TY - JOUR A1 - De Biase, Cecilia A1 - Reger, Daniel A1 - Schmidt, Axel A1 - Jechalke, Sven A1 - Reiche, Nils A1 - Martinez-Lavanchy, Paula M. A1 - Rosell, Monica A1 - Van Afferden, Manfred A1 - Maier, Uli A1 - Oswald, Sascha Eric A1 - Thullner, Martin T1 - Treatment of volatile organic contaminants in a vertical flow filter - relevance of different removal processes JF - Ecological engineering : the journal of ecotechnology N2 - Vertical flow filters and vertical flow constructed wetlands are established wastewater treatment systems and have also been proposed for the treatment of contaminated groundwater. This study investigates the removal processes of volatile organic compounds in a pilot-scale vertical flow filter. The filter is intermittently irrigated with contaminated groundwater containing benzene, MTBE and ammonium as the main contaminants. The system is characterized by unsaturated conditions and high contaminant removal efficiency. The aim of the present study is to evaluate the contribution of biodegradation and volatilization to the overall removal of benzene and MTBE. Tracer tests and flow rate measurements showed a highly transient flow and heterogeneous transport regime. Radon-222, naturally occurring in the treated groundwater, was used as a gas tracer and indicated a high volatilization potential. Radon-222 behavior was reproduced by numerical simulations and extrapolated for benzene and MTBE, and indicated these compounds also have a high volatilization potential. In contrast, passive sampler measurements on top of the filter detected only low benzene and MTBE concentrations. Biodegradation potential was evaluated by the analysis of catabolic genes involved in organic compound degradation and a quantitative estimation of biodegradation was derived from stable isotope fractionation analysis. Results suggest that despite the high volatilization potential, biodegradation is the predominant mass removal process in the filter system, which indicates that the volatilized fraction of the contaminants is still subject to subsequent biodegradation. In particular, the upper filter layer located between the injection tubes and the surface of the system might also contribute to biodegradation, and might play a crucial role in avoiding the emission of volatilized contaminants into the atmosphere. KW - Benzene KW - Biodegradation KW - Catabolic genes KW - MTBE KW - Numerical modeling KW - Radon KW - SAFIRA II KW - Stable isotope fractionation analysis KW - Tracers KW - VOCs KW - Volatilization Y1 - 2011 U6 - https://doi.org/10.1016/j.ecoleng.2011.03.023 SN - 0925-8574 VL - 37 IS - 9 SP - 1292 EP - 1303 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - De Biase, Cecilia A1 - Carminati, Andrea A1 - Oswald, Sascha Eric A1 - Thullner, Martin T1 - Numerical modeling analysis of VOC removal processes in different aerobic vertical flow systems for groundwater remediation JF - Journal of contaminant hydrology N2 - Vertical flow systems filled with porous medium have been shown to efficiently remove volatile organic contaminants (VOCs) from contaminated groundwater. To apply this semi-natural remediation strategy it is however necessary to distinguish between removal due to biodegradation and due to volatile losses to the atmosphere. Especially for (potentially) toxic VOCs, the latter needs to be minimized to limit atmospheric emissions. In this study, numerical simulation was used to investigate quantitatively the removal of volatile organic compounds in two pilot-scale water treatment systems: an unplanted vertical flow filter and a planted one, which could also be called a vertical flow constructed wetland, both used for the treatment of contaminated groundwater. These systems were intermittently loaded with contaminated water containing benzene and MTBE as main VOCs. The highly dynamic but permanently unsaturated conditions in the porous medium facilitated aerobic biodegradation but could lead to volatile emissions of the contaminants. Experimental data from porous material analyses, flow rate measurements, solute tracer and gas tracer test, as well as contaminant concentration measurements at the boundaries of the systems were used to constrain a numerical reactive transport modeling approach. Numerical simulations considered unsaturated water flow, transport of species in the aqueous and the gas phase as well as aerobic degradation processes, which made it possible to quantify the rates of biodegradation and volatile emissions and calculating their contribution to total contaminant removal. A range of degradation rates was determined using experimental results of both systems under two operation modes and validated by field data obtained at different operation modes applied to the filters. For both filters, simulations and experimental data point to high biodegradation rates, if the flow filters have had time to build up their removal capacity. For this case volatile emissions are negligible and total removal can be attributed to biodegradation, only. The simulation study thus supports the use of both of these vertical flow systems for the treatment of groundwater contaminated with VOCs and the use of reactive transport modeling for the assessment of VOCs removal and operation modes in these high performance treatment systems. KW - Benzene KW - Biodegradation KW - MTBE KW - Unsaturated zone KW - Vertical flow filters KW - Volatilization Y1 - 2013 U6 - https://doi.org/10.1016/j.jconhyd.2013.07.007 SN - 0169-7722 SN - 1873-6009 VL - 154 IS - 11 SP - 53 EP - 69 PB - Elsevier CY - Amsterdam ER -