Tab. 6-6 Practical effluent concentration levels achievable in heavy metals removal by precipitation Metal Sulfide precipitation with filtration 0.005 Barium Sulfate precipitation Hydroxide precipitation at pH 10- oprecipitation with ferric hydro 0.008 Sulfide precipitation Copper 0.02-0.07 Hydroxide precipitation 001-002 Sulfide precipitation 000050.005 Ferric hydroxide coprecipitation 0.0010.005 Hydroxide precipitation at pH 10 Sulfide precipitation Coprecipitation with Phosphorus As discussed previously, precipitation of phosphorus in wastewater is usually accomplished by the addition of coagulants, such as alum, lime or iron salts, and polyelectrolytes. Coincidentally with the addition of these chemicals for the removal of phosphorus is the removal that occurs of various inorganic ions, principally some of the heavy metals. Where both industrial and domestic wastes are treated together it may be necessary to add chemicals to the primary settling facilities, especially if onsite pretreatment measures prove to be ineffective. Wh stabilization I xicity of the precipitated heavy metals. As noted previously one of the disadvantages of chemical precipitation is that it usually results in a net increase in the total dissolved solids of the wastewater that is being treated 6-6 Chemical Oxidation Chemical oxidation in wastewater treatment typically involves the use of oxidizing agents such as ozone O3). hydrogen peroxide(H202). permanganate(MnO4). chloride dioxide(CIO2). chlorine(C12) or (HOCD. and oxvgen(O), to bring about change in the chemical composition of a compound or a group of compounds. Included in the following discussion is an introduction of the fundamental concepts involved in chemical oxidation. an overview of the uses of chemical oxidation in wastewater treatment and a discussion of the use of chemical oxidation for the reduction of bod and cod the oxidation of ammonia, and oxidation of nonbiodegradable organic compounds. Advanced oxidation process(AOPs) in which the free hydroxyl discussed in later chapters Fundamentals of Chemical Oxidation Oxidation-Reduction Reactions. Oxidation-reduction reactions(known as redox equations) take place between an oxidizing agent and a reducing agent. In oxidation-reduction reactions both electrons are exchanged as are the oxidation states of the constituents involved in the reaction. While an oxidizing age causes the oxidation to occur. it is reduced in the process. Half-Reaction Potentials. Because of the almost infinite number of possible reactions, there are no summary tables of equilibrium constants for oxidation-reduction reactions. What is done instead is the chemical and thermodynamic characteristics of the half reactions are determined and tabulated so that any combination of reactions can be studied. Representative half reactions are given in Table 6-8. Of the many properties that can be used to characterize oxidation-reduction reactions, the electrical potential 6-146-14 Tab. 6-6 Practical effluent concentration levels achievable in heavy metals removal by precipitation Coprecipitation with Phosphorus As discussed previously, precipitation of phosphorus in wastewater is usually accomplished by the addition of coagulants, such as alum, lime or iron salts, and polyelectrolytes. Coincidentally with the addition of these chemicals for the removal of phosphorus is the removal that occurs of various inorganic ions, principally some of the heavy metals. Where both industrial and domestic wastes are treated together, it may be necessary to add chemicals to the primary settling facilities, especially if onsite pretreatment measures prove to be ineffective. When chemical precipitation is used, anaerobic digestion for sludge stabilization may not be possible because of the toxicity of the precipitated heavy metals. As noted previously, one of the disadvantages of chemical precipitation is that it usually results in a net increase in the total dissolved solids of the wastewater that is being treated. 6-6 Chemical Oxidation Chemical oxidation in wastewater treatment typically involves the use of oxidizing agents such as ozone (O3), hydrogen peroxide (H202), permanganate (MnO4), chloride dioxide (ClO2), chlorine (C12) or (HOC1), and oxygen (O2), to bring about change in the chemical composition of a compound or a group of compounds. Included in the following discussion is an introduction of the fundamental concepts involved in chemical oxidation, an overview of the uses of chemical oxidation in wastewater treatment, and a discussion of the use of chemical oxidation for the reduction of BOD and COD, the oxidation of ammonia, and oxidation of nonbiodegradable organic compounds. Advanced oxidation process (AOPs) in which the free hydroxyl radical (HO. ) is used as a strong oxidant to destroy specific organic constituents and compounds that cannot be oxidized by conventional oxidants such as ozone and chlorine are discussed in later chapters. Fundamentals of Chemical Oxidation Oxidation-Reduction Reactions. Oxidation-reduction reactions (known as redox equations) take place between an oxidizing agent and a reducing agent. In oxidation-reduction reactions both electrons are exchanged as are the oxidation states of the constituents involved in the reaction. While an oxidizing agent causes the oxidation to occur, it is reduced in the process. Half-Reaction Potentials. Because of the almost infinite number of possible reactions, there are no summary tables of equilibrium constants for oxidation-reduction reactions. What is done instead is the chemical and thermodynamic characteristics of the half reactions are determined and tabulated so that any combination of reactions can be studied. Representative half reactions are given in Table 6-8. Of the many properties that can be used to characterize oxidation-reduction reactions, the electrical potential (i.e