Development and Optimization of Bioretention Systems with Modified Fillers of Corn Straw Biochar

Abstract

Bioretention systems have been proved to be a natural approach for effectively reducing stormwater runoff pollution loads. The filler is essential for the function of the bioretention systems; there are few studies on the use of biochar for bioretention. In this study, corn straw was used as raw material to prepare biochar bioretention-improved filler, and the optimal preparation scheme and filler proportioning method were determined. Three layered bioretention columns, i.e., BSM (bioretention soil media), BSM\u2009+\u20095%WTR (water treatment residues, w/w) and BSM\u2009+\u20095%CSC (corn straw biochar, w/w), were built to analyze its regulating effect on rainwater runoff. The DRAINMOD model was established based on the test results to analyze the regulating effect in different situations. The key parameters of the bioretention systems were optimized using response surface methodology (RSM). The results show that: BSM\u2009+\u20095%CSC was more stable than BSM\u2009+\u20095%WTR for water volume control effect and was better than BSM. The load reduction rates of BSM\u2009+\u20095%CSC was better than that of BSM and BSM\u2009+\u20095%WTR. When only considering the optimal nitrogen reduction effect, it was necessary to deepen the depth of the submerged area to improve the nitrogen control effect. When considering the optimal control effects of water volume and nitrogen, the thickness of the filler layer was the key factor affecting the water reduction rate. Overall, this study demonstrated that corn straw biochar can effectively improve the regulation effect of bioretention systems, and the optimization of parameters can provide references for the design of bioretention systems.