III. Water Treatment Technologies
Topic. III. 5. Micro-mesh Screens. Filters: Kinds,
Constructions and Operation
Micro-mesh Screens
I. Purpose
 For plankton removal
 For colour removal
II. Efficiency restriction
 Phytoplankton content - up to 106 cells/l
 Duration of high plankton concentration
- more than 1 month
 Removal of
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45 - 75 % of diatomite algae
60 - 95 % of blue-green algae
100 % of zooplankton
25 - 35 % of suspended solids
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Micro-mesh Screens
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Micro-mesh Screens
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Filters
Kinds:
I. According to the filtration rate
 Low rate - 0,1 - 0,3 m/h
 High rate - 5 - 10 (15) m/h
 Super high rate - 50 m/h
II. According to the filter layers
 One-layer
 Two-layers
 Multy-layers
III. According to the filter media
 Sand (quartz) filters
 Coal/sand filters
 Ceramic filters
 Ceramic/sand filters
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Filters
Kinds:
IV. According to construction
 Open (non-pressure)
 Closed (pressure)
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Vertical
Horizontal
V. According to impurities removal mechanism
 Coagulation/sorption
 Ion exchange
VI. According to reagents application
 Without reagents’ treatment
 With preliminary coagulation
 With contact coagulation
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Low Rate Sand Filters
Classical structure (Longitudinal Section)
1 - flowrate regulator; 2 - weir; 3 - inlet distribution channel; 4 - drainage pipe;
5 - filtered water pipe
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Low Rate Sand Filters
Particularities:
 Capacity limits
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Water quantity < 1000 (5000) m3/d
Turbidity < 50 mg/l
Colour < 30 - 40 grad
Filtration duration - 20 - 30 d
 Sand grains diameter def = 0,3 - 1 mm
 Sand layer height h = 0,8 - 1 m
 Water layer height H = 1,2 - 1,5 m
 Filtration rate v = 0,1 - 0,3 m/h
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Low Rate Sand Filters
Particularities:
 Filtering total capacity - Ktot
Ktot = Kb + Knet , g/m2
Ktot = 2000 - 10000 g/m2;
Kb - biofilm development capacity, g/m2; Kb = M.v0.Tb; Kb = 100 - 300 g/m2;
Knet - net filtering capacity, g/m2; Knet = M.v0.Tnet
M - coarse water turbidity, mg/l;
v0 - filtration rate during period Tb , m/h; v0 = 0,05 - 0,1 m/h;
Tb - biofilm development duration, h; Tb = 3 - 12 h at M > 100 mg/l;
Tb = 24 - 36 h at M < 100 mg/l;
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Low Rate Sand Filters
Particularities:
 Filtering total duration - Ttot
Ttot = Tb + Tnet +Tw , h
Tb - biofilm development duration, h; (time to reach bacteria
concentration less than 100 numbers per cm3 and filtrate turbidity
less than 2 mg/l);
Tnet - net filtering duration, h; Tnet = (Ktot - Kb)/v; Tnet = 500 h;
Tw - filter washing duration, h; Tw = 6 - 24 h
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High Rate Sand Filters
Scheme of Open Air Structure
1 - coarse water inlet pipe; 2 - washing water inlet pipe; 3 - filtered water pipe; 4 - wash
water pipe; 5 - wash water drain channel; 6 - distribution pipes; 7 - supporting layer;
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8 - filtering layer; 9 - wash water outflow channel
High Rate Sand Filters
Scheme of Construction and Operation
a - normal operation
б - washing
1 - filtering layer; 2 - drainage (support) layer; 3 - distribution channel; 4 - distribution (wasout)
channels; 5 - drainage system
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High Rate Sand Filters
Scheme and Operation Mode of Filtering Regulator
h1 - initial filtering head loses; h2 - operational (decreasing) filtering head loses;
H - total filtering head loses (H = h1 + h2 = const.); E - constant water level
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High Rate Sand Filters
Structure of Pressure High Rate Sand Filter
1 - coarse water inlet pipe; 2 - filtered water outlet pipe; 3 - wash water inlet pipe;
4, 5, 10 - stop valves; 6 - drainage (support) plate; 7 - filtering layer; 8 - supporting layer;
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9 - wash air inlet pipe; 11 - manometer
High Rate Sand Filters
Particularities:
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Capacity limits
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Water quantity -unlimited
Turbidity < 25 mg/l
Colour < 25 grad
Filtration duration - 12 - 24 h
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Sand grains diameter def = 0,5 - 2 mm
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Sand layer height h = 0,8 - 1,2 m
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Water layer height H = 1,5 - 2 m
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Filtration rate v = 5 - 10 (15) m/h
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High Rate Sand Filters
Particularities:
 Back-washing parameters
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Wash water intensity - 6 - 8 l/s.m2
Wash air intensity - 15 - 20 l/s.m2
First stage water/air washing duration - 4 - 5 min
Second stage water washing duration - 3 - 4 min
 Post-washing filtration
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Duration - 10 - 12 min
Filtrate wasted to the sewer
 Washing water quantity
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1 - 3 % of the water treatment plant capacity
 Number of spare filtering cells (under reparation)
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5 - 10 % of number of the constructed ones
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