Laboratory based experiments to assess the use of green and food based compost to improve water quality in a Sustainable Drainage (SUDS) device such as a swale

Many tonnes of compost are generated per year due to door step composting of both garden and kitchen waste. Whilst there are commercial outlets for the finer grade of compost (< 10 mm) in plant nurseries, there is little demand for the coarser material (> 25 mm). This paper reports part of a WRAP-sponsored (Waste Resources Action Programme) study which investigated the potential for green (GC) and mixed green and food (MC) composts to be incorporated into Sustainable Drainage (SUDS) devices such as swales, and replace the topsoil (TS) onto which turf is laid or grass seed distributed. However, it is not known whether compost can replace TS in terms of pollutant remediation, both the trapping of polluted particulates and in dealing with hydrocarbons such as oil, but also from a biofilm development and activity perspective. Using laboratory based experiments utilising leaching columns and an investigation of microbiological development in the composts studied, it was found that many of the differences in performance between MC and GC were insignificant, whilst both composts performed better in terms of pollutant retention than TS. Mixed compost in particular could be used in devices where there may be oil spillages, such as the lorry park of a Motorway Service Area due to its efficiency in degrading oil. Samples of GC and MC were found to contain many of the bacteria and fungi necessary for an active and efficient biofilm which would be an argument in their favour for replacement of TS and incorporation in swales.