Treatment of zinc-rich acid mine water in low residence time bioreactors incorporating waste shells and methanol dosing

• Published in: Journal of hazardous materials 2011-10, Vol.193, p.279-287
• Main Authors: Mayes, W.M., Davis, J., Silva, V., Jarvis, A.P.
• Format: Article
• Language: English
• Subjects: Acid mine drainage; Acids - metabolism; Agriculture, rearing and food industries wastes; Alkalinity; Applied sciences; Bacteria; Biological and medical sciences; Bioreactors; Biotechnology; Chemical engineering; Copper - isolation & purification; Dissolution; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Geologic Sediments - chemistry; Hydrogen-Ion Concentration; Lead - isolation & purification; Limit of Detection; Methanol - chemistry; Methods. Procedures. Technologies; Methyl alcohol; Mine pollution; Mining; Other industrial wastes. Sewage sludge; Others; Passive treatment; Pollution; Reactors; Sewage; Shells; Sulphate-reducing bacteria; Various methods and equipments; Wastes; Water Pollutants, Chemical - metabolism; Zinc; Zinc - analysis
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2011.07.073

► Continuous flow studies assess the efficacy of bioreactor substrates for passive mine water treatment. ► Combination of waste shells, manure and sewage sludge effective for >400 days in removing Pb, Cu and Fe. ► Sustained Zn removal in low residence time systems required methanol dosing. ► Alkalinity generation better in waste shells than traditional limestone clasts. ► Column tests inform design of pilot field systems. Bioreactors utilising bacterially mediated sulphate reduction (BSR) have been widely tested for treating metal-rich waters, but sustained treatment of mobile metals (e.g. Zn) can be difficult to achieve in short residence time systems. Data are presented providing an assessment of alkalinity generating media (shells or limestone) and modes of metal removal in bioreactors receiving a synthetic acidic metal mine discharge (pH 2.7, Zn 15 mg/L, SO 4 2− 200 mg/L, net acidity 103 mg/L as CaCO 3) subject to methanol dosing. In addition to alkalinity generating media (50%, v.v.), the columns comprised an organic matrix of softwood chippings (30%), manure (10%) and anaerobic digested sludge (10%). The column tests showed sustained alkalinity generation, which was significantly better in shell treatments. The first column in each treatment was effective throughout the 422 days in removing >99% of the dissolved Pb and Cu, and effective for four months in removing 99% of the dissolved Zn (residence time: 12–14 h). Methanol was added to the feedstock after Zn breakthrough and prompted almost complete removal of dissolved Zn alongside improved alkalinity generation and sulphate attenuation. While there was geochemical evidence for BSR, sequential extraction of substrates suggests that the bulk (67–80%) of removed Zn was associated with Fe–Mn oxide fractions.