廢水處理型人工濕地降低溫室氣體排放之研究－水質與溫室氣體減量間關係之分析

濕地雖具有碳吸存的能力，但是也因為長期水淹，因而形成厭氧環境，致使甲烷（CH_4）及氧化亞氮（N_2O）等溫室氣體的釋出，增強溫室效應。本研究以人工濕地模槽模擬鹹水型人工濕地，觀察有無種植紅樹林及槽內不同菌種是否影響微生物除污機制，進一步探討藉由改變濕地系統內之環境條件因子，以減低CH_4及N_2O等溫室氣體之生成量。試驗中將進行水質監測，分析水質因子與溫室氣體釋出量之相關性，找出最佳化條件之操作技術，以做為未來各類型人工濕地系統降低溫室氣體釋出之評估參考。根據研究的實驗結果，實驗條件為碳源水體時，氨氮之去除效果較其他操作條件明顯，推測有種植物的模槽其根系環境適合硝化菌生長，硝化速度較快。經由溫室氣體與水質相關性分析結果得知，在進流水有機碳源增加之條件下，由於脫氮作用可進行完全脫氮成N_2，也消耗更多的有機碳源，因此不利於進行甲烷發酵反應，因此偵測出釋放較少的N_2O及CH_4，但是由於厭氧或好氧呼吸作用均會排放CO_2，因此CO_2的排放則會增加。此外，研究結果亦得知N_2O的釋出量與水中總氮及硝酸鹽氮濃度呈現高度正相關。在有機碳源供應不足之下，脫硝菌將進行不完全脫硝反應，即造成中間產物N_2O產生釋出。但研究成果亦發現CH_4釋出量與水中氨氮及總氮濃度亦呈現正相關。究其原因，可能是由於植物枯萎落葉效應所產生的有機氮累積在模槽水體及土壤內，厭氧條件下礦化為氨氮，並進行甲烷發酵。

關鍵字

鹹水型人工濕地；紅樹林；水質變化；溫室氣體

並列摘要

Wetlands can absorb carbon. However, the anaerobic environment of wetlands caused by prolonged logging water may become an emitting source of greenhouse gases (GHGs), such as carbon dioxide (CO_2), methane (CH_4) and nitrous oxide (N_2O), resulting in offset of carbon sink effect in wetlands, and even becoming carbon sources, which is obviously especially for the wastewater treatment constructed wetlands and the natural wetlands contaminated by polluted water. The purpose of this study is to investigate the correlation between water quality and GHG emissions, and to find out the optimal operating conditions to reduce GHGs emissions by controlling water quality and types of wetland systems. In this study, four constructed wetland microcosms were built in this study set by four conditions of w/o additions of bacterial seeding sludge and w/o vegetation (Rhizophora stylosa) as followings: C tank (without sludge and vegetation), PA tank (with ANAMMOX bacterial sludge and vegetation), S tank (with anaerobic bacterial sludge and without vegetation), PS tank (with anaerobic bacterial sludge and vegetation). Six environmental condition factors of influent water quality and water levels were conducted in this study for analyzing optimal one to decrease GHG emissions. GHG emitted from the wetland microcosms were continuously collected and monitored concentrations by open dynamic floating chambers and NDIR facility, respectively. According to the results of this study, when the experimental conditions are carbon source water bodies, the removal effect of ammonia nitrogen is more obvious than other operating conditions. It is speculated that the root zone effect of aquatic plants is suitable for the growth of nitrifying bacteria making nitrification rate fast. According to the analytical results of correlation between greenhouse gases and water quality, for the condition of adding organic carbon sources into influent, it was found that complete denitrification was occurred due to enough carbon sources provided to denitrifiers. Meanwhile, due to consumption of organic carbon sources by denitrifiers, there was no enough organic carbon sources for methane fermentation. Hence, under this condition, it was detected that less N_2O and CH_4 were released, but more CO_2 was emitted due to anaerobic or aerobic respirations. In addition, the research results also show that the amount of N_2O released was highly positively correlated with the concentration of total nitrogen and nitrate nitrogen in the water. Under the shortage of organic carbon source supply in the influent, denitrifiers would carry out incomplete denitrification reaction, that is, the intermediate product N_2O was released. However, the research results also found that the amount of CH_4 released and the concentration of ammonia nitrogen and total nitrogen in the water also showed a positive correlation. The reason may be that the organic nitrogen produced by the wilting and falling leaves of plants accumulates in the water and soil of the mold, and mineralizes to ammonia nitrogen under anaerobic conditions and undergoes methane fermentation.

並列關鍵字

constructed wetland ； mangrove ； water quality ； greenhouse gases

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廢水處理型人工濕地降低溫室氣體排放之研究－水質與溫室氣體減量間關係之分析

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