He is a registered professional engineer, a member of the American Academy of Environmental Engineers and the Water Environment Federation. Types of Mixers Used for Maintenance of Suspended Solids in Wastewater Treatment and Chemical Mixing 335 .
Preface
- A new view of wastewater as a source of energy, nutrients, and potable water
- More stringent discharge requirements related to nitrogen and phosphorus;
- Enhanced understanding of the fundamental microbiology and physiology of the microorganisms responsible for the removal of nitrogen and phosphorus and other
- An appreciation of the importance of the separate treatment of return flows with respect to meeting more stringent standards for nitrogen removal and opportunities
Harold Leverenz of the University of California, Davis, is singled out for special acknowledgment for outstanding contributions to the development of graphics used throughout the text, chapter review. Edward Schroeder professor emeritus of the University of California at Davis reviewed portions of Chaps.
Acknowledgments
Many current and former AECOM engineers contributed to the development of the manuscript by providing design information and by reviewing certain sections of the text. Finally, the production of this textbook could not have been completed without the guidance and assistance of the following individuals.
WORKING TERMINOLOGY
The material presented in the first five sections of this chapter is intended to serve as an introduction to the subject of wastewater treatment and to provide a basis for the analysis of the unit processes that will be presented in subsequent chapters. The material presented in the last five sections of this chapter is intended to serve as a review for those readers who have already taken courses in process analysis and to provide an introduction to the subject for those new to process analysis .
1–1 EVOLUTION OF WASTEWATER TREATMENT
In general, from about 1900 to the early 1970s, treatment objectives involved (1) the removal of suspended and floating material, (2) the treatment of biodegradable organic matter, and (3) the elimination of pathogenic organisms. The need to become more efficient in resource use and the distribution of anthropogenic compounds in the environment has become a central issue in almost all aspects of society.
1–2 EVOLUTION OF REGULATIONS OF SIGNIFICANCE TO WASTEWATER ENGINEERING
By improving and optimizing existing processes and introducing new approaches and technologies, we will create the foundations for a sustainable approach to waste water management. The definition of secondary treatment is given in Table 1-2 and includes three main effluent parameters: biodegradable organic matter expressed as five-day biochemical oxygen demand (5-d BOD); total suspended solids (TSS); and hydrogen ion concentration expressed as pH.
Summary of significant U.S. Federal regulations that affect wastewater management
In 1987, Congress passed the Water Quality Act of 1987 (WQA), the first major revision of the CWA. With the implementation of the TMDL rule, the focus on water quality shifts from technology-based controls to maintaining ambient water quality.
Minimum national standards for
The TMDL represents the maximum amount of a pollutant that a water body can accept and still meet water quality standards. In addition to the requirements established under the U.S. Water Quality Act of 1987
1–3 CHARACTERISTICS OF WASTEWATER
EPA and other federal, state and local regulations must be taken into account in the planning, design, construction and operation of wastewater treatment plants. As noted earlier, the focus of wastewater treatment developments in the twentieth century has been on the removal of constituents considered pollutants when discharged into the environment.
1–4 CLASSIFICATION OF WASTEWATER TREATMENT METHODS
When using separate rainwater collection systems, it has been found that different amounts of wastewater can be present in the rainwater, depending on local conditions. In the twenty-first century, there has been a paradigm shift in the way wastewater is viewed.
Physical, chemical, and biological
Treatment methods in which the removal of constituents is achieved by the addition of chemicals or other chemical reactions are known as chemical unit processes. Treatment methods in which the removal of constituents is caused by biological activity are known as biological unit processes.
1–5 APPLICATION OF TREATMENT METHODS
For example, adsorption involves the removal of specific compounds from wastewater onto solid surfaces using the attractive forces between bodies. To further protect the environment in some critical areas, stricter standards have been directed at removing nutrients and pathogens and achieving lower levels of oxygen demand than is currently possible with secondary treatment techniques.
Levels of wastewater treatment
In general, the complexity of the treatment process flow diagram will depend on the constituents to be removed and the levels of removal required. For the most part, the methods and systems reported in Table 1-5 are used to treat the liquid portion of wastewater.
Unit processes used to remove constituents of
Residuals processing and disposal methods
Biological treatment is used to remove BOD5 and TSS disinfection is used to control microorganisms. 1–2(d) are representative of the many different processes used to treat sludge, as reported in Table 1–5.
1–6 STATUS OF WASTEWATER TREATMENT IN THE UNITED STATES
These data are useful in forming an overall picture of the current status of wastewater treatment in the United States. It is also interesting to note the shifts that have occurred in the level of treatment.
Number of wastewater treatment facilities in the United States by flow range in 1996 a and 2008 b
More than half of the current design capacity is in installations that provide more than secondary treatment. The number of treatment plants that provide more than secondary treatment has also increased from 4428 to 5071.
1–7 INTRODUCTION TO PROCESS ANALYSIS
General word statement
- The corresponding simplified word statement is
- Prepare a simplified schematic or flow diagram of the system or process for which the mass balance is to be prepared
- Draw a system boundary to define the limits over which the mass balance is to be applied. Proper selection of the system boundary is extremely important because, in
- List all of the pertinent data and assumptions that will be used in the preparation of the materials balance on the schematic or flow diagram
- List all of the rate expressions for the biological or chemical reactions that occur in the process
- Select a convenient basis on which the numerical calculations will be based
- the volumetric flowrate in to and out of the control volume is constant;
- the liquid within the control volume is not subject to evaporation (constant volume);
- the liquid within the control volume is mixed completely;
- a chemical reaction involving a reactant A is occurring within the reactor; and 5. the rate of change in the concentration of the reactant A that is occurring within the
- Simplified word statement
Prepare a simplified schematic or flow diagram of the system or process for which the mass balance is to be prepared. To apply a mass balance analysis to the liquid content of the reactor shown in FIG.
1–8 REACTORS USED IN WASTEWATER TREATMENT
Complete-mix and plug-flow reactors are the two reactor types most commonly used in the field of wastewater treatment. The ideal hydraulic flow characteristics of complete mixed and plug flow reactors are shown in Fig.
1–9 MODELING IDEAL FLOW IN REACTORS
Principal applications of reactor types used
Simplified word statement
Under ideal plug flow conditions, t, the measured residence time, should equal t, the theoretical residence time (V/Q). 1–5(b-2), it will be instructive to prepare a material balance for an ideal plug-flow reactor (without axial dispersion) in which the concentration C of the nonreactive tracer is uniformly distributed over the cross-sectional area of the control volume.
Symbolic representation (refer to Fig. 1–6) 0C
1–10 INTRODUCTION TO PROCESS KINETICS
- Consecutive reactions
- Transport of reactants from the bulk fluid to the fluid-solid interface (external sur- face of catalyst particle)
- Intraparticle transport of reactants into the catalyst particle (if it is porous) 3. Adsorption of reactants at interior sites of the catalyst particle
- Chemical reaction of adsorbed reactants to adsorbed products (surface reaction) 5. Desorption of adsorbed products
- Transport of products from the interior sites to the outer surface of the catalyst particle
From the law of mass action it can be shown that the reaction rate for a given reaction is proportional to the remaining concentration of the reactants. The temperature dependence of the rate constant is given by the van't Hoff-Arrhenius relationship.
Common constituent conversion and separation processes (i.e., fate processes) in the environment and the constituents affected
The application of various rate expressions to wastewater treatment is described in the following discussion. The terms in the denominator in Eq. 1–55) correspond to the coefficient of friction for a particle as defined by Stokes' law.
Integration and differential methods used to determine reaction rate coefficients
Determination of reaction order and reaction rate coefficient Given the following set of data obtained using a batch reactor [see Fig. 1–4(a)], determine the order of the reaction and the rate coefficient of the reaction using the integration and differential methods.
1–11 INTRODUCTION TO TREATMENT PROCESS MODELING
The general form of the mass balance equation for a perfect mixture reactor as shown in Fig. At steady state, the mass balance for the second perfect mixture reactor is 05QC12QC22kC22V.
Required reactor volumes expressed
Values of kt in the Wehner and Wilhelm equation (Eq. 1–85) versus percent remaining for various distribution factors and first-order kinetics for a plug flow reactor. It is clear that axial dispersion can affect the predicted performance of a treatment process designed to function as an ideal plug flow reactor.
PROBLEMS AND DISCUSSION TOPICS
Using these data, determine the activation energy E and the value of the rate constant at 15 °C. 1–16 The reaction rate for an enzyme-catalyzed substrate in a batch reactor can be described by the following relationship.
Coliform organisms are common in the environment and in the feces of humans and warm-blooded animals. Faecal coliforms A thermo-tolerant subgroup of total coliform group found in the intestinal tract of humans and warm-blooded animals.
2–1 WASTEWATER CHARACTERIZATION
An understanding of the nature of waste water is essential in the design and operation of collection, treatment and recycling facilities and in the technical management of environmental quality. The material in this chapter is organized in a manner similar to that used in Standard Methods (2012), the standard reference work for wastewater characterization in environmental engineering.
2–2 SAMPLING AND ANALYTICAL PROCEDURES
To promote this understanding, the information in this chapter is presented in ten sections that address (1) introduction to wastewater characterization, (2) sampling and analytical procedures, (3) physical properties, (4) inorganic nonmetallic constituents, (5) metallic constituents, (6) aggregate organic constituents, (7) individual organic constituents and compounds, (8) microbial characteristics, (9) radionuclides, and (10) toxicity tests.
Common analyses used to assess the constituents found in wastewater a
To assess the suitability of the wastewater for reuse and for toxicity effects during treatment. UBOD (also BODu, BODL ) A measure of the amount of oxygen required to biologically stabilize a waste.
Principal constituents of concern in
Reproducible: The data obtained should be reproducible by others following the same sampling and analysis protocols. Useful: The data can be used to achieve the objectives of the monitoring plan (Pepper et al., 1996).
The concentration of a component that produces a signal greater than five times the signal-to-noise ratio of the instrument. The results of the analysis of waste water samples are expressed in physico-chemical measurement units.
Units commonly used to express analytical
The calculation of the activity coefficient is illustrated in Example 2-3 after the discussion of ionic strength and solubility. The calculation of the activity coefficient is illustrated in Example 2-3, after the discussion of ionic strength and solubility.
2–3 PHYSICAL PROPERTIES
Definitions for solids found in wastewater a
- The measured values of TSS are dependent on the type and pore size of the filter used in the analysis
- Depending on the sample size used for the determination of TSS, auto filtration, where the suspended solids that have been intercepted by the filter also serve as a
- Depending on the characteristics of the particulate matter, small particles may be removed by adsorption to material already retained by the filter
- Because the number and size distribution of the particles that comprise the measured value is unknown, TSS is a lumped parameter
More TSS will be measured as the pore size of the filter used decreases. The measured TSS values depend on the type and pore size of the filter used in the analysis.
Representative analytical techniques
Definition sketch for determination of particle size distribution (by mass) using batch filtration with membrane filters. Nevertheless, this method can be used to qualitatively assess the nature and size of particles in wastewater.
2–4 INORGANIC NONMETALLIC CONSTITUENTS
The organic fraction consists of a complex mixture of components including amino acids, amino sugars and proteins (polymers of amino acids). During digestion, organic nitrogen is converted into ammonium through the action of heat and acid.
Definition of the various terms used to
Total Kjeldahl nitrogen (TKN) is determined in the same way as organic nitrogen, except that ammonia is not removed before the digestion step. An alternative method is the perfulphate digestion procedure in which organic nitrogen is oxidized to nitrate nitrogen in Table 2-6 above.
The Henry's Law constant is a function of the type of gas, temperature, and nature of the liquid. The Henry's Law constant found in the literature will vary depending on the date of reference and the specific method used to estimate the constant.
Henry’s law constants at 20°C, unitless
In the literature, the unitless form of Henry's law is often used to calculate the solubility of trace gases in water or wastewater. It should be noted that the values for the Henry's law constant given in Tables 2–7 will vary depending on the source and the method used to derive them.
Major odorous compounds and their corresponding odor thresholds associated with untreated wastewater a
Odors have been identified as the main concern of the public regarding the implementation of wastewater treatment facilities. Within the last few years, the control of odors has become an important consideration in the design and operation of facilities for the collection, treatment and disposal of wastewater, particularly with regard to the public acceptance of these facilities.
Factors that must be considered for the
In extreme situations, offensive odors can lead to the deterioration of personal and community pride, disrupt human relationships, discourage capital investment, lower socio-economic status and slow growth. Sensory methods involve exposing human subjects (often a panel of subjects) to odors diluted with odor-free air, and the number of dilutions required to minimize an odor.
The "threshold odor number" (TON) corresponds to the maximum dilution of the sample with odorless water at which the odor is barely detectable. Sensory determination of the minimum threshold concentration of an odor is subject to many errors.
Types of errors in the sensory detection of
2–54) is linearized and plotted, the slope of the line of best fit corresponds to n. The concentration of scented air increases in successive cups, typically doubling in each successive cup (ASTM, 2004).
2–5 METALLIC CONSTITUENTS
Sources of trace metals in wastewater include discharges from commercial and industrial activities, household products such as detergents and personal care products, and groundwater infiltration.
Typical metallic wastes produced by commercial, industrial, and agricultural activities that have been classified as priority pollutants
Metals important in the treatment, reuse, and disposal of treated wastewater and biowaste are summarized in Table 2–12. As the use of treated wastewater for irrigation and landscape watering increases, a variety of Tables 2-12 emerges.
Metals of importance in wastewater management a
Although macro and micro amounts of metals are required for proper growth, the same metals can be toxic when present in high concentrations. Different classes of metals are defined as (1) dissolved metals, those metals present in unacidified samples passing through a 0.45 mm membrane filter; (2) suspended metals, those metals present in unacidified samples retained on a 0.45 mm membrane filter; (3) total metals, total dissolved and suspended metals, or metal concentration determined in an unfiltered sample after digestion; and (4) acid-extractable metals, those metals in solution after an unfiltered sample is treated with a hot dilute mineral acid (Standard Methods, 2012).
2–6 AGGREGATE ORGANIC CONSTITUENTS
This determination involves the measurement of dissolved oxygen used by microorganisms in the biochemical oxidation of organic matter. Despite the widespread use of the BOD test, it has a number of limitations, as discussed later in this section.
Typical discharge limits for toxic
Sketch of the definition for the biochemical oxygen demand load containing carbon and nitrogen in a waste sample. In effect, CBOD is a measure of the oxygen demand due to oxidizing carbon in the sample.
Effect of the size of the biodegradable
As noted in Table 2–14, the observed BOD reaction rate coefficients are significantly affected by the size of the particles in wastewater. The lack of stoichiometric validity at all times reduces the usefulness of the test results.
Comparison of ratios of various parameters
In the presence of alkalis, such as sodium hydroxide, glycerine is released and alkali salts of the fatty acids are formed. The composition of the cell biomass is C5H7O2N (Hoover and Porges, 1952) with an ash content of 3 percent.
2–7 INDIVIDUAL ORGANIC COMPOUNDS
Unregulated trace organic compounds in question are largely derived from (1) human and veterinary antibiotics, (2) human prescription and nonprescription drugs, (3) industrial and domestic wastewater products, and (4) sex and steroid hormones. Volatile organic compounds are a major source of concern because (1) once such compounds are in the vapor state, they are much more mobile and therefore more likely to be released to the environment; (2) the presence of some of these compounds in the atmosphere may pose a significant public health risk; and (3) they contribute to a general increase in reactive hydrocarbons in the atmosphere, which can lead to the formation of photochemical oxidants.
Representative organic constituents
It should also be noted that many individual organic constituents can be determined by two or more of the above methods (Standardne methods, 2012). More than 180 individual organic compounds can be determined using one or more of the above methods.
2–8 RADIONUCLIDES IN WASTEWATER
Typical classes of organic compounds whose members are identified as individual compounds
The main source of natural radionuclides is uranium ore (U3O8), and its abundance in the earth's crust is 1 part per 1012 parts. No technologies have been reported in the literature for the removal of radionuclides in wastewater.
Isotopes Found in Wastewater and Sludge in the State of Washington
2–9 BIOLOGICAL CONSTITUENTS
Possible treatment technologies
A general description of the microorganisms found in wastewater is given in Table 2–21 using the terminology introduced in the previous sections. Data on the form, resistant form, and size of the microorganisms of interest are shown in Table 2-22.
Comparison of prokaryote and
Typical descriptions of the microorganisms
Typical data on the shape, size, and
An understanding of the methods used to both enumerate and identify microorganisms is important to assess the significance of the data reported in the literature. The use of the pour plate method for counting bacteriophage is illustrated in Fig.
Representative methods used to enumerate and identify microorganisms and to assess performance of various treatment processes a
To aid in the filtration process, a vacuum line is attached to the bottom of the filter apparatus. The presence-absence (P-A) test for coliform organisms is a modification of the multiple tube fermentation technique described above.
Infectious agents potentially present in untreated domestic wastewater a
Many species of harmless bacteria colonize the human intestinal tract and are routinely shed in the feces. Because pathogenic bacteria are present in the feces of infected individuals, domestic wastewater contains a wide range and concentration range of nonpathogenic and pathogenic bacteria.
Microorganism
Because these organisms are highly contagious, they are responsible for many thousands of deaths each year in areas with poor sanitation, especially in the tropics. One of the most common bacterial pathogens found in domestic wastewater is the genus Salmonella.
Bacterial pathogens of human origin commonly cause diseases of the gastrointestinal tract, such as typhoid and paratyphoid fever, dysentery, diarrhea, and cholera. The Salmonella group contains a wide variety of species that can cause disease in humans and animals.
The indicator organism must be present when fecal contamination is present
The numbers of indicator organisms present should be equal to or greater than those of the target pathogenic microorganism
The indicator organism must exhibit the same or greater survival characteristics in the environment as the target pathogen organism for which it is a surrogate
Typical pathogen survival times at
The isolation and quantification procedure for the indicator organism must be faster, simpler, and less expensive than that of the target pathogen
The organism should be a member of the intestinal microflora of warm-blooded animals
Specific organisms that have been used
Thus, over the years, the presence of coliform bacteria in environmental samples has been taken as an indication that pathogenic organisms associated with feces (eg, viruses) may also be present. The absence of coliform bacteria is taken as an indication that the water is free of disease-producing organisms.
Indicator organisms used in establishing
The coliform group of bacteria is commonly found in the environment in soil or vegetation and in the intestines and feces of humans and warm-blooded animals. Faecal coliforms, subgroup of the total coliform group, are found in large quantities in the intestines and feces of humans and warm-blooded animals.
2–10 TOXICITY
- Assess the suitability of environmental conditions for aquatic life
- Establish acceptable receiving water concentrations for conventional parameters (such as dissolved oxygen, pH, temperature, salinity, or turbidity)
- Study the effects of water quality parameters on wastewater toxicity
- Assess the toxicity of wastewater to one or more freshwater, estuarine, or marine test organisms
- Establish relative sensitivity of a group of standard aquatic organisms to effluent as well as standard toxicants
- Assess the degree of wastewater treatment needed to meet water quality requirements
- Determine the effectiveness of wastewater treatment methods
- Establish permissible effluent discharge rates
- Determine compliance with federal and state water quality standards and water quality criteria associated with NPDES permits (Standard Methods, 2012)
One of the main sources of toxicity is disinfection by-products formed during disinfection of treated wastewater with chemicals such as chlorine, chlorine dioxide and ozone. The use of the term "median tolerance limit" has been superseded by the terms median lethal concentration (LC50) and median effective concentration (EC50).
Typical examples of short-term chronic
Methods used to analyze both short-term (acute) and long-term (chronic) toxicity data are considered in the following discussion. The median lethal concentration (LC50) when mortality is the test endpoint, or median effective concentration (EC50) when a sublethal effect (eg, immobilization, fatigue in swimming, "avoidance") is the endpoint, is typically used to define acute toxicity (Stephen, 1982).
The chronic value (ChV) is calculated as the geometric mean of the LOEC and NOEC. TUa is defined as the reciprocal of the wastewater concentration that caused the acute effect by the end of the exposure period.
Results of Acute Toxicity Tests
EXAMPLE 2–14 Application of Toxicity Test Results An initial critical dilution of 100:1 is achieved for a treated effluent discharged to marine receiving waters. Based on the toxicity test results, Champia parvula was found to be the most sensitive acute endpoint (2.59 percent effluent) as measured by EC50, and also the most sensitive chronic endpoint of the species (1.0 percent) measured from NOEC.
Results of Chronic Toxicity Tests