The mineralization of 5-amino-2,4,6-triiodoisophthalic acid by a two-stage fixed-bed reactor

Anaerobic biodegradation of (emerging) organic contaminants in the aquatic environment

Although strictly anaerobic conditions prevail in several environmental compartments, up to now, biodegradation studies with emerging organic contaminants (EOCs), such as pharmaceuticals and personal care products, have mainly focused on aerobic conditions. One of the reasons probably is the assumption that the aerobic degradation is more energetically favorable than degradation under strictly anaerobic conditions. Certain aerobically recalcitrant contaminants, however, are biodegraded under strictly anaerobic conditions and little is known about the organisms and enzymatic processes involved in their degradation. This review provides a comprehensive survey of characteristic anaerobic biotransformation reactions for a variety of well-studied, structurally rather simple contaminants (SMOCs) bearing one or a few different functional groups/structural moieties. Furthermore it summarizes anaerobic degradation studies of more complex contaminants with several functional groups (CMCs), in soil, sediment and wastewater treatment. While strictly anaerobic conditions are able to promote the transformation of several aerobically persistent contaminants, the variety of observed reactions is limited, with reductive dehalogenations and the cleavage of ether bonds being the most prevalent. Thus, it becomes clear that the transferability of degradation mechanisms deduced from culture studies of SMOCs to predict the degradation of CMCs, such as EOCs, in environmental matrices is hampered due the more complex chemical structure bearing different functional groups, different environmental conditions (e.g. matrix, redox, pH), the microbial community (e.g. adaptation, competition) and the low concentrations typical for EOCs.

Cometabolic degradation of organic wastewater micropollutants by activated sludge and sludge-inherent microorganisms

Municipal wastewaters contain a multitude of organic trace pollutants. Often, their biodegradability by activated sludge microorganisms is decisive for their elimination during wastewater treatment. Since the amounts of micropollutants seem too low to serve as growth substrate, cometabolism is supposed to be the dominating biodegradation process. Nevertheless, as many biodegradation studies were performed without the intention to discriminate between metabolic and cometabolic processes, the specific contribution of the latter to substance transformations is often not clarified. This minireview summarizes current knowledge about the cometabolic degradation of organic trace pollutants by activated sludge and sludge-inherent microorganisms. Due to their relevance for communal wastewater contamination, the focus is laid on pharmaceuticals, personal care products, antibiotics, estrogens, and nonylphenols. Wherever possible, reference is made to the molecular process level, i.e., cometabolic pathways, involved enzymes, and formed transformation products. Particular cometabolic capabilities of different activated sludge consortia and various microbial species are highlighted. Process conditions favoring cometabolic activities are emphasized. Finally, knowledge gaps are identified, and research perspectives are outlined.

Isolation and identification of an iopromide-degrading strain and its application in an A2/O system

An iopromide (IOPr)-degrading bacterium was isolated from activated sludge of a wastewater treatment plant in Shanghai. Based on its morphology, physiological-biochemical characteristics and a phylogenetic analysis of its 16S rRNA sequence, the bacterium was identified and named as Pseudomonas sp. I-24. The optimum condition for degrading IOPr was at 30°C and pH 7.0. After 5 days, strain I-24 could degrade 30 mg/L IOPr by 99% in a basal salts medium with a 5% (V/V) inoculum and 200 mg/L starch as the primary substrate. When applied to an Anaerobic-Anoxic/Aerobic (A2/O) process, with the coexistence of other bacteria, the strain I-24 got lower (61.3%) IOPr removal, but in two A2/O systems (with and without I-24 inoculation), the CODcr removal were both approximately 95%. The trial dosed with strain I-24 showed better IOPr removal than the un-dosed one. I-24 sustained its abundance in the A2/O system during the experiment.

Biotransformation of selected iodinated X-ray contrast media and characterization of microbial transformation pathways

Iodinated X-ray contrast media (ICM) are commonly detected in the aquatic environment at concentrations up to the low microgram per liter range. In this study, the biotransformation of selected ICM (diatrizoate, iohexol, iomeprol, and iopamidol) in aerobic soil-water and river sediment-water batch systems was investigated. In addition, microbial transformation pathways were proposed. Diatrizoate, an ionic ICM, was not biotransformed, while three nonionic ICM were transformed into several biotransformation products (TPs) at neutral pH. Iohexol and iomeprol were biotransformed to eleven TPs and fifteen TPs, respectively, while eight TPs were detected for iopamidol. Since seven of the TPs detected during biotransformation had not been previously identified, mass fragmentation experiments were completed to elucidate the chemical structures. Oxidation of primary alcoholic moieties, cleavage of the N-C bonds (i.e., deacetylation and removal of hydroxylated propanoic acids), and decarboxylation are potential reactions that can explain the formation of the identified TPs. Iohexol and iomeprol had similar biotransformation rates, while iopamidol was biotransformed slower and to a lesser extent. A LC tandem MS method confirmed the presence of ICM TPs in aqueous environmental samples. Fifteen of the ICM TPs were even detected in drinking water with concentrations up to 120 ng/L.