contaminated with As is filled in the container along with addition of oxidant and
coagulant. The water is mixed with the help of a manually operable mixer and then
the unit is left overnight for sedimentation of precipitated As to occur. Then, next
day settled water is taken out with the help of a pipe near bottom and is passed
through sand bed before using this as drinking water (Ahmed 2001).
5.4.1.2 Bucket Treatment Unit
The bucket treatment unit operates on the principle of coagulation, co-precipitation,
and adsorption. In this technique, one bucket serves the purpose of mixing
As-contaminated water with chemicals like potassium permanganate and aluminum
sulfate, and coagulation is promoted to enhance the sedimentation rate. The second
bucket collects settled water. The water is finally filtered with a cloth and passed
through another bucket containing sand filters and water is then used for drinking
(Tahura et al. 2001).
5.4.1.3 Iron As Treatment Unit
This process involves the oxidation of soluble As forms into the insoluble forms
followed by removal through filtration. Arsenic, which is usually present in reduced
arsenite (As
+3 ) form, is oxidized to arsenate (As
+5 ) along with the oxidation of
ferrous ions to ferric ions. The As
+5 is adsorbed onto iron hydroxide and the
precipitated As is then removed from the water through filteration (Akhter et al.
2015).
5.4.1.4 Tube Well-Attached As Treatment Unit
In this method, the arsenic removal plant is attached directly to the tube well. Arsenic
removal in this technique utilizes principles of coagulation, sedimentation, and
filtration. For the coagulation and sedimentation, sodium hypochlorite and aluminum alum are commonly used. This method has been found to remove As up to
about 90% in the villages of West Bengal, India.
5.4.2 Adsorptive Processes
Adsorption involves the removal of As by surface chemical reaction that includes
passage of water through a contact bed. In India and Bangladesh where the problem
of groundwater As contamination is severe, sorptive media based on activated
alumina are being extensively used for adsorption process for water treatment of
As. In adsorption treatment no chemicals are used and the process based solely
5 Arsenic Contamination of Groundwater and Its Mitigation Strategies
113
coagulant. The water is mixed with the help of a manually operable mixer and then
the unit is left overnight for sedimentation of precipitated As to occur. Then, next
day settled water is taken out with the help of a pipe near bottom and is passed
through sand bed before using this as drinking water (Ahmed 2001).
5.4.1.2 Bucket Treatment Unit
The bucket treatment unit operates on the principle of coagulation, co-precipitation,
and adsorption. In this technique, one bucket serves the purpose of mixing
As-contaminated water with chemicals like potassium permanganate and aluminum
sulfate, and coagulation is promoted to enhance the sedimentation rate. The second
bucket collects settled water. The water is finally filtered with a cloth and passed
through another bucket containing sand filters and water is then used for drinking
(Tahura et al. 2001).
5.4.1.3 Iron As Treatment Unit
This process involves the oxidation of soluble As forms into the insoluble forms
followed by removal through filtration. Arsenic, which is usually present in reduced
arsenite (As
+3 ) form, is oxidized to arsenate (As
+5 ) along with the oxidation of
ferrous ions to ferric ions. The As
+5 is adsorbed onto iron hydroxide and the
precipitated As is then removed from the water through filteration (Akhter et al.
2015).
5.4.1.4 Tube Well-Attached As Treatment Unit
In this method, the arsenic removal plant is attached directly to the tube well. Arsenic
removal in this technique utilizes principles of coagulation, sedimentation, and
filtration. For the coagulation and sedimentation, sodium hypochlorite and aluminum alum are commonly used. This method has been found to remove As up to
about 90% in the villages of West Bengal, India.
5.4.2 Adsorptive Processes
Adsorption involves the removal of As by surface chemical reaction that includes
passage of water through a contact bed. In India and Bangladesh where the problem
of groundwater As contamination is severe, sorptive media based on activated
alumina are being extensively used for adsorption process for water treatment of
As. In adsorption treatment no chemicals are used and the process based solely
5 Arsenic Contamination of Groundwater and Its Mitigation Strategies
113