Water & Wastewater Treatment PDF

CHAPTER-2 WATER & WASTEWATER TREATMENT 39 Water Treatment  General Introduction For the existence of all living beings (human, animals and plants), water is very crucial Water is the universal solvent and in nature, it is never totally pure Water is an essentia...

CHAPTER-2 WATER & WASTEWATER TREATMENT 39 Water Treatment  General Introduction For the existence of all living beings (human, animals and plants), water is very crucial Water is the universal solvent and in nature, it is never totally pure Water is an essential commodity for anybody or any living thing so we have to supply adequate quality and quantity of water Every cell in our body contains about 90% of water In other words we can tell that in water supply engineering the major objective is to supply potable and palatable water. 40 General introduction to WWT Cont… Air, water and food are very essential for human existence These materials which are so important for human existence if they are polluted they can create problems – For example, if air is polluted there will be respiratory diseases; if the water is contaminated it can cause waterborne diseases; if food is contaminated then it could cause food poisoning These three components which are so essential for foreman human existence can also become scourge, can also become harmful for the human life.  Objectives of water treatment The principal objective of water treatment is to provide potable water that is physically, chemically and biologically safe for human consumption It should also be free from unpleasant tastes and odors Water treatment objective is to produce both "potable" and "palatable" Potable:- Water that can be consumed in any desired amount without concern for adverse health effects. Potable dose not necessarily mean that the water tastes good Palatable: - it is a water that is pleasing to drink but not necessarily safe. a) Water Characteristics 6  Properties of Water Physical, Chemical & Biological Examination of Water Water which is absolutely pure is not found in nature Because as it passes through the hydrologic cycle & it may acquire many impurities as it comes in contact with materials: in the air on the surface and beneath the surface of the earth 7 Human activities contribute further impurities in the form of industrial and domestic wastes, agricultural chemicals and other, less obvious contaminants. a) Physical Characteristics of Water This is the characteristics of water that respond to the sense of sight, touch or smell that includes suspended solids, Color, Taste, Odour, temperature and etc. Turbidity:- is a measure of the extent to which light is either absorbed or scattered by suspended material in water It measures the presence of suspended solid materials in water. Unit of measurement is NTU (nephelometry turbidity unit). 8  Physical Characteristics of Water Cont… Color-: Pure water is colorless, but water in nature is often colored by foreign substances Taste and Odour:- This is due to Minerals, Metals, Salts from the soil, End products from biological reactions, Constituents of wastewater and etc Drinking water shall be tasteless and odourless Temperature:- governs to a large extent the biological species present and their rates of activity It affects most chemical reactions that occur in natural water systems and solubility of gases in water. 9  b) Chemical Characteristics of Water Water has been called the universal solvent, and chemical parameters are related to the solvent capabilities of water Chemical parameters concerned in water quality management include: Total dissolved solids, Alkalinity, Hardness Fluorides Metals Organic 10  Nutrients and so on Chemical Characteristics of Water Cont… Total Dissolved Solids: is the material remaining in the water after filtration for suspended solids Alkalinity: Alkalinity is defined as quantity of ions in water that will react to neutralize hydrogen ions. It is a measure of the ability of water to neutralize acids Most constituents of alkalinity of natural water include: Bicarbonate (HCO3), Carbonate (CO3-2), Hydroxide (OH-) In large quantity it imparts a bitter taste to water. 11 Hardness: is defined as the concentration of multivalent metallic cations in solution. Chemical Characteristics of Water Cont… Two types of hardness can be identified- carbonate and noncarbonate hardness Carbonate hardness:-is sometimes called temporary hardness because it can be removed by boiling water Non-carbonate hardness:-cannot be broken down by boiling the water, so it is also known as permanent hardness In general, it is important to distinguish between the two types of hardness because the removal method differs for the two. 12 Chemical Characteristics of Water Cont… 13  Chemical Characteristics of Water Cont… Fluoride: is seldom found in surface waters and appears in ground water in only few geographical regions It is toxic to humans and other animals in large quantities, while small concentrations can be beneficial Concentrations of approximately 1.0mg/l in drinking water help to prevent dental cavities in children During formation of permanent teeth, fluoride combines chemically with tooth enamel, resulting in harder, stronger teeth that are more resistant to decay 14  Chemical Characteristics of Water Cont… Metals: are soluble to some extent in water Excessive amounts of any metal may present health hazards Sources of metals in natural waters include dissolution from natural deposits and discharges of domestic, industrial, or agricultural wastewaters i. Nontoxic Metals:- commonly found in water include sodium, iron, magnesium, aluminium, copper and zinc Excessive concentration of sodium can cause a bitter taste in water and are health hazard to cardiac and kidney patients Iron and manganese in very small quantities 0.3 mg/l and  0.05 mg/l, respectively may cause color problems. Chemical Characteristics of Water Cont… ii. Toxic Metals:- These include arsenic, barium, cadmium, lead, mercury, and silver. These are toxic substances and are extremely dangerous from public health viewpoint The presence of lead in excess of 0.05 mg/l or arsenic in excess of 0.05, selenium in excess of 0.01 mg/l or hexavalent chromium in excess of 0.05mg/l shall constitute grounds for rejection of the supply. Chemical Characteristics of Water Cont… 16 Organics: Many organic materials are soluble in water Organic in natural water systems may come from natural sources or may result from human activities Dissolved organics in water are usually divided into two broad categories: Biodegradable and non biodegradable. Biodegradable material consists of organics that can be utilized for food by naturally occurring microorganisms within a reasonable length of time The amount of oxygen consumed during microbial utilization of organics is called the biological oxygen demand (BOD). 17  Chemical Characteristics of Water Cont… BOD is the most commonly used parameter for determining the oxygen demand on the receiving water of a municipal or industrial discharge BOD can also be used to evaluate the efficiency of treatment processes, and is an indirect measure of biodegradable organic compounds in water The BOD is measured by determining the oxygen consumed from a sample placed in an air-tight container and kept in a controlled environment for a preselected period of time. 18  Chemical Characteristics of Water Cont… In the standard test, a 300 ml BOD bottle is used and the sample is incubated at 20oC for 5 days Because the saturation concentration for oxygen in water at 20oC is approximately 9mg/L, dilution of the sample with BOD-free, oxygen-saturated water is necessary to measure BOD values greater than just a few milligrams per litre Non-biodegradable Organics: are common organic materials in natural water systems which are resistant to biological degradation They include tannic and lignic acids, cellulose, and phenols. 19  Chemical Characteristics of Water Cont… Some non biodegradable organics are toxic to organisms. These include the organic pesticides, some industrial chemicals, and hydrocarbon compounds that have combined with chlorine. Measurement of non-biodegradable organics is usually by the chemical oxygen demand (COD) test Nutrients : are elements essential to the growth and reproduction of plants and animals and aquatic species on the surrounding water to provide their nutrients. Nutrients that are required in most abundance by aquatic species are carbon, nitrogen, and phosphorus. 20  Chemical Characteristics of Water Cont… i. Nitrogen The presence of nitrogenous compounds in surface waters usually indicates pollution Excessive amount of ammonia and organic nitrogen may result from recent sewage discharges or runoff contamination by relatively fresh pollution Therefore, waters containing high organic Nitrogen and ammonia- N levels are considered to be potentially dangerous ii. Phosphorus Phosphorus appears exclusively as phosphate (PO43-) in aquatic environments 21 Phosphate is a constituent of soils and is used extensively in fertilizer to replace and/or supplement natural quantities on agricultural lands. Chemical Characteristics of Water Cont… Runoff from agricultural areas is a major contributor to phosphate in surface waters Municipal wastewater is another major source of phosphate in surface water. Other sources include industrial waste in which phosphate compounds are used for such purposes as boiler-water conditioning. If they are available in large quantity, they can be used as a nutrient and result rapid growth of aquatic plants. 22 Phosphate, concentration as low as 0.2 mg/l, can also interfere with the treatment processes (chemical coagulation of turbidity). c) Biological Characteristics of Water The presence or absence of living organisms in water can be one of the most useful indicators of its quality A wide variety of different species of organisms usually indicates that stream or lake is unpolluted Pathogens: are organisms capable of infecting, or of transmitting diseases to, humans. These organisms are not native to aquatic systems and usually require an animal host for growth and reproduction. 23 These waterborne pathogens include species of bacteria, viruses, protozoa, and helminthes (parasitic worms). Biological Characteristics of Water Cont… Pathogen Indicators: Testing water for the presence of pathogens would be a very time-consuming and expensive proposition Tests for specific pathogens are usually made only when there is a reason to suspect that those particular organisms are present At other times, the purity of water is checked using indicator organisms 24 An indicator organism is one whose presence signals that contamination has occurred and suggests the nature and extent of the contaminant(s). Coliforms: the most important biological indicator of water quality and pollution used in public health technology is the group of bacteria called coliforms. Biological Characteristics of Water Cont… Public water suppliers are obliged to provide a supply of wholesome water, which is suitable and safe for drinking purposes. 25 A standard is a set of norms established by authorized legal body (regional, national, or international bodies), which would be implemented under legal framework. Guideline is somewhat flexible & designed to be more supportive to specific quality control activities. WHO Drinking Water Quality Guideline can be used as a general framework of UN member countries. Member countries are free to use their own standards or adopt this guideline. Biological Characteristics of Water Cont… 26 Microorganisms Bacteria:- may cause disease, taste and odors, pipe corrosion, pipe blockage Viruses:- are more resistant to disinfection than bacteria Fungi and molds:- frequently form dense, slimy mats that clog filters and other units; they can produce musty taste and filters and other units; they can produce musty taste and odors as well as color and turbidity Microorganism Cont… Algae:- may cause turbidity and color interferes with coagulation and sedimentation causing filter clogging 27 Chemicals produced by algae are precursors of and are associated with different taste and odor problems Protozoa: most of them cause disease Helminths (parasitic worms):- cause many diseases Nuisance-causing organisms:- many organisms, snails, crustaceans, and slime growth cause serious problems in raw water conveyance 28  Waterborne diseases Microorganism Diseases Virus Hepatitis, poliomyelitis Bacteria Cholera, Gastroenteritis, Leptospirosis, Paratyphoid fever, Salmonellosis, Shigellosis, Typhoid fever Protozoa Amebiasis, Giardiasis, Crptosporidiosis  Worms Ascariasis, Guinea worm, Lung fluke, Schistosomiasis 65 Comparison between ground and surface water characteristics Ground Surface Constant composition Varying composition High mineralization Low mineralization Little turbidity High turbidity Low or no color Color, taste and odour Bacteriologically safe Microorganisms present No dissolved oxygen Dissolved oxygen High hardness Low hardness 66 H S, Fe, Mn Possible chemical toxicity Drinking water quality Criteria and Guidelines There are many lists of quality criteria, standards and guidelines according to which the quality of drinking water is assessed. The most prominent include the Safe Drinking Water Act in the USA with its National Primary Drinking Water Regulations, the World Health Organization’s Guidelines for Drinking Water Quality and the European Union’s Directive related to the quality of drinking water intended for human consumption. Each of these includes lists of many substances with different maximum contaminant levels. 67 Basic quality requirements of drinking water Free from diseases causing pathogenic organisms  Contain no compounds that have adverse effect on human health Fairly clear (i.e., of low turbidity, little color) Contain no compounds that cause offensive taste and odor Free of substances and organisms that cause corrosion or encrustation of the water supply system, staining of clothes washed in it or food items cooked with it. 68 Table : Drinking Water Standards Chemical Concentration in mg/l constituents WHO Ethiopia  Maximum Permissible unit Maximum limit Highest Desirable Permissible Color (TCU) 15 50 5 50 Turbidity