| Popis: |
Urbanisation, a process associated with industrialisation and development has been characterised by unsustainable impacts such as increased impervious surfaces, increased air pollution, increased use of natural resources, increased volume of surface run-off, decreased quality of surface run-off, and depletion of biodiversity and habitats. The effects of these impacts on the environment include climate change, flooding, erosion, pollution of water bodies, and destruction of aquatic life and biodiversity. Studies have shown that sustainable designs such as Sustainable Drainage Systems (SuDS) would help mitigate some of these effects sustainably. SuDS are natural drainage systems that simulate the natural drainage of a site/catchment and work in harmony to achieve increase in ground infiltration and treatment of runoff; and reduction in flow rates and volume of surface runoff, thereby improving storm water quality, reducing erosion, recharging groundwater, improving biodiversity and ultimately improving sustainability. However, sustainability of SuDS devices are questionable because their component parts involve the use of natural resources i.e. topsoil and gravel. The overall aim of this research 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 overall sustainability. The materials applied were compost and recycled aggregates. In assessing their efficacy in vegetative SuDS, the risk these materials could pose to water quality was not overlooked but was considered in establishing an ideal model for the treatment of pollutants in vegetative SuDS. Results of this research showed that overall compost and recycled aggregates were able to perform at least as well as gravel and topsoil in vegetative SuDS in terms of characterisation, biofilm and vegetative development, and remediation of runoff pollutants thereby improving the sustainability of vegetative SuDS. Compared to gravel and topsoil, characterisation of compost and recycled aggregates was shown to be less expensive, less time consuming (except for recycled aggregates) and more sustainable, in terms of conserving natural resources. It was deduced that compost would be able to biodegrade organic pollutants in vegetative SuDS in varying conditions, compared to topsoil, thereby improving water quality. Vegetative growth in profiles containing compost were more prolific than those with topsoil alone, indicating that vegetative SuDS containing compost would attenuate stormwater and remediate pollutants by phytoremediation, better than topsoil. Results showed that 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, confirming that most pollutants are treated within the growth media of vegetative SuDS devices. This research was able to establish that SuDS components can be as unsustainable as components of conventional drainage systems in terms of their social, economic and environmental impacts; and that recycled materials could perform just as well as conventional materials, whilst improving their sustainability. This research further established that compost and recycled aggregates can be used in vegetative SuDS, such as swales, as literature has shown that the use of compost and recycled aggregates in vegetative SuDS has been limited to compost blankets and socks and substrates for green roofs. Suggestions for other waste materials that can be used instead topsoil and gravel in vegetative SuDS were also made. Results from this research were applied in the development of a swale model for the treatment of pollutants in vegetative SuDS. |
