Types of Minewater Treatment
Treatment necessary to remove minewater contamination depends upon its chemistry:
- If the minewater contains an excess of alkalinity, it will probably be amenable to by treatment by simple aeration to remove the dissolved iron, generally the major contaminant. Beneficial correction of other contaminants is also likely to occur during this process. Suspended particles generated following aeration are detained in purpose designed sedimentation ponds or a wetland system.
- If the minewater contains an excess of acidity, it will require the addition of alkalinity. The acidity is neutralised allowing the conversion of dissolved contaminants into suspended particles which are then detained in sedimentation ponds or on wetlands.
- For low flows of acidic minewater, passive treatment may be possible by the use of 'low cost' materials such as composts and limestone. Bacteriological and chemical process can generate alkalinity that allows sedimentation of generated solids. These operations require little manual intervention and minimise ongoing treatment cost. This form of treatment may be appropriate for incorporation into restoration schemes for mining sites.
- Most minewater treatment schemes incorporate wetlands technology to provide tertiary treatment to ensure that the minewater meets the standards required by the Environment Agency. The first major engineered wetland treatment scheme dealing with a minewater discharge was designed and constructed by IMC/ WYG at Woolley Colliery in 1995.
- Management of the 'ochre' sludge detained by the treatment system is important in controlling the costs of operation. Experience of collection, excavation, drying and disposal of 'ochre' will achieve system that minimises costs and maintains the security against incident during desludging.