Biosand filters are a small, household sized
adaptation of slow sand filters such that they can
be run intermittently.
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 a biofilm (schmutzdecke)
is created that further filters the water of
Operating the filter is very simple: remove the
lid, pour a bucket of water into the filter, and
immediately collect the treated water in a clean
Invented by David Manz, PhD. University of Calgary
Amount of Water Treated
Household biosand filters typically provide 30
liters of water per hour, which is sufficient for a
family of five. Flow rate may decrease over time as
the filter becomes clogged, but can be restored
Biosand filters have been shown to remove more than
90 percent of fecal coliform, 100 percent of
protozoa and helminthes, 95 to 99 percent of zinc,
copper, cadmium, and lead, and all suspended
sediments. Biosand filters have also been shown to
remove 76 to 91 percent 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 biosand filters are not able
to handle high turbidity, they may become clogged
and ineffective during monsoon or rainy seasons.
Ease of Use
Biosand filters require daily fillings during the 2
to 3 weeks when the biological layer is growing.
Biosand filters also require regular cleaning,
which involves agitating the water above the
biological layer. The filter will require 2 to 3
weeks of nonuse 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 labor,
significant training, or high cost. User error has
also been found to affect the filters’ efficiency,
especially because of the required 2 to 3 week
nonuse period for growing the biological layer.
Biosand filters can be fabricated locally in almost
all regions because they use common materials.
There may be educational and training costs
associated with teaching users how to properly
maintain their filters. Costs may vary across
regions depending on the availability of materials