Compost-based Treatment Ponds for Mine Water
- Characterisation of Bio-bed

The Coal Authority and Environment Agency have supported the development of a treatment system for metal rich mine water in the Lake District.  Sulphate reducing bacteria within a compost-based vertical flow treatment pond are removing heavy metal contaminants and improving final discharged water quality. The active life of the bio-bed in the treatment pond is projected to be at least 10 years. However our clients want to identify a sustainable recovery route for the spent material at end-of-life.

An initial assessment indicated that the compost-based media was hazardous by HP14 (ecotoxicity) due to elevated concentrations of zinc.

The Coal Authority engaged WRc to sample, characterise and provide an independent assessment of the bio-bed . WRc developed a sampling plan to remove intact core samples from under 0.5m of water from two treatment ponds.. Cores were collected from floating pontoons to provide a representative cross-section of the material A test programme is underway to provide our clients with an interim measure of metal contamination in the compost-based media, and a better estimation of operational life-time. Selective chemical speciation tests will be used to identify the metal species present to inform the ‘hazardous' property assessment. These will be completed alongside particle size and density separation techniques to minimise waste ‘disposal’ at end-of-life.

Our clients want robust evidence to better understand the whole life costs of these compost-based treatment ponds which may be used for other metal-rich mine water treatment schemes in England. A successful outcome for the project would be a non-hazardous waste classification of the exhausted bio-bed.

Dr Kathy Lewin head of resource efficiency