voltage) or emf of the half reaction is used most commonly. Thus, every half reaction involving an oxidation or reduction has a standard potential E' associated with it Tab. 6-7 Standard electrode potentials for oxidation half reactions for chemical disinfection Oxidation Disinfectant Half reaction Ozone O3+ 2e+O2+H2O +20 rogen peroxide H2O2+2H++2e→2H2 +1.78 MnO4 4H*+ 3e" +,MnO2+ 2H2O +1.67 Chlorine dioxide CiO2+e+ClO2 +1.50 ypochlorous acid HOC+H+2e + Cl-+ HO Hypoiodous acid HO+H++e-+1/22+H2O +1.4 Oxygen O2+4H++4e-+2H2O +1.23 +1.09 Hypo OCI+ H2O+ 2e +, CI+2OH +0. Chlorite CIO2+ 2H-0+ 4e"++CI+4OH +0.76 odine +0.54 The half-reaction potential is a measure of the tendency of a reaction to proceed to the right Half reactions with large positive potential. E', tend to proceed to the right as written. Conversely. half reactions with large negative potential. E, tend to proceed to the left Rate of Oxidation-Reduction Reactions. As noted previously, the half-reaction potentials can be used to predict whether a reaction will proceed as written. Unfortunately, the reaction potential provides no information about the rate at which the reaction will proceed. Chemical oxidation reactions often require the presence of one or more catalysts for the reaction to proceed or to increase the rate of reaction of Applications Some of the more important applications of chemical oxidation in wastewater management are summarized in Table 6-8. In the past, chemical oxidation was used most commonly to(I) reduce the concentration of residual organics,(2)control odors, (3)remove ammonia, and(4)reduce the bacterial and viral content of wastewaters. Chemical oxidation is especially effective for the elimination of odorous compounds(e.g, oxidation of sulfides and mercaptans). In addition to the applications reported in Table 6-8, chemical oxidation is now commonly used to(1)improve the treatability of nonbiodegradable (refractory) organic compounds, (2) eliminate the inhibitory effects of certain organic and inorganic compounds to microbial growth, and(3)reduce or eliminate the toxicity of certain organic and inorganic comBo unds to microbial growth and aquatic flora. Tab. 6-8 Typical applications of chemical oxidation in wastewater collection, treatment, and disposal Collection Slime-growth control Ch, H2O, orrosion control(H,S) Control of fungi and slime-producing bacteria Control brought about by oxidation of H S Odor control CI, HO2, O, Especially in pumping stations and long, flat sewers C Added before preperation Oxidation of organic substances Ferrous sulfate oxidation Production of ferric sfate and ferric chloride Filter-ponding control duol at filter nozzles udge-bulking control H,o mporory control measure filamentous Dilute chlorine solution sprayed on foam caused by Digester supernatant Ammonia oxidation dor contol Conversion of ammonia to nitrogen ga Cl2. H2O, O3 organic compounds Bacterial reduction C2. H2O,,O, Plant effluent, overflows, and stormwater Odor control 6-156-15 voltage) or emf of the half reaction is used most commonly. Thus, every half reaction involving an oxidation or reduction has a standard potential E。 associated with it. Tab. 6-7 Standard electrode potentials for oxidation half reactions for chemical disinfection The half-reaction potential is a measure of the tendency of a reaction to proceed to the right. Half reactions with large positive potential, E。 , tend to proceed to the right as written. Conversely, half reactions with large negative potential, E。 , tend to proceed to the left. Rate of Oxidation-Reduction Reactions. As noted previously, the half-reaction potentials can be used to predict whether a reaction will proceed as written. Unfortunately, the reaction potential provides no information about the rate at which the reaction will proceed. Chemical oxidation reactions often require the presence of one or more catalysts for the reaction to proceed or to increase the rate of reaction. Transition metal cations, enzymes, pH adjustment, and a variety of proprietary substances have been used as catalysts. Applications Some of the more important applications of chemical oxidation in wastewater management are summarized in Table 6-8. In the past, chemical oxidation was used most commonly to (I) reduce the concentration of residual organics, (2) control odors, (3) remove ammonia, and (4) reduce the bacterial and viral content of wastewaters. Chemical oxidation is especially effective for the elimination of odorous compounds (e.g., oxidation of sulfides and mercaptans). In addition to the applications reported in Table 6-8, chemical oxidation is now commonly used to (1) improve the treatability of nonbiodegradable (refractory) organic compounds, (2) eliminate the inhibitory effects of certain organic and inorganic compounds to microbial growth, and (3) reduce or eliminate the toxicity of certain organic and inorganic compounds to microbial growth and aquatic flora. Tab. 6-8 Typical applications of chemical oxidation in wastewater collection, treatment, and disposal