Study to determine the principle modes of hydrophobic organic compounds (HOCs) removal from stormwater using natural media filtration (NMF)

In this work the ability of natural media filtration (NMF) to remove colloidal particles and associated hydrophobic organic compounds (HOCs) (phenanthrene and PCBs) from the aqueous phase was studied by conducting transport column experiments. Experimental data from column experiments were evaluated using a mathematical model that accounts for advection, dispersion, deposition, and release of colloidal particles from the porous medium, as well as equilibrium and rate-limited exchange of contaminant between the true dissolved phase, the suspended and attached colloids, and the fixed solid phase.;Colloidal particles removal was evaluated as a function of ionic strength and filter media by determining first-order kinetic deposition rate coefficients from short pulse column experiments. Mushroom compost (MC) and leaf compost (LC) were tested as natural filter media and the results were compared to those obtained using sand and granular activated carbon (GAG). The highest deposition rate coefficients were observed for GAC followed by LC, MC and the lowest deposition rate coefficients were found for sand. As predicted by the DLVO theory, higher deposition rates were obtained at higher solution ionic strengths.;Removal of both dissolved and particle associated HOC (Phenanthrene) was evaluated by performing sorption and transport experiments with LC media. These results were compared to results obtained using granular activated carbon (GAC) media. Phenanthrene sorption isotherm experiments for compost and model colloidal (latex) particles found that phenanthrene has greater affinity for the colloidal particles than for the compost materials. In column experiments the transport of phenanthrene through the NMF in the presence and absence of two colloidal particles with different hydrophobicities (sulfate [more hydrophobic] and carboxylate [less hydrophobic]) showed that the effluent phenanthrene concentration in the presence of colloids, particularly sulfate latex particles, is much higher than that in the absence of colloids. The results from a mathematical model used to evaluate data from the column experiments suggest that enhancement of contaminant transport can be significant under the following conditions: high colloidal concentrations, high partition coefficient between contaminant and colloids, or a slow desorption rate of contaminant from colloids.;Removal of dissolved and particulate associated polychlorinated biphenyls (PCBs) from contaminated wastewater effluent was evaluated by performing transport column experiments with leaf compost media (LC). These results were compared to results obtained using granular activated carbon (GAC) media. The experimental results show that NMF and GAC perform with similar efficiency and that by using appropriate hydraulic loading and contact times it is possible to efficiently remove both dissolved and particulate associated PCBs. The results from a mathematical model used to evaluate data from the column experiments suggest that, under the conditions used in model simulations, total PCB breakthrough is relatively independent of influent particle concentration. However, the influent particle concentration has a significant effect on the contaminant distribution between dissolved and associated phases. PCBs are only primarily in colloidal phase at very high particle concentration and/or when partition coefficients (Kpp) are very large. Additionally, contaminant transport could be enhanced or retarded depending on the extent of interaction between particles and filter media. Both experimental and model results showed that column effluent wastewater predominantly contains moderately chlorinated congeners (tri, tetra, and penta-chlorobiphenyls) removing higher PCB homologues from solution during NMF or GAC treatment.;Overall, the experimental and model predictions suggest that NMF may be competitive with current GAC to remove HOCs from contaminated water.