Significance of bio-treatment by acid washing for enlargement of arsenic desorption in indigenous arsenic-resistant bacteria from gold mine

Abstract

Mining activities can lead to the generation of large quantities of heavy metal, specifically arsenic which is released from a gold mine, causing widespread contamination of the ecosystem. Removal of carcinogenic and toxic arsenic from wastewater is essential for the safety of water that may be used for irrigation or drinking. In this study, three different of indigenous arsenic resistant bacterial strains were isolated from gold mine environment, Bacillus thuringiensis strain WS3, Pseudomonas stutzeri strain WS9, and Micrococcus yunnanensis strain WS11. WS9, WS3, and WS11 reached stationary phase after eight, ten, and seven hours, respectively, at 37 °C when grown in LB with arsenic. Gram staining showed WS9 as gram-negative rods, WS3 as grampositive rods, and WS11 as gram-positive cocci. From the Silver nitrate test, WS3 and WS11 reduced As (V) to As (III) while WS9 oxidized As (III) to As (V). The desorption of arsenic using acid washing and parameters affecting the desorption of arsenic such as acid concentration, time, adsorbent dosage, and different volume of acid solution were investigated. The batch experiments were carried out using bacterial biomass cultured in LB with 2 mM arsenite (III) and 5 mM arsenate (V). Optimum conditions for desorption arsenic were determined, being 1 M acid concentration at 37 °C and 2 hours of contact with (50 mg) bacterial biomass in 100 ml acid solution. The removal of arsenite and arsenate increased after acid washing of bacterial biomass of the three strains. Consequently, desorption of arsenic using acid washing is essential for biomass regeneration.