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5 days ago PDF | This is a book about environmental engineering for nontechnical students. No attempt is made to cover air and water pollution, solid. ~l,~lter Research Vol. 9. pp, to Pergamon Press Printed in Great Britain. BOOK REVIEWS Environmental Pollution Control. Allan D. McKni. environmental pollution control engineering by cs rao | Get Read & Download Ebook environmental pollution control engineering by cs rao as PDF for free at.
Sample population-response curve h u m a n health or environmental risk, the consequences are adverse health effects or adverse effects on some species of plant or animal. One source is excrement, since all human and animal wastes contain C, N, and P. Most pollutants need time to react; the exposure time is thus as important as the level of exposure. The first complete treatment systems 12In, to limitthe quantity of wastewater discharge, the city of Bostonpassed an ordinance prohibiting the taking of baths without doctor's orders. The U. The range of pollutants is vast, depending only on what gets "thrown down the drain. Municipal wastewater is as important a source of water pollution as industrial waste.
Notice, however, that we do not say that cigarette smoking c a u s e s lung cancer, chronic obstructive pulmonary disease, or heart disease, because we have not identified the actual causes, or etiology, of any of them. How, then, has cigarette smoking been identified as a risk factor if it cannot be identified as the cause? This observation about cigarette smoke was not made, and indeed could not be made, until the middle of the twentieth century, when the lifespan in at least the developed countries of the world was long enough to observe the diseases that had been correlated with exposure to cigarette smoke.
In the first half of the twentieth century, infectious diseases were a primary cause of death. With the advent of antibiotics and the ability to treat such diseases, the lifespan in the developed nations of the world lengthened, and cancer and heart disease became the leading causes of death.
From the early s, when the average lifespan in the United States was about 70, lifelong habitual cigarette smokers were observed to die from lung cancer at ages between 55 and This observation, which associated early death with cigarette smoke, identified cigarette smoke as a risk factor. Identification of a substance a toxicant that may have adverse health effects Scenarios for exposure to the toxicant Characterization of health effects An estimate of the probability risk of occurrence of these health effects The decision that the concentration of a certain toxicant in air, water, or food is acceptable is based on a risk assessment.
Environmental Risk Analysis 17 Toxicants are usually identified when an associated adverse health effect is noticed. In most cases, the first intimation that a substance is toxic is its association with an unusual number of deaths.
Mortality risk, or risk of death, is easier to determine for populations, especially in the developed countries, than morbidity risk risk of illness because all deaths and their apparent causes are reported on death certificates, while recording of disease incidence, which began in the relatively recent past, is done only for a very few diseases.
Death certificate data may be misleading: An individual who suffers from high blood pressure but is killed in an automobile accident becomes an accident statistic rather than a cardiovascular disease statistic. In addition, occupational mortality risks are well documented only for men; until the present generation, too few women worked outside the home all their lives to form a good statistical base.
These particular uncertainties may be overcome in assessing risk from a particular cause or exposure to a toxic substance by isolating the influence of that particular cause. Such isolation requires studying two populations whose environment is virtually identical except that the risk factor in question is present in the environment of one population but not in that of the other. Such a study is called a cohort study and may be used to determine morbidity as well as mortality risk.
One cohort study, for example, showed that residents of copper smelting communities, who were exposed to airborne arsenic, had a higher incidence of a certain type of lung cancer than residents of similar industrial communities where there was no airborne arsenic. Retrospective cohort studies are almost impossible to perform because of uncertainties on data, habits, other exposures, and the like.
Cohorts must be well matched in size, age distribution, life-style, and other environmental exposures, and they must be large enough for an effect to be distinguishable from the deaths or illnesses that occur anyway. The response of an organism to a pollutant always depends in some way on the amount or dose of pollutant to the organism.
The magnitude of the dose, in turn, depends on the exposure pathway. The same substance may have a different effect depending on whether it is inhaled, ingested, or absorbed through the skin, or whether the exposure is external. The exposure pathway determines the biochemistry of the pollutant in the organism. In general, the human body detoxifies an ingested pollutant more efficiently than it does an inhaled pollutant.
The relationship between the dose of a pollutant and the organism's response can be expressed in a dose-response curve, as shown in Figure The figure shows four basic types of dose-response curve possible for a dose of a specific pollutant and the respective responses.
Some characteristic features of the dose-response relationship are: The existence of a threshold in health effects of pollutants has been debated for many years. A threshold dose is the lowest dose at which there is an observable effect. Curve A in Figure illustrates a threshold response: There is no observed effect until a particular concentration is reached. This concentration is designated as the threshold.
Curve B shows a linear response with no threshold; that is, the intensity of the effect is directly proportional to the pollutant dose, and an effect is observed for any detectable concentration of the pollutant in question.
Curve C, sometimes called sublinear, is a sigmoidal dose-response curve, characteristic of many pollutant doseresponse relationships.
Although Curve C has no clearly defined threshold, the lowest dose at which a response can be detected is called the threshold limit value TLV. Occupational exposure guidelines are frequently set at the TLV. Curve D displays a supralinear dose-response relationship, which is found when low doses of a pollutant appear to provoke a disproportionately large response.
Total body burden. An organism, or a person, can be exposed simultaneously to several different sources of a given pollutant. The concentration of lead in the body is thus the sum of what is inhaled and ingested and what remains in the body from prior exposure, less what has been eliminated from the body. This sum is the total body burden of the pollutant. Physiological half-life.
The physiological half-life of a pollutant in an organism is the time needed for the organism to eliminate half of the internal concentration of the pollutant, through metabolism or other normal physiological functions. Bioaccumulation and bioconcentration. Bioaccumulation occurs when a substance is concentrated in one organ or type of tissue of an organism.
Iodine, Environmental Risk Analysis 19 for example, bioaccumulates in the thyroid gland. The organ dose of a pollutant can thus be considerably greater than what the total body burden would predict. Bioconcentration occurs with movement up the food chain.
Exposure time and time vs. Most pollutants need time to react; the exposure time is thus as important as the level of exposure. An illustration of the interdependence of dose and exposure time is given for CO exposure in Chapter 18, in Figure Because of the time-response interaction, ambient air quality standards are set at maximum allowable concentrations for a given time, as discussed in Chapter Synergism occurs when two or more substances enhance each other's effects, and when the resulting effect of the combination on the organism is greater than the additive effects of the substances separately.
For example, black lung disease in miners occurs much more often in miners who smoke than in those who do not. Coal miners who do not smoke rarely get black lung disease, and smokers who are not coal miners never do. The synergistic effect of breathing coal dust and smoking puts miners at high risk. The opposite of synergism is antagonism, a phenomenon that occurs when two substances counteract each other's effects.
LCso and LDso. Dose-response relationships for human health are usually determined from health data or epidemiological studies. Human volunteers obviously cannot be subjected to pollutant doses that produce major or lasting health effects, let alone fatal doses.
Toxicity can be determined, however, by subjecting nonhuman organisms to increasing doses of a pollutant until the organism dies. LDs0 values are most useful in comparing toxicities, as for pesticides and agricultural chemicals; no direct extrapolation is possible, either to humans or to any species other than the one used for the LDs0 determination.
LD50 can sometimes be determined retrospectively when a large population has been exposed accidentally, as in the accident at the Chernobyl nuclear reactor. In particular, thresholds differ; threshold values in a population, however, generally follow a Gaussian distribution.
Figure shows the distribution of odor thresholds for hydrogen sulfide in a typical population for example. Individual responses and thresholds also depend on age, sex, and general state of physical and emotional health.
Healthy young adults are on the whole less sensitive to pollutants than are elderly people, those who are chronically or acutely ill, and children. In theory, allowable releases of pollutants are restricted to amounts that ensure protection of the health of the entire population, including its most sensitive members.
In many cases, however, such protection would mean zero release. For nonthreshold pollutants, however, no such determination can be made.
In these instances, there is no release level for which protection can be ensured for everyone, so a comparative risk analysis is necessary. Carcinogens are all considered to be in this category of nonthreshold pollutants. Most cancers grow very slowly and are detectable expressed many years, or even decades, after exposure to the potentially responsible carcinogen. The length of time between exposure to a risk factor and expression of the adverse effect is called the latency period.
Cancers in adults have apparent latency periods of between 10 and 40 years. Relating a cancer to a particular exposure is fraught with inherent inaccuracy.
Many carcinogenic effects are not identifiable in the lifetime of Environmental Risk Analysis 21 a single individual. In a few instances, a particular cancer is found only on exposure to a particular agent e. Many carcinogens are identified through animal studies, but one cannot always extrapolate from animal to human results. The U. Environmental Protection Agency EPA classifies known animal carcinogens, for which there is inadequate evidence for human carcinogenicity, as probable human carcinogens.
There is a growing tendency to regulate any substance for which there is any evidence, even inconclusive, of adverse health effects. This is considered a conservative assumption, but it may not be valid in all cases.
Such a conservative posture toward regulation and control is the result of the cumulative uncertainty surrounding the epidemiology of pollutants. The cost of such control has recently been determined to be far greater than the cost of treating or mitigating the effect. The quantitative expressions reflect both the proportionality of the risk factor to the adverse effect and the statistical significance of the effect. Risk is defined as the product of probability and consequence, and is expressed as the probability or frequency of occurrence of an undesirable event.
It is important to note that both probability and consequence must play a role in risk assessment. Arguments over pollution control often concentrate on consequence alone; members of the public fear a consequence like the Bhopal isocyanate release irrespective of its remote likelihood or low frequency of occurrence. However, pollution control decisions, like other risk-based decisions, cannot be made on the basis of consequence alone.
If we were to determine actions only with regard to their consequences, we would never travel by bicycle, automobile, or airplane, would never start a campfire or burn wood in a stove or fireplace, and never eat solid food, because death and a very unpleasant death is one possible consequence of all of these actions.
We actually take relative risk, and thereby relative probability of harm, into account in all such decisions. The probability is 0. An expression of risk incorporates both the probability and some measure of consequence. In discussing 3Tengs, T. Sample population-response curve h u m a n health or environmental risk, the consequences are adverse health effects or adverse effects on some species of plant or animal.
Challenges to the linear nonthreshold theory of carcinogenesis have been raised recently, particularly with respect to the effects of ionizing radiation. Bond et al. Several studies of the Marshall Islanders, who were exposed during the atmospheric nuclear tests in the s, indicate that there may be a threshold of radiation exposure for a population before any excess cancers are seen in that population, s and a similar phenomenon has been observed in analysis of cancer incidence in radium dial painters.
Recent Russian data for a population accidentally exposed to plutonium-contaminated water from to also show the possibility of a threshold 6 Figure There is even some epidemiological evidence that exposure to ionizing radiation just a bit higher than background stimulates some biological defense mechanisms: SBond, Victor P.
Environmental Risk Analysis 2: Sample relative risk for leukemia incidence of radon-induced lung cancer than was predicted by the linear nonthreshold theory, 7 though this is generally seen as scatter in the data. These studies include very large uncertainties, but they are the same uncertainties and have the same magnitude as studies that appear to confirm the linear nonthreshold theory of radiation-induced carcinogenesis.
The linear nonthreshold theory is clearly controversial: There are strong arguments both for and against a threshold, and dose-response curves can be linear or linear-quadratic, or can show some other dependence. The strongest argument to retain the nonthreshold hypothesis is its conservatism. On the other hand, the strongest argument for recognizing a threshold is the existence of epidemiological data showing thresholds.
As the populations that we have studied live out their lives, we get a retrospective demonstration of ionizing radiation dose vs. Relative risk is the ratio of the probabilities that an adverse effect will occur in t w o different populations. In in the United States, 3 5 0 , 0 0 0 smokers died as a result of lung cancer and heart disease.
In that year, the United 8In determining statistical significance, a test of significance like the Fisher's test or the Student's t-test appropriate to the population under consideration is applied.
Such calculations are beyond the scope of this text. Cipollino had been enticed to smoke by advertising and that the cigarette manufacturers had concealed known adverse health effects. Cipollino died of lung cancer at the age of Department of Health and Human Services States had a population of million. The probability is 1.
Table presents some typical statistics for the United States. Using data again, there were 2,, deaths in the United States that year. Of these, ,, or deaths per deaths, were related to habitual smoking. Loss of years of life depends on life expectancy, which differs considerably from one country to another. Average life expectancy in the United States is now 75 years; in Canada, These figures show that meaningful risk analyses can be conducted only with very large populations.
Health risk that is considerably lower than the risks cited in Tables and may not be observed in small populations. Chapter 18 cites several examples of statistically valid risks from air pollutants. Basic Books Example 2. The cancer death rate in the community of residents is 36 people per year, and the total death rate is people per year. Does Beaverville appear to be a healthy place to live, or is the cancer risk unusually high?
Moreover, a Beaverville resident is about 1.
We may also calculate whether cancer deaths per deaths are higher in Beaverville than in the United States as a whole. Risk assessment usually compares risks because the absolute value of a particular risk is not very meaningful.
EPA has adopted the concept of unit risk in discussion of potential risk. Unit lifetime risk is the risk to an individual from exposure to these concentrations for 70 years a lifetime, as EPA defines it. Unit occupational lifetime risk implies exposure for 8 hours per day and 22 days per month every year, or hours per year for 47 years a working lifetime.
EPA's concern with somatic risk from a number of hazardous substances is the carcinogenic potential of these substances, so the "consequence" part of the risk is given as LCFs. We can then write equations for the different expressions for unit risk and use these to calculate the estimated risk. In the example below, these calculations assume that risk increases linearly with time and concentration. EPA considers this a conservative assumption for low exposure to a carcinogen over a period of years.
Nonlinear dose-response relationships imply more complex relationships between risk, concentration, and exposure time; examples of such more complex relationships will not be considered here. For waterborne pollutants: For airborne pollutants: The risk may be estimated using either unit annual risk or unit lifetime risk. Although there is a popular tendency to translate this to an "individual risk" of "a chance of three in a billion having a fatal cancer," this statement of risk is less meaningful than the statement of population risk.
Methods for ecosystem risk assessment are now being developed. Similarities and Differences," in Landis, W. Environmental Risk Analysis 29 as human health risk assessment, except that identification of the species at risk and of the exposure pathway is a far more complex process than in human health risk assessment.
Assessment endpoints are values of the ecosystem that are to be protected and are identified early in the analysis; these endpoints may include numbers of different species, life-cycle stages for a given species, reproductive patterns, or growth patterns.
Identification of specific endpoints implies choices among potential target species. Ecosystem risk assessment is in its infancy, and details of its practice are beyond the scope of this textbook. Our industrial society needs accurate quantitative risk assessment to evaluate the protection afforded by various levels of pollution control. We must also remain aware that determination of safe levels of pollutants based on risk analysis is a temporary measure until the mechanism of the damage done by the pollutant is understood.
At present, we can only identify apparent associations between most pollutants and a given health effect. We should note that analysis of epidemiological data and determination of significance of effects requires application of a test of statistical significance. There are a number of such tests in general use, but since their application is not central to the scope of this text they not considered here.
Almost all of our knowledge of adverse health effects comes from occupational exposure, which is orders of magnitude higher than exposure of the general public. Doses to the public are usually so low that excess mortality, and even excess morbidity, are not identifiable. However, development of pollution control techniques continues to reduce risk.
The philosophy, regulatory approaches, and design of environmental pollution control make up the remainder of this book. Do you think a regulatory effort should be made to limit either smoking or the consumption of alcohol?
Why and why not? The allowed level of airborne ionizing radiation the EPA standard above background is 10 mrem per source per year. Average nonanthropogenic background is about mrem per year. How many cancers may be attributed to background? Note what "unit risk" means in this problem.
By what factor does a worker exposed to this dose over a working lifetime increase her risk of cancer? Does working in the plant present an excess cancer risk? What assumptions need to be made? How does this change your answer to Problem 2. EPA regards an acceptable annual risk from any single source to be 10 A copper smelter emits arsenic into the air, and the average concentration within a two-mile radius of the smelter is 5.
Is the risk from smelter arsenic emissions acceptable to EPA? Assuming that the residents live there throughout their lifetimes, how many excess LCFs can be expected per year in this population? Consider both the notion of a threshold and the shape of the curve. What additional data would you collect to support the arguments? Environmental Protection Agency latent cancer fatalities standard mortality ratio threshold limit value Chapter 3 Water Pollution Although people now intuitively relate filth to disease, the transmission of disease by pathogenic organisms in polluted water was not recognized until the middle of the nineteenth century.
The Broad Street pump handle incident demonstrated dramatically that water can carry diseases. A British public health physician named John Snow, assigned to control the spread of cholera, noticed a curious concentration of cholera cases in one part of London. Almost all of the people affected drew their drinking water from a community pump in the middle of Broad Street. However, people who worked in an adjacent brewery were not affected.
Snow recognized that the brewery workers' apparent immunity to cholera occurred because the brewery drew its water from a private well and not from the Broad Street pump although the immunity might have been thought due to the health benefits of beer.
Snow's evidence convinced the city council to ban the polluted water supply, which was done by removing the pump handle so that the pump was effectively unusable. The source of infection was cut off, the cholera epidemic subsided, and the public began to recognize the public health importance of drinking water supplies.
Until recently, polluted drinking water was seen primarily as a threat to public health because of the transmission of bacterial waterborne disease. In less developed countries, and in almost any country in time of war, it still is. In the United States and other developed countries, however, water treatment and distribution methods have almost eradicated bacterial contamination. Most surface water pollution is harmful to aquatic organisms and causes possible public health problems primarily from contact with the water.
Groundwater can be contaminated by various hazardous chemical compounds that can pose serious health risks. In this chapter we discuss the sources of water pollution and the effect of this pollution on streams, lakes, and oceans. Storm drainage, even though the water may enter watercourses by way of pipes or channels, is considered nonpoint source pollution. Point source pollution comes mainly from industrial facilities and municipal wastewater treatment plants.
The range of pollutants is vast, depending only on what gets "thrown down the drain. Suspended solids also contribute to oxygen depletion; in addition, they create unsightly conditions and can cause unpleasant odors. Nutrients, mainly nitrogen and phosphorus, can promote accelerated eutrophication, and some bioconcentrated metals can adversely affect aquatic ecosystems as well as make the water unusable for human contact or consumption. Heat is also an industrial waste that is discharged into water; heated discharges may drastically alter the ecology of a stream or lake.
Although local heating can have beneficial effects such as freeing harbors from ice, the primary effect is deleterious: As the level of DO decreases, metabolic activity of aerobic aquatic species increases, thus increasing oxygen demand.
Municipal wastewater is as important a source of water pollution as industrial waste. A century ago, most discharges from municipalities received no treatment whatsoever. Since that time, the population and the pollution contributed by municipal discharge have both increased, but treatment has increased also.
We define a population equivalent of municipal discharge as equivalent to the amount of untreated discharge contributed by a given number of people. The sewerage systems in older U. When these cities were first built, engineers realized that sewers were necessary to carry off both stormwater and sanitary wastes, and they usually designed a single system to carry both discharges to the nearest appropriate body of water.
Such systems are known as combined sewers. As years passed, city populations increased, and the need for sewage treatment became apparent, separate sewer systems were built: Almost all of the cities with combined sewers have built treatment plants that can treat dry weather flow--the sanitary wastes when there is no stormwa- Water Pollution 33 ter runoff.
As long as it does not rain, the plants can handle the flow and provide sufficient treatment; however, rain increases the flow to many times the dry weather flow, and most of it must be bypassed directly into a river, lake, or bay. The overflow will contain sewage as well as stormwater, and can be a significant pollutant to the receiving water. Attempts to capture and store the excess flow for subsequent treatment are expensive, but the cost of separating combined sewer systems is prohibitive.
Agricultural wastes, should they flow directly into surface waters, have a collective population equivalent of about 2 billion. Feedlots where large numbers of animals are penned in relatively small spaces provide an efficient way to raise animals for food. They are usually located near slaughterhouses and thus near cities. Feedlot drainage and drainage from intensive poultry cultivation creates an extremely high potential for water pollution.
Aquaculture has a similar problem because wastes are concentrated in a relatively small space. Sediment from land erosion may also be classified as a pollutant. Sediment consists of mostly inorganic material washed into a stream as a result of land cultivation, construction, demolition, and mining operations.
Sediment interferes with fish spawning because it can cover gravel beds and block light penetration, making food harder to find. Sediment can also damage gill structures directly.
The huge tanker, loaded with crude oil, plowed into a reef in the English Channel, even though maps showed the submerged reefs. Despite British and French attempts to burn it, almost all of the oil leaked out and fouled French and English beaches. Eventually, straw to soak up the oil and detergents to disperse it helped remove the oil from the beaches, but the detergents were found to be the cleanup method more harmful to the coastal ecology.
Oil in Alaska is produced in the Prudhoe Bay region in northern Alaska and piped down to the tanker terminal in Valdez on the southern coast. On 24 March , the Exxon Valdez, a huge oil tanker loaded with crude oil, veered off course and hit a submerged reef, spilling about 11 million gallons of oil into Prince William Sound, devastating the fragile ecology. About 40, birds died, including about bald eagles. While oil spills as large as the Exxon Valdez spill get a lot of publicity, it is estimated that there are about 10, serious oil spills in the United States every year, and many more minor spills from routine operationsthat do not make headlines.
The effect of some of these spills may never be known. The acute effect of oil on birds, fish, and microorganisms is well catalogued. The subtle effects of oil on other aquatic life is not so well understood and is potentially more harmful.
Acid mine drainage has polluted surface waters since the beginning of ore mining. Sulfur-laden water leaches from mines, including old and abandoned mines as well as active ones, and contains sulfur compounds that oxidize to sulfuric acid on contact with air.
The resulting acidity of the stream or lake into which this water drains is often high enough to kill the aquatic ecosystem. The effects of water pollution can be best understood in the context of an aquatic ecosystem, by studying one or more specific interactions of pollutants with that ecosystem.
The study of ecosystems is ecology. Although we often draw lines around a specific ecosystem to be able to study it more fully e. One of the tenets of ecology is that "everything is connected with everything else. The producers take energy from the sun and nutrients like nitrogen and phosphorus from the soil and produce high-energy chemical compounds by the process of photosynthesis.
The energy from the sun is stored in the molecular structure of these compounds. Producers are often referred to as being in the first trophic growth level and are called autotrophs by the heterotrophs. The second category of organism in an ecosystem is the consumers, who use the energy stored by photosynthesis by ingesting the high-energy compounds. Consumers in the second trophic level use the energy of the producers directly.
There may be several more trophic levels of consumers, each using the level below it as an energy source. A simplified ecosystem showing various trophic levels is illustrated in Figure , which also shows the progressive use of energy through the trophic levels. The third category of organism, the decomposers or decay organisms, use the energy in animal wastes and dead animals and plants, thereby converting the organic compounds to stable inorganic compounds. The residual inorganics e.
Ecosystems exhibit a flow of both energy and nutrients. Energy flow is in only one direction: Nutrient flow, on the other hand, is cyclic: Nutrients are used by plants to make high-energy molecules that are eventually decomposed to the original inorganic nutrients, ready to be used again. The entire food web, or ecosystem, stays in dynamic balance, with adjustments being made as required.
This balance is called homeostasis. For example, a drought may produce little grass, starving field mice and exposing them to predators like owls. Water Pollution To outer space ", -. A typical terrestrial ecosystem.
The numbers refer to trophic level above the autotrophic, and the arrows show progressive loss of energy. Saunders Used with permission. External perturbations may upset and even destroy an ecosystem.
In the previous example, use of a herbicide to kill the grass instead of merely thinning it might also destroy the field mouse population, since the mice would be more exposed to predatory attack. Most ecosystems can absorb a certain amount of damage, but sufficiently large perturbations may cause irreversible damage. The ongoing attempt to limit the logging of old growth forests in the Pacific Northwest is an attempt to limit the damage to the forest ecosystem to what it can accommodate.
The amount of perturbation a system can absorb is related to the concept of the ecological niche. The combination of function and habitat of an organism in an ecosystem is its niche. A niche is an organism's best accommodation to its environment. In the example given previously, if there are two types of grass that the mice could eat, and the herbicide destroys only one, the mice would still have food and shelter, and the ecosystem could survive.
This simple example illustrates another important ecological principle: The stability of an ecosystem is proportional to the number of organisms capable of filling various niches. A jungle is a more stable ecosystem than the Alaskan tundra, which is very fragile. Another fragile system is that of the deep oceans, a fact that must be considered before the oceans are used as waste repositories.
Inland waterways tend to be fairly stable ecosystems, but are certainly not totally resistant to destruction by outside perturbations. Other than the direct effect of toxic materials like metals and refractory organic compounds, the most serious effect on inland waters is depletion of dissolved free oxygen DO.
All higher forms of aquatic life exist only in the presence of oxygen, and most desirable microbiologic life also requires oxygen. Natural streams and lakes are usually aerobic containing DO.
If a watercourse becomes anaerobic absence of oxygen , the entire ecology changes and the water becomes unpleasant and unsafe. The DO concentration in waterways and the effect of pollutants are closely related to the concept of decomposition and biodegradation, part of the total energy transfer system that sustains life.
Energy loss in biodegradation. McGraw-Hill Consumers eat and metabolize digest these compounds, releasing some of the energy for the consumer to use.
The end products of metabolism excrement become food for decomposers and are degraded further, but at a much slower rate than metabolism. After several such steps, very low energy compounds remain that can no longer be used by microorganism decomposers as food. Plants then use these compounds to build more high-energy compounds by photosynthesis, and the process starts over. The process is shown symbolically in Figure Many organic materials responsible for water pollution enter watercourses at a high energy level.
The biodegradation, or gradual use of energy, of the compounds by a chain of organisms causes many water pollution problems. If formaldehyde could decompose aerobically, the equation for decomposition would be the reverse of Equation 3. Aerobic nitrogen, carbon, and sulfur cycles. Both are stable, low in energy, and used by plants in photosynthesis plant photosynthesis is a major CO2 sink for the earth.
Sulfur compounds like the mercaptans in mammal excrement are oxidized to SO, the sulfate ion, and phosphorus is oxidized to PO4 3-, orthophosphate. A schematic representation of the aerobic cycle for carbon, sulfur, and nitrogen is shown in Figure This figure shows only the basic phenomena and greatly simplifies the actual steps and mechanisms. Anaerobic decomposition is performed by a completely different set of microorganisms, to which oxygen is toxic.
Methane CH4 , for example, a high-energy gas commonly called marsh gas, 2 is physi2When methane is burned as a fossil fuel it is called "natural gas. Anaerobic nitrogen, carbon, and sulfur cycles. Ammonia NH3 can be oxidized, and sulfur is anaerobically biodegraded to evil-smelling sulfhydryl compounds like hydrogen sulfide H2S. Figure is a schematic representation of anaerobic decomposition.
Note that the left half of the cycle, photosynthesis by plants, is identical to the aerobic cycle. Biologists often speak of certain compounds as hydrogen acceptors.
When energy is released from high-energy compounds a C-H or N-H bond is broken and the freed hydrogen must be attached somewhere. In aerobic decomposition, oxygen serves the purpose of a hydrogen scavenger or hydrogen acceptor and forms water.
In anaerobic decomposition, oxygen is not available. The next preferred hydrogen acceptor is NH3, since in the absence of oxygen ammonia cannot be oxidized to nitrite or nitrate. If no appropriate nitrogen compound is available, sulfur accepts hydrogen to form H2S, the compound responsible for the notorious rotten egg smell. The rate of reaeration, or solution of oxygen from the air, also increases, but is often not great enough to prevent a total depletion of oxygen in the stream.
When the stream DO is totally depleted, the stream is said to become anaerobic. Often, however, the DO does not drop to zero and the stream recovers without a period of anaerobiosis. Both of these situations are depicted graphically in Figure The dip in DO is referred to as a dissolved o x y g e n sag curve. The dissolved oxygen sag curve can be described mathematically as a dynamic balance between the use of oxygen by the microorganisms deoxygenation and the supply of oxygen from the atmosphere reoxygenation.
The mathematical derivation of the oxygen sag curve is included in the appendix to this chapter. Stream flow is of course variable, and the critical DO levels can be expected to occur when the flow is the lowest. Accordingly, most state regulatory agencies base their calculations on a statistical low flow, such as a 7-day, year low flow: This is calculated by first estimating the lowest 7-day flow for each year and then assigning ranks: Dissolved oxygen downstream from a source of organic pollution.
The curve shows a DO sag without anaerobic conditions. Example 3. When the rate of oxygen use overwhelms the rate of oxygen resupply, the stream may become anaerobic. An anaerobic stream is easily identifiable by the presence of floating sludge and bubbling gas. The gas is formed because oxygen is no longer available to act as the hydrogen acceptor, and ammonia, hydrogen sulfide, and other gases are formed. Some of the gases formed dissolve in water, but others can attach themselves as bubbles to sludge solid black or dark benthic deposits and buoy the sludge to the surface.
In addition, the odor of H2S will advertise the anaerobic condition for some distance, the water is usually black or dark, and fungus grows in long slimy filaments that cling to rocks and gracefully wave streamers downstream. The outward evidence of an anaerobic stream is accompanied by adverse effects on aquatic life. Types and numbers of species change drastically downstream from the pollution discharge point.
Fewer and fewer species of fish are able to survive, but those that do find food plentiful and often multiply in large numbers. Carp and catfish can survive in waters that are quite foul and can even gulp air from the surface. Trout, on the other hand, need very pure, cold, oxygen-saturated water and are notoriously intolerant of pollution.
Numbers of other aquatic species are also reduced, and the remaining species like sludge worms, bloodworms, and rat-tailed maggots abound, often in staggering numbers--as many as 50, sludge worms per square foot.
Figure illustrates the distribution of both species and numbers of organisms downstream from a source of pollution. These reactions of a stream to pollution occur when a rapidly decomposable organic material is the waste. The number of species and the total number of organisms downstream from a point of organic pollution TABLE If the waste is toxic to aquatic life, both the kind and total number of organisms will decrease below the outfall.
The DO will not fall and might even rise. There are many types of pollution, and a stream will react differently to each Figure When two or more wastes are involved the situation is even more complicated. Light and temperature have significant influences on a lake, more so than on a stream, and must be included in any limnological 3 analysis. Light is the source of energy in the photosynthetic reaction, so that the penetration of light into the lake water is important.
This penetration is logarithmic; for example, at a depth of I foot the light intensity may be 10, ft-candles a measure of light intensity ; at a depth of 2 feet, it might be ft-candles; at 3 feet, ft-candles, and at 4 feet, 10 ft-candles.
Light usually penetrates only the top two feet of a lake; hence, most photosynthetic reactions occur in that zone. Temperature and heat can have a profound effect on a lake. Water is also a poor conductor of heat and retains it quite well. Lake water temperature usually varies seasonally. Figure illustrates these temperature-depth relationships. During the winter, assuming that the lake does not freeze, the temperature is often constant with depth.
As the weather warms in spring, the top layers begin to warm. Since warmer water is less dense, and water is a poor conductor of heat, a distinct temperature gradient known as thermal stratification is formed. These strata are often very stable and last through the summer months. The top layer is called the epilimnion; the middle, the metalimnion; and the bottom, the hypolimnion. The inflection point in the curve is called the thermocline.
Circulation of water occurs only within a zone, and thus there is only limited transfer of biological or chemical material including DO across the boundaries. As the colder weather approaches, the top layers begin to cool, become more dense, and sink. This creates circulation within the lake, known as fall turnover.
A spring turnover may also occur. The biochemical reactions in a natural lake may be represented schematically as in Figure A river feeding the lake would contribute carbon, phosphorus, and nitrogen, either as high-energy organics or as low-energy compounds.
The phytoplankton or algae microbial flee-floating plants take C, P, and N and, using sunlight as a source of energy, make high-energy compounds. Algae are eaten by zooplankton tiny aquatic animals , which are in turn eaten by larger aquatic life such as fish.
All of these life forms defecate, contributing a pool of dissolved organic carbon. This pool is further fed by the death of aquatic life. Bacteria use dissolved organic carbon and produce CO2, in turn used by algae. CO2 in addition to that dissolved directly is provided from the respiration of the fish and zooplankton, as well as the CO2 dissolved directly from the air. The supply of C, P, and N coming into an unpolluted lake is small enough to limit algae production, and productivity of the entire ecological system is limited.
When large amounts of C, P, and N are introduced into the lake, however, they promote uncontrolled growth of algae in the epilimnion, since the algae can 3Limnology is the study of lakes. Schematic representation of lake ecology [Courtesy of Donald Francisco. When the algae die, they drop to the lake bottom the hypolimnion and become a source of carbon for decomposing bacteria. Aerobic bacteria will use all available DO in decomposing this material, and DO may thereby be depleted enough to cause the hypolimnion to become anaerobic.
As more and more algae die, and more and more DO is used in their decomposition, the metalimnion may also become anaerobic, and aerobic biological activity would be concentrated in the upper few feet of the lake, the epilimnion. The aerobic biological activity produces turbidity, decreasing light penetration and in turn limiting photosynthetic algal activity in the surface layers. The amount of DO contributed by the algae is therefore decreased.
Eventually, the epilimnion also becomes anaerobic, all aerobic aquatic life disappears, and the algae concentrate on the lake surface because there is only enough light available for photosynthesis. The algal concentration forms large green mats, called algal blooms.
When the algae in these blooms die and ultimately fill up the lake, a peat bog is formed. The entire process is called eutrophication. It is the continually occurring natural process of lake aging and occurs in three stages: Natural eutrophication may take thousands of years.
If enough nutrients are introduced into a lake system, as may happen as a result of human activity, the eutrophication process may be shortened to as little as a decade. The addition of phosphorus, in particular, can speed eutrophication, since phosphorus is often the limiting nutrient for algae: The limiting nutrient for a system is that element the system requires the smallest amount of; consequently, growth depends directly on the amount of that nutrient.
One source is excrement, since all human and animal wastes contain C, N, and P. Synthetic detergents and fertilizers are a much greater source. About half of the phosphorus in U. It seems unfortunate that the presence of phosphates in detergents has received so much unfavorable attention when runoff from fertilized land is a much more important source of P. All of the components are available to make the car go faster, but it can't speed up until you "give it more gas.
Dumping excess phosphorus into a lake is like floorboarding the gas pedal. Water Pollution 47 Conversion to nonphosphate detergents is of limited value when other phosphate sources are not controlled. Phosphate concentrations between 0. High phosphorus concentration is not a problem in a moving stream, in which algae are continually flushed out and do not accumulate.
Eutrophication occurs mainly in lakes, ponds, estuaries, and sometimes in very sluggish rivers. Phosphorus is not always the culprit in accelerated eutrophication. Generally, a P: C ratio of 1: P is the limiting nutrient if N and C are in excess of this ratio. However, in some lakes, P can be present in excess and N can act as the limiting nutrient. Evidence suggests that nitrogen limits growth in brackish waters like bays and estuaries.
Interaction among the many chemical pollutants present, rather than any single chemical, is often to blame for accelerated eutrophication. Actual profiles in a lake for a number of parameters are shown in Figure The foregoing discussion clarifies why a lake is warmer on top than lower down, how DO can drop to zero, and why N and P are highly concentrated in the lake depths while algae bloom on the surface.
The manufacture of chlorine and lye from brine, called the chlor-alkali process, was identified as a major source of mercury contamination. Elemental mercury is methylated by aquatic organisms, and methylated mercury finds its way into fish and shellfish and thus into the human food chain.
Methyl mercury is a powerful neurological poison. Methyl mercury poisoning was first identified in Japan in the s as "Minamata disease. Arsenic, copper, lead, and cadmium are often deposited in lakes and streams from the air near emitting facilities. These substances may also enter waterways from runoff from slag piles, mine drainage, and industrial effluent. Effluent from electroplating contains a number of heavy metal constituents.
Heavy metals, copper in particular, may be toxic to fish as well as harmful to human health, In the past quarter century, a considerable incidence of surface water contamination by hazardous and carcinogenic organic compounds was reported in the United States. The sources of contamination include effluent from petrochemical industries and agricultural runoff, which contains both pesticide and fertilizer residues.
However, we now recognize seas and oceans as fragile environments and are able to measure detrimental effects. Ocean water is a complicated chemical solution and appears to have changed very little over millions of years. Because of this constancy, however, marine organisms have become specialized and intolerant to environmental change. Oceans are thus fragile ecosystems, quite susceptible to pollution. A relief map of the ocean bottom reveals two major areas: The continental shelf, especially near major estuaries, is the most productive in terms of food supply.
Because of its proximity to human activity, it receives the greatest pollution load. Many estuaries have become so badly polluted that they are closed to commercial fishing. The Baltic and Mediterranean seas are in danger of becoming permanently damaged. Ocean disposal of wastewater is severely restricted in the United States, but many major cities all over the world still discharge all untreated sewage into the ocean, s Although the sewage is carried a considerable distance from shore by pipeline and discharged through diffusers to achieve maximum dilution, the practice remains controversial, and the long-term consequences are much in doubt.
Rivers and streams demonstrate some capacity to recover from the effects of certain pollutants, but lakes, bays, ponds, and sluggish rivers may not recover. The oceans are far more sensitive to pollutants than was thought. The effects of pollutants on oceans and groundwater, and the effects of inorganic poisons like heavy metals, also do not receive detailed discussion here.
Phosphorus should have been included in the cycle since it exists as organically bound phosphorus in living and dead tissue and decomposes to polyphosphates such as P 4- and P s-, and finally to orthophosphates such as PO Draw a phosphorus cycle similar to Figure Suppose that analysis of lake water yields the following: Which elements are the limiting nutrients for the growth of algae in this lake?
Assume the stream flow equals the flow of wastewater. Do not calculate. You may write a computer program or use a spreadsheet program to solve this problem. The rate of oxygen use, or oxygen depletion, may be expressed as Rate of deoxygenation - - k f z where 3. This assumption is generally valid for low concentrations. The value of kl' , the rate constant, is measured in the laboratory, as discussed in the next chapter.
Integrating Equation 3. USPHS Time Although y is c o m m o n l y termed oxygen demand, it is more correctly described as the DO used. In this text, we use the terms D O demand and D O used synonymously. If this cannot be done, a generalized expression O ' C o n n o r m a y be used: From O'Connor, D. The shape of the oxygen sag curve, as shown in Figure , is the sum of the rate of oxygen use and the rate of oxygen supply. Immediately downstream from a pollution discharge into a stream, the rate of use will exceed the reaeration rate and the DO concentration will fall sharply.
As the discharged sewage is oxidized, and fewer high-energy organic compounds are left, the rate of use will decrease, the supply will begin to catch up with the use, and the DO will once again reach saturation. The rate of change in the oxygen deficit D depends on the concentration of decomposable organic matter, or the need by the microorganisms for oxygen z and the oxygen deficit at any time t.
Environmental Policies for Agricultural Pollution Control. Effluent and Water Treatment. Microbiological aspects of pollution control Fundamental aspects of pollution control and environmental science, Volume 2. Environmental Pollution. Mutagenicity testing as an analytical tool in environmental pollution control.
CECO Environmental wins orders for air pollution control equipment. McKnight, Pauline K. Marstrand and T. Craig Sinclair. Allen and Unwin, London Foreword by Lord Ashby, F. The reader wishing to obtain a fundamental grounding in the technical and legal aspects of pollution of the environment in most of its forms will find that this book has much to offer. Written by a panel of specialists it deals with technical and legal aspects, both national and international, of pollution of the air, of inland waters and of the sea, and of noise pollution and dereliction of the land.
The section on air pollution contains a comprehensive account of pollutants of the atmosphere, the sources from which they arise, their nature, reactions and removal by sedimentation and rain. Water pollution is discussed under "'Pollution of Inland Waters" and "Pollution of the Seas", both from the technical and legislative standpoints. If there is a criticism of what is otherwise a comprehensive study, it lies in the preponderance of the biological considerations; this may not of itself by unreasonable, but it is a pity, for example, that in describing the main pollutants of inland waters, the effects of ammonia as an oxygen-consuming source and the role of Introduction to Environmental Microbiology.
Ralph Mitchell Although the author states that this book is intended for students of environmental engineering and science it deserves to be widely read by everyone interested in the complex dynamic inter-relationships between microorganisms and their environment.
No knowledge of microbiology is assumed, but nevertheless a wide variety of situations in which microorganisms play a leading role are considered at a level which is high enough to hold the interest of any intelligent reader, whether professionally involved in environmental affairs or not.
The author's skill in the presentation of information combined with a lucid, unpretentious style only partly account for the pleasure the reviewer has had in reading his book.
The rest is derived from the logical arrangement of the various chapters and the excellent diagrams and tabular matter that seem to have been carefully selected to complement the text. These chapters introduce the reader to the growth and death of microorganisms, after introductory accounts of the principles of ecology and the culturing of organisms.
The public health significance of microorganisms is not overlooked--though the author might have given even greater emphasis to the important relationship between man's environmental and social conditions and the incidence of outbreaks of waterborne diseases.
The growing concern of organic compounds that resist attack by microorganisms and so remain in the environ- nitrate, in waters abstracted for public supply, as a potential cause of methaemoglobinaemia are not mentioned. By far the largest chapter deals with social and technical aspects of noise pollution.
The author presents a comprehensive survey of the relative importance of noise sources and the cost in terms of damage sustained by the human frame so exposed and also in terms of remedial costs such as sound proofing.