Development of anaerobic upflow sludge system with enhanced sulfate reduction activity for the treatment of hazardous acid mine drainage

Abstract

To develop the proper acid mine drainage (AMD) treatment system suitable for domestic environment, the characteristics of eighty-eight AMDs were analyzed. Using statistical analysis, domestic AMDs were categorized with respect to their pH and ionic strength. It was found that AMDs with high ionic strength and low pH have high potential to be hazardous to the environment and the ecosystem. Based on this observation, the focus turned to the development of a treatment system that could effectively mitigate the heavy metal toxicity and acidity of AMDs with high ionic strength and low pH. In preliminary studies, artificial AMD was designed to have high ionic strength and low pH and was used to obtain reproducible data in the laboratory scale experiments. The characteristics of the conventional components of constructed wetlands including limestone and organic substrates were investigated in continuous and batch systems. It was observed that limestone beds could not effectively remove Zn, Cd, and Mn since these metals require high pH to precipitate as metal hydroxides. It was found that the formation of metal hydroxide precipitates on the surface of limestone prevented the further dissolution of limestone. The control of oxidation-reduction potential under 100 mV could reduce the formation of hydroxide precipitates on the surface of limestone. Cow manure, oak compost, mushroom compost, and sludge cake from a municipal wastewater treatment plant were selected as organic substrates. Upflow reactors packed with cow manure or oak compost effectively removed toxic metals in AMD for 25 days. Treatment system packed with oak compost showed highest metal removal efficiency mainly by ion exchange between metal ions and Ca. The treatment system packed with cow manure removed heavy metals by sulfate reduction and ion exchange. After 25 days, the metal removal efficiencies of both systems decreased rapidly. It was observed that in both systems the effluent Ca concentration went ...