@article{DeBiaseCarminatiOswaldetal.2013, author = {De Biase, Cecilia and Carminati, Andrea and Oswald, Sascha Eric and Thullner, Martin}, title = {Numerical modeling analysis of VOC removal processes in different aerobic vertical flow systems for groundwater remediation}, series = {Journal of contaminant hydrology}, volume = {154}, journal = {Journal of contaminant hydrology}, number = {11}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0169-7722}, doi = {10.1016/j.jconhyd.2013.07.007}, pages = {53 -- 69}, year = {2013}, abstract = {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.}, language = {en} } @article{vanAfferdenRahmanMosigetal.2011, author = {van Afferden, Manfred and Rahman, Khaja Z. and Mosig, Peter and De Biase, Cecilia and Thullner, Martin and Oswald, Sascha Eric and M{\"u}ller, Roland A.}, title = {Remediation of groundwater contaminated with MTBE and benzene the potential of vertical-flow soil filter systems}, series = {Water research}, volume = {45}, journal = {Water research}, number = {16}, publisher = {Elsevier}, address = {Oxford}, issn = {0043-1354}, doi = {10.1016/j.watres.2011.07.010}, pages = {5063 -- 5074}, year = {2011}, abstract = {Field investigations on the treatment of MTBE and benzene from contaminated groundwater in pilot or full-scale constructed wetlands are lacking hugely. The aim of this study was to develop a biological treatment technology that can be operated in an economic, reliable and robust mode over a long period of time. Two pilot-scale vertical-flow soil filter eco-technologies, a roughing filter (RF) and a polishing filter (PF) with plants (willows), were operated independently in a single-stage configuration and coupled together in a multi-stage (RF + PF) configuration to investigate the MTBE and benzene removal performances. Both filters were loaded with groundwater from a refinery site contaminated with MTBE and benzene as the main contaminants, with a mean concentration of 2970 +/- 816 and 13,966 +/- 1998 mu g L(-1), respectively. Four different hydraulic loading rates (HLRs) with a stepwise increment of 60, 120, 240 and 480 L m(-2) d(-1) were applied over a period of 388 days in the single-stage operation. At the highest HLR of 480 L m(-2)d(-1), the mean concentrations of MTBE and benzene were found to be 550 +/- 133 and 65 +/- 123 mu g L(-1) in the effluent of the RF. In the effluent of the PP system, respective mean MTBE and benzene concentrations of 49 +/- 77 and 0.5 +/- 0.2 mu g L(-1) were obtained, which were well below the relevant MTBE and benzene limit values of 200 and 1 mu g L-1 for drinking water quality. But a dynamic fluctuation in the effluent MTBE concentration showed a lack of stability in regards to the increase in the measured values by nearly 10\%, which were higher than the limit value. Therefore, both (RF + PF) filters were combined in a multi-stage configuration and the combined system proved to be more stable and effective with a highly efficient reduction of the MTBE and benzene concentrations in the effluent. Nearly 70\% of MTBE and 98\% of benzene were eliminated from the influent groundwater by the first vertical filter (RF) and the remaining amount was almost completely diminished (similar to 100\% reduction) after passing through the second filter (PF), with a mean MTBE and benzene concentration of 5 +/- 10 and 0.6 +/- 0.2 mu g L(-1) in the final effluent. The emission rate of volatile organic compounds mass into the air from the systems was less than 1\% of the inflow mass loading rate. The results obtained in this study not only demonstrate the feasibility of vertical-flow soil filter systems for treating groundwater contaminated with MTBE and benzene, but can also be considered a major step forward towards their application under full-scale conditions for commercial purposes in the oil and gas industries.}, language = {en} } @article{DeBiaseRegerSchmidtetal.2011, author = {De Biase, Cecilia and Reger, Daniel and Schmidt, Axel and Jechalke, Sven and Reiche, Nils and Martinez-Lavanchy, Paula M. and Rosell, Monica and Van Afferden, Manfred and Maier, Uli and Oswald, Sascha Eric and Thullner, Martin}, title = {Treatment of volatile organic contaminants in a vertical flow filter - relevance of different removal processes}, series = {Ecological engineering : the journal of ecotechnology}, volume = {37}, journal = {Ecological engineering : the journal of ecotechnology}, number = {9}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0925-8574}, doi = {10.1016/j.ecoleng.2011.03.023}, pages = {1292 -- 1303}, year = {2011}, abstract = {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.}, language = {en} }