Household water treatment systems
Practical Action
The collected water will not have any taste, so may need some salt added to make it pleasant to
drink.
Also see Solar Distillation.
Reverse Osmosis
Reverse osmosis filters everything under high pressure. Reverse osmosis is a relatively high
technology approach that would need to have a sophisticated support system to maintain it. It is
also inherently energy hungry. It involves forcing solvents from low concentration solution to a
high concentration solution, which is the opposite of the process of osmosis. The process is used
widely for seawater and brackish water.
Small-scale stand alone reverse osmosis technology using solar power was developed by RADG.
They have also worked on low-cost bacteriological water testing.
RADG - Remote Areas Development Group
Murdoch University
Perth
Australia
etc@murdoch.edu.au
http://www.etc.murdoch.edu.au/etcV03/pages/radg/radgpages/radghome.html
CSMCRI developed a small-scale bullock-driven reverse osmosis unit in India.
Central Salt & Marine Chemicals Research Institute
Gijubhai Badheka Marg, Bhavnagar-364002, Gujarat
India
Tel: 0278-2567760 / 2568923 / 2565106
Fax: 0278-2567562 / 2566970
Email: salt@csir.res.in, salt@csmcri.org
Website: http://www.csmcri.org/
Activated carbon
A study by WEDC has been carried out to show that Granule Activated Carbon can be used to
filter iron and manganese. It has been used in Europe and North America since it is particularly
good at removing soluble organic matter. There have also been studies that show it removes
several cyanotoxins.
Activated carbon is able to adsorb compounds due to its porous nature and large surface area. It
can be added as a powder or as granules. Activated carbon is made by heating up carbonaceous
materials like wood, coal, peat or coconut shells. Organic compounds are adsorbed by the carbon
and then removed by separate treatment process. In the case of Powder Activated Carbon, the
powder is added as slurry and then removed by flocculation or mechanically. Powder Activated
Carbon (PAC) is therefore suitable for surface water treatment. Granule Activated Carbon (GAC)
is used in fixed beds, either in replacement of sand or as separate adsorption filters. Some GACs
can be reactivated by burning off the organic compounds, but some GACs and PAC can only be
used once. The treatment can effectively remove pesticides and improves the taste of water but
requires maintenance and regular replacement of the carbon, making it less suitable for
situations in developing countries.
It is possible to produce activated charcoal on a small scale using by-products from crops, like
seed husks or coconut shells. Often pit charcoaling is done in an uncontrolled environment, i.e.
oxygen entering the system cannot be 100% controlled and there is not systematic control of
temperature reached in order to activate the charcoal afterwards. Once made, the charcoal needs
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