以異營反硝化菌Pseudomonas sp. C27進行同步脫硫反硝化

Abstract

Denitrification is a critical step in biological wastewater treatment process since nitrogen reduction is easily affected by various conditions. The complicated compositions in the wastewater (such as types of carbon source, sulfide concentration) and reaction conditions (e.g. temperature, pH, dissolved oxygen) affect efficiency and pathways of the denitrifying microbial dissimilation. Previous studies are not shown clear statements on related mechanisms and constrains. As a result, this study performed a modified denitrfication process, namely simultaneous denitrification and sulfide degradation (SDSD), via one unique denitrfier, Pseudomonas sp. C27. This heterotrophic species was isolated from an expanded granular sludge bed (EGSB) reactor and is reported more efficient than autotrophic species. Experiments are carried out in a tailor-made continuous-flow stirred reactor (CSTR). Composition of feed, i.e. various carbon sources (including alcohol, organic acid and carbonhydrate), and initial sulfide concentration (0, 50, 96.1, 193.5, 302.1 and 404.6 mg.L-1), are prepared in the lab and tested SDSD efficiency. In the meanwhile, effects of operational conditions, pH (6.5, 7.0, 8.5, 9.0, 9.5, 10.15 and 11) and temperature (20, 25, 30, 35, 40, 45℃), on SDSD efficiency are investigated. Results are shown that the optimum conditions for this strain to achieve SDSD are at 25~30℃ and pH 9~9.5. The most easy assimilated carbon source for Pseudomonas sp. C27 is acetate although other smaller molecular organics (such as succinate and malate) can be biodegraded within 24 hours. The sulfide and acetate were used as electron donors, and the end product of sulfide oxidation was sulfur or thiosulfate by the NO3-N/S2—S molar ratios. Moreover, products of nitrate reduction were determined by the initial sulfide concentrations, when the initial sulfide concentrations were set below 96.1mg/L, the nitrate was conveted to nitrogen gas; Moreover, the sulfide concentration reached 193.5mg/L, the nitrite reductase was strongly inhibited by sulfide casuing the main end product of denitrification was nitrite. When the sulfide concentration was as high as 302.1mg/L, the isolate C27 didn’t display growth and the ability of denitrification. In micro-oxygen condition (DO=0~10%) the growth time of bacterium was shorted 48 hours compare with anaerobic condition, because of the specify activity of enzymes were higher than anaerobic condition. Testing in a CSTR at sustainable loadings of 0.215 kg m-3day-1 for sulfide, 0.146 kg m-3day-1 for nitrate-nitrogen , 0.092 kg m-3day-1 for acetate-carbon with 84.7%, 99.5%, 74.1% efficiency respectively. Mass balance of sulfur are calculated to facilitate analyzing microbial preferred reactions and possible SDSD pathways for Pseudomonas sp. C27 are suggested in the end of this thesis.