Endocrine disrupting compounds removal from wastewater, a new challenge

Process Biochemistry 41 (2006) 525–539 www.elsevier.com/locate/procbio Endocrine disrupting compounds removal from wastewater, a new challenge Muriel Auriol a,c, Youssef Filali-Meknassi b,c, Rajeshwar D. Tyagi a,*, Craig D. Adams c, Rao Y. Surampalli b a University of Quebec, INRS-ETE, 490 de la Couronne, QC, Canada G1K 9A9 b U.S. EPA, P.O. Box 17-2141, Kansas City, KS 66117, USA c University of Missouri-Rolla, Civil Engineering Department, 1870 Miner Circle Rolla, MO 65409-1060, USA Received 27 July 2005; received in revised form 16 September 2005; accepted 29 September 2005 Abstract Various natural chemicals and some contaminants of industrial source present an endocrine activity. Nowadays, many questions related to these compounds are not resolved and the persistent character of these compounds makes it a major problem for future generations. This study concentrated on some specific groups of endocrine disrupting chemicals (estrogens and alkylphenols). In this review, a number of treatment processes will be discussed with regard to their potential on endocrine disrupting chemicals removal. # 2005 Elsevier Ltd. All rights reserved. Keywords: Endocrine disrupting chemicals; Estrogens; Alkylphenols; EDC; Wastewater; Hormone 1. Introduction The human growth, development coordination and maturation imply a complex interaction of hormonal signals whose chronology and dose can have permanent consequences on the future form and function of many tissues [1,2]. Human exposure to very low doses during critical periods, for example at the cellular differentiation period, can alter the development course of these tissues and this may result in permanent character changes in the mature living beings [1,2]. Considering the complexity of endocrine systems, it is not surprising that a wide range and varied substances cause endocrine disruption and these include both natural and synthetic chemicals [3,4]. Indeed, according to an European Union study, 118 substances were classified as potential endocrine disrupters (EDCs); and a peculiar priority was assigned to the carbon disulfide, o-phenylphenol, tetrabrominated diphenyl ether, 4-chloro-3-methylphenol, 2,4dichlorophenol, resorcinol, 4-nitrotoluene, 2,20 -bis(4-(2,3epoxypropoxy)phenyl)propane, 4-octylphenol, estrone (E1), 17a-ethinylestradiol (EE2), and 17b-estradiol (bE2) [5]. * Corresponding author. Tel.: +1 418 654 2617; fax: +1 418 654 2600. E-mail address: tyagi@inrs-ete.uquebec.ca (R.D. Tyagi). 1359-5113/$ – see front matter # 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2005.09.017 EDCs are often dominant and can disperse quickly in the environment. EDCs are released to the atmosphere as a result of combustion and incineration activities (polycyclic aromatic hydrocarbons (PAHs), dioxins) [6], but the principal sinks for EDCs are groundwater, river, and lakes [7]. The four main classes of EDCs (natural steroidal estrogens, synthetic estrogens, phytoestrogens, and various industrial chemicals) are generally represented with respect to their estrogenic potency [8]. The natural and synthetic estrogens generally display much stronger estrogenic effects than the phyto- and xenoestrogens. However, the concentrations of phyto- and xenoestrogens in the aquatic environment are usually higher [9]. The list of trace contaminants or EDCs, resulting from human activities and found in wastewater, is long [10–12]. However, in general natural (E1, bE2, estriol [E3]) and synthetic (EE2, mestranol) hormones are the major contributors to the estrogenic activity observed in sewage effluents [13–15] and the receiving water. Recent research showed that several sewage treatment plant (STP) effluents and rivers in the United Kingdom [14,16–20] and in the United States [21,22] contain sufficient amount of estrogenic compounds to induce harmful effects on fish (Tables 1–3). Field studies using caged trout (Oncorhynchus mykiss), wild cyprinid roach (Rutilus rutilus) [40], and estuarine flounder (Platichthys flessus) [41,42] showed that the estrogenicity persists in receiving water and 526 M. Auriol et al. / Process Biochemistry 41 (2006) 525–539 Table 1 Estrogens concentrations in STP influent Sampling site Paris, France England Germany Italy Roma, Italy Roma, Italy Barcelona, Spain Japan Influent concentrations (ng/L) Estrone 17b-Estradiol Estriol 17a-Ethinylestradiol 9.6–17.6 1.8–4.1 66 52 31 44 <2.5–115 – 11.1–17.4 <0.3 22.7 12 9.7 11 <5–30.4 5 11.4–15.2 – – 80 57 72 <0.25–70.7 – 4.9–7.1 <LODa – 3 4.8 – <5 – Analysis method Reference SPE/GC-MS SPE/GC-MS-MS SPE/LC-ESI-MS-MS SPE/LC-MS-MS SPE/LC-MS-MS SPE/LC-ESI-MS-MS SPE/LC-MS SPE/ELISA [23] [24] [25] [26] [25] [27] [28] [29] ELISA: enzyme-linked immunosorbent assay; ESI: interface electrospray; GC-MS: gas chromatography-mass spectrometry; GC-MS-MS: gas chromatographytandem mass spectrometry; LC-MS: liquid chromatography-mass spectrometry; LC-MS-MS: liquid chromatography-tandem mass spectrometry; LOD: limit of detection; SPE: solid phase extraction. a 0.3 ng/L. that the concentration of these compounds present in the rivers and the estuaries are high enough to induce deleterious reproductive consequences. The incidence of hermaphroditic wild fish near STPs initiated an investigation on STPs effluent estrogenicity. Caged fish held downstream of some STPs produced vitellogenin (VTG), indicating the presence of estrogenic substances [17,18,43]. In 1990, British scientists showed that male rainbow trout produced the yolk precursor protein VTG when they were exposed to sewage effluents or contaminated surface water [44]. Other studies have also shown that birds, reptiles, and mammals in polluted areas undergo alterations of the endocrine reproductive system [45]. Natural and synthetic estrogen hormones (such as bE2, E3, E1, and EE2) seem to be responsible for endocrine disruption in fish [13,28,46]. Indeed, several studies showed that even low concentrations (ng/L) of bE2 can induce VTG in male species and rainbow trout (O. mykiss) experimentally exposed to these chemicals [46,47]. Purdom et al. [16] and Hansen et al. [48] noticed that concentrations of bE2 as low as 1 ng/L induces VTG Table 2 Estrogens concentrations in STP effluent Samplig site Paris, France Denmark Netherlands Sweden England England England Germany Germany Germany Germany (SW) Italy Roma, Italy Roma, Italy Centre Italy Barcelona, Spain Japan Japan Canada California, USA Effluent concentration (ng/L) Estrone 17b-Estradiol 17a-Estradiol Estriol 17a-Ethinylestradiol Mestranol 6.2–7.2 <2–11 <0.4–47 5.8 1.4–76 <LODb 6.4–29 9 14.6 7 <LODe–18 3 24 17 5–30 <2.5–8.1 – 2.5–34 3 – 4.5–8.6 <1–4.5 <0.6–12 1.1 2.7–48 <LODb 1.6–7.4 <LODd 4.6 6 <LODf–15 1.4 4 1.6 3–8 <5–14.5 <LODd 0.3–2.5 6 0.2–4.1 – – <0.1–5 – – – – – – – – – – – – – – – – – 5.0–7.3 – – – – – 2–4 – – 3 – 20.4 11.7 2.3 n.d.–1 <0.25–21.5 – – – – 2.7–4.5 <1–5.2 <0.2–7.5 4.5 <LODa–4.3 <LODb <LODc 1 – 3 <LODf–12 0.6 1.4 – n.d. <5 – – 9 0.2–2.4 – – – – – – – <LODd – 4 <LODg–2.7 – – – – – – – <LODd – HRGC-MS: high resolution gas chromatography-mass spectrometry; NCI: negative chemical ionization. a 0.2 ng/L. b 0.3 ng/L. c 0.05 ng/L. d 1 ng/L. e 0.7 ng/L. f 0.4 ng/L. g 0.6 ng/L. Analysis method Reference SPE/GC-MS – SPE/GC-MS-MS SPE/GC-MS SPE/GC-MS SPE/GC-MS-MS SPE/GC-NCI-MS SPE/GC-MS-MS SPE/LC-MS-MS SPE/HRGC-MS SPE/GC-MS SPE/LC-ESI-MS-MS SPE/LC-MS-MS SPE/LC-ESI-MS-MS SPE/LC-ESI-MS-MS SPE/LC-MS SPE/ELISA SPE/LC-MS-MS SPE/GC-MS-MS SPE/ELISA [23] [30] [31] [32] [13] [24] [33] [34] [25] [35] [9] [26] [25] [27] [36] [28] [29] [37] [34] [38] 527 M. Auriol et al. / Process Biochemistry 41 (2006) 525–539 Table 3 Concentrations of estrogens present in river water Sampling site France Netherlands England Germany Italy Spain (NE) Japan Tokyo, Japan Japan California, USA Concentration (ng/L) Estrone 17b-Estradiol 17a-Estradiol Estriol 17a-Ethinylestradiol Mestranol 1.1–3.0 <0.1–3.4 0.2–10 <LODd 1.5 4.3 – – 0.2–6.6 – 1.4–3.2 <0.3–5.5 <LODa–7.1 <LODd 0.11 6.3 <LODe 32 0.6–1.0 0.05–0.8 – <0.1–3 – – – – – – – – 1.0–2.5 – <LODb–3.1 – 0.33 8 – 5.5 – – 1.1–2.9 <0.1–4.3 <LODc <LODd 0.04 – – – – <0.05–0.07 – – – <LODd – – – – – – Analysis method Reference SPE/GC-MS SPE/GC-MS-MS SPE/GC-NCI-MS SPE/GC-MS-MS SPE/LC-ESI-MS-MS SPE/LC-MS SPE/ELISA SPE/TR-FIA SPE/LC-MS-MS SPE/ELISA [23] [31] [33] [34] [26] [28] [29] [39] [37] [38] TR-FIA: time-resolved fluoroimmunoassay. a 0.03 ng/L. b 0.06 ng/L. c 0.05 ng/L. d 0.5 ng/L. e 1 ng/L. in male trout. In addition, Routledge et al. [46] and Larsson et al. [32] noted that EE2 can be a potential danger to fish and other aquatic organisms, even present at concentrations of 0.1–10 ng/ L. In the study carried out by Purdom et al. [16], EE2 could induce VTG in male fish for a concentration as low as 0.1 ng/L. The alkylphenol polyethoxylates (APEOs) group and their breakdown products, alkylphenols (APs) and alkylphenol carboxylates (APECs), have been shown to be estrogenic as well [46,49]. However, NP and OP are known to be more toxic than their EO precursors [50]. Its frequent use and its stability have as a consequence increased rivers contamination and bioaccumulation risk in the trophic chain [51]. Moreover, NP is present in large amount in STPs sludge and would have as a consequence a diminution of fish reproduction in subsequent receiving water [52]. Several studies proved that NP causes production of vitellogenin in male fish [8,28,53]. Indeed, alkylphenols can have estrogenic effects in fish at concentrations from 1 to 10 mg/L [46,54]. Although nonylphenol polyethoxylates (NPnEO) have been removed from household detergents since 1986, river water quality measurements indicate that there is still NP, nonylphenol ethoxylate (NP1EO) and nonylphenol diethoxylate (NP2EO) concentrations that are as high as 0.571, 0.710, and 0.106 mg/L, respectively [55]. Moreover, Ahel et al. [56] found in Swiss rivers, concentrations in NP2EO above 2.550 mg/L. Several studies have also confirmed the presence of NPnEOs and octylphenol polyethoxylates (OPnEO) in raw sewage, final effluents, sediments, fish, mussels, and even in surface and drinking water, at concentrations ranging from ng/L to mg/L (Tables 4 and 5). Although these values were below acute and chronic toxicity levels, some studies have shown that they individually could be sufficient to produce estrogenic effects [8,46]. Some studies confirmed also the presence of alkylphenol polyethoxylates (APnEOs) in Canadian surface water, sediments, sludge, and sewage treatment plants [60,63,66–68] and St. Lawrence River downstream of the Montreal region. Sabik et al. [69] evaluated the types and levels of APnEO and their metabolites in the municipal effluent of Montreal treatment plant, in surface water, and sediments downstream from the STP. They further studied whether APnEOs were bioconcentrated by mussels (Elliptio complanata) caged and introduced into the St Lawrence River downstream of the major urban zone of Montreal. The analyses were performed on 4-tertoctylphenol (4-t-OP), 4-n-nonylphenol (4-n-NP), nonylphenol polyethoxylates (NP1–16EO), nonylphenoxyacetic acid and Table 4 Concentrations of alkylpehnols and their ethoxylates in STP effluent Sampling site Germany Spain Japan Switzerland Canada USA Concentration (mg/L) NP NP1EO NP2EO OP 0.025–0.77 6–289 0.08–1.24 8 0.8–15 LODa–37 – – 0.21–2.96 49 – – – – – 44 – – 0.002–0.673 – 0.02–0.48 – 0.17–1.7 LODb–0.673 HPLC: high-performance liquid chromatography. a 11 ng/L. b 2 ng/L. Analysis method Reference SPE/HRGC-MS SPE/LC-MS SPE/GC-MS LLE/HPLC GC-MS SPE/HPLC [35] [57] [58] [59] [60] [61] 528 M. Auriol et al. / Process Biochemistry 41 (2006) 525–539 Table 5 Concentrations of alkylpehnols and their ethoxylates in river water Sampling site Concentration (mg/L) Analysis method Reference NP NP1EO NP2EO OP Germany Spain Japan Taiwan 0.0067–0.134 LODa–644 0.05–1.08 1.8–10 – – 0.04–0.81 – – – – – 0.0008–0.054 – 0.01–0.18 – SPE/HRGC-MS SPE/LC-MS SPE/GC-MS SPE/GC-MS [35] [57] [58] [62] Canada <0.01–0.92 – – <0.02–7.8 – <0.02–10 <0.005–0.084 – GC-MS SPE/HPLC [63] USA LODb–1.19 12–95 0.077–0.416 – – 0.056–0.326 – – 0.038–0.398 LODc–0.081 – 0.00156–0.007 SPE/HPLC SPE/GCMS SPE/LC-MS [61] [64] [65] a b c 0.15 mg/L. 11 ng/L. 2 ng/L. nonylphenoxyethoxyacetic acid (NP1EC and NP2EC), and octylphenol-mono and di-ethoxycarboxylic acids (OP1EC and OP2EC). The results showed that many of the target chemicals were present in all the studied matrices (in water from ng/L to mg/L reaching ppm levels in sediments and mussels). 2. Endocrine disrupting compounds removal from wastewater The EDCs presence in the environment is likely to disturb the ecosystems and to affect human health. Thus, the need for developing reliable detection methods, analysis tools, and adapted wastewater treatment processes is now the subject of a quasi-consensus between the scientific communities. 2.1. Conventional treatment processes Municipal and industrial wastewaters contain a multitude of persistent organic compounds derived from domestic and industrial applications. These compounds pass through wastewater treatment systems without being totally intercepted (Table 6) and are continuously discharged into the environment and mainly into surface water and/or groundwater. Although APEOs are highly treatable in conventional biological treatment facilities, effluent from wastewater removed plants is still one of the major sources of APs and APEOs due to incomplete removal and degradation of these surfactants. The concentrations of these APEO metabolites varied among different treatment plants depending on the plant design and efficiency [6]. Many communities in worldwide, such as Europe, use surface or groundwater resources for drinking water production, which contain a significant portion of this wastewater effluent [4]. Svenson et al. [76] detected low but significant levels of estrogenicity in the Swedish rivers estuary, downstream of the STPs. Several studies showed that male fish feminization is linked to the estrogenic compounds occurrence in the STP effluents [9,31,32,34,40]. Current wastewater treatment plants were normally, and in the best cases, designed for carbon, nitrogen, and phosphorus (CNP) removal but a partial EDCs removal is often achieved simultaneously. However, a very few data on the EDCs, and in particular on estrogens, fate in STPs processes are available in the literature [71,77,78]. Indeed, although transformation or degradation processes may eliminate some EDCs from wastewater at variable levels, a large ambiguity persists on the occurred EDCs removal processes mechanism (Table 7). For example, removal pathways for organic pollutants during secondary biological treatment include adsorption onto microbial flocs and removal through the waste sludge, biological or chemical degradation, transformation, and volatilization during aeration [83]. However, Mastrup et al. [82] estimated that less than 10% of natural and synthetic estrogens are removed via biodegradation process, and although a considerable amount is adsorbed to the sludge, the majority of the compounds remain soluble in the effluent. Whereas Johnson et al. [25] could not determine whether biodegradation or sorption is the most important removal mechanisms of these compounds. Thus, it is necessary to look further on the removal mechanisms to improve the existing treatment systems effectiveness and to develop new treatment strategies to remove EDCs from wastewater and sludge. 2.1.1. Physical treatments The nonpolar and hydrophobic nature of many EDCs makes them sorb onto particulates. This suggests that the general effect of wastewater treatment processes would be to concentrate organic pollutants, including EDCs, in the sewage sludge. Mechanical separation techniques, such as sedimentation, would result in significant removal from the aqueous phase to primary and secondary sludges [83]. In conventional treatment system, most of compounds remain in aqueous phase in the effluent, whereas a considerable amount is adsorbed onto sludge during the treatment [81,82]. Concerning estrogens, the log Kow values of estrogens (Table 8) indicate that these compounds should appreciably adsorb onto sediment and sludge [88]. This assumption is emphasized by the detection of high concentrations of estrogens in water released by dewatering sewage sludge [89] and in digested sewage sludge (49 ng/g of bE2 and 37 ng/g 529 M. Auriol et al. / Process Biochemistry 41 (2006) 525–539 Table 6 EDCs removal during various STPs treatment processes Compound Concentration Removal efficacy (%) Treatment process Matrice type Reference >80 86 59 96 100 1 2 2 2 2 Municipal waste landfill Municipal STP Domestic STP Domestic STP Municipal STP [29] [27] [25] [70] [71] Influent Effluent 17b-Estradiol 5 ng/L 11 ng/L 9.69 ng/L 28.1 ng/L – <1 ng/L 1.6 ng/L 4 ng/L 1.2 ng/L – Estrone 44 ng/L 31 ng/L 43.1 ng/L – 17 ng/L 24 ng/L 12.3 ng/L – 61 23 69 83 2 2 2 2 Municipal STP Domestic STP Domestic STP Municipal STP [27] [25] [70] [71] Estriol 72 ng/L 57.29 ng/L 381.5 ng/L 2.3 ng/L 11.71 ng/L 5.6 ng/L 97 80 99 2 2 2 Municipal STP Domestic STP Domestic STP [27] [25] [70] 17a-Ethinylestradiol 4.84 ng/L – 1.40 ng/L – 71 78 2 2 Domestic STP Municipal STP [25] [71] Phenol Nitrophenol 2,4-Dichlorophenol NP1EO NP2EO 6 mg/L 11 mg/L 83 mg/L 140.03 mg/L 140.03 mg/L No detected No detected 16 mg/L 1.99 mg/L 1.99 mg/L – – 81 99 99 3 3 3 4 4 Municipal + tannery industry STP Municipal + tannery industry STP Municipal + tannery industry STP Industrial + domestic STP Industrial + domestic STP [72] [72] [72] [73] [73] NP 2.8 mg/L 1.5 mg/L 57.64 mg/L 10 mg/L 73 mg/L <0.05 mg/L 6.6 mg/L 0.65 mg/L 1 mg/L 47.5 mg/L >98 – 99 90 35 1 3 4 2 5 Municipal waste landfill Municipal + tannery industry STP Industrial + domestic STP Domestic STP Industrial STP [29] [72] [73] [70] [74] 4-NP 4-t-OP PCBs 2.37 mg/L 0.88 mg/L 46 ng/L 0.95 mg/L 0.32 mg/L 1.2 ng/L 60 64 97 6 6 1 Municipal STP Municipal STP Municipal waste landfill [75] [75] [29] BPA 0.13 mg/L 7.1 mg/L 2.5 mg/L 1.776 mg/L 0.55 mg/L <0.005 mg/L No detected No detected 0.210 mg/L 0.14 mg/L >96 – – 88 75 1 3 3 6 2 Municipal waste landfill Municipal + tannery industry STP Municipal STP Municipal STP Domestic STP [29] [72] [72] [75] [70] PCDD PCDF 21 pg/L 8.7 pg/L 5.2 pg/L 3.3 pg/L 75 62 1 1 Municipal waste landfill Municipal waste landfill [29] [29] (1) Biodegradation/sedimentation + additional treatment with charcoal; (2) activated sludge; (3) physicochemical treatment + biological processes; (4) pretreatment + primary clarifier + aeration tanks + secondary clarifier; (5) pretreatment + primary settling + biofilters; (6) primary clarifier + activated sludge + biological nitrogen removal + biological phosphorus removal + settle tank. of E1) [88]. In the same way, log Kow were between 4.00 and 6.19 for the APE metabolites (Table 8), suggesting that these substances are hydrophobic substances and may become associated with organic matter [6]. Other researches also studied the estrogens interactions with natural particles at expected environmental levels, or those of the activated sludge treatment. Most results proved that the adsorbed contaminants amount depends on particulate size and roughness, hence depends on the available particle surface as well as material characteristics. Whereas Schäfer and Waite [12] results showed that the adsorbed amount of a chemical is a function of particle mass. This was reflected in the results with activated sludge, where large particles of about 100 mm showed the lowest adsorption. When the particle surface area was considered, the estrogens adsorption on activated sludge was the highest of all the compounds studied [12]. However, if contaminants are adsorbed on activated sludge particles, they accumulate in the wastewater treatment plants sludge. In this case, the application of digested sludge, as fertilizer, on agricultural fields may cause a potential contamination of soil and ground water [34]. If contaminants are dissolved or associated with dissolved natural organics or even stable and unstable colloids, then they get transported easily through wastewater treatment plant [90]. Domestic sewage generally contains fats, mineral oils, greases, and surfactants [83] and so, in addition to sorption onto suspended solids as a removal mechanism, it is possible that compounds may partition onto the nonpolar fat and lipid material in raw sewage. Trace organic compounds, such as natural hormones [91], a wide range of pesticides [92], alkyl phthalates [93], and personal care and pharmaceutically active products (PPCPs) 530 M. Auriol et al. / Process Biochemistry 41 (2006) 525–539 Table 7 Ambiguity on the occurred estrogens removal processes mechanism Coumpond Sorption (%) Biodegradation Soluble Reference (%) Estriol – – 80–95 95 – – [79] [26] Estrone – a – [80] 17b-Estradiol a – 28 – 90 – – – – [80] [34] [81] 68 – – 20 – – [81] [78] 17a-Ethinylestradiol 87 b 17b-Estradiol equivalent 3b Estrogen Great amount 10 – [75] Majority [82] a Johnson and Sumpter [80] do not give a precise percentage but support that 17b-estradiol is adsorbed whereas estrone is biodegradable. b On the basis of estrogenic activity. [90] can be removed using nanofiltration (NF) or reverse osmosis (RO) and subsequently accumulate in the concentrate [90]. Schäfer et al. [91] observed that some NF membranes remove E1 by size exclusion and others by adsorption. These adsorptive effects may be driven by hydrogen bonding between E1 and the membrane [91]. Schäfer et al. [90] showed also that the presence of natural or chemical particulates, which adsorbs such contaminants, could significantly increase the potential of MF, UF, and NF to remove trace contaminants. Although MF and UF were not expected to remove such small and polar compounds, Schäfer and Waite [12] observed that trace contaminants removal using submerged MF (Memcor) and UF (Zenon) membranes was as high as during powdered activated carbon (PAC) treatment. This removal was high at low and neutral pH, while it decreased substantially at a pH higher than 10.5. Schäfer and Waite [12] attributed this to adsorption effects, comparable to hydrogen bonding and hydrophobic sorption. Indeed, the contaminants adsorption on hydrophobic membranes is expected to be higher than on hydrophilic materials. Chang et al. [94] studies on microfiltration confirmed that significant concentrations of natural hormones, such as E1, could accumulate on hydrophobic hollow fibre membranes as a result of sorption processes. Table 8 Log octanol/water partition coefficients of estrogens and xenoestrogens Compound log Kow Reference 17a-Ethinylestradiol 17b-Estradiol Estrone Estriol BPA Phenol 4-n-NP 4-t-OP NP1EO NP2EO OP1EO OP2EO 3.67–4.15 3,94–4.01 2.45–3.43 2.55–2.81 3.32, 3.43 1.48 4.48, 6.19 4.12, 5.66 4.17 4.21 4.10 4.00 [71,84,85] [84,85] [84,85] [84,85] [86] [86] [86,87] [86,87] [87] [87] [6] [6] However, they also noticed that the membrane retention decreases with increase in the amount of E1 accumulated on the membrane surface. According to Schäfer et al. [90], an appropriate wastewater pre-treatment followed by a hybrid process: MF or UF, combined with, for example, PAC, coagulation or magnetic ion exchange (MIEX), could remove a considerable amount of small-sized contaminants. These contaminants could be pharmaceuticals, EDCs, including hormones, some agrochemicals, viruses, etc. It is important to understand such retention and adsorption effects prior to membrane selection if the membrane is expected to act as a reliable barrier to contaminants. Such adsorption effects are also very important for the understanding of the pollutants fate in treatment systems and possible contaminants desorption during feed quality changes or cleaning operations [12]. Thus, investigations of both fundamental and applied aspects of membrane operation and performance must be carried out to optimize its effectiveness and to contribute to improve treatments strategies. 2.1.2. Chemical treatments Preliminary results indicate that activated carbon is effective for removing some EDCs and PPCPs. In addition, coagulants, such as aluminium and ferric salts, have been used to remove organic matter, although their use is often deemed impractical due to the high costs [95]. However, studies have done a comparative investigation of common adsorbents used in the water and wastewater treatment industry, including PAC, ferric chloride coagulant (FeCl3), and MIEX, that generally allow to remove small-sized contaminants (such as EDCs, including hormones and some agrochemicals) [12]. Results showed that both FeCl3 and MIEX1 are not very suitable to remove the majority of trace contaminants (EDCs and PPCPs). In contrast, Schäfer and Waite [12] showed that PAC is more adequate and appears to be the preferential choice for E1 removal, when PAC is added in a sufficiently high dosage. The EDCs and PPCPs removal is minimal during coagulation since the previous process tends to favour the removal of large and hydrophobic compounds. Indeed, the latter are generally responsible for subsequent adsorption and decantation processes of small-sized contaminants, such as EDCs [12]. 2.1.3. Biological treatments Biological degradation and transformation occur aerobically by biological oxidation in activated sludge, trickling filters, or anaerobically in the sewage system or anaerobic sludge digesters. However, in a study on the distribution of natural estrogens (E1 and bE2) in 18 municipal treatment plants across Canada, Servos et al. [96] noticed that the trickling filter could not reach any removal of bE2. Moreover, Svenson et al. [76] reported that trickling filters were less effective than activated sludge systems (Table 9) to eliminate estrogenic activity, and the highest removal rates were obtained at plants with comprehensive treatment technologies, i.e. combined biological and chemical removal of organic matter, nitrogen, and phosphorus. 531 M. Auriol et al. / Process Biochemistry 41 (2006) 525–539 Table 9 Estrogenic activity evaluation during various municipal STPs treatment processes Treatment process Concentration (ng estradiol equivalent/L) Biological treatment Precipitation Influent Effluent – – – – AS AS AS AS AS AS AS biosorption AS + nitrogen removal AS + nitrogen removal Trickling filter/AS Trickling filter Trickling filter Trickling filter Biorotor Direct, Al Direct, Al Direct, Fe(III) Direct, lime Pre, Fe(III) Simultaneous, Al Simultaneous, Al Simultaneous, Fe(III) Simultaneous + post, Fe(III) Pre + post, Al Post, Al Post, Al Pre, Fe(II) Pre + post, Al Pre, Al Post, Al Post, Al Post, Fe(III) 11.9 10.8 5.45 4.15 29.8 5 10.2 5 12.5 8 6.05 3.85 19.5 6.95 6.75 22.35 3.05 1.6 12.4 12.7 5.9 1.1 12.3 0.3 4.3 1.6 1.45 2.55 1.2 <0.1 <0.1 <0.1 1.7 14.85 10.75 5.25 Removal efficacy (%) – – – 73.5 58.7 94 57.8 68 88.4 68.1 80.2 >97.4 >99.5 >98.5 74.8 33.6 – – AS: activated sludge. The activated sludge process is commonly used to treat wastewater in large cities and mainly to remove organic compounds present in STP influent [80]. However, not all compounds are completely broken down or converted to biomass. Indeed, estrogenic alkylphenols and steroid estrogens, for example, found in STP effluent are the breakdown products of incomplete biodegradation of their respective parent compounds [80]. Batch studies realized by Johnson and Sumpter [80] have indicated that E1, EE2, and alkylphenols will not be completely eliminated in activated sludge, in the current configurations of the process. Field data suggested that the activated sludge process can remove over 85% of bE2, E3, and EE2, while the removal performance for E1 appears to be less and more variable [80]. Indeed, in a review on steroid estrogens removal effectiveness, Johnson et al. [25] reported that the activated sludge process could remove 88% of bE2 and 74% of E1. Moreover, Baronti et al. [26] listed six STPs using activated sludge system close to Rome. They reported average removals of 87% of bE2, 61% of E1, 85% of EE2, and 95% of E3 [26]. Ternes et al. [34] studied a number of natural and synthetic estrogens in sewage at a municipal STP near Frankfurt/Main and found that about 2/3 of the incoming bE2 and 16a-hydroxyestrone was eliminated in the STP whereas the elimination efficiencies for E1 and EE2 were low (<10%). In subsequent laboratory experiments with activated sludge from the same plants, Ternes et al. [71] confirmed the persistence of EE2 under aerobic conditions while both E1 and bE2 were degraded fairly rapidly under these conditions (bE2 via E1). In the same way, Esperanza et al. [7] reported that removal efficiencies for E1 and EE2 were around 60% and 65%, respectively, in two pilot-scale municipal wastewater treatment plants, although more than 94% of bE2 entering in the aeration tank was eliminated. Whereas high removals of E3, bE2 [26,70], and EE2 [26] were achieved, no more than 69% of E1 were removed by activated sludge treatment [26,70], and in 4 out of 30 events, E1 outlet levels were even larger than inlet levels [26]. Onda et al. [70] and Johnson and Sumpter [80] concluded that it is necessary to consider bE2 conversion to E1, in E1 effluent concentration. Indeed, batch results obtained by Onda et al. [70] and Esperanza et al. [7] indicated that bE2 was transformed to E1, such as intermediate product. Lee and Liu [97] examined the fate of bE2 in aerobic and anaerobic reactors with activated sludge and observed the rapid degradation of bE2 to E1 but did not observe any other stable major metabolites. Furthermore, Estrogens are either excreted in urine as glucuronide or sulfated conjugates in both humans and animals [98,99]. Indeed, Andreolini et al. [100] observed that E1 is excreted in latepregnancy urine preferentially in conjugated form, estrone-3sulfate (E1-3S). Adler et al. (2001, quoted by Servos et al. [96]) reported that 50% of bE2 and 58% of E1 were conjugated in raw sewage. On this basis, Johnson and Sumpter [80] supposed that the anomalous behaviour of free E1 observed in their study, in those of Shore et al. [101] and Baronti et al. [26], was the result of the microbial deconjugation of E1-3S in the sewer system during the activated sludge STP treatment. Indeed, several studies suggested that the deconjugation could occur during STPs process through microbial processes in the sewage treatment plants [13,41,71,98,99,102], and in rivers [41]. Ternes et al. [71] reported during batch reactor studies that the glucuronides of bE2 (17b-estradiol-(17 or 3)-b-D-glucuronide) were rapidly cleaved in contact with diluted activated sludge resulting in the release of bE2. After less than 15 min, the 17bestradiol-glucuronide was cleaved and both bE2 and E1 could be detected. Carballa et al. [103] investigated the behavior of natural estrogens (E1 and bE2) along the different units of a 532 M. Auriol et al. / Process Biochemistry 41 (2006) 525–539 municipal STP located in Galicia (Spain). During the secondary treatment (conventional activated sludge), the increase of E1 concentration in the effluent could be explained by the oxidation of bE2 in the aeration tank and by the cleavage of the conjugates. Furthermore, D’Ascenzo et al. [27] investigated the fate of the conjugated forms of the three most common natural estrogens occurring in the municipal aqueous environment. Levels of conjugated and free E3, bE2, and E1 were studied considering three scenarios: (1) female urine, (2) a septic tank collecting domestic wastewater, and (3) influents and effluents of six activated sludge sewage treatment plants. They confirmed through laboratory biodegradation tests that glucuronated estrogens are readily deconjugated in domestic wastewater, presumably due to the large amount of the bglucuronidase enzyme [104] produced by fecal bacteria (Escherichia coli). Since most of estrogens and androgens are mainly excreted in conjugated form, the occurrence of these free hormones in the aquatic environment (e.g., STP effluents and rivers) is probably due to their deconjugation by bacteria in situ [13,26,31,34,53,79,80,101,105]. According to D’Ascenzo et al. [27] study, the sewage treatment completely removed residues of estrogen glucuronates and with good efficiency (84– 97%) the other analytes, but not E1 (61%) and E1-3S (64%). Therefore, D’Ascenzo et al. [27] concluded following this study, that E1 appears to be the most important natural EDC, considering that (1) the amount of the E1 species discharged from STPs into the receiving water was more than ten times larger than bE2 species, (2) E1 has half the estrogenic potency of bE2, and (3) some E1-3S fraction could be converted to E1 in the aquatic environment. Moreover, the estrogens form greatly influences their estrogenic potency. Matsui et al. [89] compared the estrogenic activity of various substances using the EC50 of the YES response. For instance, the conjugated form 17b-estradiol 3sulfate was 5.3
105 and 17b-estradiol 17-b-D-glucuronide and 17b-estradiol 3-b-D-glucuronide were only 5.9
107 and 3.1
105, respectively, relative to the activity of bE2 [89]. The estrogenic potentials of the conjugated forms of estrogens are clearly much lower. The cleavage of glucuronide during treatment or in the collection system may therefore greatly increase the estrogenicity of the effluent [96]. Like natural hormones (such as bE2), synthetic hormone, EE2, used as estrogenic compound in contraceptives, is metabolized in human body before its excretion. It is found then especially in conjugated forms [99,106]. This conjugation, which inactivate hormonal action of these compounds (e.g., glucuronated and sulphates), increases its water solubility, and thus these compounds become more mobile in environment than free hormones [81]. Indeed, Carr and Griffin [106] noticed that after 24 h, only 3% of EE2 amount (20–50 mg/day) contained in contraceptives remain in plasma, whereas over 60% are excreted in urine. In activated sludge, Turan [107] reported no change in EE2 concentration over 120 h of treatment. However, when Vader et al. [108] added hydrazine as an external electron donor to provide unlimited reducing energy, EE2 degradation increases slightly. This demonstrated that EE2 degradation is mediated by monooxygenase activity. Moreover, Vader et al. [108] found that under non-nitrifying conditions, there was no degradation of EE2, while nitrifying sludge oxidized EE2 to more hydrophobic compounds. Layton et al. [98] also found in laboratory experiments that sludges, which failed to nitrify, also failed to degrade EE2. Vader et al. [108] suggested that the seasonal and temperature effects on nitrification may therefore result in changes in the ability of treatment systems to remove EE2 and related compounds. In addition, Lee and Liu [97] showed in batch experiments that bE2 was more persistent under anaerobic conditions than under aerobic conditions but was still biodegradable by the culture. In addition, Shi et al. [109] investigated the biodegradability of natural and synthetic estrogens using nitrifying activated sludge (NAS) and ammonia-oxidizing bacterium Nitrosomonas europaea. The results confirmed that NAS significantly degrades both natural and synthetic estrogens. Among the four estrogens, bE2 was most easily degraded. NAS degraded 98% of bE2 at 1 mg/L within 2 h, which indicates that NAS also has excellent bE2-degradation ability. Regarding EE2, Shi et al. [109] found a similar trend to Vader et al. [108]. Shi et al. [109] showed also that ammonia-oxidizing bacteria such as N. europaea can contribute to the estrogen degradation by NAS. However, NAS degrades estrogens and their degradation intermediates, while N. europaea only degrades estrogens with no further degradation of their intermediates. Thus, other microorganisms could exist in NAS which are not ammonia-oxidizing bacteria, and are responsible for intermediates degradation. Indeed, E1 was generated when NAS degraded bE2, whereas E1 was not generated when N. europaea degraded bE2. Obviously, bE2 degradation via E1 by NAS is considered to be caused by other heterotrophic bacteria and not by nitrifying bacterium such as N. europaea. On the other hand, since estrogens are hydrophobic organic compounds with low volatility, sorption to sludge could play an important role in removal of these compounds during the waste treatment process. Johnson and Sumpter [80] suggested that the principal mechanisms for steroid estrogens removal in activated sludge processes could be sorption and biodegradation. In general, for more hydrophobic compounds, such as EE2, sorption to sludge is likely to play a significant role in removal of these compounds from solution, while for relatively weakly hydrophobic compounds, such as E3, biodegradation would be a privileged factor [80]. In a recent Danish study on removal processes in activated sludge [30], the results indicated that at common sludge densities in Danish STPs about 35–45% of E1, 55–65% of bE2 and EE2 can be expected to be sorbed to the sludge. The degradation of these compounds was studied under aerobic and anaerobic conditions in a simulated activated sludge system. It is concluded that under anaerobic conditions, the degradation rates for E1 and EE2 were considerably (10–20 times) lower than under aerobic conditions while the degradation of bE2 was not significantly diferent [30]. Moreover, steroids removal can be influenced by hydraulic retention time (HRT) and high sludge retention time (SRT) used by STPs [83]. Indeed, in another Danish literature review on substances causing feminization of fish [77], it was concluded M. Auriol et al. / Process Biochemistry 41 (2006) 525–539 that a high HRT and SRT in the activated sludge treatment process have a positive influence on the ability of an STP to remove estrogen. However, a study of mass balance of estrogens in STP in Germany [75] demonstrated that most of the estrogenic activity in the wastewater was biodegraded during treatment rather than adsorbed onto suspended solids. There was a 90% reduction in estrogenic load, and less than 3% of the estrogenic activity was found in the sludge (Table 7). Moreover, radiolabelled bE2 was used in a study of estrogen fate in STP [110]. Fuerhacker et al. [110] concluded that at low concentration, the majority of radiolabelled bE2 remained in the liquid phase, and thus the physical-chemical properties, such as the octanol/water partition coefficient, did not reflect the situation at neon gram range [110]. In another study (Johnson, 1999, quoted by Birkett and Lester [83]), suspended solids content was an important factor. A higher suspended solids content resulted in a higher removal of estrogens, while an increase in influent estrogen concentration caused a decrease in removal, probably due to the EDCs sorption on the suspended solids. In the case of the surfactants group, the oxidative shortening of the polyethoxylate chain occurs easily and rapidly in aerobic conditions. However, complete mineralization is poor due to the presence of the highly branched alkyl group on the phenolic ring. The hydrophilic group in ethoxylated compounds contains more abundant carbon than the hydrophobic alkyl group. These moieties (available by the successive removal of ethoxy groups) are therefore potential sources of bacterial nutrients. This chain shortening results in the formation of recalcitrant intermediates such as nonylpehnol (NP), octylphenol (OP), and mono to triethoxylate alkylphenols (NP1EO, NP2EO, and NP3EO) [6]. Ultimate biodegradation of these metabolites occurs more slowly, due to the presence of the benzene ring and their limited water solubility [83]. Moreover, since APs are high lipophilic, in particular 4NP, sorb onto the solid phase making them more resistant to biodegradation [7,58,111,112], whereas APECs are more water-soluble and have a very limited tendency to be found in the solid phase. However, Ying et al. [6] reported that aerobic conditions facilitate further biotransformation of APE metabolites than anaerobic conditions. In STP, bisphenol A is easily removed by biodegradation mechanisms (Matsui et al., 1988, quoted by Birkett and Lester [83,113]). Polychlorinated biphenyls (PCBs) are stable molecules with low aqueous solubility and biological, chemical, and physical recalcitrance. As a result, they exhibit minimal degradation in the STP [114], and according to McIntyre and Lester (1981, quoted by Birkett and Lester [83]), the major removal mechanism of PCB, such as organotins [115,116], is via adsorption to suspended matter and sludge flocs. Air stripping has been also noted as an important factor for compounds with HC greater than 100 Pa m3 h1 [83]. For polyaromatic hydrocarbon compounds, degradation times could be as long as 80– 600 h in a conventional STP, since the experiments were run in ideal conditions with a temperature of 20 8C and pre-adapted bacteria. During volatilization, significant removal was seen, and during photodegradation some compounds demonstrated significant losses in settled sewage. In accordance with Melcer et al. 533 [117], Hegeman et al. [118], and Chiou et al. [119], PAH’s removal during primary sedimentation is a function of molecular weight and suspended solids removal efficiency, since they tend to partition onto the solid phase. In conclusion, activated sludge processes allow a relatively high EDCs removal [26,27,70,76,80], however it does not permit to reach lower estrogens, alkylphenols, and BPA effluent concentrations, than the maximum limit levels reported as producing estrogenic effects in fish and other aquatic organisms (Tables 6 and 9). For example, Servos et al. [96] reported that the degradation of estrogens in aerobic batch reactors with a sewage sludge was very rapid, with bE2 and E1 being reduced by >95% in less than 24 h. However, even after 120 h, traces of E1 and estrogenicity could be detected [96]. In addition, it is necessary to notice that the concentration and the removal rates obtained in different studies are not easily comparable, since the treatment conditions at the studied wastewater treatment plants are different or sometimes not clearly described. Moreover, the sampling strategy and the analytical methods vary from a study to another [80]. Membrane bioreactors can be defined as systems integrating biological degradation of waste products with membrane filtration [120]. These treatment systems proved a quite effective removal of organic and inorganic contaminants as well as biological entities from wastewater [121]. Indeed, since estrogens bind readily to organic matter, membrane bioreactor could provide a suitable environment for EDCs removal due to the high organic content in the mixed liquor, and the retention of all particular and colloidal matter before the draw phase. In addition, the possibility of maintaining high SRT in the membrane bioreactor leads to a diverse microbial culture, including slow growing organisms, capable of breaking down complex organic compounds [122]. Thus, compared to other biological treatment, Buenrostro-Zagal et al. (2000, quoted by Cicek [121]) found a better removal effectiveness of 2,4dichlorophenoxyacetic acid using a selective extractive membrane bioreactor. Furthermore, Wintgens et al. [123] investigated membrane bioreactors application and nanofiltration with the aim of evaluating the potential of EDC removal. It was obvious throughout the results, that most of the load was reduced in the membrane bioreactor, while granulated activated carbon treatment, applied downstream, was only a further polishing stage. Inded, some membrane bioreactors configurations allow the retention, and consequently break down of many EDCs without requiring sophisticated tertiary treatment processes [121]. 2.2. Advanced treatment processes 2.2.1. Chlorination process Several studies Hu et al. [124] and Moriyama et al. [125] showed that bE2 and EE2, respectively, reacted rapidly with HOCl and are completely removed (Table 10). However, several chlorinated by-products formed. Moreover, it has been reported that some of chlorinated products have carcinogenicity and/or mutagenicity [125]. Thus, it is important to identify the products from the reaction of EDCs with available chlorine and their estrogenic activities associated [124,125]. Indeed, Hu 534 M. Auriol et al. / Process Biochemistry 41 (2006) 525–539 Table 10 Removal of estrogens by advanced treatment processes Compound Concentration Removal (%) Reaction time Added dose Reference 0.015 mg/Lc 9.7–28 ng/Ld 3.0–21 ng/Ld >80 95 18 min 10 min 5 mg O3/L 5 mg O3/L [126] [127] Chlorination 17b-Estradiol 17b-Estradiol 17a-Ethinylestradiol 50 mg/Le 107 M e 0.2 mmol/Le 100 100a 100 10 min 36 h 5 min 1.46 mg/L of sodium hypochlorite 1.5 mg/L of chlorine 1 mmol/L of chlorine [124] [128] [125] MnO2 17a-Ethinylestradiol 15 mg/Le 81.7 1.12 h – [129] TiO2 17b-Estradiol 0.05–3 mmol/Le 98 3.5 h – [130] TiO2 + UV 17b-Estradiol 106 M e 30 min 3h 1.0 g/L of TiO2 in suspension [131] Ozonation Estrone Estrone, 17b-estradiol a b c d e 99 100b Complete removal of estrogenic activity. Decomposed completely into CO2. Municipal STP effluent. Wastewater from secondary treatment. Synthetic water. et al. [124] could determine mainly the formation of 4-chloroE2, 2,4-dichloro-E2, and 2,4-dichloro-E1, and others compounds non-identified. Hu et al. [124] concluded that the products in aqueous chlorinated bE2 solution elicited estrogenic activity. Moreover, Moriyama et al. [125] confirmed the formation of two products in highly chlorinated solutions after 60 min (4-chloro-EE2, 1–6 mol%; 2,4-dichloro-EE2, 3– 25 mol%). The estrogenic activities of 4-chloro-EE2 were similar to those of the parent EE2. 2.2.2. Ozonation and advanced oxidation processes Ternes et al. [126], Nakagawa et al. [127], and Kosaka et al. [132] could remove considerably various estrogens during ozonation treatment (Table 10). Huber et al. [133] determined, in bench-scale experiments, the rate constants of EE2 for ozonation (kO3 ¼ 7
109 M1 s1 ) and AOP (kOH = 9.8
109 M1 s1). However, EDCs co-exist with other organic and inorganic compounds, whose concentrations are relatively high in environmental water. The reaction of HO is less selective, and thus the generated HO is ineffectively consumed by the coexisting compounds. It is assumed that EDCs removal efficiencies are dependent on the initial concentrations of EDCs, co-existing compounds and their reactivities toward ozone and HO. Furthermore, the ozonation products formed are currently unknown [126]. However, hydroxylated estrogens should lose their affinity for the estrogen receptor to greatly reduce the known estrogenic activities of wastewater, but this assumption has not been proved [126]. Moreover, Huber et al. [133] concluded that modifications caused by ozonation or AOPs should be sufficient to eliminate the estrogenic effects of EE2. However, the reactions with ozone and OH radicals during an ozonation process will not result in the complete mineralization of EE2. 2.2.3. Treatment with manganese oxide Rudder et al. [129] obtained an EE2 removal of 81.7% using manganese oxide (MnO2) (Table 10). Moreover, since the MnO2 reactor was not yet saturated after 40 days of treatment, they concluded that EE2 was not only adsorbed to the MnO2 granules, but most probably also degraded into others compounds. Thus, the self-regenerating cycle of MnO2 seems possible. This can make this treatment cost-effective, because the matrix does not have to be replaced [129]. However, Rudder et al. [129] did not identify the EE2 metabolites and neither their estrogenic activity. 2.2.4. Photolysis reactions Photolysis reactions have been extensively studied for estrogens removal from aqueous environment [130,131,134,135] (Table 10). Liu and Liu [135] examined the UV-light and UV–vis-light (high-pressure mercury lamp) direct photolysis of two estrogens, bE2 and E1, in aqueous solution at high concentrations. They could show that the photolysis of both the estrogens causes the breakage and oxidation of benzene rings to produce compounds containing carbonyl groups. Moreover, Ohko et al. [131] concluded in his study on the bE2 degradation by titanium dioxide (TiO2) photocatalysis, that the phenol moiety of the bE2 molecule should be the starting point of the photocatalytic oxidation. In addition, since the intermediate products do not have a phenol ring, Ohko et al. [131] presumed that their estrogenic activities are negligible. 3. Discussion and conclusion It has generally been observed that primary treatment alone results in no or only limited removal of estrogens from sewage, while secondary treatment involving activated sludge reduces M. Auriol et al. / Process Biochemistry 41 (2006) 525–539 significantly all estrogens concentrations. Moreover, a long SRT appears to have a positive influence on the activated sludge system ability to eliminate estrogens. It appears also that bE2 and E3 are very efficiently removed in the latter systems while the removal rate of E1 and EE2 is somewhat lower. It seems also that EE2 only undergoes significant removal degradation when nitrification steps are present. On the other hand, according to the literature, the main estrogens removal mechanism in the activated sludge system seems to be sorption to sludge particles and/or microbiological degradation. However, due essentially to issues met during estrogens sludge analysis; there is no publication to date which could prove it. Indeed, almost all the studies only analyzed the estrogens in the STP influent and effluent, and so assumed that the difference was adsorbed in STP sludge. Moreover, the highest EDCs removal achieved with the different above exposed treatment processes does not allow generally to reach effluent concentrations, which respect the maximum limit levels determined as producing estrogenic effects in fish and other aquatic organisms (Tables 6 and 9). So, it would be interesting to look further into investigation on treatment processes to achieve concentrations in effluent below estrogenic limits. Indeed, Donova et al. [136] reported that a wide variety of microorganisms of different taxonomy could have the ability of steroids biotransformation. The use of these microorganisms in STP would be interesting to evaluate. The decomposition processes (such as ozonation and chlorination processes) display a high potential for removing recalcitrant compounds (e.g., estrogens). However, little data exists, and most of researchers used synthetic water with estrogens concentrations over environmental relevant concentrations (Table 10). Therefore, it should be investigated whether these techniques are also feasible for estrogens removal at ng/L levels and from water containing others particles, such as wastewater. Moreover, the majority of advanced treatments produce by-products whose estrogenicity is unknown or in some cases higher or similar to their precursors [124,125]. Treatment of wastewater and sludge contaminated with phenols and other aromatic compounds (e.g., BPA, bE2, and EE2) with enzymes such as peroxidases [137–140] or polyphenol oxidases [139,141,142] is a new and interesting strategy. Since current researches develop the production of enzymes by using municipal and industrial wastewater and sludge, as basic substrate, the overall costs of enzyme production would be reduced [143]. Therefore, the enzymatic treatment process would be a cost-effective alternative for removing EDCs from municipal and/or industrial wastewater. Finally, regarding to treatment processes advantages and disadvantages with respect to the EDCs removal, we could observe through this review that:  Coagulation processes using iron or aluminium salts does not allow any EDCs removal and it is an expensive treatment process.  PAC coagulation could remove a considerable amount of small-sized contaminants such as EDCs including hormones. 535  Filtration processes (UF, MF, NF), used as hybrid process or not, can allow relatively high EDCs removal, however they are also expensive, require a significant maintenance to avoid membranes clogging.  Membrane bioreactor combines the adsorption and biodegradation processes, and thus would be a good compromise for simultaneous CNP and EDCs removal.  Advanced processes allow a high removal of recalcitrant compounds, however many by-products are released and could have an estrogenic activity higher than their precursors. 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