A REVIEW ON THE APPLICATION OF GRANULAR FILTER MEDIA AND THE UTILIZATION OF AGRO-INDUSTRIAL WASTES FOR STORMWATER QUALITY IMPROVEMENT

The stormwater management practices have changed from conveyance-oriented to storage-oriented, as part of the Best Management Practices (BMPs). Still, uncontrolled development increases potential pollutants in the stormwater, which conveys into a water body or river. Continuous improvements in the filtration mechanism would complement stormwater management. For the past decades, there is progress in applying granular filter media for stormwater quality improvement. However, the reports were not systematically reviewed. In this paper, the recent five years research that utilizes granular filter media for improving stormwater quality was retrieved and reviewed. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) was referred to, where Scopus and Web of Sciences, two primary journal databases, were used. Initially, keywords searching strings have resulted in 467 articles, which were further screened. Four themes have been formed: stormwater management, stormwater characteristics, separation mechanisms, and future perspectives. Next, two sub-themes and two sub-sub-themes were further established. Then, 65 articles were included manually to complement the themes developed to explore the potential agro-industrial wastes as sustainable filter media. Therefore, this review has proven that the relatively inexpensive and renewable resources from the agro-industrial wastes can remove pollutants efficiently from the stormwater. Four main criteria affecting filter media performances are also highlighted, including the grain sizes of the media, media bed configuration, hydraulic loading rate, and the suspended solids concentration. Further study on these variables can be beneficial to explore the impact of utilizing agro-based media in stormwater filtration.

Media properties and their effect on filter performance and backwashing

Granular filter media used in water treatment have a range of physical properties. Media are usually selected on the basis of size, but bed behaviour is also affected by density and voidage of the media, particularly during backwashing. The fluidisation and backwashing bed behaviour of a number of filter media have been investigated. It has been found the fluidisation is affected by the bed packing arrangement which is determined by previous treatment. Filter media may be subject to attrition during backwashing which will affect the grain size and voidage. Combined air and water flow rates for collapse-pulsing are also affected by the media characteristics. When collapse-pulsing is used to clean triple media filters, complete mixing of the layers occurs, but restratification is possible using a high rate fluidising water wash. Backwashing is an important part of the filtration process so understanding the effect of media properties on the process is essential for optimisation.