title: Electrochemical oxidation of tramadol in low-salinity reverse osmosis concentrates using boron-doped diamond anodes.
abstract: The electrochemical treatment of low-salinity reverse osmosis (RO) concentrates was investigated using tramadol (100 μM) as a model substance for persistent organic contaminants. Galvanostatic degradation experiments using boron-doped diamond electrodes at different applied currents were conducted in RO concentrates as well as in ultra-pure water containing either sodium chloride or sodium sulfate. Kinetic investigations revealed a significant influence of in-situ generated active chlorine besides direct anodic oxidation. Therefore, tramadol concentrations decreased more rapidly at elevated chloride content. Nevertheless, reduction of total organic carbon (TOC) was found to be comparatively low, demonstrating that transformation rather than mineralization was taking place. Early stage product formation could be attributed to both direct and indirect processes, including demethylation, hydroxylation, dehydration, oxidative aromatic ring cleavage and halogenation reactions. The latter led to various halogenated derivatives and resulted in AOX (adsorbable organic halogens) formation in the lower mg/L-range depending on the treatment conditions. Characterisation of transformation products (TPs) was achieved via MS(n) experiments and additional NMR measurements. Based on identification and quantification of the main TPs in different matrices and on additional potentiostatic electrolysis, a transformation pathway was proposed.
authors: Federal Institute of Hydrology (BfG), Am Mainzer Tor 1, 56068 Koblenz, Germany.
authors: Christian
authors: C
authors: Lütke Eversloh
authors: Federal Institute of Hydrology (BfG), Am Mainzer Tor 1, 56068 Koblenz, Germany.
authors: Manoj
authors: M
authors: Schulz
authors: Max-Planck-Institute for Polymer Research (MPI-P), Ackermannweg 10, 55128 Mainz, Germany.
authors: Manfred
authors: M
authors: Wagner
authors: Federal Institute of Hydrology (BfG), Am Mainzer Tor 1, 56068 Koblenz, Germany. Electronic address: ternes@bafg.de.
authors: Thomas A
authors: TA
authors: Ternes
mesh_terms: D000327:Adsorption; D001895:Boron / Q000737:chemistry*; D001965:Bromides / Q000032:analysis; D002244:Carbon / Q000032:analysis; D002712:Chlorides / Q000032:analysis; D018130:Diamond / Q000737:chemistry*; D055664:Electrochemical Techniques / Q000379:methods*; D004566:Electrodes; D004572:Electrolysis; D007700:Kinetics; D013058:Mass Spectrometry; D009995:Osmosis; D010084:Oxidation-Reduction; D054712:Salinity; D012965:Sodium Chloride / Q000737:chemistry; D012996:Solutions; D013997:Time Factors; D014147:Tramadol / Q000737:chemistry*
chemical_list: D001965:Bromides; D002712:Chlorides; D012996:Solutions; D014147:Tramadol; D012965:Sodium Chloride; D002244:Carbon; D018130:Diamond; D001895:Boron
keywords: Electrochemical degradation; Reverse osmosis; Tramadol; Transformation products