Filter for drinking water using sand and a bacterial layer.
Remark This technology is currently being tested. Results on the water quality will be available within a few months.
This filter was created for individual use (5L/day) and is adapted from the work of NGO CAWST and Dr David Manz, who has been working since 2001 to spread bio-sand filters to families in need. The version presented in this tutorial is easier to build and more compact than the family filter version.
Multiple barriers approach:
Using multiple barriers approach is the best way to reduce risks of drinking unsafe water. Each step of the process, from sources protection to water treatment and safe storage, is responsible for a decrease of sanitary risks. The treatment process includes: water source protection, sedimentation, filtration, disinfection and safe storage.
People often focus on one-step particular technology, instead of considering water treatment process as a whole. Even though individual technologies as this filter can improve water quality, it is essential to control the whole process to ensure the best water quality.
Water treatment at home
Water treatment process at home is mainly based of pathogens elimination from drinking water, which is the most important water issue in the world. This tutorial only focuses on the filtration part.
Operating principle :
Bio-sand filter is an optimization of classic sand filter, that has been used for century to filter freshwater before drinking it.
The bio-sand filter is composed of five different areas:
Pathogens and suspended matters are eliminated by a combination of physical and biological processes, that take place in the sand and biological layers:
Theoretical efficacity :
This filter is intented for classical fresh water, non excessively polluted by elements like arsenic for example. In case of particularly polluted water, complementary filtration systems will have to be added.
Analysis results after biosand filtration with CAWST filter:
Remark : It it recommended that the cover is perfectly adapted to the tube and that is can also be used as "sieve", so that added water would fall slowly on the sand without disturbing the biological layer.
Remark: It is advised to use sand from crushed rock. In case it is not possible, rivier sand can be used. In the worst case, sea sand can also be used but has to be desalinated beforehand. In each case, the sand should be of between 0 and 1mm.
Generally 4 or 5 washes are necessary.
1) Biosand filter can be used for any source of water, including rainwater, underground water, river or lake water. The source must be as clean as possible. If the source is highly contaminated, filtered water can still contain contaminants.
2) With time, the biological layer will adapt to a certain degree of water contamination. If a source with a different level and kind of contamination is used, the layer might not be able to consume all pathogens. The biological layer may need several days to adapt to a new kind of water: its contamination and nutrients. It is advised to systematically use the same water source to ensure the best treatment quality.
3) The biological layer requires 1 month from the first filtration before being fully efficient.