Design and performance of urban sponges in red soil: improvement of physical and chemical properties

This study investigated the physical and chemical properties of a single or combination of permeable materials which can be used as fillers in the Sponge City program in China. Four types of fillers, perlite, coral sand, vermiculite and ceramsite, were selected from six alternative fillers by an analytic hierarchy process. The optimal city sponge, which consists of vermiculite (10 cm), ceramsite (15 cm), perlite (15 cm), coral sand (20 cm) and Canna indica L, was found by the orthogonal experiment (L16(45)). The results of the simulated rainwater experiment of the optimal sponge showed that the permeability coefficient K10, NH3-N, total phosphorus (TP) and chemical oxygen demand (COD) removal rate were 1.20 ± 0.23 mm/s, 96.6 ± 0.2%, 36.8 ± 0.07% and 9.6 ± 0.07% respectively. The results suggested that the optimal sponge had an excellent treatment effect on NH3-N in rainwater while ensuring rapid infiltration. It provided a simple, economical and effective method for rainwater treatment and the Sponge City program in the future.