Bioretention is considered one of the best management practices (BMPS) for managing stormwater quality and quantity. The bioretention system has proven good performance in removing total suspended solids, oil, and heavy metals. The nitrogen (N) removal efficiency of the bioretention system is insufficient, however, due to the complex forms of nitrogen. Therefore, this paper aims to review recent enhancement approaches to nitrogen (N) removal and to discuss the factors influencing bioretention efficiency. To improve bioretention efficiency, several factors should be considered when designing bioretention systems, including nitrogen concentration, climate factors, and hydrological factors. Further, soil and plant selection should be appropriate for environmental conditions. Three design improvement approaches have been reviewed. The first is the inclusion of a saturated zone (SZ), which has been used widely. The SZ is shown to have the best performance in nitrogen removal. The second approach (which is less popular) is the usage of additives in the form of a mixture with soil media or as a separated layer. This concept is intended to be applied in tropical regions with wet soil conditions and a short dry period. The third approach combines the previous two approaches (enhanced filter media and applying a SZ). This approach is more efficient and has recently attracted more attention. This study suggests that further studies on the third approach should be carried out. Applying amendment material through filter media and integrating it with SZ provides appropriate conditions to complete the nitrogen cycle. This approach is considered a promising method to enhance nitrogen removal. In general, the bioretention system offers a promising tool for improving stormwater quality.

Stormwater pollutants are one of the main problems causing environmental damage. The accumulated pollutants on urban impervious surfaces are carried by stormwater runoff and enter water bodies, therefore, caused ecological damage. To decrease the pollution effect of stormwater, best management practices (BMP), and low–impact development (LID) principles were introduced. Bioretention technology as one of these practices has been used to control stormwater quality. This technology stills not widely used in Malaysia. However, the design of bioretention system that used in Malaysia follows a conventional design and stills in the early stage. Therefore, this paper reviews the role of plants and their effect on bioretention performance in terms of nutrient removal. Bioretention system that vegetated with the plant was very effective on nutrient removal than without plant. In Malaysia, there is a need to develop the conventional bioretention system. Applying multispecies plant in bioretention system would be more effective on nutrient removal. However, limited studies have been conducted on the types of plant that are suggested in (MSMA). This paper recommends applying multispecies plant (mixture plants) to enhance the performance of conventional bioretention system in terms of nutrient removal.

Biofilters, commonly called rain gardens, are becoming increasingly popular among best-management practices (BMPs). They have recently sparked significant interest due to their ability to control stormwater quality. These systems face challenges in manipulating dissolved nitrogen and phosphorus species. This study reports the results of the removal of nitrogen and phosphorus in two modified bioretention systems. The performance of modified bioretention with coconut and durian was compared. The modified bioretention system was evaluated as a single and a series. Sequencing these systems in a series maintained the continuity of nutrient removal. Both series efficiently removed NH3-N (97% in TC5, 95% in TD5), while the removal of NO3-N was moderate (65% inTC5, 67% in TD5). Good removal efficiencies of TP were observed in two series (84% in TC5, 81% in TD5). However, the PO4 removal was equalized in all series (98%). The TN and ON removal were poor and fluctuated with time and column number in TC5, the overall removal efficiencies were (69% and 43%), respectively, while in TD5 a significant fraction of TN and ON were removed (86% and 78%), respectively. As compared with coconut husk, durian peel is considered a promising material that can enhance the water quality in bioretention systems.