Chemical Oxidation of Nonbiodegradable Organic Compounds. Typical chemical dosages for both chlorine and ozone for the oxidation of the organics in wastewater are reported in Table 6-10. As shown in Table 6-10, the dosages increase with the degree of treatment, which is reasonable when it is considered that the organic compounds that remain after biological treatment are typically composed of low-molecular-weight polar organic compounds and complex organic compounds built around the benzene ring structure. Because of the complexities associated with composition of wastewater,chemical dosages for the removal of refractory organic compounds cannot be derived from the chemical stoichiometry, assuming that it is known Pilot-plant studies must be conducted when either chlorine, chlorine dioxide, or ozone is to be used for the oxidation of refractory organics to assess both the efficacy and required dosages Chemical oxidation of ammonia The chemical process in which chlorine is used to oxidize the ammonia nitrogen in solution to nitrogen gas and other stable compounds is known as breakpoint chlorination. Perhaps the most important dvantage of this process is that, with proper control, all the ammonia nitrogen in the wastewater can be oxidized. However, because the process has a number of disadvantages including the buildup of acid(hci) hich will react with the alkalinity, the buildup of total dissolved solids, and the formation of unwanted chloro-organic compounds, ammonia oxidation is seldom used today 6-7 Chemical Neutralization, Scale Control, And Stabilization The removal of excess acidity or alkalinity by treatment with a chemical of the opposite composition is termed neutralization. In general, all treated wastewaters with excessively low or high pH will require neutralization before they can be dispersed to the environment. Scaling control is required for nanofiltration and reverse osmosis treatment to control the formation of scale, which can severely impact performance. Chemical stabilization is often required for highly treated wastewaters to control their aggressiveness with respect to corrosion ADjustment In a variety of wastewater-treatment operations and processes, there is often a need for pH adjustment Because a number of chemicals are available that can be used, the choice will depend on the suitability of a given chemical for a particular application and prevailing economics. General information on the chemicals used most commonly for pH adjustment is given in Table 6-9. Wastewater that is acidic can be neutralized with any number of basic chemicals, as reported in Table 6-9. Sodium hydroxide(NaoH, also known as caustic soda) and sodium carbonate, although somewhat expensive, are convenient and are used widely by small plants or for treatment where small quantities are adequate. Lime, which is cheaper but somewhat less convenient, is the most widely used chemical. Lime slaked hydrated lime. high-calcium or dolomitic lime. and in several physical forms m叫mmB中ym chemicals often form sludges that require disposal Tab. 6-9 Chemicals used most commonly for the control ofpH Formula Chemicals used to raise pH Calcium carbonate 100.0 96o99 Calcium hydroxide (lime) 74.1 371 82b95 Calcium oxide 280 9098 ground Dolomitic quicklime .IMg a 24.8 Lump, pebble 55-58 Cao Magnesium hydroxide Mg(OH) Magnesium oxide Sodium bicarbonate NaHcO, 840 Powder Sodium carbonate Sodium hydroxide 400 caustic soda und Bake Chemicals used to lower pH Hydrochloric acid 27931.45.35.2 Sulfuric acid 77760°Be 932{66°Bel Alkali 6-166-16 Chemical Oxidation of Nonbiodegradable Organic Compounds. Typical chemical dosages for both chlorine and ozone for the oxidation of the organics in wastewater are reported in Table 6-10. As shown in Table 6-10, the dosages increase with the degree of treatment, which is reasonable when it is considered that the organic compounds that remain after biological treatment are typically composed of low-molecular-weight polar organic compounds and complex organic compounds built around the benzene ring structure. Because of the complexities associated with composition of wastewater, chemical dosages for the removal of refractory organic compounds cannot be derived from the chemical stoichiometry, assuming that it is known. Pilot-plant studies must be conducted when either chlorine, chlorine dioxide, or ozone is to be used for the oxidation of refractory organics to assess both the efficacy and required dosages. Chemical Oxidation of Ammonia The chemical process in which chlorine is used to oxidize the ammonia nitrogen in solution to nitrogen gas and other stable compounds is known as breakpoint chlorination. Perhaps the most important advantage of this process is that, with proper control, all the ammonia nitrogen in the wastewater can be oxidized. However, because the process has a number of disadvantages including the buildup of acid (HCl) which will react with the alkalinity, the buildup of total dissolved solids, and the formation of unwanted chloro-organic compounds, ammonia oxidation is seldom used today. 6-7 Chemical Neutralization, Scale Control, And Stabilization The removal of excess acidity or alkalinity by treatment with a chemical of the opposite composition is termed neutralization. In general, all treated wastewaters with excessively low or high pH will require neutralization before they can be dispersed to the environment. Scaling control is required for nanofiltration and reverse osmosis treatment to control the formation of scale, which can severely impact performance. Chemical stabilization is often required for highly treated wastewaters to control their aggressiveness with respect to corrosion. pH Adjustment In a variety of wastewater-treatment operations and processes, there is often a need for pH adjustment. Because a number of chemicals are available that can be used, the choice will depend on the suitability of a given chemical for a particular application and prevailing economics. General information on the chemicals used most commonly for pH adjustment is given in Table 6-9. Wastewater that is acidic can be neutralized with any number of basic chemicals, as reported in Table 6-9. Sodium hydroxide (NaOH, also known as caustic soda) and sodium carbonate, although somewhat expensive, are convenient and are used widely by small plants or for treatment where small quantities are adequate. Lime, which is cheaper but somewhat less convenient, is the most widely used chemical. Lime can be purchased as quicklime or slaked hydrated lime, high-calcium or dolomitic lime, and in several physical forms. Limestone and dolomitic limestone are cheaper but less convenient to use and slower in reaction rate. Because they can become coated in certain waste-treatment applications, their use is limited. Calcium and magnesium chemicals often form sludges that require disposal. Tab. 6-9 Chemicals used most commonly for the control of pH Alkaline