The use of ubiquitous metal-reducing bacteria (MRB) and the synthesis and transforming capability of nano-sized catalysts (BNC) provide enormous potential for the transformation of environmental waste to environmental catalysts, such as abandoned mine precipitates that are transformed into nontoxic and inexpensive catalysts for remediating contaminated groundwater. In this study, BNC from acid mine drainage (AMD) precipitates are transformed to nm-sized siderite after a fermenting process under anaerobic conditions, and MRB enriched from inter-tidal flat sediments were examined for efficiency in the Cr(VI) reduction and immobilization in upward flow-through sand column tests. As a result, BNC and MRB proved to have excellent Cr(VI) reducing/immobilizing capacity independently and when used in conjunction. In addition the combination of BNC+MRB showed to have a capacity enhanced with 20% more capability of Cr(VI) reduction and immobilization in flow-through column test for 168 h.