In QLD alone, around 80 million tonnes of coal is discarded from the mining process every year. These are mainly fines and reject from wash plants, and end up in ponds where they are dried and eventually buried. This wasted coal can promote acid mine drainage in some cases.
As with any anaerobic digestion process, the cost of feedstock and disposal of residues is a significant component of the operating costs. Coal tailings ponds represent a free source of carbon, that would ordinarily go to waste. Similarly, the coal that remains undigested remains in the ponds, requiring no additional cost for disposal.
Verso Energy is currently adapting cultures to samples of coal mine tailings from a QLD location, with the view to produce gas from waste coal.
The process will utilise established covered lagoon digester technology, which is commercially proven worldwide. Ponds will effectively be converted to large bioreactors, with gas being captured and stored under large membranes. This gas would ideally be used for local power production.