Development of arsenic removal unit with electrocoagulation and activated alumina sorption: Field trial at rural West Bengal, India

Abstract

In the present study, electrocoagulation (EC) with iron electrodes along with adsorption by activated alumina has been evaluated as a treatment process for arsenic removal from groundwater. Batch scale experiments were performed with iron electrodes to assess the removal efficiency of electrocoagulation. The effects of inter-electrode distance and electro-charge loading (ECL) were evaluated on arsenic removal. EC was able to decrease the arsenic concentration in the aqueous phase below 10 ppb at ECL of 60 coulomb/L with 1 cm inter-electrode distance. The optimal condition was obtained by Response Surface Methodology (RSM) with the help of central composite design (CCD). The regression equation and analysis of variance were originated using Design-Expert software and F value (131.56), p-value (<0.05), and desirability value of 1 were obtained for the optimized model. Activated alumina adsorption has also been shown to be a promising arsenic removal technology (As5+) with 15 min of equilibrium time. An arsenic removal system was designed with EC unit, sand filter, and activated alumina column in series for field application. The field unit was able to deliver safe water to the local community. During the operation, the electrodes were passivated, and calcium-based deposition was found on the cathodes. Periodic electrode reversal was able to minimise the passivation. Due to the accumulation of ferric hydroxide flocs, the pores of the filter bed become clogged and they must be cleaned by backwashing. The Backwash system should be continued until the water runs clear. An arrangement of a suitable soak pit is made to contain the backwash water avoiding any environmental contamination. EC could be able to deliver safe water locally in rural areas at affordable prices due to its high efficiency and low operation and maintenance costs.