Occurrence and removal of emerging contaminants in wastewaters

Abstract

Over the past decade, the occurrence and removal of emerging contaminants in the environment has received much attention. Both natural and synthetic progestogens, which are hormones, and also benzotriazoles are two examples of such emerging contaminants. Sewage treatment works are recognised as one of the main routes of these compounds to the environment. Low concentrations (nanograms per litre) of biologically active chemicals may exhibit an impact on aquatic organisms and human health. This study was undertaken to determine the occurrence and removal of these two classes of chemicals at sewage treatment works, along with an evaluation of the performance of advanced treatment and also to investigate their fate in the aquatic environment. Therefore, field-based sampling campaigns were undertaken at a sewage treatment works, rivers and potable water to achieve these aims. Solid phase extraction and LC/MS/MS were used in order to analyse the samples from these different locations, along with catchment modelling and assessment of how the use of benzotriazoles may contribute to their presence in the environment.

The results have demonstrated that progestogens and benzotriazoles are in the sewage system; the natural hormone (progesterone) was the most predominant compound entering the sewage treatment work (46.9 ng/l) among the progestogens while concentrations of the benzotriazoles were two orders of magnitude higher than the progestogens. The conventional sewage treatment works were, to some extent, able to remove these compounds from wastewaters. However, this may not be adequate to afford protection to the environment. The investigation of advanced treatments, ozone, granular activated carbon and chlorine dioxide, indicated no further significant removal of progestogens, probably as a result of concentrations being close to method detection limits. However, there were indications that benzotriazoles were removed. A degradation study demonstrated that the natural hormone (progesterone) was degraded rapidly while benzotriazoles were not degraded. Catchment modelling indicated that high (up to 2,000 ng/l) concentrations of benzotriazoles would be present in surface waters used for potable supply, and consequently benzotriazoles were found in the tap water with mean concentrations of 30.9 ng/l (benzotriazole) and 15.1 ng/l for tolyltriazole. It is therefore apparent that although conventional treatment may be seen as effective, achieving over 90% removal, this may not be good enough. However, before investing in tertiary treatment, a number of factors, such as the effectiveness at different sites, the presence of degradation products and costs, both financial and in relation to energy use, need to be considered.