| With the increase of amount of municipal wastewater and sewer-laid rates and expansion of active sludge (AS) system, it brings about large amount of sludge and generates a new international tendency of sludge minimization and resource utilization. Compared with other sludge solubilization technology such as ozone oxidation, chlorine oxidation, thermal hydrolysis, acid, alkali, mechanical, ultrasonic and enzymatic directly pretreatment, solubilization by thermophilic enzyme (S-TE) based on microbial cryptic growth is more cost-effective and safer as well as lower energy cost and easier operation. Combined with the following process, S-TE not only can realize sludge "zero discharge", but simultaneously realize high effective wastewater biodegradation or enhancement of biogas production.Two thermophilic bacteria typed AT06-1 and AT06-2 were screened and isolated,and their morphologic, hysiologic and biochemical characteristics were identified.The results showed that AT06-1 and AT06-2 ,which were categorized as Bacillus stearothermophilus sp., both could secrete extracellular enzyme such as protease and amylase.The condign growing temperatures of AT06-1 and AT06-2 were between 45℃and 70℃,and both could used as the inoculation in S-TE process.Variations of primary suspended solids and kinetic analysis of VSS degradation was studied under the conditions which AT06-2(Bacillus stearothermophilus sp.) was inoculated into excess sludge with different concentrations .Sludge solubilization by thermophilic bacteria was conducted under total suspended solid(TSS) concentration with 7.792 g·L-1,14.716 g·L-1and 21.286 g·L-1 after AT06-2 culture solution incubated, comparing with uninoculation ones,of which TSS were 7.640 g·L-1,14.500 g·L-1 and 20.812 g·L-1 after adjustment. The results showed that, in S-TE process, there were two reaction mechanisms of enzyme-catalyzed reaction and thermal-hydrolyzed reaction , as well as two processes which begin with the depolymerization of sludge flocs by exoenzymes including proteases and amylases, whereafter, the cell-walls and organic matters were disintegrated and hydrolyzed further. The solubilization rate of volatile suspended solid (VSS) reached 58.76%,50.17% and 39.38% under inoculation,while they were just 34.00%,28.63%and 25.22% under uninoculation in 60 hours, respectively. VSS solubilization was affected by enzyme-catalyzed reaction and thermal hydrolysis except for solubilization time,and the minimization of TSS was affected by the component ratio of VSS and fixed suspended solid (FSS). In initial stage, VSS solubilization basically accorded with first-order reaction kinetics and the solubilization rate constant Kd markedly increased to 0.30 d-1 ,0.23 d-1 and 0.16 d-1 after inoculation.The effect of S-TE pretreatment on excess sludge solubilization and changes of chemical components under microaeration and aeration, inoculation and without inoculation,and different temperatures was also investigated. The results showed that, The optimum temperature for solubilization under inoculation was 65℃,at which the dissolving rate of total suspended solid(TSS) and volatile suspended solid (VSS)reached 34.09%and 24.16%within 2 days, respectively. Moreover, soluble chemical oxygen demand (SCOD) and volatile fatty acid (VFA) cumulated with the maximum of 4531 mg/L and 2319 mg/L at 65℃.The protein released from the cells inside and outside was hydrolyzed by highly enhanced protease activity, resulting in the change of protein and ammonia from rising to descending with the aeration. In the process, alkalinity and pH increased and then dropped slightly. Though VSS removal rate at microaerobic conditions was lower than that of at aerobic ones, VFA cumulated evidently and alkalinity were high, which were propitious to improve the anaerobic digestion of excess sludge.
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