CHAPTER 12 Self-Purification of Streams In terms of practical usefulness the waste assimilation capacity of streams as a water resource has its basis in the complex phenomenon termed stream self-purification. This is a dynamic phenomenon reflecting hydrologic and biologicvariations, and the interrelations are not yet fully un- derstood in precise terms. However, this does not preclude applying what is known. Sufficient knowledge is available to permit quantitative definition of resultant stream conditions under expected ranges of variation to serve as practical guides in decisions dealing with water resource use, develop- ment, and management C. J. Velz202 12.1 BALANCING THE 'YUXJARIUM" A N outdoor excursion to the local stream can be a relaxing and enjoyable un- dertaking. On the other hand, when you arrive at the local stream and look upon the stream's flowing mass to discover a parade of waste and discarded rub- ble bobbing along the stream's course and cluttering the adjacent shoreline and downstream areas, any feeling of relaxation or enjoyment is quickly extin- guished. Further, the sickening sensation the observer feels is made worse as closer scrutiny of the putrid flow is gained. The rainbow-colored shimmer of an oil slick, interrupted here and there by dead fish and floating refuse, and the slimy fungal growth that prevails are recognized. At the same time, the ob- server's sense of smell is alerted to the noxious conditions. Along with the fouled water and the stench, the observer notices signs warning, "DANGER-NO SWIMMING or FISHING." The observer has discovered what ecologists have known and warned about for years. That is, contrary to popular belief, rivers and streams do not have an infinite capacity for pollution. Before the early 1970s, such disgusting occurrences as the one just de- scribed were common along the rivers and streams near main metropolitan ar- 202~elz, C. J., Applied Stream Sanitation. New York: Wiley-Interscience, p. 66, 1970. Copyright © 2001 by Technomic Publishing Company, Inc. 158 SELF-PURIFICATION OF STREAMS eas throughout most of the United States. Many aquatic habitats were fouled during the past because of industrialization. However, our streams and rivers were not always in such deplorable condition. Before the Industrial Revolution of the 1800s, metropolitan areas were small and sparsely populated. Thus, river and stream systems within or next to early communities received insignificant quantities of discarded waste. Early on, these river and stream systems were able to compensate for the small amount of wastes they received. They have the ability to restore themselves through their own self-purification process. It was only when humans gathered in great numbers to form cities that the stream systems were not always able to recover from having received great quantities of refuse and other wastes. Halsam pointed out that man's actions are determined by his expediency. We have the same amount of water as we did millions of years ago, and through the water cycle, we continually reuse that same water-water that was used by the ancient Romans and Greeks is the same water being used today. Increased demand by man has put enormous stress on our water supply. Thus, man upsets the delicate balance between pollution and the purification process of rivers and streams, unbalancing the "aquarium." With the advent of industrialization, local rivers and streams became deplor- able cesspools that worsened with time. During the Industrial Revolution, the removal of horse manure and garbage from city streets became a pressing con- cern; for example, Moran et al. point out that "none too frequently, garbage col- lectors cleaned the streets and dumped the refuse into the nearest river."203 Halsam reports that as late as 1887, river keepers gained full employment by re- moving a constant flow of dead animals from a river in London. Moreover, the prevailing attitude of that day was "I don't want it anymore, throw it into the river."204 As of the early 1970s, any threat to the quality of water destined for use for drinking and recreation has quickly angered those affected. Fortunately, since the 1970s, efforts have been made to correct the stream pollution problem. Through scientific study and incorporation of wastewater treatment technol- ogy, streams have begun to be restored to their natural condition. And, the stream itself aids in restoring its natural water quality through the phenomenon of self-purification. A balance of biological organisms is normal for all streams. Clean, healthy streams have certain characteristics in common. For example, one property of streams is their ability to dispose of small amounts of pollution. However, if streams receive unusually large amounts of waste, the stream life will change and attempt to stabilize such pollutants; that is, the biota will attempt to balance 203~oran, J. M., Morgan, M. D., and Wiersma, J. H., Introduction to Environmental Science. New York: W.H. Freeman and Company, p. 21 1,1986. 204~alsam, S. M., River Pollution: An Ecological Perspective. New York: Belhaven Press, p. 21, 1990. Copyright © 2001 by Technomic Publishing Company, Inc. Sources of Stream Pollution 159 the "aquarium." However, if the stream biota are not capable of self-purifying, then the stream may become a lifeless body. The self-purification process discussed here relates to the purification of or- ganic matter only. In this chapter, organic stream pollution and the self-purifi- cation process will be discussed. 12.2 SOURCES OF STREAM POLLUTION Sources of stream pollution are normally classified as point or non-point sources. A point source (PS) is a source that discharges effluent, such as wastewater from sewage treatment and industrial plants. A point source is usu- ally easily identified as "end of the pipe" pollution; that is, it emanates from a concentrated source or sources. In addition to organic pollution received from the effluents of sewage treatment plants, other sources of organic pollution in- clude runoffs and dissolution of minerals throughout an area and are not from one or more concentrated sources. Non-concentrated sources are known as non-point sources (see Figure 12.1). Non-point source (NPS) pollution, unlike pollution from industrial and sewage treatment plants, comes from many diffuse sources. NPS pollution is caused by rainfall or snowmelt moving over and through the ground. As the Agricultural Runoff Industrial Waste Wastewater Treatment Figure 12.1 Point and non-point sources of pollution. Copyright © 2001 by Technomic Publishing Company, Inc. 160 SELF-PURIFICATION OF STREAMS runoff moves, it picks up and carries away natural and man-made pollutants, fi- nally depositing them into streams, lakes, wetlands, rivers, coastal waters, and even our underground sources of drinking water. These pollutants include the following: excess fertilizers, herbicides, and insecticides from agricultural lands and residential areas oil, grease, and toxic chemicals from urban runoff and energy produc- tion sediment from improperly managed construction sites, crop and forest lands, and eroding streambanks salt from irrigation practices and acid drainage from abandoned mines bacteria and nutrients from livestock, pet wastes, and faulty septic sys- tems Atmospheric deposition and hydromodification are also sources of non-point source pollution.205 As mentioned, specific examples of non-point sources include runoff from agricultural fields and also cleared forest areas, construction sites, and road- ways. Of particular interest to environmentalists in recent years has been agri- cultural effluents. As a case in point, farm silage effluent has been estimated to be more than 200 times as potent [in terms of biochemical oxygen demand (BOD)] as treated sewage.206 Nutrients are organic and inorganic substances that provide food for micro- organisms such as bacteria, fungi, and algae. Nutrients are supplemented by the discharge of sewage. The bacteria, fungi, and algae are consumed by the higher trophic levels in the community. Each stream, due to a limited amount of dis- solved oxygen (DO), has a limited capacity for aerobic decomposition of or- ganic matter without becoming anaerobic. If the organic load received is above that capacity, the stream becomes unfit for normal aquatic life, and it is not able to support organisms sensitive to oxygen depletion.207 Effluent from a sewage treatment plant is most commonly disposed of in a nearby waterway. At the point of entry of the discharge, there is a sharp decline in the concentration of DO in the stream. This phenomenon is known as the oxy- gen sag. Unfortunately (for the organisms that normally occupy a clean, healthy stream), when the DO is decreased, there is a concurrent massive in- crease in BOD as microorganisms utilize the DO as they break down the or- ganic matter. When the organic matter is depleted, the microbial population and BOD decline, while the DO concentration increases, assisted by stream 205~~~~~. What is Nonpoint Source Pollution? Washington, DC: United States Environmental Protection Agency, EPA-F-94-005, pp. 1-5, 1994. 206~ason, C. F., "Biological aspects of freshwaterpollution." In Pollution: Causes, Enects, and Control. Harrison, R.M. (ed.), Cambridge, Great Britain: The Royal Society of Chemistry, p. 11 3, 1990. 207~mith, R. L., Ecology and Field Biology. New York: Harper & Row, p. 323, 1974. Copyright © 2001 by Technomic Publishing Company, Inc. Saprobity of a Stream 161 flow (in the form of turbulence) and by the photosynthesis of aquatic plants. This self-purification process is very efficient, and the stream will suffer no permanent damage as long as the quantity of waste is not too high. Obviously, an understanding of this self-purification process is important to prevent over- loading of the stream ecosystem. As urban and industrial centers continue to grow, waste disposal problems also grow. Because wastes have increased in volume and are much more con- centrated than before, natural waterways must have help in the purification pro- cess. This help is provided by wastewater treatment plants. A wastewater treat- ment plant functions to reduce the organic loading that raw sewage would impose on discharge into streams. Wastewater treatment plants utilize three stages of treatment: primary, secondary, and tertiary treatment. In breaking down the wastes, a secondary wastewater treatment plant uses the same type of self-purification process found in any stream ecosystem. Small bacteria and protozoans (one-celled organisms) begin breaking down the organic material. Aquatic insects and rotifers are then able to continue the purification process. Eventually, the stream will recover and show little or no effects of the sewage discharge. This phenomenon is known as natural stream purification.208 12.3 SAPROBITY OF A STREAM Treated or untreated sewage dumped into streams can upset the ecological stability of the stream. Through natural processes and bacterial activity, streams can purify themselves. High concentrations of organic substances en- courage the growth of decomposers such as bacteria and fungi, which convert the biodegradable organic substances in the stream into their cells and into ba- sic substances like carbon dioxide, nitrates, sulfates, and phosphates. These ba- sic substances and those contributed by the dissolution of rocks are converted by producers, algae and other plants, into their protoplasm. The normal food chain is then established with higher trophic levels. All consumers produce wastes that, with the organics from runoffs and sewage, are converted by bacte- ria and fungi into basic substances, thus establishing an ecosystem or a cyclic phenomenon. Excess organic wastes upset this system by depleting the dissolved oxygen (DO) required by bacteria for aerobic decomposition of organics. In other words, the biochemical oxygen demand (BOD) of the stream increases, creat- ing an inverse relationship between sewage and oxygen in the stream. The nor- mal amount of dissolved oxygen in streams is above 9 mg/L at 20°C (68°F) wa- ter temperature. As the level of DO decreases to 5 mg/L, sensitive organisms-such as predators like trout-disappear. Figure 12.2 shows the 208~pellman, F. R. and Whiting, N. E., Water Pollution Control Technology: Concepts and Applications. Rockville, MD: Government Institutes, pp. 247-317, 1999. Copyright © 2001 by Technomic Publishing Company, Inc. SELF-PURIFICATION OF STREAMS 8 to 9 6.7 to 8 4.5 to 6.7 below 4.5 below 4 Good Slightly Moderately Heavily Gravely Polluted Polluted Polluted Polluted Figure 12.2 Water quality and DO content. (Source: Adapted from G. T. Miller, Environmental Sci- ence: An Introduction. Belmont, CA: Wadsworth, p. 351, 1988.) correlation between water quality and dissolved oxygen (DO), in parts per mil- lion at 20°C. As oxygen depletion progresses, other game fish, insects, crustaceans, roti- fers, and even sensitive protozoans tend to be absent from the food chains. Ulti- mately, bacteria of facultative (can use oxygen and, under certain conditions, can grow in the absence of oxygen) and anaerobic types exist. Due to reaeration, streams do not reach a 0 ppm DO level and, thus, seldom go anaero- bic. The degree of pollution and the character of the stream determine the amount of time the self-purification process will take. The amount of organic matter and the activity by microbial communities liv- ing on it is called the saprobity of the stream's ecosystem. The term saprobity was introduced in Germany early in the twentieth century for the assessment of water quality, and saprobity as both a term and practical approach has been pri- marily used in Europe. Waters are said to have saprobic level (which can be measured using the species present and their relative abundance), in effect, a bi- otic index of organic pollution. As mentioned, the communities change, quali- tatively and quantitatively, as organic content increases.209 12.3.1 DEFINITION OF KEY TERMS In order to better appreciate a discussion of stream saprobity (i.e., stream 209~dapted from Jeffries, M. and Mills, D., Freshwater Ecology: Principles andApplications. London: Belhaven Press, p. 154, 1990. Copyright © 2001 by Technomic Publishing Company, Inc. Saprobity of a Stream 163 pollution) and the self-purification process, a restatement, in greater detail, of two critical terms, previously defined or mentioned, is necessary: Dissolved oxygen (DO) is the amount of oxygen dissolved in a stream. It in- dicates the degree of health of the stream and its ability to support a balanced aquatic ecosystem. The oxygen comes from the atmosphere by solution and from photosynthesis of water plants. In a lentic (lake) environment, oxygen is added primarily by photosynthetic activity and secondarily by wind-in- duced wave action. In fast streams, oxygen is added primarily through reaeration from the atmosphere in rapids, waterfalls, and cascades. DO con- centrations are usually higher and more uniform from surface to bottom in streams than in lakes. Biochemical oxygen demand (BOD) is the amount of oxygen required to bi- ologically oxidize organic waste matter over a stated period of time. BOD is important in the self-purification process, because in order to estimate the rate of deoxygenation in the stream, the five-day and ultimate BOD must be known. Most sewage wastes contain high concentrations of organic substances. Their presence encourages the growth of decomposers. Decomposers consume large quantities of DO. A stream receiving an excessive amount of sewage (organic wastes) exhib- its changes, which can be differentiated and classified into zones. Upstream, before a single point of pollution discharge, the stream is defined as having a clean zone. At the point of discharge, the water becomes turbid. This is called the zone of recentpollution. Shortly below the discharge point, the level of dis- solved oxygen falls sharply and, in some cases, may fall to zero; this is called the septic zone (Figure 12.3). Point Source Pollution Clean Zone of Recent septic Zone Pollution Zone Recovery - Zone Clean Zone DO Normal DO Normal Figure 12.3 Changes that occur in a stream after it receives an excessive amount of raw sewage. Copyright © 2001 by Technomic Publishing Company, Inc. SELF-PURIFICATION OF STREAMS Low BOD (few organics to be degraded) Ihmstic Dilution and Recovery Zone - several miles High BOD (Large amount of sewage) Figure 12.4 Effect of organic wastes on DO. (Source: Adapted from E. Enger, J. R. Kormelink, B. F. Smith, and R. J. Smith, Environmental Science: The Study of Interrelationships. Dubuque, IA: Wil- liarn C. Brown Publishers, p. 41 l, 1989.) After the organic waste has been largely decomposed, the dissolved oxygen level begins to rise in the recovery zone. Eventually, given enough time and no further waste discharges, the stream will return to conditions similar to those in the clean zone. The total change in organic matter in the stream at any time can be modeled. One simple model makes the assumption that the total change in the concentra- tion of organic matter per time is a function of the initial rate of input of organic matter minus losses due to in-stream decomposition, assimilation by detritivores, and sedimentation of waste.210 In Figure 12.4 it can clearly be seen that sewage containing a high concentra- tion of organic material is attacked by organisms, which use oxygen in the deg- radation process. Thus, there is an inverse relationship between oxygen and sewage in the stream. The greater the BOD, the less desirable the stream is for human use. As stated previously, when excessive sewage is dumped into a stream, change occurs. These changes are shown in Figure 12.2. In order to foster a better appreciation for the changes that occur in each zone, the following infor- mation is provided. 12.3.1 .l Clean Water Zone The clean water zone (see Figure 12.3) is the stretch of stream above the point of discharge (and is restored downstream once the self-purification pro- 210~estman, W. E., Ecolog): Impact Assessment, and Environmental Planning. New York: John Wiley & Sons, Inc., p. 233, 1985. Copyright © 2001 by Technomic Publishing Company, Inc. Saprobity of a Stream 165 cess is complete). In this zone, the stream is in an entirely natural state and con- tains no pollutants. Many different organisms are present, including the mayfly nymph, which has a narrow range of tolerance for DO. Also, many kinds of game fish are present in this zone. The following is a list of other characteris- tics: (1) High DO (2) Low BOD (3) Clear water (low turbidity) and no odors (4) Low bacterial count (5) Low organic content (6) High species diversity (7) Bottom clean and free of sludge (8) Presence of normal communities containing sensitive organisms such as bass, bluegill, perch, crayfish, and stonefly nymphs 12.3.1.2 Zone of Recent Pollution (Degradation Zone) The zone of recent pollution (see Figure 12.3) occurs at the point of sewage discharge where turbidity increases while the DO content decreases. This sud- den introduction of a heavy load of sewage (organic pollution) increases BOD and, hence, accelerates the growth of bacteria and fungi. When the organic ma- terial is degraded by organisms, the amount of DO decreases in various points in a stream and leads to a succession of changes in community structure. Changes caused by the pollution in the environment and the community are as follows: (1) DO variable depending upon organic load (2) High BOD (3) Turbidity high (4) Bacterial count high and increasing (5) Lower species diversity (6) Increase in number of individuals per species (7) Appearance of slime molds and sludge deposits on bottom The biota is represented by the following: (1) Flora (Plants): blue-green algae, spirogyra, gomphonema (2) Annelids: sludgeworms (Tubificidae) (3) Insects: back swimmers, water boatman, and dragonflies (4) Fish: tolerant fish such as catfish, gars, and carp Copyright © 2001 by Technomic Publishing Company, Inc. 166 SELF-PURIFICATION OF STREAMS 12.3.1.3 Septic Zone (Active Decomposition) At this stage, active decomposition of the organic matter is proceeding at the optimum rate; thus, the rate of deoxygenation is greater than the supply or reaeration rate from the atmosphere. In some cases, DO is completely absent, hence the name septic zone (see Figure 12.3). In this zone, the organic waste material requires more oxygen in its decomposition than is naturally available in the stream. Only a few species other than bacteria occupy this zone. For ex- ample, in general, fish are completely absent. If the organic load is too high, bacteria may consume all the DO and start anaerobic decomposition of organics by first obtaining oxygen from nitrates and sulfates and then continu- ing without any oxygen. Anaerobic products include hydrogen sulfide, ammo- nia, methane, and hydrogen, which cause offensive odors (H2S causes rot- ten-egg odor) and a toxic environment. Sludge mats may form and rising gas bubbles result. Due to reaeration, streams normally do not go completely septic (anaerobic). The rate of reaeration increases with the decrease in dissolved oxy- gen in the water and vice versa. Other characteristics may include the follow- ing: (1) Very little to the complete absence of DO, especially during warm weather (2) BOD high but decreasing (3) Water very turbid and dark, often with an offensive odor (4) High but decreasing organic content (5) High bacterial count (6) Low species diversity (7) Slime blanket on the bottom with floating sludge (8) Oily appearance on the water surface (9) Rising gas bubbles The biota present is represented by the species that are highly adapted to pol- luted conditions: (1) Flora: only some blue-green algae (2) Annelids: sludgeworms (3) Insects: mosquito larvae and rattailed larvae (drone flies) (4) Mollusks: air-breathing snails (5) Fish: absent 12.3.1.4 Recovery Zone In the recovery zone (see Figure 12.3), the stream has nearly completed its self-purification process. Most of the organic matter has been decomposed into Copyright © 2001 by Technomic Publishing Company, Inc. [...]... increase and number of each species decrease is characteristic of which zone? 12. 2 End-of-the-pipe pollution is also known as Copyright © 2001 by Technomic Publishing Company, Inc 188 SELF- PURIFICATION OF STREAMS is caused by rainfall or snowmelt moving over and through 12. 3 the ground 12. 4 are organic and inorganic substances that provide food for microorganisms such as bacteria, fungi, and algae 12. 5... Reaeration Constants (KZ)for Water Bodies Water Body Ranges of K2 at 20°C Backwaters Sluggish streams Large streams (low velocity) Large streams (normal velocity) Swift streams Rapids Copyright © 2001 by Technomic Publishing Company, Inc 0.1 0-0 .23 0.2 3-0 .35 0.3 5-0 .46 0.4 6-0 .69 0.6 9-1 .1 5 >1.15 184 SELF- PURIFICATION OF STREAMS The reaeration constant for turbulence that is typical in deep streams can be found... Point Stream Flow - +V = 1 mph X I - -UA DO - DO Combined cOxygen Sag Curve Minimum W tc Time ) 12. 11.2 EXAMPLE 2 Calculate deoxygenation constant K, for a domestic sewage with BOD5, 135 mg/L and BOD2,, 400 mg/L - - log 0.66 5 = 0.3611 day Copyright © 2001 by Technomic Publishing Company, Inc SELF- PURIFICATIONOF STREAMS 400 300 200 0 Time i Days n Figure 12. 8 Sketch of the carbonaceous and... 9.51 4.35 10.63 3.65 11.35 3.26 11.74 3.08 11.92 3.02 11.98 3.00 12. 00 3.00 12. 00 3.00 12. 00 3.00 12. 00 3.00 12. 00 Slow Stream: 20°C Sewage Rate: 14 pprn Treatment: Primary Oxygen Waste 13.27 2.74 13.26 2.87 13.22 3.03 13.14 3.20 13.03 3.35 12. 94 3.46 12. 87 3.53 12. 83 3.57 12. 81 3.59 12. 80 3.60 12. 80 3.60 12. 80 3.60 12. 80 3.60 12. 80 3.60 12. 80 3.60 Slow River: 1°C Sewage Rate: 7 pprn Treatment: Secondary... source. 212 2'1~iller, T., Environmental Science: An Introduction Belmont, CA: Wadsworth, p 351, 1988 G 212~ nger, Kormelink, J R., Smith, B F., and Smith, R J., Environmental Science: The Studj of InterrelationE., ships Dubuque, IA: Williarn C Brown Publishers, p 312, 1981 Copyright © 2001 by Technomic Publishing Company, Inc 168 SELF- PURIFICATIONOF STREAMS 12. 4 ORGANISMS AND THEIR ROLE IN SELF- PURIFICATION... this is seldom true A stream, from reach to reach, changes Additionally, because rivers and streams are usually longer than they are wide, organic pollution mixes rapidly in these surface waters Further, some rivers and streams are wider than others Thus, the mixing of organic pollutants with river or stream water does not occur at the same rate in different rivers and streams 12. 11 l EXAMPLE 1 Use... fungi, and algae 12. 5 The amount of organic matter and the activity by microbial communities living on it is called the of the stream' s ecosystem 12. 6 is the amount of oxygen dissolved in a stream 12. 7 We can say that secondary wastewater treatment is analogous to a 12. 8 Protozoans are one-celled and 12. 9 The on bacteria is obtained using the Streeter-Phelps Equation 12. 10 Explain Henry's Law Copyright... the atmosphere and the amount of biodegradable organic matter in the stream K2, or reaeration constants, are given in Table 12. 3 The reaeration constant for a fast-moving, shallow stream is higher than that for a sluggish stream or a lake The reaeration constant for shallow streams, where vertical gradient and sheer stress exist, is commonly found using the following formulation: TABLE 12. 3 Typical Reaeration... pollution Table 12. 2e depicts sewage dumped into a fast-flowing stream and the resulting effects on environmental conditions A fast-flowing stream is constantly aerated with oxygen and will purify itself much faster than a slow stream This phenomenon is clearly evident when one compares the data in Table 12. 2e with the data presented in previous tables dealing with slower streams In Table 12. 2f, the impact... the desired end result, then convert the mg/L-I to % saturation using Figure 12. 7.221 As an example, if the water temperature was 12 C and the DO was measured at 10 mgL-l, the % saturation of oxygen is 78 12. 1 1 STREAM PURIFICATION: A QUANTITATIVE ANALYSIS222 Before sewage is dumped into a stream, it is important to determine the maximum BOD loading for the stream to avoid rendering it septic The most . Publishing Company, Inc. 168 SELF- PURIFICATION OF STREAMS 12. 4 ORGANISMS AND THEIR ROLE IN SELF- PURIFICATION As mentioned, the self- purification process in streams is similar to the puri- fication. Publishing Company, Inc. 160 SELF- PURIFICATION OF STREAMS runoff moves, it picks up and carries away natural and man-made pollutants, fi- nally depositing them into streams, lakes, wetlands, rivers,. purification of or- ganic matter only. In this chapter, organic stream pollution and the self- purifi- cation process will be discussed. 12. 2 SOURCES OF STREAM POLLUTION Sources of stream pollution