《环境工程概论》课程教学资源（教案讲义）（英语版）Chapter 2 Constituents in Wastewater

An understanding of the nature of wastewater is essential in the design and operation of collection, treatment, and reuse facilities, and in the engineering management of environmental quality. To promote this understanding, the information in this chapter is presented in eight sections dealing with (1) an introduction to the constituents found in wastewater,

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2 Constituents in Wastewate this understanding, the information in this chner,(2)sampling and analytical procedures,(3)physical ter is presented in eight sections dealing with(1)an ntroduction to the constituents found in wastewat characteristics,(4)inorganic nonmetallic constituents, (5) metallic constituents,(6) aggregate organic constituents, (7)individual organic constituents and compounds, and( 8)biological characteristics 2-1 Wastewater Constituents Constituents found in wastewater The principal physical properties and the chemical and biological constituents of wastewater, and thei sources, are reported in Tab 2-1. It should be noted that many of the biological characteristics are interrelated. For example, temperature, a physical property, affects both the amounts of gases dissolved in the wastewater and the biological activity in the wastewater Constituents of concern in wastewater treatment The important constituents of concern in wastewater treatment are listed in Tab 2-2. Secondary treatment standards for wastewater are concerned with the removal of biodegradable organics, total suspended solid and pathogens. Many of the more stringent standards that have been developed recently deal with the removal of nutrients, heavy metals, and priority pollutants. When wastewater is to be reused, standards normally include additional requirements for the removal of refractory organics, heavy metals, and in some cases, dissolved inorganic solids 2-2 Sampling and Analytical Procedures Proper sampling and analytical techniques are of fundamental importance in the characterization of wastewater. Sampling techniques, the methods of analysis, the units of measurement for chemical constituents, and some useful concepts from chemistry are considered below Sampling Sampling programs are undertaken for a variety of reasons such as to obtain () routine operating data on overall plant performance,(2)data that can be used to document the perfomance of a given treatment operation or process, (3)data that can be used to implement proposed new programs, and(4)data needed for reporting regulatory compliance. To meet the goals of the sampling program, the data collected must 1. Representative. The data must represent the e wastewater or environment being sampled. 2. Reproducible. The data obtained must be reproducible by others following the same mentation must be available to validate the sampling procedures. The data must have a known degree of accuracy and precision. Useful. The data can be used to meet the obiectives of the monitoring plan. Because the data from the analvsis of the samples will ultimately serve as a basis for implementing wastewater management facilities and programs. the techniques used in a wastewater sampling program must be such that representative samples are obtained. Table 2-1 Common analyses used to assess the constituents found in wastewa Test Abbreviation/ Use or significance of test results definition Total solids most suitable type of operations and Total volatile solids processes for its treatment Total fixed solids TFS d solid TSS Volatile suspended solids Total dissolved solids TDS(TS-TSS) VDS

2-1 2 Constituents in Wastewater An understanding of the nature of wastewater is essential in the design and operation of collection, treatment, and reuse facilities, and in the engineering management of environmental quality. To promote this understanding, the information in this chapter is presented in eight sections dealing with (1) an introduction to the constituents found in wastewater, (2) sampling and analytical procedures, (3) physical characteristics, (4) inorganic nonmetallic constituents, (5) metallic constituents, (6) aggregate organic constituents, (7) individual organic constituents and compounds,and (8) biological characteristics. 2-1 Wastewater Constituents Constituents Found in Wastewater The principal physical properties and the chemical and biological constituents of wastewater, and their sources, are reported in Tab 2-1. It should be noted that many of the physical properties and chemical and biological characteristics are interrelated. For example, temperature, a physical property, affects both the amounts of gases dissolved in the wastewater and the biological activity in the wastewater. Constituents of Concern in Wastewater Treatment The important constituents of concern in wastewater treatment are listed in Tab 2-2.Secondary treatment standards for wastewater are concerned with the removal of biodegradable organics, total suspended solids, and pathogens. Many of the more stringent standards that have been developed recently deal with the removal of nutrients, heavy metals, and priority pollutants. When wastewater is to be reused, standards normally include additional requirements for the removal of refractory organics, heavy metals, and in some cases, dissolved inorganic solids. 2-2 Sampling and Analytical Procedures Proper sampling and analytical techniques are of fundamental importance in the characterization of wastewater. Sampling techniques, the methods of analysis, the units of measurement for chemical constituents, and some useful concepts from chemistry are considered below. Sampling Sampling programs are undertaken for a variety of reasons such as to obtain (1) routine operating data on overall plant performance, (2) data that can be used to document the performance of a given treatment operation or process, (3) data that can be used to implement proposed new programs, and (4) data needed for reporting regulatory compliance. To meet the goals of the sampling program, the data collected must be: 1. Representative. The data must represent the wastewater or environment being sampled. 2. Reproducible. The data obtained must be reproducible by others following the same sampling and analytical protocols. 3. Defensible. Documentation must be available to validate the sampling procedures. The data must have a known degree of accuracy and precision. 4. Useful. The data can be used to meet the objectives of the monitoring plan. Because the data from the analysis of the samples will ultimately serve as a basis for implementing wastewater management facilities and programs, the techniques used in a wastewater sampling program must be such that representative samples are obtained. Table 2-1 Common analyses used to assess the constituents found in wastewater Test Abbreviation/ definition Use or significance of test results Physical characteristics To assess the potential of reuse a wastewater and to determine the most suitable type of operations and processes for its treatment Total solids TS Total volatile solids TVS Total fixed solids TFS Total suspended solids TSS Volatile suspended solids VSS Fixed suspended solids FSS Total dissolved solids TDS(TS-TSS) Volatile dissolved solids VDS

otal fixed dissolved solids FDS Settleable solids To determine those solids that will settle by gravity in a pec o assess the performance of treatment processes Used to assess the guality of treated wastewater Light brown, gray y, black To assess the condition of wastewater(fresh or septic) Transmittance T Used to assess the suitability of treated effluent for UV disinfection TON To determine if odors will be a problem Temperature mportant in the design and operation of biolog ical rocesses in treatment facilities Conductivity Used to assess the suitabil ity of treated effluent for Inorganic chemical characteristics NHat Used as a measure of the nutrients present and the degree of decomposition in the wastewater; the oxid ized forms can TKN be taken as a measure of the degree of oxidation Inorg phospnorus a measure of the acidity or basicity of an aqueous solution ΣHCO3“CO32+OHHA Chloride Cl To assess the suitabil ity of the wastewater for agricu tura Sulfate To assess the potential for the formation of odors and may ty of the waste sludge Metals As, Cd, Ca, Cr, Co, Cu, Pb, Mg Hg, M To assess the suitability of the wastewater for reuse and fo o, NL Se, Na, Zn toxicity effects atment Trace amounts of metals are mportant in biological treatment. To assess presence or absence of specific constituents len O2,CO2,NH3,H2SCH4 To assess presence or absence of specific gas Organic chemical characteristics ive-day carbonaceous CBODs A measure of the amount of oxygen required to stabilize a biochem ical oxyge waste biologically Ultimate carbonaceous UBOD(BODu, BODL) A measure of the amount of oxygen required to stabilize a biochemical oxygen biologically Nitrogenous oxygen NOD A measure of the amount of oxygen required to oxidize en in the wastewater to nitrate oxygen COD Often used as a substitute for the bod test Total organic carbon TOC Often used as a substitute for the bod test MBAS. CTAS To determine presence of specific organic compounds and compounds and classes to assess whether special design measures will be needed Biological characteristics MNP To assess presence of pathogenic bacteria and effectiveness Specific organisms Bairusescter ia, protozoa, helminth To assess presence of specific organ isms in connection

2-2 Total fixed dissolved solids FDS Settleable solids To determine those solids that will settle by gravity in a specified time period Particle size distribution PSD To assess the performance of treatment processes Turbidity NTU Used to assess the quality of treated wastewater Color Light brown,gray,black To assess the condition of wastewater(fresh or septic) Transmittance %T Used to assess the suitability of treated effluent for UV disinfection Odor TON To determine if odors will be a problem Temperature ℃ Important in the design and operation of biological processes in treatment facilities Density ρ Conductivity EC Used to assess the suitability of treated effluent for agricultural applications Inorganic chemical characteristics Free ammonia NH4 + Used as a measure of the nutrients present and the degree of decomposition in the wastewater;the oxidized forms can be taken as a measure of the degree of oxidation Organic nitrogen Org N Total Kjeldahl nitrogen TKN Nitrates NO2 - Total nitrogen TN Inorganic phosphorus Inorg P Total phosphorus TP Organic phosphorus Org P pH pH A measure of the acidity or basicity of an aqueous solution Alkalinity ∑HCO3 -+CO3 2-+OH- -H + A measure of the buffering capacity of the wastewater Chloride Cl- To assess the suitability of the wastewater for agricultural reuse Sulfate SO4 2- To assess the potential for the formation of odors and may impact the treatability of the waste sludge Metals As,Cd,Ca,Cr,Co,Cu,Pb,Mg,Hg,M o,Ni,Se,Na,Zn To assess the suitability of the wastewater for reuse and for toxicity effects in treatment.Trace amounts of metals are important in biological treatment. Specific inorganic elements and compounds To assess presence or absence of specific constituents Various gases O2,CO2,NH3,H2S,CH4 To assess presence or absence of specific gases Organic chemical characteristics Five-day carbonaceous biochemical oxygen demand CBOD5 A measure of the amount of oxygen required to stabilize a waste biologically Ultimate carbonaceous biochemical oxygen demand UBOD(BODu,BODL) A measure of the amount of oxygen required to stabilize a waste biologically Nitrogenous oxygen demand NOD A measure of the amount of oxygen required to oxidize biologically the nitrogen in the wastewater to nitrate Chemical oxygen demand COD Often used as a substitute for the BOD test Total organic carbon TOC Often used as a substitute for the BOD test Specific organic compounds and classes of compounds MBAS,CTAS To determine presence of specific organic compounds and to assess whether special design measures will be needed for removal Biological characteristics Coliform organisms MNP To assess presence of pathogenic bacteria and effectiveness of disinfection process Specific organisms Bairusescteria,protozoa,helminth es,v To assess presence of specific organisms in connection with plant operation and for reuse

ic unit chronic Tab 2-2 Principal constituents of concern in wastewater treatment Suspended solids uspended solids can lead to the development of sludge deposition and anaerobic conditions hen untreated wastewater is discharged in the aquatic environment Biodegradable organics Composed principally of proteins, carbohydrates, and fats. Biodegradable organics are measured most commonly in terms of BoD and COD. If discharged untreated to the environment their biological stabilization can lead to the depletion of natural oxygen Patho Communicable diseases can be transmitted by the pathogenic organisms that may be present Nutrients Both nitrogen and phosphorus, along with carbon, are essential nutrients for growth. When discharged to the aquatic env ironment, the nutrients can lead to the growth of undesirable aquatic life. When discharged in excessive amount on land, they can also lead to the pollution Priority pollutants carcinogenicity, metogenicity, teratogen icity or high acute toxicity. Many of these compounds Refractory organics These organics tend to resist conditional methods of wastewater treatment. Typical examples include surfactants phenols, and agricultural pesticides Heavy metals Heavy metals are usually added to wastewater from commercial and industr ial activities and may have to be removed if the wastewater is to be reused Dissolved inorganIcs Inorganic constituents such as calcium, sodium, and sulfate are added to the orig inal domestic water supply as a result of water use and may have to be removed if the wastewater is to be There are no universal procedures for sampling: sampling programs must be tailored individually to fit each situation. Special procedures are necessary to handle sampling problems that arise when wastes vary considerably in composition Before a sampling program is undertaken, a detailed sampling protocol must be developed along with a quality assurance project plan( QAPP)(known previously quality assurance/quality control, QA/QC).As a minimum, the following items must be specified in the QAPP. Additional details on the subject of sampling may be found in Standard Methods 1.Sampling plan. Number of sampling locations, number and type of samples, time intervals(.g, real-time and/or time-delayed samples) 2. Sample types and size, Catch or grab samples, composite samples, or integrated samples, separate samples for different analyses(e.g, for metals). Sample size(i.e, volume)required 3. Sample labeling and chain of custody. Sample labels, sample seals, field log book chain of custody record, sample analysis request sheets, sample delivery to the laboratory, receipt and logging of sample, and assignment of sample for analysis 4.Sampling methods. Specific techniques and equipment to be used(e.g, manual, automatic, or sorbent 5. Sampling storage and preservation. Type of containers(e.g, glass or plastic), preservation methods, maximum allowable holding times 6.Sample constituents. A list of the parameters to be measured 7. Analytical methods. A list of the field and laboratory test methods and procedures to be used, and the detection limits for the individual methods If the physical, chemical, and/or biological integrity of the not maintained during interim periods between sample collection and sample analysis, a car performed sampling program will become worthless. Considerable research on the problem of preservation has failed to perfect a universal treatment or method, or to formulate a set of fixed rules applicable to samples of all types Prompt analysis is undoubtedly the most positive assurance against error due to sample deterioration When analytical and testing conditions dictate a lag between collection and analysis, such as when a 24 h composite sample is collected, provisions must be made for preserving samples. Current methods of sample preservation for the analysis of properties subject to deterioration must be used. Probable errors due to deterioration of the sample should be noted in reporting analytical data Methods of Analysis The analy ses used to characterize wastewater vary from precise quantitative chemical determinations to 2-3

2-3 Toxicity TUa,TUc Toxic unit acute,toxic unit chronic Tab 2-2 Principal constituents of concern in wastewater treatment Constituents Reason for importance Suspended solids Suspended solids can lead to the development of sludge deposition and anaerobic conditions when untreated wastewater is discharged in the aquatic environment. Biodegradable organics Composed principally of proteins, carbohydrates, and fats. Biodegradable organics are measured most commonly in terms of BOD and COD. If discharged untreated to the environment their biological stabilization can lead to the depletion of natural oxygen resources and to the development of septic conditions. Pathogens Communicable diseases can be transmitted by the pathogenic organisms that may be present in wastewater. Nutrients Both nitrogen and phosphorus, along with carbon, are essential nutrients for growth. When discharged to the aquatic environment, the nutrients can lead to the growth of undesirable aquatic life. When discharged in excessive amount on land, they can also lead to the pollution of groundwater. Priority pollutants Organic and inorganic compounds selected on the basis of their known or suspected carcinogenicity, metogenicity, teratogenicity or high acute toxicity. Many of these compounds are found in wastewater. Refractory organics These organics tend to resist conditional methods of wastewater treatment. Typical examples include surfactants, phenols, and agricultural pesticides. Heavy metals Heavy metals are usually added to wastewater from commercial and industrial activities and may have to be removed if the wastewater is to be reused. Dissolved inorganics Inorganic constituents such as calcium, sodium, and sulfate are added to the original domestic water supply as a result of water use and may have to be removed if the wastewater is to be reused. There are no universal procedures for sampling; sampling programs must be tailored individually to fit each situation. Special procedures are necessary to handle sampling problems that arise when wastes vary considerably in composition. Before a sampling program is undertaken, a detailed sampling protocol must be developed along with a quality assurance project plan (QAPP) (known previously quality assurance/quality control, QA/QC). As a minimum, the following items must be specified in the QAPP. Additional details on the subject of sampling may be found in Standard Methods. 1.Sampling plan. Number of sampling locations, number and type of samples, time intervals (e.g., real-time and/or time-delayed samples). 2.Sample types and size, Catch or grab samples, composite samples, or integrated samples, separate samples for different analyses (e.g., for metals). Sample size (i.e., volume) required. 3.Sample labeling and chain of custody. Sample labels, sample seals, field log book, chain of custody record, sample analysis request sheets, sample delivery to the laboratory, receipt and logging of sample, and assignment of sample for analysis. 4.Sampling methods. Specific techniques and equipment to be used (e.g., manual, automatic, or sorbent sampling). 5.Sampling storage and preservation. Type of containers (e.g., glass or plastic), preservation methods, maximum allowable holding times. 6.Sample constituents. A list of the parameters to be measured. 7.Analytical methods. A list of the field and laboratory test methods and procedures to be used, and the detection limits for the individual methods. If the physical, chemical, and/or biological integrity of the samples is not maintained during interim periods between sample collection and sample analysis, a carefully performed sampling program will become worthless. Considerable research on the problem of sample preservation has failed to perfect a universal treatment or method, or to formulate a set of fixed rules applicable to samples of all types. Prompt analysis is undoubtedly the most positive assurance against error due to sample deterioration. When analytical and testing conditions dictate a lag between collection and analysis, such as when a 24 h composite sample is collected, provisions must be made for preserving samples. Current methods of sample preservation for the analysis of properties subject to deterioration must be used. Probable errors due to deterioration of the sample should be noted in reporting analytical data. Methods of Analysis The analyses used to characterize wastewater vary from precise quantitative chemical determinations to

the more qualitative biological and physical determinations. The quantitative methods of analysis are either gravimetric, volumetric, or physicochemical In the physicochemical methods, properties other than mass or volume are measured. Instrumental methods of analysis such as turbidimetry, colorimetry, potentiometry, polarography, adsorptio spectrometry, fluorometry, and nuclear radiation are representative of the physicochemical analyses Details concerning the various analyses may be found in Standard Methods, the accepted reference that details the conduct of water and wastewater analyses are defined and are listed below in order of increasing levey el must be specified Several detection limits Units of Measurement for Physical and Chemical Parameters The results of the analysis of wastewater samples are expressed in terms of physical and chemical terms of measurement. The most common units for these measurements are, for example, kg/m, %by volume or by mass), pg/L, ng/L, ug/L, mg/L, g/L, ppb, ppm, mol/L, eq/L, meq/L and so on. The concentration of trace constituents is usually expressed as micrograms per liter(ug/L)or nanograms per liter(ng/L) For dilute systems, such as those encountered in natural waters and wastewater, in which one liter of sample weighs approximately one kilogram, the units of mg/L or g/mare interchangeable with ppm. The terms"parts per billion"(ppb) and"parts per trillion(ppt)are used interchangeably with ug/L and ng/L, espectively 2-3 Physical Characteristics The most important physical characteristic of wastewater is its total solids content, which is composed of floating matter, settleable matter, colloidal matter, and matter in solution Other important physical characteristics include particle size distribution, turbidity, color, transmittance, temperature, conductivity and density, specific gravity and specific weight Odor, sometimes considered a physical factor, is discussed in the following section Solids Wastewater contains a variety of solid materials varying from rags to colloidal material. In the characterization of wastewater, coarse materials are usually removed before the sample is analyzed for solids. The various solids classifications are identified in Tab 2-3. The interelationship between the arious solids fractions found in wastewater is illustrated graphically on Fig. 2-1. The standard test for ttleable solids consists of placing a waste water sample in a l-liter Imhoff cone and noting the volume of lids in millimeters that settle after a specified time period (1 h Evaporation Typically, about 60 percent of the suspended solids in a municipal wastewater are settleable. Total glass fiber TS solids (TS) are obtained by TSS total sus ting a sample of wastewater IDS-total disc to dryness and measuring the mass of fitrate FSS-fixed sus of the residue. As shown on Fig.2-1 VDS- volatile dis a filtration step is used to separate FDS fixed diss the total suspended solids(TSS) TFS total fixed from the total dissolved solids (TDS). Filters with nominal pore from 0. 45 um to about 2.0 um have been used for the TSs test(see Fig 2-2) FSS Fig. 2-1 Interrelationships of solids found in water and wastewater In much of the water TFS the solids through the filter are called

2-4 the more qualitative biological and physical determinations. The quantitative methods of analysis are either gravimetric, volumetric, or physicochemical. In the physicochemical methods, properties other than mass or volume are measured. Instrumental methods of analysis such as turbidimetry, colorimetry, potentiometry, polarography, adsorption spectrometry, fluorometry, and nuclear radiation are representative of the physicochemical analyses. Details concerning the various analyses may be found in Standard Methods , the accepted reference that details the conduct of water and wastewater analyses. Regardless of the method of analysis used, the detection level must be specified Several detection limits are defined and are listed below in order of increasing level. Units of Measurement for Physical and Chemical Parameters The results of the analysis of wastewater samples are expressed in terms of physical and chemical terms of measurement. The most common units for these measurements are, for example, kg/m3 ,%(by volume or by mass), pg/L, ng/L, µg/L, mg/L, g/L, ppb, ppm, mol/L, eq/L, meq/L and so on. The concentration of trace constituents is usually expressed as micrograms per liter (µg/L) or nanograms per liter (ng/L). For dilute systems, such as those encountered in natural waters and wastewater, in which one liter of sample weighs approximately one kilogram, the units of mg/L or g/m3 are interchangeable with ppm. The terms "parts per billion" (ppb) and "parts per trillion"(ppt) are used interchangeably with µg/L and ng/L, respectively. 2-3 Physical Characteristics The most important physical characteristic of wastewater is its total solids content, which is composed of floating matter, settleable matter, colloidal matter, and matter in solution. Other important physical characteristics include particle size distribution, turbidity, color, transmittance, temperature, conductivity, and density, specific gravity and specific weight. Odor, sometimes considered a physical factor, is discussed in the following section. Solids Wastewater contains a variety of solid materials varying from rags to colloidal material. In the characterization of wastewater, coarse materials are usually removed before the sample is analyzed for solids. The various solids classifications are identified in Tab 2-3. The interrelationship between the various solids fractions found in wastewater is illustrated graphically on Fig. 2-1. The standard test for settleable solids consists of placing a wastewater sample in a 1-liter Imhoff cone and noting the volume of solids in millimeters that settle after a specified time period (1 h). Typically, about 60 percent of the suspended solids in a municipal wastewater are settleable. Total solids (TS) are obtained by evaporating a sample of wastewarer to dryness and measuring the mass of the residue. As shown on Fig. 2-1, a filtration step is used to separate the total suspended solids (TSS) from the total dissolved solids (TDS). Filters with nominal pore sizes varying from 0.45 µm to about 2.0 µm have been used for the TSS test (see Fig. 2-2). Fig. 2-1 Interrelationships of solids found in water and wastewater. In much of the water quality literature, the solids passing through the filter are called dissolved solids

Particle size distribution As noted above, TSS is a lumped parameter. In an effort to understand more nature of the particles that omprise the Tss in wastewater, measurement of particle size is undertaken and lysis of the distribution of particle sizes is conducted Information on particle size is of importance in assessing the effectiveness of treatment processes(e.g. secondary sedimentation, effluent filtration and effluent disinfection) Because the effectiveness of both chlorine and disinfection is dependent on particle size, the determination of particle size has become more important, especially with the move toward greater effluent reuse Information on the size of the biodegradable organic particles is significant from a treatment standpoint, as the biological conversion rate of these particles is dependent on size. The methods can be divided into two general categories: (I)methods based on observation and measurement and (2)methods based separation analysis techniques. The methods used most commonly to study and quantify the paticles in wastewater are: (1)serial filtration, (2)electronic particle counting, and microscopic observation(See Tab ab 2-4 Analytical techniques application to particle size analysis of wastewater contaminants Typical size range, um Observation and measurement Microscopy 0.2->100 Transmisson electron 0.2-100 Scanning electron 0.002-50 Image analysis 0.2->10 Particle counters Conductivity difference Equivalent light scattering 0.005->100 0.2->100 Centrifugation 0.08->100 Field flow fractionation 0.09->100 Gel filtration chromatography 100 Sedimentation 0.05->100 0.0001-1 Pore size Serial Filtration. In the serial filtration method, a tewater sample is passed sequentially through series of membrane filters(see Fig 2-3)with k circular openings of known diameter(typically 12, 8, 5, 3, 1. and 0. I um), and the amount of solids interesting to note is the amount of colloidal material found between 0. I and 1.0 um. If a 0. I-Hm filter had (略) instead of a filter with a nominal pore size equal to or greater than 1.0 um(2.0 ugm as specified in Standard Methods for the TSS test), more than 20 g/L of additional tss would have been measured Fig. 2-3 Definition sketch for the determination of the particle size distribution using serial filtration with membrane filters Ithough some information is gained on the size and distribution of the particles in the wastewater sample little information is gained on the nature of the individual particles. This method is useful in assessing the effectiveness of treatment methods(e. g, microfiltration) for the removal of residual TSS 2-6

2-6 Particle Size Distribution As noted above, TSS is a lumped parameter. In an effort to understand more nature of the particles that comprise the TSS in wastewater, measurement of particle size is undertaken and an analysis of the distribution of particle sizes is conducted. Information on particle size is of importance in assessing the effectiveness of treatment processes (e.g., secondary sedimentation, effluent filtration and effluent disinfection). Because the effectiveness of both chlorine and disinfection is dependent on particle size, the determination of particle size has become more important, especially with the move toward greater effluent reuse. Information on the size of the biodegradable organic particles is significant from a treatment standpoint, as the biological conversion rate of these particles is dependent on size. The methods can be divided into two general categories: (1)methods based on observation and measurement and (2) methods based on separation analysis techniques. The methods used most commonly to study and quantify the paticles in wastewater are: (1) serial filtration, (2) electronic particle counting, and microscopic observation(See Tab 2-4). Tab 2-4 Analytical techniques application to particle size analysis of wastewater contaminants Technique Typical size range,μm Observation and measurement Microscopy Light Transmissoin electron Scanning electron Image analysis Particle counters Conductivity difference Equivalent light scattering Light blockage 0.2- >100 0.2- 100 0.002- 50 0.2- >100 0.2- >100 0.005- >100 0.2- >100 Separation and analysis Centrifugation Field flow fractionation Gel filtration chromatography Sedimentation Membrane filtration 0.08- >100 0.09->100 100 0.05- >100 0.0001-1 Serial Filtration. In the serial filtration method, a wastewater sample is passed sequentially through a series of membrane filters (see Fig. 2-3) with circular openings of known diameter (typically 12, 8, 5, 3, 1. and 0. l μm), and the amount of solids retained in each filter is measured. What is interesting to note is the amount of colloidal material found between 0.1 and 1.0 μm. If a 0. l-μm filter had been used to determine TSS for the treated effluent instead of a filter with a nominal pore size equal to or greater than 1.0 μm (2.0 μgm as specified in Standard Methods for the TSS test), more than 20 mg/L of additional TSS would have been measured. Fig. 2-3 Definition sketch for the determination of the particle size distribution using serial filtration with membrane filters Although some information is gained on the size and distribution of the particles in the wastewater sample, little information is gained on the nature of the individual particles. This method is useful in assessing the effectiveness of treatment methods (e.g., microfiltration) for the removal of residual TSS

Electronic Particle Size Counting. In electronic particle size counting, particles in wastewater are counted by diluting a sample and then passing the diluted sample through a calibrated orifice or past laser presence of the particle. The conductivity is correlated to the size of an equivalent sphere. In a sIml beams. As the particles pass through the orifice, the conductivity of the fluid changes, owing to th fashion, as a particle passes by a laser beam, it reduces the intensity of the laser because of light scattering The reduced intensity is correlated to the diameter of the particle. The particles that are counted are grouped into particle size ranges(e.g,, 0.5 to 2, 2 to 5, 5 to 20 um, etc). In turn, the volume fraction corresponding to each particle size range can be computed Typical effluent volume fraction data from two activated slu treatment plant are reported on Fig. 2-5. As shown, the particle size data for small particles are the same for both treatment plants However, the particle size data for the large particles are quite different owing primarily to the design and operation of the secondary clarification. Particle size information such as that shown on Fig. 2-5, is useful in assessing the performance of condary sedimentation facilities, effluent filtration, and the potential for chlorine and ultraviolet radiation disinfection Fig. 2-4 Imhoff cone used to determine settleable solids in wastewater Solids that accumulate in the bottom of the cone after 60 min are reported as mL/L Microscopic Observation. Particles in wastewater can also be enumerated microscopically by placing a small sample in a particle counting chamber and counting the individual particles. To aid in differentiating different types of particles, various types of stains can be used. In general, microscopic counting of particles is impractical on a routine basis. Nevertheless, this method can be used to qualitatively assess the nature and size of the particles in wastewater. A quantitative assessment of wastewater particles can be btained with a microscope by means of a process called optical imaging A small sample of wastewater is placed microscope slide. The images of the o Plant 1-3.4 m(11 ft)side water depth Plant 2-5.5 m(18 ft) side water depth wastewater particles are collected with a video camera attached to a microscope and transmitted to a computer where various measurements of the wastewater particles 5 Volume fraction of particle found in the effluent from two activated-sludge plants with clarifiers having diferent side water depths Log of particle diameter, dp um The types of measurements that can be obtained are dependent on the computer software but typically include the mean, minimum, and maximum diameter, the aspect ratio(length to width ratio), the circumference, the surface area, the volume, and the centroid of various particles. Particle imaging greatly reduces the time required to measure various characteristics of wastewater particles, but the cost of the software and equipment is often prohibitive for many small laboratories Turbidity Turbidity a measure of the light-transmitting properties of water. is another test used to indicat quality of waste discharges and natural waters with respect to colloidal and residual suspended matter. measurement of turbidity is based on comparison of the intensity of light scattered by a sample to the light 2-7

2-7 Electronic Particle Size Counting. In electronic particle size counting, particles in wastewater are counted by diluting a sample and then passing the diluted sample through a calibrated orifice or past laser beams. As the particles pass through the orifice, the conductivity of the fluid changes, owing to the presence of the particle. The conductivity is correlated to the size of an equivalent sphere. In a similar fashion, as a particle passes by a laser beam, it reduces the intensity of the laser because of light scattering . The reduced intensity is correlated to the diameter of the particle. The particles that are counted are grouped into particle size ranges (e.g., 0.5 to 2, 2 to 5, 5 to 20 μm, etc). In turn, the volume fraction corresponding to each particle size range can be computed. Typical effluent volume fraction data from two activated sludge treatment plant are reported on Fig. 2-5. As shown, the particle size data for small particles are the same for both treatment plants. However, the particle size data for the large particles are quite different, owing primarily to the design and operation of the secondary clarification . Particle size information, such as that shown on Fig. 2-5 , is useful in assessing the performance of secondary sedimentation facilities, effluent filtration, and the potential for chlorine and ultraviolet radiation disinfection. Fig. 2-4 Imhoff cone used to determine settleable solids in wastewater.Solids that accumulate in the bottom of the cone after 60 min are reported as mL/L Microscopic Observation. Particles in wastewater can also be enumerated microscopically by placing a small sample in a particle counting chamber and counting the individual particles. To aid in differentiating different types of particles, various types of stains can be used. In general, microscopic counting of particles is impractical on a routine basis. Nevertheless, this method can be used to qualitatively assess the nature and size of the particles in wastewater. A quantitative assessment of wastewater particles can be obtained with a microscope by means of a process called optical imaging. A small sample of wastewater is placed on a microscope slide. The images of the wastewater particles are collected with a video camera attached to a microscope and transmitted to a computer where various measurements of the wastewater particles can be assessed. Fig. 2-5 Volume fraction of particle sizes found in the effluent from two activated-sludge plants with clarifiers having different side water depths The types of measurements that can be obtained are dependent on the computer software but typically include the mean, minimum, and maximum diameter, the aspect ratio (length to width ratio), the circumference, the surface area, the volume, and the centroid of various particles. Particle imaging greatly reduces the time required to measure various characteristics of wastewater particles, but the cost of the software and equipment is often prohibitive for many small laboratories. Turbidity Turbidity, a measure of the light-transmitting properties of water, is another test used to indicate the quality of waste discharges and natural waters with respect to colloidal and residual suspended matter. The measurement of turbidity is based on comparison of the intensity of light scattered by a sample to the light

scattered by a reference suspension under the same conditions. Formazin suspensions are used as the primary reference standard. The results of turbidity measurements are reported as nephelometric turbidity units(NTU Colloidal matter will scatter or absorb light and thus prevent its transmission. It should be noted that the presence of air bubbles in the fluid will cause erroneous turbidity readings. In general. there wastewater. There is. however. a reasonable relationship between turbidity and total suspended solids for the settled and filtered secondary effluent from the activated sludge process. The specific value of the conversion factor will vary for each treatment, depending primarily on the operation of the biological treatment process. The conservation factors for settled secondary effluent and for secondary effluent filtered with a granular-medium depth filter will typically vary from 2. 3 to 2. 4 and 1.3 to 1.6, respectively One of the problems with the measurement of turbidity(especially low values in filtered effluent)is the high degree of variability observed, depending on the light source(incandescent light versus light-emitting diodes) and the method of measurement (reflected versus transmitted light). Another problem often encountered is the light-absorbing properties of the suspended material. However, turbidity readings at a given facility can be used for process control. Some on line turbidity meters used o monitor performance of microfiltration units are affected by the air used to clean the membranes Color Historically, the term "condition"was used along with composition and concentration to describe wastewater. Condition refers to the age of the wastewater, which is determined qualitatively by its color and odor. Fresh wastewater is usually a brownish-gray color. however. as the travel time in the collection svstem increases, and more anaerobic conditions develop. the color of the wastewater changes he wastewater is often described as septic. Some industrial wastewaters may also add color to domestic wastewater. In most cases. the gray. dark gray. and black color of the wastewater is due to the formation of metallic sulfides, which form as the sulfide produced under anaerobic conditions reacts with the metals in the wastewater Absorption/Transmittance The absorbance of a solution is a measure of the amount of light, of a specified wave-length, that is absorbed by the constituents in a solution. Absorbance, measured using a spectrophotometer and a fixed path length(usually 1.0 cm), is given by following relationship Where A-absorbence absorbence unit, a u /cm lo-Initial detector reading for the blank (i.e. distilled water) after passing through a solution of 1- Final detector reading for the blank (i.e. distilled water)after passing through Absorbance is measured with a spectrophotometer using a specified wavelength, typically 254 nm Typical absorbance values for various wastewater at 254 nm are 1. Primary: 0.5 to 0.8/cm 2. Secondary: 0.3 to 0. 5/cm 3. Nitrified secondary: 0.25 to 0.45/cm 4. Filtered secondary: 0.02 to 0.40/cm Transmittance T, %=(o)X100 Activated sludge goon G50 Fig. 2-6 Transmittance 20 240 280290300310 Wavelength, nm

2-8 scattered by a reference suspension under the same conditions. Formazin suspensions are used as the primary reference standard. The results of turbidity measurements are reported as nephelometric turbidity units (NTU). Colloidal matter will scatter or absorb light and thus prevent its transmission. It should be noted that the presence of air bubbles in the fluid will cause erroneous turbidity readings. In general, there is no relationship between turbidity and the concentration of total suspended solids in untreated wastewater. There is, however, a reasonable relationship between turbidity and total suspended solids for the settled and filtered secondary effluent from the activated sludge process. The specific value of the conversion factor will vary for each treatment, depending primarily on the operation of the biological treatment process. The conservation factors for settled secondary effluent and for secondary effluent filtered with a granular-medium depth filter will typically vary from 2.3 to 2.4 and 1.3 to 1.6, respectively. One of the problems with the measurement of turbidity (especially low values in filtered effluent) is the high degree of variability observed, depending on the light source (incandescent light versus light-emitting diodes) and the method of measurement (reflected versus transmitted light). Another problem often encountered is the light-absorbing properties of the suspended material. However, turbidity readings at a given facility can be used for process control. Some on line turbidity meters used to monitor the performance of microfiltration units are affected by the air used to clean the membranes. Color Historically, the term "condition" was used along with composition and concentration to describe wastewater. Condition refers to the age of the wastewater, which is determined qualitatively by its color and odor. Fresh wastewater is usually a brownish-gray color. However, as the travel time in the collection system increases, and more anaerobic conditions develop, the color of the wastewater changes sequentially from gray to dark gray, and ultimately to black. When the color of the wastewater is black, the wastewater is often described as septic. Some industrial wastewaters may also add color to domestic wastewater. In most cases, the gray, dark gray, and black color of the wastewater is due to the formation of metallic sulfides, which form as the sulfide produced under anaerobic conditions reacts with the metals in the wastewater. Absorption/Transmittance The absorbance of a solution is a measure of the amount of light, of a specified wave-length, that is absorbed by the constituents in a solution. Absorbance, measured using a spectrophotometer and a fixed path length (usually 1.0 cm), is given by following relationship: A = log(I0/I) Where A-absorbence, absorbence unit, a.u./cm I0-Initial detector reading for the blank (i.e. distilled water) after passing through a solution of known depth I- Final detector reading for the blank (i.e. distilled water) after passing through solution containing constituents of interest Absorbance is measured with a spectrophotometer using a specified wavelength, typically 254 nm. Typical absorbance values for various wastewater at 254 nm are: 1. Primary:0.5 to 0.8/cm 2. Secondary:0.3 to 0.5/cm 3. Nitrified secondary:0.25 to 0.45/cm 4. Filtered secondary:0.02 to 0.40/cm Transmitttance T, % = (I/Io)×100 Fig. 2-6 Transmittance measured at various wavelengths for

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 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 waters, these effects are magnified. It should also be realized that a sudden change in tempe 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 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 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 29

2-9 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

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 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 mola 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 CaCO=[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/me 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 desirabe 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 2-10

2-10 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

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