Passive Remediation Using Compost
The use of compost, limestone and other materials which may be considered waste products offers the potential for 'low-cost' treatment schemes, particularly for acidic effluents. Schemes are designed to operate unattended for long periods with only a minimum of manual intervention. IMC/ WYG have designed a number of innovative schemes and are presently participating in an EU Research project into Passive In - Situ Remediation of Acidic Mine/ Industrial Drainage (PIRAMID).
Limeisa Mine, La Coruna, Spain
IMC/ WYG carried out detailed design under an ECSC contract into passive remediation of acidic mining effluents at an opencast lignite mine in Spain. Two experimental systems were constructed using limestone and local farm compost to construct anaerobic reactors and passive anoxic beds.
The first system utilised effluent flow over a lagoon containing compost into an anoxic bed. The de-oxygenated effluent contacts alkalinity in the limestone bed allowing sedimentation of dissolved solids on a subsequent wetland. The second system used a stacked compost/limestone RAPS system prior to discharge to a tertiary wetland.
The systems proved the potential for passive systems in place of active chemical options with consequential reduction in operating costs.
Renishaw Park, Derbyshire, UK
A seepage from the colliery tip has a pH of 3 and contains elevated levels of dissolved metals. The flowrate varies with rainfall.
The WYG design used an innovative use of a twin trench system to minimise land requirements for treatment. The downflow of seepage through the first trench containing compost/wood waste is followed by upflow through the adjacent trench containing limestone to impart alkalinity. Sedimentation of generated solids is on a wetland.
Aspatria, Cumbria, UK
A 8 ha abandoned colliery spoil heap discharges highly acidic drainage with excessive levels of metals which is seriously downgrading the adjacent watercourse. The tip is unrestored and heavily eroded with the discharge passing to a marsh area.
IMC/ WYG designed anaerobic test lagoons to assess the extent of remediation that can be achieved using low cost materials. Waste materials such as sewage sludge and paper waste have been used in combinations in the lagoons to provide an environmentally responsible solution to the remediation of the drainage. Sampling and analysis of the effluent from each lagoon will be carried out during 2003 with a full scale restoration should results prove effective and economic.
Conclusion
The use of compost / waste material / limestone technology offers environmental restoration the potential of a low-cost solution to drainage problems and a near walk away proposal for improvement schemes. Whilst ongoing intervention and costs of such schemes are low, major overhaul of the reactive materials will be necessary every 10-20 years.