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Standard Methods for Examination of Water & Wastewater_13

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việc sử dụng phốt-pho trong phân bón cho các trang trại, vịnh nhận được một số lượng cực kỳ lớn của đầu vào phốt pho đã kích hoạt tăng trưởng quá mức của tảo trong cơ thể nước. Hiện nay, phần lớn của vịnh eutrophied. Nếu không có nghi ngờ gì, tất cả các vịnh nhỏ và cửa sông nhỏ là nhánh sông để bay này cũng eutrophied | 14 Removal of Phosphorus by Chemical Precipitation Phosphorus is a very important element that has attracted much attention because of its ability to cause eutrophication in bodies of water. For example tributaries from as far away as the farmlands of New York feed the Chesapeake Bay in Maryland and Virginia. Because of the use of phosphorus in fertilizers for these farms the bay receives an extraordinarily large amount of phosphorus input that has triggered excessive growths of algae in the water body. Presently large portions of the bay are eutrophied. Without any doubt all coves and little estuaries that are tributaries to this bay are also eutrophied. Thus it is important that discharges of phosphorus be controlled in order to avert an environmental catastrophe. In fact the eutrophication of the Chesapeake Bay and the clogging of the Potomac River by blue greens are two of the reasons for the passage of the Federal Water Pollution Control Act Amendments of 1972. This chapter discusses the removal of phosphorus by chemical precipitation. It first discusses the natural occurrence of phosphorus followed by a discussion on the modes of removal of the element. The chemical reactions of removal unit operations of removal chemical requirements optimum pH range of operation and sludge production are all discussed. The chemical precipitation method employed uses alum lime and the ferric salts FeCl3 and Fe2 SO4 3. 14.1 NATURAL OCCURRENCE OF PHOSPHORUS The element phosphorus is a nonmetal. It belongs to Group VA in the Periodic Table in the third period. Its electronic configuration is Ne 3ỉ 23p3. Ne means that the neon configuration is filled. The valence configuration represented by the 3 the M shell shows five electrons in the orbitals 2 electrons in the Í orbitals and 3 electrons in the p orbitals. This means that phosphorus can have a maximum oxidation state of 5. The commonly observed oxidation states are 3- 3 and 5 . Phosphorus is too active a nonmetal to be found