Scrap Tire and Water Treatment Residual as Novel Green Sorbents for Removal of Common Metals from Polluted Storm Water Runoff

Although urbanization brings numerous benefits in our history, it has caused many environmental issues such as polluted urban runoff. A variety of pollutants at high concentrations, such as heavy metals, are present in urban runoff. Given that the polluted runoff is finally discharged into receiving waters and leads to non-point pollution in urbanized areas, appropriate management and treatment of the polluted urban stormwater is highly needed. However, current available best management practices (BMPs) are, to different degrees, restricted by their respective limitations. Therefore, there is an urgent demand in development of innovative, effective, and low-cost treatment methods for heavy metals in urban stormwater. The long term goal of this study is to develop an effective, low-cost BMP to address the pollution issue caused by urban runoff-induced heavy metals. Toward this goal, the overarching objective of this thesis research was to evaluate the performance of two industrial wastes, water treatment residual (WTR) and scrap tire rubber (TR), in the adsorption of Cu, Pb and Zn from water, as well as assess potential leaching of adsorbed metals from spent sorbents. The central hypothesis is that these sorbent materials provide effective adsorption for heavy metals from urban stormwater, without any significant chemical leaching from the spent WTR/TR. Bench scale tests were conducted in batch mode at pH 6.5 and room temperature to study metal adsorption by WTR alone, TR alone, and combined WTR and TR (WTR/TR), as well as Zn leaching from TR. Results show that WTR alone could rapidly and effectively adsorb the three metals, while TR adsorption was relatively slow but effective for Pb and Cu. However, TR significantly released Zn into bulk solution. The Zn leaching from TR appeared to be, at least partially, due to ion exchange between Zn in TR and Cu/Pb in bulk solution. Combination of WTR and TR could not only maintain a high adsorption potential for Cu and Pb in water, but also substantially inhibit the Zn release from TR, probably because WTR could immobilize the released Zn. Cu and Pb adsorption onto WTR/TR well followed the Freundlich adsorption isotherm model. High ionic strength enhanced WTR/TR adsorption of Cu and Pb, and 1:2 appeared to be the optimal mass ratio of WTR to TR. Desorption of Pb and Cu from spent WTR/TR was insignificant. However, in the presence of strong chelating agents such as EDTA, the absorbed metals could appreciably desorb into bulk solution. Column tests were also conducted to investigate the hydraulic behaviors and pollutant removal of the mixed WTR and TR media under continuous flow conditions. Hydraulic conductivities were affected by the mass ratio of WTR and TR and bed height. As the water flowed, the WTR powders might gradually move down to build up a sludge cake layer and clog the flow. Under certain conditions, the metals were effectively removed by the columns under a flow through condition. This study provides a preliminary investigation to apply WTR and TR for stormwater remediation. The encouraging results demonstrate that TR combined with WTR (WTR/TR) is a potential green sorbent for removal of undesirable heavy metals from urban runoff. Simultaneous of the two solid wastes substantially reduces the stormwater management costs because WTR and TR is almost “free”, as well as provides a new recycle pathway to address the two solid wastes that are originally disposed of within landfills