Household Water Treatment and Safe Storage Factsheet: Source ...

Household Water Treatment for Arsenic Removal
Fact Sheet: Coagulation-Flocculation
Bucket Treatment Unit (BTU)
Potential Treatment Capacity
Very Effective For: Somewhat Effective For: Not Effective For:
Most pathogens
Turbidity
Taste, odour, colour
Arsenic
Chemicals
What Is Bucket Treatment Unit (BTU)?
The Bucket Treatment Unit is a two bucket filter
developed within the DPHE-Danida project in
Bangladesh. It uses oxidation,
coagulation/flocculation and filtration to remove
arsenic. The BTU can be constructed from locally
available materials.
How Does It Remove Arsenic?
Arsenic is removed by:
The mixture is then allowed to settle for 1 to 4 hours
or longer (see manufacturer’s recommendation).
Then the upper tap is turned on so that the water
can pass through a cloth filter and a sand filter in
the lower bucket.
The effectiveness of the DPHE-Danida Bucket
Treatment Unit decreases if inlet water arsenic
concentrations are above 0.12 mg/L (Sutherland et
al., 2001).
Oxidation (loss of electrons) of the arsenic to
change its form from As(III) to As(V), by
applying an oxidizing agent (e.g. potassium
permanganate*)
Coagulation and flocculation using alum or
aluminum sulphate, forming flocs (large
combined particles)
Adsorption (sticking) of arsenic onto flocs
Sedimentation
Straining through a cloth
Sand filtration
*Coagulation/flocculation can also be achieved by using
iron chloride or iron sulfate.
Operation
The upper bucket is filled with inlet water, with the
tap closed. The required chemicals are added and
the water is stirred with a wooden spoon (provided
with the unit).
Recommended chemical doses are (Tanhura et al.,
no date):
200 mg/L aluminum sulphate
2 mg/L of potassium permanganate
Key Information
Treatment
Efficiency
~ 60% arsenic
removal
Bucket Treatment Unit
(Credit: T. Ngai)
Output
20 litres/hour
Cost
$10 capital cost
$15-25 chemical
cost/year