Remediation of AMD with mussel shell bioreactors

Acid mine drainage (AMD) occurs when uneconomical waste rock containing iron sulphides are exposed to the atmosphere, water, and microorganisms. This acidic water, if left untreated can damage ecosystems as it is acidic and contains high concentrations of dissolved metals and sulphate. A novel bioreactor technology, currently being studied by CRL Energy in New Zealand, is using waste mussel shells – a cheap alternative to conventional treatments. This novel treatment medium has a high neutralizing capacity, containing enough organic matter in the form of chitin (5-12wt%) to promote the growth of sulfur reducing bacteria (SRB). Mussel shells can therefore act as the sole component of the bioreactor. The mussel shell bioreactor (MSB) is currently treating an AMD seep at the Stockton coal mine on the west coast of the South Island, an area with a history of coal mining and AMD impacted freshwater streams. The coal mine is located on the Brunner Coal Measures with a lithology of coal and marine mudstones containing up to 5 wt% pyrite, with lesser carbonates providing little opportunity for natural neutralization of AMD waters (Weisener & Weber 2010; Pope et al. 2010). The MSB removes ~99% of all metals and raises the pH from 3.2-3.5, to 7.6-8.3, and is estimated to be 15 times more cost effective than traditional methods of remediation for both installation and maintenance (DiLoreto et al. 2016). Ongoing research is focused on addressing the functionality of the system, and improving on the hydro-geologic design.

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