Arsenic removal from drinking water by flocculation and microfiltration

Arsenic removal from drinking water is a major problem in many parts of the world. We have investigated arsenic removal by flocculation and microfiltration. Ferric chloride and ferric sulphate have been used as flocculants. The use of small amounts of cationic polymeric flocculants, as flocculation aids in the presence of ferric ions, has also been investigated. The results obtained here show that flocculation prior to microfiltration leads to significant arsenic removal in the permeate. Further, the addition of small amounts of cationic polymeric flocculants lead to significantly improved permeate fluxes during microfiltration. The residual turbidity, after flocculation and microfiltration, may be used as a guide to the level of arsenic removal. Since energy requirements for microfiltration are low and fluxes high, compared to other membrane processes such as reverse osmosis and nanofiltration, flocculation and microfiltration may be a cost effective method for arsenic removal from drinking water.

The feasibility of flocculation and microfiltration for arsenic removal from drinking water has been investigated. Flocculation using ferric ions can lead to significant arsenic adsorption onto the ferric complexes present. However the efficiency of this adsorption depends on the pH of the water and the presence of other ions. Microfiltration of the flocculated water results in rejection of the flocs formed by the membrane thus leading to low turbidity and arsenic removal in the filtrate. Addition of small amounts of cationic polymeric flocculant can greatly increase the permeate flux during microfiltration.