Water Pollution Control and Wastewater Treatment PDF

# Control of water pollution The following measures can be adopted to control water pollution: - The water requirement should be minimized by altering the techniques involved. - Water should be reused with or without treatment. - Recycling of water after treatment should be practiced to the maximum extent possible. - The quantity of waste water discharge should be minimized. - Modern measuring devices to track water usage It is well known that you cannot manage what you cannot measure. However, an estimated 30% of global water is not connected by any means of measurement. Many of the existing systems are outdated - they rely on " meter readers" to manually check water usage. # Waste Water Treatment - It is often necessary if surface water supplies and sometimes groundwater supplies, are to be available for human use. Because the vast majority of cities use one water distribution system for households, industries, and fire control, large quantities of water often must be made available to satisfy the highest use, which is usually drinking water. But does it make sense to produce drinkable water and then use it for other purposes, such as lawn irrigation? - Growing demands for water have prompted serious consideration of dual water supplies: one high-quality supply for drinking and other personal use and one of lower quality, perhaps reclaimed from wastewater, for urban irrigation, firefighting, and similar applications. # Wastewater Treatment - **Primary Treatment** - **Pretreatment** - Aeration allows the release of gases such as hydrogen sulfide. - Physical methods are used to remove the solid materials →→ Grit - **Sedimentation** - Suspended solids are allowed to settle out →→ Primary sludge - **Secondary Treatment** - **Biological Treatment** - Microorganisms digest the organic material in wastewater - **Sedimentation** - The microorganisms allowed to settle out →→ Secondary sludge - **Advanced Treatment** - **Specialized Treatment** - This is sometimes used to remove remaining contaminants such as phosphorus or nitrogen - **Wastewater Disinfection** - **Discharge of Effluent to Receiving Water** # The Sludge - When the wastewater is treated and discharged to a watercourse, the job is not over. Left behind are the solids, suspended in water, commonly called *sludge*. - **Source of Sludge** - The first source of sludge is the suspended solids (SS) that enter the treatment plant and are partially removed in the primary settling tank or clarifier. Ordinarily about 60 percent of the SS becomes raw primary sludge, which is highly putrescent, contains pathogenic organisms, and is very wet (about 96% water). - **Environmental Protection Agency (EPA)** has promulgated sludge disposal standards that basically divide sludges into three classifications: - **"A" Sludge** that has been completely disinfected and has low metal concentrations. - **"B" Sludge** having been treated to a point where the level of pathogens equals that typically achieved by 30 days of anaerobic digestion. - **"C" Sludge** that has not been treated in any way. # Sludge Treatment - Sludge disposal represents a major headache for many municipalities because its composition reflects our style of living, our technological development, and our ethical concerns. "Pouring things down the drain" is our way of getting rid of all manner of unwanted materials, not recognizing that these materials become part of the sludge that must be disposed of in the environment. - Currently, sludge treatment and disposal accounts for over 50% of the treatment costs in a typical secondary plant, making this none-too-glamorous operation an essential aspect of wastewater treatment. - A great deal of money could be saved, and troubles averted, if sludge could be disposed of as it is drawn off the main process train. Unfortunately, the sludges have three characteristics that make such a simple solution unlikely: They are aesthetically displeasing, they are potentially harmful, and they have too much water. # Wastewater Treatment - **Primary** - **Secondary ** - **Tertiary** | | | | | | :------------- | :------------------------------------------- | :-------------------------------------------- | :--------------------------------------- | | **Influent** | **Debris screen** | **Grit removal** | ** Primary clarification** | | | **Wastewater** | **Wastewater** | ** Sludge** | | | | | | | | | | | | | | | ** Sludge digesters** | | | | **Dewatering** | ** Landfill** | | | | | | | | | **Aeration tank** | **Secondary clarification** | | | **Sludge** | ** Sludge** | ** Activated sludge** | | | **Air** | | | | | | | | | | | | **Filters** | | | | | ** Disinfection** | | | | | ** Chlorine** | | **Effluent** | | | ** UV-light** | | | | | **Discharge to surface water** | # Definition The term "Thermal Pollution" can be defined as: (The addition of an excess of undesirable heat to water that is harmful to human, animal, or aquatic life or that significantly disrupts the activities of aquatic communities). # Sources of Thermal Pollution The sources of Thermal pollution mainly include: 1. Nuclear Power Plants 2. Coal fired Power Plants 3. Industrial effluents 4. Domestic sewage 5. Hydro-electric power # 1) Nuclear Power Plants - Emissions from nuclear reactors and processing installations are responsible for increasing the temperature of water bodies. - The operation of power reactors and nuclear fuel processing units constitute the major contributor of heat in the aquatic environment. - The liquid radioactive water consists of H-3, C-14, Fe-59, and Co-60 along with corrosion products. - In addition, accidental leakage of radiation from nuclear reactors in water raises the temperature of the surrounding aquatic system. - Heated effluents from power plants are discharged at 10° C higher than the coolant receiving waters and severely affected the aquatic flora and fauna. # 2) Coal Fired Power Plants - Their condenser coils are cooled with water from nearby lake or river and discharge the hot water back to the stream increasing the temperature of nearby water to about 15° C. - The heated effluents decrease the DO content of water resulting in the killing of fish and other marine organisms. # 3) Industrial Effluents - The industries like textile, paper, and pulp as well as sugar release heat in water. - The discharged water from steam-electric power industry using turbo generators, will have higher temperatures ranging from 6°C to 9°C than the receiving water. # 4) Domestic Sewage - Domestic sewage is commonly discharged into rivers, lakes, canals or streams with or without waste treatment. - The municipal sewage has a higher temperature than the receiving water. - The discharged sewage not only raises the stream temperature to a measurable extent, but also creates numerous deleterious effects on aquatic biota. - With the increase in temperature of the receiving water, the DO content decreases and the demand of oxygen increases. - Hence, the anaerobic conditions will set up resulting in the release of foul and offensive gases in water. - The marine organisms which depend on the dissolved oxygen of the surface water will die out. # 5) Hydro-electric power - The term hydroelectricity refers to electricity that is generated by hydropower (the process of producing electrical power by utilising the gravitational force of falling or flowing water). - Hydroelectric power generation can sometimes result in negative thermal loading in water systems. - Thermal loading is not limited to the electrical power industries. Other industries that require cooling contribute to thermal loading as well. # Impacts of Thermal Pollution The harmful impacts of thermal pollution mainly include: 1. **Reduction** in **Dissolved Oxygen (DO)** - Concentration of DO decreases with increase in temperature of water. 2. **Change** in **water properties** - A rise in temperature changes the physical and chemical properties of water. - The vapour pressure increases sharply, while the viscosity of water decreases. - The decrease in density, viscosity and solubility of gases increases the settling speed of suspended particles which seriously affects the food supply of aquatic organisms. 3. **Interference** with **biological activities** - Temperature changes disrupt the entire ecosystem. In aquatic organisms, temperature plays a vital role in controlling respiration rates, digestion, excretion, and overall development via physiology, metabolism, and biochemical process. - **Interference** with **reproduction** - In fishes, several activities like nest building, spawning, hatching, migration, reproduction etc. depend on some optimum temperature. - The warm water not only disturbs spawning, but also destroys laid eggs. 4. **Change** in **metabolic rate** - Fishes show a marked rise in basal rate of metabolism with temperature to lethal point. The respiratory rate, oxygen demand, food uptake, and swimming speed in fishes increase. 5. **Increased vulnerability** to **disease** - Activities of several pathogenic microorganisms are accelerated by high temperature. - Hot water causes bacterial disease in Salmon fish. 6. **Invasion** of **destructive organisms** - Thermal pollutants may permit the invasion of organisms that are tolerant to warm water and highly destructive. 7. **Undesirable changes** in **algae production** - The life in an aquatic ecosystem is greatly influenced by the growth of algae. - Excess nutrients from the wash out waters from farmlands combined with thermal pollution cause an excessive algal growth with consequent acceleration of eutrophic and other undesirable changes. # Controlling Thermal Pollution Thermal pollution must be controlled in order to prevent further detrimental effects on aquatic ecosystems in the future. Several methods can be employed in order to control thermal pollution, including: 1. Cooling Towers 2. Cooling Ponds 3. Artificial Lakes # 1) Cooling Towers - The use of water from water systems for cooling purposes with subsequent return to the water way after passage through the condenser is termed as cooling process. - Cooling towers transfer some of the heat from cooling water to the surrounding atmosphere by the process of evaporation. # 2) Cooling Ponds - Cooling ponds or reservoirs constitute the simplest method of cooling thermal discharges. - Heated effluents on the surface of water in cooling ponds maximize dissipation of heat to the atmosphere and minimize the water area and volume. # 3) Artificial Lakes - Artificial lakes are man-made bodies of water which offer possible alternatives to once through cooling. - The heated effluents can be discharged into the lake at one end, and the water for cooling purposes may be withdrawn from the other end. - The heat is eventually dissipated through evaporation. So, these lakes must be rejuvenated continuously.

Water Pollution Control and Wastewater Treatment PDF

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