以異營反硝化菌Pseudomonas sp. C27進行同步脫硫反硝化

Abstract

本文測試異營反硝化菌Pseudomonas sp. C27在不同碳源、溫度、酸鹼、初始硫化物濃度、溶氧量下同步去除硫、氮及碳之效率，並進行連續式反應器的操作。 結果顯示此菌種最容易利用之碳源為Acetate，適合在溫度25~30℃與pH為9~9.5的環境中生長。不同初始硫化物濃度會影響硫化物最終產物型態，在初始NO3--N為105mg/L、硫化物濃度小於100mg/L時，硫化物會被先氧化至Sulfur，Sulfur會進一步被殘餘的Nitrate轉化成Thiosulfate，而當Sulfide被完全氧化後異營反硝化作用才會進行，以過量Acetate將剩餘的Nitrate與Nitrite，在初始Sulfide濃度100mg/L以下時完全反硝化為N2。當初始Sulfide濃度達到200mg/L以上時反硝化最終產物為NO2-而非N2。在微氧條件下(DO=0~10%)反應遲滯期較厭氧條件下縮短了48小時，且能夠進行完全反硝化，Sulfide Oxidase、Nitrate Reductase及Nitrite Reductase活性在微氧條件皆高於厭氧條件下，但繼續提高溶氧量則此效果降低。 在連續式反應器中Pseudomonas sp. C27在微氧條件下可在Sulfide、NO3--N、Ac-C負荷量分別為0.215kg/m3day、0.146kg/m3day、0.092 kg/m3day達到84.7%、99.5%及74.1%之移除率。 使用Pseudomonas sp. C27進行同步脫硫反硝化程序不需仰賴其它菌種協同作用共生完成，與生長速度快，為新型的脫硫反硝化程序。

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.