Chapter 3: Pollutant Classification PDF

College of Engineering AꞌSharqiyah University WATE211 Introduction to Water Quality Chapter 3: Pollutant Classification Place photo here Dr. Motasem Alazaiza Associate Professor ...

College of Engineering AꞌSharqiyah University WATE211 Introduction to Water Quality Chapter 3: Pollutant Classification Place photo here Dr. Motasem Alazaiza Associate Professor  WATER POLLUTION If pure water does not exist, outside of a chemist’s laboratory, how can a distinction are made between polluted and unpolluted water? Infact, the distinction depends on the type and the concentration of impurities as well as on the intended use of the water. In general terms, water is considered to be polluted when it contains enough foreign materials to render it unfit for a specific benefit use, such as for drinking, recreation, or fish propagation. Actually, the term pollution usually implies that human activities are the cause of the poor water quality.  CLASSIFICATION OF WATER POLLUTANTS First, a pollutant can be classified according to the nature of its origin as either a point sources of a Dispersed (Non Point) sources pollutant  CLASSIFICATION OF WATER POLLUTANTS (Cont) Point Sources pollutant are easies to deal with than are dispersed sources pollutant; those from a point source have being collected and convened to a single point where they can removed from the water in the treatment plant and the point discharges from treatment plant can easily be monitor by regulatory agencies. Pollutants from dispersed sources are much more difficult to control. Many people think that sewage is the primary culprit in water pollution problems, but dispersed sources cause a significant fraction of the water pollution in Nigeria. The most effective way to control the dispersed sources is to set appropriate restriction on land use.  CLASSIFICATION OF WATER POLLUTANTS (Cont) In addition to being classified by there origin, water pollutant can be classified into group of substances base primarily on there environmental or health effect. e.g., the following lists identify 9 specific types of pollutants. -Pathogenic organism, -Oxygen- demanding substances, -Plant nutrients - Toxic organics, -Inorganic chemicals, - Sediments, -Radioactive substances, - Heat, -Oil  WATER QUALITY EXPRESSION EXPRESSING CONCENTRATION The properties of solutions, suspensions and colloids depend to large extent on their concentrations. Since concentrations need to be expressed quantitatively, instead of qualitatively terms like dilute or strong, concentration are usually expressed in terms of mass per unit volume, part per million or billion, or percent.  MASS PER UNIT VOLUME: One of the common types of concentration is milligram per liter (mg/L). If 0.3g of salt is dissolved in 1500mL of water, then the concentration is expressed as 300mg/1.5L=200mg/L, where 0.3g = 300mg and 1500mL = 1.5L (1g=1000mg/L; 1L=1000mL). For example, a concentration of 0.004mg/L is preferably written as its equivalent 4g/L. Since 1000g=1mg, e.g., a concentration of 1250g/L is equivalent to 1.25mg/L. In air, concentrations of particulate matter of gases are commonly expressed in terms of micrograms per cubic meter (g/m3).  PART PER MILLION: One liter of water has a mass of 1kg. But 1kg is equivalent to 1000g or 1 million mg. therefore, if 1 mg of a substance is dissolved in 1 L of water, we can say that there is 1 mg of solute per million mg of water. In other words, there is one part per million (1 ppm) 1mg/L=1ppm. MICROg/L is preferred over its equivalent of ppb.  PERCENTAGE CONCENTRATION: Concentrations in excess of 10000mg/L are generally expressed in terms of percent, for conveniences. For practical purposes, the conversion of 1 percent = 10000 mg/L be used even though the density of the solutions are slightly more than that of pure water (10000mg/L = 10000mg/1000000mg = 1 mg/100 mg = 1 percent). A concentration expressed in terms of percent may be also computed using the following expression. Percent = (Mass of Solute (mg)/ Mass of Solvent (mg)) X 100  Work out EXAMPLE: A 500-mL aqueous solution has 125mg of salt dissolved in it. Express the concentration of this solution in terms of (a) mg/L, (b)ppm, (c)gpg (d) Percent and (e) lb/mil gal Solution (125mg/500mL)X1000mL/L = 250mg/L 250mg/L = 250 ppm (250 mg/L X 1gpg)/17.1 mg/L = 14.6 gpg Applying this equation Percent = (Mass of Solute (mg)/ Mass of Solvent (mg))X 100 Percent = 0.125g/500g X 100 = 0.025 percent Or divide 250mg/L by 10,000 to get 0.025 percent 250 mg/L X 8.34 = 2090 lb/mil gal  TOXIC AND RADIOACTIVE SUBSTANCES: A wide variety of toxic inorganic and organic substances may be found in water in very small or trace amount. Even in trace amounts, they can be a danger to public sources, but many come from industrial activities and improper management of hazardous waste A toxic chemical may be a poison, causing death, or it may cause disease that is not noticeable until many years after exposure. A carcinogenic substance is one that causes cancer; substances that are mutagenic cause harmful effects in the offspring of exposed people. Some heavy metals that are toxic are Cadmium, Cd, Chromium, Cr, Lead, Pb, Mercury, Hg, and Silver, Ag. Arsenic, as, Barium, Bar, and Selenium, Se, are also poisonous in organic elements that must be monitored in drinking water.  RADIATION: The emission of subatomic particles or energy from unstable nuclei of certain atoms, referred to as radiation, poses a serious public health hazard. Obviously, the consumption of radioactive substances in water is undesirable, and maximum allowable concentrations of radioactive materials have been established for public water supplies. Potential sources of radioactive pollutants in water include wastes from nuclear power plants, from industrial or medical research using radioactive chemicals, and from refining of uranium ores. Radon sometimes occurs naturally in groundwater.  BIOLOGICAL PARAMETERS OF WATER QUALITY The presence or absence of living organisms in water can be one of the most useful indicators of its quality. In the streams, river, and lakes, the diversity of fish and insect species provide a measure of the biological balance or health of the aquatic environment. A wide variety of different species of organisms usually indicates that the stream or lake is polluted. The disappearance of certain species and overabundance of other groups of organisms is generally one of the effects of pollution.  examples BACTERIA: ALGAE: PROTOZOA: VIRUESE: COLIFORM: AEROBIC AND ANAEROBIC DIGESTION AND TYPES OF DECOMPOSITION  Microorganisms , like all living things, require food for growth. Biological sewage treatment consists of a step-by-step, continuous, sequenced attack on the organic compounds found in wastewater and upon which the microbes feed. In the following sections we will look at the processes of aerobic and anaerobic digestion and the decomposition of waste in each process.  Aerobic Digestion Aerobic digestion of waste is the natural biological degradation and purification process in which bacteria that thrive in oxygen-rich environments break down and digest the waste. During oxidation process, pollutants are broken down into carbon dioxide (CO2), water (H2O), nitrates, sulphates and biomass (microorganisms). By operating the oxygen supply with aerators, the process can be significantly accelerated. Of all the biological treatment methods, aerobic digestion is the most widespread process that is used throughout the world. Aerobic bacteria demand oxygen to decompose dissolved pollutants. Large amounts of pollutants require large quantities of bacteria; therefore the demand for oxygen will be high. Advantages of Aerobic Digestion Aerobic bacteria are Path of Aerobic Digestion very efficient in breaking down waste products. The result of this is; aerobic treatment usually yields better effluent quality that is obtained in anaerobic processes. The aerobic pathway also releases a substantial amount of energy. A portion is used by the microorganisms for synthesis and growth of new microorganisms.  Aerobic Decomposition A biological process, in which, organisms use available organic matter to support biological activity. The process uses organic matter, nutrients, and dissolved oxygen, and produces stable solids, carbon dioxide, and more organisms. The microorganisms which can only survive in aerobic conditions are known as aerobic organisms. In sewer lines the sewage becomes anoxic if left for a few hours and becomes anaerobic if left for more than 1 1/2 days. Anoxic organisms work well with aerobic and anaerobic organisms. Facultative and anoxic are basically the same concept.  Anoxic Decomposition A biological process in which a certain group of microorganisms use chemically combined oxygen such as that found in nitrite and nitrate. These organisms consume organic matter to support life functions. They use organic matter, combined oxygen from nitrate, and nutrients to produce nitrogen gas, carbon dioxide, stable solids and more organisms.  Anaerobic Digestion Anaerobic digestion is a complex biochemical reaction carried out in a number of steps by several types of microorganisms that require little or no oxygen to live. During this process, a gas that is mainly composed of methane and carbon dioxide, also referred to as biogas, is produced. The amount of gas produced varies with the amount of organic waste fed to the digester and temperature influences the rate of decomposition and gas production.  Anaerobic digestion occurs in four steps: Hydrolysis : Complex organic matter is decomposed into simple soluble organic molecules using water to split the chemical bonds between the substances. Fermentation or Acidogenesis: The chemical decomposition of carbohydrates by enzymes, bacteria, yeasts, or molds in the absence of oxygen. Acetogenesis: The fermentation products are converted into acetate, hydrogen and carbon dioxide by what are known as acetogenic bacteria. Methanogenesis: Is formed from acetate and hydrogen/carbon dioxide by methanogenic bacteria.  Advantages of Anaerobic Digestion Wastewater pollutants are transformed into methane, carbon dioxide and smaller amount of bio-solids. The biomass growth is much lower compared to those in the aerobic processes. They are also much more compact than the aerobic bio-solids.  Anaerobic Decomposition A biological process, in which, decomposition of organic matter occurs without oxygen. Two processes occur during anaerobic decomposition. First, facultative acid forming bacteria use organic matter as a food source and produce volatile (organic) acids, gases such as carbon dioxide and hydrogen sulfide, stable solids and more facultative organisms. Second, anaerobic methane formers use the volatile acids as a food source and produce methane gas, stable solids and more anaerobic methane formers. The methane gas produced by the process is usable as a fuel. The methane former works slower than the acid former, therefore the pH has to stay constant consistently, slightly basic, to optimize the creation of methane.  DEMINERALIZATION Water, even if it is occurring in nature, consists of lot of minerals which is harmful for both humans and animals. The consumption of these harmful minerals can be avoided by using demineralizer. The minerals present in water are normally calcium, magnesium, sodium, alkalinity, chlorides, sulfates, nitrates, and silica which can also harm industrial pipes, boilers etc by causing corrosion, scale building, spotting on finished surfaces, precipitation in chemical products and other related problems. The demineralizer is designed to sort out these problems.  DEMINERALIZATION Dissolved ionic material from water is removed by demineralization process. This process is followed to obtain pure water. Demineralization takes place in an ion exchange unit called as demineralizer or deionizer that consist of cation bed, an anion bed and a mixed bed in series. The mixed bed consist of both cation and anion resins and is called as polisher. The mixed bed provides the highest ion removal efficiency. Positively charged ions like calcium, magnesium and sodium are removed by the cation bed whereas negatively charged ions like sulfate and chloride are removed by the anion beds.  It was only after the production of different types of resins demineralization on large scale began. The popular resin used for demineralization purpose are: Strong Acid Cation Weak Acid Cation Strong Base Anion Weak Base Anion Water softening process can be summarized in following chemical equation: Softening Process  WHAT IS DESALTING Water desalting, or desalination, has long been utilized by water-short nations worldwide to produce or augment drinking water supplies. The process dates back to the 4th century BC when Greek sailors used an evaporative process to desalinate seawater. Today, desalting plants worldwide have the capacity to produce over 6.0 billion gallons a day – enough water to provide over 15 gallons a day for every person in the United States. About 1,200 desalting plants are in operation nationwide. Most United States plants are used for brackish (moderately salty) ground water treatment for softening and organics removal, or to produce highly purified water for industrial use.  Uses of Desalting The conversion of salt water to drinking water is the most publicly recognized desalting use. Desalting processes are also used in home water treatment systems, to treat industrial wastewater, to produce high-quality water for industrial purposes, to improve the quality of drinking water from marginal or brackish sources, and for the treatment and recycling of municipal wastewater.  The Process Water desalting is a process used to remove salt and other dissolved minerals from water. Other contaminants, such as dissolved metals, radionuclides, bacterial and organic matter may also be removed by some desalting methods. In addition, desalting processes are used to improve the quality of hard waters (high in concentrations of magnesium and calcium), brackish waters (moderate levels of salt), and seawater. Desalting separates saline water into two products: fresh water and water containing the concentrated salts, or brine. Such separation can be accomplished by a number of processes. The two most widely used are thermal processes and membrane processes.  Thermal (Distillation) Processes Nature, through the hydrologic cycle, provides our planet with a continuous supply of fresh, distilled water. Water evaporates from the ocean (salt water) and other water bodies, accumulates in clouds as vapor, and then condenses and falls to the Earth’s surface as rain or snow (fresh water).  Thermal (Distillation) Processes Distillation desalting processes work in the same way. Over 60% of the world’s desalted water is produced by heating salty water to produce water vapor that is then condensed to form fresh water. Since heat energy represents a large portion of overall desalting costs, distillation processes often recover and reuse a portion of the heat required to decrease overall energy requirements. Boiling in successive vessels, each operated at a lower temperature and pressure can also significantly reduce the amount of energy needed. Depending on the plant design, distilled water produced from a distillation plant has salt concentrations of 5 to 50 parts per million (ppm) Total Dissolved Solids (TDS). Between 25 and 50% of the source water is recovered by most distillation methods.  Membrane Processes Both the electrodialysis (ED) and reverse osmosis (RO) processes use membranes to separate salts from water. No one desalting process is “the best.” A variety of factors come into play in choosing the appropriate process for a particular situation. These factors include the quality of the source water, the desired quantity and quality of the water produced, pretreatment, energy and chemical requirements, and concentrate disposal.  ELECTRODIALYSIS Electrodialysis is an electrochemical process in which the salts pass through the membrane, leaving the water behind. It is a process typically used for brackish water. Because most dissolved salts are ionic (either positively or negatively charged) and the ions are attracted to electrodes with an opposite electric charge, membranes that allow selective passage of either positively or negatively charged ions can accomplish the desalting. Freshwater recovery rates for this type of unit range from 75 to 95% of the source water.  REVERSE OSMOSIS In reverse osmosis, salt water on one side of a semi-permeable plastic membrane is subjected to pressure, causing fresh water to diffuse through the membrane and leaving behind a concentrate solution, containing the majority of the dissolved minerals and other contaminants. The major energy requirement for reverse osmosis is for pressurizing the source, or “feed,” water. Depending on the characteristics of the feed water, different types of membranes may be used. Because the feed water must pass through very narrow passages in the membrane, larger suspended solids must be removed during an initial treatment phase (pretreatment).  Conclusion Nanofiltration plants typically operate at 85 to 95% recovery. Brackish water RO plants typically recover 50 to 80% of the source water and seawater RO recovery rates range from 30 to 60%.