Chapter 23: Household water treatment option: removal of arsenic in presence of natural Fe-containing groundwater by solar oxidation.

Recently, high As ground waters have been significantly recognized from vast alluvium of Bengal Delta Plain (BDP) and arsenicosis has emerged as an issue of great concern during the past decade due to rise in number of cancer cases. In BDP, arsenic removal plants (ARP) are often malfunctioning and field experience reveals that ARP needs serious attention from both implementers and beneficiaries, otherwise the quality of treated water is often questionable. The present study deals with groundwater (hydro) chemistry (high redox sensitive species, alkalinity and low E_h, SO₄^2-, NO₃^-, DO) and development of anoxic condition of the affected aquifers. High As_T/As(III) groundwater (As_T - 475-532 μg L^-1, As(III) - 290-316 μg L_-1) is often associated (r²=0.43) with high Fe (16.20-2.23 mg L^-1). Most of the FeT in the aqueous phase are Fe(II) (>95%) and the catalytic action of Fe(II) plays an important role in the fresh oxidative precipitation of Fe(III)(hydr)oxide and that can effectively disturb the Fe(III)/Fe(II) redox equilibria. BDP groundwaters (both natural and synthetic) are exposed (4 hrs, 9 am-1 pm) to sunlight to demonstrate effective As removal (98-95%). The batch studies illustrate that increasing initial As(III) concentration (600-1000 μg L^-1) decreases As removal (83 to 54%). Attempt is made to optimize and accelerate the As removal by adding various water-soluble chelating agents (EDTA, Na-citrate, oxalic and tartaric acid) and EDTA is the best among the lot (98% removal) whereas Na-citrate is the another suitable option (92% removal). The later chemical agent can be easily replaced with locally available natural source (lemon). The green chemistry approach and user-friendly technique can be further recommended for large-scale field trials. [ABSTRACT FROM AUTHOR]