reuse of wastewater The sources of inorganic nonmetallic and metallic constituents in wastewater derive from the background levels in the water supply and from the additions resulting from domestic use, from the addition of highly mineralized water from private wells and groundwater, and from industrial use. Domestic and industrial softeners also contribute significantly to the increase in mineral content and, in some areas, may represent the major source. Occasionally, water added from private wells and groundwater infiltration will serve to dilute the mineral concentrauon in the wastewater. Inorganic nonmetallic constituents considered in this section include pH, nitrogen, phosphorus, alkalinity, chlorides, sulfur, other inorganic constituents gases, and odors Chlorides Chloride is a constituent of concern in wastewater as it can impact the final reuse applications of treated wastewater. Chlorides in natural water result from the leaching of chloride-containing rocks and soils with which the water comes in contact, and in coastal areas from saltwater intrusion. In addition agricultural industrial, and domestic wastewaters discharged to surface waters are a source of chlorides Human excreta, for example, contain about 6 g of chlorides per person per day. In areas where the hardness of water is high, home regeneration type water softeners will also add large quantities of chlorides. Because conventional methods of waste treatment do not remove chloride to any significant extent, higher than usual chloride concentrations can be taken as an indication that a body of water is being used for waste disposal Infiltration of groundwater into sewers adjacent to saltwater is also a potential source of high chlorides as well as sulfates Alkalinity Ikalinity in wastewater results from the presence of the hydroxides [OH-], carbonates [Co,2],and bicarbonates [HCO3] of elements such as calcium, magnesium, sodium, potassium, and ammonia Of these, calcium and magnesium bicarbonates are most common Borates, silicates, phosphates, and similar compounds can also contribute to the alkalinity. The alkalinity in wastewater helps to resist changes in pH caused by the addition of acids. In some cases, wastewater may be alkaline, receiving its alkalinity from the water supply, the groundwater, and the materials added during domestic use. The concentration of alkalinily in wastewater is important where chemical and biological treatment is to be used, in biological nutrient removal, and where ammonia is to be removed by air stripping Ikalinity is determined by titrating against a standard acid; the results are expressed in terms of calcium carbonate, mg/L as CaCO3. For most practical proposes alkalinity can be defined in terms of molar quantities, as eq/m=meq/L=[HCO3]+2 [CO3]+ [OH]-HI The corresponding expression in terms of equivalents is In practice, alkalinity is expressed in terms of calcium carbonate. To convert from meq/L to mg/L as helpful to i Milliequivalent mass of CaCO3=[100(mg/mmole)(2 meq/mmole]=50 mg/meq Thus 3 meq/l of alkalinity would be expressed as 150 mg/L as Caco3 ity, Alk as CacO3 =3.0meq/LX50mg/meq CacO3 =150 mg/L as Ca Nitrogen The elements nitrogen and phosphorus, essential to the growth of microorganisms, plants, and animals, are known as nutrients or biostimulants. Trace quantities of other elements, such as iron, are also needed for biological growth, but nitrogen and phosphorus are, in most cases, the major nutrients of importance Because nitrogen is an essential building block in the synthesis of protein, nitrogen data will be required to evaluate the treatability of wastewater by biological processes. Insufficient nitrogen can necessitate the addition of nitrogen to make the waste treatable. Nutrient requirements for biological waste treatment are or reduction of nitrogen in wastewater prior to discharge may be desirable ving water is necessary, removal Sources of Nitrogen. The principal sources of nitrogen compouns are(1)the nitrogenous compounds of plant and animal origin,(2)sodium nitrate, and (3 )atomspheric nitrogen. Ammonia derived from the distillation of bituminous coal is an example of nitrogen obtained from decayed plant material. Sodium nitrate(NaNOs) is found principally in mineral deposits in Chile and in the manure found in seabird rookeries. The production of nitrogen from the atmosphere is termed fixation Because fixation is biologically mediated process and because NaNO, deposits are relatively scarce, most sources of nitrogen in soil/groundwater are of biological origin Forms of Nitrogen. The chemistry of nitrogen is complex, because of the several oxidation states that 2-102-10 reuse of wastewater. The sources of inorganic nonmetallic and metallic constituents in wastewater derive from the background levels in the water supply and from the additions resulting from domestic use, from the addition of highly mineralized water from private wells and groundwater, and from industrial use. Domestic and industrial water softeners also contribute significantly to the increase in mineral content and, in some areas, may represent the major source. Occasionally, water added from private wells and groundwater infiltration will serve to dilute the mineral concentrauon in the wastewater. Inorganic nonmetallic constituents considered in this section include pH, nitrogen, phosphorus, alkalinity, chlorides, sulfur, other inorganic constituents, gases, and odors. Chlorides Chloride is a constituent of concern in wastewater as it can impact the final reuse applications of treated wastewater. Chlorides in natural water result from the leaching of chloride-containing rocks and soils with which the water comes in contact, and in coastal areas from saltwater intrusion. In addition, agricultural, industrial, and domestic wastewaters discharged to surface waters are a source of chlorides. Human excreta, for example, contain about 6 g of chlorides per person per day. In areas where the hardness of water is high, home regeneration type water softeners will also add large quantities of chlorides. Because conventional methods of waste treatment do not remove chloride to any significant extent, higher than usual chloride concentrations can be taken as an indication that a body of water is being used for waste disposal. Infiltration of groundwater into sewers adjacent to saltwater is also a potential source of high chlorides as well as sulfates. Alkalinity Alkalinity in wastewater results from the presence of the hydroxides [OH- ], carbonates [CO3 2- ], and bicarbonates [HCO3 - ] of elements such as calcium, magnesium, sodium, potassium, and ammonia. Of these, calcium and magnesium bicarbonates are most common. Borates, silicates, phosphates, and similar compounds can also contribute to the alkalinity. The alkalinity in wastewater helps to resist changes in pH caused by the addition of acids. In some cases, wastewater may be alkaline, receiving its alkalinity from the water supply, the groundwater, and the materials added during domestic use. The concentration of alkalinily in wastewater is important where chemical and biological treatment is to be used, in biological nutrient removal, and where ammonia is to be removed by air stripping. Alkalinity is determined by titrating against a standard acid; the results are expressed in terms of calcium carbonate, mg/L as CaCO3. For most practical proposes alkalinity can be defined in terms of molar quantities, as: Alk, eq/m3 = meq/L = [HCO3 - ] + 2 [CO3 2- ] + [OH- ] –[H+ ] The corresponding expression in terms of equivalents is Alk, eq/m3 = (HCO3 - ) + (CO3 2- ) + (OH- ) - (H+ ) In practice, alkalinity is expressed in terms of calcium carbonate. To convert from meq/L to mg/L as CaCO3, it is helpful to remember that Milliequivalent mass of CaCO3 = [100 (mg/mmole)]/[2 meq/mmole]=50 mg/meq Thus 3 meq/L of alkalinity would be expressed as 150 mg/L as CaCO3. Alkalinity, Alk as CaCO3 =3.0meq/L×50mg/meq CaCO3 = 150 mg/L as CaCO3 Nitrogen The elements nitrogen and phosphorus, essential to the growth of microorganisms, plants, and animals, are known as nutrients or biostimulants. Trace quantities of other elements, such as iron, are also needed for biological growth, but nitrogen and phosphorus are, in most cases, the major nutrients of importance. Because nitrogen is an essential building block in the synthesis of protein, nitrogen data will be required to evaluate the treatability of wastewater by biological processes. Insufficient nitrogen can necessitate the addition of nitrogen to make the waste treatable. Nutrient requirements for biological waste treatment are discussed in the later chapters. Where control of algal growths in the receiving water is necessary, removal or reduction of nitrogen in wastewater prior to discharge may be desirable. Sources of Nitrogen. The principal sources of nitrogen compouns are (1)the nitrogenous compounds of plant and animal origin, (2) sodium nitrate, and (3)atomspheric nitrogen. Ammonia derived from the distillation of bituminous coal is an example of nitrogen obtained from decayed plant material. Sodium nitrate (NaNO3) is found principally in mineral deposits in Chile and in the manure found in seabird rookeries. The production of nitrogen from the atmosphere is termed fixation. Because fixation is a biologically mediated process and because NaNO3 deposits are relatively scarce, most sources of nitrogen in soil/groundwater are of biological origin. Forms of Nitrogen. The chemistry of nitrogen is complex, because of the several oxidation states that