Water Treatment During Reconstruction
Practical Action
However, it does require regular and extensive maintenance to ensure that performance does not
drop below satisfactory levels; the cleaning of the filter requires significant labour, although this
can have benefits in terms of hygiene education and skill sharing. Additionally, it has a bulky and
heavy design, putting severe limitations on movability. For these reasons, it is not generally
considered practical for the earlier stages of the reconstruction process, but can provide reliable
supply of safe water in large quantities once installed.
Further information on the technology can be found in the Practical Action technical brief Bio-
Sand Water Filters.
Slow-Sand Filter Treatment
Slow-sand filtration is a very effective method of removing particulate and suspended matter.
Essentially a scaled-up version of the household bio-sand filter, it can be used for groundwater
containing suspended solids but is more often used to remove organic material and pathogens
from surface water, applying aeration and filtering processes to supplied water.
Water stands in a tank 1m above a sand filter bed and moves down at about 0.1- 0.2 m/hr.
Different grades of sand can filter out physical impurities and they can also eliminate pathogens
as they develop a layer of algae that feeds on the bacteria. This occurs at the top of the sand bed
and is called a schmutzdecke. The schmutzdecke is effective at killing and retaining various
bacteria, pathogens and viruses, which makes it more effective than a rapid sand filter. The
sand filter will block up over time with inorganic matter but this can be removed by backwashing.
Inorganic matter can be removed through rough filtering or by using sedimentation tanks.
Slow-sand treatment plants are significant constructions, and require regular maintenance. It is
essential that communities that will benefit from the filters are involved in the construction and
maintenance processes, allowing for continued use of the filter for several years. The technology
is very much suited to permanent housing reconstruction, and allows for the engagement of local
populations. Additionally, it could be considered for Internally Displaced Person (IDP) camps that
are unlikely to move in the short-term. The community construction and use of a slow-sand plant
could be intrinsically linked with some of the principles of PCR.
Figure 4: Schematic of a basic Slow-Sand Filter plant
Source: Engineering in Emergencies, © Practical Action Publishing
Sand filter systems are described at length in the document Slow Sand-Filtration Water
Treatment Plants produced by Soluciones Prácticas (Practical Action’s Spanish Language sister
site).
Further information on the technology can also be found at:
http://www.biosandfilter.org/biosandfilter/index.php/item/330
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