Chapter 9 - Water Treatment Questions and Answers 2023

Chapter 9 - Water Treatment Questions and Answers 2023 How do we select the type of water treatment technologies we will use? 1. Reliability 2. Source of water quality 3. Existing conditions 4. Process flexibility 5. The cost of the methods What does the degree of water treatment depend on? 1. Source of water 2. Existing conditions of water 3. Cost of the treatment process What are the steps of a conventional surface water treatment plant? 1. Bar rack 2. Screening 3. Flow measurement 4. Coagulation (Mixing) 5. Flocculation 6. Sedimentation 7. Filtration 8. Clear Well 9. High-service pumps 10. Disinfection/Oxidation How does coagulation/flocculation work? Coagulation works by having the dirt particles in water collect together as a result of chemical reaction - then the dirt and unwanted particles can therefore be seen and easy to remove by other methods of water treatment. What are coagulants and coagulant aids? Coagulants are chemicals that are used in the Coagulation Process. What are coagulants used for? Coagulants, once dissolved in water, separate water from unwanted in impurities for easy separation. How do we know how many coagulants to add? The amount of coagulants to be used depends upon the amount of water to be treated and the concentration. What causes water to be hard? Dissolved magnesium and calcium ions. What types of problems are associated with hard water? Mineral buildup in pipes and heating systems and poor soap/detergent performance. What is water softening? How is it achieved? Water softening is the process of making hard water soft. It is achieved by lime softening or ion-exchange resins. How does a sedimentation reactor work? It uses gravity to remove suspended solids from water. Why do filters need to be backwashed? Filters need to be backwashed so they can be reused. What are the categories of human enteric pathogens? -Salmonella -Escherichia Coli -Campylobacter -Shigella What are the common disinfectants used for water treatment? Which one is used most often? Common water disinfectants include UV light and chlorine, but the most commonly used is chlorine. How do water disinfectants work? What are the mechanisms? Microorganisms are destroyed or deactivated resulting in termination of growth and reproduction. What are the pros and cons of alternative water disinfectants? Pros: -Ozone: THMs aren't formed. Cons: -Chlorine dioxide: may reduce to chlorate. UV Radiation: no residual UV Radiation: quartz-sleeves must be cleaned periodically. What is chlorine residual? How much chlorine residual is provided at the furthest tap in the system? Chlorine residual is the little amount of chlorine that remains in water after its application. 2 mg/L of chlorine residual is provided at the furthest tap in the system. What are disinfection by products (DBPs)? How do they form? Disinfection-by-Products are chemicals resulting from a process of purifying water using disinfectants. They from from the reaction between water and chemicals. Unit Operation A water treatment method involving physical forces. Unit Process Water treatment technologies that are biological or chemical. Water Hardness A condition of water caused by polyvalent metallic cations. Coagulation A part of the unit process consisting of the addition and mixing of a chemical reagent to destabilize colloidal and fine solids suspended in water. Flocculation A part of the coagulation process that involves slow stirring or gentle agitation to promote agglomeration of the destabilized particles formed during coagulation, so that heavy, rapid-settling flocs are formed. Sedimentation/Settling A part of the unit process involving solids-liquid separation by gravitational settling to remove suspended solids. Filtration A unit process that involves the separation of non-settable solids from water or wastewater by passing the water through a porous medium. Granular Media Gravity filters consisting of dual or multiple layers of coarse granular media that is most widely used in water treatment. Disinfection A unit process in which a chemical is added to the treated water to oxidize residual organics and pathogens. Sterilization A process who's objective is to destroy all microorganisms. Disinfectant A chemical liquid that destroys bacteria. Coagulant Aid Aids that include acids and bases that may be added to water to maintain a specific pH. Coagulant Chemicals that are added to water for destabilizing colloidal particles. Floc A type of chemical added to water for destabilizing colloidal particles. Colloidal particle A particle that has a range from 1nm to 1um and tends to acquire a negative surface charge. Water softening A unit process involving the addition of chemicals to water for the removal of ions that cause hardness. Chemical precipitation The primary means of removing hardness from water. Headloss A portion of energy that is lost in a pipe due to the resistance of flow. Clogging To hinder or obstruct with thick or sticky matter. Filter Backwash A form of preventive maintenance so that the filter media can be reused. Human Enteric Pathogens Rod-shaped, gram-negative bacteria that mostly occur normally or pathogenically in intestines of humans and animals.