Study On The Mechanisms Of Biodegaradation And Bioremoval Of Sulfide And Siloxane In Biogas

Exploitation of biogas is clearly limited by the presence of sulfide and siloxanes. Therefore, bioremoval of sulfide and siloxane from biogas was as the main target in this dissertation. Hydrogen sufide(H2S), methanethiol(MT) and octamethylcyclotetrasiloxane(D4) were selected as model chemicals of impurities in biogas. And the biotrickling filters were set up for bioremoval of sulfide and siloxane from biogas. The process for bioremoval of sulfide and siloxane from biogas was investigated. The main research contents are as follows:Three bacteria were screened from activated sewage sludge. The bacterium capable of H2 S degradation was identified as Paenibacillus sp. Y5, the bacterium capable of MT degradation was identified as Paenibacillus polymyxa CZ05, and the bacterium capable of D4 degradation was identified as Pseudomonas putida H4. The growth characteristics of the three strains were investigated. Then, three biotrickling filters with lava stone as the carrier, were employed to evaluate the effect of the three strains in the removal of impurities in simulated biogas. At the optimal conditions, the removal efficiency(RE) of H2 S was more than 90% under 400 ppmv inlet concentration, the RE of MT was more than 99.5% on 60 ppmv inlet concentration, and the RE of D4 was more than 82% on 60 mg m-3 inlet concentration.The co-culture of the three strains and how each impurity influenced each other in the combined bioremoval process were examined. Dissolved oxygen(DO) was proposed to provide for the microbiota in the bio-trickling filter, therefore the risk of explosion was avoided when the biogas contacted the oxygen. On this basis, A series-operating bio-trickling filter composed by three towers was used for combined bioremoval of H2 S, MT and D4 in this study. The combined RE were REMT = 99.7±0.04%, REH2 S = 99.2±0.05% and RED4 = 68±0.07% respectively, under the optimal operating conditions of CMT = 20 ppmv, CH2 S = 300 ppmv, CD4 = 140 mg m-3.It was the first report that a bacterium capable of MT degradation was identified as Paenibacillus polymyxa CZ05. Whereafter,the removal mechanism of MT was: firstly, MT was dissolved in nutrient solution; secondly, it reacted with the alkaline material secreted by P. polymyxa CZ05 to lead the increase of the MT solubility in water; then, MT was biodegraded as CO2 and S0 by P. polymyxa CZ05 in towers.The microbial community by PCR and PCR-DGGE analysis showed that the composion of microbial community in NO.1 tower and NO.3 tower were changing. The results of Biolog analysis showed that the metabolic performance of microbial communities were very vigorous in NO.1 tower and NO.3 tower. However, the metabolic characteristic were obviously different in such two towers.