Abstract
The development of compact and cost-effective passive treatment systems is of critical importance for acid mine drainage (AMD) remediation in Japan. The purpose of this study was to construct an AMD treatment system comprising a sulfate-reducing bioreactor using rice bran as a carbon source for sulfate-reducing bacteria (SRB) and to demonstrate its stable operation for at least a year in terms of continuous sulfate reduction and metal removal. Our 35 L bioreactor comprised a packed inoculum layer of a mixture of rice husks, limestone, and field soil, which was covered with rice bran. During operation, the AMD input flow rate was adjusted to 11.7 mL/min (hydraulic retention time, HRT; 50 h). Throughout the year, physicochemical analyses of system input and output AMD samples revealed that both pH and oxidation–reduction potential values were consistent with the process of sulfate reduction by SRB, although this reduction was observed to be stronger in summer than in winter. Efficient metal removal was observed, with concentrations at the outlet port of <0.33 mg/L Zn, <0.08 mg/L Cu, and <0.005 mg/L Cd, more than meeting Japan’s national effluent standards. Illumina sequencing of 16S rRNA genes revealed that Desulfatirhabdium butyrativorans-related species, which belong to a lineage within Deltaproteobacteria, were dominant (39–48% of the total SRB population) within the bioreactor.
Highlights
Acid mine drainage (AMD) from metal and coal mines is a significant environmental concern if it is discharged untreated into rivers (Colmer and Hinkle 1947; Price and Errington 1998)
As the laboratory room temperature was not controlled, the temperature of the acid mine drainage (AMD) within the column at times fell below 10 °C in winter
Regarding the pH of the AMD in the bioreactor, an increasing tendency was observed over time (Fig. 3b)
Summary
Acid mine drainage (AMD) from metal and coal mines is a significant environmental concern if it is discharged untreated into rivers (Colmer and Hinkle 1947; Price and Errington 1998). Many treatment methods have been used to neutralize and remove harmful metals from AMD (Rakotonimaro et al 2016). In Japan, there are many abandoned mine sites where metal-containing AMD occurs. The business of AMD treatment is non-profit; cost savings are required where possible. Most AMD treatment methods at mine sites in Japan have used active treatment processes with chemical reagents, e.g. neutralization and sedimentation, because such approaches can shorten the processing time and are controllable. In Japan, the treatment of AMD effluents costs ≈$37.8 million per year (Mine Safety and Explosives Control Division, METI, Japan 2013)
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