BEIRUT ARAB UNIVERSITY FACULTY ACULTY OF O F ENGINEERING ENG INEERING CIVIL & ENVIRONMENTAL ENGINEERING DEPT.
SANITARY SANITARY COURSE COU RSE (CIVE434)
CHAPTER 2: WATER TREATMENT SEDIMENTATION FALL 2012-2013 2012-20 13
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SOURCES OF DRINKING WATER In order to print this document from Scribd, you'll first need to download it.
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Groundwater:
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Soil & Rock layers naturally filter the ground water to a high degree. Deep ground water is of very high bacteriological quality (pathogenic bacteria are typically absent). Water is rich in dissolved solids (carbonates and sulfates of Water calcium and magnesium). Chloride and bicarbonate ions may be present To make it pleasant for drinking, cooking, etc.. We We need to reduce the iron or manganese man ganese content. Disinfection Disinfection may be required. requ ired.
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SOURCES OF DRINKING WATER In order to print this document from Scribd, you'll first need to download it.
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Groundwater:
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Soil & Rock layers naturally filter the ground water to a high degree. Deep ground water is of very high bacteriological quality (pathogenic bacteria are typically absent). Water is rich in dissolved solids (carbonates and sulfates of Water calcium and magnesium). Chloride and bicarbonate ions may be present To make it pleasant for drinking, cooking, etc.. We We need to reduce the iron or manganese man ganese content. Disinfection Disinfection may be required. requ ired.
document SOURCESPrintOF DRINKING WATER
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Upland Lakes & Reservoirs Cancel
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Located above human habitation.
Bacteria and pathogen path ogen are low. low.
Some bacteria, like protozoa protozoa and algae may be present.
May have have low pH, p H, which requires adjustment
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Rivers & Canals
Have significant significant bacterial load and variety of dissolved constituents Atmospheric water generation is a new technology that can provide high quality drinking water by extracting water from the air by cooling thus condensing water vapor.
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Rainwater Harvesting: Used in areas with dry season and experience fog.
SOURCES OF DRINKING WATER Print document
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Desalination of seawater
Download Print Storage – Water fromCancel rivers may beAndstored in reservoirs for periods between days and months to allow natural biological purification. And, to provide storage against drought periods.
Pre-Conditioning: Used for water rich in hardness salts. Soda ash is added.
Pre-Chlorination
pH Adjustment o
o
o
o
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Distilled water pH<7 Sea water pH around 8.2 For acidic water (pH<7), lime or soda ash is added Lime is cheap, it also adds to the resulting water hardness. For alkaline water (pH>7), HCL and CO2 are added.
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Water Treatment Plant In order to print this document from Scribd, you'll first need to download it.
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And Print Water treatmentCanceltypeDownload depends on the quality of the water to be treated
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Water quality depends o the source
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Usually, groundwater requires less treatment than water from lakes and rivers
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Water Treatment Plant In order to print this document from Scribd, you'll first need to download it.
Cancel Download And Print Water treatment plants are designed to provide complete purification system composed of:
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Pre-sedimentation
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Softening
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Disinfection
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Taste & Odor Reduction
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Filtration
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General Layout of Water Treatment Plant (WTP)
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Hydraulic Line of Water Treatment Plant (WTP)
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Sea or River Water Intake
Raw WaterPrintSump & Low Lift Pump document
Raw Water is collectedIninto raw water order toa print this document fromsump, Scribd, you'llthen it is pumped to need to download it. water treatment plant first units through pumps called “Low lift pumps”. Pumps should be selected taking into consideration the following: Cancel Download And Print -Number of pumps should be selected based on various conditions of operation. - Stand-By pumps should be provided -Minimum number of pumps is two. - Total Dynamic Head of the pumps is equal to the static head plus the head losses (friction & minor losses). -The static head is the difference between the maximum water level at the discharge side and the minimum water level at the raw water sump. -Minimum water level in the sump should be higher than the discharge
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Print documentMIXING FLASH
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- To provide the dispersion of the coagulants in a rapid way Cancel
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- To ensure equal hydraulic distribution to all sedimentation tanks though a weir - Detention Time : 20 to 60 seconds
GENTLE MIXING - To ensure chemical reaction between the coagulants and the particles in the water - Detention Time : 20 to 40 minutes - Small particles get incorporated into larger ones
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SEDIMENTATION Print document
In order to print this document from Scribd, you'll Flocculation: Is the process which clarifies water. first need to download it. Cancel And Print Clarifying water means removal ofDownload any turbidity or color in order to get clear and colorless water.
It is the process of causing a precipitate to form then to be removed using physical methods. Several parameters affect the design & operation of sedimentation tanks: - Horizontal water velocity - Tank surface area - Inlet & outlet of the tank - Method of sediments removal
SEDIMENTATION Print document
-Settleable Solids
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- Suspended Solids Cancel
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Parameters affecting the sedimentation efficiency: - Turbidity level - Shape of particles causing turbidity - Volume of particles causing turbidity - Density of particles causing turbidity - Water temperature - Water viscosity - Retention time
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SEDIMENTATION Print document
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Coagulants or flocculating agents help the sedimentation process to be done efficiently. Cancel Download And Print Small particles in water get incorporated into the large particles that coagulation produces. Coagulants: -Aluminum Hydroxide - Aluminum Sulphate Coagulant + water = flocculation= flocs Flocs + suspended solids= fast sedimentation
Jar Test Print document
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Jar test is a valuable tool to determine types and amounts of In order to print this document from Scribd, you'll chemicals to use forfirst optimum floc formation. It simulate the need to download it. coagulation/flocculation process in a batch mode.
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The jar test should simulate actual plant operating conditions,
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such as mixing rates and detention times. •
The most important part of the jar test is to document the procedures used to enable replication in the future.
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References for detailed instructions for performing a jar test:
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AWWA. 1992. Operational Control of Coagulation and Filtration Processes. M37.
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California State University. 1994. Water Treatment Plant Operation.
Jar Test Procedure Print document
1. Fill 6 jars one-liter samples of the water or wastewater to be treated. In order to print this document from Scribd, you'll 2. Prepare chemical dosages (coagulant) first need to download it. 3. Immediately after the coagulant is added the samples are "flash mixed" for approximately one minute. Cancel Download And Print 4. The stirrer speed is then reduced to simulate a flocculation basin. Flocculation mode is maintained for about 20 minutes. 5. At the end of the flocculation period the stirrers are turned off and the floc is allowed to settle for one-half hour. 6. After this settling period supernatant samples are drawn off from each sample and analyzed for turbidity and sometimes alkalinity and pH. Settling Flocculation Filtration
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SEDIMENTATION Print document
-The minimum clarifier Inretention time is hours order to print this document from4Scribd, you'll first need to download it.
- A layer of sludge is formed on the floor of the tank Download And - Amount of sludge 3-5% of Cancel total volume ofPrint water that is treated
- The tank may be equipped with mechanical cleaning devices that continually clean the bottom of the tank or the tank can be taken out of service.
SEDIMENTATION Print document
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Overflow Rate (OFR): Average flow rate per surface area
Over Flow Rate = OFR = Q/A (m3/day/m2) Detention Time (DT) or Hydraulic Retention Time (HRT): Is the duration that a water particle stays in the tank from the time it enters till the time it leaves.
DT=HRT=T =Q ÷ Vol. Vol. = Q/T
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Design Criteria of Sedimentation Tank Print document
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- OFR = 20 – 40 (m3/m2Cancel /day)
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- Detention time is 4 hours - Tank Depth 3 to 6 meters - For rectangular tanks; maximum tank length 40m, Preferable 30m - L:W = 4:1 - For circular tanks, maximum diameter 40m including the gentle mixing - Average water flow at weir = 450 m3/m/day
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EXAMPLE:
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For flow rate of 120000 m /d, design the following: to print this document from Scribd, you'll - Flash mixing tank. Infirstorder need to download it. - Circular sedimentation tank. - Rectangular Sedimentation tank & gentle Cancel Download And Print mixing - Aluminum sulfate for coagulation for one year if dose = 30ppm and cost of one ton = 250 $ - Volume of sludge m 3/d if turbidity = 60ppm
SOLUTION: Flash mixing:
Hydraulic Retention Time (HRT) = 20-60 seconds, take=40sec. Volume = Q * HRT = 120000*40/(24*60*60) = 55 m 3 For circular tank (Assume D=H); then D=4.2m
Circular Sedimentation zone: Print document
3/m2/d Over Flow Rate (OFR) = 30 m In order to print this document from Scribd, you'll Area surface = 120000 / 30 = 4000 m2 first need to download it. HRT = 3 hours Cancel Download And Print Volume = 120000 *3/24 = 15000 m 3 Depth = volume/area = 15000/4000 = 3.75 m
Gentle mixing zone:
HRT = 30 min Volume = 120000*30/24*60 = 2500 m3 Depth = 3.75 0.50 = 3.25 m Area = 2500/3.25 = 769 m2 Total area of sedimentation and gentle mixing zones = Area of sedimentation tank = 4000+769 = 4769 m2 take 6 tanks, the area of tank = 4769/6 = 795m 2 Diameter of sedimentation tank = 32 m Area of one gentle mixing tank = 769/6 Diameter of gentle mixing zone = 12.8m –
Rectangular Sedimentation zone: Print document
Over Flow Rate (OFR) = 30 m3/m2/d to print this document2from Scribd, you'll Area surface = 120000Infirst/order 30 = 4000 m need to download it. Assume L=32 m. L:W=4; then W=8m 2 Area of one tank = 32*8=256 Cancelm Download And Print Number of Tanks = 4000/256 = 15.6 Take 16 Tanks Therefore Actual Area = 4000/16 = 250 m 2 (31.25*8m) HRT = 3 hours Volume = 120000 *3/24 = 15000 m3 Depth = volume/area = 15000/4000 = 3.75 m
Gentle mixing zone:
Number of Tanks = 16 HRT = 30 min Volume = 120000*30/24*60 = 2500 m 3 Area = 2500/16 = 156.25 m2 Width = 8m same as the rectangular tank; Assume 3m depth Then L= 7.75m
Coagulants:
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Dose = 30 ppm, Q= 120000m /d Weight of Alum. Sulphate = 30*120000/1000*1000 = 3.6 ton /d Cancel Download And Print = 3.6 * 365 = 1314 ton/year Cost of coagulants every year = 1314*250=328500 $ Sludge Volume:
Turbidity of solids = 60ppm Efficiency of sedimentation = 90% Weight of dry solids = 120000*60*0.90/1000*1000 = 6.47 ton/d If water percentage in the sludge = 98% and dry solids = 2% If specific gravity of sludge = specific gravity of water = 1ton /m 3 Volume of sludge = 6.47 *100/2 = 324 ton/d
