Sorption of Stormwater Pollutants for Five Material Mixtures: A batch Equlibrium Study

Abstract: Blue-green infrastructure have been more lucrative during the last 30 years, since urbanizationbrings more impervious surfaces that increases stormwater runoff volumes. Amongst thedifferent blue-green infrastructures there are e.g., constructed wetlands and swales. Blue-greeninfrastructure means more natural management of the stormwater, such as infiltration. Forinfiltration of water, the hydraulic conductivity is an important parameter, but also the abilityto remove dissolved pollutants. In literature, various studies of filter materials are only testedfor single dissolved pollutants, which might be a disadvantage as this does not represent fieldconditions where metals usually co-exist. Economic costs are also an important parameter,unfortunately not always targeted in research. In this thesis, the efficiency of five different material mixtures for removing typical dissolvedstormwater pollutants: chromium (Cr), copper (Cu), nickel (Ni), phosphorus (P), lead (Pb) andzinc (Zn) were studied. The mixtures were following: 1) crushed rock + soil (RO_SO) 2)crushed rock + soil + LECA 4/10 + biochar (RO_SO_BC_LC4). 3) crushed rock + soil + LECA10/20 + biochar (RO_SO_BC_LC10). 4) Soil (SO). 5) crushed rock + soil + biochar(RO_SO_BC). This study was a part of blue-green investments that is being made in Östersundmunicipality and the use of low-cost materials for stormwater treatment are examined. The study was made using batch equilibrium tests, to determine the sorption capacity fordifferent material mixtures, using dissolved metal- and P-solutions. The measured data werefitted to Freundlich, Langmuir, Temkin, Dubinin-Radushkevich and Redlich-Petersonisotherms. Economic feasibility has also been compared between the material mixtures.Results showed that SO had the best sorption capacity for all metals and P, with rankingPb > Cr > Cu > Ni > Zn for the metals. All material mixtures showed a removal efficiency of79-99%, at the lowest concentration (1mg/L) for the metals and 31-62% for the lowestconcentration of P-single solution (1mg/L). Using additional materials in the mixtures, such asbiochar, slightly improved the sorption capacities of Pb and P. Redlich-Peterson isothermsprovided the best fits to the data. An economic evaluation of the ingoing materials shows thatSO and RO_SO are undoubtedly the most feasible alternatives for removal of targeted metalsand P.