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Standard Methods for Examination of Water & Wastewater_14

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Để áp dụng đầy đủ các kiến thức về các phản ứng sinh học để xử lý nước và nước thải, chất hóa học của các phản ứng này phải được giai đoạn trung tâm. Nói cách khác, để kiểm soát quá trình loại bỏ nitơ bởi quá trình nitrat hóa-khử, các phản ứng hóa học bên trong phải được làm sáng tỏ và hoàn toàn hiểu. | 15 Removal of Nitrogen by NitrificationDenitrification We define a biological reaction as a reaction mediated by organisms. It encompasses both the organisms and the underlying chemical reactions. To fully apply the knowledge of biological reactions to the treatment of water and wastewater the chemical nature of these reactions must be given center stage. In other words to control the process of removing nitrogen by nitrification-denitrification the intrinsic chemical reactions must be unraveled and fully understood. The organisms only serve as mediators i.e. the producer of the enzymes needed for the reaction . Thus on the most fundamental level nitrogen removal is a chemical process more accurately a biochemical process and the treatment for removal of nitrogen by nitrificationdenitrification as used in this textbook is chemical in nature and the process is a chemical unit process. In fact nitrification-denitrification removal of nitrogen can be effected by purely enzymatic means by providing the needed enzymes externally without ever using microorganisms. Similar to phosphorus nitrogen is a very important element that has attracted much attention because of its ability to cause eutrophication in bodies of water. As stated in the chapter on phosphorus removal the Chesapeake Bay in Maryland and Virginia is fed by tributaries from farmlands as far away as New York. Because of the use of nitrogen in fertilizers for these farms the bay receives an extraordinarily large amount of nitrogen input that has triggered excessive growths of algae in the water body. Presently large portions of the bay are eutrophied. This chapter discusses removal of nitrogen using the unit process of nitrification followed by denitrification. Half reactions are utilized in the discussion of the chemical reactions. Whether or not a particular reaction will occur can be determined by the free energy change of the reactants and products. Thus half reactions are normally tabulated in terms of .