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Bioretention systems are among the most popular stormwater best management practices (BMPs) for urban runoff treatment. Studies on the plant performance using bioretention systems have been conducted, especially in developed countries with a temperate climate, such as the United States and Australia. However, these results might not be applicable in developing countries with tropical climates due to the different rainfall regimes and the strength of runoff pollutants. Thus, this study focuses on the performance of tropical plants in treating urban runoff polluted with greywater using bioretention system. Ten different tropical plant species were triplicated and planted in 30 mesocosms with two control mesocosms without vegetation. One-way ANOVA was used to analyse the performance of plants, which were then ranked based on their performance in removing pollutants using the total score obtained for each water quality tests. Results showed that vetiver topped the table with 86.4% of Total Nitrogen (TN) removal, 93.5% of Total Phosphorus (TP) removal, 89.8% of Biological Oxygen Demand (BOD) removal, 90% of Total Suspended Solids (TSS) removal and 92.5% of Chemical Oxygen Demand (COD) removal followed by blue porterweed, hibiscus, golden trumpet and tall sedge which can be recommended to be employed in future bioretention studies.

Constructed wetlands are an affordable and reliable green alternative to conventional mechanical systems for treating domestic sewage. This study investigates the potential of 14 tropical wetland plant species for removing heavy metals from domestic sewage through the bioconcentration factor (BCF), translocation factor (TF), enrichment factor (EF), and geoaccumulation index (Igeo) using batch mesocosm studies. Plants with BCF > 1 and TF > 1 are classified as phytoextractors, while species with BCF > 1 and TF < 1 are phytostabilisers. The results indicate that 11 out of 14 species are magnesium phytostabilisers, 10 are calcium phytoextractors, and no plant species demonstrate ferrum phytoextraction properties. As for manganese phytoremediation, only three species depicted phytoextraction and phytostabilisation properties. The enrichment factor (EF) for all of the studied metals with ferum as a reference metal in all of the soil samples decreased after the phytoremediation of domestic sewage experiments, indicating depletion to mineral enrichment (EF < 2). All of the soil samples are generally classified as uncontaminated based on Igeo indices. Based on the factors and indices, it is suggested that the plants may have facilitated heavy metal removal from domestic sewage through uptake into the plant tissues from the roots.

Bioretention is a water management practice that is increasingly being applied for runoff quality control. Although previous Bioretention studies have used some techniques to improve nutrient removal, some nutrients still leach out. Therefore, this study used Cascaded Bioretention (CB) by connecting three Bioretention columns in series. The planted Bioretention Column was retrofitted by adding a subsurface drainage module (SDM) below the gravel layer to create a dual saturated zone. This study aimed to investigate the effect of the number of treatments, vegetation, and modified saturated zone on enhancing nutrient removal from agricultural runoff and to understand nutrient removal mechanisms. The removal efficiencies of NH3-N, NO3-N, NO2-N, and TN improved to 89.8%, 49.7%, 49.2%, and 53.4%, respectively. The only negative removal was ON, which significantly decreased by incorporating vegetation and a modified saturated zone. Increasing the number of treatments significantly enhanced TN and ON while maintaining stable removal for other nitrogen compounds. However, phosphorus was less sensitive to increasing the number of treatments. Nitrogen removal could be enhanced by different removal processes such as nitrification, denitrification, mineralization, assimilation by plant uptake, and Anammox. However, phosphorus removal was less complicated, as adsorption and infiltration are likely to be the main removal mechanisms.

This paper reviews the design and component of two types of RWHS, namely roof harvesting system (RHS) and pond harvesting system (PHS). The performance in terms of quantity and quality of collected rainwater and energy consumption for RWHS with different capacities were evaluated, as well as the benefits and challenges particularly in environmental, economic and social aspects. Presently, RHS is more commonly applied but its effectiveness is limited by its small scale. The PHS is of larger scale and has greater potentials and effectiveness as an alternative water supply system. Results also indicate the many advantages of PHS especially in terms of economics, environmental aspects and volume of water harvested. While RHS may be suited to individual or existing buildings, PHS has greater potentials and should be applied in newly developed urban areas with wet equatorial climate.

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.

Rapid urbanization, population explosion and climate change have threatened water security globally, regionally and locally. While there are many ways of addressing these problems, one of the innovative techniques is the recent employment of Sustainable Urban Drainage Systems (SUDS) which include rainwater harvesting systems (RWHS). Therefore, this paper reviews the design and component of two types of RWHS, the namely roof harvesting system (RHS) and the pond harvesting system (PHS). The performance in terms of quantity and quality of collected rainwater and energy consumption for RWHS with different capacities were evaluated, as well as the benefits and challenges particularly in environmental, economic and social aspects. Presently, the RHS is more commonly applied but its effectiveness is limited by its small scale. The PHS is of larger scale and has greater potentials and effectiveness as an alternative water supply system. Results also indicate the many advantages of the PHS especially in terms of economics, environmental aspects and volume of water harvested. While the RHS may be suited to individual or existing buildings, the PHS has greater potentials and should be applied in newly developed urban areas with wet equatorial climate.

Bioretention systems have been implemented as stormwater best management practices (BMPs) worldwide to treat non-point sources pollution. Due to insufficient research, the design guidelines for bioretention systems in tropical countries are modeled after those of temperate countries. However, climatic factors and stormwater runoff characteristics are the two key factors affecting the capacity of bioretention system. This paper reviews and compares the stormwater runoff characteristics, bioretention components, pollutant removal requirements, and applications of bioretention systems in temperate and tropical countries. Suggestions are given for bioretention components in the tropics, including elimination of mulch layer and submerged zone. More research is required to identify suitable additives for filter media, study tropical shrubs application while avoiding using grass and sedges, explore function of soil faunas, and adopt final discharged pollutants concentration (mg/L) on top of percentage removal (%) in bioretention design guidelines.

Water pollution is a major challenge in urban areas. The main source of water pollution is the runoff accelerated from impervious areas and agricultural land. In recent years, planning and designing of urban water management in Malaysia is moving away from the conventional thinking of designing for flooding to balancing the impact of urban drainage on flood control and quality management. In order to minimize the environmental impact of water pollution, Best management practices (BMPs) and Low impact development (LID) approaches have been used to manage runoff as close as possible to its source. The individual practices often have a low ability to provide consistent pollutant removal. Therefore, the arrangement of several LID-BMPs is recommended. This arrangement in series is called a treatment train. There is a need to review findings in the use of treatment train for water quality control. Therefore, this review paper discussing the ability of the treatment train for water quality control of runoff in urban areas in Malaysia. In addition, it compares a single treatment with the treatment train. The use of treatment train was very effective for stormwater control when compared with a single treatment practice. However, the use of treatment train for treating other types of runoff such as agricultural runoff still not implemented yet. It is recommended to use this system for treating other types of runoff such as agricultural runoff in the future work.

Bioretention media composition plays an important role in maintaining hydraulic conductivity within appropriate range and treating stormwater runoff to reduce pollution to receiving water bodies. This study investigated 4 types of bioretention media, 2 of which different types of compost and another 2 using shredded newspaper and crushed cockle shell as additives to modify the bioretention media. The objective of the study was to provide insight on hydraulic performance and media characteristics that control bioretention stormwater treatment performance. Results showed that organic matter content has no effect on hydraulic conductivity and nutrient removal performance of the media. Comparison of hydraulic conductivity and nutrient removal showed that reduced hydraulic conductivity (from 250mm/hr to 159mm/hr) increased total suspended solids (TSS) removal of the media (up to 98.5%) but has no effect on total nitrogen (TN) and total phosphorus (TP). The preliminary pollutant test using natural runoff showed that bioretention media enhanced with 10% shredded newspaper performed the best in TN removal (up to 85.3%) and bioretention media enhanced with 10% crushed cockle shell removed the most TP (up to 95.6%).

One of the best management practices (BMPs) for stormwater quality and quantity control is a bioretention system. The removal efficiency of different pollutants under this system is generally satisfactory, except for nitrogen which is deficient in certain bioretention systems. Nitrogen has a complex biogeochemical cycle, and thus the removal processes of nitrogen are typically slower than other pollutants. This study summarizes recent studies that have focused on nitrogen removal for urban stormwater runoff and discusses the latest advances in bioretention systems. The performance, influencing factors, and design enhancements are comprehensively reviewed in this paper. The review of current literature reveals that a bioretention system shows great promise due to its ability to remove nitrogen from stormwater runoff. Combining nitrification and denitrification zones with the addition of a carbon source and selecting different plant species promote nitrogen removal. Nevertheless, more studies on nitrogen transformations in a bioretention system and the relationships between different design factors need to be undertaken.