Occurrence of iodinated X-ray contrast media and their biotransformation products in the urban water cycle

A LC tandem MS method was developed for the simultaneous determination of four iodinated X-ray contrast media (ICM) and 46 ICM biotransformation products (TPs) in raw and treated wastewater, surface water, groundwater, and drinking water. Recoveries ranged from 70% to 130%, and limits of quantification (LOQ) varied between 1 ng/L and 3 ng/L for surface water, groundwater and drinking water, and between 10 ng/L and 30 ng/L for wastewater. In a conventional wastewater treatment plant, iohexol, iomeprol, and iopromide were transformed to >80%, while iopamidol was transformed to 35%. In total, 26 TPs were detected above their LOQ in WWTP effluents. A significant change in the pattern of ICM TPs was observed after bank filtration and groundwater infiltration under aerobic conditions. Predominately, these TPs are formed at the end of the microbial transformation pathways in batch experiments with soil and sediment. These polar ICM TPs, such as iohexol TP599, iomeprol TP643, iopromide TP701A, and iopromide TP643, were not or only partially removed during drinking water treatment. As a consequence, several ICM TPs were detected in drinking water, at concentration levels exceeding 100 ng/L, with a maximum of 500 ng/L for iomeprol TP687.     

Rapid metal-catalyzed hydrodehalogenation of Iodinated x-ray contrast media

Iodinated X-ray contrast media (ICM) are detected in natural waters at high concentrations relative to other pharmaceuticals due to extensive use in medical diagnostics and high recalcitrance during conventional wastewater treatment. This study examines, for the first time, reductive treatment of ICM in water with hydrogen gas in combination with supported palladium and porous nickel catalysts. Kinetic experiments demonstrate rapid and complete hydrodehalogenation of both ionic (diatrizoate) and neutral (iopromide) ICM. Reaction rates in batch systems (continuous mixing, P(H2) = 0.1 MPa, 25 degrees C) appear to be surface-reaction controlled and are dependent upon catalyst identity (e.g., 5 wt % versus 1 wt % Pd/ Al2O3) as well as the concentration of ICM and catalyst. Reaction rates are not markedly affected by ICM structure, pH, or by the presence of many common ions (Na+, Ca2+, Mg2+, F-, Cl-, Br-, ClO4-, SO4(2-), HCO3-, and NO3-). In contrast, elevated concentrations of iodide, (bi)sulfide, and dissolved organic matter inhibit hydrodehalogenation of ICM. However, catalyst activity can be regained by washing the catalyst (e.g., with water, NaOCl, or alkaline solution). Catalytic reduction of ICM present in treated wastewater effluent is slower than in deionized water, but similar reaction rates are observed when the effluent is pretreated to reduce the level of dissolved organic matter. The high selectivity of reductive catalytic treatment processes suggest that this is a promising strategy for targeted treatment of ICM present in mixed waste streams and natural water matrices containing much higher concentrations of nontarget constituents.     

Construction of hydrogen fermentation from garbage slurry using the membrane free bioelectrochemical system

The aim of this study was to show the effectiveness of the membrane free bioelectrochemical system (BES) using three electrodes on inhibition of methanogenesis and construction of hydrogen fermentation from the artificial garbage slurry. The electrical redox-potential on the working electrode was adjusted to -1.0V (vs. Ag/AgCl) that has positive effect on methanogenesis. The redox-potential on the counter electrode was measured to be 1.6V. The pH in the effluents was 5.5-6.4. Hydrogen production rate at the cathode side was similar to that at the anode side and much higher than that calculated from current, and reached a maximum of 2445±815 (average±standard deviation) mL?L(-1)?d(-1) at an organic loading rate of 58.7g dichromate chemical oxygen demand per L d(-1). Methane production was negligible throughout the experiment. Acetate and butyrate were the main products of the fermentation using a BES; these offered favorable conditions for hydrogen production. The bacterial community in the bioelectrochemical hydrogen fermentor differed from that in the methanogenic seed sludge and included hitherto unknown species. These results show that high redox-potential on the anodic electrode and acidic pH in the membrane free BES can be utilized for hydrogen fermentation from the artificial garbage slurry by avoiding methanogenesis.     

Trichloroethene dechlorination and H2 evolution are alternative biological pathways of electric charge utilization by a dechlorinating culture in a bioelectrochemical system

Recently,the proof-of-principle of an innovative bioelectrochemical process fortrichloroethene (TCE) bioremediation was presented. In this newly developed process, a solid-state electrode polarized to -450 mV (vs SHE), in the presence of a low-potential redox mediator (methyl viologen), is employed as an electron donor for the microbial reductive dechlorination of TCE to lower or nonchlorinated end products. In the present study, we investigated the influence of methyl viologen and TCE concentrations on process performance. Using a highly enriched hydrogenotrophic dechlorinating culture, as a source culture in batch experiments, we found that TCE dechlorination and H2 evolution were the two main biological reactions which were stimulated. The relative contribution of the two reactions appeared to be strongly dependent on the mediator concentration. At the lowest methyl viologen (MV) concentrations (25-750 microM), only TCE dechlorination was stimulated, and no H2 was produced; at higher MV concentrations, both reactions occurred simultaneously, although they showed distinct kinetic features. In batch experiments in which TCE was omitted from the system, the rate of H2 production was remarkably increased (up to 80 times), suggesting that protons represented an alternative electron sink in the absence of the more energetically favorable TCE. Clearly, optimization of the process for TCE dechlorination requires H2 evolution to be minimized by, for instance, operating the system at low mediator concentrations, and this can be possibly achieved through proper physical immobilization of the mediator at the electrode surface. On the other hand, the observed bioelectrocatalytic H2 production occurred at virtually no overpotentials with respect to the thermodynamic 2H+/H2 potential. This finding revealed that the dechlorinating culture employed represented quite an exceptional and previously unrecognized biocatalytic system for H2 production.     

Development of a novel bioelectrochemical membrane reactor for wastewater treatment

A novel bioelectrochemical membrane reactor (BEMR), which takes advantage of a membrane bioreactor (MBR) and microbial fuel cells (MFC), is developed for wastewater treatment and energy recovery. In this system, stainless steel mesh with biofilm formed on it serves as both the cathode and the filtration material. Oxygen reduction reactions are effectively catalyzed by the microorganisms attached on the mesh. The effluent turbidity from the BEMR system was low during most of the operation period, and the chemical oxygen demand and NH(4)(+)-N removal efficiencies averaged 92.4% and 95.6%, respectively. With an increase in hydraulic retention time and a decrease in loading rate, the system performance was enhanced. In this BEMR process, a maximum power density of 4.35 W/m(3) and a current density of 18.32 A/m(3) were obtained at a hydraulic retention time of 150 min and external resister of 100 Ω. The Coulombic efficiency was 8.2%. Though the power density and current density of the BEMR system were not very high, compared with other high-output MFC systems, electricity recovery could be further enhanced through optimizing the operation conditions and BEMR configurations. Results clearly indicate that this innovative system holds great promise for efficient treatment of wastewater and energy recovery.     

Reduction of pH buffer requirement in bioelectrochemical systems

Low pH buffer capacity of waste streams limits further development of bioelectrochemical systems (BES) because accumulation of protons potentially leads to acidification of the anodic biofilm. Here we introduce a system that makes it possible to recover alkalinity in an extra recovery compartment. The system consisted of this extra compartment which was located between anode and cathode compartment. The compartment was separated from the anode by a cation exchange membrane and from the cathode by an anion exchange membrane, which made clean hydrogen production possible. To compensate for the charge movement as a result of the flow of electrons, both cations and hydroxyl ions moved into the new recovery compartment. When a synthetic waste stream was fed through this recovery compartment, both pH and conductivity increased. When this stream is then fed to the anode of the BES, no additional buffer was required to produce the same current (3.5 A/m(2)) at an applied voltage of 1 V.     

Transformation of the X-ray contrast medium iopromide in soil and biological wastewater treatment

In water/soil systems, the iodinated contrast medium iopromide was quantitatively biotransformed into several transformation products (TPs). Twelve TPs were identified via HPLC-UV and LC tandem MS. The chemical structures of the TPs were elucidated via fragmentation in MS2 and MS3 of LC tandem MS with a linear ion trap and 1H and 13C NMR analyses. All TPs exhibited transformations at the side chains containing either carboxylic moieties and/or primary and secondary amide moieties, while the triiodoisophthalic acid structure remained unaltered. A transformation pathway was proposed based on the sequence of TP formation in aerobic batch experiments. Additionally, the occurrence of iopromide TPs was investigated in native water samples. All TPs identified were found in municipal WWTP effluents because of their formation during biological wastewater treatment with maximum concentrations of up to 3.7 +/- 0.9 microg/L (TP 819). Predominantly, those TPs were present at higher concentrations in WWTP effluents which were formed at the beginning of the transformation pathway. Furthermore, four TPs formed at the end of the transformation pathway (TP 759, 701A/B, and 643) were also found in bank filtrate up to 0.050 microg/L and in groundwater of an wastewater irrigation area up to 4.6 microg/L.     

Pore-scale characterization of organic immiscible-liquid morphology in natural porous media using synchrotron X-ray microtomography

The objective of this study was to quantitatively characterize the pore-scale morphology of organic immiscible liquid residing within natural porous media. Synchrotron X-ray microtomography was used to obtain high-resolution, three-dimensional images of solid and liquid phases in packed columns. The image data were processed to generate quantitative measurements of organic-liquid blob morphology. Three porous media, comprising a range of particle-size distributions, were used to evaluate the impact of porous-medium texture on blob morphology. The sizes and shapes of the organic-liquid blobs varied greatly, ranging from small spherical singlets (> or = 0.03 mm in diameter) to large, amorphous ganglia with mean lengths of 4-5 mm. The smaller blobs were composed primarily of singlets, which comprised approximately half of all blobs for all three media. Conversely, large, complex blobs comprising four or more bodies composed 11-24% of the total number of blobs. However, the majority of the total organic-liquid surface area and volume was associated with the largest blobs. The ratio of median blob size to median grain size was close to unity for all three systems. The distribution of blob sizes was greatest for the porous medium with the broadest particle-size and pore-size distributions. These results illustrate the utility of synchrotron X-ray microtomography for characterizing fluid distributions at the pore scale in natural porous media.