Treatment efficiency of synthetic urban runoff by low-cost mineral materials under various flow conditions and in the presence of salt: Possibilities and limitations

摘要

Urban runoff belongs to important carriers of pollutants that during infiltration can accumulate in the soil/water environment One of the protection solutions may be the enhancement of infiltration systems by horizontal permeable treatment zones. The article presents the results of column tests carried out in order to determine (1) the influence of the hydraulic loading rate on the dynamic capacities of selected reactive materials: low-cost mineral materials (zeolite, limestone sand, halloysite) and reference material (activated carbon), and control soils (top-soil and Vistula sand) against Zn, NH_4~+ and PO_4~(3-), and (2) remobilization of contaminants under the influence of salt (NaCl 5 g/L) present in synthetic runoff water. The research has revealed that the most useful for the removal of zinc ions was limestone sand (>4.36 mg/g), of orthophosphates - halloysite (2.29 mg/g on the average), and of ammonium ions - zeolite (2.75 mg/g on the average). The control soils were characterized by low ability to immobilize the contaminants tested. In addition, increase in the hydraulic loading rate of synthetic runoff water reduced the dynamic capacity of materials to a variable degree depending on the material applied and the contamination removed (by 24% for limestone sand-PO_4~(3-) system to 95% for activated carbon-NH_4~+ system). The presence of NaCl caused significant leaching of ammonium ions from zeolite and halloysite filter beds (up to 99.3%), and phosphates from the activated carbon filter bed (up to 41.3%). All tracer contaminants tested leached intensively from the Vistula sand filter bed, while only ammonium ions leached from the topsoil filter bed. It seems justified to support the performance of infiltration systems by layers of: limestone sand, to enhance the processes of heavy metal precipitation and ammonium ion volatilization by increasing the pH, and halloysite for the sorption of phosphates.