IMPROVED AND INOVATIVE

RURAL WATER SUPPLY

DESIGN CONCEPTS

THE NEED FOR WATER TREATMENT

The purpose of water treatment is to provide a continuous supply of safe, palatable/potable drinking

water

RRPN Ratnayake

Free of unpleasant characteristics

Free of Disease-causing (biological) contaminants

Free of chemical contaminants

Colour

Turbidity

Taste and odour

Free of plants like algae

All the above physical and chemical characteristics are mainly due to suspended matter or dissolved chemical constituents in the water

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In simple terms Water treatment is the removal of Unwanted suspended /dissolved matter (solids, liquids or gases) from water

SLS 614 USEPA drinking Water Regulations

Particle Size & Settling Rates

Type ofParticle

Particle Size(mm)

Settling Time through1 m of Water

Gravel 10 1 second

Sand 1 10 second

Fine Sand 0.1 2 minutes

Clay & Silt 0.01 2 hours

Bacteria 0.001 8 days

Colloid 0.0001 2 years

Colloid 0.00001 20 years

Colloid 0.000001 200 years

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TRAY AERATOR

4Fe2++ O2+10H2O 4Fe(OH)3+8H+

When PH above 7.5

2Mn2++ O2+2H2O 2MnO2+4H+

(Better if PH >9.0 for Mn oxidation)

Trays filled with coke, crushed stone, lime stone or plastic media up to a depth of 300-450mm.

RRPN Ratnayake

INDUSTRIAL POLLUTANTS

Slow sand filtration

Plain sedimentation for >8 days

Slow sand filtration

Roughing filtration

Aeration

Aeration

Turbidity< average of 5 NTU, Algae (Chlorophil <.05µ)g/l,Colour, Taste, Odour, Iron<.3mg/l, Manganese<0.05mg/l, Algal toxins (to be tested) Slow sand

filtrationTurbidity< average of 20 NTU and maximum up to 50 NTU, Algae (Chlorophil <.05µ)g/l,Colour, Taste, Odour, Iron<.3mg/l, Manganese<0.05mg/l, Algal toxins

Slow sand filtration

AerationTurbidity< average of 20 NTU and maximum up to 200 NTU, Algae (Chlorophil <.05µ)g/l,Colour, Taste, Odour, Iron<.2mg/l, Manganese<2mg/l, Algal toxins, fluoride<0.8mg/l

Roughing filtration

Turbidity< average of 60 NTU and maximum up to 500 NTU, Algae (Chlorophil <.05µ)g/l,Colour, Taste, Odour, Iron<.2mg/l, Manganese<2mg/l, Algal toxins, fluoride<0.8mg/l

TREATMENT PROCESS SELECTION

Plain sedimentation for 8 days

Slow sand filtration

Roughing filtration

Aeration/Ozonation

Granular Activated carbon

Turbidity< average of 60 NTU and maximum up to 500 NTU, Algae (Chlorophil <.05µ)g/l,Colour, Taste, Odour, Iron<.2mg/l, Manganese<2mg/l, Algal toxins(high), fluoride<0.8mg/l

To Storage

Filter Bed No. 1

Influent Structure

Filter Bed No. 2Collection Pipes

A

Section A

WaterCollection Manifold

SandPerforated Pipe

SLOW SAND FILTER

Scrape off the top 2-5cm sand layerfor cleaning after cloggingTimber planks should be used to move on sand bed

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RRPN Ratnayake

Floating intake

One square kilo meter of 1 meter thick humus layer can store about 400,000 cubic meters of rainwater