Simulated acid mine drainage treatment in iron oxidizing ceramic membrane bioreactor with subsequent co-precipitation of iron and arsenic

Abstract

Acid mine drainage (AMD), generated in the active and abandoned mine sites, is characterized by low pH and high metal concentrations. One AMD treatment possibility is biologically oxidizing Fe2+ followed by precipitation through pH control. As compared to autotrophic iron oxidizing microbial community, a microbial community enriched in the presence of organic nutrients was hypothesized to yield higher biomass during commissioning the bioreactor. In this study, the treatment of Fe, Cu, Co, Mn, Zn, Ni, and As containing simulated AMD was studied using an iron-oxidizing ceramic membrane bioreactor (CMBR) at varying hydraulic retention times (HRTs) (6-24 h) and two different feed Fe2+ concentrations (250 and 750 mg/L). The impact of tryptone soya broth (TSB) on the CMBR performance was also investigated. Almost complete Fe2+ oxidation and sustainable flux at around 5.0 L/(m2.h) were obtained in the CMBR with the Alicyclobacillus tolerans and Acidiphilium cryptum dominated enrichment culture. The Fe2+ oxidation rate, as assessed in batch operation cycles of CMBR, increased significantly with increasing Fe2+ loading to the bioreactor. The iron oxidation rate decreased by the elimination of organic matter from the feed. The increase of the CMBR permeate pH to 3.5-4.0 resulted in selective co-precipitation of As and Fe (over 99%) with the generation of biogenic schwertmannite.