Abstract
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.
Highlights
Land use change caused by urbanization can cause detrimental impacts on natural waters as a consequence of infiltration decreasing and runoff volumes increasing dramatically by high-density and impervious surfaces [1,2]
With influent levels of Cu, Zn, and Pb at 500, 1000 and 10 μg L−1, removal efficiencies greater than 93% were observed in our Bioretention cells (BCs) for each of the metals tested (Figure 4)
This study demonstrated a new module bioretention system with great flexibility and simple maintenance in urban area of Sponge City, China
Summary
Land use change caused by urbanization can cause detrimental impacts on natural waters as a consequence of infiltration decreasing and runoff volumes increasing dramatically by high-density and impervious surfaces [1,2]. Increased pollutant loads accumulated in surface runoff from impervious catchments without rational management discharged to the received water-bodies can make the quality. Previous studies have demonstrated that BCs implemented in relatively small catchments effectively improve both water quantity and quality in response to frequent storm events [9,10,11]. Research has shown that BCs can effectively improve water quantity and remove suspended solids [17,18], nutrients [19,20,21], and heavy metals [22,23]. It is difficult to meet or maintain a consistently satisfactory performance for reducing nitrogen due to a lack of effective denitrification [24,25]
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