Visit : Civildatas.blogspot.in
colour, dissolved gases and murkiness of water objectionable tastes and odours disease producing micro organisms so water is safe for drinking purpose hardness of water suitable for wide industrial purposes like brewing, dyeing and steam
sp ot. in
OBJECTIVES o To remove o To remove o To remove o To remove o To make it generation
UNIT – III WATER TREATMENT
Unit Operations (UO) Unit operations are primary treatment of water which uses physical forces to create the desirable changes during water treatment Unit operations causes physical change to the water to be treated Unit operations are mixing, agitating, aeration, absorption, membrane separation, distillation, sedimentation and filtration
s.b
log
Unit process (UO) Unit processes are secondary treatment of water which uses chemicals to get desirable changes during water treatment Unit process causes chemical changes to the water treated Unit processes are oxidation, nitrification, coagulation, chlorination and disinfection Units
UO (or) UP
Principle Applications
1.
Micro strainer
UO
Remove algae and plankton from the raw water
2.
Aeration
UP
3.
Mixing
UO
4.
Pre-oxidation
UP
Strips and oxidizes taste and odour causing volatile organics and gases and oxidizes iron and manganese. Aeration systems include gravity aerator, spray aerator, diffuser and mechanical aerator. Provides uniform and rapid distribution of chemicals and gases into the water. Application of oxidizing agents such us ozone, potassium permanganate, and chlorine compounds in raw water and in other treatment units; retards microbiological growth and oxidizes taste, odor and colour causing compounds
Ci
vil d
ata
S.N o
Visit : Civildatas.blogspot.in
Coagulation
UP
6.
Flocculation
UO
7.
Sedimentation
UO
8.
Filtration
UO
9.
Disinfection
UP
Coagulation is the addition and rapid mixing of coagulant resulting in destabilization of the colloidal particle and formation of pin head floc Flocculation is aggregation of destabilized turbidity and colour causing particles to form a rapid-settling floc Gravity separation of suspended solids or floc produced in treatment processes. It is used after coagulation and flocculation and chemical precipitation. Removal of particulate matter by percolation through granular media. Filtration media may be single (sand, anthracite, etc.), mixed, or multilayered. Destroys disease-causing organisms in water supply. Disinfection is achieved by ultraviolet radiation and by oxidative chemicals such as chlorine, bromine, iodine, potassium permanganate, and ozone, chlorine being the most commonly used chemical
log
5.
sp ot. in
Visit : Civildatas.blogspot.in
vil d
ata
s.b
Water treatment process Screening, Aeration, Sedimentation, filtration and disinfection
Ci
Screening: Screens acts as protective device which protects the treatment plant from sticks, branches, leaves and fine particles of sand and silt. Types: (i) Coarse screen (ii) Fine screen (iii) Micro strainers Coarse screens * Coarse screens or bar screens are used to stop gross floating materials * 25 mm size bars are placed at 75 to 100 mm centre to centre Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
* Usually bars are inclined on a slope of 3 to 6 vertical to 1 horizontal
* Strained water enters vertical screens leaving behind leaves, debris as sediment * Straining is achieved by upward flow leaving behind debris and waste * Self flushing inclined screen
vil d
ata
s.b
log
Fine screens * Water enters through fine screens after passing through coarse screen * Fine screens are assembled as end less bands or drums with perforations 6mm diameter * Usually fine screens are automatic strainers which continuously remove solids from water and deposit it to collecting tray * Fine screen strainers are partly submerged in water
Ci
Micro strainers * Micro strainers have 23 micron and 35 micron of stainless steel wire cloth wrapped around revolving drum with continuous back washing assembly * Used to clean stored water with less suspended matter but with plankton, algae and micro particles * Installed before rapid or slow sand filters which increases efficiency of filters by 50% * While operation drum is submerged 2/3 rds of total size and water enters in to the drum and passes out radially * The solids are carried upside of drum and collected to get washed of by jet of water which is 1% of total water strained Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
log
sp ot. in
* 3m X 3m drum strains 50000 to 80000 lph and it cannot remove colour and finely divided clay
ata
s.b
Coagulation: Coagulation is the destabilization of colloids by addition of chemicals that neutralize the negative charges The chemicals are known as coagulants, usually higher valence cationic salts (Al3+, Fe3+ etc.) Coagulation is essentially a chemical process
vil d
Floc: When coagulant is dissolved in water and thoroughly mixed in it, thick gelatinous precipitate know as floc is formed
Ci
Flocculation: Flocculation is the agglomeration of destabilized particles into large size particles known as flocs which can be effectively removed by sedimentation or flotation. Colloidal Characteristics: Water colloids classified according to water affinity Hydrophilic colloids and hydrophobic colloids Hydrophilic colloids These types of colloids have affinity towards water due to presence of water soluble compounds like amino, carboxyl, sulfonic, hydroxyl groups on the colloidal surface. Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
These groups of compounds promote hydration which causes water film collection and surround the hydrophilic colloid Example: Proteins soaps and synthetic detergents
sp ot. in
Hydrophobic colloids These type of colloids have little affinity towards water, so no significant water film or hydration is observed. Example: Clay, metal Test to determine optimum pH and Coagulant The jar test – a laboratory procedure to determine the optimum pH and the optimum coagulant dose A jar test simulates the coagulation and flocculation processes
log
Determination of optimum pH
Ci
vil d
ata
s.b
Optimum pH:
Fill the jars with raw water sample (500 or 1000 mL) – usually 6 jars Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
Adjust pH of the jars by mixing using H2SO4 or NaOH/lime (pH: 5.0; 5.5; 6.0; 6.5; 7.0; 7.5) Add same dose of the selected coagulant (alum or iron) to each jar (Coagulant dose: 5 or 10 mg/L) Rapid mix each jars at 100 to 150 rpm for 1 minute. The rapid mix helps to disperse the coagulant throughout each container Reduce the stirring speed to 25 to 30 rpm and continue mixing for 15 to 20 mins. This slower mixing speed helps promote floc formation by enhancing particle collisions, which lead to larger flocs Turn off the mixers and allow flocs to settle for 30 to 45 mins Measure the final residual turbidity in each jar Plot residual turbidity against pH
s.b
log
Determination of Optimum Coagulant Dosage
ata
Jar Test Apparatus
Ci
vil d
Repeat all the previous steps This time adjust pH of all jars at optimum (6.3 found from first test) while mixing using H2SO4 or NaOH/lime Add different doses of the selected coagulant (alum or iron) to each jar (Coagulant dose: 5; 7; 10; 12; 15; 20 mg/L) Rapid mix each jars at 100 to 150 rpm for 1 minute. The rapid mix helps to disperse the coagulant throughout each container Reduce the stirring speed to 25 to 30 rpm for 15 to 20 mins Turn off the mixers and allow flocs to settle for 30 to 45 mins Then measure the final residual turbidity in each jar Plot residual turbidity against coagulant dose The coagulant dose with the lowest residual turbidity will be the optimum coagulant dose
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
Optimum coagulant dose: 12.5
log
Coagulant Dose
ata
s.b
Factors influencing selection of Coagulant 1. Easily availability in dry and liquid forms 2. Economical 3. Effective over wide range of pH 4. Produces less sludge 5. Less harmful for environment 6. Quick reaction to form flocs
Ci
vil d
Factors affecting coagulation 1. Types of coagulant 2. Quantity or dose of coagulant 3. Characteristics of water such as - Type and quantity of suspended matter - Temperature of water - pH of water 4. Time, turbulence and method of mixing Commonly used coagulants are: Aluminum Sulphate or Alum Chlorinated Copperas Ferrous sulphate and lime Magnesium Carbonate Polyelectrolytes Sodium Aluminate Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
Aluminium sulphate or Alum Commonly used coagulant with chemical formula Al2(SO4)3 18H2O Many waters have bicarbonate alkalinity which is required for alum coagulation Water insoluble compound aluminium hydroxide is formed which is floc Al2(SO4)3 18H2O + 3Ca(HCO3)2 = 2Al(OH)3 + 3CaSO4 + 18H2O + 6CO2 Natural alkalinity is insufficient to react with alum, so lime is added which forms Calcium hydroxide or hydrated lime (Ca(OH)2) Al2(SO4)3 18H2O + 3Ca(OH)2 = 2Al(OH)3 + 3CaSO4 + 18H2O Sodium carbonate is added to form alkalinity which does not hardness but it is expensive Al2(SO4)3 18H2O + 3Na2CO2 = 2Al(OH)3 + 3NaSO4 + 18H2O + 3CO2
log
Advantages Alum is effective for water pH between 6.5 to 8.5 Dosage varies between 10 to 30 mgl/L depends on turbidity, colour, taste, pH and temperature Alum reduces taste, odour and turbidity Cheap and strong flocs Produces crystal clear water Alum recovery at ¼ th of the cost of alum is possible
ata
s.b
Disadvantage Alum coagulation results in permanent hardness resulting in calcium sulphate Metal corrosive carbon dioxide is formed while coagulation Sludge dewatering is difficult Limited pH range of 6.5 to 8.5 which requires additional salts which is costly Land fill of alum sludge in low lying lands are difficult which results in salinity
Ci
vil d
Chlorinated Copperas Hydrated Ferrous sulphate (FeSO4.7H2O) is referred as copperas High solubility makes it usable as coagulant at usual pH range After chlorination it is oxidised to ferric sulphate (Fe2(SO4)3) and ferric chloride (FeCl3) before mixing with bulk water Ferric sulphate and ferric chloride are called as copperas they immediately form ferric hydroxide floc Fe2(SO4)3 + 3Ca(OH)2 = 3CaSO4 + 2Fe(OH)3 2FeCl3 + 3Ca(OH)2 = 3CaCl2 + 2Fe(OH)3 Advantages Quickly flocs are formed Chlorinated copperas is effective in removing colour Theoretical ratio of chlorine to copperas is 1 to 7.8 Independent use of ferric chloride is effective for 3.5 to 6.5 and above 8.5 pH High pH level it is suitable for removing manganese Independent use of ferric sulphate is effective over a pH range of 4 to 7 and above 9 Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Disadvantages Low solubility in cold water Cost is high when compared to alum Special solution arrangements are required in cold water
log
sp ot. in
Ferrous sulphate and lime Ferrous sulphate reacts with natural bicarbonate alkalinity slowly Lime is added to copperas to speed up flocculation FeSO4.7H2O + Ca(OH)2 = Fe(OH)2 + CaSO4 + 7H2O Formed ferrous hydroxide (Fe(OH)2) floc is oxidised by dissolved oxygen in water to ferric hydroxide 4 Fe(OH)2 + O2 + 2H2O = 4Fe(OH)3 Advantages Ferric hydroxide is a gelatinous floc heavier than alum floc Effective pH range is 8.5 and above Suitable for alkaline water Disadvantages Ferrous sulphate is not suitable for soft coloured waters Not suitable for pH range 7.0 and below pH 7.0
vil d
ata
s.b
Magnesium Carbonate and lime Magnesium carbonate and lime forms magnesium hydroxide and calcium carbonate MgCO3 + Ca(OH)2 = Mg(OH)2 + CaCO3 Advantages Useful for removing organic colour, iron and manganese Disadvantages Magnesium hydroxide and calcium carbonate are water soluble Slurry is formed due to solubility Not commonly used to treat water
Ci
Polyelectrolytes Polyelectrolytes are high molecular water soluble polymers Classified based on charge as anionic, cationic and non ionic Cationic polyelectrolytes are independent effective coagulants Other polyelectrolytes are used as coagulant aids With polyacrylamides non polymer materials should be absent Advantages Polyelectrolytes increase pH range reducing primary coagulant volume to 1 ppm Polyelectrolyte is very small when compared to coagulant but effective in flocculation Cationic polyelectrolytes trade names are Floccal N, Magnifloc 972 and Mogul 980 Disadvantages Costly when compared to alum Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
Sodium Aluminate Sodium aluminate (Na2Al2O4) is alkaline in reaction which reacts with calcium and magnesium Na2Al2O4 + Ca(HCO3)2 = CaAl2O4 + a2CO3 + CO2 + H2O Na2Al2O4 + CaCl2 = CaAl2O4 + 2NaCl Na2Al2O4 + CaSO4 = CaAl2O4 + Na2SO4 Advantages Coagulant removes temporary and permanent hardness Can be used for naturally available water with pH 6 to 8.5 Disadvantages Costly than alum Can be used only for natural water with pH range 6 to 8.5 Not suitable for acidic and alkaline water
Ci
vil d
ata
s.b
log
Coagulant feeding methods (i) Dry feeding Simple operation and requires less space Cheap but dosing control is difficult (ii) Wet feeding Dosage can be adjusted automatically Chemicals of corrosive nature causes problems (i) Dry feeding Chemical in powder form is placed in hopper bottom tank Agitating plates are placed to prevent arching inside tank Venture device connected to the raw water pipe rotates the toothed wheel or helical screw according to the flow of the water
Dry feeding methods Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
(ii) Wet Feeding Coagulant is prepared to required strength and stored in storage a tank which is fed in proportion to raw water according to the flow. The mixing is carried out by regulating devices
sp ot. in
(a) Conical Plug and Float Coagulant solution is stored in constant head feeding tank Coagulant feed is controlled by conical plug which is connected to float by rod rotated by rack and pinion arrangement Raw water channel and float channel are inter connected to maintain same water level When water level rises the rack and pinion arrangement rotates to raise the conical plug to feed more quantity of coagulant solution When water flow is stopped float moves down this rotates conical plug in same direction through rack and pinion stops flow of coagulant which is automatic
Ci
vil d
ata
s.b
log
(b) Adjustable weir and float Adjustable weir in the form of sliding cylinder having rectangular holes in the surface and its movement is controlled by a lever system moved by the float When flow increases float moves upwards opening the mouth of wier coagulant flow increases. When flow decreases the wier is closed which is automatic
Visit : Civildatas.blogspot.in
log
sp ot. in
Visit : Civildatas.blogspot.in
s.b
Coagulant Mixing methods (i) Centrifugal Pump Centrifugal pump is used to raise the raw water to the settling tank Required dose of chemical is passed through suction pipe it mixes at impeller of pump When water is delivered gentle agitation is required to get good results of coagulation and sedimentation
ata
(ii) Compressed air agitation Vigorous agitation is carried out by diffusing compressed air from bottom of tank
Ci
vil d
Narrow mixing Channel with flume Coagulant is fed from feeding tank to the narrow mixing channel with vertical baffles Flume is provided to develop hydraulic jump to cause turbulence and to measure the flow
Channel with baffles
Visit : Civildatas.blogspot.in
sp ot. in
Visit : Civildatas.blogspot.in
Channel with overflow wier
log
Channel with flume for hydraulic jump
Mixing basins with baffle wall Water flows horizontally for short distance and takes complete turn which causes turbulence resulting in mixing and this assembly is called as round the end type
Ci
vil d
ata
s.b
Water flows up and down due to vertical baffle walls it is called as vertical or over and under type
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Used in smaller water treatment plants Mix basins with baffle basins are not used now due to high head loss and velocity variations
s.b
log
sp ot. in
Mixing basins with mechanical devices Flash mixer is used in water treatment plant now In flash mixer coagulant is agitated vigorously by a paddle operated by a variable speed motor Figure shows vane type flash mixer
vil d
ata
Intensity of mixing depends upon temporal mean velocity gradient (G) Turbulence and mixing intensity depends on power input Propeller type impeller rotates at 400 to 1400 rpm it is widely used Impeller speed is between 100 to 250 rpm Detention time of 30 to 60 seconds is practised Flash mixer units are circular or square tanks with height to diameter ratio of 1:1 to 3:1 Mean velocity gradient (G) is kept above 300 s-1 to 900 s-1 Power requirements are from 1 to 3 watts per m3/hr of flow Ratio of impeller diameter to tank diameter is 0.2:1 to 0.4:1 shaft speed of propeller is kept that the tangential velocity greater than 3m/s is imparted at the tip of the blades
Ci
Mean velocity gradient: It is defined as the rate of change of velocity per unit distance normal to a section (metres/ seconds /metres) G = √ (P/ (µV)) P = power dissipated in watts µ = absolute viscosity in N-s/m2 V = the volume to which P is applied in m3 G = temporal mean velocity gradient (s-1) Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Flash Mixer types (a) Mechanical Vane type Propeller type Jet type
log
sp ot. in
(b) Hydraulic Hydraulic jump Baffled channel Design Criteria Impeller speed is between 100 to 250 rpm Detention time of 30 to 60 seconds is practised Flash mixer units are circular or square tanks with height to diameter ratio of 1:1 to 3:1 Mean velocity gradient (G) is kept above 300 s-1 to 900 s-1 Power requirements are from 1 to 3 watts per m3/hr of flow Ratio of impeller diameter to tank diameter is 0.2:1 to 0.4:1 shaft speed of propeller is kept that the tangential velocity greater than 3m/s is imparted at the tip of the blades
s.b
Design of mechanical rapid mix unit # Design of mechanical rapid mix unit for a design flow to be treated equal to 300 m3/h. Assume suitable permissible values for various parameters of design. Assume a temperature of 20˚C
vil d
ata
Design parameters Adopt design parameters (i) Detention time = 30 secs (ii)Velocity gradient G = 600 s-1 (iii) Rotational speed of impeller: 125rpm (iv) Ratio of tank height to diameter = 1.5:1 (v) Ratio of impeller diameter to tank diameter = 0.04:1
Ci
STEP 1 Determination of dimensions of the tank Volume of tank = flow x detention time = 300/3600 x 30 = 2.5m3 Volume = Area x depth = (π/4 x D2) x (1.5D) 2.5 = π/4 x D3 D = 1.285 m Tank diameter = 1.3 Depth of tank = 1.3 x 1.5 = 1.95m + free board of 0.2 m = 2.15 m
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
STEP 2 Computation of power requirements P = G2µV µ = 1.0087 x 10-3 at 20˚C P = 6002 x 1.0087 x 10-3 x 2.5 = 908 watts Power per unit volume = 908/2.5 (vol. of tank) = 363 watts/m3 Power per unit flow of water = 908/300 (flow) = 3.03 watts/m3/hr of flow Determination of dimensions of flat blades and impeller Diameter of impeller = 0.4 x tank diameter = 0.4 x 1.3 0.52m Velocity at the tip of the impeller vp = ((2πrn)/60) m/s = 2π x (0.52/2) x (125/60) = 3.40m/s
log
½ x CD x ρ x Ab x vr3 area of blades relative velocity of blades = (1 - k) vp velocity at the tip of the impeller or blade power spent = 908 density of water = 998 kg/m3 at 20˚C 0.25 (1 - 0.25) vp = 0.75vp = 0.75 x 3.40 = 2.55 m/s 1.8 for blades ½ x 1.8 x 998 x Ab x (2.55)3
s.b
= = = = = = = = = =
ata
Pc Ab vr vp Pc ρ k vr CD 908
Ab = 0.06097 m2, provide six blades of each blades area = 1/6 x 0.06097 = 0.01m2 Each blades size = 0.09 x 0.12 = 9 cm x 12 cm = 108 cm2
Ci
vil d
# A coagulant sedimentation plant clarifies 50 MLD. The raw water alkalinity equivalent of 4 mg/l of CaCO3. The filter alum required at the plant is 20 mg/l. Determine the filter alum and quick lime (containing 88% to CaO) required per year by the plant. Use the following molecular weights: (Al = 27, S = 32, O = 16, H = 1, Ca = 40, C = 12) Solution: Alum required per day = 50 x 106 x 20 = 1000 x 106 mg/day = 1000 kg/day = 365 tonnes/year Chemical reactions when water has sufficient alkalinity CaCO3 + H2O + CO2 = Ca(HCO3)2 Mol. Wt of Al2(SO4)3 18H2O = (2x27) + 3(32 + 4 x 16) + 18(2 + 16) = 666 Mol. Wt of Ca(HCO3)2 = 40 + 2(1 + 12 + 48) = 162 Mol. Wt. of CaCO3 = 40 + 12 + 48 = 100 Mol. Wt. of CaO = 40 + 16 = 56 Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
Alum requires 3 x 162 (486) parts of natural alkalinity, Ca(HCO3)2 for every 666 parts of alum 162 parts of Ca (HCO3)2 natural alkalinity is equivalent to 100 parts of alkalinity as CaCO3. Required alkalinity as CaCO3 for water containing alum of 20 mg/l = (3 x 100 x 20)/ 666 = 9.01 mg/l Natural alkalinity available as CaCO3 = 4 mg/l Additional alkalinity required to be added in the form of lime = 9.01 – 4 = 5.01mg/l as CaCo3 Since 100 parts of CaCo3 produces 56 parts of CaO, then quantity of CaO required = (5.01 x 56)/ 100 = 2.806 mg/l Market available quick lime contains only 88% of CaO Quick lime required = (2.806 x 100) / 88 = 3.188 mg/l Quantity of quick lime per day = 50 x 106 x 3.188 mg = 159.4 kg/day = 58.2 tonnes/day
ata
s.b
log
Flocculation: Flocculation is slow mixing or agitating process in which destabilised colloidal particles are brought into intimate contact in order to promote their agglomeration. The operation of slow mixing is achieved in a basin commonly known as the flocculator. Factors affecting flocculation Type of turbidity Concentration of turbidity Type of coagulant Dosage of coagulant Temporal mean velocity gradient (G)
Ci
vil d
Flocculation methods: (i) Gravitation or Hydraulic methods (a) Horizontal flow baffled flocculator (b) Vertical flow baffled flocculator (c) Jet flocculator (ii) Mechanical methods (iii) Pneumatic flocculation Design Criteria for flocculator Depth of tank : 3 to 4.5 m Detention time : 10 to 40 minutes, normal 30 min Velocity of flow : 0.2 to 0.8 m/s, 0.4 m/s normal Total area of paddles : 10 to 25 % of cross sectional area of tank Peripheral velocity of blades : 0.2 to 0.6 m/s normal 0.3 to 0.4 m/s Velocity gradient (G) : 10 to75 s-1 Factor G.td : 104 to 105 Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
: 10 to36 kW/MLD : 0.15 to 0.25 m/s
Ci
vil d
ata
s.b
log
sp ot. in
Power consumption Outlet flow velocity
CD = 1.8 for flat blades Distance between paddle edge and side of the basin = 15 to 40 cm K=0.25 Relative velocity is 75% of paddle velocity i.e. vr = 0.75% x vp Area of paddles = length of blades x width x no. of blades in that compartment i.e. Ap = lb x w x n Distance between two paddles in same compartment (in plan) = about 1m Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
# Design a flocculator for design of flow to be treated equal to 300 m3/h. Assume suitable permissible values of various parameters of design. Assume a temperature of 20˚C. Solution: Design Parameters The following design parameters are assumed: Detention period : 20 minutes Avg. value of G : 40s-1 Speed of paddles : 4.5 rpm Area of paddles : 15 % of the cross sectional area of basin Velocity ratio k = 0.25 µ = 1.0087 x 10-3 N-s/m2 at 20˚C ρ = 998 kg/m3 at 20˚C Ratio of length to width of the tank = 2 Distance between paddle edge and side of the basin = 15 to 40 cm
Ci
vil d
ata
s.b
log
STEP 1 Computation of volume of flocculation tank Volume of tank V = Design flow x detention time = (300/60) x 20 = 100 m3 Let the depth of the tank = 0.4B Let the length of the tank = 2B B x 2B x 0.4B = 100, B = 5 m, L = 5 x 2 = 10 m, H = 0.4 x 5 = 2 m STEP 2 Computation of power required P = G2 x V x µ = (40)2 x 100 x 1.0087 x 10-3 = 161.4 watts STEP 3 Computation of velocity difference between the paddle and water Let us provide paddles attached to three horizontal shafts running parallel to the length. Let each shaft be located at mid depth of the tank. Let us provide four paddles to each shaft each running parallel to the shaft Distance between paddle edge and side of the basin (15 to 40 cm) = 20 cm Distance between adjacent paddles = 20 cm Total distance for clearance between three paddles = 4 x 20 cm = 80 cm Space remaining for three paddles = 5m – 0.80 m = 4.2 m Space for single paddle assembly = 4.2/3 = 1.4 = dia of single paddle assembly r = 1.4/2 = 0.7, vp = (2π x 0.7 x 4.5) / 60 = 0.3299 m/s vr = (1-k) vp = (1-0.25) x 0.3299 = 0.2474 m/s STEP 4 Computation of paddle size P = ½ x CD x ρ x Ap x vr3 , CD = 1.8 for flat blades Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
161.4 = ½ x 1.8 x 998 x Ap x (0.2474)3 Ap = 11.87 m2 There are total of 3 x 4 = 12 paddles, Area of each paddle = 11.87/12 = 0.989 m/s Length of each paddle = 4.8, width of each paddle = 0.989/4.8 = 0.206 m Provide 25 cm wide paddle with length of 4.8 m.
sp ot. in
Sedimentation: Sedimentation is the removal of suspended particles by gravitational settling Sedimentation tanks are designed to reduce velocity of flow of water so as to permit suspended solids to settle out of the water by gravity Plain sedimentation: When impurities are separated from water due to action of gravity alone then it is called plain sedimentation
log
Sedimentation with coagulation or clarification: When chemicals or other substances are added to induce the suspended solids to aggregation to form flocs then it is called as sedimentation with coagulation or clarification
s.b
Chemical precipitation: When chemicals are added to throw dissolved impurities out of solution it is called as chemical precipitation
ata
Discrete particles: A particle that does not alter its size, shape, and weight while settling in water is known as discrete particle
Ci
vil d
Types of settling: Type I: Discrete particle settling Particles settle individually without interaction with neighbouring particles. Type II: Flocculent Particles – Flocculation causes the particles to increase in mass and settle at a faster rate. Type III: Hindered or Zone settling –The mass of particles tends to settle as a unit with individual particles remaining in fixed positions with respect to each other. Type IV: Compression – The concentration of particles is so high that sedimentation can only occur through compaction of the structure. In water treatment Type – I and Type – II settlements are encountered
Visit : Civildatas.blogspot.in
log
sp ot. in
Visit : Civildatas.blogspot.in
Column test for a suspension exhibiting zone-settling behavior of all types of settling Type I Settling
Size, shape and specific gravity of the particles do not change with time.
Settling velocity remains constant.
s.b
ata
If a particle is suspended in water, it initially has two forces acting upon it: (1) force of gravity: Fg=ρpgVp (2) buoyant force quantified by Archimedes as: Fb=ρgVp
vil d
If the density of the particle differs from that of the water, a net force is exerted and the particle is accelerated in the direction of the force: Fnet=(ρp-ρ)gVp , This net force becomes the driving force
Ci
Once the motion has been initiated, a third force is created due to viscous friction. This force, called the drag force, is quantified by: Fd=CDApρv2/2, CD = drag coefficient, Ap = projected area of the particle Because the drag force acts in the opposite direction to the driving force and increases as the square of the velocity, acceleration occurs at a decreasing rate until a steady velocity is reached at a point where the drag force equals the driving force: (ρp-ρ)gVp = CDApρv2/2 Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
For spherical particles, Vp=πd3/6 and Ap=πd2/4
sp ot. in
Thus, v2= 4g(ρp-ρ)d 3CDρ Expressions for CD change with characteristics of different flow regimes. For laminar, transition, and turbulent flow, the values of CD are: CD = 24 (laminar) Re CD= 24 + 3 + 0.34 (transition) 1/2 Re Re CD= 0.4 (turbulent) Where Re is the Reynolds number: Re=vd
log
Reynolds number less than 1.0 indicate laminar flow, while values greater than 10 indicate turbulent flow. Intermediate values indicate transitional flow.
s.b
Stokes Flow For laminar flow, terminal settling velocity equation becomes: v= (p-)gd2 18 which is known as the stokes equation.
ata
Transition Flow Need to solve non-linear equations:
vil d
v2= 4g(p-)d 3 CD CD= 24 + 3 +0.34 1/2 Re Re Re=vd
Ci
Types of Sedimentation tanks Depending upon the types of operation there are two types (i) The Quiescent or fill and draw type (ii) The continuous flow type (i) Fill draw type Sedimentation tank is filled with incoming water and is allowed to rest for a 24 hours Suspended particles settle down at the bottom of the tank during rest The clear water is drawn out and the tank is cleaned which takes 6 to 12 hours Cycle of operation takes 30 to 36 hours Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
Minimum of three units are required for constant supply
s.b
log
(ii) Continuous flow type tank In factors controlling settling or sedimentation under gravity, velocity of flow can be controlled in continuous flow type tanks In continuous flow type tanks water flows at constant velocity in the tank The particles settle at bottom during flow of water before it reaches to tank outlet (a) Horizontal flow tank (b) Vertical flow tank The horizontal flow type tank is generally rectangular in plan with length twice as width and water flows at velocity 0.3 m/sec Vertical flow type tanks are deep circular or rectangular with hopper bottom
ata
Design of Horizontal flow sedimentation tank The objective of design is to achieve ideal conditions of equal velocity at all vertical points in the settling zone
Ci
vil d
Assumptions o With in sedimentation zone the particles similarly as it would happen in quiescent tank of equal depth o Flow is horizontal, steady with uniform velocity in all parts of settling zone for detention period o Concentration of suspended particles of all size is similar at vertical cross section at the inlet end o A particle is removed when it reaches the bottom of settling zone The settling basin can be divided onto four zones (i) inlet zone in which the influent stream disperse over the cross section at right angles to flow (ii) the settling zone (iii) bottom or sludge zone
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
log
sp ot. in
(iv) the outlet zone in which the water and remaining suspended particles assemble to be carried away to effluent conduit
Ci
vil d
ata
s.b
Let L and H be the length and depth of the settling zone. Let Q be discharge and B be width of the tank. The horizontal discharge velocity Vd is given by Vd = Q HB The time of horizontal flow t0 = L = LBH Vd Q Consider a particle entering the tank with vertical falling speed Vs. The time for falling through distance H will be H. when time of horizontal flow is equal Vs to time of fall it should be equal to time of horizontal flow So, H = LBH. From which Vs = Q = Q = surface flow rate Vs Q LB A Surface flow rate or over flow rate is numerically equal to flow divided by the plan area of the basin Vd = L , t0 = H Vs H Vs Particle with velocity greater than velocity Vs will settle before reaching to outlet end of tank. Time of horizontal flow is t0 = H is known as detention period Vs If smaller particle falling at speed of Vs’ < Vs enters the tank at point h, it will settle through only height h during the detention time t0 is given by H = t0 = LBH , h = LBH Vs’ = Vs’ .H Vs’ Q Q Vs Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
The particle will not settle if it enters above h. the ratio of removal of this particle size to that of settling value is given by Xr = h = Vs’ = Vs’ (Hazens equation) H Vs Q/A Hazens equation states that for discrete particles and unhindered settling, basin efficiency is solely a function of settling velocity of particles and of the surface area of the basin relative to the flow rate. Settling efficiency is independent of the basin depth and detention period
log
Design Elements 1. Detention period and displacement efficiency Detention time is theoretical time taken by a particle of water to pass between entry and exit of the settling tank t0 = Volume of tank Rate of flow Rectangular tank = BLH Q 2 Circular tank = d (0.011d + 0.785H) d = diameter of tank, H = depth at wall Q Actual detention period should be twice as the theoretical detention period
s.b
Flow through Period (td) Average time required for a batch of water to pass through the settling tank
ata
Displacement Efficiency (ηd) The ratio of flow through period to the detention period is called as displacement efficiency
vil d
Displacement efficiency = Flow through period = td (0.2to 0.5) Detention period t0
Ci
2. Over flow rate and surface loading The quantity of water passing per hour per unit horizontal area is known as the over flow rate or surface loading. Vs (cm/sec) = 1 Q 864000 A 3. Basin Dimension The surface area of the basin is determined on the basis of the overflow rate or surface loading rate Surface area A =
Volume of water in litres/ hour Surface loading rate in litres per hour/m2 Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Length to width ratio of rectangular tanks = 3:1 to 5:1 Depth = 2.5 to 5 m (preferred 3 m inclusive of sludge and free board) Horizontal velocity= 0.2 to 0.4 m/minute (0.3 m/minute) Bottom slope = 1% in rectangular and 8% in circular Slope of sludge hopper = 1.2:1 to 2:1 (vertical to horizontal)
sp ot. in
4. Inlet and outlet arrangements Inlet and outlet should not cause disturbances due to influent and effluent Great weight due to turbidity may cause sinking and rising at outlet which may cause back flow at inlet reducing detention period
Ci
vil d
ata
s.b
log
Inlet Ideal inlet properties (i) distribute water uniformly throughout width and depth of tank (ii) mix it with water in tank to prevent density current (iii) minimise large scale turbulence (iv) initiate longitudinal or radial flow to achieve high removal efficiency Inlet must face baffle, uniform velocity is achieved by passing water through dispersion wall with perforated holes or slots Slots are placed such that (i) velocity of flow through slots is about 0.2 to 0.3 m/s (ii) head loss is 1.7 times the velocity head (iii) diameter of the hole no to be larger than the thickness of the diffuser wall
Outlet Consists of (i) weirs, notches or orifices (ii) effluent trough or launder (iii) outlet pipe
Visit : Civildatas.blogspot.in
sp ot. in
Visit : Civildatas.blogspot.in
Weir frequently consists of V notches approximately 50 mm depth placed at 150 – 300 mm on centres with baffle provided in front of the weir to stop floating matter entering into effluent
log
Assuming the curve defined by water surface as parabolic and neglecting friction the equation formed
vil d
ata
s.b
H = h2 + 2q2 L2 n2 1/2 gb2h H = water depth at upstream of launder h = water depth at down stream end, at distance L q = discharge per unit length of weir b = width of launder or trough h = number of sides the weir receives the flow In absence of control device we assume that flow at the lower end of the launder will be at critical depth h = Q2 1/3 Q = total discharge in the launder = qL b2 g Normal weir loadings are up to 300 m3/day/m length
Ci
Scour velocity Flow velocity should not be more than the scour velocity which will cause uplift the particles in the sludge zone Scour velocity, Vd = √8β g (G-1) d f’ 0.04 for unigranular sand, 0.06 for non uniform sticky material f’ = 0.025 to 0.03(Darcy weisbach friction factor) 5. Sludge removal Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Sludge is settled particles in basin which is removed mechanically or manually When sludge quantity is less and cleaning is required once in 2 to 4 months When sludge is organic septic condition is encountered resulting in odour and foul smell So sludge is removed with rotating scrapers move sludge to collecting points from there it is sucked through pumps
sp ot. in
Details of Plain Sedimentation tanks Plain sedimentation tanks are in following shapes a) Rectangular tanks with Horizontal flow b) Circular tank with radial flow c) Hopper bottom with vertical flow
ata
s.b
log
(a) Rectangular tanks with Horizontal flow Rectangular sedimentation tanks are provided with baffles to avoid short circuiting Up and down, around the end baffle tanks are provided for sedimentation Rectangular sedimentation tanks are also designed without baffles but with sludge hopper and sloping floor Sludge is scrapped with scrappers and stored in sludge hopper From sludge hopper sludge is sucked through sludge pipe using sludge pump
Ci
vil d
Short circuiting If water currents permit a substantial portion of the water to pass directly through the tank with out being detained for intended time the flow is said to be short circuited
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Ci
vil d
ata
s.b
log
sp ot. in
(b) Circular tank with radial or spiral flow Circular tanks are costlier to install but installed with mechanical scrappers Circular tanks have radial or spiral flow The path of water is from distributor at the centre to decanting weir at the circumference The influent enters through a central pipe and raises upto the baffle box or influent well from where it flows radialy towards the circumference The racking arms move slowly to scrap sludge which is removed through the sludge pipe connected to the sludge pump In case of circular tank with spiral flow inlet is provided at the circumference and directed at an angle between a radius and a tangent The outlet is provided in the form of a submerged weir is also provided at the outer circumference but of short length The inlet velocity rotates the water in the tank and induces spiral path for water from inlet to outlet
Circular tank with spiral flow
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
ata
s.b
log
sp ot. in
(c) Hopper bottom tank with vertical flow Water enters through the centrally placed inlet pipe and is deflected downwards by the action of a deflection box Water travels downwards The sludge settles at the bottom of the hopper from where it is removed with the help of a sludge pipe connected to sludge pump In upward flow settling tank water enters at top centre and flows downwards through a mixing compartment Then the water passes through small openings upward through the outside compartment which has sloping side which reduces vertical flow The solids form blanket at the zone where the vertical velocity is reduced which is sufficient to sustain them The formed blanket is effective in straining out rising particle which are too small to settle against the current
Ci
vil d
Hopper bottom sedimentation tank Hopper bottom tank upward flow Sedimentation with Coagulation Particles in relatively dilute concentration with smaller size sometimes will not act as discrete particles (as the grit particles behave in grit chamber) but these particles will coalesce during sedimentation. As flocculation occurs, the size of the particle increases and it settles faster. The magnitude of flocculation will depend upon the opportunity for contact between the particles, which depends upon overflow rate, temporal mean velocity gradient in the system (representing mixing) and concentration and size of the particles. Although, settling rate of particle is independent of depth of basin, the basin depth will decide liquid detention time in the tank and sufficient depth should be provided for settling to separate it from sludge settled zone. The effect of these variables on settling can only be determined by sedimentation tests, and classical laws of sedimentation are not applicable, due to change in characteristics of the particle during settling. Settling column is used to determine the settling characteristics of the Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Ci
vil d
ata
s.b
log
sp ot. in
suspension of flocculant particles. A column with diameter of 15 cm and height of 3.0 m can give satisfactory results, with 5 to 6 ports provided over the height for sampling. The height of the tank should be ideally equal to side water depth of the settling tank for proper results. The solution containing suspended solids should be added in the column in such a way that uniform distribution of solid particles occur from top to bottom. Settling should takes place under quiescent conditions. It is important to maintain uniform temperature throughout the experimental column to avoid convection currents. At various time intervals, samples are withdrawn from the ports and analyzed for suspended solids. Percentage removal of solids is calculated for each sample analyzed and is plotted as a number (%) against time and depth. The curve of equal percentage removal is drawn between the plotted points. The efficiency of the sedimentation tank, with respect to suspended solids and BOD removal, is affected by the following: o Eddy currents formed by the inertia of incoming fluid, o Wind induced turbulence created at the water surface of the uncovered tanks, o Thermal convection currents, o Cold or warm water causing the formation of density currents that moves along the bottom of the basin, and o Thermal stratification in hot climates
Because of the above reasons the removal efficiency of the tank and detention time has correlation R = t/(a+b.t), where ‘a’ and ‘b’ are empirical constants, ‘R’ is expected removal efficiency, and ‘t’ is nominal detention time. To account for the non optimum conditions encountered in the field, due to continuously wastewater coming in and going out of the sedimentation tank, due to ripples formed on the surface of the water because of wind action, etc., the settling velocity (overflow rate) Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
obtained from the column studies are often multiplied by a factor of 0.65 to 0.85, and the detention time is multiplied by a factor of 1.25 to 1.50. This will give adequate treatment efficiency in the field conditions as obtained under laboratory test.
s.b
log
sp ot. in
Design Criteria Surface over flow rates = 12 – 18 m3/day/m2 for plain sedimentation tanks = 24 – 30 m3/day/m2 for sedimentation with coagulation Depth = 1.8 to 6m (normal 3-4.5m) Volume of tank = Detention time x discharge Volume of tank = Breadth x Length x Height (Rectangular) Volume of tank = D2(0.011D + 0.785H) D = diameter of tank, H = Height of tank at edge of the tank Detention time = 4-8 hrs for plain sedimentation tank Detention time = 2-4 hrs for coagulation sedimentation tank Breadth of tank = 10 – 12 metres Length of the tank = 1 to 6 times of breadth (normal 4 times of Breadth) Horizontal flow velocity = 0.15 – 0.9 m/min (normal 0.3 m/min) Sludge deposit heights for plain sedimentation tank = 0.8 – 1.2 m Free board = 0.5 m Surface area of Sedimentation tank = discharge or flow Surface over flow rate # Design a rectangular sedimentation tank to treat 2.4 million litres of raw water per day. The detention period may be assumed to be 3 hours.
ata
Raw water flow per day is 2.4 x 106 litres. Detention period is 3h. Volume of tank = Flow x Detention period = 2.4 x 103 x 3/24 = 300 m3 Assume depth of tank = 3.0 m. Surface area = 300/3 = 100 m2
vil d
L/B = 3 (assumed). L = 3B. 3B2 = 100 m2 i.e. B = 5.8 m L = 3B = 5.8 X 3 = 17.4 m Hence surface loading (Overflow rate) = 2.4 x 106 = 24,000 l/d/m2 < 40,000 l/d/m2 (OK) 100
Ci
# Design a circular sedimentation tank to treat 3 million litres per day. Assume detention period to be 4 hrs. Rate of flow per day = 3 x 106 litres. Detention period 4 hours Volume of tank = 3 x 106 x 4 = 500 m3 1000 x 24 Assume depth = 3 m. Surface area = 500 = 166.666 = 167 m2 3 Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
A circular sedimentation tank is generally provided with its bottom cone shaped with slope 1 vertical to 12 horizontal. For this condition volume is given by V = D2 (0.011D + 0.785H) D = Diameter, H = height in wall side 500 = 0.011D3 + 2.355 D2 0.011D3 + 2.355 D2 – 500 = 0, by solving Diameter, D = 14.1 m
sp ot. in
Surface overflow rate = 3x106 = 17964.0718 l/m2/d < 40000 l/m2/day 167 Hence safe
log
# Design a coagulation sedimentation tank with a continuous flow for treating water for a population of 45,000 persons with an average daily consumption of 135 L/person. Assume a surface loading rate of 0.9 m3m-2h-1 and that the weir loading rate is within acceptable limits. Solution Average consumption = 135 x 45,000 = 6,075,000 L/d.
506 m2.
s.b
Allow 1.8 times for maximum daily consumption: Maximum daily consumption = 1.8 x 6,075,000 = 10,935m3/d. Therefore, required surface area of the tank = (10,935/24)/0.9 = Assume minimum depth of tank = 3.5 m. Therefore, (settling) volume of the tank = 506 x 3.5 = 1772 m3.
ata
Assume a length to breadth ratio of the tank of 3.5:1. Therefore the breadth would be = 506/3.5B2 m = 12m
vil d
Therefore, length of tank = 3.5 x 12 = 42 m. Assuming a bottom slope of 1 in 60. Depth of the deep end (at the effluent end) = 3.5 + (1/60) x 42 = 4.2 m. Provide sludge deposit height of 0.8 m. and free board of 0.8 m Height of sedimentation tank = 0.8 + 0.8 + 3.5 = 5.1 Dimensions of sedimentation tank is = 42m x 12m x 5.1m
Ci
A floc chamber should be provided, at the entry to the tank, Assume detention time of 30 minutes, then Volume of floc chamber V = discharge x detention period = 10,935 x 30 = 228 m3 24 x 60 If the depth of floc chamber is 2.5 m and breadth of floc chamber is 12m then length of the floc chamber = 228 = 7.6m 12 x 2.5 Dimensions of floc chamber is = 7.6m x 12m x 2.5m Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Filtration It is a solid-liquid separation process in which the liquid passes through a porous medium to remove as much fine suspended solids as possible.
sp ot. in
Mechanical Straining • Simplest action during filtration. • Suspended particles having size more than that of filter voids are arrested and removed, when water passes through filter media. • Takes place in few centimetres of depth of filter media. Sedimentation • Finer particles are arrested by sedimentation. • Continuous voids of filter media acts as ‘tube settler’ i.e. shallow depth sedimentation tank. • All colloids are removed by this action
s.b
log
Biological Action • After few days of working of filter, upper grains of sand layer become coated with a reddish brown coloured sticky deposit. • It consists of organic matter and Fe, Mg, Al and silica. • Further after 2-3 weeks, a film consisting of algae and protozoa etc is developed. • This film is known as ‘dirty skin’ or ‘Schmutzdecke’. • Organic impurities in water are used as food by this film, thus removing the organic matter from water.
vil d
ata
Electrolytic Action • Particulate matter is removed by electrostatic action. • Charge on filter medium neutralizes charge on floc particles, thereby permitting the floc to be removed. • During back washing the electrostatically removed material is removed and thus charge on filter material is replaced.
Ci
Classification 1. Slow sand filter 2. Rapid sand filter - Gravity type - Pressure type
Filter differs with respect to i. Head required for filtration ii. Rate of filtration iii. Composition of filter media iv. Method and frequency of cleaning Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Filter media • Commonly used filter materials are i. Sand ii. Anthracite iii. Garnet sand or limenite iv. Other locally available material
sp ot. in
Sand • Cheapest and widely used • Sand should be free from clay, silt, loam and Suspended Solids and organic matter. • Effective size: -It is sieve size in mm through which 10% of sand by weight passes. • Uniformity coefficient (Cu):- Ratio of sieve size through which 60% of sand passes to the effective size of sand. i.e. Cu= D60/D10
ata
s.b
log
• Essentials of filter sand 1. Shall be hard 2. Shall be free from clay, fine particles, grains and dirt 3. Ignition loss should not exceed 0.7% 4. Soluble fraction in HCl shall not exceed 5%. 5. Gs= 2.55 to 2.65 6. Wearing loss shall not exceed 7% 7. Effective size shall be i. 0.2 to 0.3 mm for slow sand filters ii. 0.45 to 0.7 mm for rapid sand filters 8. The uniformity coefficient shall be i. 3 to 5 for slow sand filter ii. Not less than 1.3 and not more than 1.7 for rapid sand filter
vil d
Anthracite • Substitute for sand • Can be used in conjunction with sand • Cost is more as compared to sand
Ci
Garnet sand • Heavier than normal sand (Gs = 4.2) • Used in mixed media filters. Locally Available Material • Shredded coconut husk, burnt rice husk, crushed glass and metallic ores can be used as filter media
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Gravel • The layers of sand may be supported on gravel, which permits the filtered water to move freely to the under drains, and allows the wash water to move uniformly upwards. • Should be hard, durable, rounded, free from flat or long pieces and impurities
sp ot. in
SLOW SAND FILTER 1. Enclosure tank • Slow Sand Filter is open basin, rectangular shape and built below finished ground level • Floor has Bed slope of 1:100 to 1:200 towards central drain • Surface area (As) of tank varies from 50 to 1000 m2 • Filtration rate – 100 to 200 lit/m2/hr • Depth – 2.5 to 4 m
vil d
ata
s.b
log
2. Filter media: Sand • Thickness of sand layer - 90 to 110 cm • Effective size – 0.2 to 0.35 (Common value -0.3) • Coefficient of uniformity – 2 to 3 (Common value - 2.5)
Ci
3. Base material: Gravel • Thickness of gravel bed - 30 to 75 cm Layer Topmost
Dept h Size in mm 15 cm 3 to 6
Intermediate Intermediate
15 cm 15 cm
6 to 20 20 to 40
Bottom
15 cm
40 to 65
4. Under drainage system • Base material and filter media are supported by under drainage system. Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
• Under drainage system collects filtered water and delivers it to thereservoir • Laterals – earthenware pipes of 7.5 to 10 cm dia. • Spacing of laterals- 2 to 3 m c/c
sp ot. in
5. Appurtenances Devices are required for i. Measuring head loss through filter media ii. Controlling depth of water above filter media iii. Maintaining constant rate of filtration through the filter
ata
s.b
log
Working of slow sand filter • In a slow sand filter impurities in the water are removed by a combination of processes: sedimentation, straining, adsorption, and chemical and bacteriological action.
Ci
vil d
• During the first few days, water is purified mainly by mechanical and physical-chemical processes. The resulting accumulation of sediment and organic matter forms a thin layer on the sand surface, which remains permeable and retains particles even smaller than the spaces between the sand grains. • As this layer (referred to as “Schmutzdecke”) develops, it becomes living quarters of vast numbers of microorganisms which break down organic material retained from the water, converting it into water, carbon dioxide and other oxides. • Most impurities, including bacteria and viruses, are removed from the raw water as it passes through the filter skin and the layer of filter bed sand just below. • The purification mechanisms extend from the filter skin to approx. 0.3-0.4 m below the surface of the filter bed, gradually decreasing in activity at lower levels as the water becomes purified and contains less organic material.
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
• When the micro-organisms become well established, the filter will work efficiently and produce high quality effluent which is virtually free of disease carrying organisms and biodegradable organic matter. • They are suitable for treating waters with low colors, low turbidities and low bacterial contents.
s.b
log
sp ot. in
RAPID SAND FILTER (GRAVITY TYPE) ESSENTIAL FEATURES
Ci
vil d
ata
Enclosure tank • Smaller in size, therefore can be placed under roof. • Rectangular in shape and constructed of concrete or masonry. • Depth – 2.5 to 3.5
• Surface area – 20 to 50 m2 Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
• L/B ratio – 1.25 to 1.35. • Designed filtration rate are 3000 to 6000 lit/m2/hr
ata
s.b
log
sp ot. in
Filter media • Should be free from dirt, organic matter and other Slow Sand. • It should be hard and resistant. • Depth of sand media – 0.6 to 0.9 m • Effective size – 0.35 to 0.6 mm (Common value 0.45) • Uniformity coefficient – 1.2 to 1.7 (Common value -1.5)
Ci
vil d
Estimation of sand depth • The depth of sand bed should be such that flocs should not break through the sand bed. • Depth varies from 60 to 90 cm • Min depth required is given by Hudson’s formula [ (q . D3. H) / l] = Bi x 29323 Where, • q = Filtration rate in m3/m2/hr [Assumed filtration rate x Factor of safety (2)] (Factor of safety 2 is taken to cater emergency situation) • D = sand size in mm • H = terminal head loss in m • l = depth of sand bed in m • Bi = Break through index= 4 x 10-4to 6 x 10-3
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Base material • Depth 45 to 60 cm
Layer topmost Intermediate Intermediate
Dept h Size in mm 15 cm 3 to 6 15 cm 15 cm
6 to 12 12 to 20
sp ot. in
Bottom 15 cm 20 to 50 Estimation of gravel size gradation • To start with, a size gradation of 2 mm at top and 50 mm at bottom is assumed. • The required depth (l) in cm of a component of gravel layer of size d (mm) can be computed by following equation l = 2.54. K. (log d) K can be taken as 12 d = gravel size in mm
s.b
Ci
vil d
ata
Appurtenances 1. Wash water troughs 2. Air compressors 3. Rate control device
log
Under drainage system • Objectives of under drainage system 1. To collect filtered water uniformly over the area of gravel bed 2. It provides uniform distribution of back wash water without disturbing or upsetting gravel layer and filter media
WORKING AND BACKWASHING OF Rapid Sand Filter • All valves are kept closed except valves A and B. • Valve A is opened to permit water from clarifier Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
s.b
log
sp ot. in
• Valve B is opened to carry filtered water to clear water sump • Head of 2m over sand bed is maintained • Designed filtration rate are 3000 to 6000 lit/m2/hr • Filter run depends on quality of feed water • Filter run may range between less than a day to several days • Objective of backwash is to remove accumulated particles on the surface and within the filter medium • Backwash is performed using wash water or air scouring.
ata
Back washing • Filter is back washed when head loss through it has reached the maximum permissible. • RSF are washed by sending air and water upwards through the bed by reverse flow through the collector system. • 2% - 4% filtered water is used for backwashing
Ci
vil d
Steps in back washing 1. Close influent valve A 2. Close effluent valve B 3. Open air valve F, so that air blows at rate of 1 to 1.5 m 3free air /min/m2of bed area for @ 2 to 3 min. this will break up the scum and loosen the dirt. 4. Close the air valve F and open the wash water valve E gradually to prevent the dislodgement of finer gravel. 5. Open the wastewater valve D to carry wash water to drain. Continue backwashing till wash water appears fairly clear. 6. Close the wash water valve E. Close the wastewater valve D. wait for some time till all matter in bed settles down. 7. Open valve A slightly, open valve C for carrying filtered water to drains for few minutes. Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
8. Close the valve C and open valve B. Open valve A completely to resume normal filtration
s.b
log
sp ot. in
Negative head and filter troubles • When clean bed is put into operation the loss of head will be small usually in order of 15 to 30 cm. • During filtration impurities get arrested in the voids and head loss goes on increasing. • Loss of head can be measured by using two piezometric tubes as shown in figure
vil d
ata
• As thickness or depth of suspended matter on the sand bed increases, the head loss increased. • A stage comes when frictional resistance exceeds the static head above the sand bed. • At this stage, lower parts of sand bed and under drainage system are under partial vacuum or negative head. • Because of negative head water is being sucked rather than being filtered. • In Rapid Sand Filter head loss may be 2.5 to 3.5 m • Permissible negative head may be 0.8 to 1.2 m. • Filter run is terminated and filter is then backwashed when these values are reached. • Frequency of backwashing is 2-4 days for Rapid Sand Filter in normal conditions
Ci
FILTER TROUBLES Following filter troubles are commonly observed 1. Cracking and clogging of filter bed 2. Formation of mud balls 3. Air binding 4. Sand Incrustation 5. Jetting and Sand boils 6. Sand leakage Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
1. Cracking and clogging of filter bed • Surface clogging and cracking are usually caused by rapid accumulation of solids on the top of filter media. • Cracks are more at wall junctions.
s.b
log
2. Formation of mud balls • Mud balls are formed because of conglomeration of turbidity, floc, sand and other binders. • Formed because of insufficient washing of sand grains. • Size may be pea size to 2 to 5 cm or more in dia.
vil d
ata
3. Air binding • It is caused by release of dissolved gases and air from water to form bubbles. • These bubbles occupy void space of the filter media sand and drainage system. • It is caused by negative head loss, warm water and increased DO in water. • It can be minimized by avoiding excess head loss, warming of water, control of algal growth and avoiding super saturation of water with air.
Ci
4. Sand Incrustation • It occurs due to accumulation of sticky gelatinous material or crystallization of calcium carbonate. • Sand grains enlarge in size and effective size changes • Carbonization of water can be done to prevent this problem. • Some times Sodium hexa-meta Phosphate can be added to keep calcium carbonate in dissolved state 5. Jetting and Sand boils • These are produced when during backwashing water follows path of least resistance and break through to the scattered points due to small differences in porosity and permeability. Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
• Jetting can be avoided by surface wash or air scour. • Use of 8 cm thick layer of coarse garnet is also recommended.
vil d
ata
s.b
log
6. Sand leakage • It results when smallest gravels are displaced during backwashing. • Water will enter the under-drainage system unfiltered. • It can be reduced by properly proportioning of sand and gravel layer. • In between sand and gravel garnet layer can be used to tackle this type of problem.
Ci
Comparison between Slow and Rapid sand filter Item Slow sand Filter Rate of filtration 100 to 200 lit/m2/hr Loss of head Surface area Coagulation
15 cm initial to 100 cm final large Not required
Rapid sand Filter 3000 to 6000 lit/m2/hr 30 cm initial to 3 m final small Required Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Filter media of sand
Base material of Gravel Under drainage system
Effective size –0.2 to 0.35 and Cu= 2 to 3 Depth – 105 cm Size – 3 to 65 mm Depth – 30 to 75 cm Split tile laterals or perforated pipe laterals Scrapping of top layer 15 to 25 mm
Amount of wash water
0.2 to 0.6 % of filtered water 1 to 2 months
Penetration of Suspended Solids Further treatment needed Efficiency
Superficial Chlorination
log
Period of cleaning
sp ot. in
Method of cleaning
Depreciation cost
Relatively low
s.b
Skilled supervision
Very efficient in bacterial removal but can not remove colour and turbidity High initial cost Not flexible in meeting variations in demand Not required
Chlorination
Less bacterial removal efficiency but can remove colour and turbidity Less initial cost Quite flexible in meeting variations in demand Required as it involves backwashing Relatively high
vil d
ata
Economy Flexibility
Effective size – 0.35 to 0.60 and Cu= 1.2 to 1.7 Depth – 75 cm Size – 3 to 40 mm Depth – 60 to 90 cm Perforated of laterals with nozzles or strainer system Backwashing with compressed air and water 2 to 4 % of filtered Water 2 to 3 days (24 hrs usually) Deep
Ci
Problems Slow sand filtration Design criteria: Floor bed slope = 1:100 to 1:200 Surface area = 50 – 1000m2 Filtration rate = 100 – 200 litres/m2/hr Depth = 2.5 to 4m Sand layer for filtration = 90 – 110cm Base material with under drain = 30 to 75 cm Under drainage system: Lateral pipe diameter = 7.5 – 10 cm Spacing of laterals = 1.5 – 3 m centre to centre Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Spacing of holes in lateral pipes = 0.15 m Size of holes in lateral pipes = 3mm Maximum velocity in manifold = 0.3 m/s Manifold pipe area = 2 x Cross sectional area of lateral pipes Free board = 0.5m Total depth of filter = free board + supernatant water + sand layer + Base material with under drain
sp ot. in
# Design a slow sand filter for a town of population 60,000 provided water supply at a rate of 160 lpcd. Take filtration rate as 2.5 litres per minute per sq. metre. L/B ratio is 2. Maximum demand as 1.8 times as average demand. Solution: Given, population = 60,000, lpcd= 160, L = 2B, Maximum demand = 1.8, Filtration rate = 2.5 l/min/m2 = 2.5 x 10-3 m3/min/m2, water requirement = 60000 x 160 = 9.6 MLD
ata
s.b
log
Maximum demand = 9.6 x 1.8 = 17.28 MLD = 17280 m3/day = 12 m3/min Area of filter = 12 = 4800m2 2.5 x 10-3 Since one filter bed maximum area = 1000m2. Divide the available area by 5. Area per filter bed = 4800 = 960 m2 5 Length to breadth ratio = 2:1, L= 2B, L x B = 960 m2. 2B2 = 960, B = 21.9 = 22m L= 44m Area per filter = 44 m x 22 m = 968m2 Assume sand layer of 100 cm, Base material of 50cm with under drains
Ci
vil d
Under drain system Provide lateral pipe diameter = 8 cm, Cross section area of lateral pipe = 50.27cm2 Manifold pipe area = 2 x Cross section area of lateral pipe = 100.54 cm2 Diameter of manifold pipe = 11.32= 12cm Lateral spacing = 2m centre to centre Hole spacing of lateral pipe = 0.15 m Size of holes in lateral pipes = 3mm Velocity of water in lateral and main pipes = 0.2 m/s < 0.3 m/s Total height of filter = free board + supernatant water + sand layer + base material = 0.5 + 1 + 1 + 0.5 = 3m < 4.5m Rapid Sand filter Design Criteria Surface area – 20 to 50 m2 Length to breadth ratio = 1.25:1 – 1.35:1 Rate of filtration = 3000 – 5000 litres/m2/minute Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
log
sp ot. in
Maximum loss of head = 2.5 – 3m Under drains Length of lateral pipe > 60 Diameter Diameter of perforations in lateral pipe = 6mm and 13mm at spacing of 7.5 cm and 20cm respectively Total area of perforation = 0.2% – 0.3% Total filter area Total area of perforations = 0.25 for diameter of 6mm perforations Total area of lateral pipe = 0.50 for diameter of 13mm perforations Spacing of laterals = 30 cm maximum Total area of manifold = 1.75 – 2 times the sum of the cross sectional area of laterals Rate of washing = 15 – 90 cm rise per minute. Amount of wash water 2 to 4 percent of the total volume of water filtered Time of washing = 30minutes between 24 to 48 hours Wash water pressure = 0.4kg/cm2 Maximum permissible velocity in the manifold = 1.8 – 2.4 m/s Problem: Design a rapid sand filter to treat 10 million litres of raw water per day allowing 0.5% of filtered water for backwashing. Half hour per day is used for backwashing. Assume necessary data.
s.b
Solution: STEP: 1
ata
Total filtered water = 10.05 x 106 = 0.42766 Ml / h 24 - 0.5 Let the rate of filtration be 5000 l / h / m2 of bed.
vil d
Area of filter = 10.05 x 106 x 1 = 85.5 m2 23.5 5000
Provide two units. Each bed area 85.5/2 = 42.77. L/B = 1.3; 1.3B2 = 42.77 m2 B = 5.75 m ; L = 5.75 x 1.3 = 7.5 m
Ci
Assume depth of sand = 50 to 75 cm. STEP: 2
Under drainage system: Total area of holes = 0.2 to 0.5% of bed area. Assume 0.2% of bed area = 0.2 x 42.77 = 0.086 m2 100 Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Area of lateral = 2 (Area of holes of lateral) Area of manifold = 2 (Area of laterals) So, area of manifold = 4 x area of holes = 4 x 0.086 = 0.344 = 0.35 m2. Diameter of manifold = x 0.35 1/2 = 66 cm
Length of lateral = (5.75 - 0.66)/2 = 2.545 m.
sp ot. in
Assume c/c of lateral = 30 cm. Total numbers = 7.5/ 0.3 = 25 on either side. (50 nos)
C.S. area of lateral = 2 x area of perforations per lateral. Take dia of holes = 13 mm Number of holes: n (1.3)2 = 0.086 x 104 = 860 cm2 4 n = 4 x 860 = 648, say 650 (1.3)2
log
Number of holes per lateral = 650/50 = 13
Area of perforations per lateral = 13 x (1.3)2 /4 = 17.24 cm2 Spacing of holes = 2.545/13 = 19.5 cm.
s.b
C.S. area of lateral = 2 x area of perforations per lateral = 2 x 17.24 = 34.5 cm2. Diameter of lateral = (4 x 34.51/2 = 6.63 cm
ata
Check: Length of lateral < 60 d = 60 x 6.63 = 3.98 m. l = 2.545 m (Hence acceptable). STEP: 3
vil d
Back washing
Rising wash water velocity in bed = 50 cm/min. Wash water discharge per bed = (0.5/60) x 5.75 x 7.5 = 0.36 m3/s.
Ci
Velocity of flow through lateral = 0.36 Total lateral area Manifold velocity =
0.36 0.35
= 0.36 x 10 4 = 2.08 m/s (ok) 50 x 34.5
= 1.02 m/s < 2.25 m/s (ok)
STEP: 4 Washwater gutter Discharge of wash water per bed = 0.36 m3/s. Size of bed = 7.5 x 5.75 m. Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Assume 3 troughs running lengthwise at 5.75/3 = 1.9 m c/c. Discharge of each trough = Q/3 = 0.36/3 = 0.12 m3/s. Q =1.71 x b x h3/2 Assume b =0.3 m
sp ot. in
h3/2 = 0.12 = 0.234 1.71 x 0.3 h = 0.378 m = 37.8 cm = 40 cm
= 40 + (free board) 5 cm = 45 cm; slope 1 in 40 STEP: 5 Clear water reservoir for backwashing
log
For 4 times filter capacity, Capacity of tank = 4 x 5000 x 7.5 x 5.75 x 2 = 1725 m3 1000 Assume depth d = 5 m. Surface area = 1725/5 = 345 m2 L/B = 2; 2B2 = 345; B = 13 m & L = 26 m.
s.b
Dia of inlet pipe coming from two filter = 50 cm.
Velocity <0.6 m/s. Diameter of wash water pipe to overhead tank = 67.5 cm.
ata
Air compressor unit = 1000 l of air/ min/ m2 bed area.
For 5 min, air required = 1000 x 5 x 7.5 x 5.77 x 2 = 4.32 m3 of air.
Ci
vil d
Disinfection Partial destruction and inactivation of disease-causing organisms from exposure to chemical agents (e.g., chlorine) or physical processes (e.g.,UV irradiation). (or) A process that eliminates a defined scope of microrganisms, except most spores, viruses and prions. The purpose of disinfection prevents transmission of certain microorganisms with objects, hands or skin and prevent spreading the infection Principle of Disinfection Decontamination- removal of microorganisms contaminating an object Preservation- preventing methods of microbe caused spoilage of susceptible products (pharmaceuticals, foods) Sanitisation - removal of microbes that pose a threat to the public health, food industry, water conditioning sanitizer - an agent, usually a detergent, that reduces the numbers of bacteria to a safe level Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Aseptic techniques- prevent microbial contamination of materials or wounds Antisepsisdisinfection of living tissues (e.g., in a wound), achieved through the use of antiseptics Antiseptics are applied (do not kill spores) to reduce or eliminate the number of bacteria from the skin Disinfection methods Chemical agents Alcohols Aldehydes Halogens Phenols Surfactants Heavy metals Dyes Oxidants
sp ot. in
Physical methods Boiling and pasteurization Ultraviolet radiation
ata
s.b
log
Factors influencing Disinfection Types of organisms Number of organisms Concentration of disinfecting agent Presence of organic material (e.g., serum, blood) Nature (composition) of surface to be disinfected Contact time Temperature pH Biofilms Compatibility of disinfectants and sterilants
vil d
Sterilization Total destruction of disease-causing germs and other organisms. physical methods are used mainly to achieve sterilization
Ci
Sterilization methods Physical methods Moist heat in autoclaves Dry-heat in ovens Gamma irradiation Filtration Plasma sterilization
Chemical agents Ethylene oxide Glutaraldehye (high concentration)
Methods of Disinfection (a) Physical methods (i) Boiling of water (ii) Solar Disinfection Visit : Civildatas.blogspot.in
(b)
Visit : Civildatas.blogspot.in
Chemical methods
(a) Physical methods Boiling This is the most effective method of killing bacteria but impracticable in large scale. Most of bacteria are destroyed when the water has attained of about 80˚C temperature. Prolonged boiling is unnecessary and wasteful
sp ot. in
Solar Disinfection Solar disinfection is a thermal process consisting of raising water temperature for a long enough period of time in containers that have been prepared to absorb the heat generated by solar radiation for disinfection of water
Ci
vil d
ata
s.b
log
Installation requirements Equipment Installation and installation requirements Solar heaters Solar heaters are fairly easy to install or to adapt to any other installation. All that is needed is to raise the hot water collector tank about 60 cm above the highest point of the collector. No special pressure is required for their operation. It is enough for the water feeding tank to be placed next to the collector, which should be on a slant approximately equivalent to the latitude of the site (between 15° and 35º, for example) and face the sun. Solar stoves These devices can be easily installed anywhere. Before and adopting this method, however, it is important to perform concentrators some tests by taking the water temperature after four or five hours (in the case of the stoves). The water is drinkable only if the average temperature is always above 60 °C. If solar concentrators are well built, they should disinfect water more by boiling than by pasteurizing. Solar stills No special requirements need to be met in the case of solar stills, which are very simple devices with no movable parts. It is important to keep animals away from the equipment, however. Bottles and Solar disinfection requires clean water with very little containers turbidity. Otherwise, it must be filtered beforehand using a household sand filter or very fine fabric. The bottles can be placed on any reflecting surface, such as aluminium foil. The use of coloured soft drink bottles is not recommended.
Visit : Civildatas.blogspot.in
Ci
vil d
ata
s.b
log
sp ot. in
Visit : Civildatas.blogspot.in
Operation and maintenance Equipment Operation and maintenance Solar heaters Operation of this equipment is simple; all that needs to be Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
ata
Bottles and containers
s.b
log
Solar stills
sp ot. in
Solar stoves and concentrators
done is to open the line valve during the day and close it at night. Its maintenance consists of keeping the collector cover clean; dirt reduces the amount of radiation that can reach the collector. The frequency of cleaning will depend on the degree of atmospheric pollution. The use of acrylic covers is not recommended because they are easily scratched and deformed. To operate this device, place the pot inside the solar stove and direct the sun’s rays to the inside of the box using the reflector. It is very easy to maintain. All that needs to be done is to keep the inside, glass and reflectors clean. To keep the water clean, it is advisable to leave it in the covered container until it is to be used. This system requires feeding the still with the water for treatment, either continuously or discretely –in other words– in batches. Rural families tend to use the latter method. Otherwise, the systems can be used by combining it with preheating using a solar heater. Common household stills on sunny days produce between three and five litres a day per square meter. This is equivalent to a reduction in the depth of the distillant of from 0.3 to 0.5 cm/day, which means that the feeding process can be done once a day. The water should be either drunk or thrown out within the following 24 hours. The plastic container must be very clean before the water it contains can be purified. In this case, as in all of those described above, the disinfected water must be kept in the same or another closed container in a cool place.
Ci
vil d
Monitoring At effluent temperatures of over 55 ºC, total coliform inactivation has been demonstrated in 99% of the cases. For safety reasons, however, the golden rule is to have a margin of safety and to set 65 ºC as the minimum temperature for disinfection. Monitoring of these systems should confirm that the water at the outlet of any of these systems or following treatment reached 65 ºC. In as much as solar heaters were not designed for water disinfection, but merely to heat it, there is no way to check whether the temperature reached the pasteurization point. Therefore, it would be advisable to install a thermostat connected to a valve that would allow the water passage only at a temperature of over 65 ºC. A thermometer can be attached to the cover of solar stoves or bottles; in other cases, bottles can be fitted with small ampoules containing a substance that will melt at a temperature of above 65 °C, ensuring that the required pasteurization temperature has been attained. Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Disadvantages Cannot be used on cloudy or rainy days. Offer no residual protection
vil d
ata
s.b
log
sp ot. in
Advantages and disadvantages of solar disinfection Equipment Advantages Solar heaters Not dependent on conventional energy, whose cost rises with the growing demand. Avoid the use of toxic chemicals. Require relatively simple and low-cost equipment that is easily recovered and provides drinking water for many years. Not environmentally damaging. Solar stoves Do not consume firewood and thus help to and avoid deforestation and erosion in rural concentrators areas. It has been calculated that approximately one kilogram of firewood is needed to raise one litre of water to a boiling point. Nor do they use fossil fuels. This is particularly useful in the rural area, where it is difficult to obtain gas. Do not smoke like open fires that can cause respiratory diseases. Not expensive and easy to build. Bottles and Extremely simple and inexpensive. containers Easily accepted by the communities.
Twice as slow as conventional stoves. Cannot be used on cloudy or rainy days. Provide no residual protection.
Offer no residual protection. Require clean water. Cannot be used to disinfect large volumes of water.
Ci
(b) Chemical Methods Use of Disinfectants as Chemical Oxidants Oxidation is a chemical reaction where electrons are transferred from one species (the reducer) to another species (the oxidant) Disinfectants are used for more than just disinfection in drinking water treatment. While inactivation of pathogenic organisms is a primary function, disinfectants are also used oxidants in drinking water treatment for several other functions: 1. Minimization of Disinfection Byproducts formation : Several strong oxidants, including potassium permanganate and ozone, may be used to control DBP Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
2. Prevention of re-growth in the distribution system and maintenance of biological stability; – Removing nutrients from the water prior to distribution; – Maintaining a disinfectant residual in the treated water; and – Combining nutrient removal and disinfectant residual maintenance 3. Removal of color: Free chlorine is used for color removal. A low pH is favored. Color is caused by humic compounds, which have a high potential for DBP formation 4. Improvement of coagulation and filtration efficiency; a. Oxidation of organics into more polar forms; b. Oxidation of metal ions to yield insoluble complexes such as ferric iron complexes; c. Change in the structure and size of suspended particles.
log
5. Oxidation is commonly used to remove taste and odor causing compounds. Because many of these compounds are very resistant to oxidation, advanced oxidation processes (ozone/hydrogen peroxide, ozone/UV, etc.) and ozone by itself are often used to address taste and odor problems. The effectiveness of various chemicals to control taste and odors can be site-specific.
s.b
6. Removal of Iron and Manganese Oxidant
Iron (II) (mg/mg Fe) 0.62
Manganese (II) (mg/mg Mn) 0.77
Chlorine Dioxide, ClO2
1.21
2.45
Ozone, O3
0.43
0.88*
Oxygen, O2
014
0.29
Potassium Permanganate, KMnO4
0.94
1.92
vil d
ata
Chlorine Cl2
Ci
7. Prevention of algal growth in sedimentation basins and filters: Prechlorination will prevent slime formation on filters, pipes, and tanks, and reduce potential taste and odor problems associated with such slimes. Factors affecting disinfection effectiveness • Time • pH • Temperature • Concentration of the disinfectant • Concentration of organisms • Nature of the disinfectant Visit : Civildatas.blogspot.in
• •
Visit : Civildatas.blogspot.in
Nature of the organisms to be inactivated Nature of the suspending medium
vil d
ata
s.b
log
sp ot. in
Chlorine Chlorine has many attractive features that contribute to its wide use in the industry. Four of the key attributes of chlorine are that it: • Effectively inactivates a wide range of pathogens commonly found in water; • Leaves a residual in the water that is easily measured and controlled; • Is economical; and • Has an extensive track record of successful use in improving water treatment operations There are, however, some concerns regarding chlorine usage that may impact its uses such as: • Chlorine reacts with many naturally occurring organic and inorganic compounds in water to produce undesirable Disinfectant By Products; • Hazards associated with using chlorine, specifically chlorine gas, require special treatment and response programs; and • High chlorine doses can cause taste and odor problems. • Chlorine purposes in water treatment • Taste and odor control; • Prevention of algal growths; • Maintenance of clear filter media; • Removal of iron and manganese; • Destruction of hydrogen sulfide; • Bleaching of certain organic colors; • Maintenance of distribution system water quality by controlling slime growth; • Restoration and preservation of pipeline capacity; • Restoration of well capacity, water main sterilization; and • Improved coagulation by activated silica. Chlorine Chemistry • Chlorine gas hydrolyzes rapidly in water to form hypochlorous acid
Ci
Cl2+ H2O = H++ Cl- + HOCl (hypochlorous acid)
•
Hypochlorous acid is a weak acid (pKa of about 7.5), meaning it dissociates slightly into hydrogen and hypochlorite ions HOCl = H++ OCl-
•
Between a pH of 6.5 and 8.5 this dissociation is incomplete and both HOCl and OCl- species are present to some extent (White, 1992). Below a pH of 6.5, Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
•
no dissociation of HOCl occurs, while above a pH of 8.5, complete dissociation to OCl- occurs. As the germicidal effects of HOCl is much higher than that of OCl-, chlorination at a lower pH is preferred.
log
sp ot. in
Effect of pH on relative amount of hypochlorous acid and hypochlorite ion at 20°C.
Ci
vil d
ata
s.b
Commonly Used Chlorine Sources Sodium hypochlorite and calcium hypochlorite are the most common sources of chlorine used for disinfection of onsite water supplies. • Sodium Hypochlorite (common household bleach) • Sodium hypochlorite is produced when chlorine gas is dissolved in a sodium hydroxide solution. NaOCl (sodium hypochlorite) + H2O = Na++ OH-+ HOCl • Clear to slightly yellow colored liquid with a distinct chlorine odor. • Common laundry bleach - 5.25 to 6.0 percent available chlorine, when bottled. • Do not use bleach products that contain additives such as surfactants, thickeners, stabilizers, and perfumes. • Always check product labels to verify product content and use instructions. • Higher concentrations of chlorine in sodium hypochlorite solutions are generally not available. • Above 15 percent, the stability of hypochlorite solutions is poor, and decomposition and the concurrent formation of chlorate is of concern • Sodium hypochlorite solutions are of an unstable nature due to high rates of available chlorine loss • Over a period of one year or less, the amount of available chlorine in the storage container may be reduced by 50 percent or more. • Solutions more than 60 days old should not be counted upon to contain the full amount of available chlorine originally in solution • Swimming pool chlorine - 10.0 to 12.0 percent available chlorine. Visit : Civildatas.blogspot.in
•
sp ot. in
•
Visit : Civildatas.blogspot.in
The stability of hypochlorite solutions is greatly affected by heat, light, pH, initial chlorine concentration, length of storage, and the presence of heavy metal cations These solutions will deteriorate at various rates, depending upon the specific factors: • The higher the concentration, the more rapidly the deterioration. • The higher the temperature, the faster the rate of deterioration. • The presence of iron, copper, nickel, or cobalt catalyzes the deterioration of hypochlorite. Iron is the worst offender
Calcium hypochlorite is formed from the precipitate that results from dissolving chlorine gas in a solution of calcium oxide (lime) and sodium hydroxide. Ca(OCl)2 + 2H2O = Ca+++ 2OH-+ 2HOCl
•
log
Calcium Hypochlorite • Dry white powder, granules, or tablets - 60 to 70 percent available chlorine - 12month shelf life if kept cool and dry - If stored wet, looses chlorine rapidly and is corrosive. A chlorine test kit should be used to check the final chlorine residual in a prepared chlorine solution to assure that you have the concentration intended.
Ci
vil d
ata
s.b
• Sodium Hypochlorite or Calcium Hypochlorite • Sodium hypochlorite is more effective • This may be associated with the quality of the ground water in the well being treated rather than with the source of the chlorine itself. • If there is an abundance of calcium based materials in both bedrock wells. Calcium hypochlorite already has a high concentration of calcium. • At 180 ppm of hardness, water is saturated with calcium to the point that it precipitates out of the solution, changing from the dissolved state to a solid state. • Introducing a calcium hypochlorite solution into a calcium rich aquifer can cause the formation of a calcium carbonate (hardness) precipitate that may partially plug off the well intake. • Sodium hypochlorite does not have the tendency to create the precipitate. • If the calcium carbonate concentration in the ground water is above 100 ppm (mg/l), the use of sodium hypochlorite is recommended instead of calcium hypochlorite. Typical Chlorine Dosages at Water Treatment Plants
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
• •
monochloramine (NH2Cl), dichloramine (NHCl2 ), and trichloramine (NCl3), each contribute to the total (or combined) chlorine residual in a water. The terms total available chlorine and total oxidants refer, respectively, to the sum of free chlorine compounds and reactive chloramines, or total oxidating agents. Under normal conditions of water treatment, if any excess ammonia is present, at equilibrium the amount of free chlorine will be much less than 1 percent of total residual chlorine.
log
•
sp ot. in
DISINFECTANT DEMAND REACTIONS • Reactions with Ammonia • In the presence of ammonium ion, free chlorine reacts in a stepwise manner to form chloramines
Ci
vil d
ata
s.b
Chlorine residual • Chlorine persists in water as ‘residual’ chlorine after dosing and this helps to minimize the effects of re-contamination by inactivating microbes which may enter the water supply after chlorination. It is important to take this into account when estimating requirements for chlorination to ensure residual chlorine. • The level of chlorine residual required varies with type of water supply and local conditions. • In water supplies which are chlorinated there should always be a minimum of 0.5mg/l residual chlorine after 30 minutes contact time in water. • Where there is a risk of cholera or an outbreak has occurred the following chlorine residuals should be maintained: – At all points in a piped supply 0.5mg/l – At standposts and wells 1.0mg/l – In tanker trucks, at filling 2.0mg/l • In areas where there is little risk of a cholera outbreak, there should be a chlorine residual of 0.2 to 0.5 mg/l at all points in the supply. This means that a chlorine residual of about 1mg/l when water leaves the treatment plant is needed. Combined Chlorine • Free chlorine that has combined with ammonia (NH3) or other nitrogen-containing organic substances. • Typically, chloramines are formed. Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
NH3 Present in some source waters (e.g., surface water). Contamination; oxidation of organic matter
• • •
Chloramines still retain disinfect capability (~5 % of FAC, Free Available Chlorine) Chloramines not powerful enough to form THMs. Last a lot longer in the mains than free chlorine, – Free chlorine + Combined chlorine = Total Chlorine Residual Can measure “Total” Chlorine Can measure “Free” Chlorine Combined Chlorine can be determined by subtraction
sp ot. in
• • •
Ci
vil d
ata
s.b
log
pH Effect on Chlorine • Chlorine is a more effective disinfectant at pH levels between 6.0 and 7.0, because hypochlorous acid is maximized at these pH levels • Any attempt to disinfect water with a pH greater than 9 to 10 or more will not be very effective. • The pH determines the biocidal effects of chlorine. • Chlorine will raise the pH when added to water. • By increasing the concentration of chlorine, and subsequently raising the pH, the chlorine solution is actually less efficient as a biocide. • Controlling the pH of the water in the aquifer is not practical. However buffering or pH-altering agents may be used to control pH in the chlorine solution being placed in the well.
Temperature Effect on Chlorine • As temperatures increase, the metabolism rate of microorganisms increases. •
With the higher metabolic rate, the chlorine is taken into the microbial cell faster, and its bactericidal effect is significantly increased. Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
The higher the temperature the more likely the disinfection will produce the desired results.
•
Virus studies indicate that the contact time should be increased by two to three times to achieve comparable inactivation levels when the water temperature is lowered by 10°C (Clarke et al., 1962).
•
Steam injection has been used to elevate temperatures in a well and the area surrounding the Well bore
sp ot. in
•
Ci
vil d
ata
s.b
log
Contact time • Time is required in order that any pathogens present in the water are inactivated. • The time taken for different types of microbes to be killed varies widely. • it is important to ensure that adequate contact time is available before water enters a distribution system or is collected for use • In general, amoebic cysts are very resistant and require most exposure. Bacteria, including free-living Vibrio cholerae are rapidly inactivated by free chlorine under normal conditions. • For example, a chlorine residual of 1mg/l after 30 minutes will kill schistosomiasis cercariae, while 2mg/l after 30 minutes may be required to kill amoebic cysts. • Contact time in piped supplies is normally assured by passing the water, after addition of chlorine, into a tank from which it is then abstracted. • In small community supplies this is often the storage reservoir (storage tank). In larger systems purpose-built tanks with baffles may be used. These have the advantage that they are less prone to "short circuiting" than simple tanks. • Germicidal Efficiency of Chlorine • The major factors affecting the germicidal efficiency of the free chlorine residual process are: chlorine residual concentration - contact time – pH - water temperature. • Increasing the chlorine residual, the contact time, or the water temperature increases the germicidal efficiency. Increasing the pH above 7.5 drastically decreases the germicidal efficiency of free chlorine. • Chlorine dissolved in water, regardless of whether sodium hypochlorite or calcium hypochlorite is used as the source of the chlorine, generally exists in two forms, depending on the pH of the water: - HOCl - hypochlorous acid (biocidal) - OCl - hypochlorite ion (oxidative) • Hypochlorous acid is the most effective of all the chlorine residual fractions • Hypochlorous acid is 100 times more effective as a disinfectant than the hypochlorite ion Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
s.b
log
sp ot. in
Breakpoint Chlorination • The type of chlorine dosing normally applied to piped water supply systems is referred to as breakpoint chlorination. Sufficient chlorine is added to satisfy all of the chlorine demand and then sufficient extra chlorine is added for the purposes of disinfection. • As the applied Cl2: N ratio increases from 5:1 to 7.6:1, breakpoint reaction occurs, reducing the residual chlorine level to a minimum. • Breakpoint chlorination results in the formation of nitrogen gas, nitrate, and nitrogen chloride. • At Cl2:N ratios above 7.6:1, free chlorine and nitrogen trichloride are present.
ata
The importance of break-point chlorination lies in the control of taste and odour
Ci
vil d
Chlorine is reduced to chlorides by easily oxidizable stuff (H2S, Fe2+, etc.)
Cl2 consumed Chloramines by reaction broken down & with organic converted to matter. If NH3 nitrogen gas is present, which leaves chloramine the system formation (Breakpoint). begins.
At this point,THM formation can occur
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
s.b
log
sp ot. in
Advantages • Chloramines are not as reactive with organics as free chlorine in forming Disinfectant By Products. • The monochloramine residual is more stable and longer lasting than free chlorine or chlorine dioxide, thereby providing better protection against bacterial regrowth in systems with large storage tanks and dead end water mains. However excess ammonia in the network may cause biofilming. • Because chloramines do not tend to react with organic compounds, many systems will experience fewer incidences of taste and odor complaints when using chloramines. • Chloramines are inexpensive. • Chloramines are easy to make. Disadvantages • The disinfecting properties of chloramines are not as strong as other disinfectants, such as chlorine, ozone, and chlorine dioxide. • Chloramines cannot oxidize iron, manganese, and sulfides. • When using chloramine as the secondary disinfectant, it may be necessary to periodically convert to free chlorine for biofilm control in the water distribution system. • Excess ammonia in the distribution system may lead to nitrification problems, especially in dead ends and other locations with low disinfectant residual. • Monochloramines are less effective as disinfectants at high pH than at low pH. • Dichloramines have treatment and operation problems. • Chloramines must be made on-site.
Ci
vil d
ata
Dechlorination • Dechlorination (removing residual chlorine from disinfected wastewater prior to discharge into the environment/sensitive aquatic waters or in a treated water to be lowered prior to distribution • the chlorinated water can be dosed with a substance that reacts with or accelerates the rate of decomposition of the residual chlorine. • Compounds that may perform this function include thiosulfate, hydrogen peroxide, ammonia, sulfite/bisulfite/sulfur dioxide, and activated carbon; • Hydrogen peroxide is not frequently used because it is dangerous to handle • only the latter two materials have been widely used for this purpose in water treatment (Snoeyink and Suidan, 1975). • (1) SO3-2 + HOCl = SO4-2 + Cl- + H+ • (2) SO3-2 + NH2Cl+ H20 = SO4-2 + Cl- + NH4+ • On a mass basis, 0.9 parts sulfur dioxide (or 1.46 parts NaHSO3 or 1.34 parts Na2S2O5) is required to dechlorinate 1.0 part residual chlorine. Advantages • Protects aquatic life from toxic effects of residual chlorine. Visit : Civildatas.blogspot.in
•
Visit : Civildatas.blogspot.in
Prevents formation of harmful chlorinated compounds in drinking water through reaction of residual chlorine with water born organic materials.
sp ot. in
Disadvantages • Chemical dechlorination can be difficult to control when near zero levels of residual chlorine are required. • Significant overdosing of sulfite can lead to sulfate formation, suppressed dissolved oxygen content, and lower pH of the finished effluent.
• •
ata
s.b
log
Ozone • Nascent oxygen is very powerful in killing bacteria. • Ozone is unstable and doesnot remain in water when reaches the consumer. • Ozoniser:
Dosage of ozone is about 2 to 3 p.p.m. to obtain residual ozone of 0.10 p.p.m Contact period is about 10 minutes
vil d
Uses of Ozone Ozone is used in drinking water treatment for a variety of purposes including: • Disinfection; Inorganic pollutant oxidation, including iron, manganese, and sulfide;
•
Organic micropollutant oxidation, including taste and odor compounds, phenolic pollutants, and some pesticides; and
•
Organic macropollutant oxidation, including color removal, increasing the biodegradability of organic compounds, DBP precursor control, and reduction of chlorine demand.
Ci
•
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
Pathogen Inactivation and Disinfection Efficacy • Ozone has a high germicidal effectiveness against a wide range of pathogenic organisms including bacteria, protozoa, and viruses. • Ozone cannot be used as a secondary disinfectant because the ozone residual decays too rapidly. • Ozone disinfection efficiency is not affected by pH although because of hydroxyl free radicals and rapid decay, efficiency is the same but more ozone should be applied at high pH to maintain “C”. • Inactivation of bacteria by ozone is attributed to an oxidation reaction. The first site to be attacked appears to be the bacterial membrane . Also, ozone disrupts enzymatic activity of bacteria • The first site of action for virus inactivation, particularly its proteins and RNA • aqueous ozone penetrates into the Giardia cysts wall and damages the plasma membranes, additional penetration of ozone eventually affects the nucleus, and ribosome Advantages Ozone is more effective than chlorine, chloramines, and chlorine dioxide for inactivation of viruses, Cryptosporidium, and Giardia.
•
Ozone oxidizes iron, manganese, and sulfides.
•
Ozone can sometimes enhance the clarification process and turbidity removal.
•
Ozone controls color, taste, and odors.
•
One of the most efficient chemical disinfectants, ozone requires a very short contact time.
•
In the absence of bromide, halogen-substitutes DBPs are not formed.
•
Upon decomposition, the only residual is dissolved oxygen.
•
Biocidal activity is not influenced by pH.
vil d
ata
s.b
log
•
Disadvantages (DBPs = Disinfectant by products) DBPs are formed, particularly by bromate and bromine-substituted DBPs, in the presence of bromide, aldehydes, ketones.
Ci
•
•
The initial cost of ozonation equipment is high.
•
The generation of ozone requires high energy and should be generated on-site.
•
Ozone is highly corrosive and toxic.
•
Biologically activated filters are needed for removing assimilable organic carbon and biodegradable DBPs. Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
•
Ozone decays rapidly at high pH and warm temperatures.
•
Ozone provides no residual.
•
Ozone requires higher level of maintenance and operator skill
log
sp ot. in
ULTRA-VIOLET RAY TREATMENT • For generating these rays, the mercury is enclosed in one or more quartz bulbs and electric current is then passed through it. • The water should be passed round the bulbs several times. • Depth of water over the bulbs should not exceed 10 cm.
Ci
vil d
ata
s.b
Terms and Dosage Terms • UV Output - Energy Delivered (W/lamp) • UV Intensity - Rate of Energy Delivery (mW/cm)2 • UV Transmittance - Ability of water to transmit UV light UV Dosage D = I · t Where: D = UV Dose, mW×s/cm2 I = Intensity, mW/cm2 t = Exposure time, s
Two main factors affect ultraviolet intensity: WATER QUALITY - Water quality refers to the clarity of the water to be treated and the degree to which it allows ultraviolet light to pass through it unobstructed
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
LAMP OUTPUT - Proper lamp output is easily maintained by regular cleaning of the quartz sleeve that encases the lamp (generally every six months) and by lamp replacement once per year.
log
sp ot. in
Measuring UV Dosage • Intensity (Irradiance) – actinometry (instruments used to measure the heating power of radiation) is a chemical system or physical device which determines the number of photons in a beam integrally or per unit time. – Radiometers or UV sensors – Mathematical models • Time: The time of exposure to ultraviolet light (retention time) is directly related to the flow rate of water passing through the disinfection chamber. By changing the retention time for a given ultraviolet intensity, the dosage can be increased or decreased as needed. • Bioassay Methods: (is a type of scientific experiment to measure the effects of a substance on a living organism )
ata
s.b
UV Applications in Drinking Water • Disinfection of Surface Water • Disinfection of Ground Water • Oxidation of Organic Chemicals • Oxidation of NOM • By Using UV methods: no natural physiochemical features of the water are changed and no chemical agents are introduced into the water. • formation of THM or other DBPs with UV disinfection is minimal
Ci
vil d
Inactivation Mechanism • UV radiation is efficient at inactivating vegetative and sporous forms of bacteria, viruses, and other pathogenic microorganisms. • Electromagnetic radiation in the wavelengths ranging from 240 to 280nm effectively inactivates microorganisms by irreparably damaging their nucleic acid. • The germicidal effects of UV light involve photochemical damage to RNA and DNA within the microorganisms. • DNA damage irreversible over time so UV contactors should be designed to either shield the process stream or limit the exposure of the disinfected water to sunlight immediately following disinfection. Limitations of UV treatment “Point” Disinfection • UV units only kill bacteria at one point in a watering system and do not provide any residual germicidal effect downstream. If just one bacterium passes through unharmed (100% destruction of bacteria cannot be guaranteed. Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Cells Not Removed • Bacteria cells are not removed in a UV unit but are converted into pyrogens. The killed microorganisms and any other contaminants in the water are a food source for any bacteria that do survive downstream of the UV unit. •
Due to these limitations, the piping in a watering system treated by UV disinfection will need to be periodically sanitized with a chemical disinfectant.
Ci
vil d
ata
s.b
log
sp ot. in
Benefits of UV • Effective for Crypto/virus • No chemicals added to water • Small footprint • Pressurized system • Cost Effective • No DBPs • Oxidize organic chemicals
Minor Methods of disinfection EXCESS LIME TREATMENT • Treatment of lime is given to the water for the removal of dissolved salts. • Excess lime added to water works as disinfecting material. • When pH value is about 9.50, bacteria can be removed to the extent of 99.93 per cent. • Lime is to be removed by recarbonation after disinfection. Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
IODINE AND BROMINE TREATMENT • Use of iodine or bromine is limited to small water supplies such as swimming pools, troops of army, private plants, etc. • Dosage of iodine or bromine is about 8 p.p.m. • Contact period with water is 5 minutes. • Available in the form of pellets or small pills.
sp ot. in
SILVER TREATMENT • Colloidal silver is used to preserve the quality of water stored in jars. • Metallic silver is placed as filter media. Water get purified while passing through theses filters. • Dosage of silver varies from 0.05 to 1 p.p.m. • Contact period is about 15 minutes to 3 hours. • It is costly and limited to private individual houses only.
s.b
log
POTASSIUM PERMANGANATE TREATMENT (KMnO4) • It is a powerful oxidising agent, effective in killing cholera bacteria • Restricted to disinfection of water of village wells and ponds • Dosage is about 2.1 ppm • Contact period of 3 to 4 hours • The treated water produces a dark brown coating on porcelain vessels and this is difficult to remove except with scratching or rubbing
Ci
vil d
ata
Residue management Residue Sources, contaminants and disposal methods VOC = volatile organic compound, SOC = Synthetic organic compounds, TDS = total dissolved solids, SS = suspended solids Coagulation/Filtration Typical Residual Typical Contaminant Typical Disposal Waste Streams Methods Generated Aluminum hydroxide, Metals, suspended Land filling ferric hydroxide, or solids, organics, polyaluminum chloride, radionuclides, biological, Disposal to sanitary sludge with raw water inorganics sewer/WWTP suspended solids, polymer and natural Land application organic matter (sedimentation basin Surface discharge residuals) Spent backwash filterMetals, organics, Recycle to-waste suspended solids, Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
biological, radionuclides, Surface discharge inorganics (pumping, disinfection, Dechlorination) Disposal to sanitary sewer/WWTP
vil d
Disposal to sanitary sewer/WWTP
log
Metals, organics, suspended solids, biological, radionuclides, Surface Discharge inorganics (pumping, disinfection, dechlorination) Disposal to sanitary sewer/WWTP
Membrane Separation Typical Contaminant Typical Disposal Methods Metals, radionuclides, TDS, high molecular, weight contaminants, nitrates
Surface discharge (pumping, etc.) Deep well injection Discharge to sanitary sewer/WWTP
Ci
Typical Residual Waste Streams Generated
Landfilling
Land application Recycle
ata
Typical Residual Waste Streams Generated Reject streams containing raw water suspended solids (microfiltration), raw water (nanofiltration), brine (RO)
Metals, suspended solids organics, unreacted lime, radionuclides
s.b
Spent backwash filterto-waste
sp ot. in
Typical Residual Waste Streams Generated Calcium carbonate and magnesium hydroxide sludge with raw water suspended solids and natural organic matter
Precipitative Softening Typical Contaminant Typical Disposal Methods
Radioactive storage Ion Exchange Typical Contaminant
Typical Disposal Methods
Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Brine stream
Metals, TDS, hardness nitrates
Surface discharge Evaporation ponds
Typical Residual Waste Streams Generated Spent GAC requiring disposal and/or reactivation, spent backwash, and gas-phase emissions in reactivation systems
sp ot. in
Discharge to sanitary sewer/WWTP Granular Activated Carbon (GAC) Typical Contaminant Typical Disposal Methods VOCs, SOCs (nonvolatile Landfill pesticides), radionuclides, heavy Regeneration (on/off metals site) Incineration
Ci
vil d
ata
s.b
log
Radioactive storage Return spent GAC to supplier Stripping Process (mechanical or packed tower) Typical Residual Typical Contaminant Typical Disposal Waste Streams Methods Generated Gas phase emissions VOCs, SOCs, radon Discharge to atmosphere GAC adsorption of off-gas (contaminant type and concentration dependent) Spent GAC if used for VOCs, SOCs GAC adsorption of offgas-phase control radionuclides gas (contaminant type and concentration dependent) Return spent to GAC to supplier
Construction Aspects of WTP Treatment Plant Layout and Siting Plant layout is the arrangement of designed treatment units on the selected site. Siting is the selection of site for treatment plant based on features as character, Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
sp ot. in
topography, and shoreline. Site development should take the advantage of the existing site topography. The following principles are important to consider: o A site on a side-hill can facilitate gravity flow that will reduce pumping requirements and locate normal sequence of units without excessive excavation or fill. o When landscaping is utilized it should reflect the character of the surrounding area. Site development should alter existing naturally stabilized site contours and drainage as little as possible. o The developed site should be compatible with the existing land uses and the comprehensive development plan.
log
Operations and Maintenance Aspects of WTP Maintenance Maintenance refers to keeping civil, mechanical and electrical components through normal repair to function at design capacity for their design period Operation Operation refers to the art of handling the plant and equipment optically so that the designed quality and quantity of water can be produced Represents hourly and daily operation of plants, equipments, machinery and valves
ata
s.b
Features of Operations and maintenances (1) Availability detailed plans, drawings, operations and manuals (2) Schedule of daily operations (3) Equipment and machinery record register (4) Records of quality of water (5) Records of key activities of Operations and Maintenance (6) Staff Position (7) Inventory of Stores
Ci
vil d
Operations and Maintenance Aspects of WTP 1. Problems Fluctuation in the quality of water Fluctuations in the quantity and changes in the flow pattern Malfunctioning of the units Mechanical and electrical equipments 2. Requirements Plans with details of units and layout Systematic plan of daily operations Daily machinery inspection schedule for lubrication Data record for equipment cleaning and replacement of parts Record of water analysis at various points to identify effects on quality Safety measures including house keeping Visit : Civildatas.blogspot.in
Visit : Civildatas.blogspot.in
Ci
vil d
ata
s.b
log
sp ot. in
3. Raw water 4. Flow measuring devices 5. Chemical feeding unit 6. Rapid mixer 7. Slow mixer 8. Clarifier or Sedimentation tanks 9. Rapid gravity filters Defective gauges Inadequate media on the filter bed Air binding Incrustation of media Cracking of sand beds Bumping of filters Mud balls Sand boils Slime growths Back wash requirements 10. Slow sand filters 11. Chlorinators 12. Clear water sump and reservoir 13. Treated water 14. Aerators 15. Master balancing Reservoirs and elevated reservoirs 16. Distribution system 17. Water quality control 18. Taste and odour control 19. Staff pattern
Visit : Civildatas.blogspot.in
