Occurrence and removal of selected organic micropollutants at mechanical, chemical and advanced wastewater treatment plants in Norway
Introduction
The discharge of organic matter and nutrients from Norwegian domestic wastewater treatment plants (WWTPs) is regulated on a national level to limit the total load to the different recipients, thereby minimizing potential problems with high oxygen consumption and eutrophication in the receiving waters. So far, no such regulations exist regarding organic micropollutants in the effluents from Norwegian WWTPs. Hence, the WWTPs are designed and dimensioned to achieve their prescribed removal of organic matter and nutrients, where the discharge limits are given by the sensitivity of the local recipient and the size of the particular treatment plant.
A number of studies have focused on the removal of organic micropollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), nonylphenols and their ethoxylates, phthalates and linear alkylbenzene sulphonates (LAS) at WWTPs applying different types of biological treatments (McNally et al., 1998; Fauser et al., 2003; Marttinen et al., 2003; Blanchard et al., 2004; Katsoyiannis and Samara, 2004). Very few studies have focused on the removal efficiency of these pollutants in mechanical and chemical treatment plants. Though, chemical precipitation has been the preferred method to remove phosphorous from wastewater in Norway, also at biological WWTPs. Simple mechanical treatment, primarily for the removal of particulate matter, is dominating at small and medium sized WWTPs along the western and northern coast of Norway. Since many of the priority substances are rather lipophilic in character (octanol-water partition coefficient, ), and therefore tend to associate with the particulate matter, even mechanical treatment may contribute to the removal of these substances. On the other hand, the lack of any biological step may have significant influence on the overall removal of some of the more biodegradable compounds, such as the phthalates, LAS, some short-chained nonylphenol ethoxylates and the lighter PAHs (McNally et al., 1998; Fauser et al., 2003).
The main detrimental effects of organic micropollutants are connected to their potential acute toxicity or sub-lethal effects on the biota (Eljarat and Barceló, 2003). Toxic effects of effluent samples from WWTPs to algae, crustacean and fish have frequently been reported (Fischer et al., 1998; Schroder et al., 1991; Aguayo et al., 2004), and endocrine disruption of fish and freshwater mussels has been observed in rivers downstream biological WWTPs (Sumpter, 1995; Gagne et al., 2001; Tilton et al., 2002). The latter was primarily ascribed to the presence of oestrogenic chemicals (oestrogen mimics) in the WWTP effluents. Alkyl phenols, synthetic pharmaceutical steroids and naturally excreted steroid hormones usually represent the majority of the oestrogen-like potency (Desbrow et al., 1998; Utsunomiya, 1999; Quinn et al., 2004), though phthalates, polybrominated diphenyl ethers (PBDEs), PCBs, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and pesticides have also been known to show oestrogen-like potency (World Health Organization, 2002).
The objective of the present study was to investigate the occurrence of selected organic pollutants in Norwegian urban wastewater, and the capability of typical Norwegian WWTPs applying chemical or mechanical treatment for removal of these pollutants. The capability was compared to the removal efficiencies obtained in a WWTP applying more advanced combined biological and chemical treatment. Both chemical and ecotoxicological techniques were used to characterize the influent and effluent water, and to identify the changes that took place during the various treatments. In the present paper, the results and conclusions based on the chemical analysis are presented.
Section snippets
WWTPs
Of the five WWTPs included in this study (see Fig. 1), one had biological treatment (anoxic and aerobic-activated sludge process) with simultaneous chemical precipitation (plant A), three had chemical treatment (plant B–D) and one had only mechanical treatment (plant E). Details from the WWTPs are shown in Table 1. The WWTPs were located in four different parts of Norway and had a rather wide variation in capacity (capacities 15 000–300 000 person equivalents, PE).
Sampling
Seven to 10 days
PAHs
As shown in Table 2, the concentrations of the sum of 16 different PAH congeners (ΣPAH16) in the influents to the five Norwegian WWTPs in the present study were within 0.2–1.3 μg/L, which is in the low range of what was reported (0.05–625 μg/L) in an EC urban wastewater survey (Thornton et al., 2001) and generally somewhat lower than the levels (1.3–8.0 μg/L) found in wastewaters in the Paris area (Blanchard et al., 2004). The two- and three-ring PAHs (2, 3 PAHs) dominated in most of the inlet
Conclusions
Concentrations of PAHs, nonylphenols, phthalates, PCBs and PBDEs in the influents to the Norwegian WWTPs were generally in the low range of what have been reported by others for domestic wastewater elsewhere in Europe and North-America. A strong reduction in nonylphenol concentrations in samples collected in 2004, compared to concentrations in samples from the same WWTPs in 2002, indicate the effect of restrictions on the use of this compound implemented by the Norwegian authorities in 2002.
Acknowledgements
The presented work was a part of a Strategic Institute Program at the Norwegian Institute for Water Research supported by the Norwegian Research Council and Ministry of the Environment.
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