The development of biotechnological processes involving the reduction of sulphur species was driven in large part by the need to provide reliable and economic methods to treat acidic, metal-contaminated waters found at mining operations all over the world.  For small, lightly-contaminated flows, passive treatment in which one or more natural biological processes and mechanisms can reduce contaminant loads as water flows through natural or engineered wetlands, can be successful. In this regard, the biological reduction of dissolved sulphate in water to produce sulphide which in turn can remove metals from solution as insoluble metals sulphides is of particular interest.   However, to treat high flows of water with significant metal and acidic loadings commonly found at mining operations, processes must be reliable and capable of treating water a high rate. The company BioteQ initially developed biological sulphate reduction to treat mine waters but found that high capital and operating costs were one of the barriers to commercial implementation at a large scale.  The company has since commercialized processes involving the reduction of elemental sulphur to produce sulphide which can remove metals from contaminated waters more cost effectively.  In these processes, metals can be precipitated selectively and recovered as high-grade products that can be sold to produce a revenue stream to offset treatment costs.  In some cases, the value of the recovered metals is sufficient for profitable operation.