無機碳對硝化反應的限制原本往往被忽略，但隨著近年來大量產生的產業高氮廢水，硝化系統的無機碳源需求增加，逐漸有研究討論關於無機碳於硝化反應中扮演之角色與其限制。先前的研究(Whang et al., 2009)發現添加Na2CO3較添加NaOH做為高氮低碳石化廢水（C/N大約等於1）硝化處理系統中的化學緩衝溶液可促進硝化反應效率，並且首先觀察到氨氧化菌族群在不同添加物操作時期的改變現像，但其確切機制仍未知，因此本研究針對無機碳對氨氧化菌族群生態以及其硝化反應表現進行探討。
本研究假設不同的無機碳濃度會優厚培養（enrich）出不同的氨氧化菌族群，藉由設立兩個相同植種源、不同進流無機碳濃度的CSTR生物反應槽進行探討，一為充足且過量的無機碳（100 mg-C/L，高無機碳），另一為給與有限的無機碳濃度（15 mg-C/L，低無機碳），進流基質氨氮濃度皆為250mg/L，在操作期間可維持約95%的良好硝化效率，硝酸氮為出流水主要產物，進流基質與出流水的氮系化合物質量平衡可達90%以上，根據amoA（ammonia monooxygenase gene subunit A）功能性基因選殖（cloning）與定序（sequencing）結果發現高無機碳生物反應槽內Nm. nitrosa lineage為優勢氨氧化菌族群，而低無機碳生物反應槽則以Nm. europaea lineage為優勢氨氧化菌族群，顯示確實不同的無機碳濃度條件所馴養之氨氧化菌族群有別，再進一步分析amoA功能性基因之尾端修飾限制片段長度多型性（Terminal Restriction Fragment Length Polymorphism，T-RFLP）反應槽氨氧化菌族群監測結果，顯現在經過大約40天的馴養之後，兩個生物反應槽的T-RFLP圖譜結果出現差異，高無機碳生物反應槽圖譜以48/135 TF（terminal fragment）為主要，而低無機碳生物反應槽圖譜則以219/270 TF為大宗；以批次實驗進行硝化動力探討，在不同無機碳濃度對氨氧化速率的實驗結果發現當初始添加無機碳濃度低於50 mg-C/L時對高無機碳生物反應槽內Nm. nitrosa-like氨氧化菌有抑制，導致氨氧化速率減低，然而在低無機碳反應槽則是直到初始添加之無機碳濃度低於10 mg-C/L才有顯著的氨氧化速率降低，以上結果證實本研究的初始實驗假設，不同的氨氧化菌族群有不同的無機碳親和力，並且在不同無機碳濃度條件下確實可被選擇與馴養。

Inorganic carbon (IC) limitation in nitrogen removal process is often neglected, as it is usually present in abundance in full-scale wastewater systems due to the oxidation of organic matter by heterotrophic activity and is high enough for the autotrophic bacteria to grow. Recently, wastewaters with low organic carbon to nitrogen ratio, such as rejection water of digested, sludge have been studied for development of optimized nitrogen removal systems, but little is known regarding the effects of inorganic carbon limitation on ammonia-oxidizing bacteria (AOB) populations in such systems. Whang et al. (2009) reported that addition of Na2CO3, compared with addition of NaOH, as pH adjusting chemical would improve nitrification performance by providing sufficient inorganic carbon for nitrifying bacteria. In addition to improvement on nitrification performance, addition of Na2CO3 or NaOH would also influence the dominant AOB populations presented in the bioreactors. Results showing the effects of adding different buffering chemicals such as NaOH or Na2CO3 on AOB populations have never been demonstrated until Whang et al., although the exact mechanisms are still not clear at this time. Therefore, the effects of inorganic carbon concentration on microbial ecology of AOB and their nitrification performance were investigated in this study.
The hypothesis that different inorganic carbon concentrations would enrich different AOB populations was examined by operating two chemostat bioreactors fed with different influent carbonate concentrations at 15 and 100 mg-IC/L, respectively. During the operation period, both bioreactors were able to maintain satisfactory nitrification efficiency, more than 95% of an influent ammonium concentration of 250 mg-N/L was oxidized to nitrate, without nitrite accumulation. Based on cloning/ sequencing results targeting on ammonia monooxygenase gene subunit A (amoA), Nitrosomomas nitrosa lineage was the dominant AOB population in the high-IC bioreactor, while Nm. europaea lineage was dominant in the low-IC bioreactor. According to the amoA-based terminal restriction fragment length polymorphism (T-RFLP) electropherogram result, the dominant terminal fragments (TF) changed after 40 days of operation. The high-IC bioreactor seemed to be dominated by Nm. nitrosa-like AOB (48/135 TF signature), while Nm. europaea-like AOB (219/270 TF signature) was dominant in the low-IC bioreactor. Furthermore, results of batch experiments on effects of IC concentration on ammonia-oxidation rate indicated that low IC conditions (lower than 50 mg-C/L) had negative impact on Nm. nitrosa-like AOB dominated in the high-IC bioreactor, but not on Nm. europaea-like AOB enriched in the low-IC bioreactor until the IC concentrations lower than 10 mg-C/L. These findings confirmed the hypothesis that different AOB populations with different IC affinity may be enriched/selected under different inorganic carbon concentrations.

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