The Use of Compost and Recycled Aggregates in the Treatment of Runoff Pollutants in Vegetated Sustainable Drainage Devices

Urbanisation has been characterised by unsustainable impacts such as depletion of natural resources, increased pollution, increased volume of surface runoff , decreased quality of storm water and destruction of aquatic life and biodiversity. Studies have shown that Sustainable Drainage Systems (SuDS) would help mitigate some of these effects. However, sustainability of some SuDS devices is questionable because their component parts involve the use of natural resources, i.e., topsoil and gravel.The overall aim of this study was to evaluate the efficacy of the application of recycled/waste materials in performing at least as well as topsoil and gravel in vegetative SuDS, thereby improving water quality and the overall sustainability of the devices. The materials investigated were compost and recycled aggregates with topsoil and gravel as control. Compost used included green compost and mixed compost while recycled aggregates comprised of crushed old and new bricks, as well as recycled limestone aggregates. Methodology included baseline characterisation of the materials followed by leaching experiments with heavy metals and motor oil, biomass determination and microbiological assessments.Application of recycled aggregates was shown to be more sustainable in terms of conserving natural resources, compared to topsoil and gravel. Results showed that compost would significantly biodegrade organic pollutants in vegetative SuDS under varying conditions, compared to topsoil. Also, vegetative growth in profiles containing compost was significantly more prolific than those with topsoil alone. Compost and recycled aggregates performed as well as gravel and topsoil in remediating pollutants, with >98% of pollutants being retained mostly within the growth media. This highlights the potential application of recycled aggregates and compost in SuDS devices which could reduce cost and provide use for used materials, which could have been disposed of in landfills or brownfields with huge negative environmental impacts.