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Feminisation of fish

12. Influence of the type of treatment plants on the removal efficiency of estrogens and xenoestrogens

The fate of estrogens, bisphenol A, alkylphenols and the parent compounds of alkylphenols in STPs was considered in Chapter 11. The fate of the compounds in STPs is mainly correlated with the intrinsic properties of the compounds, i.e. physico-chemical properties and degradability. There is, however, no doubt that the type of treatment plant and the operation conditions are important for the overall removal of the compounds in STPs and thus the final concentrations in effluent and sludge.

An evaluation of the influence of the type of treatment process is given in this chapter. The evaluation is based on data and information on STPs collected from a number of studies. Details about the STPs are given in Appendix A, Table A.1. The concentrations of the compounds from each of the STPs are listed in the Tables A.2, A.3 and A.4.

There are several difficulties in comparing the different studies. As already mentioned in the previous chapters, different analytical methods and sampling strategies have been used in the different studies. Treatment conditions of the STPs studied are often not completely described. E.g. hydraulic retention time (HRT), sludge retention time (SRT), temperature, denitrification, nitrification and phosphate elimination will all have an important bearing on the plant efficiency (95).

12.1 Estrogens

The concentration ranges of the estrogens in effluent of STPs are approximately at the same levels in the different countries (Table 5.1 and Appendix A, Table A.2). The concentrations varied from the lowest detection limits up to approx. 220 ng of estrone/l. This high concentration was found in a British STP in Chelmsford in 1997-98. The analysed samples from Chelmsford were 5 days composite samples taken at noon every day, i.e. grab samples. The high concentration may therefore represent a single high peak of estrogens in the effluent.

Apparently, there is a tendency to higher concentrations of estrogens in effluents from the U.K. compared to the other European countries. However, the available data do not allow any final conclusions regarding potential differences between countries.

Comparing data within single studies, in which the sampling techniques and analytical methods are identical, should give the best basis of an evaluation of the importance of the different treatment processes. Desbrow et al. (253) studied the concentrations of estrogens in the effluent of seven British STPs with a range of treatment processes. The samples were taken throughout a 24-h cycle. The results of the investigation indicate that the effluent concentration is reduced when the treatment is increased with e.g. tertiary lagoons as in Rye Meads STP. However, the analyses were only performed on sample fractions with estrogenic activities and do not necessarily include the total amount of estrogens.

STPs with only primary and secondary treatment as well as plants with primary, secondary, tertiary and advanced treatment (e.g. microfiltration followed by reverse osmosis) have been examined in California (97). All the plants were equipped with a final disinfection step. Estradiol and ethinylestradiol were the only estrogens analysed in the study. The investigation indicated that the removal efficiency of these compounds increases with improving of the primary and secondary treatment with a tertiary treatment step. Advanced treatment with reverse osmosis resulted in a very low concentration of <0.4 ng/l in the effluent before the disinfection.

Danish investigations performed at low and high technology STPs in Århus during 1998-2001 show that the lowest effluent concentrations of estrogens (max. 9.2 ng/l) were obtained in the high technology plants. The low technology plants had concentrations of estrogens of up to 140 ng/l (sum of estrone, estradiol and ethinylestradiol). These low technological plants are placed in the "open land" treating household waste water from areas with scattered houses (99). The details of the different STPs in this investigation are included in Appendix A, Table A.1.

An investigation of five British STPs with different types of treatment by Kirk et al. (254) indicates that the major reduction of estrogenic activity occurs during the secondary treatment, i.e. the biological process, presumably mainly due to biological degradation. There were, however, two exceptions showing considerable reductions after both primary and secondary treatment. The hydraulic retention times in these plants were longer (13 h) and maybe also in the primary treatment and this may be the reason for the increased removal. Generally, the plants with the longest hydraulic retention time (HRT) (13-13.5 h) showed the greatest removal of estrogenic activity. Tertiary treatment (ammonia removal in a Biostyr plant and ultraviolet treatment) was seen to further remove estrogens. Kirk et al. (254) conclude that the more efficient STPs are capable of removing most of the activity (>70 %) but less-modern plants, with no tertiary treatment or less efficient processes than the currently available, are less efficient and removal rates are lower. It should be noticed that Kirk et al. (254) measured the estrogenic activity using yeast-based assay and not specific chemical analyses. The study, therefore, illustrates the influences of the type of plant regarding the overall removal of estrogens and xenoestrogens together.

The hydraulic retention time in a STP plays an important role for the biodegradability of a compound. Long retention in the biological treatment step increases the time of degradation. Only few of the investigators have reported the HRT of the plants. The reported HRTs are in the range of 11 to 26 hours. Another important process parameter is the sludge retention time (SRT). A long SRT of e.g. 25 days compared to a short retention time of e.g. 5 days may possibly increase the possibility of establishing and maintaining a microbial flora capable of degrading the estrogens. Increasing the SRT could also increase the removal of e.g. estradiol and ethinylestradiol from the water phase by sorption to the sludge particles. The effect of the HRT and SRT in STPs cannot be evaluated on the basis of the available data in literature. However, an investigation of influent and effluent samples from three Dutch STPs based on the activated sludge system showed that the highest removal efficiency of estrone and estradiol was obtained in the two plants with the highest HRTs (18 and 26 h) and SRTs (11 and 20 d) (88)

The biodegradation rate of a compound is a function of the temperature and the degradation rate may be reduced considerably at low temperatures. Studies by Ternes et al. (86) and Rodgers-Gray et al. (255) indicate that temperature variations in STPs affect the concentration of the estrogens in the final effluent. Ternes et al. (86) observed lower absolute removal rates in a German plant than in a plant in Brazil and concluded that it might be due to the low temperature of –2 °C in Germany at the sampling time compared to above 20 °C in Brazil. A very high concentration of estrone at 220 ng/l has been found in the effluent of Chemsford STP as mentioned above. This concentration was found during the winter season, when the temperature was 12.3 ± 0.4 °C. The concentrations were generally higher during this period compared to a period with higher temperatures of 17.2 ± 0.7 °C. The observed differences could be a result of the variations in the temperature. However, Johnson et al. (88) did not find a correlation between the temperature and estradiol removal obtained in Dutch STPs.

12.2 Alkylphenols

One of the most extensive investigations of the fate of alkylphenols and their parent compounds in STPs was performed by Ahel et al. (93). The study included analyses of NP, NPnEO (n = 1-18) and NPnEC (n = 1-2) as stated in Chapter 2. However, only few details on the operation of the treatment plants were given in the study. The plants were of the same type, i.e. consisting of primary sedimentation, activated sludge, final sedimentation and anaerobic digestion. The overall removal of the NP-c was 26-79 % based on the molarity in the effluents from primary and final sedimentation, and the total concentrations of NP-c for primary and secondary effluents ranged from 1,090 to 2,060 µg/l and from 240 to 760 µg/l, respectively. A detailed evaluation of the data showed that the highest elimination rates were achieved in the STPs characterised by low-sludge loading rates and nitrifying conditions. The percentage of NP-c remaining in secondary effluents correlated (r= 0.9035) with the actual STP loads, expressed as the percentage of their design capacity. Furthermore, the data on the removal of the hydrophobic compounds (NP, NP1EO, NP2EO) in periods with varying temperature indicated a temperature dependence of the removal (93).

A study of sewage samples from a Canadian STP from March 1997 to February 1998 confirmed the results obtained by Ahel et al. (93) (94). The Canadian STP was of the same type as the STPs investigated by Ahel et al. (93) and showed a similar mean elimination rate. The elimination varied widely as mentioned in Chapter 2 but the removal of APEO and their metabolites in the STP did not seem to be ambient temperature dependent.

Introduction of a disinfection step using chlorination may result in the formation of halogenated (chlorinated or brominated) NPnEOs and NPnECs as seen in an investigation of forty STPs in Japan (246). The STPs studied by Fujita et al. (246) consisted of primary clarifiers, aeration tanks, secondary clarifiers and disinfection processes with a few exceptions without disinfection processes. Halogenated compounds were found in 25 STPs.

Bennie et al. (244) investigated 16 STPs in Canada with different treatment systems. Although only NP, NP1EO and NP2EO were analysed, some tendencies were obvious. Plants with only primary treatment tended to be less efficient. The tertiary treatment systems at Cambrige-Galt and Guelph STPs were among the most efficient as regards removal of NP and OP from the water phase. The sludge was treated in anaerobic digesters at nine of the STPs. There was no biological treatment of the sludge at the remaining seven plants. NP, NP1EO and NP2EO were found in concentrations of up to 909 mg/kg dry weight in the anaerobically digested sludge.

It is possible to reduce the concentration of AP, AP1EO and AP2EO in anaerobically digested sludge by introducing a post-aeration step. The effect of the post-aeration has been investigated in lab-scale (batch test) as well as in the continuous full-scale process at Usserød STP in Denmark. It was demonstrated that it is possible to reduce the content of e.g. APnEO (n = 0-2) with 75-95 %. Furthermore, it was demonstrated that the dewaterability of the post-aerated sludge was nearly as efficient as for digested sludge.

The Danish investigations of STPs in Århus during 1998-2001 also included analyses of AP and APnEO (n = 1-15) (98;99). The tendency in the results was the same as obtained for the estrogens. The highest effluent concentrations of NPnEO (n = 0-2) of 1.83-7.62 µg/l were found in the plant with the lowest technology, i.e. Tåstrup STP consisting of only a mechanical treatment system. However, concentrations were seen at the same level in one of the high technology plants Søholt STP. Analysis of influent samples from this STP showed correspondingly high concentrations. Identification of the sources of NPnEO in the catchment area showed that 52 % of the NPnEO (n = 0-15) in the influent was discharged from a single industry. The concentrations of NPnEO (n = 0-2) in the effluent from the other high technology plants were in the range of approx. 0.2 to 1.2 µg/l. The investigations did not include analysis of carboxylated alkylphenol ethoxylates and data from these studies do not allow further assessment of the influence of the type of STP. However, the investigations confirm the finding of other investigators that the removal efficiency of the compounds to a certain extent depends on the level of applied technology at the STPs.

12.3 Bisphenol A

The highest of the reported effluent concentrations of bisphenol A was found in the Danish Randers STP at 4,000 ng/l (98). The plant is upgraded to nutrient removal and 26 % of the influent water is coming from industries. The bisphenol A concentrations in two influent samples of 700 and 3,000 ng/l are not remarkably high compared to the influent concentrations obtained in samples from other STPs. However, the analytical results for Randers STP are probably not from parallel sampled influent and effluent samples. It is obvious that the lowest of the reported removal efficiencies was found at the low technology plant, Tåstrup in Denmark with only mechanical treatment.

The available data for bisphenol A do not allow any further assessment of the influence of the type of STP on the removal of bisphenol A.

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