Study On The Behavior Of Excess Sludge Solubilization By Thermophilic Enzyme

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. According to production principle of excess activated sludge in biological treatment process, the possible approaches for sludge reduction may be based on there aspects: uncoupling metabolism, cryptic growth enhanced through cell lysis. Relevant research works were reviewed, and characteristics of each technology were compared. 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.The influence of S-TE (Solubilization by Thermophilic Enzyme) pretreatment on excess sludge characteristics and changes of chemical components was investigated. The domesticated seed sludge containing mixed thermophilic bacterium was inoculated in excess sludge, and the solubilization of solid organic substance under different temperature was examined by way of batch operation. The results show that thermophilic bacterium promoted the dissolution of sludge, and the optimum temperature for thermophilic enzyme solubilization was 65℃, in which the solubilization rate of total suspended solid (TSS) and volatile suspended solid (VSS) reached 31.94% and 48.04% within 56h, which were improved by 7.57% and 6.87% than that without inoculation. The maximal soluble chemical oxygen demand (SCOD) can be reached at 4699 mg/L at 65℃, 72h, which would be beneficial to the further anaerobic digestion process. On account of the inoculation of mixed thermophilic accelerating dissolve of protein, the protein and ammonia concentration raise a lot and then fall slowness, which make out that homeostasis of protein dissolving and ammonia concentrations was exists in S-TE process.The influence of different DS/FS(DS:digested sludge; FS:feed sludge) ratio was also investigated in this study.The impact of the ration was evaluated with respect to its capability for removal of the total suspended solids(TSS) and volatile suspended solids(VSS). The DS/FS ratio 3 results in the maximum VSS 60.5%. The increase of the DS/FS ratio associated with increased in VSS and TSS destruction, respectively. The protease activity was caculated to suggest the ability of thermophilic bacteria in the sludge treatment to degradation of organic solids. Assuming pseudo-first-order kinetics, it was shown that while organic solid destruction rate constants (k) are inversely related to DS/FS ratio.The effect of the dissolve of dissolved oxygen (DO) on the excess sludge solubilization by the S-TE technology is studied in this paper. The optimical DO is 1mg/L for the sludge solubilization in the experiment. And the removal rate of the VSS is decrease when the DO increased. The most capable reason for this is, the simply increase of the aeration, not only can not improve the excharge of the dissolved oxygen (DO), but also push the heat into the air. This process leads to a decrease of the temperature. Thus, the temperature can't meet the need of the thermophilic bacteria and as a result of the solids solution rate decrease.