MODULE 2 DRINKING WATER TREATMENT

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1 Water Quality MODULE 2 DRINKING WATER TREATMENT Approximately 80% of the US population depend on tap water. EPA has defined three types of public water systems Community Water System (CWS) supplies to same population all year round Non-Transient Non-Community Water Systems (NTNCWS): supplies water to at least 25 of the same people six months per year but not year-round. Transient Non-Community Water Systems: supplies water to people who are not around for a long time Potable water water that is safe for consumption Palatable water water that tastes good Contamination of water happens due to the dissolution of foreign substances in water as it propagates. In general, surface water is more polluted than groundwater. Drinking water quality can be described using four categories Physical Chemical Microbial Radiological Water Quality Standards National Safe Drinking Water Act (SDWA) was signed into law in 1974 and EPA was directed to establish maximum contaminant levels (MCLs) for clean drinking water. These MCLs are determined using Maximum Contaminant Level Goals (MCLG). MCLGs are determined based on the adverse health effects caused by contaminant. MCLGs are generally lower than MCLs. Surface Water Treatment Rule (SWTR) set forth primary drinking water regulations requiring treatment of surface water. The regulations require specific treatment technique instead of MCLs. Total Coliforms are regulated based on the presence or absence of organisms. For example: large systems are required to collect at least 40 samples (minimum volume of 100 ml) per month and cannot contain coliform-positive results in more than 5% of the samples collected each month. The methods for determination of presence of coliforms are: Multiple-tube fermentation technique (MTF) Membrane Filtration Technique Minimal media ONPG-MUG test (MMO-MUG) Presence-absence coliform test (P-A) Colisure technique 1

2 Problem 1 What are the MCLs for the parameters below Parameter Units MCL ph Dissolved Oxygen Alkalinity Hardness Conductivity Turbidity Color Nitrate Phosphate Lead Copper 2

3 Surface(Water(Treatment(Plant Coagulant Intake Structure Sedimentation Flocculation Basins Filtration Disinfection Clear well To Distribution System Ground'Water'Treatment'Plant Pump Aeration Disinfection Softening Lime Soda-ash Well Clear well To Distribution System 3

4 The different processes involved in drinking water treatment are Sedimentation removal of sediments Coagulation & Flocculation removal of suspended solids Softening removal of hardness Adsorption removal of ions Gas Transfer addition of dissolved oxygen Disinfection removal of pathogens Mixing Chemicals are dispersed quickly and uniformly in water through the process of mixing. The precipitates formed during this process are called flocs. The degree of mixing (G) measured as velocity gradient P=Power input V=volume of mixing in water tank µ = dynamic viscosity Pa.S G = P µv Axial or radial flow Paddle mixer Pneumatic mixing P = N p n 3 D i5 ρ P = C Aρ(v 3 D p) P = KQ a ln h N p =impeller constant n =revolutions per second D i =Diameter of impeller r =density of the liquid C D =drag coefficient A=cross sectional area of paddles v p =relative velocity of paddles with respect to fluid r=density of the liquid Q a =air flow rate at atmospheric pressure h=air pressure at the point of discharge K =

5 Problem 2 A city is planning the installation of a new water treatment plant to supply a growing population. There will be only one rapid mix basin and then the flow will be evenly split between two flocculator trains, each with three basins equal in volume. The required water depth of all basins is 4.0m. Determine the correct basin volumes, basin dimensions, tank equivalent diameter, required input power and impeller diameter from the table below, and the rotational speed using the following parameters: Q= m 3 /d, Rapid mix t o =2 mins Rapid mix G= 600s -1 Total flocculation, to = 30 mins Flocculators G = 70, 50, 30 s -1 Water temperature is 5 C Place impeller at one-third the water depth Impeller type Impeller diameters Power Number (Np) Radial Axial