Stability against arsenic leaching from biogenic arsenosulphides generated under reduced environment

Abstract

This paper examines the stability of biogenic arsenosulphides formed in the absence of iron and other metal sulphides, in a sulphidogenic attached growth reactor (AGR) through long term column leaching, aging and Toxicity Characteristics Leaching Procedure (TCLP). Around half of the reactor was packed with waste activated carbon (WAC) to promote biofilm growth and applied for treatment of arsenic spiked water. The FESEM/EDX and XRD analyses confirmed that the biosolids largely consists of orpiment and realgar. While aging and TCLP experiments were performed in anoxic and oxic environment with the goal to assess the stability of bio-sludge carrying arsenosulphides, the long term leaching experiments were performed through passing aerated distilled water to assess the stability of the exhausted WAC. With the prolonged aging period, leached arsenic was at the maximum of 167 and 306 μg/L during anoxic and oxic aging periods, respectively. In conformity with the results of the tests conducted, it can be concluded that the biogenic arsenosulphides formed under reduced environment is stable and do not falls under the category of hazardous waste.