以固定化微生物降低廢水中四甲基氫氧化銨及氨氮

Abstract

高科技製造業中的顯影液，四甲基氫氧化氨 (tetramethyl ammonium hydroxide, TMAH) 為強鹼性的毒性物質。在一般生活污水生物處理中難以被去除，而TMAH經馴養後之活性污泥降解後產生的氨氮需要進一步進行硝化作用去除氨氮。 硝化作用進行時會消耗水中無機碳，而無機碳的來源主要為二氧化碳。但廢水中的無機碳常常不足以提供高濃度氨氮進行硝化時所需，因此需要額外添加碳酸氫鈉或碳酸鈣作為無機碳源。以二氧化碳化學吸收法可以利用強鹼 (NaOH或TMAH) 吸收二氧化碳將無機碳源貯存於水中，近而可得到提供硝化的無機碳源。 本研究之硝化污泥與TMAH降解污泥分別以批次好氧的方式由生活污泥馴養。由於硝化污泥與TMAH降解污泥的沉降性不佳，生物質量容易流失，在固液分離時會遇到困難。因此，本研究採用聚乙烯醇 (Polyvinyl Alcohol, PVA) 包埋微生物進行生物處理，在固定化顆粒中不但可以保有高濃度的微生物還可以減少污泥的產生量。固定化顆粒的比重也略大於水，因此有非常良好的沉降性。 PVA以硼酸-磷酸酯化 (boric acid-phosphorylated) 固定，在固定之初會有大量的PVA溶出。PVA溶出可藉由反覆替換水溶液，在3天左右可達到穩定狀態。將馴養得到的污泥進行包埋，以離心污泥重PVA體積10% (w/v) 的比例包埋。在12小時水利停留時間下以1 L之反應槽進行反應，包埋硝化污泥的氨氮體積負荷為0.47 - 0.53 Kg-N/m3/day；包埋TMAH降解污泥的體積負荷為1.3 - 1.5 Kg-TMAH/m3/day。 由本研究的結果顯示，以固定化微生物的方式對有機氮TMAH有良好的去除效果，藉由固定化微生物也可以提高自營硝化與異營分解共存的穩定性。高科技產業中除了TMAH外，也使用了其他的鹼性有機氮。此類有機物以二氧化碳曝氣，不但可以中和其強鹼性，也可以提供其降解後產生的氨氮進行硝化使用。

Tetramethyl ammonium hydroxide (TMAH) is a strong base and toxic substance primarily used as photoresist developer in electronic industry. In domestic wastewater treatment, TMAH can only be removed minimal amount by conventional biological treatments. In addition, the ammonium released from THMA after biodegradation will increase the ammonia concentration substantially. Therefore, additional nitrification process is required for biological treatment of TMAH wastewater. Carbon dioxide is the main source of inorganic carbon for nitrification. Alkaline solution such as NaOH and TMAH can absorb carbon dioxide and increase the inorganic carbon concentration. These solutions can be used as carbon source stock solution to enhance nitrification process. In this study, the active sludge for nitrification and TMAH degradation was enriched by batch culture and followed by immobilized microorganism in polyvinyl alcohol (PVA). PVA entrapment not only can keep high concentration of biomass but also reduce the amount of the sludge production. Besides, the specific density was slightly higher than water so it was easy to settle out of the water. The sludge was centrifuged and entrapped with 10% (w/v).The reaction was processed at 12 h hydraulic retention time and the reactor was 1 L. In these conditions, the loading rate of nitrification was 0.47 - 0.53 Kg-N/m3/day and the loading rate of TMAH was 1.3 - 1.5 Kg-TMAH/m3/day. In conclusion, the treatment process by PVA-entrapped nitrifying organisms has good removal efficiency. Also, PVA-entrapment provided a better condition for both autotrophic nitrifying bacteria and heterotrophic TMAH degrading bacteria to co-exist simultaneously. Besides TMAH, other alkaline wastewater can use similar process to neutralize wastewater by carbon dioxide and to enhance nitrification process in wastewater treatment.