No abstract

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) represent hazardous pollutants and are frequently detected in the environment, e.g. in contaminated groundwater. PFASs are persistent to biodegradation and conventional oxidation processes such as ozonation. In this study electrochemical degradation of PFASs on boron-doped diamond (BDD) electrodes is demonstrated. Experiments were performed with model solutions and contaminated groundwater with a dissolved organic carbon (DOC) content of 13 mg/L. The perfluorinated carboxylic acids (PFCAs) perfluorobutanoate, perfluoropentanoate, perfluorohexanoate, perfluoroheptanoate and perfluorooctanoate, and the perfluorinated sulfonic acids (PFSAs) perfluorobutane sulfonate, perfluorohexane sulfonate, perfluorooctane sulfonate and 6:2 fluorotelomer sulfonate were detected in the groundwater samples. At PFAS concentrations ranging from 0.26 to 34 mg/L (0.7 to 79 μM), the degradation of PFASs was achieved despite of the high DOC background. Pseudo first-order kinetic constants of PFSA degradation increased with the increase of carbon chain length. Fluoride formation as well as the generation of PFCAs with shortened chain lengths was observed. Inorganic byproducts such as perchlorate were also formed and have to be considered in further process optimization.

No abstract

The aim of this study is to develop a long lasting, sequential anaerobic/aerobic biological activated carbon barrier. In the biobarrier, pollutant adsorption on granular activated carbon (GAC) and biodegradation occur simultaneously. Trichloroethene (TCE), chlorobenzene (CB), and benzene were used as model pollutants. In the first barrier, that was operated under anaerobic conditions with sucrose and ethanol as auxiliary substrates, TCE was completely converted to lower chlorinated metabolites, predominantly cis-dichloroethene (cis-DCE). The reductive dechlorination process was stable for about 300 d, although the concomitant sulphate-reducing and methanogenic processes varied considerably. In the second barrier, that was operated with addition of hydrogen peroxide and nitrate, dechlorination was limited by a lack of oxygen and restricted mainly to CB biodegradation. Additional aerobic batch tests revealed that the metabolites of anaerobic TCE dechlorination, i.e. cis-DCE and vinyl chloride, were oxidatively dechlorinated in the presence of suitable auxiliary substrates such as ethene, CB, benzene, or sucrose and ethanol. During periods of low biological activity, elimination of TCE and CB occurred by adsorption in the GAC barriers. The pre-sorbed pollutants were available for subsequent biodegradation resulting in a bioregeneration of the activated carbon barriers.

No abstract

The availability of electron acceptors and nutrients is often limiting the microbiological clean-up of polluted groundwater at contaminated sites. In this study, the feasibility of electrokinetic processes to improve mass transfer was demonstrated in a model system simulating laminar groundwater flow conditions. Electrokinetic nitrate transport and enhanced biodegradation of toluene under denitrifying conditions was studied as function of voltage gradient in a new flow-through system. The study was done in a three-dimensional anaerobic model aquifer system filled with coarse sand. The influent area was divided into seven chambers thus enabling a separate addition of toluene and nitrate. Mesh electrodes were inserted laterally in order to form an electric field perpendicular to the flow direction with voltage gradients of 0, 0.125 and 0.25 V cm -1 , respectively. Biodegradation was studied after inoculation with a denitrifying microbial mixed culture. Application of the electric field resulted in nitrate migration into areas containing toluene. In the presence of denitrifying bacteria, the availability of nitrate in toluene polluted areas resulted in toluene biodegradation, demonstrated by nitrite formation and decreased toluene concentration.

a b s t r ac tIodinated X-ray contrast media (IXCM) represent widespread water pollutants due to their poor elimination by common wastewater treatment techniques such as aerobic and anaerobic biodegradation. In this study, we demonstrate the removal of six IXCM (iotalamic acid, iopamidol, iohexol, iopromide, iomeprol and diatrizoate) by electrochemical treatment with boron-doped diamond electrodes. Experiments were performed with model solutions and field water samples. Electrochemical treatment of IXCM in synthetic solution resulted in complete deiodination and generation of the oxidation product iodate. We observed a dissolved organic carbon (DOC) decrease of 30%-80% in IXCM solutions, indicating partial mineralisation. Electrochemical IXCM degradation followed pseudo-first-order kinetics. In experiments with surface water and effluent from a wastewater treatment plant, successful degradation of IXCM was achieved despite the high DOC background. These results demonstrate that electrochemical treatment is a promising method for IXCM removal. Further studies into biodegradation of transformation products are recommended.

No abstract