Physico-Chemical Processes in Water and Wastewater Engineering PDF

Subject Code: ENR-1101 Physico-Chemical processes in water and waste water engineering By Anita Sharma Temporary Faculty PEC-CHD 1 The main objectives of this course ar...

Subject Code: ENR-1101 Physico-Chemical processes in water and waste water engineering By Anita Sharma Temporary Faculty PEC-CHD 1 The main objectives of this course are: 1. To introduce the concept of water quality. 2. To understand the various Physico-Chemical unit processes and operations as applied to water and wastewater systems. 3. To provide a hands on experience in environmental quality monitoring of Water and wastewater systems 2  Introduction of Water Quality Pure water is colourless, tasteless, and odourless. An excellent solvent that can dissolve most minerals that come in contact with it. That is the reason that there is no such thing as pure water in nature; it always contains chemicals and biological impurities. Water quality is a measure of the physical, chemical, and biological characteristics of water, typically in respect to its suitability for a particular purpose such as drinking, irrigation, or ecosystem support. Understanding water quality is critical for maintaining human health, protecting ecosystems, and ensuring safe water use in industrial and agricultural activities. 3  Physical, Chemical, and Biological Parameters of Water Quality A. Physical Parameters Physical parameters affect the appearance and usability of water. These include: Temperature: Affects the rate of chemical reactions in water and the metabolism of aquatic organisms. High temperatures reduce dissolved oxygen, affecting aquatic life. Turbidity: A measure of water clarity, typically affected by suspended solids like soil particles, algae, and microbes. High turbidity can reduce light penetration and affect aquatic ecosystems. Color: Can be due to natural or anthropogenic sources, such as dissolved organic matter or industrial pollutants. Odor and Taste: Often caused by organic and inorganic materials in the water, which may arise from natural processes or pollution. Example: A river near a construction site might exhibit high turbidity due to sediment runoff. As turbidity increases, aquatic plants may struggle to photosynthesize due to decreased light 4 availability. B. Chemical Parameters Chemical parameters provide insight into the composition of the water and the presence of pollutants or naturally occurring compounds. pH: The measure of acidity or alkalinity. Natural waters typically range from pH 6 to 8. pH can be altered by acid rain, industrial discharges, or natural sources. Dissolved Oxygen (DO): Essential for aquatic life, DO indicates the oxygen available for organisms. Low DO levels can lead to anoxic conditions harmful to most aquatic life. Nutrients: Key nutrients like nitrogen (N) and phosphorus (P) are necessary for plant growth but can cause eutrophication in excess. Heavy Metals: Lead (Pb), mercury (Hg), arsenic (As), and cadmium (Cd) are toxic even at low concentrations. Total Dissolved Solids (TDS): A measure of all dissolved substances in water. High TDS can affect water taste, cause scaling in pipes, and harm aquatic life. Example: In agricultural regions, excessive use of fertilizers can lead to high levels of nitrate (NO3-) in nearby lakes and rivers, resulting in eutrophication and fish kills due to oxygen depletion. 5 C. Biological Parameters Biological parameters assess the presence and health of living organisms in the water. Coliform Bacteria: Indicates fecal contamination and potential pathogens in water. Escherichia coli (E. coli) is a common indicator organism. Biological Oxygen Demand (BOD): Measures the amount of oxygen required by aerobic organisms to break down organic material in water. High BOD indicates high levels of organic pollution. Chlorophyll-a: An indicator of algae biomass, which can signal nutrient pollution and potential harmful algal blooms. Example: A river downstream from a wastewater treatment plant may have elevated BOD and coliform levels, indicating the release of untreated or poorly treated sewage, which can be harmful for human health and aquatic organisms. 6 Water Quality Requirements A. Potable Water Standards Potable water is safe for human consumption. Standards are set by agencies like the World Health Organization (WHO), the Environmental Protection Agency (EPA), or national bodies. The water must be free from pathogens, harmful chemicals, and toxins. Standard Code: IS 10500:2012 - Drinking Water Specification. Key Parameters: This standard specifies the permissible limits for various physical, chemical, and biological parameters in drinking water. Some critical aspects include: Physical: Color, turbidity, odor, taste Chemical: pH, total dissolved solids (TDS), hardness, fluoride, arsenic, lead, nitrate, etc. Biological: Total coliform bacteria, E. coli 7 Wastewater Effluent Standards: Effluent standards regulate the quality of water discharged from industrial or municipal sources to prevent environmental damage. These standards control parameters like: Wastewater Effluent Standards Standard Codes: While there isn't a single code for all industries, the Central Pollution Control Board (CPCB) provides guidelines outlining effluent discharge standards for various sectors. These standards fall under Schedule VI of the Environment (Protection) Rules, 1986. Key Parameters: The specific parameters will vary depending on the industry, but some common ones include: Physical: Temperature, color, turbidity, total suspended solids (TSS) Chemical: pH, biochemical oxygen demand (BOD), chemical oxygen demand (COD), oil and grease, heavy metals Biological: Fecal coliform bacteria 8 Water Quality Indices (WQI): A Water Quality Index (WQI) is a simplified representation of water quality data, converting complex parameters into a single value that represents overall water quality. It is used for comparing water bodies or tracking changes over time. Standard Code: IS 2296-1984 - Grading of water. Purpose: This standard provides a method for calculating a Water Quality Index (WQI) based on a weighted average of several water quality parameters. The WQI provides a single score to represent the overall water quality of a source, simplifying water quality assessment. Parameters Used: The specific parameters used in the WQI calculation can vary depending on the intended water use. Common parameters include: Dissolved oxygen (DO) pH BOD Total coliform bacteria Nitrate 9 The formula for calculating the Water Quality Index (WQI) is given in IS 2296-1984. It involves a weighted average of several water quality parameters. WQI = ∑(Wₙ * Qₙ) / ∑Wₙ Where: WQI is the Water Quality Index Wₙ is the unit weight assigned to parameter n Qₙ is the quality rating of parameter n Quality rating (Qₙ) is calculating using the expression Qₙ = [(Vₙ –𝐕𝐢𝐝 / (Sₙ – 𝐕𝐢𝐝 )] * 100 Where, Vₙ = Estimated value of nth water quality parameter at a given sample location. 𝐕𝐢𝐝 = Ideal value for nth parameter in pure water. (𝐕𝐢𝐝 for pH = 7 and 0 for all other parameters ) Sₙ = Standard permissible value of nth water quality parameter 10 Unit weight The unit weight (Wₙ) is calculated using the expression Wₙ = k / Sₙ Where, Sₙ = Standard permissible value of n th water quality parameter. k = Constant of proportionality and it is calculated by using the expression given k = [ 1 / ( 1/ 𝑺𝐧=𝟏,𝟐,……𝐧 ) ] 11 WQI and corresponding water quality status 12 13