Day 4

Props: perforated pipe and ceramic pot

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Sand

Soil

Large stone

Gravel

PebblesCoconut shavingBroken Bricks

Or rice husk...

Conclusions:

• Did you record the experiment?

• What were your conclusions about the various materials?

Layering

• The different materials depends on the PURPOSE of the filter.

• We are now going to look in detail at the filtration process.

Pre treatment/ Grey water processAbstraction

Storage

Sedimentation

Aeration

Roughing filtration

Coagulation with settlement

To make white water this is the pre treatment process

Abstraction

• When finding water – try to remove level of suspended solids.

• E.g. Take water to treat from A or B?

Storage and Sedimentation

• Natural settlement of solids

• Natural die off of pathogenic bacteria.

• Maximise settlement time

• Sunlight can reduce bacteria in open storage tanks. However in the presence of organic matter it can encourage growth of algae.

Aeration

• Tastes and smells are commonly due to the presence of hydrogen sulphide in the groundwater or decaying organic and bacterial matter in surface water.

• These tastes and smells can be reduced by aeration.

• Maximise air/water contact area. • Discharge in a spray into tank. • If space let water fall down steps of

perforated tiles or steps.

Coagulation

• Some particles in water are quite small and do not settle to the bottom of the tank during sedimentation.

• These particles must be encouraged to combine together to create heavier particles and then they can settle.

• This process is called coagulation (and flocculation)

• Chemicals: Most common coagulant is alum (aluminimum suphate)

• Natural: Alum rock, crushed seedsof some plants but may provide organic matter for the growth of bacteria.

• Stages: Rapid mixing and Flocculation

Roughing Filters

Infiltration rate

SandClay

Clay isImpermeable

Sand is Permeable

(Rate which water will filter into soil)

Infiltration time

• Do you think rock has a longer or shorter infiltration rate?

• Water will flow through rock quicker than both sand and clay.

Soil infiltration rate for white and dirty water

Soil Type Infiltration Rate (l/m2/day) Infiltration Rate (l/m2/day)

Clean Water Dirty Water

Sand 2000 50

Clay 100 Not suitable

Clay isImpermeable

Sand is Permeable

Extras

• For storage of non-chlorinated water for filter rinsing and use in bio carbon tank.

• Special iron fillings to filter our arsenic

Roughing filters

• For pre-treatment removal of iron, parasites, colour, cysts,manganese, arsenic, lead, mercury and turbidity.

• Can be used as a pre treatment for a slow sand filration

• Can be used for grey water treatment as long as not near a water source and is not going to be drunk directly.

Roughing filter: Layers

• Horizontal roughing filter

• Vertical roughing filter

• In series or separate tanks

We used the Vertical roughing filter

• But how well it filters the material also depends on the size of the filter.

• Today we are going to look at volumes of materials we could use as filter.

1) Ceramic pot

2) Barrel

Can you think of any other materials?

Calculating Volume

• There are two methods to do this.

• But first we need to agree on the Units to use. (e.g. Feet, inches, centimetre and meters)

• We are going to use meters.

• Therefore our final volume will be in m 3

3

Method 1

• First: Calculations

– Step 1: Measure the dimensions of the object.

– Step 2: Work out the cross sectional area

– Step 3: Times the cross sectional area by the height of the object.

– How do you calculate the cross sectional area ofa) Rectangle and b) Circle?

Method 1

• Area of cross section is LxB.

• What if it is a square?

Length

BreadthHeight

• Diameter is 2m, what is the area?

• Height is 1m, what is the volume of this cylinder?

Method 2

• Work out how many litres of water you can fit into the object.

• 1Litre = 0.001 m 3

Question

• Volume of

– A) Ceramic pot

– B) One barrel

– C) Half a barrel