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III. Water Treatment TechnologiesTopic. III. 5. Micro-mesh Screens. Filters: Kinds,

Constructions and OperationMicro-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

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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FiltersKinds:

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)

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 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 Structure1 - 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; 8 - filtering layer; 9 - wash water outflow channel

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High Rate Sand Filters

Scheme of Construction and Operationa - 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 Filter1 - 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; 9 - wash air inlet pipe; 11 - manometer

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High Rate Sand Filters

Particularities:

Capacity limits Water quantity -unlimited Turbidity < 25 mg/l Colour < 25 grad Filtration duration - 12 - 24 h

Sand grains diameter def = 0,5 - 2 mm

Sand layer height h = 0,8 - 1,2 m

Water layer height H = 1,5 - 2 m

Filtration rate v = 5 - 10 (15) m/h

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High Rate Sand Filters

Particularities:

Back-washing parameters 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 Duration - 10 - 12 min Filtrate wasted to the sewer

Washing water quantity 1 - 3 % of the water treatment plant capacity

Number of spare filtering cells (under reparation) 5 - 10 % of number of the constructed ones