module 2 – drinking water treatment
TRANSCRIPT
Environmental Engineering I Jagadish Torlapati Fall 2017
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MODULE 2 – DRINKING WATER TREATMENT Water Quality 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
Environmental Engineering I Jagadish Torlapati Fall 2017
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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
Environmental Engineering I Jagadish Torlapati Fall 2017
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Intake Structure
Coagulant
Flocculation BasinsSedimentation
Clarifier
Filtration
Disinfection
Clear well
To Distribution System
Sludge
Surface(Water(Treatment(Plant
Aeration
Clarifier
SofteningDisinfection
Clear wellTo Distribution System
Sludge
Sludge
ClarifierPump
Well
LimeSoda-ash
Ground'Water'Treatment'Plant
Environmental Engineering I Jagadish Torlapati Fall 2017
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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
Axial or radial flow Paddle mixer Pneumatic mixing
Np=impeller constant n =revolutions per second Di =Diameter of impeller r =density of the liquid
CD=drag coefficient A=cross sectional area of paddles vp =relative velocity of paddles with respect to fluid r=density of the liquid
Qa=air flow rate at atmospheric pressure h=air pressure at the point of discharge K =1.689
G = PµV
P = Npn3Di
5ρP =
CDAρ(vp3 )
2P = KQa ln
h +10.3310.33
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Environmental Engineering I Jagadish Torlapati Fall 2017
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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= 11.5´103 m3/d, Rapid mix to=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 0.8 1.1 1.4 5.7 Axial 0.8 1.4 2.0 0.31