Arsenic, iron and nitrate removal from groundwater by mixed bacterial culture and fate of arsenic-laden biosolids

Abstract

Arsenic, iron and nitrate coexist in groundwater at a wide range of concentrations in various regions of the world. This study aims at investigating the concurrent arsenic and iron removal by combining the advantages of nitrate removal in a sulphidogenic bioreactor. A laboratory-scale suspended growth reactor was used to assess the performance of mixed bacterial culture at different arsenic, iron and nitrate concentrations. A semi-batch reactor (SmBR) was operated for more than 400 days in anoxic conditions at 30 ± 4 °C with different influent arsenate (250–1000 µg/L as arsenic), iron (2.0 mg/L) and nitrate (100–250 mg/L) concentrations in simulated groundwater and HRT of 3–6 days. Effects of different electron donors to deliver removing power on arsenic, iron and nitrate were also investigated. Nitrate was completely removed at all tested concentrations, while concentration of arsenic and iron met drinking water standards. The reactor was also charged with actual groundwater containing arsenic (up to 226 µg/L) as well as iron (up to 8.3 mg/L) and was able to remove both the contaminants below drinking water standards after addition of sufficient amount of sulphate. Toxicity characteristics leaching procedure results indicated that leachate arsenic concentrations were below the maximum United States Environmental Protection Agency guideline value for arsenic and biosolids which did not impose any environmental hazard.