Study On Screening Predominant Thermophiles For Sludge Digestion And Its Effect

Rapid increase in quality and quantity of municipal wastewater treatment recently resulted in a large amount of excess sludge. Since the sludge contains varieties of toxic and harmful substances and would cause serious secondary pollution to the environment if it is not properly disposed. Compared to the widely used physical and chemical methods such as ultrasonic, ozonation, mechanical destruction, alkali treatment, biological method has been paid much more attention. Thermophiles aerobic digestion is a promising technique, easy in operation and economical in maintenace. This research focused on screening specific predominant thermophiles and optimizing the parameters of thermophiles aerobic digestion reactor in a lab scale. The results of the research are as follows:1. Six predominant strains were selected from eleven strains of screened and isolated thermophiles based on their protease activity, amylase activity and sludge digestion by single strain. These six strains were taken into all the permutation and combination to check out their capability on sludge digestion. Statistical analysis showed that the combination composed of F2, F4 and F7 had a greater positive effect on sludge digestion than other combinations. F2, F4 and F7 were identified as Baclicus lincheniformis, Alcaligenes faecalis and Pseudomonas respectively.2. It was observed that the biological solubilization of sludge conducted by thermophiles was significantly influenced by reaction temperature and dissolved oxygen. With reaction temperature of 65℃, the solubilization rate of TSS and VSS reached up to 32.46% and 44.72% respectively, higher than those at 55℃,60℃and 70℃. In addition, the content of SCOD and ammonia nitrogen was accumulated greatly, and their maximum values were much higher than those under other temperatures. On the other hand, when the dissolved oxygen content reached 2mg/L in the reactor, the solubilization rate of TSS and VSS achieved 33.22% and 44.66% respectively, higher than the rates around 1 mg/L and 4 mg/L. Moreover, the content of SCOD had a sharp and large increase, and ammonia nitrogen also held a big accumulation with the dissolved oxygen content of 2 mg/L.3. Comparison of aerobic sludge digestion process with and without predominant combination showed that the solubilization rate of TSS and VSS in thermophilic aerobic digestion inoculated with thermophiles were 33.22% and 44.66%, which were 14.53% and 24.73% respectively higher than that in conventional aerobic digestion. The VSS solubilizaion rate in early stage was found to fit for the first-order reaction dynamic model, and the dissolving rate constant increased from 0.0709 d-1 to 0.1834d-1 after thermophiles inoculated. The SCOD content reached quickly up to the peak value and then followed by a gradual reduction. Meanwhile the contents of protein and ammonia nitrogen also showed a similar pattern as SCOD. The pH value in the reactor inoculated with thermophiles grew up and remained at 7.5 for the duration, which was beneficial for aerobic digestion. It was also found that extracellular enzyme, especially protease and amylase, played an important role in sludge decomposition by the way of accelerating organic matter hydrolyzing. The parameters obtained in the research could be helpful for the pilot experiment of aerobic digestion of sludge mediated by thermophiles.