A bioretention system is a low-impact and sustainable treatment facility for treating urban stormwater runoff. To meet or maintain a consistently satisfactory performance, especially in terms of increasing nitrogen removal efficiency, the introduction of a submerged (anoxic) zone (SZ) combined with a module-based carbon source (C) has been recommended. This study investigated the removal of nitrogen (N), phosphorus (P) and heavy metals with a retrofitted bioretention system. A significant (p < 0.05) removal enhancement of N as well as total phosphorus (TP) was observed, in the mesocosms with additions of exogenous carbon as opposed to those without such condition. However, even in the mesocosm with SZ alone (without exogenous C), TP removal showed significant enhancement. With regard to the effects of SZ depth on nutrient removal, the results showed that the removal of both N and P in module with a shallow SZ (200 mm) showed significant enhancement compared to that in module with a deep SZ (300 mm). Removal efficiencies greater than 93% were observed for all three heavy metals tested (Cu, Pb, and Zn) in all mesocosms, even in the bioretention module without an SZ or plants, and it indicated that adsorption by the filtration media itself is probably the most important removal mechanism. Only Cu (but not Pb or Zn) showed significantly enhanced removal in module with an SZ as compared to those without an SZ. Carbon source played a minor role in metal removal as no significant (p > 0.05) improvement was observed in module with C as compared to that without C. Based on these results, the incorporation of SZ with C in stormwater biofilters is recommended.

This study compares stormwater management in two coastal cities: Hong Kong and Singapore. Hong Kong adopted conventional urban stormwater management for flood control and embraced hard-engineering infrastructure in the scheme. In contrast, Singapore has put in place a series of holistic management practices to manage urban runoff. By comparing the stormwater management practices in these two cities, the differences in approaches to non-structural and structural practices were elucidated. Life cycle costing and environmental benefit analysis indicate that holistic urban stormwater management can lead to higher economic efficiency, sustainability and environmental friendliness, compared to conventional urban stormwater management.

Quantifying the water layout factors in a campus square helps to lay out water bodies more scientifically and utilize the microclimate effect to alleviate the heat and humidity of campus squares in summer. The West Gate Square of Fujian Agriculture and Forestry University in China has been used as the primary theoretical model, and the landscape pattern index from landscape ecology has been used to quantify the scale, shape, and dispersion of water bodies. Consider the typical weather, the summer solstice, as the experiment time. The relationship between the water body layout factors and cooling effect, the humidification effect, and the wind speed is clarified from both temporal and spatial perspectives. The data were analyzed with ENVI-met and Arcgis software. Then, the optimum campus square water body layout mode was concluded. The results show that: (1) The scale, dispersion, and shape of the water body has a significant effect on the campus temperature and humidity, while the effect on wind speed is not significant. (2) From the cooling and humidifying effect, the ranking of the regulating ability of the water body layout factors is scale > shape > dispersion; the ranking of the influence range is shape > scale > dispersion. (3) When the boundary of the square is determined, the optimum water body layout mode is that the water body area accounts for 36% of the total square area. The shape of the water body is concentrated and not dispersed square. When the water body layout is determined, the optimum layout mode of the boundary is length:width = 1:2.