Biochar Incorporation into Bioretention for Enhanced Ammonium Removal and Runoff Retention

Incorporating biochar into bioretention filter media was proposed to enhance urban stormwater treatment. Pinewood biochar pyrolysed at 550℃ was used to investigate its impact on the physicochemical properties of bioretention filter media and their ammonium sorption capacities in artificial stormwater. Water retention curves of the control and 4% biochar-amended filter media were measured at -15 300 to 0 cm H2O suction pressure. Hydraulic conductivities of two filter media were measured at field pilot-scale bioretention using a tension disc infiltrometer and analysed with DISC software. The results indicate that biochar amendment increased the pH of the acid filter medium, decreased bulk density by 7%, and increased total porosity and cation exchange capacity by 28% and 33%, respectively. Biochar incorporation increased ammonium removal of the control filter medium from -26%-28% to 50%-90%. The Freundlich model fitted the ammonium sorption isotherms of the three materials well. Biochar increased available water content of the control filter medium from 0.016 to 0.063 cm3/m-3 and saturated hydraulic conductivity by 1.5 times. The Van Genuchten model fitted the water retention curves of the control and biochar-amended filter media well. Incorporating biochar into bioretention filter media can enhance nitrogen removal from the perspective of water quality and quantity and benefit urban rainwater flood control.