Air Pollution Combined PPT PDF

evs- the combined ppt Air pollution Air pollution is the introduction of chemicals, particulate matter, or biological materials that cau...

evs- the combined ppt Air pollution Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere. Natural – Volcanic eruptions, forest fires, decaying vegetation Anthropogenic – Vehicular emission, Industries, etc. Types of Air Pollutants 1. Gaseous Pollutants – Hydrocarbons, CO2, CO, SO2, H2S, NO2, N2O, NO, NH3, Ozone, Chlorinated hydrocarbons, Bromine, Mercury, Lead 2. Particulate Pollutants – Occurs as solid or liquid 1. Settleable – larger than 10 micron Eg: sand, water drops, etc. 2. Suspended – remains suspended in air Eg: dust, smoke, pollens, aerosols, etc. Particulate Matter (PM) a) Particles < 100 µ (PM100) - “Inhalable” b) Particles < 10 µ (PM10) – “Thoracic” c) Particles < 4 µ (PM4) - “Respirable” d) Particles < 2.5 µ (PM2.5,) - “Fine” e) Particles < 0.1 µ (PM0.1,) - “Ultrafine” AIR POLLUTANTS Classification Primary pollutants are substances that are directly emitted into the atmosphere from sources 1. Carbon compounds - CO, CO2, CH4 and VOCs 2. Nitrogen compounds - NO, N2O, and NH3 3. Sulfur compounds - H2S and SO2 4. Halogen compounds - chlorides, fluorides, and bromides 5. Particulate Matter (PM or “aerosols”) Secondary pollutants are not directly emitted from sources, but instead form in the atmosphere from primary pollutants a) NO2 and HNO3 formed from NO b) Ozone (O3) formed from photochemical reactions of nitrogen oxides and VOCs c) H2SO4 and HNO3 droplets formed from SO2 and NO2 respectively d) Sulfates and nitrates aerosols formed from reactions of H2SO4 and HNO3 droplets with NH3 e) Organic aerosols formed from VOCs in gas-to-particle reactions Sources of Air Pollution Combustion of fossil fuels, thermal power plants, automobiles, aircrafts, burning of agricultural wastes, industries, etc. 1. Stationary combustion sources Burning of fuels in industries, residential complex, hotels, thermal power plants, brick kilns, etc. Produce a mixture of oxides of carbon, fly ash, nitrogen and sulphur 2. Mobile combustion sources Automobiles, aircrafts, railways, etc. Gaseous pollutants, particulate lead, benzopyrene, aerosols 3. Industrial Sources Metallurgical processing, metal-plating, synthetic chemicals, etc. Oxides of carbon, nitrogen and sulphur Methyl Isocyanate (MIC) – released from Union Carbide, Bhopal in 1984 killed thousands of lives Aerosols of chlorine, bromine, particulates like dust, fly ash, soot Radioactive isotopes – highly harmful to the vegetation, animals and humans Burning of plastics – release polychlorinated biphenyls (PCB) Pollen grains and microbes – natural air pollutants Pesticides spray Smog The word smog is derived from smoke and fog. Occurs in many cities throughout the world. There are two types of smog: (a) Classical smog occurs in cool humid climate. It is a mixture of smoke, fog and sulphur dioxide. Also called as reducing smog. (b) Photochemical smog occurs in warm, dry and sunny climate. The main components of the photochemical smog result from the action of sunlight (UV) on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories. It is a mixture of Ozone, Peroxyacetyl nitrate (PAN) and NOx. Also called as oxidizing smog. Effects of Air Pollution 1. Effect on Human health Dust, Soot, Smog – cause respiratory illness like bronchitis, asthma, lung cancer, etc. Disease like Asbestosis, Silicosis, Siderosis, Pneumonia, etc. Fly ash – cause headache, dizziness, anemia, insomnia, etc. Sulphur dioxide – cause sore throat, eye irritation, skin cancer, etc. Carbonmonoxide – mixes with hemoglobin in blood and reduce oxygen carrying capacity of blood. Ozone – cause coughing, eye irritation, respiratory problems, allows UV rays to reach Earth’s surface which is highly harmful 2. Effect on Vegetation Dust, smoke, particulate matters – reduces photosynthesis in plants Sulphur dioxide – cause chlorosis, membrane damage, etc. Ozone – cause necrosis, damage leaves Hydrocarbons – cause early leaf fall, fruit drop, discolouration, etc. Acid rain – affects the vegetation and damages the soil nutrition 3. Effect on Animals Damages the livestock population 4. Deterioration of materials NOx, SOx – harmful for buildings, metals, marbles, textiles, etc. Acid rain – Corrosion of metals and buildings Hydrogen sulphide – discoloration of paints Ozone – affects rubber materials 5. Aesthetic loss Smoke / Haze reduces the vision Foul odor makes urban life unpleasant Dust from industries gives a dirty impression where it settles 6. Effect on Climate Heat discharged from industries cause a rise in temperature Increased greenhouse effect – causes global warming ultimately Depletion of Ozone layer by CFCs cause harmful UV ray penetration Air Pollution Control Methods to control air pollution 1. Source Correction Methods 2. Pollution Control equipment 3. Diffusion of pollutant in air 4. Vegetation 5. Zoning 1. Source Correction Methods 1. Substitution of raw materials: Low sulphur fuel, LPG / LNG 2. Process Modification Washing coal before pulverization reduces fly ash Fly-ash emissions at power plants by air intake of furnace 3. Modification of Existing Equipment Replacing open hearth furnaces with controlled oxygen furnaces or electric furnaces Storage tanks with floating roof cover / Pressurizing the storage tanks – prevents loss of hydrocarbon vapours 4. Maintenance of Equipment Open hearth furnace Washing coal Storage tanks with floating roof cover  AIR POLLUTION CONTROL Some of the effective methods to control air pollution are as follows: (a) Source Correction Methods (b) Pollution Control equipment (c) Diffusion of pollutant in air (d) Vegetation (e) Zoning. 1. Source Correction Methods: Industries make a major contribution towards causing air pollution. Formation of pollutants can be prevented and their emission can be minimized at the source itself. By carefully investigating the early stages of design and development in industrial processes e.g., those methods which have minimum air pollution potential can be selected to accomplish air-pollution control at source itself. These source correction methods are: i. Substitution of raw materials: If the use of a particular raw material results in air pollution, then it should be substituted by another purer grade raw material which reduces the formation of pollutants. Thus, a) Low sulphur fuel which has less pollution potential can be used as an alternative to high Sulphur fuels, and, b) Comparatively more refined liquefied petroleum gas (LPG) or liquefied natural gas (LNG) can be used instead of traditional high contaminant fuels such as coal. ii. Process Modification: The existing process may be changed by using modified techniques to control emission at source. For example, (a) If coal is washed before pulverization, then fly-ash emissions are considerably reduced. (b) If air intake of boiler furnace is adjusted, then excess Fly-ash emissions at power plants can be reduced. iii. Modification of Existing Equipment: Air pollution can be considerably minimized by making suitable modifications in the existing equipment: (a) For example, smoke, carbon-monoxide and fumes can be reduced if open hearth furnaces are replaced with controlled basic oxygen furnaces or electric furnaces. 1  (b) In petroleum refineries, loss of hydrocarbon vapours from storage tanks due to evaporation, temperature changes or displacement during filling etc. can be reduced by designing the storage tanks with floating roof covers. (c) Pressurizing the storage tanks in the above case can also give similar results. iv. Maintenance of Equipment: An appreciable amount of pollution is caused due to poor maintenance of the equipment which includes the leakage around ducts, pipes, valves and pumps etc. Emission of pollutants due to negligence can be minimized by a routine checkup of the seals and gaskets. 2. Pollution Control Equipment: Sometimes pollution control at source is not possible by preventing the emission of pollutants. Then it becomes necessary to install pollution control equipment to remove the gaseous pollutants from the main gas stream. The pollutants are present in high concentration at the source and as their distance from the source increases they become diluted by diffusing with environmental air. Pollution control equipment’s are generally classified into two types: (a) Control devices for particulate contaminants. (b) Control devices for gaseous contaminants. Control Devices for Particulate Contaminants: (1) Gravitational Settling Chamber: For removal of particles exceeding 50 µm in size from polluted gas streams, gravitational settling chambers are put to use. This device consists of huge rectangular chambers. The gas stream polluted with particulates is allowed to enter from one end. The horizontal velocity of the gas stream is kept low (less than 0.3 m/s) in order to give sufficient time for the particles to settle by gravity. The particulates having higher density obey Stoke’s law and settle at the bottom of the chamber from where they are removed ultimately. The several horizontal shelves or trays improve the collection efficiency by shortening the settling path of the particles. 2 (2) Cyclone Separators (Reverse flow Cyclone): Instead of gravitational force, centrifugal force is utilized by cyclone separators, to separate the particulate matter from the polluted gas. Centrifugal force, several times greater than gravitational force, can be generated by a spinning gas stream and this quality makes cyclone separators more effective in removing much smaller particulates than can possibly be removed by gravitational settling chambers. A simple cyclone separator consists of a cylinder with a conical base. A tangential inlet discharging near the top and an outlet for discharging the particulates is present at the base of the cone. The dust laden gas enters tangentially, receives a rotating motion and generates a centrifugal force due to which the particulates are thrown to the cyclone walls as the gas spirals upwards inside the cone (i.e. flow reverses to form an inner vortex which leaves flow through the outlet). The particulates slide down the walls of the cone and are discharged from the outlet. (3) Fabric Filters (Baghouse Filters): In a fabric filter system, a stream of the polluted gas is made to pass through a fabric that filters out the particulate pollutant and allows the clear gas to pass through. The particulate matter is left in the form of a thin dust mat on the insides of the bag. This dust mat acts as a filtering medium for further removal of particulates increasing the efficiency of the filter bag to sieve more sub micron particles (0.5 µm). A typical filter is a tubular bag which is closed at the upper end and has a hopper attached at the lower end to collect the particles when they are dislodged from the fabric. Many such bags are hung in a baghouse. For efficient filtration and a longer life the filter bags must be cleaned occasionally by a mechanical shaker to prevent too many particulate layers from building up on the inside surfaces of the bag. 3 (4) Electrostatic Precipitator: An electrostatic precipitator (ESP) is a particle control device that uses electrical forces to move the particles out of the flowing gas stream and onto collector electrodes. They range in size from those installed to clean the flue gases from the largest power plants to those used as small household air cleaners. The particles are given an electrical charge by forcing them to pass through a corona, a region in which gaseous ions flow. The electrical field that forces the charged particles to the walls comes from discharge electrodes maintained at high voltage in the center of the flow lane. Once the particles are on the collecting electrodes, they must be removed from the surface without re-entrained them into the gas stream. This is usually accomplished by knocking them loose from the plates; allowing the collected layer of particles to slide down into a hopper from which they are evacuated. Some ESPs remove the particles by intermittent or continuous washing with water. Precipitators are unique among particulate matter control devices in that the forces of collection act only on the panicles and not on the entire gaseous stream. This phenomenon typically results in high collection efficiency (above 99.57%) with a very low gas pressure drop. 4 (5) Wet Collectors (Scrubbers): In wet collectors or scrubbers, the particulate contaminants are removed from the polluted gas stream by incorporating the particulates into liquid droplets. (i) Spray Tower: Water is introduced into a spray tower by means of a spray nozzle (i.e. there is downward flow of water). As the polluted gas flows upwards, the particulates (size exceeding 10 µm) present collide with the water droplets being sprayed downward from the spray nozzles. Under the influence of gravitational force, the liquid droplets containing the particulates settle to the bottom of the spray tower. Control Devices for Gaseous Contaminants: (1) Absorption Absorption is a process where transfer of a gaseous component from gas phase to liquid phase takes place. More specifically in air pollution control, absorption involves the removal of objectionable gaseous contaminant from a process stream by dissolving them in liquid. Packed Tower: In packed tower the contact time between vapour and liquid is increased by introducing packing. The packing material has a large surface to volume ratio and a large void ratio that offers minimum resistance to gas flow. Generally packed tower are operated counter currently, with gas entering at the bottom of tower and liquid entering from the top. Liquid flows over the surface of the packing in a thin film causing continuous contact with the gases. Packed towers are highly efficient but they become easily clogged when gas with high particulate loads are introduced. 5 (2) Adsorption In adsorption process the contaminant removal is done by passing a stream of effluent gas through a pours solid material (adsorbent) contained in adsorption bed. The surface of porous solid material attracts and holds the gas (the adsorbate) by either by physical or chemical adsorption. The basic difference between physical and chemical adsorption is the manner in which the gas molecule is bonded to the adsorbent. Steps in Adsorption Process Adsorption occurs in three steps 1. The contaminant diffuses from the bulk gas stream to the external surface of the adsorbent material. 2. The contaminant molecule migrate external surface to the macropores, transitional pores, and micropores within each adsorbent. 3. The contaminant molecule adheres to the surface in the pore. Following figure illustrates this overall diffusion and adsorption process. 6 (3) Incineration Incineration, also known as combustion, is most used to control the emissions of volatile organic compounds from process industries. This control technique refers to the rapid oxidation of a substance through the combination of oxygen with a combustible material in the presence of heat. When combustion is complete, the gaseous stream is converted to carbon dioxide and water vapor. 1. Direct combustor is a device in which air and all the combustible waste gases react at the burner. Complete combustion must occur instantaneously since there is no residence chamber. A flare can be used to control almost any emission stream containing volatile organic compounds. Studies conducted by EPA have shown that the destruction efficiency of a flare is about 98 percent. 2. In thermal incinerators the combustible waste gases pass over or around a burner flame into a residence chamber where oxidation of the waste gases is completed. Thermal incinerators can destroy gaseous pollutants at efficiencies of greater than 99 percent when operated correctly. 3. Catalytic incinerators are very similar to thermal incinerators. The main difference is that after passing through the flame area, the gases pass over a catalyst bed. A catalyst promotes oxidation at lower temperatures, thereby reducing fuel costs. Destruction efficiencies greater than 95 percent are possible using a catalytic incinerator. 7 3. Diffusion of Pollutants in Air Dilution of the contaminants in the atmosphere is another approach to the control of air pollution. If the pollution source releases only a small quantity of the contaminants then pollution is not noticeable as these pollutants easily diffuse into the atmosphere but if the quantity of air contaminants is beyond the limited capacity of the environment to absorb the contaminants then pollution is caused. However, dilution of the contaminants in the atmosphere can be accomplished through the use of tall stacks which penetrate the upper atmospheric layers and disperse the contaminants so that the ground level pollution is greatly reduced. The height of the stacks is usually kept 2 times the height of nearby structures. Dilution of pollutants in air depends on atmospheric temperature, speed and direction of the wind. The disadvantage of the method is that it is a short term contact measure which in reality brings about highly undesirable long range effects. This is so because dilution only dilutes the contaminants to levels at which their harmful effects are less noticeable near their original source whereas at a considerable distance from the source these very contaminants eventually come down in some form or another. 4. Vegetation Plants contribute towards controlling air-pollution by utilizing carbon dioxide and releasing oxygen in the process of photosynthesis. This purifies the air (removal of gaseous pollutant CO2) for the respiration of men and animals. Gaseous pollutants like carbon monoxide are fixed by some plants, namely, Coleus Blumeri, Ficus variegata and Phascolus Vulgaris. Species of Pinus, Quercus, Pyrus, Juniperus and Vitis depollute the air by metabolising nitrogen oxides. Plenty of trees should be planted especially around those areas which are declared as high-risk areas of pollution. 5. Zoning: Zoning advocates setting aside of separate areas for industries so that they are far removed from the residential areas. The heavy industries should not be located too close to each other. New industries, as far as possible, should be established away from larger cities and the locational decisions of large industries should be guided by regional planning. The industrial estate of Bangalore is divided into three zones namely light, medium and large industries. In Bangalore and Delhi very large industries are not permitted. 8 WATER POLLUTION Water pollution is the contamination of water bodies (e.g. lakes, rivers, oceans and groundwater). Water pollution affects plants and organisms living in these bodies of water and in almost all cases the effect is damaging not only to individual species and populations, but also to the natural communities. Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds. SOURCES OF WATER POLLUTION Point source pollution refers to contaminants that enter a waterway through a discrete conveyance, such as a pipe or ditch. Examples of sources in this category include discharges from a sewage treatment plant, a factory, or a city storm drain. Non-point source pollution: Non-point source (NPS) pollution refers to diffuse contamination that does not originate from a single discrete source. NPS pollution is often the cumulative effect of small amounts of contaminants gathered from a large area. The leaching out of nitrogen compounds from agricultural land which has been fertilized is a typical example. Nutrient runoff in storm water from “sheet flow” over an agricultural field or a forest is also cited as examples of NPS pollution. Contaminated storm water washed off of parking lots, roads and highways, called urban runoff, is sometimes included under the category of NPS pollution. However, this runoff is typically channeled into storm drain systems and discharged through pipes to local surface waters, and is a point source. However where such water is not channeled and drains directly to ground it is a non-point source. Nonpoint source pollution can include:  Excess fertilizers, herbicides and insecticides from agricultural lands and residential areas  Oil, grease and toxic chemicals from urban runoff and energy production  Sediment from improperly managed construction sites, crop and forest lands, and eroding streambanks  Salt from irrigation practices and acid drainage from abandoned mines  Bacteria and nutrients from livestock, pet wastes and faulty septic systems  Atmospheric deposition and hydromodification 1 TYPES OF WATER POLLUTION There are two types of water pollution: Ground water pollution & Surface water pollution 1. Groundwater Pollution: Considerable amount of Earth’s water is found in soil or under rock structures called aquifers. People use aquifers to obtain drinking water and build wells to access it. In case this water becomes polluted, it is called groundwater pollution. This is caused by pesticide contamination from the soil and this can infect the drinking water and lead to huge problems. Groundwater refers to water collected under the Earth’s surface. The sources of groundwater are rain, snow, hail, sleet, etc. Water that falls on the Earth’s surface continues to travel downwards due to gravity, until a zone comes where it is saturated with water. At this depth, the spaces between the soil and rock particles are filled up with water. This particular zone is known as the saturated zone. The topmost portion of the saturated zone is referred to as water table. The level of water table changes depending upon the season, it is highest in spring and lowest in summer. Groundwater is connected to surface water such as rivers, streams and lakes. In fact, there is continuous exchange of water between surface water and groundwater. Groundwater pollution is a change in the properties of groundwater due to contamination by microbes, chemicals, hazardous substances and other foreign particles. It is a major type of water pollution. The sources of groundwater pollution are either natural (mineral deposits in rocks) or man-made. Natural sources are less harmful compared to hazardous chemicals generated by human activities. Any chemical present on the surface can travel underground and cause groundwater pollution. The seepage of the chemical depends on the chemical type, soil porosity and hydrology. One of the major sources of groundwater pollution is industries. Manufacturing and other chemical industries require water for processing and cleaning purposes. This used water is recycled back to water sources without proper treatment, which in turn, results in groundwater pollution. It is also to be noted that solid industrial wastes that are dumped in certain areas also contribute to groundwater pollution. When rainwater seeps downwards, it dissolves some of these harmful substances and contaminates groundwater. Another source of groundwater pollution is agriculture; the fertilizers, pesticide and other chemicals used in growing plants contaminate groundwater. Residential areas also generate pollutants (microorganisms and organic compounds) for groundwater contamination. Groundwater pollutant can be divided into point source and non-point source based on the nature 2 of disposal. The former refers to contaminants originating from a particular source such as sewage pipe or tank; whereas non-point source is spread over large areas (for example, pesticides and fertilizers). Groundwater pollution cannot be prevented completely. As there are varied sources, it is not always practical to prevent the contamination of groundwater. However, there is no doubt that individuals can contribute in many ways to reduce groundwater pollution. 2. Surface Water Pollution: These are the natural water resources of the Earth. These are found on the exterior of the Earth’s crust, oceans, rivers and lakes. Water is an essential commodity for survival. We need water for drinking, cooking, bathing, washing, irrigation, and for industrial operations. Most of the water for such uses comes from rivers, lakes or groundwater sources. Water has the property to dissolve many substances in it, therefore, it can easily get polluted. CLASSIFICATION OF WATER POLLUTANTS The various types of water pollutants can be classified in to following major categories: 1) Organic pollutants, 2) Pathogens, 3) Nutrients and agriculture runoff, 4) Suspended solids and sediments, 5) Inorganic pollutants (salts and metals), 6) Thermal Pollution 7) Radioactive pollutants, 8) Sewage ORGANIC POLLUTANTS Organic pollutants can be further divided in to following categories: a) Oxygen Demanding Wastes: The wastewaters such as, domestic and municipal sewage, wastewater from food processing industries, canning industries, slaughter houses, paper and pulp mills, tanneries, breweries, distilleries, etc. have considerable concentration of biodegradable organic compounds either in suspended, colloidal or dissolved form. These wastes undergo degradation and decomposition by bacterial activity. The dissolved oxygen available in the water body will be consumed for aerobic oxidation of organic matter present in the wastewater. Hence, depletion of the DO will be a serious problem adversely affecting aquatic life, if the DO falls below 4.0 mg/L. This decrease of DO is an index of pollution. b) Synthetic Organic Compounds Synthetic organic compounds are also likely to enter the ecosystem through various manmade activities such as production of these compounds, spillage during transportation, and their uses in different applications. These include synthetic pesticides, synthetic detergents, food additives, pharmaceuticals, insecticides, paints, synthetic fibers, plastics, solvents and volatile organic compounds (VOCs). Most of these compounds are toxic and biorefractory organics i.e., they are 3 resistant to microbial degradation. Even concentration of some of these in traces may make water unfit for different uses. The detergents can form foams and volatile substances may cause explosion in sewers. Polychlorinated biphenyls (PCBs) are used in the industries since 1930s which are complex mixtures of chlorobiphenyls. Being a fat soluble they move readily through the environment and within the tissues or cells. Once introduced into environment, these compounds are exceedingly persistent and their stability to chemical reagents is also high. c) Oil Oil is a natural product which results from the plant remains fossilized over millions of years, under marine conditions. It is a complex mixture of hydrocarbons and degradable under bacterial action, the biodegradation rate is different for different oils, tars being one of the slowest. Oil enters in to water through oil spills, leak from oil pipes, and wastewater from production and refineries. Being lighter than water it spreads over the surface of water, separating the contact of water with air, hence resulting in reduction of DO. This pollutant is also responsible for endangering water birds and coastal plants due to coating of oils and adversely affecting the normal activities. It also results in reduction of light transmission through surface waters, thereby reducing the photosynthetic activity of the aquatic plants. Oil includes polycyclic aromatic hydrocarbons (PAH), some of which are known to be carcinogenic. PATHOGENS The pathogenic microorganisms enter in to water body through sewage discharge as a major source or through the wastewater from industries like slaughterhouses. Viruses and bacteria can cause water borne diseases, such as cholera, typhoid, dysentery, polio and infectious hepatitis in human. Coliform bacteria are a commonly used bacterial indicator of water pollution, although not an actual cause of disease. Other microorganisms sometimes found in surface waters which have caused human health problems include: Burkholderia pseudomallei, Cryptosporidium parvum, Giardia lamblia, Salmonella Sp., Parasitic worms (helminths). High levels of pathogens may result from inadequately treated sewage discharges. This can be caused by a sewage plant designed with less than secondary treatment (more typical in less- developed countries. In developed countries, older cities with aging infrastructure may have leaky sewage collection systems (pipes, pumps, valves), which can cause sanitary sewer overflows. Some cities also have combined sewers, which may discharge untreated sewage 4 during rain storms. Pathogen discharges may also be caused by poorly managed livestock operations. NUTRIENTS The agriculture run-off, wastewater from fertilizer industry and sewage contains substantial concentration of nutrients like nitrogen and phosphorous. These waters supply nutrients to the plants and may stimulate the growth of algae and other aquatic weeds in receiving waters. Thus, the value of the water body is degraded. In long run, water body reduces DO, leads to eutrophication and ends up as a dead pool of water. People swimming in eutrophic waters containing blue-green algae can have skin and eye irritation, gastroenteritis and vomiting. High nitrogen levels in the water supply, causes a potential risk, especially to infants under six months. This is when the met-haemoglobin results in a decrease in the oxygen carrying capacity of the blood (blue baby disease) as nitrate ions in the blood readily oxidize ferrous ions in the haemoglobin. SUSPENDED SOLIDS AND SEDIMENTS These comprise of silt, sand and minerals eroded from land. These appear in the water through the surface runoff during rainy season and through municipal sewers. This can lead to the siltation, reduces storage capacities of reservoirs. Presence of suspended solids can block the sunlight penetration in the water, which is required for the photosynthesis by bottom vegetation. Deposition of the solids in the quiescent stretches of the stream or ocean bottom can impair the normal aquatic life and affect the diversity of the aquatic ecosystem. If the deposited solids are organic in nature, they will undergo decomposition leading to development of anaerobic conditions. Finer suspended solids such as silt and coal dust may injure the gills of fishes and cause asphyxiation. INORGANIC POLLUTANTS Apart from the organic matter discharged in the water body through sewage and industrial wastes, high concentration of heavy metals and other inorganic pollutants contaminate the water. These compounds are non-biodegradable and persist in the environment. These pollutants include mineral acids, inorganic salts, trace elements, metals, metals compounds, complexes of metals with organic compounds, cyanides, sulphates, etc. The accumulation of heavy metals may have adverse effect on aquatic flora and fauna and may constitute a public health problem where contaminated organisms are used for food. Algal growth due to nitrogen 5 and phosphorous compounds can be observed. Metals in high concentration can be toxic to biota e.g. Hg, Cu, Cd, Pb, As, and Se. Copper greater than 0.1 mg/L is toxic to microbes. THERMAL POLLUTION Considerable thermal pollution results due to discharge of hot water from thermal power plants, nuclear power plants, and industries where water is used as coolant. As a result of hot water discharge, the temperature of water body increases, which reduces the DO content of the water adversely, affecting the aquatic life. This alters the spectrum of organisms, which can adopt to live at that temperature and DO level. When organic matter is also present, the bacterial action increases due to rise in temperature; hence, resulting in rapid decrease of DO. The discharge of hot water leads to the thermal stratification in the water body, where hot water will remain on the top. RADIOACTIVE POLLUTANTS Radioactive materials originate from the following: 1. Mining and processing of ores 2. Use in research, agriculture, medical and industrial activities, such as I131, P32, Co60, Ca45, S35, C14, etc. 3. Radioactive discharge from nuclear power plants and nuclear reactors, e.g., Strontium Sr90, Cesium Cs137, Plutonium Pu248, Uranium-238, Uranium-235. 4. Uses and testing of nuclear weapons. 5. These isotopes are toxic to the life forms; they accumulate in the bones, teeth and can cause serious disorders. The safe concentration for lifetime consumption is 1 x 10-7 microcuries per ml. SEWAGE With billions of people on the planet, disposing of sewage waste is a major problem. According to 2013 figures from the World Health Organization, some 780 million people (11 percent of the world's population) don't have access to safe drinking water, while 2.5 billion (40 percent of the world's population) don't have proper sanitation (hygienic toilet facilities); although there have been great improvements in securing access to clean water, relatively little progress has been made on improving global sanitation in the last decade. Sewage disposal affects people's immediate environments and leads to water-related illnesses such as diarrhoea that kills 760,000 children under five each year. (Back in 2002, the World Health Organization estimated that water-related diseases could kill as many as 135 6 million people by 2020.) In developed countries, most people have flush toilets that take sewage waste quickly and hygienically away from their homes. Yet the problem of sewage disposal does not end there. When you flush the toilet, the waste has to go somewhere and, even after it leaves the sewage treatment works, there is still waste to dispose of. Sometimes sewage waste is pumped untreated into the sea. In theory, sewage is a completely natural substance that should be broken down harmlessly in the environment: 90 percent of sewage is water. In practice, sewage contains all kinds of other chemicals, from the pharmaceutical drugs people take to the paper, plastic, and other wastes they flush down their toilets. When people are sick with viruses, the sewage they produce carries those viruses into the environment. It is possible to catch illnesses such as hepatitis, typhoid, and cholera from river and sea water. E-WASTES India generated about 1050 tonnes of electronic scrap per year as reported in April 2005 which increased to 146,000 tonnes of e-waste per year as reported in May 2007. This would go on increasing year by year. A study by U.S. environmental protection agency shows that e-waste forms about 1% of municipal solid waste in USA. California alone discards 6000 computers daily. They have estimated that about 70% of heavy metals found in the land fills there, come from electronic discards which may contaminate ground waters. When e-waste is incinerated with other wastes it leads to hazardous emission-containing ‘Dioxins’. The commonly found metals in e-waste like copper are catalyst for ‘Dioxin’ formation. ACID MINE DRAINAGE Acid mine drainage is water with a high concentration of sulfuric acid (H2SO4) that drains from mines—mostly coal mines but also metal mines (copper, lead, and zinc). Coal and the rocks containing coal are often associated with a mineral known as fool’s gold or pyrite (FeS2), which is iron sulfide. When the pyrite, which may be finely disseminated in the rock and coal, comes into contact with oxygen and water, it weathers. A product of the chemical weathering is sulfuric acid. In addition, pyrite is associated with metallic sulfide deposits, which, when weathered, also produce sulfuric acid. The acid is produced when surface water or shallow groundwater runs through or moves into and out of mines or tailings. If the acidic water runs off to a natural stream, pond, or lake, significant pollution and ecological damage may result. The acidic water is toxic to the plants and animals of an aquatic ecosystem; it damages biological productivity, and fish and other aquatic life may die. Acidic water can also seep into and pollute 7 groundwater. Acid mine drainage is produced by complex geochemical and microbial reactions. The general equation is as follows: 4FeS2 + 15O2 + 14H2O = 4Fe(OH)3 + 8H2SO4 To treat acid mine drainage, the simplest and least expensive method is to divert acidic water to an open limestone channel, where it reacts with crushed limestone and the acid is neutralized. A general reaction that neutralizes the acid is: H2SO4 + CaCO3 = CaSO4 + CO2 + H2O 8 EFFECTS The polluted water may have undesirable colour, odour, taste, turbidity, organic matter contents, harmful chemical contents, toxic and heavy metals, pesticides, oily matters, industrial waste products, radioactivity, high Total Dissolved Solids (TDS), acids, alkalies, domestic sewage content, virus, bacteria, protozoa, rotifers, worms, etc. The organic content may be biodegradable or non-biodegradable. Pollution of surface waters (rivers, lakes, ponds), ground waters, sea water are all harmful for human and animal health. Pollution of the drinking water and that of food chain is by far the most worry-some aspect. There are numerous ill effects of pollution, each type of pollutants having different effect, on human/animal health and ecology. Plants and agriculture are also badly affected by water pollution. The pollutants enter the plants, fruits, grains, vegetables, and fodder, thus entering the food chain ultimately showing ill effects and diseases which may be very serious sometimes. Eutrophication Eutrophication is the process by which a body of water develops a high concentration of nutrients, such as nitrogen and phosphorus (in the forms of nitrates and phosphates). The nutrients increase the growth of aquatic plants in general, as well as production of photosynthetic blue-green bacteria and algae. Algae may form surface mats that shade the water and block light to algae below the surface, greatly reducing photosynthesis. The bacteria and algae die, and as they decompose, BOD increases, reducing the water’s oxygen content, sometimes to the point where other organisms, such as fish, will die. They die not from phosphorus poisoning but from a chain of events that started with the input of phosphorus and affected the whole ecosystem. The unpleasant effects result from the interactions among different species, the effects of the species on chemical elements in their environment, and the condition of the environment (the body of water and the air above it). A lake that has a naturally high concentration of the chemical elements required for life is called a eutrophic lake. A lake with a relatively low concentration of chemical elements required by life is called an oligotrophic lake. The water in oligotrophic lakes is clear and pleasant for swimmers and boaters and has a relatively low abundance of life. Eutrophic lakes have an abundance of life, often with mats of algae and bacteria and murky, unpleasant water. The word eutrophication was derived from the Greek word which means well- nourished as (eu:true, trophos:feeding) 9 Waterborne Disease 10 Adverse effects of various pollutants on human and animal life and agriculture are indicated in the following table: Sl.No Pollutant Effects 1 Cadmium (Cd) Cd is very toxic, 50 mg may cause vomiting, diarrhoea, abdominal pains, loss of consciousness. It takes 5–10 years for chronic Cd intoxication. During first phase, discoloration of teeth, loss of sense of smell, mouth dryness occurs. Afterwards it may cause decrease of red blood cells, impairment of bone marrow, lumber pains, disturbance in calcium metabolism, softening of bones, fractures, skeletal deformations, damage of kidney, hypertension, tumor formation, heart disease, impaired reproductive function, genetic mutation, etc. 2 Mercury (Hg) Mercury is very toxic. Excess mercury in human body (more than 100 mg) may cause headache, abdominal pain, diarrhoea, destruction of haemoglobin, tremors, very bad effects on cerebral functions and central nervous system, paralysis, inactivates functional proteins, damage of renal tissues, hyper coagulability of blood, minamata disease, and even death. It may cause impairment of vision and muscles and even coma. It disturbs reproductive and endocrine system. Also causes insomnia, memory loss, gum inflammation, loosening of teeth, loss of appetite, etc. 3 Lead (Pb) More than 400 mg of lead in human body can cause brain damage, vomiting, loss of appetite, convulsions, uncoordinated body movements, helplessly amazed state, coma. It is retained in liver, kidney, brain, muscle, soft tissues, bones. Leads to high rate of miscarriages, affects skin, and respiratory system, damages kidney, liver and brain cells. Disturbs endocrine system, causes anaemia, and long term exposure may cause even death. 4 Arsenic (As) Poisonous to fishes, animals and humans. Greater than 25 mg of arsenic causes vomiting, diarrhoea, nausea, irritation of nose and throat, abdominal pain, skin eruptions inflammations and even death. It binds globulin of blood hemoglobin in erythrocytes. May cause cancer of skin, lungs and liver, chromosomal aberration and damage, gangrene, loss of hearing, injury to nerve tissue, liver and kidney damage. Minor symptoms of As poisoning, weight loss, hair loss, nausea, depression, fatigue, white lines across toe nails and finger nails. 5 Radioactive These generally cause ‘Gene’ mutation, ionization of body materials / metals / fluids, chromosomal mutations and cancers. Destroy body cell substances tissue, adversely effects reproductive system. When mother is exposed to radiation during pregnancy, it causes severe mental retardation and leukemia in infants. Radioactive metals like heavy metals are nephrotoxic and damage kidneys. 11 6 Chromium (Cr) Any chromium compound is toxic but hexavalent Cr greater than 70 mg is very toxic. It causes cancer, anuria, nephritis, gastrointestinal ulceration, perforation in partition of nose. It penetrates cell membrane and badly affects central nervous system. Causes respiratory trouble, lung tumors when inhaled. May cause complications during pregnancy. Has an adverse effect on aquatic life. Trace amount of CrIII is essential for normal glucose, protein and fat metabolism and hence it is an essential trace element in diet. 7 Oil / Grease / Oil Petroleum product in general is very harmful for soils, aquatic Sludge life, animal, human and plant life. They are very toxic. Agricultural land may suffer accumulation of oily waste affecting aeration and fertility. Many constituents of oily sludge are even carcinogenic and potent immunotoxicants. 8 Pesticides / Highly poisonous for humans and animals. Also they lower Insecticides seed germination, plays a role in development of Parkinson’s disease, destruction of nerve cells in certain regions of brain resulting in loss of dopamine which is used by nerve cells to communicate with brain. Some of these are physical poisons, some are protoplasmic poisons causing liver damage, some are respiratory poisons and some are nerve poisons. Aquatic Life Write a detailed note on OIL Spills and it’s effect on aquatic Life 12  WASTEWATER TREATMENT The treatment of water may be divided into three major categories: Purification for domestic use Treatment for specialized industrial applications 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. INDUSTRIAL / SEWAGE WASTEWATER TREATMENT Typical industrial / 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 flotsam ranging from children’s socks to sponges. It is the job of the waste treatment plant to remove as much of this material as possible. Preliminary treatment The purpose of preliminary treatment is to protect the operation of the wastewater treatment plant. This is achieved by removing from the wastewater any constituents which can clog or damage pumps, or interfere with subsequent treatment processes. Preliminary treatment devices are, therefore, designed to: (1) Remove or to reduce in size the large, suspended or floating solids. These solids consist of pieces of wood, cloth, paper, plastics, garbage, etc. (2) Remove heavy inorganic solids such as sand and gravel as well as metal or glass. These objects are called grit. (3) Remove excessive amounts of oils or greases. a. Screening: may include coarse and fine screening, usually mechanically operated to intercept floating and suspended debris with ancillary equipment to remove the screenings. The main constituents of screenings are rags, paper, plastics, timbers, leaves etc. Although large screens are sometimes set vertically, screens are usually set at an angle of 45 to 60 degrees. The incoming wastewater is passed through the bars or screens and periodically the accumulated material is removed. 1 The functions of screening equipment as part of the pretreatment works are:  To protect downstream mechanical plant from damage or obstruction due to large objects in the wastewater flow;  To separate and remove the larger material which might interfere with the efficient operation of wastewater treatment processes  To ensure the absence of unsightly floating matter at outfalls or in receiving waters Screen Type Aperture (Bar Screen / Mesh Screen)  Coarse > 50 mm  Medium 15-50mm  Fine 3-15 mm  Milli 0.25-3 mm  Micro 0.025-0.2 mm b. Comminutor Grinders, cutters and shredders. These are devices to break or cut up solids to such size that they can be returned to the wastewater without danger of clogging pumps or piping or affecting subsequent treatment devices. They may be separate devices to grind solids removed by screens or a combination of screen and cutters installed within the wastewater flow channel in such a manner that the objective is accomplished without actually removing these larger solids from the wastewater. c. Grit removal: Grit in wastewater consists of such materials as sand, gravel, cigarette buds and coffee grounds 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. d. Pre-aeration: Methods of introducing supplemental oxygen to the raw wastewater are sometimes done prior to primary treatment. The objectives are to:  Provide odor control and BOD reduction.  To obtain a greater removal of suspended solids in sedimentation tanks.  To assist in the removal of grease and oil carried in the wastewater. 2  e. pH control The use of pH control as a preliminary treatment step is usually limited to treatment of industrial process wastes. It is necessary to regulate pH since treatment processes can be harmed by excessively acidic or basic wastes. Regulation of this parameter may be necessary to meet effluent levels specified for secondary treatment. Control of the pH at elevated levels is usually required to precipitate certain heavy metals and/or alleviate an odor producing potential. f. Flotation In preliminary treatment, flotation is sometimes used for wastes which have heavy loads of grease and finely divided suspended solids. These are mainly systems having large industrial discharges and domestic waste may also contain large quantities of grease from food preparation. Use of air to float materials may relieve scum handling in a sedimentation tank and lower the grease load to subsequent treatment units. Grit removal is often incorporated with a flotation unit providing sludge-removal equipment. Primary Treatment 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. In addition to fatty substances, the grease consists of 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 it may be removed by a skimming device. a) Coagulation Chemical treatment typically is applied prior to sedimentation and filtration to enhance the ability of a treatment process to remove particles. Two steps typically are employed: coagulation and flocculation. Coagulation is a process to neutralize charges and then to form a gelatinous mass to trap particles thus forming a mass large enough to settle or be trapped in the filter. Flocculation is gentle stirring or agitation to encourage the particles thus formed to agglomerate into masses large enough to settle or be filtered from solution. 3 Colloids are stable in water because:  Colloids have a very large surface area relative to their mass  Colloids typically have a static electric charge mostly a negative charge  The particles cannot agglomerate into larger particles and settle because 1) They repel one another. 2) The force of repulsion exceeds the force of gravity that otherwise would cause them to settle! The particles suspended in natural surface water are considered to be thermodynamically stable, meaning that the particles will remain suspended in the water indefinitely if nothing is changed. There is the possibility of instable particles in natural water, for example sand suspended in a fast flowing river will settle to the bottom when the current slows down. ‘Natural Organic Matter,’ (NOM) are produced by the decomposition of organic matter such as leaves, living organisms, aquatic plants, etc. NOM has functional groups that at neutral pH’s are negatively charged, giving the overall charge of the particles. Because all of the particles are negatively charge, they are repelled by one another so that the particles cannot collide and stick together to form larger and larger particles. Therefore, the goal of the first process in water treatment, coagulation, is to destabilize the particles and allow them to collide and stick together. Iron and aluminum form many different cationic species in the pH range of 7 - 8, which help destabilize the NOM by compressing and or eliminating the negative charge on the particles. Divalent ions are more effective coagulants than monovalent and trivalent ones are more effective than divalent. The most common sources of trivalent positive ions are aluminium and iron (III), salts. Aluminium sulphate, iron chloride and iron sulphate are all readily available. Many other salts and materials can add cations into the water, but what is unique about iron and aluminum is that when they are added at a high concentration they will begin to precipitate in the form of iron hydroxide, FeOH(s), and aluminum hydroxide, AlOH(s). The hydroxide solids not only help to eliminate the negative charges on the particles, but form a fluffy and sticky layer around the particles, effectively destabilizing them. 4  b) Flocculation Once the particles in the water are destabilized, they are now able to collide with each other and stick together. Once particles have stuck together they are called a floc, and the process of encouraging the formation of flocs is called flocculation. During the process of flocculation the water is mixed and agitated at a specific rate to encourage the most collisions between the particles as possible. In the flocculation basin of water treatment plants, paddles are attached to a rotating axil to mechanically mix the water. The rate of mixing should be aggressive enough to optimally cause collision, but not too vigorous as to break up the flocs that have already been formed. For this reason, a common flocculation basin design include two or three different basins in series, starting with a fast mixing rate and ending with a slow mixing rate in the last flocculation basin, so that as the flocs increase in size, the rate of mixing decrease. The average time that water spends in the flocculation basin(s) is 20-30 mins, after which the water flows into the sedimentation basin. c) Sedimentation Sedimentation is a physical water treatment process used to settle out suspended solids in water under the influence of gravity. The last process to the first barrier against water contamination is sedimentation. During sedimentation, the flow of the water is slowed to resemble a calm environment. As the water is calmed, the large flocs that have been formed settle to the bottom of the sedimentation basin, sometimes called a clarifier. As the flocs are settling to the bottom, the relatively particle free water passes over a system of weirs and moves to the filtration process. Sedimentation basins are designed to be rectangles or circles, but in both cases the water is commonly introduced at the bottom of the basin to give the flocs the best chance at completely settling out. 5 Filtration Filtration is a process of removing particulate matter from water by forcing the water through a porous media. This porous media can be natural, in the case of sand, gravel and clay, or it can be a membrane wall made of various materials. The size of materials that can be removed during filtration depends upon the size of the pores of the filter. The flow velocity is slow and on the surface of the sand a gelatinous layer form that removes turbidity, colour, taste and odours. a) Slow sand filtration is a biological process, because it uses bacteria to treat the water. The filters are carefully constructed using graded layers of sand, with the coarsest sand, along with some gravel, at the bottom and finest sand at the top. The bacteria establish a community on the top layer of sand and clean the water as it passes through, by digesting the contaminants in the water. The layer of microbes is called a schmutzdecke (or biofilm), and requires cleaning every couple of months, when it gets too thick and the flow rate declines. These microbes usually come from the source water and establish a community within a matter of a few days. The fine sand and slow filtration rate facilitate the establishment of this microbial community. The majority of the communities are predatory bacteria that feed on water-borne microbes passing through the filter. However, slow sand filtration systems require large areas of land to operate. 6  b) Rapid sand filtration is a physical process that removes suspended solids from the water. Rapid sand filtration is much more common than slow sand filtration, because rapid sand filters have fairly high flow rates and require relatively little space to operate. The filters are generally cleaned twice per day with backwashing and are put back into operation immediately. Water moves vertically through sand which often has a layer of activated carbon or anthracite coal above the sand. The top layer removes organic compounds, which contribute to taste and odour. Most particles pass through surface layers but are trapped in pore spaces or adhere to sand particles. Effective filtration extends into the depth of the filter. This property of the filter is key to its operation: if the top layer of sand were to block all the particles, the filter would quickly clog. To clean the filter, water is passed quickly upward through the filter, opposite the normal direction (called backflushing or backwashing) to remove embedded or unwanted particles. Prior to this step, compressed air may be blown up through the bottom of the filter to break up the compacted filter media to aid the backwashing process; this is known as air scouring. 7 SECONDARY TREATMENT Resources of organic wastewater There are several contaminants in wastewater, with organic pollutants playing the major role. Many kinds of organic compounds, such as polychlorinated biphenyls (PCBs), pesticides, herbicides, phenols, polycyclic aromatic hydrocarbons (PAHs), aliphatic and heterocyclic compounds are included in the wastewater, and industrial and agricultural production as well as the people living could be the source of organic wastewater endangering the safety of the water resource. The wastewater of the farmland may contain high concentration of pesticides or herbicides; the wastewater of the coke plant may contain various PAHs; the wastewater of the chemical industry may contain various heterogeneity compounds, such as PCB; the wastewater discharged by the food industry contains complex organic pollutants with high concentration of SS and BOD; and the municipal sewage contains different type of organic pollutants, such as oil, food, some dissolved organics and some surfactants. These organic pollutants in water can harm the environment and also pose health risks for humans. The most obvious harmful effect of biodegradable organic matter in wastewater is BOD, microorganism-mediated degradation of the organic matter. 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. The waste is oxidized biologically under conditions controlled for optimum bacterial growth, and at a site where this growth does not influence the environment. Secondary (biological) treatment processes has been further divided into the following two categories: 1. Suspended growth processes refer to treatment systems where microorganisms and wastewaters are contained in a reactor. Oxygen is introduced to the reactor allowing the biological activity to take place. Examples of suspended growth processes include ponds, lagoons and activated sludge systems. 2. Fixed growth processes refer to systems where a biological mass is allowed to grow on a medium. Wastewater is sprayed on the medium or put into contact in other manners. The biological mass stabilizes the wastewater as it passes over it. Examples of fixed growth processes include trickling filters and rotating biological contractors. 8  1. Trickling filters A trickling filter is a fixed film attached growth aerobic process for treatment of organic matter from the wastewater. The surface of the bed is covered with the biofilm and as the wastewater trickles over this media surface, organic matter from the wastewater comes in contact with the aerobic bacteria and oxidation of organic matter occurs. In the past rock was used as a bed material with size ranging from 25 mm to 100 mm. Now plastic media which offers higher surface area per unit volume is used. The media is randomly packed in the reactor and the wastewater is applied on the top through rotary arm which trickles down over the filter media surface. Hence, this reactor is known as trickling filter. The particles should be uniform such that 95 per cent of the particles have a diameter between 7 and 10 cm. The stones become coated with a zoogloea film (a jelly-like growth of bacteria, fungi, algae, and protozoa), and air circulates by convection currents through the bed. Most of the biological action takes place in the upper 0.5 m of the bed. The end product CO2 diffuses out of the biofilm into the flowing liquid. Treated wastewater is collected from the bottom of the bed through an under drainage system and is settled in the final settling tank. The overall reduction of BOD for a complete trickling filter system averages around 80–90 per cent. As the thickness of the slime layer increases the condition near the surface of the media becomes anaerobic because of limitations of availability of oxygen. At this stage the microbes lose their ability to cling to the surface of the media and the slime layer gets detached and washed out along with flowing liquid. This phenomenon is called as ‘sloughing’. Soon after the sloughing the new slime layer formation starts. Hence secondary sedimentation tank (SST) is provided to settle this washed out biomass. Advantages of Trickling Filter 1. Rate of Filter loading is high as required less land areas and smaller quantities of filter media for their installations. 2. Effluent obtained from the trickling filter is sufficient stabilized. 3. Working of Trickling filter is simple and does not require any skilled supervision. 4. They are flexible in operation. 5. They are self-cleaning. 6. Mechanical wear and tear is small as they contain less mechanical equipment. 9 Disadvantages of Trickling Filter 1. The beds loss through these filters is high. 2. Construction cost is high 3. These filters cannot treat raw sewage and primary sedimentation is must. 4. Fly nuisance and odor nuisance may prevail. 2. Rotating Biological Contactors (RBC) RBC consists of groups of large plastic discs mounted close together on a rotating shaft. The device is positioned such 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 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. The RBC rotates at a speed of one to two rpm and provides a high degree of organic removal. Both trickling filters and rotating biological reactors are examples of fixed-film biological (FFB) 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. 10  3. Activated Sludge Process The activated sludge process is probably the most versatile and effective of all wastewater 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. 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. In addition to BOD removal, phosphorus and nitrogen removal must also be taken into account. 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, then to nitrate by Nitrobacter. As the sewage sludge settles out in the settler, the bacteria in the sludge carry out denitrification while using this nitrate as an oxygen source producing N2. Nitrification 2NH4+ + 3O2 Nitrosomonas 4H+ + 2NO2- + 2H2O 2NO2- + O2 Nitrobacter 2NO3- Denitrification 4NO3- + 5CH2O + 4H+ Denitrifiers 2N2 + 5CO2 + 7H2O 11  4. Oxidation Ponds (Anerobic Lagoons)  An oxidation pond is an artificial pond of controlled design, in which sewage can be retained for sufficient time to satisfy the BOD.  The change in the character of the sewage and waste matter occur due to the action of anaerobic bacteria. It has three stages.  Stage 1 (Hydrolysis) - The anaerobic bacteria secretes enzymes which breaks down fats, proteins and carbohydrates into simple sugars, amino acids and fatty acids.  Stage 2 (Acidoegenesis and Acetogenesis) – Acidogenic bacteria converts sugars, amino acids and fatty acids into CO2, H2, Acetic acids (CH3COOH) and Alcohol.  Stage 3 (Methanogenesis) – Methanogenic bacteria converts CH3COOH into Methane (CH4) and CO2.  Oxidation ponds are capable of treating successfully both the raw or settled sewage. Advantages 1. Produces energy rich CH4 fuel. 2. Sludge generated is comparatively less than aerobic processes. Disadvantages 1. Cost effective to operate. 2. Must be totally oxygen free. 3. Produces NH3 and H2S which are unpleasant odours. 4. Lagoons must be constructed in clay soil or be lined to prevent leakage 5. May overflow occasionally during extended periods of heavy rainfall 6. Lagoons are not aesthetically acceptable and required to be fenced 5. Imhoff tank system An Imhoff tank is a combined sedimentation or settling tank and digestion tank. It consists of an upper compartment for settling out solids from slowly flowing sewage and a lower compartment for anaerobic digestion of the sludge. With an average flow, solids settle in the upper compartment in 2½ hours, pass downward through the slot, and settle to the bottom of the lower compartment where they are digested. 12 TERTIARY 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 3 general categories: (1) suspended solids, (2) dissolved organic compounds, and (3) dissolved inorganic materials, including the important class of algal nutrients. Each of these categories presents its 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, dysenteric bacteria (Bacillus dysenteriae, Shigella dysenteriae, Proteus vulgaris), cholera bacteria (Vibrio cholerae), and bacteria causing typhoid fever (Salmonella typhosa, Salmonella paratyphi). In addition, viruses causing diarrhea, eye infections, infectious hepatitis, and polio may be encountered. REMOVAL OF DISSOLVED ORGANICS Water disinfection processes, which by their nature involve chemically rather severe conditions, particularly of oxidation, have a tendency to produce disinfection by-products. Some of these are chlorinated organic compounds produced by chlorination of organics in water, especially humic substances. Removal of organics to very low levels prior to chlorination has been found to be effective in preventing trihalomethane formation. Another major class of disinfection by-products consists of organooxygen compounds such as aldehydes, carboxylic acids, and oxoacids. Varieties of organic compounds survive or are produced by secondary wastewater treatment and should be considered as factors in discharge or reuse of the treated water. Almost half of these are humic substances with a molecular-weight range of 1000-5000. Humic substances are degradation-resistant materials formed during the decomposition of vegetation that occur as deposits in soil, marsh sediments, peat, coal, lignite, or in almost any location where large quantities of vegetation have decayed. Among the remainder are found 13 ether extractable materials, carbohydrates, proteins, detergents, tannins, and lignins. The humic compounds, because of their high molecular weight and anionic character, influence some of the physical and chemical aspects of waste treatment. Activated Carbon Adsorption Adsorption When a solution containing absorbable solute comes into contact with a solid with a highly porous surface structure, liquid–solid intermolecular forces of attraction cause some of the solute molecules from the solution to be concentrated or deposited at the solid surface. The solute retained (on the solid surface) in adsorption processes is called adsorbate, whereas, the solid on which it is retained is called as an adsorbent. This surface accumulation of adsorbate on adsorbent is called adsorption. The exact nature of the bonding depends on the details of the species involved, but the adsorption process is generally classified as physisorption (characteristic of weak Van Der Waals forces) or chemisorption (characteristic of covalent bonding). The factors affecting the adsorption process are: (i) surface area, (ii) nature and initial concentration of adsorbate, (iii) solution pH, (iv) temperature, (v) interfering substances, and (vi) nature and dose of adsorbent. 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 or the carbon may be oxidized by water at 800-900°C. 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. One reason for the effectiveness of this material as an adsorbent is its tremendous surface area. A solid cubic foot of carbon particles may have a combined pore and surface area of approximately 10 square miles! 14  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. Economics require regeneration of the carbon, which is accomplished by heating it to 950°C in a steam-air atmosphere. This process oxidizes adsorbed organics and regenerates the carbon surface, with an approximately 10% loss of carbon. 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. One of the most obvious methods for removing inorganics from water is distillation. However, the energy required for distillation is generally quite high, so that distillation is not generally economically feasible. This leaves membrane processes as the most cost-effective means of removing inorganic materials from water. Membrane processes considered most promising for bulk removal of inorganics from water are filtration, electro-dialysis, ion exchange, and reverse osmosis. a. Microfiltration / Ultrafiltration A microfiltration filter has a pore size around 0.1 µ, so when water undergoes microfiltration, many microorganisms are removed, but viruses remain in the water. An ultrafiltration filter has a pore size around 0.01 µ. Ultrafiltration would remove larger particles, and may remove some viruses. Neither microfiltration nor ultrafiltration can remove dissolved substances unless they are first adsorbed (with activated carbon) or coagulated (with alum or iron salts). b. Nanofiltration A nanofiltration filter has a pore size around 0.001 µ. Nanofiltration removes most organic molecules, nearly all viruses, most of the natural organic matter and a range of salts. Nanofiltration removes divalent ions, which make water hard, so nanofiltration is often used to soften hard water. Table: Substances Removed From Water by Membrane Filtration Processes Monovalent Multivalent Viruses Bacteria suspended ions ions Solids Microfiltration √ √ Ultrafiltration √ √ √ Nanofiltration √ √ √ √ Reverse Osmosis √ √ √ √ √ 15  c. Reverse osmosis Osmosis occurs when a semi-permeable membrane separates two salt solutions of different concentrations. The water will migrate from the weaker solution to the stronger solution, until the two solutions are of the same concentration, because the semi-permeable membrane allows the water to pass through, but not the salt. Reverse osmosis filters have a pore size around 0.0001 micron. After water passes through a reverse osmosis filter, it is essentially pure water. In addition to removing all organic molecules and viruses, reverse osmosis also removes most minerals that are present in the water. Reverse osmosis removes monovalent ions, which means that it desalinates the water. Reverse osmosis removes a number of healthy minerals from water, in addition to the harmful minerals and particles. The removal of these minerals, including calcium and magnesium, can actually make water unhealthy, especially for people with inadequate diets and people who live in hot climates, as water can provide these necessary minerals. d. Electrodialysis 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 principle involved in electrodialysis treatment is shown in the following figure. 16 Fouling caused by various materials can cause problems with reverse osmosis treatment of water. Although the relatively small ions constituting the salts dissolved in wastewater readily pass through the membranes, large organic ions (proteins, for example) and charged colloids migrate to the membrane surfaces, often fouling or plugging the membranes and reducing efficiency. In addition, growth of microorganisms on the membranes can cause fouling. Experience with pilot plants indicates that electrodialysis has the potential to be a practical and economical method to remove up to 50% of the dissolved inorganics from secondary sewage effluent after pretreatment to eliminate fouling substances. Such a level of efficiency would permit repeated recycling of water without dissolved inorganic materials reaching unacceptably high levels. e. Ion exchange Hardness of Water Hardness in water is that characteristic, which prevents the lathering of soap. This is due to the presence of certain salts of Calcium (Ca+2), Magnesium (Mg+2) and other heavy metals dissolved in it. Hardwater causes scaling and corrosion in boilers. A sample of hardwater, when treated with soap does not produce lather, but on the other hand forms a white curdy precipitate. The precipitated is formed due to the formation of insoluble soaps of calcium and magnesium. 2C17H35COONa + CaCl2  (C17H35COO)2Ca + 2NaCl 2C17H35COONa + MgSO4  (C17H35COO)2Mg + Na2SO4 Types of hardness 1. Total hardness = Calcium (Ca+2) hardness + Magnesium (Mg+2) hardness 2. Carbonate hardness = carbonate & bicarbonate salts of Ca & Mg, which are Ca(HCO3)2 and Mg(HCO3)2 3. Non-Carbonate hardness = Ca & Mg salts other than carbonates and bicarbonates Eg: CaCl2, CaSO4, MgCl2, MgSO4 Softening Softening is a process used in water treatment to remove hardness from water. a. Lime Soda Softening 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. 17 As slacked lime is added to water, it will react with any carbondioxide present as follows: Ca(OH)2 + CO2 →CaCO3 ↓ +H2O The lime will react with carbonate hardness as follows Ca(OH)2 + Ca(HCO3)2 →2CaCO3 ↓ +2H2O Ca(OH)2 + Mg(HCO3)2 →MgCO3 + CaCO3 ↓ +2H2O The product magnesium carbonate in equation is soluble. To remove it, more lime is added Ca(OH)2 + MgCO3 →CaCO3 ↓ +Mg(OH)2 ↓ Also, magnesium non-carbonate hardness, such as magnesium sulfate, is removed: Ca(OH)2 + MgSO4 →CaSO4 + Mg(OH)2 ↓ Lime addition removes only magnesium hardness and calcium carbonate hardness. In equation magnesium is precipitated, however, an equivalent amount of calcium is added. The water now contains the original calcium non-carbonate hardness and the calcium non-carbonate hardness produced in equation. Soda ash is added to remove calcium non-carbonate hardness Na2CO3 + CaSO4 → Na2SO4 + CaCO3 ↓ To precipitate CaCO3 requires a pH of about 9.5; and to precipitate Mg(OH)2 requires a pH of about 10.8. b. Ion exchange softening The term “ion exchange” describes the process: as water flows through a bed of ion exchange material, undesirable ions are removed and replaced with less objectionable ones. For example, in softening processes, calcium and magnesium ions (hardness) are exchanged for sodium ions. With proper design and operation, ion exchange processes are capable of removing selected ions almost completely. The removal of NaCl from solution by two ion exchange reactions is a good illustration of this process. First the water is passed over a solid cation exchanger in the hydrogen form: H+ - {Cat(s)} + Na+ + Cl- Na+ - {Cat(s)} + H+ + Cl- Next, the water is passed over an anion exchanger in the hydroxide ion form: OH- + {An(s)} + H+ + Cl- Cl- + {An(s)} + H2O Thus, the cations in solution are replaced by hydrogen ion and the anions by hydroxide ion, yielding water as the product. 18  The softening of water by ion exchange does not require the removal of all ionic solutes, just those cations responsible for water hardness. Generally, therefore, only a cation exchanger is necessary. Furthermore, the sodium rather than the hydrogen form of the cation exchanger is used, and the divalent cations are replaced by sodium ion. Sodium ion at low concentrations is harmless in water to be used for most purposes, and sodium chloride is a cheap and convenient substance with which to recharge the cation exchangers. The water-softening capability of a cation exchanger is shown in Figure 8.6, where sodium ion on the exchanger is exchanged for calcium ion in solution. The same reaction occurs with magnesium ion. Water softening by cation exchange is now a widely used, effective, and economical process. Periodical need to regenerate a water softener with sodium chloride in order to displace calcium and magnesium ions from the resin and replace these hardness ions with sodium ions is necessary. Ca2+ - {Cat(s)} + 2Na+ + 2Cl- 2Na+ - {Cat(s)} + Ca2+ + 2Cl- A number of materials have ion-exchanging properties. Among the minerals especially noted for their ion exchange properties are the aluminum 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. Synthetic zeolites have been prepared by drying and crushing the white gel produced by mixing solutions of sodium silicate and sodium aluminate. 19  c. Hot Lime-Soda Softening It involves in treating water with softening chemicals at a temperature of 80 to 150° C. Since hot process is operated at a temperature close to the boiling point of the solution, (a) the reaction proceeds faster; (b) the softening capacity of hot process is increased to many fold; (c) the precipitate and sludge formed settle down rapidly and hence, no coagulants are needed; (d) much of the gases (such as CO2 and air) driven out of the water; (e) Viscosity of softened water is lower, so filtration of water becomes much easier. This in-turn increases the filtering capacity of filters, and (f) Hot Lime-Soda produces water of comparatively lower residual hardness of 15 to 30ppm. Hot lime-soda plant consists essentially of three parts (a) a ‘reaction tank’ in which raw water, chemicals and steam are thoroughly mixed; (b) a ‘conical sedimentation vessel’ in which sludge settles down, and (c) a ‘Sand filter’ which ensures complete removal of sludge from the softened water. Advantages of L.S.Process: (i) Economical, lesser amount of coagulants shall be needed, Fe & Mg are also removed (ii) The process increases the pH of the treated water, thereby reduce corrosion (iii) Due to alkaline nature of treated water, amount of pathogenic bacteria’s is considerably reduced Disadvantages of L.S.Process: (i) Disposal of large amounts of sludge (insoluble precipitate) poses a problem. However, the sludge may be disposed off in raising low-lying areas of the city. (ii) For efficient and economical softening, careful operation and skilled supervision is required 20 Removal of Pathogens Disinfection is an important step in ensuring that water is safe to drink. Water systems add disinfectants to destroy microorganisms that can cause disease in humans. Primary methods of disinfection are chlorination, ozone, and ultraviolet light. Other disinfection methods include chlorine dioxide, potassium permanganate, and nanofiltration. a. Chlorination Chlorine is the most commonly used disinfectant employed for killing bacteria in water. Chlorine may be applied in a number of forms such as chlorine gas, sodium hypochlorite or chlorine dioxide. When chlorine is added to water, it rapidly hydrolyzes according to the reaction Cl2 + H2O H+ + Cl- + HOCl Hypochlorous acid, HOCl, is a weak acid that dissociates according to the reaction, HOCl 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 + HOCl NHCl2 (dichloramine) + H2O NHCl2 + HOCl 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. At sufficiently high Cl:N molar ratios in water containing ammonia, some HOCl and OCl- remain unreacted in solution, and a small quantity of NCl3 is formed. The ratio at which this occurs is called the breakpoint. Chlorination beyond the breakpoint ensures disinfection. It has the additional advantage of destroying the more common materials that cause odor and taste in water. 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. 21  b. Ozonation Ozone is sometimes used as a disinfectant in place of chlorine. Figure shows the main components of an ozone water treatment system. 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. Concern over possible production of toxic organochlorine compounds by water chlorination processes has increased interest in ozonation. Furthermore, 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 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. c. Ultraviolet Light (UV) Ultraviolet (UV) radiation is generated by a special lamp. When it penetrates the cell wall of an organism, the cell’s genetic material is disrupted and the cell is unable to reproduce. The effectiveness of UV radiation disinfection depends on the energy dose absorbed by the organism, measured as the product of the lamp’s intensity (the rate at which photons are delivered to the target) and the time of exposure. If the energy dosage is not high enough, the organism’s genetic material might only be damaged instead of destroyed. To provide a safety factor, the dosage should be higher than needed to meet disinfection requirements. No chemical oxidant required; therefore, microorganisms can be killed without generating by-products of chemical oxidation or halogenation. 22 Sludge Treatment Perhaps the most pressing water treatment problem has to do with sludge collected or produced during water treatment. Finding a safe place to put the sludge or a use for it has proven troublesome, and the problem is aggravated by the growing numbers of water treatment systems. Some sludge is present in wastewater prior to treatment 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. 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. Sludge may be further conditioned chemically by the addition of iron or aluminum 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. Heat may be used to aid the drying process. Ultimately, disposal of the sludge is required. Two of the main alternatives for sludge disposal are land spreading and 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. 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 under drained 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 destroyed by lime stabilization in which sufficient lime is added to raise the pH of the sludge to 12 or higher. 23 Soil Pollution By Dr. M. PRABHU INBARAJ  Soil Formation of soil from the parent material (bedrock): mechanical weathering of rocks by temperature changes, abrasion, wind, moving water, glaciers, chemical weathering activities and lichens. Under ideal climatic conditions, soft parent material may develop into 1 cm of soil within 15 years.  O-horizon: freshly-fallen & partially-decomposed leaves, twigs, animal waste, fungi & organic materials. Colour: brown or black. A-horizon: humus/partially decomposed organic matter & some inorganic mineral particles. darker & looser than the deeper layers. O & A-horizon: contain a large amount of bacteria, fungi, earthworms, small insects, forms complex food web in soil, recycles soil nutrients, & contribute to soil fertility. B-horizon /(subsoil): less organic material & fewer organisms than A- horizon. C-horizon: consists of broken-up bedrock, does not contain any organic materials. Chemical composition helps to determine pH of soil & also influences soil’s r