysis 170?,30min;Mesophilic anaerobic digestion, HRT=13days, TS=8%. |
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