Simultaneous Biological Removal of Arsenic, Iron, and Nitrate From Groundwater By a Terminal Electron Accepting Process

Abstract

Groundwater contamination, natural, and/or anthropogenic is a major concern to human health. There are several reports of arsenic and iron co-contamination of groundwater from many parts of the world including northeastern states of India. Along with arsenic and iron, there are reports on co-occurrence of nitrate in groundwater of Assam, Jharkhand (India) and many other areas of the world. Several groundwaters contain increased concentrations of these pollutants that are observed either isolated or in pairs, or all three together. Although several physicochemical and/or biological processes have been established for the removal of one of the above-mentioned contaminants, but till now very few studies have been performed on the efficient and cost-effective simultaneous removal of two or more contaminants from groundwater. In the present study, the performance of suspended growth batch bioreactors on simultaneous removal of arsenic, iron, and nitrate by mixed bacterial culture was evaluated by means of terminal electron accepting process in the presence of sulfate. A series of conical flasks were used as batch reactors were inoculated with mixed bacterial culture mainly collected from a wastewater treatment plant and acclimatized in the presence of arsenic, nitrate, and sulfate. The reactors were fed with real contaminated ground-water containing 30–125 μgl–1 of arsenic, 1.5–3.0 mgl–1 of iron, 50 mgl–1 of 248nitrates, 25 mgl–1 of sulfate, along with 105 mgl–1 of COD. The reactors were operated for a period of 7 days at 30°C in an incubator shaker. The removal approach consists of reduction of arsenic and nitrate coupled with oxidation of an electron donor (acetic acid). Complete nitrate removal was observed whereas arsenic and iron were below drinking water permissible limits of 10 μgl–1 and 0.3 mgl–1, respectively within 3–4 days of operation. The insoluble bio-precipitates of arsenic and/or iron sulfides were the main arsenic and iron removal mechanism in the studied system.