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

Household Water Treatment for Arsenic Removal
Fact Sheet: Coagulation-Flocculation
2-Kolshi Filter
Potential Treatment Capacity
Very Effective For: Somewhat Effective For: Not Effective For:
Arsenic
Pathogens
Taste, odour, colour
Chemicals
What Is 2-Kolshi?
2-Kolshi is an arsenic removal method using two
buckets, developed by ENPHO in Nepal. The first
step is a coagulation process, followed by a
filtration through a ceramic filter.
How Does It Remove Arsenic?
Coagulation/flocculation is a traditional treatment
process in which the user adds a chemical
coagulant (typically iron sulphate or iron chloride) to
contaminated water. The coagulant helps
precipitate dissolved and suspended contaminants
so that they will settle out by gravity or can be
removed by filtration. Using this process, arsenic is
co-precipitated with iron.
In the 2-Kolshi system, iron sulphate is used as a
coagulant. The iron sulphate, sodium hypochlorite
and ash are added to the water and stirred. During
this process, the arsenic in the water changes form
(As(III) oxidizes to As(V)). The new form of arsenic
can co-precipitate with iron, forming flocs or large
particles. The water is then filtered to remove the
flocs. Ceramic filtration also removes pathogens.
Operation
Add chemicals (e.g. iron sulphate, sodium
hypochlorite and ash) to a bucket of water
Stir water for a few minutes
Let settle for one hour or more
Pass the water through a ceramic filter in the
bottom bucket
Key Information
Treatment
1 Output Cost
Efficiency
90% arsenic removal
99% microbial
removal
1 (Hwang, 2002)
2-Kolshi System
(Credit: T. Ngai)
3-5 litres/hour
$10 capital cost
$10-20 chemical
cost/year