Insights into the pollutant-removal performance and DOM characteristics of stormwater runoff during grassy-swales treatment

ABSTRACT

The water purification performance of grassy swales for treating stormwater road runoff was evaluated using a simulated experimental device in two different seasons. The results showed that the removal rates for total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) reached 89.90%, 56.71%, 32.37%, and 19.67%, respectively, in summer, and 34.09%, 7.75%, 56.71%, and 13.33%, respectively, in winter, suggesting that grassy swales showed higher water purification performance in summer than in winter. Soil filtration in grassy swales also showed high removal rates of TSS, COD, TN and TP in summer (98.13%, 59.10%, 33.82%, and 24.59% respectively). The structure, composition and source of dissolved organic matter (DOM) were investigated using ultraviolet visible (UV–Vis) spectra and fluorescence spectra. The spectral parameters indicated a relatively high humification and aromaticity of DOM, and a relatively higher contribution of organic matter derived from microbial substances in summer than in winter. In addition, grassy-swale treatment showed a slight decrease in metal-ion concentrations at the surface, while the removal rates in the bottom samples were 38.42%, 40.59%, 33.81%, and 40.06% for Cu²⁺, Cd²⁺, Pb²⁺, and Zn²⁺, respectively. The results of 2D-COS suggested that grass swales treatment can change the binding sites and binding sequencing of DOM with heavy metals and further influence the metal speciation, mobility and biotoxicity.

KEYWORDS:

• Grassy swales
• road runoff
• water purification
• dissolved organic matter
• spectral techniques

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was financially supported by the National Natural Science Foundation of China [grant number 51578037] and Beijing outstanding talent project for excellent youth team [grant number 2015000026833T0000].