電生物薄膜之開發: 去除水中氨氮及減緩薄膜積垢

Abstract

生物薄膜程序為近年廢水生物處理程序中一嶄新之研究，由於利用薄膜單元取代傳統的沉澱池，使生物薄膜程序具有良好的固液分離效果，故可有效提升出流水水質並增加污泥停留時間，如此可提高污泥濃度，減少反應槽體積，增加水力負荷。SRT的增加，不僅可減少污泥生成量30 ~ 80 %，降低後續處理費用，也使得一些生長較慢的自營菌，如硝化菌得以在生物反應槽中大量生長，有助於去除水中氨氮。然而，生物薄膜中薄膜的阻塞卻限制其廣泛的應用，因為薄膜的阻塞會導致出水通量衰減、增加薄膜的清洗和更換次數，使操作成本增加。水中氨氮會消耗水中溶氧，造成水質惡化、水體優養化及危害水中生物，因此法規對於水中氨氮管制日趨嚴格。雖然生物薄膜程序可有效將氨氮硝化成硝酸鹽，但硝酸鹽仍會對人體造成危害，如新生兒藍嬰症。因此本研究擬結合生物電化學及生物薄膜程序，將水中氨氮經生物薄膜程序中的硝化菌硝化成硝酸鹽，並以陰極上的自營脫硝菌利用電解產生的氫氣當成電子供應者，以硝酸鹽當電子接受者，進行脫硝作用。同時利用陽極氧化產生的金屬離子產生電混作用，去穩定帶負電的生物污泥顆粒，減緩薄膜積垢之速率。

Membrane bioreactor (MBR) processes, in which a membrane filtration is combined with biological degradation for organic degradation and particles separation, have become dominant in future water and wastewater treatment because of the superior effluent quality. Longer sludge retention time (SRT) in MBR can greatly increase sludge concentration in the bioreactor to reduce footprint and sludge production. In addition, longer SRT in MBR can retain slow growing autotrophic microorganisms such as nitrifying microorganisms to enhance ammonia removal in MBR. However, the applications of MBR can be seriously hindered by their excessive operation cost due to membrane fouling. Membrane fouling reduces water production and the life of membrane, thereby, increasing operation and maintenance costs. More stringent regulation for ammonia allowance in water has been legislated due to its impact on health and aquatic ecosystem. Although MBR was proven effective in turning ammonia into nitrate by nitrifying microorganisms, nitrate is toxic to human bodies. High concentration of nitrate in drinking water has been linked to serious health problems such as blue baby syndrome. Therefore, denitrification is the ultimate solution for ammonia removal. In this study, we plan to develop a novel electro-membrane bioreactor (EMBR) system by combining MBR with bio-electrochemical treatment method. In this system, ammonia is oxidized to nitrite and then to nitrate by nitrifying microorganisms, which are retained in MBR. The autohydrogenotrophic microorganisms grown on the cathodes will then utilize nitrate and hydrogen as the electron acceptor and electron donor, respectively, to reduce nitrate to nitrogen gas. Furthermore, on the anode metal ions are spontaneously released, which act as coagulants to destabilize sludge suspension. As a result, membrane fouling can be reduced by the electrocoagulation.