TDP 05 - A Reducing and Alkalinity Producing System (RAPS) for passive treatment of acidic, aluminium rich mine waters (2006)
This Technology Demonstration Project Report describes a reducing and alkalinity producing system (RAPS) for the passive treatment of acidic, aluminium rich mine waters. The RAPS was constructed at Bowden Close in County Durham following successful pilot-scale field tests that showed that it is feasible to passively treat these leachates using subsurface flow biogeochemical reactors containing a mixture of compost and limestone. The RAPS improve water quality by the combined action of
bacterial sulphate reduction and limestone dissolution, safeguarding the porosity of the limestone layer.
The full-scale system incorporates two RAPS units and a polishing aerobic wetland. The RAPS units were specifically designed to optimise aluminium removal, as well as other contaminants, and consist of a mixed one-layer substrate, in contrast to the conventional dual-layer approach.
The performance data from the new system are very encouraging: pH rises to neutral values and key
pollutants are almost completely removed. Based on the performance data, the pilot study and experiences with other passive treatment sites, lifetime and life-cycle costs were calculated. These estimations demonstrate the economic advantages of passive treatment, in particular over extended periods of operation.