Abstract
Biofiltration systems, as one of the best management practices, have good potentials to improve stormwater quality and hydrology of urban catchments. While biofiltration systems are well-studied in developed countries, the majority of those studies are conducted for temperate climate and there is a lack of lab-scale and field-scale studies on such systems under tropical conditions. This paper focuses on the performance of a lab-scale prototype biofiltration systems in stormwater retention efficiency as well as pollutants removal (including heavy metals and nutrients) from synthetic stormwater reproducing tropical rainfall events. A three-layer sand-based filter media with two different native plants including Pedilanthus tithymaloides and Cyperus alternifolius was selected for this study. Results showed that the system with Cyperus has a better stormwater retention capacity compared to the one with Pedilanthus. In addition, the observed infiltration rate in Cyperus and Pedilanthus were 338 mm/h and 267 mm/h, respectively. The better hydraulic performance in the system with Cyperus was attributed to the deeper and more extensive root penetration of this plant (as deep as 800 mm) compared to Pedilanthus (as deep as 250 mm). While both systems failed to perform well in removing total nitrogen, they performed significantly better in removing total phosphorus (Cyperus and Pedilanthus removed 67.3% and 62.5% of total phosphorus, respectively). The statistical analysis of results showed that the top 100 mm layer of filter media is the main contributor to total phosphorus removal. However, no major differences were observed between the two systems in phosphorus removal. Moreover, both systems were also capable of removing the available heavy metals (i.e., Fe, Cu, Mn, Ni, Pb, and Zn) as the removal efficiencies exceeded 90%, except for Fe (76%). Similar to phosphorus, it was concluded that the top layer is the major contributor to the heavy metals removal. Overall, the biofiltration system using Cyperus was found to be a successful system for operating under tropical conditions.
Highlights
IntroductionIn the 20th and 21st centuries, global-scale transformation of rural to urban areas has happened rapidly and by 2050 the percentage of the world’s population lives in the urban area and will increase to 66% compared to 30% recorded in 1950 [1]
The biofiltration system with Cyperus alternifolius had a higher infiltration rate and larger retention efficiency when compared to the one with Pedilanthus tithymaloides
Total phosphorus removal showed positive correlation with the depth of the filter media. This trend in phosphorus removal could be attributed to the adsorption mechanism in filter media; this cannot be confirmed by the limited results of this study
Summary
In the 20th and 21st centuries, global-scale transformation of rural to urban areas has happened rapidly and by 2050 the percentage of the world’s population lives in the urban area and will increase to 66% compared to 30% recorded in 1950 [1]. Excess phosphorus from decaying plants, birds and animals faeces, detergents, and fertilizers is another example of pollution in urban water bodies [9]. Based on a case study in an urban catchment, Todeschini [10] concluded that peak flows, volume, and pollutant loads increased significantly after conversion of 33% of nonurban pervious area to the impervious one. To overcome these issues, water sensitive urban design (WSUD), which is an approach for engineering design, can be used to minimize the stormwater pollution and maximize water resources recharge in urban areas through an integrated urban water planning approach. WSUD is developed and practiced in Australia and is conceptually similar to the Low-impact development (LID), which is common in USA and Canada
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