Xenobiotic organic micropollutants in urban wastewater : levels, distribution patterns and the impact of advanced treatment technologies on their presence in wastewater from different sources

Abstract

This study investigated the occurrence of 52 xenobiotic micropollutants pharmaceuticals, metabolites, transformation products, and organophosphorus compounds (OPs) in hospital and municipal wastewater. It aimed to characterise the xenobiotic fingerprint in raw wastewater from different sources and the impact of different advanced treatment technologies on concentration levels and distribution patterns of xenobiotic micropollutants. Thus, temporal concentration profiles of the influent and effluent of a nanofiltration membrane biofilm reactor (NF-MBR) situated at the influent of a municipal wastewater treatment plant (population equivalent: 300,000) as well as of a particle-supported biofilm reactor (PS-BFR) installed at the main effluent of a municipal hospital (186 beds, about 200 medical staff) were studied. Furthermore, the occurrence of xenobiotics in biosolids was addressed. For this, a multi-residue extraction method was developed and subsequently used to determine the micropollutants in sewage sludge from the NF-MBR and in sludge and carrier material from the PS-BFR. Ultimately, an aquatic environmental assessment for the investigated micropollutants was carried out based on the results of the presented study.It shows that a wide range of xenobiotics is present in both municipal and hospital wastewater. In summary, it can be said that there are basic differences between wastewater streams originating from the hospital and from mixed municipal sources regarding concentrations for iodinated contrast media, while other pharmaceuticals are more evenly distributed. For OPs, similar overall concentrations in the two wastewater types derived from a very different set of single substances. Regarding the contribution of hospitals to the overall xenobiotic load of municipal wastewater, it was found that even a small hospital can contribute greatly to the overall annual load: 21.5% of the annual load of diatrizoic acid reaching the municipal wastewater treatment plant is estimated to originate from the investigated hospital. While the NF-MBR revealed a much greater potential for micropollutant removal than the PS-BFR, even this system showed unsatisfactory results (< 75% removal) for 45% of the investigated substances. The NF-MBR was especially efficient with regard to biodegradation, while the removal of non-biodegradable substances (e.g. carbamazepine) was insufficient, which suggests that the filtration capacity of the loose NF membrane yielded retention results that were no better than those previously described for wider membrane types. The seasoned PS-BFR (start-up time prior to the study: 199 days) successfully adapted to the dynamic matrix which hospital wastewater represents, and demonstrated basic potential for biodegradation by stable removal rates of over 75% for primidone, ibuprofen and morphine, but failed in terms of increased overall xenobiotic degradation. However, high concentrations (ranging up to over 2,000 ng/g d.w.) of clarithromycin found in the biosolids (sludge and biofilm of the carrier material) might indicate that the system has a high sorption potential for ionic compounds. The aquatic environmental assessment showed that wastewater, both raw and treated, represents a risk when it reaches receiving waters. High risk levels are being caused by substances from not just a single therapeutic group but several (psycho-active compounds, antibiotics, non-steroidal anti-inflammatory drugs). However, in all wastewater types investigated, the highest risk was found to be the psycho-active compound oxazepam. Taking all of the above mentioned into account, it is impossible to say with certainty that pharmaceuticals and other xenobiotics in (waste)water are not a threat to the aquatic environment. To compensate for the lack of knowledge, precautionary principles must be applied, and these xenobiotics should be kept from reaching the aquatic environment.