Abstract: Background, aim, and scope Bioretention, a promising technology for urban stormwater pollution treatment. The mixture of soil, sand and coir was recommended to use as a bioretention media in the sponge city of the Fengxi New Town. The media amelioration was significantly enhanced soil infiltration, however, there were still problems on soil purification and the coir was floating with the stormwater. In order to improve the current situation, this study mixed PAM with the soil, sand and coir (the volume ratio is 4∶4∶2), to investigate the effects of different dosages of PAM on saturated water content, saturated water conductivity and pollutant removal rate. Materials and methods The emulsive PAM with different dosages (0%, 0.5%, 0.75%, 1%, 1.5%) (w/w) were mixed with the soil, sand and coir (the volume ratio is 4∶4∶2), which was incubated at laboratory lasted 20 days, the medium water content kept at 15% during the incubation study. And then saturated water conductivity, water content and chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), copper, zinc and cadmium contents in different leachates were measured to evaluate the pollution removal rate. Results The ratio of different amount of PAM and coconut chaff was important to improve the physical and chemical properties of the filter media. Compared with the control, the medium bulk density was decreased by 9.1%, 10.8% and 12.2% under PAM amendment at 0.75%, 1% and 1.5%, respectively. The saturated water content and saturated water conductivity were increased by 30.0% and 52.6% under PAM amendment at 1.5% treatment, respectively. However, there was no significant difference between other treatments and the control. Compared to the control, the content of COD and total nitrogen of the leachate was no significant under PAM amendment. However, the content of phosphorus of the leachate increased by 20.1%, 31.3% and 51.1% under PAM amendment at 0.75%, 1% and 1.5%, respectively. The addition of PAM increases the removal rate of Zn, Cu and Cd. DiscussionPAM can effectively improve soil structure, reduce soil bulk density, increase the total soil porosity and capillary porosity, maintain the stability of soil particles and pore structure, thereby increasing soil infiltration rate and soil moisture content. PAM directly affects the adsorption of pollutants by the media through its molecular structure, and indirectly affects the adsorption of pollutants by the media through the effect on soil structure. Application of PAM can influence on soil physical and chemical properties, and the changes depended on the emulsive PAM rate. Conclusions The mixture of soil, sand, coir (4∶4∶2 (v∶v∶v)) and with PAM (1.5% (w/w)) amendment was recommended to use as a soil amelioration in the sponge city of the Fengxi New Town. Recommendations and perspectives We should be based on the actual situation of the soil, and comprehensively consider the effects of the infiltration, retention and purification, in order to select a suitable replacement media for the local.
Keywords: polyacrylamide; coir; soil amelioration; physical properties; pollutant removal rate