NCYWG

We find nowadays, almost on a daily basis, media reports of some or other occurrence concerning some form of pollution. Of very serious concern, are the regular reports of pollution concerning the water reserves of this country.

We have had numerous occurrences of life threatening diseases due to the contamination of our waters. The sources of pollution are multiple. Amongst these sources is possibly one, that if not addressed with great urgency, could have very serious implications for this beautiful country as a whole. This source, is the inadequate infrastructure to deal with sewage.  Some of the effects of this type of pollution is discussed.

NOTE: This document is incomplete due to ongoing research.

The term environment broadly indicates the surroundings of an individual organism or a community of organisms, ranging up to the entire biosphere, the zone of Earth that is able to sustain life. By surroundings is meant all the non-living and living materials that play any role in an organism's existence, from soil and air to what the organism feeds on, and the organisms that may feed on it. Any other   factors acting on the organism, such as heat and light and gravitation, make up its environment as well. In the case of human beings, cultural factors may also be included in the term.

The environmental science of ecology is the observation and analysis of the interactions of organisms with their environment.  Because of the complexity of the subject matter, workers in this field call upon a wide range of disciplines in the physical and life sciences, for example, geology, meteorology, and microbiology, among many others. These separate disciplines themselves often incorporate areas of environmental specialization. The word environment is in fact most commonly encountered in association with the adverse effects of human activities on their surroundings and society's efforts to prevent or alleviate the damage. 

So what do we look for?

Environmental pollution is any discharge of material or energy into water, land, or air that causes or may cause acute (short-term) or chronic (long-term) detriment to the Earth's ecological balance or that lowers the quality of life. Pollutants may cause primary damage, with direct identifiable impact on the environment, or secondary damage in the form of minor breakdowns in the delicate balance of the biological food web that are detectable only over long time periods.

Until relatively recently in humanity's history, where pollution has existed, it has been primarily a local problem. The industrialization of  society, the introduction of motorized vehicles, and the explosion of the human population, however, have caused an exponential growth in the  production of goods and services. Coupled with this growth has been a tremendous  increase in waste by-products. The indiscriminate discharge of untreated industrial and domestic wastes into waterways, the spewing of thousands of tons of particulates and airborne gases into the atmosphere, the "throwaway" attitude toward solid wastes, and the use of newly developed chemicals without considering potential consequences have resulted in major environmental disasters, some as yet undetected. Technology has  begun to solve some pollution problems. Public awareness of the extent of pollution will eventually in many instances, force governments to undertake more effective environmental planning and adopt more effective antipollution  measures.

Water pollution is the introduction into fresh or ocean waters of chemical, physical, or biological material that degrades the quality of the water and affects the organisms living in it. This process ranges from simple addition of dissolved or suspended solids ( treated sewage) to discharge of the most  insidious and persistent toxic pollutants (such as pesticides, heavy metals, and non degradable,  bio accumulative, chemical  compounds). A pollutant need not be harmful in itself. Carbon dioxide, for example, is a normal component of the atmosphere and a by-product of respiration that is found in all animal tissues; yet in a concentrated form it can kill animals. Human sewage can be a useful fertilizer, but when concentrated too highly it becomes a serious pollutant, menacing health and causing the depletion of oxygen in bodies of water.

Conventional or classical pollutants are generally associated with the direct input of (mainly human) waste products.  Rapid urbanization and rapid population increase have produced sewage problems because treatment facilities have not kept pace with need. Untreated and partially treated sewage from municipal wastewater systems and septic tanks in unsewered     areas or non compliant sewer plants, contribute significant quantities of nutrients, suspended solids, dissolved solids, oil,   metals (arsenic, mercury, chromium, lead, iron, and manganese), and biodegradable organic carbon to the water environment.  Conventional pollutants may cause a myriad of water pollution problems. Excess suspended solids block out energy from the sun and thus  affect the carbon dioxide-oxygen conversion process, which is vital to the maintenance of the biological food chain. Also, high concentrations of suspended solids silt up rivers and dams.  Excess dissolved solids make the water undesirable for drinking and for crop irrigation. Although  essential to the aquatic habitat, nutrients such as nitrogen and phosphorus may also cause over fertilization and  accelerate the natural aging process (eutrophication) of  dams and lakes.

This acceleration in turn produces an overgrowth of aquatic   vegetation, massive algal blooms, and an overall shift in the  biologic community--from low productivity with many diverse species to high productivity with large numbers of a few species of an undesirable  nature. The lower Vaal  suffered heavily from algal bloom during the latter part of 2005.

Bacterial action oxidizes biodegradable organic carbon and consumes dissolved oxygen in the water. In extreme cases where the organic-carbon loading is high, oxygen  consumption may lead to an oxygen depression: (less than 2 mg/l compared with 5 to 7 mg/l for a healthy stream) is sufficient to cause a fish kill and seriously  disrupt the growth of associated organisms that require oxygen to survive.

Non conventional pollutants

The non conventional pollutants include dissolved and particulate forms of metals, both toxic and non toxic, and degradable and persistent organic carbon compounds discharged into water as a by-product of  industry or as an integral part of marketable  products. Thousands of environmentally untested chemicals are routinely discharged into waterways; an estimated 200 to 300 new compounds are  marketed each year.  Non conventional pollutants vary from biologically inert materials such as clay and iron  residues to the most toxic and insidious materials such as halogenated hydrocarbons (DDT, kepone, mirex, and polychlorinated biphenyls--PCB). The  latter group may produce damage ranging from acute biological effects (complete sterilization of stretches of waterways) to chronic sub lethal effects that may go undetected for years. The chronic low-level pollutants are proving to be the most difficult to correct and abate because of their ubiquitous nature and  chemical stability ( fabric dyes- nitrous acid  HNO₂   a prime example.)

Abatement

Conventional pollutants can be readily treated and abated with the construction of adequate wastewater-treatment facilities. Most industrialized countries are building new plants or enlarging old plants to reduce pollutants from conventional waste sources.
Non conventional pollution abatement is a more serious and elusive problem. Some governments impose stringent  effluent-discharge limits on industrial plants that discharge wastes into waterways--the first step in abatement. Also, regulatory agencies now require that certain new products or chemicals be examined prior to marketing for potential acute and chronic effects on the biological community.

Thermal pollution is the discharge of waste heat via energy dissipation into cooling water and subsequently into nearby waterways. The major sources of thermal pollution are fossil-fuel         electric-power generating facilities and, to a lesser degree, cooling operations  associated with industrial manufacturing, such as steel foundries, other primary-metal manufacturers, and chemical and petrochemical producers. The discharge temperatures from electric-power plants generally range from 5 to 11°C  above ambient water temperatures. An estimated 50% of all water consumption, excluding agricultural use, is for cooling or energy dissipation.

The discharge of heated water into a waterway often causes ecologic imbalance, sometimes resulting in major fish kills near the discharge source. The increased temperature accelerates chemical-biological processes and decreases the ability of the water to hold dissolved oxygen. Thermal changes affect the aquatic system by limiting or changing the type of fish and aquatic biota able to grow or reproduce in these waters. Thus rapid and dramatic changes in biologic communities often occur in the  vicinity of heated discharges.

What is water?

Pure water is a clear, colourless liquid made up of oxygen and hydrogen. It is the most common substance on the Earth's surface. In  either liquid or solid form (ice), it covers more than 70% of the planet. It is also present in the atmosphere as a gas (water vapour or steam). Water is essential to life on Earth and constitutes a large part of most living things. Human beings, for example, are about  two-thirds water. The exact chemical formula of the water molecule, H₂O (two atoms of hydrogen and one atom of oxygen), was established in 1860 by the Italian scientist Stanislao Cannizzarro. Water is a  powerful solvent and acts as a catalyst for many reactions. It also stores heat and cold well. Although pure water is a poor conductor of electricity, the impurities found in water in nature transform it into a relatively good one. In terms of its composition, water has an unusually high boiling point (100 ºC and freezing point 0º C). It also shows unusual volume changes with temperature: as it cools it contracts, until it reaches a maximum density of 1 gram per cm³ at 4ºC. At this point 1 litre weighs 1 kg. Further cooling causes it to expand, and another expansion  occurs when the liquid freezes.  Temperature exerts a profound effect on the solubility of gases in water. A change from 5° to 35° C reduces the oxygen content of fresh water by nearly half.

Water quality is determined by the amounts and kinds of suspended and dissolved substances; the degree of acidity or alkalinity; temperature; colour and transparency; taste and odour; and the presence of undesirable micro organisms. All natural waters contain dissolved inorganic and organic substances. The total dissolved-solids burden of rivers is generally between 20 and 2,000 parts per million and may be higher in groundwater. In natural (unpolluted) surface waters, the major dissolved solids are calcium, magnesium, sodium,  potassium, sulphates, chloride, carbonate,  bicarbonate, and silica. The relative amounts of these substances are controlled mostly by rock types, whereas the concentrations depend largely on climate. The average concentration ranges from about 50 parts per million in the humid areas and up to 1,000 parts per million in the arid non mountainous regions.

For any given stream, the concentration of dissolved matter increases as stream flow decreases. Many pollutants also may be found in solution. These may be large increases of substances normally present, such as nitrates,  phosphates, and certain metals, or they may be materials not naturally found, such as pesticides.

A pollutant need not be harmful in itself. Carbon dioxide, for example, is a normal component of the atmosphere and a by-product of respiration that is found in all animal tissues; yet in a concentrated form it can kill animals. Human sewage can be a useful fertilizer, but when concentrated too highly it becomes a serious pollutant, menacing health and causing the depletion of oxygen in bodies of water.

The pH

The quantitative measure of the acidity or basicity of aqueous or other liquid solutions (water). The term, widely used in chemistry,  biology, and agronomy, translates the values of the concentration of the hydrogen ion—which ordinarily ranges between about 1 and 10^-14 gram-equivalents per litre—into numbers between 0 and 14. In pure water, which is neutral (neither acidic nor alkaline), the concentration of the hydrogen ion is 10^-7 gram-equivalents per litre, which corresponds to a pH of 7. A solution with a pH less than 7 is considered acidic; a solution with a pH greater than 7 is considered basic, or alkaline eg.  Vinegar is an acid & Bi-carbonate of soda  is an alkaline. Stream waters usually range from pH 6.5 (slightly acid) to pH 8.5 (somewhat alkaline). Rainwater is naturally acidic (pH 5-6), but its acidity has been greatly increased (pH 4 to 5) in some regions by  industrial atmospheric pollutants such as sulphur dioxide.( rain water combines with sulphur dioxide to form sulphuric acid.) In most instances an aquatic habitat reflecting a pH of as near neutral as possible is considered the ideal.

Oxygen

Animals that live in water depend on dissolved oxygen for life; thus the concentration of oxygen is a critical determinant of water quality. The maximum possible concentration decreases from 14.5 parts per million at 0ºC  to 7.7 parts per million at 30ºC  and the actual amount present depends on the balance among contributions from the atmosphere and plant  photosynthesis and  extractions by respiration and from decay of organic matter. A marked decrease of dissolved oxygen  because of  bacterial decay of organic wastes has been a major impact of water pollution. Dissolved oxygen bears no relationship to the  molecular structure H₂O of water. It is purely how much O₂ can be dissolved into the substance eg. similar  to the CO₂ forced into fizzy  drinks. In rivers this action is achieved by rapids, waterfalls etc. coupled with the quality of the water at the source.  The output of industries, agriculture, and urban communities generally exceeds the biologic capacities of aquatic systems, causing waters to become choked with an excess of organic substances and organisms to be poisoned by toxic materials. When  organic matter exceeds the capacity of those micro organisms in water that break it down and recycle it, the excess of  nutrients in such matter encourages rapid growth, or blooms, of algae. When they die, the remains of the dead algae add further to the organic wastes already in the water; eventually, the water becomes deficient in oxygen. Anaerobic organisms (those that do not require oxygen to live) then attack the organic wastes, releasing gases such as methane and hydrogen sulphide, which are harmful to the oxygen-requiring (aerobic) forms of life. The result is a foul-smelling, waste-filled body of water, a situation that has already occurred in the freshwater lakes of Europe and North America. The  process by which a lake or any other body of water changes from a clean, clear condition—with a relatively low concentration of dissolved nutrients and a balanced aquatic community—to a nutrient-rich, algae-filled body and thence to an oxygen-deficient, waste-filled condition is known as accelerated eutrophication.

Suspended sediment is an important constituent of water quality, because it affects light penetration, smothers fish eggs and other bottom life, fills lakes, rivers and reservoirs, and makes water undesirable for many uses. Sediment is also linked to other water-quality factors because  pesticides, phosphates, and bacteria may be attached to sediment particles.  The average concentration in streams is 100 parts per million or less in humid forests but up to 100,000 parts per million in desert areas. Concentrations of suspended sediment increase rapidly as stream flow increases. Temperature exerts a profound effect on the solubility of gases in  water. A change from 5° to 35° C reduces the oxygen  content of fresh water by nearly half.

Fecal-coliform bacteria in water are an important index of water quality. These bacteria, derived from the intestines of mammals (including humans), indicate the possibility that disease organisms are present. Cholera appeared in London in 1848 and claimed 14,600 lives and 10,675 lives in 1854. The spread of the disease was linked to the contaminated water supply, and the control of the disease was hindered by the lack of adequate sewers.
Medical microbiology is concerned with the behaviour and control of pathogens, which are micro organisms that cause infectious diseases in humans and other animals.

Biochemical Oxygen Demand - the amount of oxygen used by micro organisms in the process of breaking down organic matter in water. The more organic matter there is (e.g., in sewage), the greater the number of microbes. The more microbes there are, the greater the need of oxygen to support them; consequently, less oxygen is available for higher animals such as fishes. The BOD is therefore a reliable gauge of the organic pollution of a body of water. One of the main reasons for treating sewage or waste water prior to its return to a water resource is to lower its BOD - ie., reduce its need of oxygen and thereby lessen its demand from the streams or rivers.

Bacteria are so small that they can be seen only when magnified 1,000-fold under a light microscope; details of their internal    structure can be observed only with the aid of the much more powerful electron microscope. Unless special phase-contrast microscopes are used, bacteria have to be stained with a coloured dye so that they will stand out from their background. One of the most useful staining reactions for bacteria is called the Gram stain, developed by the Danish physician Hans Christian Gram. Bacteria in suspension are fixed to a glass slide by brief heating and then exposed to two dyes that combine to form a blue dye complex within each cell. When the slide is flushed with an alcohol solution, Gram-positive bacteria retain the blue colour and Gram -negative bacteria lose it. The slide is then stained with a weaker pink dye; the gram-positive bacteria remain blue, and the gram-negative bacteria become pink. The Gram stain reacts to differences in the structure of the bacterial cell surface,  differences that become apparent when the cells are viewed under an electron microscope.

BACTERIA - SIZE AND HABITAT
Thirty trillion bacteria of average size weigh about 28 g (1 oz). Bacteria are measured in microns (0.001 mm, about 0.00004 in), and most types range from 0.1 to 4.0 microns in width and 0.2 to 50 microns in length. They are found everywhere.  Thousands of species are already known, many living in conditions that would destroy other organisms--in the almost airless reaches of the upper atmosphere, below the ocean surface to depths of 10 km  and in sulphurous hydrothermal vents, in frozen soil, and on rocks in hot springs. Some bacteria produce a resting stage, the endospore, the most resistant living thing known. It can be killed only by boiling in steam under  pressure for many hours. Not all bacteria require oxygen for survival. In fact excesses of O₂ will kill certain types. We call them obligate anaerobes.

BLUE-GREEN ALGAE
Nutritionally self-sufficient organisms, blue-green algae are ecologically important. Species that obtain their nitrogen from the atmosphere make nitrogen readily available to other organisms. In parts of Southeast Asia many farmers use nitrogen-fixing blue-green algae in place of nitrogen fertilizers to enrich rice paddies. Some nitrogen-fixing blue-green algae live symbiotically in a mutually beneficial relationship with fungi as lichens. Most nutrients that limit the growth of blue-green algae are usually inorganic, and pollution of fresh water with inorganic phosphate is likely to result in blooms of blue-green algae. These organisms are able to reproduce in a short period of time, particularly in stagnant waters, often resulting in noxious odours and compounds that are toxic to fish.

The water mould, genus Saprolegnia, is a species of aquatic mould belonging to the phylum Oomycetes of the kingdom Fungi. Water mould appears most commonly as a grey fuzz on dead animals in water. The mould causes diseases in fish and fish eggs and may do significant damage in fish hatcheries.

VIRAL INFECTIONS

Why you should never drink untreated river water!
Some bacteria are adept at invasion of a host and are called pathogens.

Hepatitis A
Once called infectious hepatitis, is the most common cause of acute hepatitis. Usually transmitted by food and water contaminated by human waste, infections can reach epidemic proportions in regions lacking adequate sanitary systems. Hepatitis A is spreading among drug abusers. Hepatitis B is spread mainly by blood or blood products, but can be transmitted from mother to foetus, and by intimate contact, including sexual intercourse. Type B virus is resistant to sterilization of instruments in hospitals and is also frequently seen in drug addicts who have shared needles. It often causes an initial episode of liver disease and occasionally leads to chronic hepatitis. There are seven known hepatitis viruses, which are labelled  A, B, C, D, E, F, and G. Hepatitis A, E, and F viruses are transmitted through the ingestion of contaminated food or water (called the faecal-oral route); the spread of these agents is aggravated by crowded conditions and poor sanitation. The B, C, D, and G viruses are transmitted mainly by blood or bodily fluids; sexual contact or exposure to contaminated blood are common modes of transmission.

Cholera
In the 1980s and 1990s Cholera spread among the crowded refugee camps and city slums of famine-stricken countries in Africa, particularly Ethiopia and The Sudan. Following a 70-year absence from the Western Hemisphere, there was a major outbreak of Cholera in Peru in 1991. in South Africa this disease is witnessed in communities with poor sanitation infrastructure. The vibrio enters the body via the mouth, usually in contaminated water or foods, and causes an infection in the mucous membranes    lining the lumen of the small intestine. The diarrhea is caused by the action of the Vibrio cholerae toxin in the  intestine. This toxin combines with a substance in the cells of the intestinal wall, activating an enzyme system that causes the rapid excretion of body fluids containing bicarbonate and sodium. Micro organisms cause gastroenteritis by secreting toxins that stimulate excessive water and electrolyte loss, thereby causing watery diarrhea, or directly invading the walls of the gut, triggering inflammation that upsets the balance between the absorption of nutrients and the secretion of wastes. After an incubation period of 12 to 28 hours, the disease usually starts with an abrupt, painless, watery diarrhea that may amount to a volume of 15 to 20 litres or more in 24 hours. This purging diarrhea is soon followed by vomiting, and the patient rapidly  becomes dehydrated; the skin becomes cold and withered, and the face is drawn; the blood pressure falls, and the pulse becomes faint; muscular cramps may be severe, and thirst intense. As dehydration increases, the person becomes stuporous and comatose and may die in shock. The disease ordinarily runs its course in three to seven days. With prompt fluid and salt repletion, which is accomplished by the oral or intravenous administration of an alkaline solution of  sodium chloride, recovery can be remarkably rapid; but if therapy is inadequate, the mortality rate is high. The administration of  antibiotics during the first day of treatment usually shortens the period of diarrhea and decreases the requirement for fluid replacement.

The prevention of cholera outbreaks rests upon better sanitation, particularly the use of clean drinking water. Immunization with a vaccine of killed vibrio bacteria provides partial protection in individuals for a limited time, but its use on a massive scale does not prevent the spread of infection. This can be accomplished only by attacking the source of the  infection, usually the water supply. Numerous viruses, bacteria, and parasites can cause gastroenteritis.

So why be concerned?  The simple truth is that existing sewage treatment infrastructure is outdated, broken down with little or no maintenance, in some cases non existent , managed by inefficient staff and running at full capacity with many plants not  coping. Every day that goes by the problem grows. The  Vaal dam receives reasonably good quality water from the highlands scheme but most of the water entering the Vaal below the Barrage is sewer water from  the settlements in the catchment area  below the Barrage. Yes, you are not in good quality water when fishing the lower Vaal - This once majestic waterway is steadily being turned into a sewer conduit - you are in sewer water!

THE NATIONAL WATER ACT

Part 3: The Reserve

Part 3 deals with the reserve, which consists of two parts - the basic human needs reserve and the ecological reserve.  The basic human needs reserve provides for the essential needs of individuals served by the water resource in question and includes water for drinking, food preparation and personal hygiene.  The ecological reserve relates to the water required to protect the aquatic ecosystems of the water resource.  The Reserve refers to both the quantity and quality of the water in the resource and will vary depending on the class of the resource.  If a resource has not yet been classified, a preliminary determination of the Reserve may be made and later superseded by a new one.  Once the Reserve is determined for a water resource, it is binding in the same way as the class and the resource quality objectives.

The Vaal in very poor condition - Warrenton 2005

The National Water Act stipulates  that a reserve be determined to protect the aquatic ecosystems of the water resource. This means the protection of the system in it’s entirety. The Vaal river in particular suffers from excessive abstraction, not so noticeable in the upper reaches, but very obvious in the lower sections from Warrenton to Douglas.

So why do we see fish dying in our rivers?

The reasons are many and complex. Some factors that contribute to the degradation of our water systems could be summarised as follows:

UNABATED ABSTRACTION

1. Reduced flow leading to lower aeration ( O₂)   rates at rapids/weirs. Shallower secluded pools stagnate leading to higher concentrations of dissolved pollutants. For any given stream, the concentration of dissolved matter increases as stream flow decreases. Many pollutants may also be found in solution. These may be large increases of substances normally present, such as nitrates, phosphates, and certain metals, or they may be materials not naturally found, such as pesticides.

SEWAGE

2. Influx of nutrients from sewage. It is ironical that smallmouth Yellows flourish in this nutrient rich environment which potentially translates into an ecological time bomb. The threat from a human health aspect cannot be over emphasized.  In a sense, bacteria are the dominant living creatures on Earth, having been present for perhaps three-quarters of Earth history and having adapted to almost all available ecological habitats. Studies of the relationships among different groups of bacteria  continue to yield new insights into the origin of life on Earth and the directions of evolution.

Nitrifying Bacteria
Any of a small group of aerobic bacteria (family Nitrobacteraceae) that use inorganic chemicals as an energy source. They are microorganisms that are important in the nitrogen cycle as converters of soil ammonia to nitrates, compounds usable by plants. The nitrification process requires the mediation of two distinct groups: bacteria that convert ammonia to nitrites (Nitrosomonas, Nitrosospira, Nitrosococcus, and Nitrosolobus) and bacteria that convert nitrites (toxic to plants) to nitrates (Nitrobacter, Nitrospina, and Nitrococcus). In agriculture, irrigation with dilute solutions of ammonia results in an increase in soil nitrates through the action of nitrifying bacteria.

Coliform bacteria

Microorganisms that usually occur in the intestinal tract of animals, including man, and are the most widely accepted indicators of water quality. More precisely they are evidence of recent human fecal contamination of water supplies. The coliforms are facultative anaerobic (not requiring oxygen), nonsporulating, rod-shaped bacteria that produce acid and gas from the fermentation of  lactose sugar:  Escherichia coli, Enterobacter aerogenes, and Klebsiella pneumoniae.

The beneficial role of bacteria is worth emphasizing, since the popular idea that all bacteria are hostile stems from the prominent historical connection between bacteria and disease. Most important bacteria are harmless to humans, and many are essential to the existence of plant and animal life. Only a small fraction cause disease; most bacteria attack organic matter only after it is dead. Were it not for bacteria that decompose animal waste matter and the bodies of dead animals and plants, these materials would accumulate almost indefinitely. Bacteria also enrich the soil in various ways. The so-called nitrogen-fixing bacteria take nitrogen gas from the atmosphere and convert it to a form (nitrate) that green plants use for growth. Bacteria are important industrially in the production of cheese, yogurt, buttermilk, vinegar, and sauerkraut; in the preparation of antibiotics such as Streptomycin, which is extracted from soil bacteria; in the tanning of leather and hides and the curing of tobacco; and in sewage disposal plants to render organic wastes harmless. Cattle, sheep, and goats live on grass; yet without bacteria they would not be able to digest the tough fibers of plant cellulose.

ENVIRONMENTAL LAW

Environmental law exists at many levels and is only partly constituted by international declarations, conventions, and treaties. In addition, many countries have included some right to environmental quality in their national constitutions. Since 1994, for example, environmental protection has been enshrined in the German Grundgesetz (“Basic Law”), which now states that the government must protect for “future generations the natural foundations of life.” Similarly, the Chinese constitution declares that the state “ensures the rational use of natural resources and protects rare animals and plants”; the South African constitution recognizes a right to “an environment that is not harmful to health or well-being; and to have the environment protected, for the benefit of present and future generations”; the Bulgarian constitution provides for a “right to a healthy and favourable environment, consistent with stipulated standards and regulations”; and the Chilean constitution contains a “right to live in an environment free from contamination.”

Environmental law regularly operates in areas complicated by high levels of scientific uncertainty. In the case of many activities that entail some change to the environment, it is impossible to determine precisely what effects the activity will have on the quality of the environment or on human health. It is generally impossible to know, for example, whether a certain level of air pollution will result in an   increase in mortality from respiratory disease, whether a certain level of water pollution will reduce a healthy fish population, or whether oil development in an environmentally sensitive area will significantly disturb the native wildlife. The precautionary principle requires that, if there is a strong suspicion that a certain activity may have environmentally harmful consequences, it is better to control that activity now rather than to wait for incontrovertible scientific evidence. This principle is expressed in the Rio Declaration, which stipulates that, where there are “threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.”

Water, the essence of all life. This poses particularly urgent problems. Man is especially sensitive to it as his needs grow daily. The need to find sources of fresh uncontaminated water is aggravated by the extent to which possible sources are being contaminated. The main effects on inland water are those due to factory waste, human sewage and agricultural runoffs. In the case of the Vaal we can include mineral exploitation.

Water Treatment
The degree to which wastewater must be treated varies, depending on local environmental conditions and governmental standards. Two pertinent types of standards are stream standards and effluent standards. Stream standards, designed to prevent the deterioration of existing water quality, set limits on the amounts of specific pollutants allowed in streams, rivers, and dams. The limits depend on a classification of the “maximum beneficial use” of the water. Water quality parameters that are regulated by stream standards include dissolved oxygen, coliforms, turbidity, acidity, and toxic substances. Effluent standards, on the other hand, pertain directly to the quality of the treated wastewater discharged from a sewage treatment plant. The factors controlled  under these standards usually include biochemical oxygen demand, suspended solids, acidity, and coliforms.

There are three levels of wastewater treatment: primary, secondary, and tertiary (or advanced). Primary treatment removes about 60 percent of total suspended solids and about 35 percent of BOD; dissolved impurities are not removed. It is usually used as a first step before secondary treatment. Secondary treatment removes more than 85 percent of both suspended solids and   Biochemical Oxygen Demand. A minimum level of secondary treatment is usually required in developed countries. When more than 85 percent of total solids and BOD must be removed, or when dissolved nitrate and phosphate levels must be reduced, tertiary treatment methods are used. Tertiary processes can remove more than 99 percent of all the impurities from sewage, producing an effluent of almost drinking-water quality. Tertiary treatment can be very expensive, often doubling the cost of secondary treatment. It is used only under special circumstances.

Disinfection
For all levels of wastewater treatment, the last step prior to discharge of the sewage effluent into a body of surface water is disinfection. Disinfection is usually accomplished by mixing the effluent with chlorine  in a contact tank for at least 15 minutes.  Because chlorine residuals in the effluent may have adverse effects on aquatic life, an additional chemical may be added to dechlorinate the effluent. Ultraviolet radiation, which can disinfect without leaving any residual in the effluent, is becoming more competitive with chlorine as a wastewater disinfectant.

The activated sludge treatment system consists of an aeration tank followed by a secondary clarifier. Settled sewage, mixed with fresh sludge that is re-circulated from the secondary clarifier, is introduced into the aeration tank. Compressed air is then injected into the mixture through porous diffusers located at the bottom of the tank. As it bubbles to the surface, the diffused air provides oxygen and a rapid mixing action. Air can also be added by the churning action of mechanical propeller-like mixers located at the tank surface.

Under such oxygenated conditions, micro organisms thrive, forming an active, healthy suspension of biological solids (mostly bacteria) called activated sludge. About six hours of detention is provided in the aeration tank. This gives the microbes enough time to absorb dissolved organics from the sewage, reducing the BOD.