Water Pollution Lecture Notes PDF

 WATER POLLUTION  Water gets polluted when its normal functions and properties are altered.  Water pollution means the state of deviation from the quality and purity of water sample.  Water pollution shows the addition of foreign substances, either from natural or...

 WATER POLLUTION  Water gets polluted when its normal functions and properties are altered.  Water pollution means the state of deviation from the quality and purity of water sample.  Water pollution shows the addition of foreign substances, either from natural or anthropogenic sources, may be harmful to life because of their toxicity, reduction of normal oxygen level of water, and spread epidemic diseases.  It is the natural or induced change in the quality of water which renders it unsuitable and toxic as regards food, man and animal health, industry, agriculture, fishing or leisure pursuits. ‫األنشطة الترفيهية‬  Water pollution may be in ground water, surface water, lake, river or ocean water. Sources of Water Pollution:  Inorganic Pollutants: Consists of acids, alkalies, soluble and insoluble salts, metallic complexes, trace elements, organometallic compounds, polyphosphatic detergents from chemical industries, metallurgical processes, coal mines and numerous natural processes causing pollution in water.  Toxic Metals: Toxic metals are added to water from industrial activities, domestic sewage discharges, land run off and fossil fuel burning. Traces of heavy metals such as Hg, Cd, Pb, As, Co, Mn and Cr have been identified deleterious to aquatic ecosystem and human health. In fish; mercury is present as (CH3)2Hg which is known to concentrate in food chain. Manganese also enters the water system through industrial effluents and dry cell batteries. Selenium content of most drinking  Organic Pollutants: Organic pollutants enter into water system through domestic sewage, industrial wastes from paper mills, waste from slaughterhouses, meat packing plants, plant nutrients, detergents, biocides etc. The addition of carbohydrates, fatty acids, proteins, aldehydes, polychlorinated biphenyls (PCBs), phenolic compounds and polycyclic aromatic hydrocarbons deteriorate water quality.  Sewage and Domestic Wastes: Sewage is a cloudy dilute aqueous solution containing mineral and organic matter. About 75% of water pollution is caused by sewage, domestic wastes, food processing plants, garden wastes and sewage sludge …… etc. Sewage contains decomposable organic matter and exerts oxygen demand on the receiving waters. Domestic sewage contains trace quantities of toxic metals also. Sewage treatment deposits sludge at the bottom while liquid waste consists of ions such as Ca2+, Mg2+, Na+, K+, CI–, NO2–, SO42-, PO43-, –  Sediments: The natural process of soil erosion gives rise to sediments in water. Sediments include soil, sand and mineral particles washed into aquatic environment by flood waters.  Synthetic Detergents: Detergents include ingradients like surfactants, ‫المواد الخافضة للتوتر السطحي‬, additives, stabilizers and soil suspending carboxymethyl cellulose etc. Oxygen Demanding Wastes Causing Pollution: Decrease in dissolved oxygen (DO) level is an indication of pollution due to organic matter, e.g., sewage, industrial wastes from food processing plants, run off from agricultural lands etc. All these materials undergo degradation by microbial activities in presence of DO. It causes deoxygenation process and quick depletion of DO. Biological Oxygen Demand (BOD): The degree of microbially mediated oxygen consumption in water is known as BOD. It is a measure of oxygen utilized by micro-organisms during the oxidation of organic material in a five-day period. The demand for O2 is directly proportional to the amount of organic waste which has to be broken down. Hence BOD is a direct measure of biodegradable organic matter. Drinking water has a BOD of less than 1 mg/L. When BOD level reaches 5 mg/L, the water is said to be polluted. Plant Nutrients as Pollutant: Plant nutrients constitute an important limiting factor for plant growth. Nitrogen and phosphorus are the main nutrient species which enter fresh and marine systems changing oligotrophic water ‫ قليلة التغذية‬to intensely productive eutrophic conditions. Thermal Pollutants in Water: Thermal pollution of water may be defined as the warming up of an aquatic ecosystem to the point where desirable organisms are adversely affected. Chemical industries, electric power plants, atomic energy plants discharge their heated effluents into nearby lakes or rivers. Pesticide and Fertilizer Pollutants in Water: Pesticides like insecticides, fungicides, herbicides, rodenticides and molluscicides enter in water through rain-water, spray drift, run off from agricultural fields, domestic sewage, accidental spillage and industrial effluents etc. Pesticides hit the aquatic ecosystem and terrestrial organisms ranging from acute toxicity to invisible chronic effects in man, animals and plants.  Control Measures of Water Pollution: Minimising Water Pollution: Following methods can be adopted: 1. Stabilisation of the Ecosystem: This technique include reduction of the waste at source, harvesting and removal of biomass, trapping of the nutrients, fish management and aeration.  2. Using Water Hyacinth to Remove Water Pollutants: Water hyacinth is extremely efficient in absorbing and concentrating dissolved nutrients from water in which it lives. Introduction of this weed in the lagoon enhances even 1000 times purifying capacity of water. Water hyacinth is capable to absorb phenolic compounds commonly found in domestic and industrial sewage. The phenols so absorbed are broken down and can be utilized rapidly. 3. Chemical Methods: Generally, chemical precipitation, solvent extraction, electro-deposition, ion-exchange, ultrafiltration, and activated carbon adsorption systems are applied to remove heavy metals. All these methods are extremely expensive. 4. Cooling Methods: In some developed countries, thermal pollution abatement schemes are used to control water pollution. These methods include once-through cooling, cooling ponds, wet cooling towers, evaporative towers and dry cooling towers. 5. Solar Power: Solar energy is used for purifying the polluted waste water at low cost. Experiments concluded that a combination of sunlight and a catalyst such as titanium dioxide can dissociate chemical toxicants. Purification of Water for Municipal Purposes: The processes used in the purification of water are as follows: 1. Aeration: The raw water is first aerated by bubbling compressed air. This removes bad odours and CO2 while Fe and Mn salts get precipitated as their hydroxides. 2. Sedimentation: The water is then allowed to stand in large settling tanks. Some of the heavier impurities present in water agglomerate and settle down by gravity. 3. Coagulation: The suspended impurities are removed by coagulation using alum, FeCl3, lime or soda ash. The coagulant sodium aluminate removes HCO3–, Cl–, SO42- responsible for temporary and permanent hardness of water. By coagulation, turbidity is reduced to 20 ppm and bacterial load by 5%, thereby bringing about partial clarification of water. 4.Flocculation: ‫التلبد‬ The process of coagulation can be intensified by adding flocculants such as polyacrylamide, starch and activated silica. 5. Filtration: The partially clarified water is then filtered through sand gravity filter. 6. Disinfection: The elimination of offensive odour caused by dissolved organic substances in water is done by ozonization, chlorination, aeration, coagulation and ultra-violet light treatment. 7. Ozonization: The water is treated with ozonised oxygen. Ozone sterilizes, bleaches, decolourises and deodourises water. 8. Chlorination: Chlorination is the best and the cheapest method of sterilization of water. For chlorination, chlorine may be used directly in the liquid form or hypochlorates of calcium and sodium, e.g., bleaching powder. It kills viruses and bacteria. The purified water is then supplied by municipalities through pipes for domestic purposes  Waste Water and Industrial Effluents In sewage treatment; plants, microorganisms are used to remove the more common pollutants from waste water before it is discharged into rivers or the sea. Increasing industrial and agricultural pollution has led to a greater need for processes that remove specific pollutants such as nitrogen and phosphorus compounds, heavy metals and chlorinated compounds. Methods include aerobic, anaerobic and physico-chemical processes in fixed-bed filters and in bioreactors in which the materials and microbes are held in suspension. Five Stages are Recognized in Wastewater Treatment: a) Preliminary treatment – grit, heavy metals and floating debris are removed. b) Primary treatment – suspended matters are removed. c) Secondary treatment – bio-oxidize organic materials by activities of aerobic and anaerobic microorganisms. d) Tertiary treatment – specific pollutants are removed (ammonia and phosphate). e) Sludge treatment – solids are removed (final stage). Aerobic Biological Treatment: Trickling filters, rotating biological contactors or contact beds, usually consist of an inert material (rocks/ash/ wood/ metal) on which the microorganisms grow in the form of a complex biofilm. These have been used for more than 70 years for sewage and waste water treatment. In these processes the degradable organic matter is oxidized by the microorganisms to CO2 that can be vented to the atmosphere. Activated Sludge Process: This process is used for treatment and removal of dissolved and biodegradable wastes, such as organic chemicals, petroleum refining wastes textile wastes and municipal sewage. The microorganisms found in this sludge are usually bacteria, fungi, protozoa. Petroleum hydrocarbons are degraded by species of bacteria (Acinetobacter, Mycobacteria, Pseudomonas etc.), yeasts, Cladosporium and Scolecobasidium. Pesticides (aldrin, dieldrin, parathion, malathion) are detoxified by fungus Xylaria xylestrix. Pseudomonas (a predominant soil microrganism) can detoxify organic compounds like hydrocarbons, phenols, organophosphates, polychlorinated biphenyls and polycyclic aromatics. The costs of wastewater treatment can be reduced by the conversion of wastes into useful products. Most anaerobic wastewater treatment systems produce useful biogas. In some cases, the by-products of the pollution-fighting microorganisms are themselves useful. Methane, for example, can be derived from a form of bacteria that degrades sulphur liquor, a waste product of paper manufacturing.