Biogenic metals for the oxidative and reductive removal of pharmaceuticals, biocides and iodinated contrast media in a polishing membrane bioreactor
Research highlights
► Oxidative properties of biologically precipitated manganese oxides. ► Reductive properties of nanosized palladium particles. ► Removal of recalcitrant trace compound from wastewater effluent.
Introduction
Public health facilities and general welfare increase our quality of life, but they constitute a major burden for water resources through the constant input of trace amounts of drugs, cosmetics, UV blockers, fragrances, insect repellants, etc. This problem is challenging, since thousands of different substances are being used in medicine, agriculture, personal care and industrial processes (Ternes et al., 2004). Joss et al. (2006) suggested a classification scheme to characterize the biological degradation of 35 compounds, illustrating the poor efficiency of sewage treatment plants (STP) in degrading pharmaceutical and personal care products (PPCPs). Antibiotics, anti-epileptics, antiphlogistics, iodinated contrast agent and lipid regulators are removed between 20 and 90% in nutrient removing STPs. Iodinated contrast media (ICM) are widely used in human medicine for imaging of organs or blood vessels during diagnostic tests (Pérez and Barcelo, 2007) and occur in secondary effluent at several μg L−1 (Ternes and Hirsch, 2000). Organic contaminants used in agriculture such as biocides and veterinary pharmaceuticals enter the environment in a more diffuse way through application of manure and water runoff. Several studies, which report the toxicity of secondary effluents (Dizer et al., 2002, Aguayo et al., 2004, Cao et al., 2009), describe sublethal effects for aquatic organisms. Therefore, the search for mitigation technologies and strategies for wastewater reclamation to protect the aquatic environment is of uttermost importance.
Ozonation and advanced oxidation processes (AOPs), have been applied during the last decade for the abatement of pollution caused by the presence of residual pharmaceuticals in water and wastewaters (Klavarioti et al., 2009). Although ozonation is an effective technique to oxidize pharmaceuticals from wastewater effluents (Ternes et al., 2003), its application in wastewater management would result in an increased cost of 12% (Hollender et al., 2009). Moreover, an increase in genotoxicity may be expected after ozonation because of the formation of nitrosamines, hydroxylamines and bialdehydes as reported by Guzzella et al., 2002, Schmidt and Brauch, 2008 and Benner and Ternes (2009).
Recently, manganese oxides, have been applied to oxidatively remove different kinds of organic micropollutants, including antibacterials and related compounds with phenolic and fluoroquinolonic moieties, aromatic N-oxides, tetracyclines (Zhang et al., 2008a), estrogenic compounds such as the synthetic hormone 17α-ethinylestradiol (Sabirova et al., 2008) and the anti-inflammatory drug diclofenac (Forrez et al., 2010). A mechanism involving sorption of the compound to the oxide surface and subsequent electron transfer has been proposed (Zhang and Huang, 2005). In this context, biologically produced manganese oxides (BioMnOx) offer perspectives due to their characteristics, i.e. high specific surface areas (98–224 m2 g−1) (Hennebel et al., 2009a) and the ability of the manganese-oxidizing bacteria to reoxidize the formed MnII, thus increasing the reactivity of the Mn oxides with a factor 10 (Forrez et al., 2010).
Highly substituted aromatic compounds such as ICM are hard to oxidize and therefore recalcitrant towards ozonation (Ternes et al., 2003, Hollender et al., 2009, Huber et al., 2005). Recently, the reductive hydrodehalogenation of diatrizoate with supported Pd and porous Ni catalysts (Knitt et al., 2008) and with biologically produced nanopalladium catalyst (Bio-Pd) (Hennebel et al., 2010) was reported. In the presence of a hydrogen donor (H2 or HCOOH), Pd0 nanoparticles become charged with molecular hydrogen, which can subsequently reduce halogenated compounds (Hennebel et al., 2009b).
In this work, both the biogenic metals BioMnOx and Bio-Pd were evaluated for their practical feasibility to polish secondary effluent. More specifically, STP-effluent was treated in lab-scale membrane bioreactors (MBR) to remove anti-inflammatory drugs, tranquilizers, anti-epileptics, lipid regulators, antibiotics, iodinated contrast agent and biocides. Special attention was paid to matrix effects and the effect of low nutrient concentrations on the reactivity of the biogenic Mn oxide and biological reoxidation of MnII. A novel reductive technology using nano-Pd on a microbial carrier (Bio-Pd) was tested for the removal of several ICM at environmental concentrations in a continuous MBR.
Section snippets
Biogenic metals
Biogenic manganese oxides (BioMnOx) were produced by means of an axenic culture of Pseudomonas putida MnB6 (BCCM/LMG 2322) as described by Forrez et al. (2010). Bio-palladium (Bio-Pd) was produced by the metal-respiring bacterium Shewanella oneidensis (BCCM/LMG 19005) as described by De Windt et al. (2005). Bacterial cells can reduce PdII and subsequently precipitate it as Pd0 nanocrystals on their cell wall and in their periplasmatic space.
Batch tests
To evaluate the matrix effects of sewage treatment
Fate of pharmaceuticals, biocides and ICM in a BioMnOx-MBR
Table 1 and Fig. 2 show the removal of diclofenac in both MBRs operated respectively on STP-effluent spiked with 3 mg diclofenac L−1 and on non-spiked STP-effluent. The feed of the latter was not altered, resulting in a variable influent diclofenac concentration, i.e. 790 ± 53 ng L−1 and 390 ± 8 ng L−1 of diclofenac for the period 0–14 and 14–45 days, respectively.
The removal of diclofenac in both MBRs was initially more than 90% and decreased during the subsequent 14 days. In the spiked
Removal at environmental relevant concentrations
The use of biogenic metals for micropollutant removal is only valuable if they can remove several pollutants at environmentally relevant concentrations (ng-μg L−1). The diclofenac removal kinetics with BioMnOx were not influenced at 663 ng L−1 and 3 mg L−1 in STP-effluent indicating that the technology can work at low environmental relevant pollutant concentrations. In the batch test with STP-effluent, diclofenac (95%), ibuprofen (>95%), codeine (67%), bezafibrate (>65%), triclosan (>40%) and
Conclusions
Removal of more than 60% of 14 out of 29 micropollutants, detected in STP-effluent, occurred in a continuous MBR module containing BioMnOx in the outer compartment. The main putative removal mechanisms were: chemical oxidation by biogenic manganese oxides (diclofenac, triclosan, chlorophene, naproxen and diuron), biological degradation (ibuprofen, codeine, dihydrocodeine, morphine, N-acetyl-sulfamethoxazole, iopromide, iomeprol and iohexol) and adsorption (clarithromycin). Successful removal of
Acknowledgement
This study was part of the EU Neptune project (Contract No 036845, SUSTDEV-2005-3.II.3.2), which was financially supported by the EU Commision (FP6-2005-Global-4). Marta Carballa was supported by the Xunta de Galicia (Isidro Parga Pondal program, contract IPP-08-37) and Tom Hennebel (7741-02) was supported by the Fund of Scientific Research-Flanders (Fonds voor Wetenschappelijk Onderzoek (FWO) Vlaanderen).
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