Joseph YN Philip Lecture 3 Notes Page 1 · joseph yn philip lecture 3 notes page 1 university of dar es salaam faculty of science ev 200: environmental science environmental pollution,

Joseph YN Philip Lecture 3 Notes

Page 1

UNIVERSITY OF DAR ES SALAAM FACULTY OF SCIENCE

EV 200: ENVIRONMENTAL SCIENCE ENVIRONMENTAL POLLUTION, DEGRADATION AND TOXICOLOGY

Chemistry Department October 31, 2008 Effects of Photochemical smog

1. Plants – At low concentrations photochemical smog can reduce plant growth rates and at higher concentrations can kill plant tissues and entire plants.

2. Animals – The effects of photochemical smog on animals involves reduced visibility and health problems (eye irritations and aggravate respiratory illnesses).

3. Climate – Photochemical smog is involved in global climate change (tropospheric ozone is a greenhouse gas).

Air Pollution Control. Several strategies have been used to reduce atmospheric pollution. Some polluters use a number of techniques to redistribute pollutants to areas not occupied by humans or other forms of life. Smelters and power plants use tall smoke stacks to disperse pollutants at higher levels within the atmosphere. Other atmospheric polluters have relocated their particular industry to remote locations. However, it is very difficult to dilute pollution in finite atmosphere. Sooner or later residual amounts of pollution reach levels that are hazardous to some form of life. Humans have developed a number of technological solutions to atmospheric pollution. Filters have been used to stop particles from reaching the atmosphere. Some power plants use electrostatic precipitators to reduce pollution output by as much as 99%. The addition of limestone with coal in specialized burners can reduce sulfur emissions from this fossil fuel by up to 90%. Catalytic converters in cars and other forms of transportation have been used to reduce emissions of nitrogen oxides, hydrocarbons, and carbon monoxide by up to 90%. Many automobile companies are now working on the development of hydrogen powered or electric vehicles to reduce emissions of several pollutants. One of the quickest and most common approaches car companies have used to reduce engine emissions is to increase fuel efficiency. Cars must be inspected frequently to insure emissions controls are working properly. Indoor pollution can be reduced by the modification of building codes. These modifications can be used to control materials used in construction and to ensure proper ventilation is set up in the building. Fuel switching and fuel cleaning can reduce the emissions of sulfur and heavy metals from so called 'dirty' fossil fuels like soft coal. Finally, the surest way to control atmospheric pollution is to avoid the creation of the pollutants. The following general recommendations for developing a cleaner atmosphere should be adopted by all nations:

• Preventing pollution emission rather than controlling it. • Improve the energy efficiencies. • Use cleaner fuels. • Develop nonpolluting energy sources like solar energy, wind power, and hydropower. • Encourage mass transit and less polluting forms of transportation (e.g., switch from air

travel to rail travel). • Slow population growth; • Include environmental costs in the pricing of energy resources and other activities that

produce atmospheric pollution. Water Pollution Overview. Water pollution is the contamination of water by foreign matter that deteriorates the quality of the water. Water pollution covers pollutions in liquid forms, i.e., oceans, lakes and rivers. As the term applies, liquid pollution occurs in the oceans, lakes, streams, rivers, underground water and bays, in short liquid-containing areas. It involves the release of toxic substances, pathogenic germs, substances that require much oxygen to decompose, easy-soluble substances, radioactive substances, etc., that their accumulations will interfere with the condition of aquatic ecosystems. For example, the eutrophication: lack of oxygen in a water body caused by excessive algae growths because of enrichment of pollutants. Sources of Water Pollution. Degradation of water quality is measured by biological, chemical,


Page 2

or physical criteria and is generally judged in terms of the intended use, departure from normal, effects on public health or ecological impacts. There are many different materials that may pollute surface water or groundwater. We can classify major sources that lead to water pollution to the following categories: petroleum products, synthetic agricultural chemicals, heavy metals, hazardous wastes, excess organic matter, sediment, infectious organisms, air pollution, thermal pollution and soil pollution. The major forms and sources of water pollution are briefly described below.

(a) Oil (petroleum products) discharge. The sources of petroleum products include: Manufacture of plastics, lubricants, solvents, and synthetic fabrics. Fractional distillation of crude oil to produce vehicle fuel, paraffin wax, refinery gases for domestic cooking, and bitumen for road surfacing and roofing. Water pollution by petroleum products is mainly due to accidental spills from ships, tanker trucks, pipelines and leaky underground storage tanks. Other ways include old and faulty machineries in industries, which are inefficient, and improper refinery processes that produce toxic byproducts. Oil discharge into surface water e.g. ocean, has caused major pollution problems such as loss of aquatic life.

(b) Synthetic chemical pesticides. Pesticides such as herbicides, insecticides, fungicides etc used in agriculture and public health programmes to control pests are an import source of water pollution. They get into water sources through run-off and atmospheric transport and deposition. Persistent pesticides accumulate in plants and animals, when they die they are spread to water sources, thus increasing water toxicity.

(c) Nutrients and organic matter. Nutrients (like nitrogen and phosphorus) released by human activity can cause lake eutrophication and nitrite contamination of drinking water. Excess nitrogen and phosphorous from agricultural chemical fertilizers, farm, animal waste, and sewage sludge, are causing a major pollution problem in streams, lakes, and the coastal marine environment in many nations. Nutrients stimulate algae growth and during decomposition of algae, dissolved oxygen in water bodies is consumed, thus decreasing the level of oxygen in aquatic ecosystem, thus increase the mortality rate (death rate) of aquatic flora and fauna. At the same time, decaying material will turn the water murky. This is called eutrophication. The addition of organic matter to water usually initiates the process of decomposition. Most decomposers require oxygen to complete this process. As a result, oxygen levels in the water decline with this activity. Humans commonly use water bodies, like rivers, lakes and ocean, as a means of disposing off organic wastes (e.g. industrial, institutional and domestic waste water or sewage effluent). However, adding too much organic matter to a water body can cause it to become polluted because of a reduction in oxygen content. Low levels of oxygen can kill aquatic organisms. Biochemical Oxygen Demand (BOD) is a measure of the amount of oxygen consumed in water by bacteria activity. BOD is measured as milligrams per liter of oxygen consumed over 5 days at 20 °C. All water bodies have some capability to degrade organic waste. Problems result when the water body is overloaded with organic waste.

(d) Heavy metals. Heavy metals such as mercury and cadmium are dangerous pollutants. They are often deposited with sediment in the bottoms of streams. If these metals are deposited on surface sediments - they may become incorporated in plants, food crops, and animals. If they are dissolved and the water is withdrawn for agriculture or human use, poisoning can result. One of the most famous cases of heavy metal pollution occurred in Minamata, Japan in the 1950s. The cause of this disaster has been associated with dumping of about 27 tons of mercuric waste by the Chisso Corporation into Minamata Bay during the 1950s and 1960s. People of Minamata consumed fish from the Bay in their diet and this led to an accumulation of toxic methyl mercury in their bodies. Over 3,000 victims have been recognized as having "Minamata Disease". The sources of heavy metals include mining, automobile exhaust, metallurgy, manufacture of semiconductors, manufacture of batteries and machineries. The methods of pollution include: leaky pipelines, unfiltered industrial discharge which flows into water sources, emission of oxides of lead from tractors and machineries used during mining or in industries which dissolve in water, improper


Page 3

storage of heavy metals and parts of machines wear off and release toxic metals. (e) Hazardous wastes. Hazardous wastes e.g. radioactive materials, corrosive materials,

reactive materials and ignitable materials in water may be dangerous pollutants. Of particular concern are possible effects to people due to long-term exposure to low doses of radioactivity. Improper treatment of wastes, which are still toxic upon release, is one of the methods of pollution.

(f) Sediment. By volume, sediment is the greatest water pollutant. In many areas, sediment is choking streams and filling lakes, reservoirs, ponds, canals, drainage ditches, and harbours. Human activity has increased the amount of sediment entering the hydrologic system mainly through the disturbance of natural habitats, agriculture, and forestry. All of these activities enhance the process of erosion either through the removal of vegetation or via processes that disturb the soil surface layer (soil cultivation). Soil erosion and soil particulates washed by storms and floodwaters from unprotected soils cause accumulation of sediments in water and turn the water murky. Mass flow of mud into water source system will alter the clarity of water.

(g) Infectious organisms. Infectious organisms such as faecal coliform bacteria, protozoa and viruses are important biological pollutants. Many of these organisms increase in numbers when water is polluted with organic matter and waste. During the growth of these microorganisms, they consume the nutrients in lakes, rivers and oceans. They infect plants and animals in the aquatic ecosystem, which die and upon decomposition accumulate in sediments and organic matters, which turn the water source murky thereby polluting it. Among the major waterborne human diseases are cholera and typhoid, which are common in many developing countries.

(h) Air pollution. Acid rain alters the pH and composition of water. Acid rain enhances the dissolution of metallic substances and the resulting metallic ions are transported to water bodies.

(i) Soil pollution. Runoff and seeping of rainwater containing chemical and biological pollutants such as chemical fertilizers and pesticides from soil surface and through underground soil which flows into water systems.

(j) Thermal pollution. The heating of water bodies from hot-water emission from industrial and power plants causes thermal pollution. Many industries cool machinery and products with water drawn from rivers, lakes, or the ocean. After the heat is dissipated into the water, the water is returned to its source. Heated water changes the nature of the aquatic system by reducing its ability to hold dissolved oxygen and by favouring species of fauna and flora that are adapted to warmer conditions.

Major sources that lead to thermal pollution can be classified to the following categories: power plants creating electricity from fossil fuel; water as a cooling agent in industrial facilities; deforestation of the shoreline and soil erosion. (i) Power plants creating electricity from fossil fuel. Electricity is generated by heat

stored in the fossil fuels and the stored energy creates a heat flow that drives turbines. The turbines then generate electricity. Organization of this sort is created by man and so it does not occur naturally. Excess heat is then created because of the unnatural processes involved.

(ii) Water as cooling agent. Heat exchangers - exchange heat with other streams in the factory because there are steps which need heat while other steps generate heat. Water is drawn from rivers and lakes to be used as coolants in factories and power plants. Warmer water returned to rivers and lakes will alter the species makeup of the aquatic ecosystem, introducing infectious organisms and others which are adaptable to warmer temperature, which will alter the water composition in the lake or river. Level of oxygen in water sources will be reduced, threatening the aquatic ecosystem, which will lead to the death of many species and in turn make the water murky.

(iii) Evaporate cooling - steam is used in many final heating processes. Cooling by condensation generates great amount of waste heat from factory. Cooling comes from evaporation because ambient air is not saturated with water. Air discharged from cooling tower is a direct contribution to global warming.

(iv) Deforestation of shoreline, which further contributes to the problem in two ways: aggravates soil erosion activity and increases amount of light that strikes the water.

(v) Soil erosion. Sedimentation at lakes and streams makes the water muddy. Muddy


Page 4

water lowers the clarity of water, with the introduction of impurities to the water, containing microbes and dissolved minerals, which increase the light absorption from the atmosphere. Increase light absorption will rise the temperature of water from the heat energy of light.

Water Conservation and Management. Water conservation refers to reducing use of fresh water, through technological or social methods. The goals of water conservation efforts include: Sustainability - To ensure availability for future generations, i.e., the withdrawal of fresh water from an ecosystem should not exceed its natural replacement rate. Energy conservation - Water pumping, delivery, and wastewater treatment facilities consume a significant amount of energy. Habitat conservation - Minimizing human water use helps to preserve fresh water habitats for local wildlife and migrating waterfowl, as well as reducing the need to build new dams and other water diversion infrastructure. A number of techniques and technologies can be used to make agricultural, industrial and domestic water use more efficient. Reductions can easily occur in the following areas: reducing agricultural waste, reducing industrial waste and reducing domestic waste. Water management refers to the practices of planning, developing, distribution and optimum utilizing of water resources under defined water polices and regulations. It may mean: (i) management of water treatment of drinking water, industrial water, sewage or wastewater, (ii) management of water resources, (iii) management of flood protection, or (iv) management of irrigation. The treatment of water may be divided into three major categories: (i) Purification for domestic use, (ii) Treatment for specialized industrial applications, and (iii) Treatment of wastewater to make it acceptable for release or reuse. The type and degree of treatment are strongly dependent upon the source and intended use of the water. Water for domestic use must be thoroughly disinfected to eliminate disease-causing microorganisms, but may contain appreciable levels of dissolved calcium and magnesium (hardness). Water to be used in boilers may contain bacteria but must be quite soft to prevent scale formation. Wastewater being discharged into a large river may require less rigorous treatment than water to be reused in an arid region. As world demand for limited water resources grows, more sophisticated and extensive means will have to be employed to treat water. Most physical and chemical processes used to treat water involve similar phenomena, regardless of their application to the three main categories of water treatment listed above. Therefore, after introductions to water treatment for municipal use, industrial use, and disposal, each major kind of treatment process is discussed as it applies to all of these applications. Municipal Water Treatment. The raw water taken from wells first goes to an aerator. Contact of the water with air removes volatile solutes such as hydrogen sulfide, carbon dioxide, methane, and volatile odorous substances such as methane thiol (CH3SH) and bacterial metabolites. Contact with oxygen also aids iron removal by oxidizing soluble iron(II) to insoluble iron(III). The addition of lime as CaO or Ca(OH)2, after aeration raises the pH and results in the formation of precipitates containing the hardness ions Ca2+, and Mg2+. These precipitates settle from the water in a primary basin. Much of the solid material remains in suspension and requires the addition of coagulants (such as ferric and aluminium sulfates, which form gelatinous metal hydroxides) to settle the colloidal particles. Activated silica or synthetic polyelectrolytes may also be added to stimulate coagulation or flocculation. The settling occurs in a secondary basin after the addition of carbon dioxide to lower the pH. Sludge from both the primary and secondary basins is pumped to a sludge lagoon. The water is finally chlorinated, filtered; and pumped to the city water mains. Treatment of Water for Industrial Use. Water is widely used in various process applications in industry. Other major industrial uses are boiler feedwater and cooling water. The kind and


Page 5

degree of treatment of water in these applications depends upon the end use. As examples: cooling water may require only minimal treatment; removal of corrosive substances and scale-forming solutes is essential for boiler feedwater; and water used in food processing must be free of pathogens and toxic substances. Improper treatment of water for industrial use can cause problems, such as corrosion, scale formation, reduced heat transfer in heat exchangers, reduced water flow, and product contamination. These effects may cause reduced equipment performance or equipment failure, increased energy costs due to inefficient heat utilization or cooling, increased costs for pumping water, and product deterioration. Sewage Treatment. Typical municipal sewage contains oxygen-demanding materials, sediments, grease, oil, scum, pathogenic bacteria, viruses, salts, algal nutrients, pesticides, refractory organic compounds, heavy metals, and an astonishing variety of debris. It is the job of the waste treatment plant to remove as much of this material as possible. Several characteristics are used to describe sewage. These include turbidity (international turbidity units); suspended solids (ppm); total dissolved solids (ppm); acidity (H+ ion concentration or pH); and dissolved oxygen (in ppm O2). Biochemical oxygen demand is used as a measure of oxygen-demanding substances. Current processes for the treatment of wastewater may be divided into three main categories of primary treatment, secondary treatment, and tertiary treatment. Waste from a municipal water system is normally treated in a publicly owned treatment works. Primary Waste Treatment. Primary treatment of wastewater consists of the removal of insoluble matter such as grit, grease, and scum from water. The first step in primary treatment normally is screening. Screening removes or reduces the size of trash and large solids that get into the sewage system. These solids are collected on screens and scraped off for subsequent disposal. Most screens are cleaned with power rakes. Comminuting devices shred and grind solids in the sewage. Particle size may be reduced to the extent that the particles can be returned to the sewage flow. Grit in wastewater consists of such materials as sand, which do not biodegrade well and generally have a high settling velocity. Grit removal is practiced to prevent its accumulation in other parts of the treatment system, to reduce clogging of pipes and other parts, and to protect moving parts from abrasion and wear. Grit normally is allowed to settle in a tank under conditions of low flow velocity, and it is then scraped mechanically from the bottom of the tank. Primary sedimentation removes both settleable and floatable solids. During primary sedimentation there is a tendency for flocculent particles to aggregate for better settling, a process that may be aided by the addition of chemicals. The material that floats in the primary settling basin is known collectively as grease. The grease consists of fatty substances, oils, waxes, free fatty acids, and insoluble soaps containing calcium and magnesium. Normally, some of the grease settles with the sludge and some floats to the surface, where a skimming device may remove it. Secondary Waste Treatment by Biological Processes. The most obvious harmful effect of biodegradable organic matter in wastewater is BOD. Secondary wastewater treatment is designed to remove BOD, usually by taking advantage of the same kind of biological processes that would otherwise consume oxygen in water receiving the wastewater. Secondary treatment by biological processes takes many forms but consists basically of the following: Microorganisms provided with added oxygen are allowed to degrade organic material in solution or in suspension until the BOD of the waste has been reduced to acceptable levels. The waste is oxidized biologically under conditions controlled for optimum bacterial growth and at a site where this growth does not influence the environment. One of the simplest biological waste treatment processes is the trickling filter in which wastewater is sprayed over rocks or other solid support material covered with microorganisms. The structure of the trickling filter is such that contact of the wastewater with air is allowed and degradation of organic matter occurs by the action of the microorganisms. Rotating biological reactors, another type of treatment system, consist of groups of large plastic discs mounted close together on a rotating shaft. The device is positioned so that at any particular instant half of each disc is immersed in wastewater and half exposed to air. The shaft rotates constantly, so that the submerged portion of the discs is always changing. The discs, usually made of high-density polyethylene or polystyrene, accumulate thin layers of attached biomass, which degrades organic matter in


Page 6

the sewage. Oxygen is absorbed by the biomass and by the layer of wastewater adhering to it during the time that the biomass is exposed to air. Both trickling filters and rotating biological reactors are examples of fixed-film biological or attached growth processes. The greatest advantage of these processes is their low energy consumption. The energy consumption is minimal because it is not necessary to pump air or oxygen into the water, as is the case with the popular activated sludge process described below. The trickling filter has long been a standard means of wastewater treatment, and a number of wastewater treatment plants use trickling filters at present. The activated sludge process is probably the most versatile and effective of all waste treatment processes. Microorganisms in the aeration tank convert organic material in wastewater to microbial biomass and CO2. Organic nitrogen is converted to ammonium ion or nitrate. Organic phosphorus is converted to orthophosphate. The microbial cell matter formed as part of the waste degradation processes is normally kept in the aeration tank until the microorganisms are past the log phase of growth, at which point the cells flocculate relatively well to form settleable solids. These solids settle out in a settler and a fraction of them is discarded. Part of the solids, the return sludge, is recycled to the head of the aeration tank and comes into contact with fresh sewage. The combination of a high concentration of "hungry" cells in the return sludge and a rich food source in the influent sewage provides optimum conditions for the rapid degradation of organic matter. The degradation of organic matter that occurs in an activated sludge facility also occurs in streams and other aquatic environments. However, in general, when a degradable waste is put into a stream, it encounters only a relatively small population of microorganisms capable of carrying out the degradation process. Thus, several days may be required for the buildup of a sufficient population of organisms to degrade the waste. In the activated sludge process, continual recycling of active organisms provides the optimum conditions for waste degradation, and a waste may be degraded within the very few hours that it is present in the aeration tank. The activated sludge process provides two pathways for the removal of BOD. BOD may be removed by (1) oxidation of organic matter to provide energy for the metabolic processes of the microorganisms, and (2) synthesis, incorporation of the organic matter into cell mass. In the first pathway, carbon is removed in the gaseous form as CO2. The second pathway provides for removal of carbon as a solid in biomass. That portion of the carbon converted to CO2 is vented to the atmosphere and does not present a disposal problem. The disposal of waste sludge, however, is a problem, primarily because it is only about 1% solids and contains many undesirable components. Normally, partial water removal is accomplished by drying on sand filters, vacuum filtration, or centrifugation. The dewatered sludge may be incinerated or used as landfill. To a certain extent, sewage sludge may be digested in the absence of oxygen by methane-producing anaerobic bacteria to produce methane and carbon dioxide, a process that reduces both the volatile-matter content and the volume of the sludge by about 60%. One of the most desirable means of sludge disposal is to use it to fertilize and condition soil. However, care has to be taken that excessive levels of heavy metals are not applied to the soil as sludge contaminants. Nitrification (the microbially mediated conversion of ammonium nitrogen to nitrate, is a significant process that occurs during biological waste treatment. Ammonium ion is normally the first inorganic nitrogen species produced in the biodegradation of nitrogenous organic compounds. It is oxidized, under the appropriate conditions, first to nitrite by Nitrosomonas bacteria,

2NH4+ + 3O2 → 4H+ + 2NO2

- + 2H2O then to nitrate by Nitrobacter:

2NO2- + O2 →2NO3

- These reactions occur in the aeration tank of the activated sludge plant and are favoured in general by long retention times, low organic loadings, large amounts of suspended solids, and high temperatures. Nitrification can reduce sludge settling efficiency because the denitrification reaction occurring in the oxygen-deficient settler causes bubbles to form on the sludge floc (aggregated sludge particles), making it so buoyant that it floats to the top. This prevents settling of the sludge and increases the organic load in the receiving waters. Under the appropriate conditions, however, advantage can be taken of this phenomenon to remove nutrient nitrogen from water.

4NO3- + 5{CH2O} + 4H+ → 2N2(g) + 5CO2(g) + 7H2O


Page 7

Tertiary Waste Treatment. Tertiary waste treatment (sometimes called advanced waste treatment) is a term used to describe a variety of processes performed on the effluent from secondary waste treatment. The contaminants removed by tertiary waste treatment fall into the general categories of (1) suspended solids; (2) dissolved organic compounds; and (3) dissolved inorganic materials. Each of these categories presents their own problems with regard to water quality. Suspended solids are primarily responsible for residual biological oxygen demand in secondary sewage effluent waters. The dissolved organics are the most hazardous from the standpoint of potential toxicity. The major problem with dissolved inorganic materials is that presented by algal nutrients, primarily nitrates and phosphates. In addition, potentially hazardous toxic metals may be found among the dissolved inorganics. In addition to these chemical contaminants, secondary sewage effluent often contains a number of disease-causing microorganisms, requiring disinfection in cases where humans may later come into contact with the water. Among the bacteria that may be found in secondary sewage effluent are organisms causing tuberculosis, dysentery, cholera, and typhoid fever. In addition, viruses causing diarrhea, eye infections, infectious hepatitis, and polio may be encountered. Physical-Chemical Treatment of Municipal Wastewater. Complete physical-chemical wastewater treatment systems offer both advantages and disadvantages relative to biological treatment systems. The capital costs of these facilities can be less than those of biological treatment facilities, and they usually require less land. They are able to cope with toxic materials and overloads. However, they require careful operator control and consume relatively large amounts of energy. Basically, a physical-chemical treatment process involves:

• Removal of scum and solid objects. • Clarification, generally with addition of a coagulant, and frequently with the addition of

other chemicals (such as lime for phosphorus removal). • Filtration to remove filterable solids. • Treatment with activated carbon. • Disinfection.

Industrial Wastewater Treatment. Wastewater to be treated must be characterized fully, particularly with a thorough chemical analysis of possible waste constituents and their chemical and metabolic products. The biodegradability of wastewater constituents should also be determined. One of two major ways of removing organic wastes is biological treatment by an activated sludge, or related process. The other major process for the removal of organics from wastewater is sorption by activated carbon, usually in columns of granular activated carbon. Activated carbon and biological treatment can be combined with the use of powdered activated carbon in the activated sludge process. The powdered activated carbon absorbs some constituents that may be toxic to microorganisms and is collected with the sludge. A major consideration with the use of activated carbon to treat wastewater is the hazard that spent activated carbon may present from the wastes it retains. These hazards may include those of toxicity or reactivity. Regeneration of the carbon is expensive and can be hazardous in some cases. Wastewater can be treated by a variety of chemical processes, including acid/base neutralization, precipitation, and oxidation/reduction. In some cases these treatment steps must precede biological treatment; for example, wastewater with extremes pH must be neutralized in order for microorganisms to thrive in it. Cyanide in the wastewater may be oxidized with chlorine and organics with ozone; hydrogen peroxide promoted with ultraviolet radiation, or dissolved oxygen at high temperatures and pressures. Heavy metals may be precipitated with base, carbonate, or sulfide. Wastewater can be treated by several physical processes. In some cases, simple density separation and sedimentation can be used to remove water-immiscible liquids and solids. Filtration is frequently required and flotation by gas bubbles generated on particle surfaces may be useful. Evaporation, distillation, and membrane processes, including reverse osmosis, hyperfiltration, and ultrafiltration, can be used to concentrate wastewater solutes. Solvent extraction, air stripping, or steam stripping can be used to remove organic constituents. Synthetic resins are useful for removing some pollutant solutes from wastewater. Organophilic resins have proved useful for the removal of alcohols; aldehydes; ketones; hydrocarbons;


Page 8

chlorinated alkanes, alkenes, and aryl compounds; esters, including phthalate esters; and pesticides. Cation exchange resins are effective for the removal of heavy metals. Removal of Solids. Relatively large solid particles are removed from water by simple settling and filtration. A special type of filtration procedure known as microstraining is especially effective in the removal of the very small particles. The removal of colloidal solids from water usually requires coagulation. Salts of aluminium and iron are the coagulants most often used in water treatment. Of these, alum or filter alum is most commonly used. This substance is a hydrated aluminium sulfate, Al2(SO4)3.18H2O. When this salt is added to water, the aluminium ion hydrolyzes by reactions that consume alkalinity in the water, such as:

Al(H2O)63+ + 3HCO3

- → Al(OH)3(s) + 3CO2 + 6H2O The gelatinous hydroxide thus formed carries suspended material with it as it settles. Metal ions in coagulants also react with virus proteins -and destroys up to 99% of the virus in water. Anhydrous iron(III) sulfate added to water forms ferric hydroxide in a reaction analogous to Equation above. An advantage of iron(III) sulfate is that it works over a wide pH range of approximately 4-11. Hydrated iron(II) sulfate, FeSO4.7H2O or copperas, is also commonly used as a coagulant. It forms a gelatinous precipitate of hydrated iron(III) oxide; in order to function, it must be oxidized to iron(III) by dissolved oxygen in the water at a pH higher than 8.5, or by chlorine, which can oxidize iron(II) at lower pH values. Sodium silicate partially neutralized by acid aids coagulation, particularly when used with alum. The chemical mechanism by which this activated silica operates is still not known with certainty. Natural and synthetic polyelectrolytes are used in flocculating particles. Among the natural compounds so used is starch and cellulose derivatives, proteinaceous materials, and gums composed of polysaccharides. More recently, selected synthetic polymers that are effective flocculants have come into use. Coagulation-filtration is a much more effective procedure than filtration alone for the removal of suspended material from water. The process consists of the addition of coagulants that aggregate the particles into larger size particles, followed by filtration. Either alum or lime, often with added polyelectrolytes, is most commonly employed for coagulation. The filtration step of coagulation-filtration is usually performed on a medium such as sand or anthracite coal. Often, to reduce clogging, several media with progressively smaller interstitial spaces are used. One example is the rapid sand filter, which consists of a layer of sand supported by layers of gravel particles, the particles becoming progressively larger with increasing depth. The substance that actually filters the water is coagulated material that collects in the sand. As more material is removed, accumulation of the coagulated material eventually clogs the filter and must be removed by back flushing. An important class of solids that must be removed from wastewater consists of suspended solids in secondary sewage effluent that arise primarily from sludge that was not removed in the settling process. These solids account for a large part of the BOD in the effluent and may interfere with other aspects of tertiary waste treatment. For example, these solids may clog membranes in reverse osmosis water treatment processes. The quantity of material involved may be rather high. Processes designed to remove suspended solids often will remove organic material from secondary sewage effluent. In addition, a small amount of the inorganic material is removed as well. Removal of Calcium and Magnesium. Calcium and magnesium salts, which generally are present in water as bicarbonates or sulfates, cause water hardness. One of the most common manifestations of water hardness is the insoluble "curd" formed by the reaction of soap with calcium or magnesium ions. Although ions that cause water hardness do not form insoluble products with detergents, they do adversely affect detergent performance. Therefore, calcium and magnesium must be complexed or removed from water for detergents to function properly. Another problem caused by hard water is the formation of mineral deposits. For example, when water containing calcium and bicarbonate ions is heated, insoluble calcium carbonate is formed:

Ca2+ + 2HCO3- → CaCO3(s) + CO2(g) + H2O


Page 9

This product coats the surfaces of hot water systems, clogging pipes and reducing heating efficiency. Dissolved salts such as calcium and magnesium bicarbonates and sulfates can be especially damaging in boiler feedwater. Clearly, the removal of water hardness is essential for many uses of water. Several processes are used to soften water. On a large scale, such as in community, water-softening operations, the lime-soda process is used. This process involves the treatment of water with lime, Ca(OH)2, and soda ash, Na2CO3. Calcium is precipitated as CaCO3, and magnesium as Mg(OH)2. When the calcium is present primarily as "bicarbonate hardness," it can be removed by the addition of Ca(OH)2 alone:

Ca2+ + 2HCO3- + Ca(OH)2 → 2CaCO3(s) + 2H2O

When bicarbonate ion is not present at substantial levels, a source of CO3

- must be provided at a high enough pH to prevent conversion of most of the carbonate to bicarbonate. These conditions are obtained by the addition of Na2CO3. For example, calcium present as the chloride can be removed from water by the addition of soda ash:

Ca2+ + 2Cl-+ 2Na+ + CO3- → CaCO3(s) + 2Cl- + 2Na+

The precipitation of magnesium as the hydroxide requires a higher pH than the precipitation of calcium as the carbonate:

Mg2+ + 2OH- → Mg(OH)2(s) The high pH required may be provided by the basic carbonate ion from soda ash:

CO3- + H2O- → HCO3

- + OH- Some large-scale, lime-soda softening plants make use of the precipitated calcium carbonate product as a source of additional lime. The calcium carbonate is first heated to at least 825 oC to produce quicklime, CaO:

CaCO3 + heat → CaO + CO2(g) The quicklime is then slaked with water to produce calcium hydroxide:

CaO + H2O → Ca(OH)2 The water softened by lime-soda softening plants usually suffers from two defects. First, because of super-saturation effects, some CaCO3 and Mg(OH)2, usually remain in solution. If not removed, these compounds will precipitate at a later stage and cause harmful deposits or undesirable cloudiness in water. The second problem results from the use of highly basic sodium carbonate, which gives the product water an excessively high pH, up to pH 11. To overcome these problems, the water is recarbonated by bubbling CO2 into it. The carbon dioxide converts the slightly soluble calcium carbonate and magnesium hydroxide to their soluble bicarbonate forms:

CaCO3(s) + CO2 + H2O → Ca2+ + 2HCO3-

Mg(OH)2(s) + 2CO2 → Mg2+ + 2HCO3 The pH generally is brought within the range 7.5-8.5 by recarbonation. The source of CO2 used in the recarbonation process may be from the combustion of carbonaceous fuel. Scrubbed stack gas from a power plant frequently is utilized. Calcium may be removed from water very efficiently by the addition of orthophosphate:

5Ca2+ + 3PO43- + OH- → Ca5OH(PO4)3(s)


Page 10

It should be understood that the chemical formation of a slightly soluble product for the removal of undesired solutes such as hardness ions must be followed by sedimentation in a suitable apparatus. Frequently, coagulants must be added, and filtration employed for complete removal of these sediments. Ion exchange, the reversible transfer of ions between aquatic solution and a solid material capable of bonding ions may be used to purify water. A number of materials have ion-exchanging properties. Among the minerals especially noted for their ion exchange properties are the aluminium silicate minerals, or zeolites. An example of a zeolite which has been used commercially in water softening is glauconite, K2(MgFe)2Al6(Si4O10)3(OH)12. Resin based cation exchangers include SO3

-H+ (a strong acid), -CO2H (a weak acid) and N+(CH3)3OH- (strongly basic). Strongly acidic cation exchangers are used for the removal of water hardness. Weakly acidic cation exchangers having the -CO2H group as a functional group are useful for removing alkalinity. Alkalinity generally is manifested by bicarbonate ion. This species is a sufficiently strong base to neutralize the acid of a weak acid cation exchanger:

2R-CO2H + Ca2+ + 2HCO3- → [R-CO2

-]2Ca2+ + 2H2O + 2CO2 Chelation or sequestration is an effective method of softening water without actually having to remove calcium and magnesium from solution. A complexing or chelating agent (e.g. polyphosphate salt, or EDTA) is added which greatly reduces the concentrations of free hydrated cations. For example, chelating calcium ion with excess EDTA anion (Y4-), Ca2+ + Y4- → CaY2-, reduces the concentration of hydrated calcium ion, preventing the precipitation of calcium carbonate: Ca2+ + CO3

2- → CaCO3(s). Removal of Iron, Manganese and Heavy Metals. Soluble iron and manganese are found in many groundwaters because of reducing conditions that favour the soluble +2 oxidation state of these metals. The basic method for removing these metals depends upon oxidation to higher insoluble oxidation states. The oxidation is generally accomplished by aeration. The rate of oxidation is pH-dependent in both cases, with a high pH favouring more rapid oxidation. The oxidation of soluble Mn(II) to insoluble MnO2 is a complicated process. It appears to be catalyzed by solid MnO2, which is known to adsorb Mn(II). This adsorbed Mn(II) is slowly oxidized on the MnO2 surface. Chlorine and potassium permanganate are sometimes employed as oxidizing agents for iron and manganese. In water with a high level of carbonate, FeCO3 and MnCO3 may be precipitated directly by raising the pH above 8.5 by the addition of sodium carbonate or lime. This approach is less popular than oxidation. Relatively high levels of insoluble iron(III) and manganese(IV) frequently are found in water as colloidal material which is difficult to remove. These metals may be associated with organic material that binds to colloidal metal oxides thus stabilizing the colloid. Heavy metals such as copper, cadmium, mercury, and lead are found in wastewaters from a number of industrial processes. Because of the toxicity of many heavy metals, their concentrations must be reduced to very low levels prior to release of the wastewater. A number of approaches are used in heavy metals removal. Lime treatment removes heavy metals as insoluble hydroxides, basic salts, or coprecipitated with calcium carbonate or ferric hydroxide. This process does not completely remove mercury, cadmium, or lead, so their removal is aided by addition of sulfide (most heavy metals are sulfide-seekers):

Cd2+ + S2- → CdS (s) Heavy chlorination is frequently necessary to break down metal-solubilizing ligands. Lime precipitation does not normally permit recovery of metals and is sometimes undesirable from the economic viewpoint. Electrodeposition (reduction of metal ions to metal by electrons at an electrode), reverse osmosis, and ion exchange are frequently employed for metal removal. Solvent extraction


Page 11

using organic-soluble chelating substances is also effective in removing many metals. Cementation, a process by which a metal deposits by reaction of its ion with a more readily oxidized metal, may be employed:

Cu2+ + Fe (iron scrap) → Fe2+ + Cu Activated carbon adsorption effectively removes some metals from water at the parts per million levels. Sometimes a chelating agent is adsorbed to charcoal to increase metal removal. Even when not specifically designed for the removal of heavy metals, most waste treatment processes remove appreciable quantities of the more troublesome heavy metals encountered in wastewater. Biological waste treatment effectively removes metals from water. These metals accumulate in the sludge from biological treatment, so sludge disposal must be given careful consideration. Various physical-chemical treatment processes effectively remove heavy metals from wastewaters. One such treatment is lime precipitation followed by activated-carbon filtration. Activated-carbon filtration may also be preceded by treatment with iron(III) chloride to form an iron(III) hydroxide floc, which is an effective heavy metals scavenger. Similarly, alum, which forms aluminium hydroxide, may be added prior to activated-carbon filtration. The form of the heavy metal has a strong effect upon the efficiency of metal removal. For instance, chromium(VI) is normally more difficult to remove than chromium(III). Chelation may prevent metal removal by solubilizing metals. Removal of Dissolved Organics. The standard method for the removal of dissolved organic material is adsorption on activated carbon, a product that is produced from a variety of carbonaceous materials, including wood, pulp-mill char, peat, and lignite. The carbon is produced by charring the raw material anaerobically below 600 °C followed by an activation step consisting of partial oxidation. Carbon dioxide may be employed as an oxidizing agent at 600-700 °C, CO2 + C → 2CO, or the carbon may be oxidized by water at 800-900 °C, H2O + C → H2 + CO. These processes develop porosity, increase the surface area, and leave the C atoms in arrangements that have affinities for organic compounds. Activated carbon comes in two general types: granulated activated carbon, consisting of particles 0. 1 -1 mm in diameter, and powdered activated carbon, in which most of the particles are 50-100 μm in diameter. Although interest is increasing in the use of powdered activated carbon for water treatment, currently granular carbon is more widely used. It may be employed in a fixed bed, through which water flows downward. Accumulation of particulate matter requires periodic backwashing. An expanded bed in which particles are kept slightly separated by water flowing upward may be used with less chance of clogging. Removal of organics may also be accomplished by adsorbent synthetic polymers. Such polymers as Amberlite XAD-4 have hydrophobic surfaces and strongly attract relatively insoluble organic compounds, such as chlorinated pesticides. They are readily regenerated by solvents such as isopropanol and acetone. Under appropriate operating conditions, these polymers remove virtually all nonionic organic solutes. Oxidation of dissolved organics holds some promise for their removal. Ozone, hydrogen peroxide, molecular oxygen (with or without catalysts), chlorine and its derivatives, permanganate, or ferrate can be used. Electrochemical oxidation may be possible in some cases. A promising new development is the use of high-energy electron beams produced by high-voltage electron accelerators to destroy organic compounds in water. Removal of Dissolved Inorganics. In order for complete water recycling to be feasible, inorganic-solute removal is essential. The effluent from secondary waste treatment generally contains 300-400 mg/L more dissolved inorganic material than does the municipal water supply. It is obvious, therefore, that 100% water recycle without removal of inorganics would cause the accumulation of an intolerable level of dissolved material. Even when water is not destined for immediate reuse, the removal of the inorganic nutrients phosphorus and nitrogen is highly desirable to reduce eutrophication downstream. In some cases, the removal of toxic trace metals is needed.


Page 12

One of the most obvious methods for removing inorganics from water is distillation. Unfortunately, the energy required for distillation is generally too high for the process to be economically feasible. Furthermore, volatile materials such as ammonia and odorous compounds are carried over to a large extent in the distillation process, unless special preventative measures are taken. Freezing produces very pure water, but is considered uneconomical with present technology. Membrane processes considered most promising for bulk removal of inorganics from water are electrodialysis, ion exchange, and reverse osmosis. Other membrane processes used in water purification are nanofiltration, ultrafiltration, microfiltration, and dialysis. Electrodialysis consists of applying a direct current across a body of water separated into vertical layers by membranes alternately permeable to cations and anions. Cations migrate toward the cathode and anions toward the anode. Cations and anions both enter one layer of water, and both leave the adjacent layer. Thus, layers of water enriched in salts alternate with those from which salts have been removed. The water in the brine-enriched layers is recirculated to a certain extent to prevent excessive accumulation of brine. The ion exchange process used for removal of inorganics consists of passing the water successively over a solid cation exchanger and a solid anion exchanger, which replace cations and anions by hydrogen ion and hydroxide ion, respectively. The net result is that each equivalent of salt is replaced by a mole of water. For the hypothetical ionic salt MX, the reactions are:

H+- {Ce(s)} + M+ + X- → M+- {Ce(s)} + H+ + X- OH-+{Ae(s)} + H+ + X- → X-+ {Ae(s)} + H2O

where – {Ce(s} represents the solid cation exchanger and + {Ae(s)} represents the solid anion exchanger. The cation exchanger is regenerated with strong acid and the anion exchanger with strong base. Reverse Osmosis consists of forcing pure water through a semipermeable membrane that allows the passage of water but not of other material. This process depends on the preferential sorption of water on the surface of the membrane, which is composed of porous cellulose acetate or polyamide. Pure water from the sorbed layer is forced through pores in the membrane under pressure. Phosphorus Removal. Advanced waste treatment normally requires removal of phosphorus to reduce algal growth. Municipal wastes contain phosphate as orthophosphates, polyphosphates, and insoluble phosphates. The removal of phosphate may occur in the sewage treatment process (1) in the primary settler; (2) in the aeration chamber of the activated sludge unit; or (3) after secondary waste treatment. Normally, the activated sludge process removes about 20% of the phosphorus from sewage. Thus, an appreciable fraction of largely biological phosphorus is removed with the sludge. Detergents and other sources contribute significant amounts of phosphorus to domestic sewage and considerable phosphate ion remains in the effluent. However, some wastes, such as carbohydrate wastes from sugar refineries, are so deficient in phosphorus that supplementation of the waste with inorganic phosphorus is required for proper growth of the microorganisms degrading the wastes. Under some sewage plant operating conditions, much greater than normal phosphorus removal has been observed. In such plants, characterized by high dissolved oxygen and high pH levels in the aeration tank, removal of 60-90% of the phosphorus has been attained, yielding two or three times the normal level of phosphorus in the sludge. In a conventionally operated aeration tank of an activated sludge plant, the CO2 level is relatively high because of release of the gas by the degradation of organic material. A high CO2 level results in a relatively low pH, due to the presence of carbonic acid. The aeration rate generally is not very high because oxygen is transferred relatively more efficiently from air when the dissolved oxygen levels in water are relatively low. Therefore, the aeration rate normally is not high


Page 13

enough to sweep out sufficient dissolved carbon dioxide to bring its concentration down to low levels. Thus, the pH generally is low enough that phosphate is maintained primarily in the form of the H2PO4

- ion. Chemically, phosphate is most commonly removed by precipitation. Some common precipitants and their products are shown in Table below. Precipitation processes are capable of at least 90-95% phosphorus removal at reasonable cost. Table 3. Chemical Precipitants for Phosphate and Their Products

Precipitant Product Ca(OH)2 Al2(SO4)3 FeCl3 MgSO4

Ca5OH(PO4)3 (hydroxyapatite) AlPO4 FePO4 MgNH4PO4

Lime, Ca(OH)2, is the chemical most commonly used for phosphorus removal:

5Ca(OH)2 + 3HPO42- → Ca5OH(PO4)3(s) + 3H2O + 6OH-

Lime has the advantages of low cost and ease of regeneration. Phosphate can be removed from solution by adsorption on some solids, particularly activated alumina, Al2O3. Removals of up to 99.9% of orthophosphate have been achieved with this method. Nitrogen Removal. Nitrogen is the algal nutrient most commonly removed as part of advanced wastewater treatment. The techniques most often used for nitrogen removal are summarized below: Air stripping ammonia: Ammonium ion is the initial product of biodegradation of nitrogenous waste. It is removed by raising the pH to approximately 11 with lime and stripping ammonia gas from the water by air in a stripping tower. Scaling, icing, and air pollution are major disadvantages. Ammonium ion exchange: This is made possible by the development of clinoptilolite, a natural zeolite selective for ammonia:

Na+(dinoptilolite) + NH4+ → Na+ + NH4

+ (clinoptilolite). Regenerated with sodium or calcium salts. Biosynthesis: The production of biomass in the sewage treatment system and its subsequent removal from the sewage effluent result in a net loss of nitrogen from the system. Nitrification-denitrification: Several schemes are based on the conversion of ammonium nitrogen to nitrate under aerobic conditions.

2NH4+ + 3O2 + Nitrosomonas → 4H+ + 2NO2

- + 2H2O 2NO2

- + O2 + Nitrobacter → 2NO3-

followed by production of elemental nitrogen (denitrification):

4NO3- + 5{CH2O} + 4H+ + denitrifying bacteria → 2N2(g) + 5CO2(g) + 7H2O

Denitrification may be accomplished in an anaerobic activated sludge system or in an anaerobic column. Sometimes additional organic matter (methanol) is added. Chlorination: Reaction of ammonium ion and hypochlorite (from chlorine) results in denitrification by chemical reactions:


Page 14

NH4+ + HOCI → NH2C1 + H2O + H+

2NH2CI + HOCI → N2(g) + 3H+ + 3Cl- + H2O Nitrogen in municipal wastewater generally is present as organic nitrogen or ammonia. Ammonia is the primary nitrogen product produced by most biological waste treatment processes. This is because it is expensive to aerate sewage sufficiently to oxidize the ammonia to nitrate through the action of nitrifying bacteria. If the activated sludge process is operated under conditions such that the nitrogen is maintained in the form of ammonia, the latter may be stripped in the form of NH3 gas from the water by air. For ammonia stripping to work, the ammoniacal nitrogen must be converted to volatile NH3 gas, which requires a pH substantially higher than the pKa of the NH4

+ ion. In practice, the pH is raised to approximately 11.5 by the addition of lime (which also serves to remove phosphate). The ammonia is stripped from the water by air. Nitrification followed by denitrification is a promising technique for the removal of nitrogen from wastewater. The first step is an essentially complete conversion of ammonia and organic nitrogen to nitrate under strongly aerobic conditions, achieved by more extensive than normal aeration of the sewage:

NH4+ + 2O2 (Nitrifying bacteria) → NO3

- + 2H+ + H2O The second step is the reduction of nitrate to nitrogen gas. This reaction is also bacterially catalyzed and requires a carbon source and a reducing agent such as methanol, CH3OH.

6NO3- + 5CH3OH + 6H+ (Denitrifying bacteria) →3N2(g) + 5CO2 + 13H2O

The denitrification process may be carried out either in a tank or on a carbon column. In pilot plant operation, conversions of 95% of the ammonia to nitrate and 86% of the nitrate to nitrogen have been achieved. Sludge. Some sludge is present in wastewater and may be collected from it. Such sludge includes human wastes, garbage grindings, organic wastes and inorganic silt and grit from storm water runoff, and organic and inorganic wastes from commercial and industrial sources. There are two major kinds of sludge generated in a waste treatment plant. The first of these is organic sludge from activated sludge, trickling filter, or rotating biological reactors. The second is inorganic sludge from the addition of chemicals, such as in phosphorus removal. Most commonly, sewage sludge is subjected to anaerobic digestion in a digester designed to allow bacterial action to occur in the absence of air. This reduces the mass and volume of sludge and ideally results in the formation of stabilized humus. Disease agents are also destroyed in the process. Following digestion, sludge is generally conditioned and thickened to concentrate and stabilize it and make it more dewaterable. Relatively inexpensive processes, such as gravity thickening, may be employed to get the moisture content down to about 95%. Sludge may be further conditioned chemically by the addition of iron or aluminium salts, lime, or polymers. Sludge dewatering is employed to convert the sludge from an essentially liquid material to a damp solid containing not more than about 85% water. This may be accomplished on sludge drying beds consisting of layers of sand and gravel. Mechanical devices may also be employed, including vacuum filtration, centrifugation, and filter presses. Heat may be used to aid the drying process. Some of the alternatives for the ultimate disposal of sludge include land spreading, ocean dumping, and incineration. Each of these choices has disadvantages, such as the presence of toxic substances in sludge spread on land, or the high fuel cost of incineration. Rich in nutrients, waste sewage sludge contains around 5%N, 3% P, and 0.5% K on a dry-weight basis and can be used to fertilize and condition soil. The humic material in the sludge improves the physical properties and cation-exchange capacity of the soil. Among the factors limiting this application of sludge are excess nitrogen pollution of runoff water and groundwater, survival of pathogens, and the presence of heavy metals in the sludge.


Page 15

Possible accumulation of heavy metals is of the greatest concern insofar as the use of sludge on cropland is concerned. Sewage sludge is an efficient heavy metals scavenger. These and other metals tend to remain immobilized in soil by chelation with organic matter, adsorption on clay minerals, and precipitation as insoluble compounds, such as oxides or carbonates. However, increased application of sludge on cropland has caused distinctly elevated levels of zinc and cadmium in both leaves and grain of corn. Therefore, caution has been advised in heavy or prolonged application of sewage sludge to soil. The problem of heavy metals in sewage sludge is one of the many reasons for not allowing mixture of wastes to occur prior to treatment. Sludge does, however, contain nutrients, which should not be wasted, given the possibility of eventual fertilizer shortages. Prior control of heavy metal contamination from industrial sources should greatly reduce the heavy metal content of sludge and enable it to be used more extensively on soil. An increasing problem in sewage treatment arises from sludge sidestreams. These consist of water removed from sludge by various treatment processes. Sewage treatment processes can be divided into mainstream treatment processes (primary clarification, trickling filter, activated sludge, and rotating biological reactor) and sidestream processes. During sidestream treatment sludge is dewatered, degraded, and disinfected by a variety of processes, including gravity thickening, dissolved air flotation, anaerobic digestion, aerobic digestion, vacuum filtration, centrifugation, belt-filter press filtration, sand-drying-bed treatment, sludge-lagoon settling, wet air oxidation, pressure filtration, and Purifax treatment. Each of these produces a liquid by-product sidestream, which is circulated back to the mainstream. These add to the biochemical oxygen demand and suspended solids of the mainstream. Various water treatment and industrial processes produce a variety of chemical sludges. Among the most abundant of such sludges is alum sludge produced by the hydrolysis of Al(III) salts used in the treatment of water, which creates gelatinous aluminium hydroxide:

Al3+ + 3OH-(aq) → Al(OH)3 (s) Alum sludges normally are 98% or more water and are very difficult to dewater. Both iron(II) and iron(III) compounds are used for the precipitation of impurities from wastewater via the precipitation of Fe(OH)3. The sludge contains Fe(OH)3 in the form of soft, fluffy precipitates that are difficult to dewater beyond 10 or 12% solids. The addition of either lime, Ca(OH)2, or quicklime, CaO, to water is used to raise the pH to about 11.5 and cause the precipitation of CaCO3, along with metal hydroxides and phosphates. Calcium carbonate is readily recovered from lime sludges and can be converted to produce CaO, which can be recycled through the system. Metal hydroxide sludges are produced in the removal of metals such as lead, chromium, nickel, and zinc from wastewater by raising the pH to such a level that the corresponding hydroxides or hydrated metal oxides are precipitated. The disposal of these sludges is a substantial problem because of their toxic heavy metal content. Reclamation of the metals is an attractive alternative for these sludges. Pathogenic (disease-causing) microorganisms may persist in the sludge left from the treatment of sewage. Many of these organisms present potential health hazards, and there is risk of public exposure when the sludge is applied to soil. Therefore, it is necessary both to be aware of pathogenic microorganisms in municipal wastewater treatment sludge and to find a means of reducing the hazards caused by their presence. Several ways are recommended to significantly reduce levels of pathogens in sewage sludge. Aerobic digestion involves aerobic agitation of the sludge for periods of 40 to 60 days (longer times are employed with low sludge temperatures). Air drying involves draining and/or drying of the liquid sludge for at least three months in a layer 20-25 cm thick. This operation may be performed on underdrained sand beds or in basins. Anaerobic digestion involves maintenance of the sludge in an anaerobic state for periods of time ranging from 60 days at 20 °C to 15 days at temperatures exceeding 35 °C. Composting involves mixing dewatered sludge cake with bulking agents subject to decay, such as wood chips or shredded municipal refuse, and allowing the action of bacteria to promote decay at temperatures ranging up to 45-65 °C. The higher temperatures tend to kill pathogenic bacteria. Finally, pathogenic organisms may be


Page 16

destroyed by lime stabilization in which sufficient lime is added to raise the pH of the sludge to 12 or higher. Water Disinfection. This process makes water safe to drink by killing of pathogenic (disease-causing) organisms. Physical methods. The techniques employing physical principles for disinfection of water include ultraviolet light (UV radiation), electronic radiation, gamma rays, ultrasound, ultrafiltration, reverse osmosis, heating, freezing, direct exposure to solar radiation and ionizing radiation. Chemical methods. Chemical methods depend mostly on selected chemicals with oxidizing and biocidal properties. Chemical disinfectants kill microorganisms by oxidizing vital molecules (often with unsaturated carbon bond) in them. Their practical applications range from removing undesirable constituents to disinfecting water supplies, wastewater treatment effluent, or industrial waters. The most commonly used chemicals include ozone, chlorine and some of its compounds, potassium permanganate, hydrogen peroxide, bromine, iodine, bromine chloride (BrCl), metal ions e.g. copper (Cu2+) and silver (Ag+), alcohols, soaps and detergents, acids and bases. Chlorine Chlorine is the most commonly used disinfectant employed for killing bacteria in water. When chlorine is added to water, it rapidly hydrolyzes according to the reaction:

Cl2 + H2O → H+ + Cl- + HOCI Hypochlorous acid, HOCl, is the active disinfection component and dissociates according to the reaction:

HOCI ↔ H+ + OCl-

Sometimes, hypochlorite salts are substituted for chlorine gas as a disinfectant. Calcium hypochlorite, Ca(OCl)2 is commonly used. The hypochlorites are safer to handle than gaseous chlorine. The two chemical species formed by chlorine in water, HOCl and OCl-, are known as free available chlorine. Free available chlorine is very effective in killing bacteria. In the presence of ammonia, monochloramine, dichloramine, and trichloramine are formed:

NH4+ + HOCl → NH2Cl (monochloramine) + H2O + H+

NH2Cl + HOCI → NHCl2 (dichloramine) + H2O NHCl2 + HOCI → NCl3 (trichloramine) + H2O

The chloramines are called combined available chlorine. Chlorination practice frequently provides for formation of combined available chlorine, which although a weaker disinfectant than free available chlorine, is more readily retained as a disinfectant throughout the water distribution system. Too much ammonia in water is considered undesirable because it exerts excess demand for chlorine. Chlorine is effective and relatively cheap. The persistence of HOCl allows the disinfection of surrounding water infiltrated through old and leaky pipes. However, HOCl can act as a chlorinating agent to produce a variety of chlorinated organic compounds (e.g., CHCl3). Many of the Cl-containing organics are toxic and non-biodegradable. Some (e.g. CH2Cl2, CHCl3) are suspected carcinogens. Chlorine is used to treat water other than drinking water. It is employed to disinfect effluent from sewage treatment plants, as an additive to the water in electric power plant cooling towers, and to control microorganisms in food processing. Chlorine dioxide. Chlorine dioxide, ClO2, is an effective water disinfectant that is of particular interest because, in the absence of impurity Cl2, it does not produce impurity trihalomethanes in water treatment. In acidic and neutral water, respectively, the two half-reactions for ClO2


Page 17

acting as an oxidant are the following:

ClO2 + 4H+ + 5e- Cl- + 2H2O ClO2 + e- ClO2

- In the neutral pH range, chlorine dioxide in water remains largely as molecular ClO2 until it contacts a reducing agent with which to react. Chlorine dioxide is a gas that is violently reactive with organic matter and explosive when exposed to light. For these reasons, ClO2 is not shipped, but is generated onsite by processes such as the reaction of chlorine gas with solid sodium hypochlorite:

2NaClO2(s) + Cl2(g) 2ClO2(g) + 2NaCl(s) A high content of elemental chlorine in the product may require its purification to prevent unwanted side-reactions from Cl2. As a water disinfectant, chlorine dioxide does not chlorinate or oxidize ammonia or other nitrogen-containing compounds. ClO2 is more expensive than Cl2. Some concern has been raised over possible health effects of its main degradation by-products, ClO2

- and ClO3-.

Ozone. Ozone is sometimes used as a disinfectant. Basically, air is filtered, cooled, dried, and pressurized, then subjected to an electrical discharge of approximately 20,000 volts. The ozone produced is then pumped into a contact chamber where water contacts the ozone for 10-15 minutes. Ozone is more destructive to viruses than is chlorine. Unfortunately, the solubility of ozone in water is relatively low, which limits its disinfective power. A major consideration with ozone is the rate at which it decomposes spontaneously and rapidly in water, according to the overall reaction.

2O3 → 3O2(g) Because of the decomposition of ozone in water, some chlorine must be added to maintain disinfectant throughout the water distribution system. O3 is more expensive than Cl2 and needs to be generated on-site. Iron(VI) in the form of ferrate ion, FeO4

2-, is a strong oxidizing agent with excellent disinfectant properties. It has the additional advantage of removing heavy metals, viruses, and phosphate. It may well find limited application for disinfection in the future. Water reuse and recycling are becoming much more common as demands for water exceed supply. Unplanned reuse occurs as the result of waste effluents entering receiving waters or groundwater and subsequently being taken into a water distribution system. Planned reuse utilizes wastewater treatment systems deliberately designed to bring water up to standards required for subsequent applications. The term direct reuse refers to water that has retained its identity from a previous application; reuse of water that has lost its identity is termed indirect reuse. The distinction also needs to be made between recycling and reuse. Recycling occurs internally before water is ever discharged. An example is condensation of steam in a steam power plant followed by return of the steam to boilers. Reuse occurs when another user takes up, water discharged by one user for example, from a river. Reuse of water continues to grow because of two major factors. The first of these is lack of supply of water. The second is that widespread deployment of modern water treatment processes significantly enhances the quality of water available for reuse. These two factors come into play in semi-arid regions in countries with advanced technological bases. Since drinking water and water used for food processing requires the highest quality of all large applications, intentional reuse for potable water is relatively less desirable, though widely practiced unintentionally or out of necessity. This leaves three applications with the greatest potential for reuse: Irrigation for cropland, and other applications requiring water for plant growth. This is the largest potential application for reused water and one that can take


Page 18

advantage of plant nutrients, particularly nitrogen and phosphorus, in water. Cooling and process water in industrial applications. For some industrial applications, relatively low quality water can be used and secondary sewage effluent is a suitable source. Soil Pollution Overview. Soil pollution involves the following mechanisms: deposition of solid waste; accumulation of non-biodegradable materials; toxification of chemicals into poisons or alteration of soil chemical composition (imbalance of chemical equilibrium to soil medium). The causes for such devastation are generally due to two forms of malpractices:

i) Unhealthy soil management methods such as: (a) improper tillage of soil which results in the deterioration of soil structure; (b) non-maintenance of a proper supply of organic matter in the soil; (c) use of excessive synthetic chemicals (fertilizers and pesticides), which are resistant to biodegradation and accumulate in the soil system which eventually destroy useful organisms such as bacteria, and fungi, and (d) improper maintenance of the correct soil acidity which ultimately disrupts the adaptation of vegetation as the solubility of minerals present will be affected.

ii) Improper irrigation practices; e.g.: (a) poorly drained soil result in salt deposits leading to high salinity that inhibit plant growth (b) irregular irrigation leads to decreasing moisturization of land for soil medium and replenishments of solvents for minerals.

Sources and Ways of Soil Pollution. We can classify major sources that lead to soil pollution to the following categories. Their ways of pollution are also outlined:

(i) Agriculture: accumulation of animal manures; excessive input of chemical fertilizers and pesticides; illicit dumping of tainted crops on land etc.

(ii) Mining and quarrying: using explosives to blow up mines; using of machineries, which emit toxic byproducts that leak to the ground etc.

(iii) Sewage sludge: improper sanitation system causes sludge to leak at surrounding soil (iv) Household: improper sanitation and waste disposal systems cause waste accumulation (v) Demolition and construction: non biodegradable rubbles or debris which are not cleared

settled in the soil undergo chemical reactions and increase soil toxicity. (vi) Industrial: poisonous/toxic emissions of gases which are not filtered or neutralized;

production and disposal of solid and hazardous wastes etc.

As an example, mining and quarrying can course what is called Acid Mine Drainage (AMD).

AMD is drainage flowing from or caused by surface mining, deep mining or coal refuse piles

that is typically highly acidic with elevated levels of dissolved metals.

How is AMD formed? The formation of AMD is primarily a function of the geology, hydrology

and mining technology employed for the mine site. AMD is formed by a series of complex geo-

chemical and microbial reactions that occur when water comes in contact with pyrite (iron

disulfide minerals) in coal, refuse or the overburden of a mine operation. The resulting water is

usually high in acidity and dissolved metals. The metals stay dissolved in solution until the pH

raises to a level where precipitation occurs. Solubility charts for the various metals show the

pH at which precipitation begins and the pH at which maximum insolubility occurs.

Basic AMD Chemistry. There are four commonly accepted chemical reactions that represent

the chemistry of pyrite weathering to form AMD. An overall summary reaction is as follows:


Page 19

4FeS2 + 15O2 + 14H2O 4Fe(OH)3↓ + 8H2SO4

Pyrite + Oxygen + Water "Yellowboy" + Sulfuric Acid

The first reaction in the weathering of pyrite includes the oxidation of pyrite by oxygen. Sulfur

is oxidized to sulfate and ferrous iron is released. This reaction generates two moles of acidity

for each mole of pyrite oxidized.

2FeS2 + 7O2 + 2H2O 2Fe2+ + 4SO42- + 4H+

Pyrite + Oxygen + Water Ferrous Iron + Sulfate + Acidity

The second reaction involves the conversion of ferrous iron to ferric iron. The conversion of

ferrous iron to ferric iron consumes one mole of acidity. Certain bacteria increase the rate of

oxidation from ferrous to ferric iron. This reaction rate is pH dependant with the reaction

proceeding slowly under acidic conditions (pH 2-3) with no bacteria present and several orders

of magnitude faster at pH values near 5. This reaction is refered to as the "rate determining

step" in the overall acid-generating sequence.

4Fe2+ + O2 + 4H+ 4Fe3+ + 2H2O

Ferrous Iron + Oxygen + Acidity Ferric Iron + Water

The third reaction which may occur is the hydrolysis of iron. Hydrolysis is a reaction which

splits the water molecule. Three moles of acidity are generated as a byproduct. Many metals

are capable of undergoing hydrolysis. The formation of ferric hydroxide precipitate (solid) is pH

dependant. Solids form if the pH is above about 3.5 but below pH 3.5 little or no solids will

precipitate.

4Fe3+ + 12H2O 4Fe(OH)3 ↓ + 12H+

Ferric Iron + Water Ferric Hydroxide (yellowboy) + Acidity

The fourth reaction is the oxidation of additional pyrite by ferric iron. The ferric iron is

generated in reaction steps 1 and 2. This is the cyclic and self propagating part of the overall

reaction and takes place very rapidly and continues until either ferric iron or pyrite is depleted.

Note that in this reaction iron is the oxidizing agent, not oxygen.


Page 20

FeS2 + 14 Fe3+ + 8 H2O 15 Fe2+ + 2 SO42- + 16 H+

Pyrite + Ferric Iron + Water Ferrous Iron + Sulfate + Acidity

Noise Pollution. Overview. This particular pollution is ever increasing due to the rise in the utilization of heavy duty machineries of industrial facilities and vehicles, synonymous to the increase in the standard of living in most countries. Noise pollution causes annoyance and disturbances in intercity housing, with the industries, centre and transportation hub situated. Sources, Ways and Effects of Noise Pollution. We can classify major sources that lead to noise pollution to the following categories: (i) Road traffic. Increasing community reliance on road transportation, and a reluctance to accept partial solutions involving greater use of public transport. Land use planning has not been well integrated with transport planning, allowing residential developments and major transport corridors to occur in close proximity without appropriate buffer zones or treatment to buildings. Traffic on many existing roads through built up areas has increased well beyond expectations prevailing during planning or constructions of the roadways. Inconsiderate drivers speeding at the same time honking uncontrollably for no apparent reason, which terms these drivers as road bullies. (ii) Air traffic. Military air force training with war planes and fighters flying at low altitude in close proximity to residential areas. Increased numbers of commercial flights over the years to accommodate the increasing demand to the number of passengers throughout the world. Flight path taken through densely populated area causing disturbances and interfere with the tranquility of the environment. (iii) Rail traffic. Construction of rail infrastructure involves in drilling and other heavy machineries which emit loud and deafening noises. Maintenance of rail infrastructure using heavy machineries emitting loud noises. Operation of trains increasing everyday. Use of petrol and diesel engines in poor countries than the quieter electric train and also older version of rolling stock. Unsuitable stopping pattern and topography which can lead to localized problem where the noise concentration is high in a particular area. (iv) Neighbourhood and domestic noise. Close proximity of home with each other without a good sound barrier often results in neighbours to endure the noises made. Outdoors which includes barking dogs repeatedly during nighttime where the whole neighbourhood is calm. Car alarms and other social gathering creating noises. (v) Industrial noises. Improper determination of land zoning where heavy industrial sites are not separated from residential areas by light industries, resulting in noise disturbances in the residential area. Heavy machineries mechanisms during combustions produce deafening sounds. Mining also results in increase noise level involved. Extractions of pure metals in coke ovens under high pressure. Electrical components manufacturing and fertilizer plants. The effects of noise pollution include: (i) irritation to daily activities; (ii) cause for boilermaker's disease; (iii) anxiety, nervousness and loss of sleep; (iv) hearing loss e.g age-related hearing loss (presbycusis), and loss of hearing due to social noise (sociocusis); (v) certain hazardous materials which is part of the machine (i.e. cadmium in nuclear factor regulator) may wear off and released to environment. Impacts of Pollution. Each kind of pollution has significant impacts to our everyday lives, affecting all living and non-living factors in the biosphere and the atmosphere and also


Page 21

involves socio-economic factors. These impacts have caused significant changes to the environment. Impacts can be seen from the following aspects:

• Acid rain • Ozone depletion • Climatic pattern change • Biodiversity degradation and diseases • Food contamination and food web distortion • Economical effects • Alteration to geographical landscapes • Alteration to lifestyle • Reduced visibility/clarity of air

Acid rain is the kind of precipitation that contains larger amounts of acid than normal. This is caused by the presence of air pollutants, like sulfur dioxide and nitrogen oxides, which produce acids if combined with water. The impacts of acid rain include deterioration of building that is made of rock, acidification of soil and lakes, deterioration of trees and forests and separation of poisonous minerals such as aluminium and mercury from the surrounding ground, increasing the risk of contamination to lakes/water sources causing damage to organisms. Climatic pattern change resulting from pollution finally causes global warming, El Nino and La Nina. Depletion of the ozone layer has been caused by pollutants such CFCs (chlorofluorocarbons) that are usually contained in refrigerators, coolants, and aerosol sprays. Some other substances, like bromine halocarbons and nitrous oxides are also possible threats. Ozone layer depletion results into more ultraviolet rays to reach the Earth’s surface and more heat, thus leading to harmful effects to organisms. Biodiversity degradation. Disturbances to biotic factors (temperature, light, water, humidity, wind, air currents, pH, topography, etc.) and abiotic factors (predation, competition, habitat, pollination and mimicry - resemblance between animals and part of a plant/species happens to be unpalatable to a predator) will lead to environmental resistance. This is due to shortage of food, water and oxygen, low light intensity, predators and parasites, destruction of habitat, diseases, accumulation of toxic waste, psychological factors and harsh climate. This will lead to exponential decrease in population of ecosystems that will cause high extinction rate of biodiversity. If this condition is severe, the ecology of the ecosystems will be permanently damaged. Emergence of variant diseases.is a combination of the following happenings: unhygienic practices by individuals; poor sanitation of habitation; uncontrollable emission/release of particulates containing pathogenic microorganisms and pollutants; mismanagement of treatment, control and storage plants in containment of pollutants and deterioration of machineries and facilities of treatment, control and storage plants; which will result in:

• exposure of contaminants to the environment. • accumulation of poisonous/hazardous substance incorporated into the physiological

functions and systems of living organisms • harmless microorganisms due to evolution undergo rapid mutation of deleterious genes

into pathogenic / viral microorganisms; • diversifications with the existence of ‘superclasses’ of microorganisms which are

aggressive and invasive against the protective immunities provided by the immune systems in organisms;

• more powerful and larger doses of medications, ranging from vaccines to antibiotics produced to battle and immunize against stronger pathogen attack; strong medication may produce side effects and harmful to physiological functions/systems of organisms.

Food contamination leading to food shortage. A combined event of (a) free flow and emission of non biodegradable industrial discharge and noise disturbances due to usage of heavy machineries; (b) illegal dumping and spraying of toxic and hazardous chemicals on land and


Page 22

water; and (c) mismanagement in regulation of treatment and control of heat and radioactive substances; will lead to high density toxicity concentration on soil, water and air. The impacts of this are:

• fertile land becoming poisonous for living organisms and nutrients lost, locked up or become toxic;

• aquatic ecosystem depletes further and non-consumable water supplies; • detrimental health effects to the organisms in ecosystems.

This situation continues to the rise of mortality rate of domesticated animals, failure of reproduction, and failure of cultivation of crops. This is also due to rapid mutation of deleterious genes; deterioration on metabolic and physiology functions of systems in plants and animals. Finally, as a result, there will be low productivity of food; occurrence of starvation and dehydration, and if severe, exponential increase in mortality rate of floras and faunas worldwide. Food web distortion. Pollution of food supplies and habitats of certain organisms in combination with other factors such as uncontrollable hunting of exotic/rare/endangered species will lead to the disequilibria of species population. The next impact will be the imbalance in the ration of producers, consumers and decomposers in the ecology system, which consequently distorts the pattern of energy flow through the chain/web. This will bring to disruption of ecological food pyramid. When ecological food pyramid is disrupted, insufficient consumption of food causes organisms to be deprived of energy, thus affecting the organism's metabolism or its biochemical activities. Then, growth and development of organisms will be affected, and lead to mass starvation and mortality in world population. On the other hand, particular species extinction will occur while its predators dominates, thus ecological niche in ecosystems change. Economical effects. Continuous development for globalization due to increasing activity of agriculture, industrialization, fisheries, timber and mining will lead to rapid and excessive constructions of factories and building; increase in emissions of toxic and poisonous gases and destruction of ecosystems. These will finally lead to permanent and irreversible damage to the environment. In the events of pollution that are reversible, greater finance and grants are needed for the following purposes:

• conservation of remaining ecosystem; • rehabilitation contaminated ecosystems; • clean up of toxic waste; • restoration of historical landscapes; • revival of biodiversity to a new ecosystem; • preservation of endangered species.

Alteration to geographical landscapes is a combination of the following events: constructions of housing and industries for development; economical activities of mining, timber and agriculture; clearing of rainforest and hillside, and natural disasters like earthquakes which involve the shifting of earth surface, which will result in:

• alteration to chemical composition of soil by substitution, utilization and drainage; • increase in soil temperature; • soil fertility decreases which gradually turns to a barren land due to desertification; • decrease in soil stability and grip, which acts as foundation; • displacement of upper layer of soil due to external forces of nature becomes easier; • significant alteration to original geographical landscape; • decrease of visibility of atmosphere; • deforestation, desertification, erosion and landslide.

Alternating lifestyle. Combined extent impacts of air, water, and soil pollution will cause irreversible environmental damage which is permanent, and will lead to toxic environment. As a result, the earth will be uninhabitable environment for living organisms. This will lead to high rates of extinction of biodiversity and high death rates of human and the rapid undergoing of adaptable species to mutate to better evolve in the sudden change in environment.


Page 23

Therefore in search of survival on Earth for humans: • water resources become scarce, leading to rationing and search for alternatives,

development of synthetic liquid similar to water; • unusable land due to toxic soil will change agricultural practice; poisonous foundation

for humans to stay on in effect human habitat will be shifted underground to support large population;

• artificial synthetic air/recycled air/purified air used as a result of poisonous atmosphere;

• alternative food supplies consumed as wide spread species extinction and mutation which are toxic and poisonous;

• emergence of evolved species due to mutation which are predatory and dangerous to human populations;

• economies change due to changing human activities in order to adapt to the new living environment.

POLLUTANTS: TYPES, SOURCES, PROPERTIES AND EFFECTS Pollutants are substances that have harmful effects on the health, survival, or activities of humans or other living organisms. They are any substances that under excessive quantity in a wrong place and a wrong time will cause impurity to the living environment. Simply put, they are the substanses that cause pollution, e.g. chemicals, ashes, sediment, organisms, heat, radiation, etc. Common pollutants that exist today include biological pollutants, heavy metals, synthetic chemicals, and radioactive materials. Biological pollutants. Biological pollutants are biodegradable substances, which can be considered one of the 'cleanest' pollutants; however rate of accumulation currently in an area, which is higher than the rate of decomposition, has made this an undisputable contributory factor to pollution. Types, Sources and Effects of Biological pollutants:

(i) Organic matter: From faecal matter of animals, or decomposition of dead organisms, decay of leaf litter. Due to soil erosion on hill slope or coastline are washed down and carried to streambed, lake or ocean. The effect of organic matter includes unbearable unpleasant smell of decomposing materials as a result of formation of such gases as CH4 and CO2. Other effects are leaching of organic matter to streambed, lake or ocean that cause eutrophication; reduced lake depth as a result of sedimentation; as well as change in original geographical landscape.

(ii) Microorganisms: Microscopic organisms can be viruses, bacteria or protozoa. Effects of microorganisms include production of gases such as CH4, SO2, and CO2 formed from decomposition of materials. Clarity of water in lakes is also reduced. Microorganisms transmit diseases to any living organisms consuming them, through secretion of poison and cause diseases e.g. malaria, typhoid, skin rash, and diarrhoea due to contamination of drinking water, food and air; deadly attack by microorganisms can cause death to living organisms.

(iii) Particulate matter: Spores, insect fragments, grains, pollen, hair, feathers etc. Their effects include reduce atmospheric visibility (haze, smog); gases such as CH4, SO2, NO2 and CO2 formed from decomposing materials and combustion of wood, hair, feathers etc; build up of toxic chemicals in the atmosphere harmful to living organisms; adverse respiratory illness e.g. frequent asthma attack.

Heavy metals are metals with a specific gravity greater than about 5.0, especially ones that are poisonous, such as lead or mercury. Heavy metals readily accumulate through food webs from producers to consumers. The following sections describe the uses, sources and impacts of some of the common heavy metal pollutants. Mercury (Hg). It is used in thermometers, barometers, fluorescent lamps, and electrodes in the amalgamation of electrolysis of brine. It alloys easily with many metals, such as gold, silver, and tin. These alloys are called amalgams. Its ease in amalgamating with gold make it to be used in the recovery of gold from its ores. The most important mercury salts are mercuric chloride HgCl2 (corrosive sublimate - a violent poison), mercurous chloride Hg2Cl2 (calomel, still used in medicine occasionally), mercury fulminate (Hg(ONC)2, a detonator used in explosives) and mercuric sulfide (HgS, vermillion, a high-grade paint pigment).


Page 24

Sources of mercury in the environment include broken barometers, thermometers and fluorescent light bulbs, leaching due to acid deposition which causes breakdown of minerals in rocks and soil, creation of new reservoirs, combustion of fossil fuel, household waste, pesticides (e.g. fungicides), laboratory chemicals, sewage effluent, mining industries, gold mining, industrial waste, atmospheric deposition, waste incineration, dumping of sewage sludge and smelting. Mercury is associated with the following effects in humans and other organisms:

• Causes kidney damage, lung irritation, eye irritation, vomiting and diarrhea. • Causes ulcers. • Causes death if in the form of methyl mercury, the most toxic form because of fat

solubility, a property that assists in the distribution throughout the body. • Causes Minamata disease. • Carcinogenic, typically causes cancer. • Mutagenic - DNA and chromosomal damage. • Cause for neurological disorder. • Damage to brain functions. Damaged brain functions can cause degradation of learning

abilities, personality changes, tremors, vision changes, deafness, muscle incoordination and memory loss. Chromosomal damage is known to cause mongolism.

• Disruption of the nervous system. • Cause for blindness. • It is a teratogen-associated with reproductive defects e.g. sperm damage, birth defects

and miscarriages. • Causes allergic reactions, resulting in skin rashes, tiredness and headaches. • Damaging to aquatic life. • Causes embryocidal, cytochemical, and histopathological effects.

In aquatic organisms it adversely affects reproduction, growth, behavior, osmoregulation, and oxygen exchange. It may also cause kidney lesions, neurological damage, and reduced food intake leading to weight loss, progressive weakness in wings and legs and an inability to coordinate muscle movements in marine birds. Microorganisms can convert mercury to methyl mercury, a substance that can be absorbed quickly by most organisms and is known to cause nerve damage. Fish are organisms that absorb great amounts of methyl mercury from surface waters every day. As a consequence, methyl mercury can accumulate in fish and in the food chains that they are part of. The effects that mercury has on animals are kidneys damage, stomach disruption, and damage to intestines, reproductive failure and DNA alteration. Lead (Pb). Lead is used as a protective shield from radioactivity, lead acid accumulator, for manufacture of antiknock, tetraethyl lead Pb(C2H5)4 in petrol and in pigments e.g., white basic lead carbonate, Pb(OH)2 or orange pigment ‘red lead’, Pb3O4. The sources of lead in the environment include mining industries, industrial and municipal discharges, incinerator ash, weathering processes, tap water from lead pipes, atmospheric deposition, automobile exhaust, highway runoff, paintworks, cables, pesticides, cigarette smoke and contaminated foods such as fruit, meat, vegetables, grains, and seafood. Lead causes health effects in human such as kidney damage, metabolic interference, central and peripheral nervous system toxicity-disruption of nervous systems, brain damage, depressed biosynthesis of protein, nerve and red blood cells, irritability, anaemia, and rise in blood pressure. It also causes mental retardation in children, behavioural disruptions of children, such as aggression, impulsive behaviour and hyperactivity. It can enter a foetus through the placenta of the mother. Because of this it can cause serious damage to the nervous system and the brains of unborn children. It causes general weakness, disability, nervous disorders and eventual death. It causes miscarriages and subtle abortions, and declined fertility of men through sperm damage. In the environment, when Pb pollutes soils and surface waters, it is not broken down; it is only converted to other forms. It accumulates in the bodies of organisms, thus disturbs their body functions; it also accumulates in entire food chains. Soil functions and organisms are disturbed by lead poisoning.


Page 25

Cadmium (Cd). Cadmium is used in Ni-Cd batteries, nuclear reactor regulator and red/yellow pigments. Some of the sources of cadmium are sewage effluent, electroplating, plastics industry, mining industry, smelting, burning coal and oils, and from wear of vehicle tires. Cd is toxic and poisonous, causes renal disease, kidney damage, and bone damage in human. It also causes suppressed egg production, and eggshell thinning in birds. Arsenic (As). Arsenic is used in glass, metal for mirrors, lasers, light emitting diodes (LED) and semiconductors. It is a deadly poison in shotgun pellets. Sources of As include mining industry, natural mineralization, pesticides e.g. herbicides, wood preservatives, smelter wastes and naturally occurring in many household products. Arsenic causes hyperkeratosis, hyperpigmentation, skin tumors, damage to gastrointestinal tract and liver. It is carcinogenic-associated with lung cancer, results in skin cancer. It is toxic when ingested. Aluminium (Al). Sources of pollution include leaching due to acid deposition. Al is linked to Alzheimer's disease (memory disorder), anaemia, softening of bones and senile dementia (deterioration of mental faculties and emotional stability in old age). Synthetic chemicals. The most important synthetic chemical pollutants include pesticides, volatile organic compounds (VOCs), and polychlorinated biphenyls (PCBs), which pollute soil, water, biota and air. Pesticides are substances or mixtures of substances used to manage, kill, attract or repel pests, including insects, rodents, worms, weeds, and fungi. The ideal pesticides have the following characteristics: (i) kill only the target pest, (ii) have no short- or long- term health effects on non-target organisms, including people, (iii) can be broken down into harmless chemicals in a fairly short time, (iv) prevent the development of genetic resistance in target organisms, and (v) save money compared with making no effort to control pest species. Pesticides can be classified on the basis of the target pests as herbicides (for weeds), insecticides (for insects), fungicides (for fungi), nematicides (for nematodes), avicides (for birds), acaricides, miticides (for ticks and mites), bactericides (for bacteria) and rodenticides (for rodents). Pesticides can also be classified based on their mode of action as protectants, fumigants, sterilants, broad-spectrum, selective, contacts and systemics. Protectants are used to prevent pest establishment and may include repellents. Fumigants produce a vapor that kills organisms. Sterilants are used to manage pests by rendering them incapable of normal reproduction. Broad-spectrum pesticides control a wide range of pests. Selective pesticides kill only a specific pest or group of pests. Contacts are pesticides that kill pests by coming into contact with them. Systemics are pesticides that are absorbed by one part of the animal or plant and distributed internally to other parts of the plant or animal. Synthetic pesticides can be grouped by their active ingredient (the chemical class to which a toxic components belongs). Major chemical groups are: organochlorines, organophosphates, carbamates, pyrethroids, organometallics, nitrophenols, and herbicides. Organochlorines e.g. DDT (1,1,1-Trichloro-2,2-bis(4-chlorophenyl)ethane), and lindane (γ-1,2,3,4,5,6-hexachlorocyclohexane) contain C, H and Cl atoms. They are generally characterized by low volatility, chemical stability, lipid solubility and slow biotransformation and degradation.

DDT

Cl

Cl

Cl

ClCl

Cl

Lindane Organophosphates contain mainly C, H and P atoms. Their general structure is:


Page 26

RO P X

OR

S

RO P X

OR

O

or where X: SR' or OR' or OPh group

Examples are parathion (O,O-Diethyl-O-4-nitro-phenylthiophosphate), and chlorpyrifos (O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate).

O

N+O -

P

S

O

CH3CH2O

CH3CH2O

Parathion

N

Cl

Cl

Cl

OP

SCH3CH2O

CH3CH2O

Chlorpyrifos Organophosphorus pesticides affect the nervous system by disrupting the enzyme that regulates acetylcholine, a neurotransmitter. They inhibit cholinesterase, an enzyme found in mammals that helps to regulate the activity of nerve impulses. They have higher water solubility and lower lipid solubility than the organochlorines. Organophosphates are reactive and generally susceptible to hydrolysis in the environment. Most organophosphorus pesticides are of comparatively low volatility because they have low vapour pressures. They are highly toxic. Their lack of environmental persistence leads to a lack of bioaccumulation capacity. Carbamates e.g. carbaryl (1-naphthyl methylcarbamate). These are highly toxic; they are similar to organophosphates in mode of action because they inhibit cholinesterase. They are relatively water-soluble, and they lack environmental persistence.

O NH

O

CH3

Carbaryl

Pyrethroids e.g. permethrin (3-phenoxybenzyl (1RS)-cis,trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate), and deltamethrin ([cyano-(3-phenoxyphenyl)-methyl] 3-(2,2-dibromoethenyl)-2,2-dimethyl-cyclopropane-1-carboxylate) were developed as synthetic versions of the naturally occurring pesticide pyrethrin, which is found in chrysanthemums. These show properties of low mammalian toxicity but good activity against insects, ticks and mites. Most pyrethroids are safer than the organochlorines, organophosphates, and carbamates, although some synthetic pyrethroids are toxic to the nervous system. Pyrethroids have been modified to increase their stability in the environment, and many different pyrethroids are being used today.

OO

O

Cl

Cl

Permethrin

OO

O

Br

Br

N

Deltamethrin Organometallic pesticides e.g. various arsenic and mercury compounds. Herbicides are chemicals used to destroy unwanted plants (terrestrial or aquatic) called weeds. Herbicides fall into two broad categories: inorganic (e.g., copper sulfate, sodium chlorate, and sodium arsenite) and organic (e.g., chlorophenoxy compounds, dinitrophenols, carbamates, amide herbicides, and bipyridyl compounds e.g. paraquat [N,N'-Dimethyl-4,4'-bipyridinium dichloride]). Historically, inorganic compounds were the first available and the first used. There has been over a long period a continuous effort to develop herbicide compounds that are more selective—that affect weeds, as opposed to desirable plants.

+N N+ CH3H3C 2Cl -

Paraquat Nitrophenols e.g. 2,4-dinitrophenol


Page 27

NO2

NO2

HO

2,4-Dinitrophenol Advantages of Pesticides:

• Pesticides save lives. In WWII, at least 7 millions of lives were saved because use of DDT and other pesticides kept insect-transmitted diseases under control.

• Pesticides increase food supplies and lower food cost. • Pesticides increase profits for farmers – For every $1 spent on pesticides, $3-$5 would

result from an increase in crop yield. • They work faster and better than other alternatives: Pesticides control most pests

quickly and at a reasonable price. They are easily shipped and applied. They have a relatively long shelf. When genetic resistance occurs, pests can still be controlled by applying stronger doses and switching to other pesticides.

The health risks of pesticides are insignificant compared with their health and other benefits – When handled probably, pesticides are safe to use. Safer and more effective products are continually being developed. Disadvantages of Pesticides:

• development of genetic resistance. • killing of natural pest enemies. • bioaccumulation and short-term threats to human health from pesticide use and

manufacture. Volatile Organic Compounds (VOCs). Volatile organic compounds (VOCs) are compounds which transfer easily through air, soil and water. They are used in household products: paints, and other solvents, wood preservatives, aerosol sprays, cleansers, disinfectants, repellents, air refreshers, stored fuels and automotive products, hobby supplies and dry cleaning clothing. They include hydrocarbons, aldehydes, ketones and other solvents. Their effects to living organisms include eye, nose and throat irritation, headache, loss of coordination, nausea, damage to liver, kidney and central nervous systems and cause cancer (carcinogenic) in animals. Polychlorinated Biphenyls (PCBs)–are compounds used in electrical system. (details on persistent organic pollutants). Radioactive Materials Overview . The 1940's was the era where the first nuclear bomb was developed, and that is why it is called the nuclear era. However, nuclear energy has already researched back since 1900. Nuclear era reached its greatest peak in the world war, by showing its massive ability of destroying things. Nuclear energy is a form of energy that is released by the splitting of atoms. Since scientists have found a way to make use of the energy, it has also been used to generate electricity. Nuclear energy has been recognized as a clean energy because it does not release pollutants such as CO2 to the atmosphere after its reaction that could damage our environment. Despite the advantage of nuclear as a clean energy, the big concern is the waste resulted from nuclear reaction, which is a form of pollution, called radioactivity. Radioactivity is a form of radiation (a form of energy that travels through space). Some elements in this world are naturally radioactive while some others are made to be. Radioactivity is emitted when radioactive elements become unstable and begin to decay in the attempt to regain their molecular stability. When an element decays, it emits energy and small particles. If it is still radioactive, it will repeat the process, until it finally regains its molecular stability and stop decaying. The time that it takes for half way of decaying process is called half-life. It possibly takes up to 4.5 billion years (Uranium 238) and as short as 8 days (Iodine


Page 28

131). There are commonly three types of radiation, namely:

• Alpha particles - can be blocked by a piece of paper and human skin. • Beta particles - can penetrate through skin, while can be blocked by some glass and

metal. • Gamma rays - can penetrate easily to human skin and damage cells on its way

through, reaching far, and can only be blocked by a very thick, strong, massive piece of concrete.

Sources of Radioactive Pollutants. The major sources of radioactive pollutants are described below. Nuclear power plants. The radioactive waste resulted from nuclear power stations bring hazard when unsafely maintained. Nuclear power plant accidents release high amount of radioactive materials that endanger life and the surrounding environment. Nuclear weapon. Nuclear weapon tests that are conducted above ground or under water also release high amount of radioactive materials that endanger life and the surrounding environment. Nuclear bombing such as what happened in Hiroshima and Nagasaki will create a vast and thorough devastation in a short time. Transportation of nuclear wastes. Transportation of nuclear wastes from one place to another, by any forms of transportation (air, land, water, sea) will possibly bring serious hazards to the environment if they are not maintained carefully and/or facing accidents. Disposal of nuclear waste. The decaying process of radioactive wastes takes a very long time in progress. Some radioactive substances have a half-life of more than 10,000 years, which means they are dangerous in that great amount of time. There are common ways to dispose nuclear waste (nuclear wastes are resulted from many kinds of use, for example medical use, mining, etc.): burying under ground very deeply and burying under the sea and even an idea that to send them to outer space. Uranium mining. Uranium, substance that is used in nuclear power plants, is harvested from uranium mining. Uranium mining results in radioactive waste that pollutes the surrounding environment. Uses and Effects of Radioactive Pollutants Radium (Ra) source from treating neoplastic disease; radon source in radiography of metals; neutron source for research. Exposure via inhalation has resulted in acute leucopoenia. Oral exposure has resulted in anaemia, necrosis of the jaw, abscess of the brain and terminal bronchopneumonia. Via oral exposure is known to cause lung, bone, brain and nasal passage tumours. Radon (Rn) source from cancer treatment, earthquake prediction, and experimental studies. This is a health threat of lung cancer. Exposure via inhalation has resulted into respiratory effects (chronic lung disease, pneumonia, fibrosis of the lung). Animal studies have reported effects on the blood and a decrease in body weight. Uranium (U) is used in glass pigments, fuel in nuclear reactors and nuclear bombs. Uranium miners have shown an increase in lung cancer and tumors of the lymphatic and haematopoietic tissues from inhalation exposure. Plutonium (Pu) is used in bombs and reactors. It is carcinogenic as it promotes cancer development, mutation to body tissues and cells and disruption to normal foetal development. Lead (Pb) is used as a protective shield from radioactivity, lead acid accumulator, manufacture antiknock (tetraethyl lead Pb(C2H5)4 in petrol), pigments e.g., white basic lead carbonate, Pb(OH)2 and orange pigment ‘red lead’, Pb3O4. Lead causes mental retardation among children exposed to lead in water resulting from lead pipes and solders in older water systems. Exhibit weakness, general disability, nervous disorders and eventual death.


Page 29

Mercury (Hg) is used as electrodes in the amalgamation during electrolysis of brine. It is also used in thermometers, barometers and fluorescent lamps. Mercury is carcinogenic and Mutagenic. It is known to cause kidney damage, neurological disorder, blindness, birth defects and damage to aquatic life. Arsenic (As) is used as a deadly poison in shotgun pellets, mirrors, glass, lasers, light emitting diodes (LED) and semiconductors. It is also found in pesticides, wood preservatives and in many household products. Arsenic is known to be carcinogenic, associated with lung and skin cancer. It has a power to damage intestines and liver. It is toxic when ingested. Cadmium (Cd) is used in nickel-cadmium batteries, nuclear reactor regulator and in red/yellow pigments. It is toxic and poisonous. Persistent Organic Pollutants (POPs) are chemical substances that persist in the environment, bioaccumulate through the food web, and pose a risk of causing adverse effects to human health and the environment. Where do POPs come from? Most POPs are man-made. POPs include organochlorine pesticides and several industrial chemical products or byproducts. While most POPs have been banned or severely restricted in some countries for years, they are still produced, used and released in a number of other countries. POPs include many of the first generation organochlorine pesticides such as DDT, aldrin, dieldrin, endrin, chlordane, heptachlor, hexachlorocyclohexane, toxaphene, mirex and chlordecone and several industrial chemical products or byproducts including polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (dioxins) and dibenzo-p-furans (furans) and PAHs, which result from the combustion of substances. Persistent Organochlorine Pesticides are man-made organic chemicals containing chlorine atoms, which are extremely persistent and bioaccumulative in the environment and in people's bodies. They include the following compounds:

DDT

ClCl

ClCl

Cl

Cl Aldrin

ClCl

ClCl

Cl

ClO

Dieldrin

ClCl

ClCl

Cl

Cl O Endrin

Heptachlor

Mirex

Chlordane

Toxaphene

Polychlorinated Biphenyls (PCBs) are mixtures of chlorinated hydrocarbons that have been used extensively since 1930 in a variety of industrial uses, including as dielectrics in transformers and large capacitors, as heat exchange fluids, as paint additives, in carbonless copy paper and in plastics. The value of PCBs for industrial applications is related to their


Page 30

chemical inertness, resistance to heat, non-flammability, low vapour pressure and high dielectric constant. There are 209 possible PCBs, from three monochlorinated isomers to the fully chlorinated decachlorobiphenyl isomer. They include congener groups such as tetrachlorobiphenyl, pentachlorobiphenyl, hexacholorbiphenyl, octachlorobiphenyl, nonachlorobiphenyl and decachlorobiphenyl. Generally, their water solubility and vapour pressure decrease as the degree of substitution increases, and the lipid solubility increases with increasing chlorine substitution. The general structure for PCBs is shown below. Note that R represents chlorine atoms and hydrogen atoms.

R R R R

RR

RRRR

Polychlorinated Dibenzo - P - Dioxins and Furans (dioxins) and polychlorinated dibenzofurans (furans) are two groups of tricyclic compounds that have very similar chemical structures and properties. They may contain 1 to 8 chlorine atoms; dioxins have 75 possible isomers and furans have 135 isomers. They are generally very insoluble in water, are lipophilic and are very persistent. Neither dioxins nor furans are produced commercially, and they have no known use. They are by-products resulting from the production of other chemicals. Dioxins may be released into the environment through the production of pesticides and other chlorinated substances. Furans are a major contaminant of PCBs. Both dioxins and furans are related to a variety of incineration reactions, and the synthesis and use of a variety of chemical products. Dioxins and furans have been detected in emissions from the incineration of hospital waste, municipal waste, hazardous waste, car emissions, and the incineration of coal, peat and wood. The following are examples of dioxins and furans:

O

OCl

Cl

Cl

Cl 2,3,7,8-Tetrachlorodibenzo-p-dioxin

O

Cl

Cl

Cl

Cl 2,3,7,8-Tetrachlorodibenzo-p-furan

Polycyclic Aromatic Hydrocarbons (PAHs) are a class of very stable organic molecules made up of only carbon and hydrogen. They are products of combustion from automobiles and airplanes and some (such as benzo[a]pyrene and phenanthrene) are present in charcoal broiled hamburgers.

Benzo(a)pyrene

Phenanthrene

References 1. Naylor, M. and C. Bernes, Persistent Organic Pollutants–Monitor 16, Swedish

Environmental Protection Agency, 1998. 2. Suter II, G.W., Ecological Risk Assessment, Lewis Publishers, Boca Raton. FL,1993. 3. Van Leeuwen, C.J. and J. Hermans, Risk Assessment of Chemicals: An Introduction,

Kluwer Academic Publishers, Dortrecht, The Netherlands, 1995. REVIEW QUESTIONS Q1. Discuss some strategies that are used to reduce or control air pollution. Q2. Explain the major sources and ways that lead to water pollution. Q3. Outline the major sources and methods that lead to (a) soil pollution (b) noise pollution.


Page 31

Q4. Environmental pollution has significant impacts to our everyday lives and the environment. Outline nine aspects from which the impacts of pollution can be seen. Q5. What are pollutants? Outline four major types of common pollutants that exist today. Suggest the type(s) of pollution caused by each type of pollutants. Q6. Explain the sources of pollution and health effects of the following heavy metal pollutants: mercury, lead, arsenic, cadmium and aluminium. Q7.Describe the sources and effects of the following radioactive pollutants: radium, radon, uranium and plutonium. Q8 (a) What are persistent organic pollutants (POPs)? Give examples of POPs including their sources in the environment. (b) Discuss the science of persistent organic pollutants (POPs) by explaining five properties which they possess. (c) Why are persistent organic pollutants (POPs) a problem? (d) Which international actions have been developed on persistent organic pollutants (POPs)?

Documents

Joseph YN Philip Lecture 3 Notes Page 1 · joseph yn philip lecture 3 notes page 1 university of dar es salaam faculty of science ev 200: environmental science environmental pollution,