厭氧硫化物氧化耦合硝酸鹽還原與其對甲烷化之影響

Anaerobic Sulfide Oxidation Coupled to Nitrate Reduction and Its Effects on Methanogenesis

黃炳友(Biing-Teo Wong)

指導教授 ： 李篤中

國立臺灣大學/工學院/化學工程學研究所/博士(2012年)

https://doi.org/10.6342/NTU.2012.10318

摘要

近年來，厭氧微生物處理技術由於其高效與節能獲得了相當的關注。生物硝酸鹽還原已成功地運用於同步去除污水中的有機物、硝酸鹽和硫化物。本研究探討在厭氧條件下，硫化物氧化耦合硝酸鹽還原作用與其對甲烷生成所造成的影響。
在含有硫、氮和高有機碳含量的合成廢水中，第一部分中探討硫化物( 0 or 25 mg-S L-1 )對硝酸鹽( 0, 25, 50 and 75 mg-N L-1 )還原和甲烷生成的影響。在無硫化物的培養基中，25-75 mg-N L-1-硝酸鹽有效地抑制了乙酸化和甲烷化過程的效率。加入25 mg-S L-1可有效的增加含有硝酸鹽培養基中甲烷的生產。低濃度的硫化物促使硝酸鹽還原途徑從反硝化轉移到異化硝酸鹽還原至氨(DNRA)，從而減少了抑制甲烷化中含毒性的一氧化氮(NO)與一氧化二氮(N2O)的濃度。在以異化硝酸鹽還原至氨為主的過程中，25 mg-S L-1　硫化物被完全氧化。氧化型態的硫化物重新還原，限制了異營反硝化路經。硝酸鹽還原至氨細菌，反硝化菌，硫酸還原菌和甲烷菌等一系列的行動減輕了硝酸鹽在厭氧化過程中對甲烷生成的毒性。
第二部份探討高濃度硫化物( 90-189 mg-S L-1 )與硝酸鹽( 25-75 mg-N L-1 )對甲烷生成的抑制作用。在初始階段的90 mg L-1 硫化物測試中，以硫化物作為電子供體的硝酸鹽自營反硝化過程先進行。然後硫酸還原菌將產生的硫通過異營氧化途徑還原成硫化物。甲烷生成在僅添加硫化物為90 mg-S L-1的劑量中沒有被明顯的抑制。當25-75 mg-N L-1硝酸鹽存在時，甲烷生成的啟動被嚴重地拖延。氮氧化物(NOx)，通過反硝化途徑中硝酸鹽還原的中間體，抑制了甲烷的生成。90 mg-S L-1的硫化物使硝酸鹽還原偏向了異化硝酸鹽還原至氨(DNRA)。
在第三部份中，硫化物( 0-135 mg-S L-1 )對一氧化氮氣體還原的影響被探討( 0.32 and 0.64 mg-N NO L-1 )。一氧化氮在含硫化物的甲烷菌群中造成了毒性更高的多硫化物產生。在含0.32 mg-N L-1 NO不含硫化物的測試中，甲烷的產生不受影響但有停滯現象。硫化物(16-135 mg-S L-1)的加入對甲烷產生速率與丁酸降解速率造成87-93%和62-78%的抑制。在含有0.64 mg-N L-1 NO和0-135 mg-S L-1硫化物的測試中，觀察到無甲烷產生但有N2O釋放。NO造成的多硫化物的還原是造成大部分菌群死亡的原因。在含有硫化物及硝酸鹽的甲烷菌群中，雷射掃描式共軛焦顯微鏡觀察到元素硫的前驅物產生並對甲烷菌造成攻擊。
在含有硫、氮和低有機碳含量的合成廢水中，本研究以共生的化能無機營養菌探討其在自營（僅提供硝酸鹽與硫化物），混營（提供硝酸鹽，硫化物與乙酸）與異營（僅提供硝酸鹽與乙酸）的生長條件下硝酸鹽、乙酸與硫化物的移除效果。在自營與混營生長中，硝酸鹽還原與硫化物氧化依據下列途經：NO3- -> NOX -> NO2- -> N2 與 S2- > Sx2- -> S0。透過雷射掃描式共軛焦顯微鏡觀察到元素硫的前驅物(SNO)的產生。在自營生長中，雷射掃描式共軛焦顯微鏡（CLSM）和穿透式電子顯微鏡（TEM）影像中顯示大部分細胞的分解與破損。在混營生長中，雖然大部分的細胞在反硝化過程中死亡，乙酸的加入使反硝化過程縮短，從而降低了反硝化過程中的毒性。相反地，此毒性在異營生長中則沒被觀察到。在固定硝酸鹽和硫化物濃度，給予不同濃度乙酸的測試中，硫化物、硝酸鹽、乙酸及亞硝酸鹽的去除只有在適當的化學計量下可達到。此外，在探討在固定乙酸和硫化物濃度，給予不同濃度硝酸鹽的測試中，增加硝酸鹽劑量造成了更高的NOx產生。
最後，硝酸鹽還原與硫化物氧化在此系統中的反應路徑與其中間產物間的交互作用力在此提出。

關鍵字

厭氧 ； 硫化物氧化 ； 硝酸鹽還原 ； 甲烷產生

並列摘要

In recent years,　anaerobic wastewater treatment technology has recently received considerable attention due high efficiency and low cost. Biological nitrate reduction has been successfully used for the simultaneous removal of nitrate and sulfide from wastewater. In this study, the effects of anaerobic sulfide oxidation coupled to nitrate reduction on chemolithotrophic bacteria and methanogenic cultures were investigated in batch test.
In the synthetic wastewater containing sulfur, nitrogen and high organic carbon content, a mixed mesophilic methanogenic culture was used to investigate the effects of sulfide on the nitrate and NO reduction. In part one, the effects of sulfide (0 or 25 mg-S L-1) on nitrate (0, 25, 50 and 75 mg-N L-1) reduction and methanogenesis using butyrate as a carbon source were investigated.　In the sulfide-free medium, 25-75 mg-N L-1 nitrate markedly inhibited the efficiencies of acetogenesis and methanogenesis processes. Adding 25 mg-S L-1 increased methane production in nitrate-amended medium. Low sulfide levels shifted the nitrate reduction pathway from denitrification to dissimilatory nitrate reduction to ammonia (DNRA), thereby reducing the amounts of toxic nitric oxide and nitrous oxide produced that inhibit methanogenesis. The dose of 25 mg-S L-1 sulfide was oxidized completely, during which heterotrophic DNRA predominated. The oxidized forms of sulfide reformed, limiting induction of the heterotrophic denitrification pathway. The actions of heterotrophic and autotrophic DNRA bacteria, denitrifiers, sulfate-reducing bacteria and methanogens mitigate nitrate toxicity during methanogenesis in an anaerobic process.
In part two, the inhibitory effects of 90-189 mg-S L-1 of sulfide and 25-75 mg-N L-1 of nitrate on methanogenesis were investigated further. In the initial phase of 90 mg L-1 S2- test, autotrophic denitrification of nitrate occurred with sulfide as the electron donor. Then the sulfate-reducing strains converted the produced sulfur back to sulfide via heterotrophic oxidation pathway. Methanogenesis was not markedly inhibited when 90 mg-S L-1 of sulfide was dosed alone. When 25-75 mg-N L-1 of nitrate was presented, initiation of methanogenesis was seriously delayed. Nitrogen oxides (NOx), the intermediates for nitrate reduction via denitrification pathway, inhibited methanogenesis. The 90 mg-S L-1 of sulfide favored heterotrophic dissimilatory nitrate reduction to ammonia (DNRA) pathway for nitrate reduction. Possible ways of maximizing methane production from an organic carbon-rich wastewater with high levels of sulfide and nitrate were discussed.
In part three, the effects of sulfide on the reduction of free NO gas (0.32 and 0.64 mg-N L-1) were investigated. NO induced the formation of toxic polysulfide. Reduction of polysulfide was the main step to cause disruption of methanogenic culture. In 0.32 mg-N L-1 NO test without sulfide, no inhibition to methane production but only lag time was observed. Addition of sulfide (16-135 mg-S L-1) caused 87-93% and 62-78% inhibition of methane production rate and butyrate degradation rate. In the test with 0.64 mg-N L-1 NO and 0-135 mg-S L-1 sulfide, no methane production but obvious nitrous oxide emission was observed. In sulfide-, nitrate-amended methanogenic cultures, CLSM imaging showed the formation of elemental sulfur precursor and it exerted toxicity to methanogen.
In the synthetic wastewater containing sulfur, nitrogen and low organic carbon content, the removal of nitrate, acetate and sulfide was investigated by a co-culture of chemolithotrophic bacteria under autotrophic (supplied with nitrate and sulfide), mixotrophic (supplied with nitrate, sulfide and acetate) and heterotrophic growth condition (supplied with nitrate and acetate). In autotrophic and mixotrophic growth, the nitrate reduction and sulfide oxidation pathway followed NO3- -> NOx -> NO2- -> N2 and S2- -> SX2- -> S0. Production of precursor of elemental sulfur (SNO) was examined by CLSM. In autotrophic growth, CLSM and transmission electron microscopy (TEM) imaging showed that disruption of the cells and cell yield in the end of the tests. In mixotrophic growth, although most of cells dead during denitrification, addition of acetate reduced denitrification intermediate and nitrite to dinitrogen gas, hence decreased the toxicity. In contrast, toxicity of denitrification intermediate was not observed by CLSM imaging in heterotrophic growth. In the test with supplied with different concentrations of acetate with fixed sulfide and nitrate concentration, complete removal of nitrate, sulfide and acetate was only achieved under suitable stoichiometry. In the test with supplied with different concentrations of nitrate with fixed sulfide and acetate concentration, increasing nitrate dose caused higher NOx production.
Finally, the reaction pathway of nitrate reduction and sulfide oxidation in this system and the interactions between its intermediate were proposed.

並列關鍵字

anaerobic digestion ； nitrate reduction ； sulfide oxidation ； methanogenesis

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