activated-sludge effluents and lagoon effluents The principal wastewater characteristics that affect the percent transmission include selected inorganic compounds (e.g, copper; iron, etc. ) organic compounds (e. g, organic dyes, humic substances, and conjugated ring compounds such as benzene and toluene), and TSs. Of the inorganic compounds which affect transmittance, iron is considered to be the most important with respect to UV absorbance because dissolved iron can absorb UV light directly and because iron will adsorb onto suspended solids, bacterial clumps and other organic compounds. The sorbed iron can prevent the UV light from penetrating the article and inactivating organisms that may be embedded within the particle. Where iron salts are added in the treatment process, dosage control is extremely important when Uv disinfection is to be used Organic constituents, identified as being absorbers of UV light are compounds with six conjugated carbons or a five-or six-member conjugated ring The reduction in transmittance observed during storm events is often ascribed to the presence of humic substances from stormwater flows. Typical transmittance values for treated wastewater from several activated-sludge biological treatment plants and two lagoon systems are presented on Fig. 2-6. Percent transmittance is affected by all substances in wastewater that can absorb or scatter light. Unfiltered and filtered transmittance are mearsured in wastewater in connection with the evalution and design of UV disinfection systems Ter The temperature of wastewater is commonly higher than that of the local water supply, because of the ddition of warm water from households and industrial activities. As the specifc heat of water is much greater than that of air. the observed wastewater temperatures are his geographic location, the mean annual temperature of wastewater in the United States varies from about 3 to 27C: 15.6C is a representative value. Temperatures as high as 30 to 50 C have been reported for countries in Africa and the Middle East han the corresponding influent values. Depending on the location and time of vear the effluent Effects of Temperature. The temperature of water is a very important parameter because of its effect on chemical reactions and reaction rates, aquatic life, and the suitability of the water for beneficial uses. Increased temperature. for example, can cause a change in the species of fish that can exist in the receiving water bodv Industrial establishments that use surface water for cooling water purposes are articulally concerned with the temperature of the intake water. In addition, oxygen is less soluble in warm water than in cold water. Thethe rate of biochemical reactions that accompanies an increase in temperature, combined with the decrease in the quantity of oxvgen resent in surface waters, can often cause serious depletions in dissolved oxygen concentrations in the summer months. When significantly large quantities of heated water are discharged to natural receiving growth of undesirable water plants and wastewater fungus Optimum Temperatures for Biological Activity. Optimum temperatures for bacterial activity are in the range from 25 to 35C. Aerobic digestion and nitrification stops when the temperature rises to 50C. When the temperature drops to about 15 C, methane-producing bacteria become quite inactive, and at about 5C, the autotrophic-nitrifying bacteria practically cease functioning. At 2 C, even the chemoheterotrophic acteria acting on carbonaceous material become essentially dormant. The effects of temperature on the performance of biological treatment processes are considered in greater detail in latter chapters Conductivity The electrical conductivity (EC)of a water is a measure of the ability of a solution to conduct an electrical current. Because the electrical current is transport ted by the ions in solution, the conductivity increases as the concentration of ions increases. In effect the measured eC value is used as a surrogate measure of total dissolved solid(TDS )concentration. At present, the eC of a water is one of the important parameter used to determine the suitability of a water for irrigation. The salinity of treated wastewater to be used for irrigation is estimated by measuring its electrical conductivity 2-4 Inorganic Nonmetallic Constituents The chemical constituents of wastewater are typically classified as inorganic and organic. Inorganic chemical constituents of concern include nutrients, nonmetallic constituents, metals, and gases. Organic constituents of interest in wastewater are classified as aggregate and individual. Aggregate organic constituents are comprised of a number of individual compounds that cannot be distinguished separately Both aggregate and individual organic constituents are of great significance in the treatment, disposal, and 292-9 activated-sludge effluents and lagoon effluents The principal wastewater characteristics that affect the percent transmission include selected inorganic compounds (e.g., copper; iron, etc.), organic compounds (e.g., organic dyes, humic substances, and conjugated ring compounds such as benzene and toluene), and TSS. Of the inorganic compounds which affect transmittance, iron is considered to be the most important with respect to UV absorbance because dissolved iron can absorb UV light directly and because iron will adsorb onto suspended solids, bacterial clumps and other organic compounds. The sorbed iron can prevent the UV light from penetrating the particle and inactivating organisms that may be embedded within the particle. Where iron salts are added in the treatment process, dosage control is extremely important when UV disinfection is to be used. Organic constituents, identified as being absorbers of UV light, are compounds with six conjugated carbons or a five- or six-member conjugated ring. The reduction in transmittance observed during storm events is often ascribed to the presence of humic substances from stormwater flows. Typical transmittance values for treated wastewater from several activated-sludge biological treatment plants and two lagoon systems are presented on Fig. 2-6. Percent transmittance is affected by all substances in wastewater that can absorb or scatter light. Unfiltered and filtered transmittance are mearsured in wastewater in connection with the evalution and design of UV disinfection systems. Temperature The temperature of wastewater is commonly higher than that of the local water supply, because of the addition of warm water from households and industrial activities. As the specifc heat of water is much greater than that of air, the observed wastewater temperatures are higher than the local air temperatures during most of the year and are lower only during the hottest summer months. Depending on the geographic location, the mean annual temperature of wastewater in the United States varies from about 3 to 27℃; 15.6℃ is a representative value. Temperatures as high as 30 to 50 ℃ have been reported for countries in Africa and the Middle East. Depending on the location and time of year, the effluent temperatures can be either higher or lower than the corresponding influent values. Effects of Temperature. The temperature of water is a very important parameter because of its effect on chemical reactions and reaction rates, aquatic life, and the suitability of the water for beneficial uses. Increased temperature, for example, can cause a change in the species of fish that can exist in the receiving water body. Industrial establishments that use surface water for cooling water purposes are particulally concerned with the temperature of the intake water. In addition, oxygen is less soluble in warm water than in cold water. The the rate of biochemical reactions that accompanies an increase in temperature, combined with the decrease in the quantity of oxygen present in surface waters, can often cause serious depletions in dissolved oxygen concentrations in the summer months. When significantly large quantities of heated water are discharged to natural receiving waters,these effects are magnified. It should also be realized that a sudden change in temperature can result in a high rate of mortality of aquatic life. Moreover, abnormally high temperatures can foster the growth of undesirable water plants and wastewater fungus. Optimum Temperatures for Biological Activity. Optimum temperatures for bacterial activity are in the range from 25 to 35℃. Aerobic digestion and nitrification stops when the temperature rises to 50℃. When the temperature drops to about 15℃, methane-producing bacteria become quite inactive, and at about 5℃, the autotrophic-nitrifying bacteria practically cease functioning. At 2℃,even the chemoheterotrophic bacteria acting on carbonaceous material become essentially dormant. The effects of temperature on the performance of biological treatment processes are considered in greater detail in latter chapters. Conductivity The electrical conductivity (EC) of a water is a measure of the ability of a solution to conduct an electrical current. Because the electrical current is transported by the ions in solution, the conductivity increases as the concentration of ions increases. In effect, the measured EC value is used as a surrogate measure of total dissolved solid(TDS)concentration. At present, the EC of a water is one of the important parameter used to determine the suitability of a water for irrigation. The salinity of treated wastewater to be used for irrigation is estimated by measuring its electrical conductivity. 2-4 Inorganic Nonmetallic Constituents The chemical constituents of wastewater are typically classified as inorganic and organic. Inorganic chemical constituents of concern include nutrients, nonmetallic constituents, metals, and gases. Organic constituents of interest in wastewater are classified as aggregate and individual. Aggregate organic constituents are comprised of a number of individual compounds that cannot be distinguished separately. Both aggregate and individual organic constituents are of great significance in the treatment, disposal, and