BEIRUT ARAB ARAB UNIVERSITY FACULTY OF ENGINEERING CIVIL & ENVIRONMENT ENV IRONMENTAL AL ENGINEERING ENGINEERI NG DEPT DE PT..
FALL 2016-2017 2016- 2017 Prof. Hamdy Seif
Disinfection •
Disinfection is accomplished by both: - Filtering out harmful microbes - Adding disinfectant disinfec tant chemicals
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Water is disinfected to kill any pathogens patho gens in the water (Viruses, (Viruses, bacteria) Disinfectant residual in water distribution network
Disinfection - Chlorination •
The most common method. Increase in dose may cause odor & taste. Insufficient dose may not kill the micro-organisms.
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Chlorine can be easily applied, measured and controlled.
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It is relatively cheap.
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Chlorine or its compounds: Chloramine, Chlorine dioxide
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Chlorine is strong oxidant that rapidly kills micro-organisms
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Chlorine is a toxic gas.
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Use Sodium Hypochlorite that releases free chlorine when dissolved in water. Solid form: Calcium Hypochlorite releases chlorine on contact with water. Liquid Sodium hypochlorite is inexpensive and safer than the use of gas or solid chlorine. Chlorine reacts with natural organic compounds and form (THM) & (HAA), Carcinogenic, EPA.
Disinfection Chlorination •
Chlorine is added to the water entering the contact tank.
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Water stays in the contact/mixing tank for 6 hrs
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20-30 min are required for chlorine to react with water
Disinfection - Chlorination
Example: For Flow Rate= 120000 m3/day ; Chlorine Dose = 1 ppm Calculate the chlorine storage for 6 months.
Solution: •
Total wt of Cl 2 for one day = 120000*1/1000 = 120Kg
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Total wt of Cl 2 for 6 months = 120*6*30/1000=21.6 ton
Disinfection – Ozone (O3) •
Unstable molecule
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Strong Oxidant
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No odor or taste
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2-3 ppm after 10 min becomes 0.1 ppm
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Production of fewer by-products
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Leaves no disinfectant residual in water
Disinfection – UV(Sunrays)
Disinfection – UV (Light)
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Light Radiation.
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Very effective as long as water has a low level of color.
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Leaves no disinfectant residual in water.
Ground Water Tank for Clear Water It can be constructed below or above ground for the following purposes: •
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Provide necessary and unexpected water demand for ex: fire fighting. Water Balance due to variation of water demand. This is to ensure balance between the rate of water production and the rate of water demand. Emergency cases due to out of service of any treatment unit. Helps in water disinfection by allowing a contact period between the disinfectant and the substances.
Ground Water Tank– Design Criteria •
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Storage Volume = Average Demand x Storage Duration Number of Tanks = Storage Volume / Volume of 1 tank
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Minimum number of tanks is 2
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Tank shape can be rectangular, circular, square
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Water Depth in the tank = 2-6 meters
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Roof Level is at least 50 cm above high water level
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Circular deep tanks can be made of steel
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Tanks should be designed with baffle walls
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Design of inlet, outlet, overflow and drain
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Provide ventilation openings
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Minimum floor slope = 0.5%
Ground water tank: •
DT=2 to 4 hrs
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V= Q*T
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A<1000m2 ;
H<15m ; Volume = or <5000m3
Example: For flow rate = 120000 design the ground water tanks.
Solution •
Let
T =4 hrs
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Q=120000 m3 /d =5000m3/hrs
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Volume=5000*4=20000m3
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Circular tank: take 4 units:
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Volume of one unit=5000m3
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H=8m = A=625m2 = 3.14*D2/4 = D=28 m
OK
Ground (elevated) tank : •
This system will be related to the ground water supply system.
Case one Design: •
Q of well = 0.01824m3/sec
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in 2045 we need 28 wells 6” each
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= Q=28*0.01824 = 0.15m 3/sec= 1836m3/hr.
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DT=4hrs. =V=7344m 3
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Take 2 circular tanks with depth = 4m
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= A1 tank = 918m2=3.14*D2/4
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=D1tank = 35m
Case one criteria: •
Design:
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Let T=12 hrs
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Q=1836m3/hrs Volume=1836*12=22032m3
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Rectangular tank: take 6 units:
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V1 unit=22032/6=3672 m3<5000
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H=6m => A1 unit t = 612m2 = (3.14D2/4)
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D =28m = < 40m …. OK
OK
House Filters •
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Treated Water is the water leaving the WTP after passing through all treatment stages. Available chlorine residual decreases gradually as the water goes into the network. Chlorine decay, Pipe decay It is always recommended to install a water filter in the house
Types of House Filter Single stage filter 1. Wool glass 2. Clay 3. Activated carbon Double stage filter Can be made of wool glass and clay (1 or 2) Or Clay with activated carbon. Triple stage filter Made of wool glass, clay and activated carbon.
