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Hazardous_Waste_Management_An_Introduction_----_Hazardous_Waste_Management_Chapter_07.pdf

c h a p t e r

Hazardous waste regulations apply to the storage, transportation, and treatment of hazardous waste, but in general terms; these regula-tions do not apply when the waste is discharged to an air pollution control system or a wastewater treatment system. That does not mean the waste ceases to be hazardous when discharged to another system; it means the discharge has crossed a “regulatory boundary.” Air discharges are regu- lated under the Clean Air Act and waste water discharges are regulated under the Clean Water Act.

7 In This Chapter

●● U.S. wastewater regulations ●● Sources of contamination of wastewaters ●● Classification of water pollutants ●● Characteristics of wastewater ●● Wastewater treatments ●● U.S. storm water regulations ●● Case study and field article

WasteWater ManageMent

Numerous portions of this chapter have been quoted directly with permission from Dr. S. Amal Raj, Introduction to Environmental Science and Technology. Laxmi Publications Pvt. Ltd. 2008. 42-56.

VanGuilder, C. (2018). Hazardous waste management : An introduction. ProQuest Ebook Central <a onclick=window.open('http://ebookcentral.proquest.com','_blank') href='http://ebookcentral.proquest.com' target='_blank' style='cursor: pointer;'>http://ebookcentral.proquest.com</a> Created from apus on 2020-11-09 03:03:19.

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This chapter provides basic information on the treatment of wastewater as it pertains to hazardous waste. These sources are primarily from indus- tries and wastewater treatment plants.

First, let’s discuss the regulations governing wastewater.

7.1 U.S. WASTEWATER REGULATIONS

The first major law governing water pollution was the Federal Water Pollution Control Amendment of 1948, passed as a measure to govern and control water pollution. Significant amendments were introduced in the Clean Water Act, passed on October 18, 1972, which set up the National Pollutant Discharge Elimination System (NPDES), creating permits for point sources of pollution. These permits applied to municipal and indus- trial wastewater discharges [WIKI 11f].

“The 1972 Amendments to the Federal Water Pollution Control Act (Public Law 92-500), known as the Clean Water Act (CWA), established the foundation for wastewater discharge control in this country. The CWA’s pri- mary objective is to ‘restore and maintain the chemical, physical and bio- logical integrity of the nation’s waters.’

The CWA established a control program for ensuring that communities have clean water by regulating the release of contaminants into our country’s waterways. Permits that limit the amount of pollutants discharged are required of all municipal and industrial wastewater dischargers under the National Pollutant Discharge Elimination System (NPDES) permit pro- gram. The NPDES permit process relies on self-monitoring and reporting by the permit holder vis Discharge Monitoring Reports (DMRs). In addition, a construction grants program was set up to assist publicly owned wastewater treatment works build the improvements required to meet these new limits.

The 1987 Amendments to the CWA established State Revolving Funds (SRF) to replace grants as the current principal federal funding source for the construction of wastewater treatment and collection systems.

Over 75 percent of the nation’s population is served by centralized wastewater collection and treatment systems. The remaining population uses septic or other onsite systems. Approximately 16,000 municipal waste- water treatment facilities are in operation nationwide. The CWA requires that municipal wastewater treatment plant discharges meet a minimum of

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Wastewater Management • 179

‘secondary treatment.’ Over 30 percent of the wastewater treatment facili- ties today produce cleaner discharges by providing even greater levels of treatment than that offered by secondary treatment” [EPA 04, p.4].

“Water pollution can be defined as any alteration in physical, chemical, or biological properties of water, rendering the water harmful to public health and the environment” [Raj 08].

Nonpoint sources, such as storm water runoff and runoff from agricul- tural areas, were not addressed in the 1972 amendments. Although this text does not deal with nonpoint sources in detail, an overview of the various categories of nonpoint sources is given in Section 7.3. A brief but useful and informative history of the federal storm water regulatory program is sum- marized in Section 7.6 of this chapter.

7.2 SOURCES OF CONTAMINATION OF WASTEWATER

“For convenience, the sources of contamination of water can be classi- fied as natural and anthropogenic (man-made). [We] will not deal with nat- ural sources, since the subject is hazardous waste, which is entirely man-made” [Raj 08].

Anthropogenic (Man-Made) Sources “Man-made sources of wastewater are the result of industrial, domes-

tic, agricultural, and mining activities of humans, and can be characterized as follows:

●■ Industrial sources: The discharges from most industries are subject to industrial pretreatment requirements where necessary, and then dis- charged to a publicly owned treatment works (POTW) or discharged di- rectly to surface water under a NPDES permit. Examples of industries that generate fairly large quantities of wastewater are: pulp and paper mills, tanneries, and chemical manufacturing facilities.

●■ Domestic sources: For the most part, domestic wastewater comes from residences, commercial offices buildings, schools, and other insti- tutions. There can be hazardous constituents in these wastewaters, such as household cleaners, laboratory wastes from schools, and household hazardous wastes dumped down the sewer.

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●■ Agricultural sources: can include soil and silt from erosion, agricul- tural run-off, and synthetic fertilizers, herbicides, and insecticides. Out of these pollutants, only the pesticides (herbicides and insecticides) might be hazardous wastes. One of the problems with several synthetic pesticides, particularly the chlorinated hydrocarbons (DDT, endrin, chlordane, etc.) is that they are persistent in the environment, meaning they are resistant to degradation, so they stay in the environment in their original form for a very long time.

●■ Mining activities: Mining operations can produce soluble toxic mate- rial, acid drainage, and silt and other fines in runoff” [Raj 08].

Fines refers to the finely crushed or powdered particles of ore found in a mixture of particulates of varying sizes.

7.3 CLASSIFICATION OF WATER POLLUTANTS

“To fully understand the effects of water pollution and the technologies applied to its control, it is useful to classify pollutants into various categories. First, as mentioned earlier, a pollutant can be classified according to its nature of origin, as either a point source or a nonpoint (dispersed) source” [Raj 08].

Point Sources The treatments of discrete discharges from pipes and other conduits

from identifiable point sources, such as manufacturing plants, businesses, industries, and wastewater treatment plants serving all of these industries, together with residences, are discussed in other chapters of this text. To briefly review, examples of nonresidential point sources include: chemical manufacturing facilities, tanneries, electroplating facilities, auto body shops, laboratories, and mining operations. In this section, we will deal pri- marily with nonpoint sources.

Nonpoint Sources Some of the nonpoint sources of concern in the hazardous waste

field are:

Oxygen-Demanding Substances

“Dissolved oxygen is a key element in water quality that is necessary to support aquatic life. A demand is placed on the natural supply of dissolved oxygen by many pollutants in wastewater.

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Wastewater Management • 181

This is called biochemical oxygen demand, or BOD, and is used to measure how well a sewage treatment plant is working. If the effluent, the treated wastewater produced by a treatment plant, has a high content of organic pollutants or ammonia, it will demand more oxygen from the water and leave the water with less oxygen to support fish and other aquatic life.

Organic matter and ammonia are ‘oxygen-demanding’ substances. Oxy- gen-demanding substances are contributed by domestic sewage and agri- cultural and industrial wastes of both plant and animal origin, such as those from food processing, paper mills, tanning, and other manufacturing pro- cesses. These substances are usually destroyed or converted to other com- pounds by bacteria if there is sufficient oxygen present in the water, but the dissolved oxygen needed to sustain fish life is used up in this break down process” [EPA 04, p.8].

Pathogens

Pathogens are agents that cause disease, like bacteria, fungi, and viruses. “Disinfection of wastewater and chlorination of drinking water supplies has reduced the occurrence of waterborne diseases such as typhoid fever, chol- era, and dysentery, which remain problems in underdeveloped countries while they have been virtually eliminated in the U.S.

Infectious micro-organisms, or pathogens, may be carried into surface and groundwater by sewage from cities and institutions, by certain kinds of industrial wastes, such as tanning and meat packing plants, and by the con- tamination of storm runoff with animal wastes from pets, livestock and wild animals, such as geese or deer. Humans may come in contact with these pathogens either by drinking contaminated water or through swimming, fishing, or other contact activities. Modern disinfection techniques have greatly reduced the danger of waterborne disease.

Nutrients

Carbon, nitrogen, and phosphorus are essential to living organisms and are the chief nutrients present in natural water. Large amounts of these nutrients are also present in sewage, certain industrial wastes, and drainage from fertilized land. Conventional secondary biological treatment processes do not remove the phosphorus and nitrogen to any substantial extent—in fact, they may convert the organic forms of these substances into mineral

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182 • hazardous Waste Management, Second edition

form, making them more usable by plant life. When an excess of these nutrients over stimulates the growth of water plants, the result causes unsightly conditions, interferes with drinking water treatment processes, and causes unpleasant and disagreeable tastes and odors in drinking water. The release of large amounts of nutrients, primarily phosphorus but occa- sionally nitrogen, causes nutrient enrichment which results in excessive growth of algae. Uncontrolled algae growth blocks out sunlight and chokes aquatic plants and animals by depleting dissolved oxygen in the water at night” [EPA 04, p. 8].

“The release of nutrients in quantities that exceed the affected water body’s ability to assimilate them results in a condition called eutrophication or cultural enrichment” [EPA 04, p.8].

Inorganic and Synthetic Organic Chemicals

A vast array of chemicals is included in this category. “Examples include detergents, household cleaning aids, heavy metals, pharmaceuticals, syn- thetic organic pesticides and herbicides, industrial chemicals, and the wastes from their manufacture. Many of these substances are toxic to fish and aquatic life and many are harmful to humans. Some are known to be highly poisonous at very low concentrations. Others can cause taste and odor problems, and many are not effectively removed by conventional wastewater treatment.

Thermal

Heat reduces the capacity of water to retain oxygen. In some areas, water used for cooling is discharged to streams at elevated temperatures from power plants and industries. Even discharges from wastewater treat- ment plants and storm water retention ponds affected by summer heat can be released at temperatures above that of the receiving water, and elevate the stream temperature. Unchecked discharges of waste heat can seriously alter the ecology of a lake, a stream, or estuary” [EPA 04, p. 8].

Fertilizers and Other Chemicals

“Chemicals that provide nutrients to plants, such as nitrogen and phos- phorous and compounds containing these nutrients, may result from agri- cultural runoff and sewage treatment plant effluents. These nutrients stimulate the growth of aquatic plants, which interfere with water uses and later decay to add biological oxygen demand (BOD) to water.

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Wastewater Management • 183

Sediments

The natural process of soil erosion gives rise to sediments in water. Sed- iments are particles and other matter from eroded soil, sand, and minerals. Rivers have always carried sediments to the oceans, but erosion rates in many areas have been greatly accelerated by human activities. In general, sediments contain soil and mineral particles that are washed from the land, agricultural fields, forest, grazing lands, and construction sites. As described briefly above, the U.S. Congress set up a federal storm water program (MS4) to require municipalities to address these problems” [Raj 08].

Radioactive Pollutants

The discharge of uranium, thorium, and other radioactive materials from hospitals and laboratories contaminate the surface water and remain a problem until they are removed or until they naturally decay, which can sometimes take a very long time.

7.4 WASTEWATER CHARACTERIZATION

“The characterization of wastewater is necessary to find out the various types of contaminants present in the wastewater, along with their concentration. This information will help in identifying the specific pollut- ants and the type of treatment necessary before disposal.

Characteristics of waste water are:

●■ Physical, as in color, odor, turbidity, temperature, and solids content

●■ Chemical, as in pH, alkalinity, inorganic constituents like chlorides, heavy metals, nitrogen, phosphorous, etc., dissolved oxygen, biochemi- cal oxygen demand (BOD), and chemical oxygen demand (COD)

●■ Biological, as in bacteria, algae, protozoa, viruses, and coliforms.

Some physical, chemical, and biological parameters are described below:

●■ pH: An expression of both acidity and alkalinity on a scale of 0 - 14, with 7 representing neutrality. Numbers less than 7 indicate increasing acidity, and numbers higher than 7 indicate increasing alkalinity. pH is expressed on a logarithmic scale, so each whole pH value above and below 7 is ten times more basic or acidic than the next higher value.

●■ Alkalinity: Alkalinity in waste water results from the presence of hydroxides, carbonates, and bicarbonates of elements such as calcium,

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184 • hazardous Waste Management, Second edition

magnesium, sodium, potassium, or ammonia. The alkalinity in wastewa- ter helps to resist changes in pH caused by the addition of acids.

●■ Dissolved oxygen: The amount of oxygen freely available in water and necessary for aquatic life and the oxidation of organic materials.

●■ Oxygen demand: Chemical and biological oxygen demand (COD and BOD) are measures of the oxygen consumed when a substance de- grades. Materials such as food waste and dead plant or animal tissue use up dissolved oxygen in water when decomposed through chemical or biological processes.

●■ Biological oxygen demand (BOD): The amount of oxygen required by aerobic biochemical processes to break down the organic matter in water. BOD is a measure of the pollutional strength of biodegradable waste on dissolved oxygen in water.

●■ Chemical oxygen demand (COD): The amount of oxygen utilized in chemical reactions that occur in water as a result of the addition of wastes. COD is a measure of the pollutional strength of organic waste on dissolved oxygen in water.

●■ Coliform bacteria: A group of bacteria used as an indicator of sanitary quality in water. Exposure to these organisms in drinking water causes diseases such as E-coli” [Raj 08].

7.5 WASTEWATER TREATMENT

“The principle objective of wastewater treatment is generally to allow sewage and industrial effluents to be disposed without any danger to human health or damage to the environment. Conventional wastewater treatment consists of a combination of physical, chemical, and biological processes and operations to remove solids, organic matter, chemicals, and sometimes nutrients from wastewater. Wastewater treatment methods can be broadly classified as:

●■ Physical unit operation: The removal of pollutants by physical forces.

●■ Chemical unit operations: The removal of pollutants by addition of chemicals or by chemical reactions.

●■ Biological unit operation: The removal of pollutants by biological activities.

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Wastewater Management • 185

These treatment methods occur in a variety of combinations in wastewater treatment systems, to provide various levels of wastewater treatment” [Raj 08].

The typical flow diagram for wastewater treatment is shown in Figure 7.1.

Flow measurement

Raw wastewater from collection

system

Screening and/or comminutor

Grit chamber

Pre-aeration

Flow equalization

Primary sedimentation

Primary sludge management

Activated sludge Trickling �lter

Discharge

Secondary sludge

management

Secondary clari�er

Disinfection Discharge

DischargeDisinfection

Solids removal nitrogen control

phosphorus removal

Tertiary sludge management

Sludge disposal

either/or

FIGURE 7.1 possible flow diagram for sanitary wastewater treatment. there really isn’t a typical industrial treatment process due to the high variability in the nature of industrial wastewater.

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There are generally four levels of wastewater treatment:

●■ Preliminary treatment

●■ Primary treatment

●■ Secondary treatment

●■ Tertiary/advanced treatment

Preliminary Treatment “Preliminary treatment is the first step in wastewater treatment. The

purpose of preliminary treatment is the removal of coarse solids and other materials often found in wastewater. This treatment consists mainly of physical unit operations such as:

●■ Screening: The removal of coarse solids in wastewater, which may obstruct or clog the mechanical equipment and pipes. Bar racks are common types of screening devices. Most screens in wastewater treat- ment plants consist of parallel bars placed at an angle in a channel in such a manner that the wastewater flows through the bars. Trash col- lects on the bars and is periodically raked off by hand or by mechanical means. In most places, these screenings are disposed of by landfilling or incineration.

●■ Comminution (grinding): The grinding of course solids into smaller and more uniform particles, which are then returned to the flow stream for subsequent treatment.

●■ Flotation: The separation of suspended and floatable solid particles from wastewater. This can be achieved by introducing fine air bubbles into the wastewater.

●■ Grit removal: Grit includes sand, ash, cinder, egg shells, etc., of di- ameter less than 0.2 mm. The specific gravity of grit varies from 2.0 to 2.6. Grit should be removed early in the treatment process because it is abrasive and rapidly wears out pumps and other equipment. Since it is mostly inorganic, it cannot be broken down by biological treatment processes and thus should be removed as soon as possible” [Raj 08].

Grit is usually removed in a long narrow trench called a “grit channel” (See Figure 7.2)

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Wastewater Management • 187

Primary Treatment “After preliminary treatment, wastewater undergoes primary treat-

ment. The objective of primary treatment is the removal of settleable organic solids by sedimentation and the removal of materials that float (scum) by skimming.

Primary sedimentation tanks (see Figure [7.3]) or clarifiers may be circu- lar or rectangular basins, typically 3 to 5 m deep, with hydraulic retention time (time taken by a particle to travel from inlet to outlet) ranging between two and three hours. In a circular basin, the flow pattern is radial. To achieve the radial flow pattern, the wastewater enters a circular well, designed to distrib- ute the flow equally in all directions. The scraper pushes the settleable solids (sludge) toward the center and into the sludge hopper. The settled solids are known as primary sludge. They are collected for further treatment prior to disposal” [Raj 08].

Grit settling area

Central wall

Weirs when used

Slide gales

Grit settling area

Inlet Flow

Outlet

Stop gates insert when cleaning to prevent backflow

FIGURE 7.2 Grit channel. (permission granted courtesy of Laxmi publications pvt. Ltd.)

Sludge scraper blades

Influent

Influent Weir plate

Effluent Clarified

water effluent

Sludge hopper

Sludge withdrawal

Free board

Water surface

Sludge scraper truss arm

Influent baffle

FIGURE 7.3 Sectional view of a circular sedimentation tank. (permission granted courtesy of Laxmi publications pvt. Ltd.)

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“Scum is collected by a rotating blade at the surface. The clear surface water of the primary tank flows from the tank by passing over a weir. The weir must be long enough to allow the treated water to leave at a low veloc- ity. If it leaves the tank at a high velocity, particles settling at the bottom may be picked up and carried from the tank.

Approximately 30% of the incoming biochemical oxygen demand (BOD), 50-70% of the total suspended solids (SS) and 65% of the oil and grease are removed during primary sedimentation. The effluent from pri- mary sedimentation units is called the primary effluent” [Raj 08].

Secondary Treatment (Biological Treatment) “The goal of all biological treatment systems is to remove the dissolved

and nonsettling organic solids from the primary effluent by using microbial populations. Biological treatments are generally part of secondary treat- ment systems. The microorganisms used are responsible for the degrada- tion of organic matter and the stabilization of organic wastes. The way oxygen is utilized is classified into:

●■ Aerobic (require oxygen for their metabolism)

●■ Anaerobic (grow in the absence of oxygen)

●■ Facultative (can proliferate either in the presence or absence of oxygen)

Stabilization of organic matter by microorganisms in a natural or con- trolled environment or biological treatment process is accomplished by two distinct metabolic processes:

●■ Respiration and Synthesis

Respiration is a microbial process in which a portion of the available organic substrate is oxidized by microorganisms to liberate energy. The energy derived from respiration is used to synthesize new microbial cells.

The biological treatment processes used for wastewater treatment are broadly classified as aerobic (in the presence of oxygen) and anaerobic (in the absence of oxygen).

Aerobic Process

Aerobic degradation occurs in two steps. In the first step, complex organics (carbohydrates, proteins, lipids, etc.) are broken down by extracel- lular enzymes into simple organic compounds. In the second step, aerobic

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Wastewater Management • 189

microorganisms (in the presence of oxygen) convert simple organic com- pounds into oxidized end products such as carbon dioxide, nitrates, and phosphates. The energy released in this process is used for biosynthesis of more bacterial cells” [Raj 08].

Figure 7.4 diagrams the aerobic process.

Complex organic matter (carbohydrate, proteins, lipids)

Hydrolysis Extracellular enzymes

Simple organic compounds

Aerobic microorganisms

Synthesis

Energy

Protoplasm (new cells)

End products (CO2, H2O, NH4*etc.)

FIGURE 7.4 Microbiology of aerobic process. (permission granted courtesy of Laxmi publications pvt. Ltd.)

“If the microorganisms are suspended in wastewater during treatment, the operation is called ‘suspended growth process.’ So the conversion of organic matter to gaseous end products and cell tissues (biomass) can be accomplished aerobically, anaerobically, or facultatively, using suspended and attached growth systems.

Aerobic Biological Treatment Systems

The main aerobic biological wastewater treatment processes include high-rate processes and low-rate processes:

High rate processes are characterized by relatively small reactor vol- umes and high concentration of microorganisms when compared with low- rate processes. Consequently, the growth rate of new organisms is much greater in high-rate systems, because of the well-controlled environment, and include: activated sludge, oxidation ditch, trickling filter, biofilter (biotower), and rotating biological contactor.

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●■ Activated sludge process: a widely-used biological treatment process for both domestic and industrial wastewaters. The activated sludge process refers to a continuous aerobic method for biological wastewater treatment, including carbonaceous oxidation and partial nitrification. The expression ‘activated sludge’ alludes to a slurry of microorganisms that remove organic compounds from wastewater. These microorgan- isms are themselves removed by sedimentation under aerobic condi- tions. In an activated sludge system, soluble and unsettleable, biode- gradable organic compounds are degraded by bacteria in an aerated basin, and biomass is carried over with the effluent into a secondary settling tank, where solids are allowed to settle and concentrate; then they are removed. Part of the activated sludge (settled solids) is drawn off as waste, and the rest (30–40%) is recycled to the aeration basin to maintain a constant population of microorganisms” [Raj 08].

“This [activated sludge] process originated in England in the early 1900s and earned its name because a sludge (mass of microbes) is produced which aerobically degrades and stabilizes the organic matter of a wastewater” [Raj 08].

“The process relies on a dense microbial population being mixed in suspension with the wastewater under aerobic conditions. In the presence of adequate nutrients and oxygen, a high rate of microbial growth and res- piration is achieved. This results in the utilization of organic matter present, to produce end products such as carbon dioxide, ammonia, phosphate, and sulfate, and biosynthesis of more microorganisms. In activated sludge sys- tems, organic load removals of 85-95% can be achieved” [Raj 08]. Figure 7.5 displays the layout of an activated sludge process.

●■ “A trickling filter: or biofilter consists of a circular basin or tower filled with support media such as broken stones, slag, plastic rings, modular plastic fills, etc. (see Figure [7.6]). Wastewater is distributed over the media continuously. Microorganisms become attached to the media to form a biological slime layer (biofilm or microbial slime). Organic matter in the wastewater diffuses into the biofilm, where it is stabilized. Oxygen is supplied to the film by the natural flow of wastewater through the media, depending on the relative wastewater temperature and ambient air temperature. The thickness of the biofilm increases as new microorganisms grow. Frequently, portions of the biofilm slough off the media. The sloughed biomass is separated from the liquid in a secondary

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Wastewater Management • 191

settling tank, and is discharged to sludge processing. Clear liquid from the secondary settling tank is called secondary effluent, and a portion is often recirculated to the trickling filter to maintain constant hydraulic distribution of the wastewater over the filter” and to improve the level of treatment to achieve more stringent discharge limits. [Raj 08].

In�uent Aeration tank

Aeration tank

Sludge pump

Return activated sludge (30–40%)

Excess sludge

to processing unit

Secondary settling tank

E�uent

In�uent

(E�uent from primary settling tank)

Plan View

Section View

FIGURE 7.5 Flow diagram for activated sludge process. (permission granted courtesy of Laxmi publications pvt. Ltd.)

Waste water distributor

Filter medium

Ventilation port

Drainage collector

R ec

ir cu

la ti

o n

FIGURE 7.6 Schematic representation of conventional trickling filter. (permission granted courtesy of Laxmi publications pvt. Ltd.)

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●■ Rotating biological contactors (RBCs): “(RBCs) are fixed-film reac- tors similar to trickling filters, in that microorganisms responsible for biodegradation of organic contaminants are attached to support media. In the case of the RBC, the support media are slow rotating discs that are partially submerged in a semicircular tank receiving primary efflu- ent.

A biological contactor consists of a series of closely spaced plastic discs made of poly-vinyl chloride (PVC). The discs are partially submerged in wastewater. By gentle rotation of the discs, the biofilms are alternately exposed to the contaminants in the wastewater and oxygen in the atmo- sphere. The disc rotation speed affects oxygen mass transfer and main- tains the biomass in aerobic conditions. Oxygen is supplied to the attached biofilm from the air when the biofilm is out of water and from the liquid when submerged. Oxygen is transferred to the wastewater by surface tur- bulence created by disc rotation. Sloughed pieces of biofilm from the disc surfaces are removed and segregated by providing a secondary settling tank [Figure 7.7].

Disc

Effluent

Sludge to treatment or disposal

Influent

Primary sludge

Secondary sludge

FIGURE 7.7 Schematic representation of rotating biological contactor. (permission granted courtesy of Laxmi publications pvt. Ltd.)

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Wastewater Management • 193

High-rate biological treatment processes remove not less than 85% of the BOD5 and suspended solids originally present in raw municipal sew- age. Activated sludge process generally produces an effluent of slightly higher quality than a biofilter or RBCs. However, they remove very little phosphorous, nitrogen, and non-biodegradable organics” [Raj 08].

Low-rate biological treatment systems

“Natural low-rate biological treatment systems are available for the treatment of municipal sewage and tend to be lower in cost and less sophis- ticated in operation and maintenance, and include: facultative stabilization ponds; aerated lagoons; and batch reactors.

●■ Stabilization pond: shallow ponds, typically 1–2m (3–6ft) deep, where raw sewage or partially treated sewage can be decomposed by symbi- otic action of algae and bacteria. These ponds are designed to maintain aerobic conditions throughout, but more often the decomposition taking place near the top layer is aerobic, while the bottom (benthic) layer is anaerobic.

In stabilization ponds, algae utilize carbon dioxide, sulfates, nitrates, phosphates, water, and sunlight to synthesize their own cellular material and give off free oxygen as a waste product. This oxygen, dissolved in pond water, is available to bacteria and other microbes for their meta- bolic process, which include respiration and degradation of organic mate- rial in the pond. The settleable organic matter deposits at the bottom to undergo anaerobic decay. [Figure 7.8].

This is the algal-bacterial symbiosis, in which microorganisms use oxy- gen dissolved in the water and break down organic waste materials to produce end products such as carbon dioxide, water, and plant nutri- ents. Algae use materials such as nitrates, phosphates, and sulfates as raw material in photosynthesis, to give out oxygen, thus replenishing the depleted oxygen supply and maintaining an aerobic environment” [Raj 08].

●■ Aerated lagoon: “a suspended growth process. The aerated lagoon system consists of a large pond or tank that is equipped with mechani- cal aerators to maintain an aerobic environment and to prevent settling of the suspended biogas. Initially, the population of microorganisms in an aerated lagoon is much lower than that in an activated sludge system because there is no recirculation of sludge. Therefore, a significantly

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longer residence time is required to achieve the same effluent quality. The effluent from the aerated lagoon may flow to a settling basin for removal of suspended solids. Alternatively, the mechanical aerators in the system may be shut off for a period of time to facilitate settling prior to discharge of the effluent. The settled solids are generally dewatered prior to disposal” [Raj 08].

Anaerobic Biological Treatment

“Anaerobic treatment converts organic matter in wastewater into a small quantity of sludge and a large quantity of biogas (methane and car- bon dioxide), while leaving some pollutants unremoved. In contrast, aero- bic processes produce a large quantity of sludge and no biogas, while also leaving some pollution, though less than in the anaerobic treatment pro- cess. The main advantages of anaerobic treatment over aerobic treatment are:

Sun

Algal growth and photosynthesis

Gas transfer

Aerobic

Bacteria

Anaerobic

Influent waste (complex organics)

Organics + Anaerobic bacteria

CO2, NH4, NO3, PO4

CO2 + CH4 + H2S

FIGURE 7.8 Stabilization pond. (permission granted courtesy of Laxmi publications pvt. Ltd.)

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Wastewater Management • 195

●■ Low operating costs

●■ Less space requirements; energy recovery (biogas production)

●■ Low sludge production

Anaerobic stabilization occurs in three stages. In the first stage, com- plex organics (cellulose, proteins, lip- ids, etc.) are broken down by extracellular enzymes into soluble organic fatty acids, alcohols, and car- bon dioxide. In the second stage, the products of the first stage are con- verted into various organic acids and alcohols by acid-forming bacteria. In the third stage, one group of meth- ane-forming bacteria converts hydro- gen and carbon dioxide to methane, and another group converts acetate to methane and carbon dioxide” [Raj 08]. The anaerobic process is depicted in Figure 7.9.

“The biological degradation of complex organic matter takes place in several consecutive biochemical steps, each performed by different groups of specialized bacteria. In practice, the acetogenic and metha- nogenic phases are the rate-limiting steps. On the other hand, the genera-

tion of methane gas can only happen as fast as methane-forming bacteria receive their substrate. Methane-forming bacteria only use acetic acid (CH

3 COOH), hydrogen gas (H

2 ), and carbon dioxide (CO

2 ) as substrate.

It is well known that the rate-limiting stage (i.e., the stage that is the slowest) controls the process. In anaerobic processes, methane-forming bacteria reproduce very slowly. These methane-forming bacteria are also very sensitive to environmental factors such as pH, alkalinity, temperature,

Water containing complex organic matter (carbohydrates, proteins, lipids)

Hydrolysis (extracellular enzymes)

Simple organic compounds (sugar, amino acids, peptides)

Acidogenesis

Acetogenesis

Methanogenesis

Methane, CO2

H2, CO2, organic acids, alcohols

H2, CO2, acetic acid

FIGURE 7.9 Microbiology of anaerobic process. (permission granted courtesy of Laxmi publications pvt. Ltd.)

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and toxins. Therefore, controlling these factors is very important to control the speed of the process of digestion.

Anaerobic Digestion of Wastewater Sludges

In primary and secondary treatment processes, a significant fraction of the removed BOD is extracted as sludge. This sludge must be treated fur- ther before its safe disposal. One of the most widely employed sludge treat- ment technologies is anaerobic digestion. Here, a large portion of the organic matter in the sludge is converted to carbon dioxide and methane by microorganisms that act in the absence of oxygen.

The treatment of wastewater sludges consists of two main phases. In the first phase, the objective is to separate the water from the sludge by adopting thickening and dewatering processes. The second phase is known as sludge stabilization. There are three primary objectives of sludge stabili- zation:

●■ To reduce the level of pathogens in the residual solids

●■ To eliminate offensive odors

●■ To reduce potential for putrefaction

Figure [7.10] shows one of the configurations used for anaerobic sludge digestion. It consists of two identical reactors, with the first one sealed to maintain anaerobic conditions. The second tank may either be sealed for additional gas collection or may be open to the atmosphere. The input for the digester is typically a mixture of solids from the primary settling tank, wasted microbes from the secondary settling tank, and surface scums from both the primary and secondary settling tanks. These sludges are added to the first reactor either continuously or intermittently. This first stage reac- tor is heated and mixed to accelerate the biological conversion. After a typ- ical residence time of 10-20 days, the mixed digested sludge passes to the second reactor. Here it is retained for further digestion without mixing and heating. Settled sludge is removed from the reactor, either intermittently or continuously. The removed sludge is then dewatered and disposed. The supernatant liquid may be recycled to the beginning of the wastewater treatment plant, if necessary” [Raj 08].

“The significance of the microbiology of anaerobic digestion is manifest in optimum system design and operation. Process design should be directed toward maintaining a large, stable population of methane-forming bacteria.

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Typically, inadequate system design or operation will result in a relatively high volatile acid accumulation in the digester. The excess acid accumula- tion may create an imbalance between the population of acid-forming and methane-forming bacteria. In a severe case, excessively high volatile acid production will depress the pH to a level that essentially stops the activity of methanogens entirely. Stable performance can be achieved through careful consideration of the fundamentals of anaerobic treatment. The fol- lowing environmental and operational parameters are to be considered while designing and operating an anaerobic system:

●■ Environmental parameters: pH, alkalinity, temperature, nutrient content, and toxic compounds

●■ Operational parameters: solids retention time, and substrate char- acteristics such as; concentration, composition, and biodegradability” [Raj 08]

Facultative processes are a combination of aerobic and anaerobic activ- ity used in the breakdown of organic matter, and are not discussed in detail in this book. “Facultative lagoon systems, like evaporative (ET) systems, are not widely used for onsite wastewater treatment. They are large in size, expensive to build, perform only a portion of the treatment necessary to permit surface discharge or reuse, and produce large concentrations of algae, which negates their use as direct pretreatment before soil infiltration.

Biogas (CH4 + CO2)

Scum layer

Digested sludge

Supernatant outlet

Supernatant layer

First stage (completely mixed)

Second stage

Sludge heater

Raw sludge inlet

FIGURE 7.10 Schematic representation of anaerobic digester. (permission granted courtesy of Laxmi publications pvt. Ltd.)

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They have been used in a few states as an alternative system when a subsur- face wastewater infiltration system (SWIS) is not feasible, usually to discharge without further treatment to surface waters, which is generally unacceptable under normal circumstances. In some states intermittent dis- charge lagoons are required. Storage volume is for all cold weather months (four to six months), making the size of these systems too large for most applications” [EPA 11n].

Tertiary/Advanced Wastewater Treatment Tertiary and/or advanced wastewater treatment is employed when spe-

cific wastewater constituents that cannot be removed by secondary treat- ment must be removed. Individual treatment processes are necessary to remove excess nitrogen, phosphorous, additional suspended solids, refrac- tory organics, heavy metals, and dissolved solids. Because advanced treat- ment usually follows high-rate secondary treatment, it is sometimes referred to as tertiary treatment.

Dealing with the Biosolids

“In many areas, biosolids are marketed to farmers as fertilizer. Federal regulation (40 CFR Part 503) defines minimum requirements for such land application practices, including contaminant limits, field management prac- tices, treatment requirements, monitoring, recordkeeping, and reporting requirements.

Properly treated and applied biosolids are a good source of organic matter for improving soil structure and help supply nitrogen, phosphorus, and micronutrients that are required by plants. Biosolids have also been used successfully for many years as a soil conditioner and fertilizer, and for restoring and revegetating areas with poor soils due to construction activi- ties, strip mining, or other practices.

Under this biosolids management approach, treated solids in semi-liq- uid or dewatered form are transported to the soil treatment areas. The slurry or dewatered biosolids, containing nutrients and stabilized organic matter, is spread over the land to give nature a hand in returning grass, trees, and flowers to barren land. Restoration of the countryside also helps control the flow of acid drainage from mines that endangers fish and other aquatic life and contaminates the water with acid, salts, and excessive quan- tities of metals” [EPA 04, p. 20].

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Disinfection

Domestic wastewater contains microorganisms or pathogens that pro- duce human diseases. Processes used to kill or deactivate these harmful organisms are called disinfection. Chlorine is the most widely used disinfec- tant, but ozone and ultraviolet radiation are also frequently used for waste- water effluent disinfection.

Chlorine

Chlorine kills microorganisms by destroying cellular material. This chemical can be applied to wastewater as a gas, a liquid, or in a solid form similar to swimming pool disinfection chemicals. However, any free (uncombined) chlorine remaining in the water, even at low concentrations, is highly toxic to aquatic life. Therefore, removal of even trace amounts of free chlorine by dechlorination is often needed to protect fish and aquatic life. Due to emergency response and potential safety concerns, chlorine gas is used less frequently now than in the past.

Ozone

Ozone is produced from oxygen exposed to a high voltage current. Ozone is very effective at destroying viruses and bacteria and decomposes back to oxygen rapidly without leaving harmful byproducts. Ozone is not very economical due to high energy costs.

Ultraviolet Radiation

Ultraviolet (UV) disinfection occurs when electromagnetic energy in the form of light in the UV spectrum produced by mercury arc lamps pen- etrates the cell wall of exposed microorganisms. The UV radiation retards the ability of the microorganisms to survive by damaging their genetic material. UV disinfection is a physical treatment process that leaves no chemical traces. Organisms can sometimes repair and reverse the destruc- tive effects of UV when applied at low doses” [EPA 04, p. 16].

7.6 U.S. STORM WATER REGULATIONS

While Congress did not deal with storm water in the laws, rules, and regulations before 1990, they passed significant measures to reduce the effect of nonpoint sources and eventually combined sewer overflows

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(CSOs), a major source of pollution during and after significant storm events. Here is a brief history of the U.S. storm water regulations:

●■ “In 1990 EPA issued Storm Water Regulation Phase I with implementa- tion to begin in 1992. The Phase I program targeted municipalities over 100,000 people and certain industrial activities.

●■ In 1992 EPA issued the Storm Water Baseline Industrial General Per- mit (industrial including construction > 5 acres).

●■ In 1995 EPA developed the NPDES Storm Water Multi-Sector General Permit for Industrial Activities (MSGP) - did not include construction

●■ In 1998 Final Modification of the NPDES Storm Water Multi-Sector General Permit for Industrial Activities and Termination of the EPA Storm Water Baseline Industrial General Permit occurred.

●■ In 1998 reissuance of NPDES General Permits for Storm Water Dis- charges from Construction Activities (CGP).

●■ In 1999 Storm Water Regulations Phase II were developed with imple- mentation set for March 2003.

●■ October 2000 (NPDES) Storm Water Multi-Sector General Permit for Industrial Activities (MSGP 2000).

●■ July 1, 2003 NPDES General Permit for Discharges for Large and Small Construction Activities was issued.

●■ June 30, 2008 NPDES General Permit for Discharges for Large and Small Construction Activities was issued” [EPA 11o].

The storm water pollution control program requires municipalities to develop and implement a program called Municipal Separate Storm Sewer Systems (MS4). This program makes the communities deal with the separa- tion of combined sanitary/storm water sewer systems and their overflow systems (CSOs), prohibits non-storm water discharges, implements erosion and sediment control programs, addresses construction and post-construc- tion runoff, and develops and implements pollution prevention measures in the municipality to minimize discharges.

This is a major initiative nationwide, and the costs are very high, espe- cially because the sanitary sewer systems and storm water systems are com- bined under most major cities.

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Industrial Pretreatment The National Pretreatment Program, a cooperative effort of Federal,

state, POTWs (publicly owned treatment works) and their industrial dis- chargers, requires industry to control the amount of pollutants discharged into municipal sewer systems. This is critical in the hazardous waste program, where industries often discharge hazardous waste into publicly-owned waste- water treatment plants. It is critical the hazardous constituents be reduced to a level where they will not upset the treatment process at the POTW.

Pretreatment protects the wastewater treatment facilities and its work- ers from pollutants that may create hazards or interfere with the operation and performance of the POTW, including contamination of sewage sludge, and reduces the likelihood that untreated pollutants are introduced into the receiving waters.

Under the Federal Pretreatment Program, governed by the U.S. Storm- water Regulations, municipal wastewater plants receiving significant indus- trial discharges must develop local pretreatment programs to control industrial discharges into their sewer system. These programs must be approved by either EPA or a state acting as the Pretreatment Approval Authority. “More than 1500 municipal treatment plants have developed and received approval for a Pretreatment Program” [EPA 11p].

7.7 CASE STUDIES

Illegal wastewater treatment is sometimes difficult to detect, because the facility can give misleading information that is difficult to refute. The following case study illustrates illegal wastewater treatment at a facility that conducted electroplating activities and did not dispose of their wastewater as they claimed.

Case Study

Illegal Wastewater Treatment

at an inspection of a manufacturing facility that electroplated the products it manufactured, the inspector was told by the facility operator that the electroplating wastes were run through a pretreatment program prior to discharge to a publicly- owned treatment system. the inspector completed the inspection, and when

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he went back to the office, inquired about the discharge. It turned out the discharge was to the facility’s residential septic system, which was designed for only human waste. When the owner had the septic system pumped, the contents were hauled to a local publicly owned wastewater treatment plant by a septic hauler who was not licensed to haul hazardous waste. Upon further investigation, the septic system and leach field were highly contaminated with plating chemicals and had to be cleaned up at the owner’s expense, together with a fine for an illegal industrial discharge. the three key violations were: treatment of hazardous waste without a permit, illegal underground discharge of industrial waste without a permit, and transporting hazardous waste without a permit.

Note that this facility later became a hazardous waste cleanup site because the contamination was so extensive, the plume of electroplating wastes extended over a five-acre area.

There are many challenges facing wastewater treatment operators. In the following case study, the operator needed to figure out how to treat a toxic contaminant in low concentrations to save the company millions of dollars annually.

Case Study

From the Field: How to Start Treating a Difficult Wastewater

In one large industrial wastewater treatment plant, the industry was using sequencing batch reactors to treat a very toxic chemical in dilute concentrations (2% solution in water). there was a great deal of interest in using wastewater treatment, because the only other form of treatment to dispose of the waste was incineration, and a great deal of energy was required to burn the water along with the chemical.

Because it was almost impossible to develop microbes in the wastewater lab to treat this toxic chemical, the company found a municipal treatment plant that treated very dilute amounts of these chemicals, so they introduced some activated sludge containing the modified microbes, and it worked. the biota in the reactors took a few weeks to adjust to the higher concentration of the chemical, but the plant is successfully treating thousands of gallons of this waste daily, saving the company millions of dollars each year.

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Summary

In this chapter, you learned about U.S. wastewater regulations, the sources of contamination of wastewaters, how to classify water pollutants, how to characterize wastewater, discovered different kinds of wastewater treatment, read a summary of the U.S. storm water regulations, and read a case study on illegal wastewater treatment. Finally, you read an article from the field on how to start treating a difficult wastewater.

In the next chapter, you will read about solid waste regulations, learn the types and sources of solid wastes, read about municipal solid waste, learn how to estimate quantities of solid waste, how to characterize solid waste, learn about solid waste collection and recycling of solid waste. You will also discover the problems associated with e-waste and read a case study on Love Canal—Lessons Learned.

Exercises

1. Name four man-made sources of water pollution.

2. What are three categories of wastewater characteristics?

3. What are the three stages of wastewater treatment?

4. Explain how a trickling filter treats wastewater.

5. What are the similarities of a trickling filter and a rotating biological contactor?

6. What is the main difference between a tricking filter and a rotating bio- logical contactor (RBC)?

7. What is a combined sewer overflow?

REFERENCES

[EPA 04] Primer for Municipal Wastewater Treatment Systems EPA 832-R-04-001

September 2004, online at http://water.epa.gov/type/watersheds/wastewater/ upload/Primer-for-Municipal-Wastewater-Treatment-Systems.pdf, (accessed May 2011).

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[EPA 11n] USEPA Onsite Wastewater Treatment Systems Technology Fact Sheet 7, available online at http://www.epa.gov/nrmrl/pubs/625r00008/html/tfs7. htm, (accessed May 2011).

[EPA 11o] USEPA Office of Wastewater Management NPDES Stormwater Program online at http://www.dec.state.ak.us/water/wnpspc/stormwater/ fedleghistory.htm, (accessed May 2011).

[EPA 11p] USEPA NPDES Stormwater Program, available online at http://cfpub. epa.gov/npdes/home.cfm?program_id=3, (accessed May 2011).

[Raj 08] Raj, S. Amal. 2008. Introduction to environmental science and technology. 42–56. Laxmi Publications Pvt, Ltd.

[WIKI 11f] Wikipedia.com. Clean Water Act, online at http://en.wikipedia.org/ wiki/Clean_Water_Act, (accessed May 2011).

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