As(III) oxidation by MnO2 during groundwater treatment

Abstract

The top layer of natural rapid sand filtration was found to effectively oxidise arsenite (As(III)) in groundwater treatment. However, the oxidation pathway has not yet been identified. The aim of this study was to investigate whether naturally formed manganese oxide (MnO), present on filter grains, could abiotically be responsible for As(III) oxidation in the top of a rapid sand filter. For this purpose As(III) oxidation with two MnO containing powders was investigated in aerobic water containing manganese(II) (Mn(II)), iron(II) (Fe(II)) and/or iron(III) (Fe(III)). The first MnO powder was a very pure - commercially available - natural MnO powder. The second originated from a filter sand coating, produced over 22 years in a rapid filter during aeration and filtration. Jar test experiments showed that both powders oxidised As(III). However, when applying the MnO in aerated, raw groundwater, As(III) removal was not enhanced compared to aeration alone. It was found that the presence of Fe(II)) and Mn(II) inhibited As(III) oxidation, as Fe(II) and Mn(II) adsorption and oxidation were preferred over As(III) on the MnO surface (at pH 7). Therefore it is concluded that just because MnO is present in a filter bed, it does not necessarily mean that MnO will be available to oxidise As(III). However, unlike Fe(II), the addition of Fe(III) did not hinder As(III) oxidation on the MnO surface; resulting in subsequent effective As(V) removal by the flocculating hydrous ferric oxides.

Arsenite Removal in Groundwater Treatment Plants by Sequential Permanganate―ferric Treatment

“…The observed oxidation of As(III) in 9.3 min of rapid sand filtration was higher-than-expected because As(III) oxidation by dissolved oxygen alone proceeds slowly [53,54]. Similar rapid oxidation of As(III) during rapid sand filtration was reported by Gude et al [36] and Katsoyiannis et al [34] and may be attributed to the manganese oxides or microbial activity in the filter bed [38,46,68]. With MnO 4¯e Fe(III) dosing, the dissolved As in the supernatant and filtrate consisted entirely of As(V) ( Fig.…”

“…The concentration of Fe nevertheless can be increased by dosing an Fe(III) or Fe(II) based coagulant such as ferric chloride (FeCl 3 ) or ferrous sulfate (FeSO 4 ). The As removal efficiency may differ when Fe(II) or Fe(III) is dosed, per equal concentration of precipitated Fe [46,47]. In The Netherlands, FeCl 3 is the most widely used coagulant in drinking water production and for this reason we chose it as the source of Fe in this study.…”

Arsenite removal from groundwater by iron–manganese oxides filter media: Behavior and mechanism

“…Pre‐oxidation of As(III) to As(V) is often necessary for effective As(III) removal from water. Manganese oxides are extensively used as the oxidizing agent (Gude, Rietveld, & Halemm, ; Lafferty, Gindervogel, & Sparks, ). An increasing number of treatments are adopting natural sorbents, particularly metal oxides, such as iron (hydr) oxides (Dixit & Hering, ; Maji, Kao, Liao, Lin, & Liu, ), alumina (Arai, Elzinga, & Sparks, ).…”

The properties of sludge formed as a result of coagulation of backwash water from filters removing iron and manganese from groundwater

“…The safety of drinking water is a significant issue all over the world. The groundwater is contaminated by iron, manganese, ammonium, nitrate compounds as well as heavy metals and organic matter; however, mainly groundwater is contaminated by iron and manganese compounds [1].…”