Household water treatment systems
Practical Action
The filter consists of a layer of gravel overlain with prepared sand media contained within a
filter body or box, usually constructed on concrete. A shallow layer of water sits atop the
sand, where the biofilm (schmutzdecke) is created.
Operating the filter
The lid in removed,
A bucket of water or other container is poured into the top of the filter.
The diffusion plate slows the force of the water.
Water then travels slowly into the biological layer at the top of the sand.
Water continues slowly through the sand bed.
After passing through both levels of gravel, the water is propelled up and out.
Then treated water is collected in a clean container.
Amount of Water Treated
Household bio-sand filters typically provide 30 to 60 litres of water per hour, which is
sufficient for a family of five to ten members. The flow rate may decrease over time as the
filter becomes clogged, but can be restored with cleaning.
Contaminant removal
Bio-sand filters have been shown to remove more than 90% of faecal coliform, 100% of
protozoa and helminthes, 95 to 99% of zinc, copper, cadmium, and lead, and all suspended
sediments. Bio-sand filters have also been shown to remove 76 to 91% of arsenic, reducing it
to acceptable concentrations. These filters do not sufficiently remove dissolved compounds
such as salt and fluoride or organic chemicals such as pesticides and fertilizers. The
biological layer’s effectiveness is influenced by temperature. Ammonia oxidation stops below
6° Celsius and alternative treatment methods are required below 2° Celsius. Additionally,
because bio-sand filters are not able to handle high turbidity, they may become clogged and
ineffective during monsoon or rainy seasons.
Ease of Use
Bio-sand filters require daily fillings during the 2 to 3 weeks when the biological layer is
growing. Bio-sand filters also require regular cleaning, which involves agitating the water
above the biological layer. The filter will require 1 to 2 weeks of non-use after agitation to
allow for the regrowth of the biological layer. On occasion, the sand in the filter needs to be
cleaned as well. There are several different methods to clean the sand, though all of them
require significant labour, significant training, or high cost. User error has also been found to
affect the filters’ efficacy, especially because of the required 2 to 3 week non-use period for
growing the biological layer. Bio-sand filters can be fabricated locally in because they use
common materials.
Benefits & drawbacks
Advantages
Removal of turbidity, colour, odour.
Good microbial removal.
High flow rate.
Can be constructed of local materials.
Income generation.
Durable.
Minimal maintenance.
Drawbacks
Not 100% microbial removal; may require post-disinfection.
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