TECHNICAL ARTICLE The Use of Mussel Shells in Upward-Flow Sulfate-Reducing Bioreactors Treating Acid Mine Drainage Benjamin Uster • Aisling D. O’Sullivan • Su Young Ko • Alex Evans • James Pope • Dave Trumm • Brian Caruso Received: 23 January 2014 / Accepted: 14 July 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract In this study, sulfate-reducing bioreactors (SRBRs) efficiently treated acid mine drainage (AMD) for a contiguous period of 5 months. The AMD was sourced from an active coal mine on the South Island of New Zealand and typically had a pH \ 3, 1,700 mg/L of sulfate, 50 mg/L of Fe, 18 mg/L of Al, 15 mg/L of Mn, 4 mg/L of Zn, and lower concentrations of other contaminants. Two alkalinity-generating materials (mussel shells and lime- stone) and two hydraulic retention times (HRTs) of 3 and 10 days were evaluated. Influent and effluent water quality parameters were monitored weekly. Each SRBR system successfully increased the pH (C6) and the alkalinity (B350 mg/L CaCO 3 ) of the water while removing sub- stantial amounts of dissolved metals at both HRTs (C90 % Al, C86 % Fe, C87 % Cu, C99 % Zn). Mn removal was lower and ranged from 19 to 55 %. Increasing the HRT from 3 to 10 days significantly improved effluent water quality in terms of pH, alkalinity, and metals and sulfate removal. SRBRs using mussel shells in their reactive mixtures were more effective than those using limestone, with a higher (60–113 %) alkalinity generation and a better (3–5 %) metal removal. This study showed that mussel shells are an inexpensive and sustainable alternative to mined limestone for AMD passive treatment, and that better treatment efficiency resulted from a longer HRT. Keywords Mine water  Passive treatment  Organic substrate  Alkalinity generation  Metal removal rates Introduction Acid mine drainage (AMD) is a multi-factor source of pollution that typically exhibits low pH and contains high concentrations of metals and sulfate (Blowes et al. 2003; Nordstrom and Alpers 1999; Pope et al. 2010; Younger et al. 2002). It can be severely detrimental to aquatic life and usually needs to be treated before being discharged into the environment (Byrne et al. 2012; Salomons 1994; Younger 2004). Numerous treatment methods based on mechanical and chemical processes or relying on natural (bio)geochemical processes have been developed (Hedin et al. 1994; Johnson and Hallberg 2005; Lens et al. 1998; Skousen et al. 2000; Watzlaf et al. 2004; Wildeman and Schmiermund 2004; Younger et al. 2002). Sulfate-reducing bioreactors (SRBRs) are a promising technique that has gained prevalence in the past few years because they concomitantly remove the key contaminants of acidity, metals, and sulfate from AMD (Garcia et al. 2001; Johnson and Hallberg 2005; Zagury et al. 2005). Other advantages of this treatment approach include relatively low mainte- nance costs, minimal energy requirements, and the possi- bility of using natural organic wastes in the reactive mixture (Rose 2010; URS 2003; Wildeman et al. 2006). SRBR relies on the principle of sulfidogenesis, during which sulfate-reducing bacteria (SRB) oxidize a carbon source (i.e. the organic substrate) and reduce sulfate to sulfide through a dissimilatory process (Eq. 1), where CH 2 O represent a simple carbon/electron source (Hao et al. 1996; Widdel 1988). Typically, a substrate comprises a mixture of organic and alkaline materials. B. Uster (&)  A. D. O’Sullivan  S. Y. Ko  A. Evans  B. Caruso Department of Civil and Natural Resources Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand e-mail: benjamin.uster@pg.canterbury.ac.nz J. Pope  D. Trumm CRL Energy Ltd, 97 Nazareth Ave, PO Box 29-415, Christchurch 8540, New Zealand 123 Mine Water Environ DOI 10.1007/s10230-014-0289-1