Day 5

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When do we need each type of filter?

• Contains human waste

• Needs pre treatment

Black water

• All used water without sewage.

Grey Water

• Water suitable for drinking

White Water

Septic Tank/ Soak Pit

Municipal waste treatment

Used for irrigation

Grey water recycling: Used to flush toilets, etc.

FILT

ER

FILT

ER

FILTER

FILTER

Household water treatment systems

• Boiling• Storage (for settlement)• Sand filters (need maintenance)• Ceramic filters. • Disinfection and Sterilisation (e.g. Adding

chloring)• Ultraviolet (UV) treatment• Bio-sand filter.

Bio-filter• Developed by ‘Practical Action’ in Peru and Bangladesh.

First used in Haiti in 1999. • 30-60 litres of water per hour (family of 5-10 members). • Advantages:

– Removal of turbidity, colour and odour– Good microbial removal– High flow rate– Can be constructed with local materials– Income generation– Durable– Minimal maintence

• Disadvantages: – Not 100% microbial removal; may require post-

disinfection– Limited transportation due to weight (not portable)– Turbiity should not exceed 100NTU

• Cost:– Around 990-1300 Rupees– Cost may vary depending on the availability of

materials and labour.

Municipal definition

• Municipal Water refers to a water supply provided from a central point and piped to individual users under pressure. It may be from a central well or be treated surface water. This is as opposed to each user having a separate water source and pressure system.

Potters for Peace

UV Water Purification• Prevents enzymes in water

from reproducing • Water turbidity (i.e., the

amount of suspended & colloidal solids contained in the water to be treated) must be low, such that the water is clear, for UV purification to work well. Also, water treated with UV still has the microbes present in the water, only with their means for reproduction turned "off".

Extra slides – not used in lesson

Slow sand filtration

• First used in the U.S.A in 1872. Slow sand filters are the oldest type of municipal water filtration.

• Municipal Water refers to a water supply provided from a central point and piped to individual users under pressure. It may be from a central well or be treated surface water. This is as opposed to each user having a separate water source and pressure system.

• Suitable for small systems with low turbidity or algae containing waters.

• SSF does not require pretreatment • Simple and reliable process, inexpensive but does

require some highly skilled operators• No chemicals are added to aid the filtration

process.• Can remove suspended organic and inorganic

matter. Also may remove pathogenic organisms.

• SSF reduces bacteria, cloudiness and organic levels.

• Sludge handling problems are minimal• Close operator or supervision is not necessary• Can use local materials and labor.

• Can use granular activated carbon (GAC) layer. • Water is only applied to filters when the

turbidity level is lower than 10 NTU. • Less effective with cold water. • Filtration rate: 0.15 gallons per minute per

square foot of bed area. • Biological matter forms on sand surface and

helps strain particals.

• Models are always nessessary to design SSF. • Operation of a small model filter, preferably

over several seasons of the year, will insure adequate performance of the full-scale plant.

• Parameters– Plant filtration rate– Bed depth– Sand size

• Monitoring:– Head loss– Flow rate– Water temperatire– Turbidity

• Filters should operate at constant rate of water.

• Storage of filtered water is essential.

Roughing filters

Advantages:Built by local and local materialsReduce turbidity and suspended solidsReduce organice matterNo chemicals neded

They are appropriate and economical for rural water treatment

Parameters

• Filter media sizes• Filtration rate• Filtration length

Roughing filters

• Filtration rate depends on:– Type of filter– Water characteristics– Desired turbidity reduction– No of filter layers– Height and width of filter bed. – PARTICLE SIZE AND DISTRUBTION OF FILTER

MATERIAL. – Most filters have 3 layers.

Filter size

• Is it better to build a water filtration system for one house or a bigger one for lots of homes?

• Small scale home filtration systems are not as reliable as ‘municipal’ ones.