The role of denitrification on arsenite oxidation and arsenic mobility in an anoxic sediment column model with activated alumina

Abstract

Arsenite (As(III)) is the predominant arsenic (As) species in reducing environments. As(III) is less strongly adsorbed than As(V) at circumneutral pH conditions by common non-iron metal oxides in sediments such as those of aluminum. Therefore, oxidation of As(III) to As(V) could contribute to an improved immobilization of As and thus help mitigate As contamination in groundwater. Microbial oxidation of As(III) is known to readily under aerobic conditions, however, the dissolved oxygen (O2) concentration in groundwater may be limited due to the poor solubility of O2 and its high chemical reactivity with reduced compounds. Nitrate (NO3−), can be considered as an alternative electron acceptor, which can support oxidation of As(III) to As(V) by denitrifying bacteria. In this study, two up-flow sediment columns packed with activated alumina (AA) were utilized to demonstrate the role of denitrification on the oxidation of As(III) to As(V) and its contribution to improved As adsorption onto AA. One column was supplied with NO3− (C1) and its performance was compared with a control column lacking NO3− (C2). During most of the operation when the pH was in the circumneutral range (d 50–250), the release of arsenic was greater from C2 compared to C1. The effluent As concentrations started increasing on d 60 and d 100 in C2 and C1, respectively. Complete breakthrough started on d 200 in C2; whereas in C1, complete breakthrough was never achieved. The effluent and solid phase As speciation was dominated by As(V) in C1, indicating the occurrence of As(III) oxidation due to NO3−; whereas in C2, only As(III) was dominant. This study illustrates a bioremediation or natural attenuation process based on anoxic microbial NO3−-dependent oxidation of As(III) to more readily adsorbed As(V) as a means to enhance the immobilization of As on alumina oxide particles in subsurface environments.

Chemolithotrophic denitrification in biofilm reactors

“…The gradual increase of the feed nitrate from 30 to 130 mg/L increased the denitrification rate up to 0.18 kg N-NO 3 À /m 3 d, whereas hydrogenotrophic denitrification was inhibited at higher influent nitrate concentrations. C/N ratio [57] in the range 0.9-2.2 resulted in a slight influence on denitrification efficiency which was stable in the range 94-96%, whereas a 6.56% drop was observed when the C/N ratio was reduced to 0.3, which was insufficient for denitrifiers to grow. Optimal pH and temperature ranged from 7 to 8 and from 25 to 35°C, respectively.…”

“…[65] to enhance As(V) immobilization onto biogenic Fe(III) (hydr)oxides. As(III) and total arsenic removals of 99.7% and 97.2% were respectively achieved with a HRT of 1 d. In another study, total arsenic removal up to 98.3% was achieved in a column packed with activated alumina (AA) at circumneutral pH and HRT of 13 d [57].…”

Anaerobic As(III) Oxidation Coupled with Nitrate Reduction and Attenuation of Dissolved Arsenic by Noviherbaspirillum Species

“…Some of the microbes oxidize As­(III) either for detoxification or to generate energy for growth under oxic conditions . Others can grow with As­(III) as an electron donor using nitrate as the terminal electron acceptor, reducing it to nitrite or completely denitrifying to N 2 Strain HC18 cannot oxidize As­(III) under oxic conditions but instead couples As­(III) oxidation with nitrate reduction.…”

Model-based evaluation on simultaneous nitrate and arsenite removal in a membrane biofilm reactor

“…As(V) is the dominant form under oxidizing conditions while As(III) mainly exists in reduced anaerobic environments (Sun et al, 2010). Efforts should be dedicated to achieving the efficient removal of NO 3 and As(III) from groundwater where these two toxicants are solely or collectively present, considering their individual as well as synergistic risks to human health as well as ecological system.…”

“…AsOB can use the energy and reducing power from As(III) oxidation for carbon dioxide (CO 2 ) fixation and cell growth under both aerobic and anaerobic NO 3 --reducing conditions (Zhang et al, 2015a). The oxidized As(V) produced is generally regarded as less mobile in the environment and less toxic to organisms than As(III) (Sun et al, 2010). Through proper introduction of CH 4 in conjunction with the creation of a favourable reactor configuration, the coculture of DAMO microorganisms and AsOB could be facilitated to likely achieve the simultaneous removal of NO 3 and As(III) from groundwater with various contamination conditions.…”