Utilization of a mesophilic consortium for arsenic removal from a copper smelting wastewater

Arsenic is one of the most hazardous pollutants released by the mining industry. Processes such as ore concentration and smelting produce high volumes of arsenic-rich wastewater, and several methods have been proposed to treat this arsenical wastewater. Arsenic precipitation using ferric ions yields compounds such as scorodite, a kind of ferric arsenate, while similar compounds can also be produced by iron-oxidizing microorganisms. However, both cases require high temperatures, potentially leading to significant economic costs when industrial applications are conceived. Then, arsenic removal with mesophilic iron-oxidizing microorganisms would greatly benefit from a decrease in operational temperature. Hence, this work aims to evaluate the biological removal of arsenic in wastewater, using a consortium of mesophilic (35 degrees C) iron-oxidizing microorganisms adapted to As (III). Our results indicate that arsenic speciation is a key factor for microbiologically assisted arsenic removal efficiency. Indeed, a maximum of 25 % or 91 % of arsenic was removed using As (III) or As (V), respectively. The effect of iron concentration was also evaluated, and the results showed that increasing iron concentration led to an increase in arsenic removal. Chemical controls removed more arsenic than inoculated assays when Fe:As molar ratios 1.0, 1.5, and 2.0 were used. Interestingly, inoculated tests achieved the best arsenic removal within a shorter timeframe (48 h) when a high Fe:As molar ratio (3.5) was used. This highlights the advantage of using a biological approach for arsenic removal under mesophilic conditions. In assays performed with smelting wastewater from a Chilean copper smelter, inoculated tests achieved 66 % arsenic removal when compared to 7 % obtained in chemical control. Energy dispersive X-ray spectroscopy analysis confirmed the presence of arsenic and iron in the solid residues, with no other metals detected. This finding opens the possibility of sustainable secondary copper recovery by reprocessing rich-arsenic smelting wastewater.