Ecotoxicology and Environmental Safety 270 (2024) 115915 Available online 9 January 2024 0147-6513/© 2024 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by- nc-nd/4.0/). Influence of effluent particles and particle-bound micropollutants on the removal of micropollutants and UVA254 in wastewater effluent ozonation Jueying Qian , Hana Atallah Al-asad , Janna Parniske , Andrea Brandl , Monika Degenhardt , Tobias Morck * University of Kassel, Chair of Urban Water Engineering, Kurt-Wolters-Street 3, 34125 Kassel, Germany A R T I C L E I N F O Keywords: Ozone Organic micropollutants Effluent suspended solids Wastewater Wastewater particles Ozone exposure A B S T R A C T This study systematically investigated the influence of effluent particles and activated sludge (AS) particles on the removal of micropollutants via wastewater effluent ozonation within typical effluent total suspended solids (TSS) concentrations. A series of batch experiments revealed that particle concentrations up to 30 mg/L had a minor impact on the removal of organic micropollutants (OMPs) in the aqueous phase. Moreover, the reduction of UV absorbance at 254 nm (UVA254) was negatively correlated to the level of particle concentration at ozone doses higher than 0.5 gO3/gDOC. It indicates that UVA254 abatement was more sensitive to the presence of particles compared to OMP removal. Organic micropollutants (OMPs) sorbed on effluent particles and sludge particles were extracted before and after ozonation. OMP sorption in effluent particles was 2–5 times higher than that in sludge particles. During the ozonation of raw secondary effluent, particle-bound micropollutants were removed comparably to the micropollutants in the aqueous phase. This suggests that the boundary layer sur- rounding the particle didn’t affect the removal of OMPs in the particle phase. Furthermore, the removal of existing OMPs (irbesartan, sulfamethoxazole, and metoprolol) in the effluent was used to assess the ozone and OH exposure. In water samples with and without particles, the elimination of OMPs could be reliably predicted (R2 > 0.95) by calculated ozone and OH exposures. 1. Introduction Ozone degrades many organic micropollutants (OMPs) in waste- water efficiently and is widely used for advanced treatment of municipal and industrial wastewater (Lee et al., 2014; Huber et al., 2005; Alsager et al., 2018). The OMP removal during ozonation is mainly achieved by its reaction with ozone and hydroxyl radicals (OH); the latter is pro- duced from the ozone decomposition (von Sonntag and von Gunten, 2012; Lee et al., 2014). According to ozone and OH rate constants, Lee et al. categorized the OMPs into five groups (Lee et al., 2013). Group I and II are compounds with high (kO3  10 5 M 1s 1) or relative high ozone reaction rates (10  kO3 < 10 5 M 1s 1); Group III contains compounds with low ozone rate constants, but high OH rate constants (kO3 < 10 M 1s 1 and kOH  5 109 M 1s 1); and compounds with low OH rate constants belong to Group IV (1 109  kOH < 5 109 M 1s 1) and Group V (kOH < 1 109 M 1s 1† (Lee et al., 2013). More often, OMPs were divided into different groups such as ozone-reactive and ozone-refractory contaminants (Pocostales et al., 2010); fast-reacting, moderately-reacting, and slowly-reacting contam- inants (Zucker et al., 2015; Sauter et al., 2021), based on the levels of removal by ozonation. The efficiency of ozonation in municipal wastewater treatment plants (WWTPs) for OMP removal depends on the ozone and OH ex- posures, which are influenced by factors such as dissolved organic and inorganic matter, temperature, and pH in wastewater (Wert et al., 2009; Lee and Gunten, 2010; Hoigne et al., 1985; Mathon et al., 2021). Inor- ganic and organic matter may promote and inhibit the ozone chain Abbreviations: AS, activated sludge; COD, chemical oxygen demand, mg/L; DOC, dissolved organic carbon, mg/L; DOM, dissolved organic matter; EPS, extra- cellular polymeric substances; KS, acid capacity, mmol/L; LOQ, limit of quantification; OMPs, organic micropollutants; pCBA, 4-chlorobenzoic acid; PE, population equivalent; RE, raw effluent; RE‡AS, raw effluent doped with activated sludge; SRT, sludge retention time, d; TSS, total suspended solids, mg/L; UVA254, ultraviolet absorbance at the wavelength of λ ˆ 254 nm; VSS, volatile suspended solids, mg/L; WWTP, wastewater treatment plant. * Corresponding author. E-mail address: morck@uni-kassel.de (T. Morck). Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv https://doi.org/10.1016/j.ecoenv.2023.115915 Received 30 September 2023; Received in revised form 23 December 2023; Accepted 28 December 2023 Ecotoxicology and Environmental Safety 270 (2024) 115915 2 reaction and thus affect the ozone and OH exposures (Johannes Stae- helin et al., 1985; Guo et al., 2023; Ma and Graham, 1999; Gonzales et al., 2012). However, there is limited and sometimes controversial information regarding the impact of particles on ozonation. Juarez et al. reported that elevated total suspended solids (TSS) concentrations, mainly from 50 to 200 mg/L by the addition of thickened activated sludge (AS), had a negative effect on the removal of OMPs compared to that in the filtered secondary effluent (Juarez et al., 2021). Zucker et al. claimed that particles in secondary effluent (<50 µm) may adversely affect ozonation (Zucker et al., 2015). Contrary to the above-mentioned studies, Huber et al. found that the effluent particles and the addition of 15 mg/L AS had a minor influence on the oxidation efficiency of micropollutants during ozonation of raw effluent (RE) in a pilot plant at ozone doses from 0.07 - 0.7 mgO3/gDOC (Huber et al., 2005). They suggested that ozone absorption on particles was limited by ozone diffusion across the boundary layer surrounding the sludge particles (Huber et al., 2005). Based on the previous work, more studies are necessary to address the impact of native effluent particles and native AS particles at typical effluent concentrations on the OMP removal during ozonation of RE. Investigations of the impact of particles on ozonation are of research interest for the application in practice. The necessity of pre-filtration or even post-filtration is to be determined. The effluent and sludge particles are flocs containing mainly mi- croorganisms and extracellular polymeric substances (EPS). EPS are a complex mixture of high molecular weight polymers secreted by mi- croorganisms (Staudt et al., 2004; Wagner et al., 2009). EPS in the matrix of biofilms protect the microbial communities from harsh envi- ronments and chemicals such as antimicrobial agents (Mittelman, 1998; De Beer et al., 1994). Particles play different roles during the ozonation of wastewater. Particles may compete with the dissolved substances for ozone and OH during the oxidation reactions (Zucker et al., 2015). At high particle concentrations, less ozone and OH are thus available for OMP oxida- tion. Secondly, OMPs can be sorbed to AS particles (Mailler et al., 2014; Gonzalez-Gil et al., 2016; Lajeunesse et al., 2012; Svahn and Bjorklund, 2015; Xiao et al., 2022). In fewer studies, OMP sorption (such as ben- zotriazole) in effluent particles was analyzed (Asimakopoulos et al., 2013; Stasinakis et al., 2013). It is still unclear if sorbed OMPs in the particle phase may desorb into the aqueous phase after ozonation. This study aimed to determine the impact of particles at typical effluent concentrations on the removal efficiency of OMPs during ozonation. For that, this paper examines the OMP removal and the reduction of ultraviolet absorbance at the wavelength of λ ˆ 254 nm (UVA254) in the aqueous phase at different ozone doses and TSS con- centrations up to 30 mg/L. Specifically, this study extends the knowl- edge of the fate of OMPs in the particle phase during ozonation by evaluating the sorption of eleven OMPs on the effluent particles and AS particles, as well as the removal of particle-bound OMPs. 2. Materials and methods 2.1. Wastewater and suspended solids samples Grab water samples were taken at the secondary effluent of WWTP-A and WWTP-B in Germany. In the catchment area of WWTP-A (13,000 PE), there are around 12,000 inhabitants and six rehabilitation clinics with almost no indus- trial wastewater input. The conventional treatment in WWTP-A includes sand and grease traps and no primary clarifier. The total sludge retention time (SRT) of the subsequent AS process is between 20 to 25 days. WWTP-B has a capacity of 350,000 PE. The inflow consists of around 65% domestic and 35% industrial wastewater. The WWTP-B is equipped with screens, sand and grease traps, primary clarifiers, conventional activated sludge tanks, and secondary clarifiers. The SRT of the AS process in WWTP-B is between 10 to 14 days. Water and AS samples were taken in polyethylene containers and stored in the dark at 4 C before use. The samples were tested within a month. The characteristics of the water samples are listed in Table S1, Supplementary Information. 2.2. Wastewater types To study the influence of particles on OMP removal during ozona- tion, three wastewater types with different TSS concentrations were prepared in the study. They were: 1) the permeate from membrane filtration with a pore size of 0.45 µm prepared from secondary effluent (cellulose acetate filter, Sartorius GmbH, Goettingen, Germany). TSS concentration was 0 mg/L; 2) raw effluent (RE) with original TSS concentration in the effluent (Table S2, Supplementary Information); 3) raw effluent ‡ activated sludge (RE‡AS): native AS was dosed into the unfiltered effluent in order to achieve a TSS concentration of 30 mg/L, simulating an AS treatment with suboptimal clarification. Effluent samples and sludge samples from the same WWTP were mixed together. 2.3. OMP removal in the water phase The three wastewater types with different TSS concentrations from WWTP-A and WWTP-B were doped with the following OMPs at a con- centration of 2 µg/L shortly before ozonation: benzotriazole, carba- mazepine, diclofenac, 4-/5-methyl-benzotriazole, metoprolol, and sulfamethoxazole. The three water types were ozonated at six ozone doses, and the OMP removal in the water phase was analyzed. The specific ozone doses were achieved by adding ozone stock so- lution into each water sample with gas-tight ozone-resistant syringes. A detailed description of the production and dosage of the ozone stock solution can be found in Text S1 in the Supplementary Information. The ozone concentration of the stock solution was determined by the indigo method (Bader and Hoigne, 1981; envilab, 2021). Detailed measure- ment protocol can be found in Text S2 in the Supplementary Information. The abatement of an OMP can be predicted by a second-order kinetic equation (Eq. 1) consisting the ozone and OH rate constants (kO3 ;OMP and kOH;OMP) as well as the ozone and OH exposures ( R ‰O3Šdt and R ‰  OHŠdt). ln  ‰OMPŠ ‰OMPŠ0  ˆ kO3 ;OMP  Z ‰O3Šdt ‡ kOH;OMP  Z ‰  OHŠdt (1) 2.4. Particle-bound OMPs The particle-bound OMPs were extracted by ultrasound-assisted extraction adopted from the studies of Ternes et al. and Boix et al., who focused on the extraction of OMPs from sludge and sediments (Ternes et al., 2002; Boix et al., 2016). To be more detailed, 4000 ml RE or 500 ml RE‡AS were filtered with cellulose acetate filters (100 mm, 0.45 µm, Sartorius Corporate Administration GmbH, Goettingen, Ger- many). Each filter was carefully cut into small pieces after filtration, and the OMPs in the filter were extracted with 20 ml of MeOH:Water (50:50) 0.5% HCOOH, using an ultrasonic bath for 10 min. The supernatants were collected into a glass bottle, and the extraction procedure was repeated. Both supernatants were mixed and filtered through a syringe filter (0.45 µm, cellulose acetate filter, Sartorius GmbH, Goettingen, Germany). The filtered supernatants were evaporated to dryness at 60 C and finally reconstituted with 20 ml of water with 0.1% HCOOH. 2.5. Removal of particle-bound OMPs In order to study the removal of particle-bound OMPs, RE and J. Qian et al. Ecotoxicology and Environmental Safety 270 (2024) 115915 3 RE‡AS were ozonated at two ozone doses: 0.2 gO3/gDOC and 0.5 gO3/ gDOC. The OMPs in the particle phase after ozonation were extracted using the same method described above. 2.6. Analytical methods DOC measurements were performed on equipment DIMATOC 2000 (DIMATEC Analysetechnik GmbH, Essen Germany) as described by DIN EN 1484. NO2 - -N was determined by the photometric method according to DIN EN 26777. TSS was measured according to DIN 38414–2 with glass filters. pH was measured by TitroLine alpha (Schott Instruments GmbH, Germany) according to DIN 38409–7. The measurement of acid capacity to pH 4.3 was also performed by the equipment TitroLine alpha. Organic micropollutants were determined using HPLC-MS/MS and performed by a certified lab, IUTA, Germany. The following OMPs were analyzed in the study: 4 N-Acetylsulfamethoxazole, benzotriazole, candesartan, carbamazepine, clarithromycin, diclofenac, hydrochloro- thiazide, irbesartan, metoprolol, Ʃ4,5-methyl-benzotriazole, and sulfa- methoxazole. These micropollutants were measured with an Agilent 1100 LC system (Agilent Technologies Deutschland GmbH, Germany) coupled to a Sciex QTRAP 6500 mass spectrometer (AB Sciex Germany GmbH, Germany) according ISO 21676 (2018). LC-MS-grade water and acetonitrile (both with 0.1% formic acid) were used as solvents. The limit of quantification (LOQ) of these compounds is listed in Table S3 in the Supplementary Information. 3. Results and discussion 3.1. Extraction of micropollutants from particles To comprehensively investigate the role of particles on OMP removal via ozonation, the OMP sorption on effluent and sludge particles was analyzed and presented in this section. Fig. 1 shows that the OMP concentration in the effluent particles from the two WWTPs (columns with diagonal design) ranged from 0.1 - 40 µg/gTSS. Benzotriazole, 4- and 5-methyl-benzotriazole, and carba- mazepine were among the most sorbed OMPs. For instance, 12 and 37 µg benzotriazole were found in one gram of effluent particles in WWTP-A and WWTP-B, respectively. Since industrial wastewater contributed ca. 40% of the whole influent in WWTP-B, more than three times of benzotriazole was measured in the effluent particles in WWTP-B than that in WWTP-A. Similar was found for 4- and 5-methyl-benzotria- zole, which are also corrosion inhibitors like benzotriazole. On the other hand, higher concentrations of pharmaceutical residues were detected in the effluent particles from WWTP-A compared to that in WWTP-B since city A has many rehabilitation clinics. Comparing the OMP sorption on raw effluent (RE) particles (columns with diagonal design in Fig. 1) and that in the effluent plus AS (RE‡AS) particles (columns in blue), the effluent particles were more loaded with OMPs compared to that in the RE‡AS particles. Based on the OMP sorption on RE and RE‡AS, the OMP sorption on sludge particles alone was calculated. Table S4 in the Supplementary Information shows the ratio between extracted OMPs in effluent particles [µg/g] and OMPs in AS particles [µg/g]. It can be seen that the effluent particles contained 2 - 5 times more OMPs compared to sludge particles, except for carba- mazepine, which was 16 - 18 times more sorbed in effluent particles than in the sludge in the two WWTPs. The effluent particles were more loaded than the sludge flocs. This is because effluent particles are, on average, smaller than sludge flocs. The reported peak particle size for volume distribution was about 50 µm for effluent particles (Khanam et al., 2016; Puig-Bargues et al., 2005), whereas that for sludge flocs was between 80 - 130 µm (Kusnierz, 2018; Li and Ganczarczyk, 1991). More OMPs could be sorbed on the effluent particles’ surface due to the larger surface area of the smaller particles. 3.2. Removal of particle-bound OMPs Fig. 2 compares the OMP removal in aqueous and particle phases from RE samples of WWTP-B. The OMP removal in the solid phase was analyzed after ozonation of the raw effluent at 0.2 or 0.5 gO3/gDOC, followed by OMP extraction from the particles. Fig. 2 reveals that the percentages of OMP removal in the aqueous phase were similar to that in the particles. Data regarding WWTP-A can be found in the Supplemen- tary Information (Fig. S1) and demonstrates comparable results to those of WWTP-B. To the authors’ knowledge, no other study has investigated the OMP removal in effluent particles by ozonation. Huang et al. eval- uated the removal of endocrine-disrupting chemicals in the colloidal and soluble phases by ozone (Huang et al., 2019). Their research found that the respective removal efficiencies of endocrine-disrupting chemicals in colloidal and soluble phases were similar (Huang et al., 2019), which is, to a certain extent, similar to the results of this study. Similar to the experiments regarding the OMP removal in the effluent particles, the OMP removal in the effluent doped with AS particles (RE‡AS) was also investigated and presented in Figs. S2 and S3 (Sup- plementary Information). The removal of OMPs in the aqueous phase and RE‡AS particle phase were similar, except for benzotriazole. The concentrations of metoprolol and irbesartan in the particle phases were relatively low ( 0.5 µgOMP/gTSS) in the RE‡AS samples of WWTP-B (see Fig. 1), and thus, the lower removal in the particle phase compared to that in the aqueous phase may due to the measurement uncertainty. Fig. 1. Extracted OMPs from raw effluent (RE) particles and RE‡AS particles in (a) WWTP-A and (b) WWTP-B. Error bars indicate standard deviations based on double measurements (n ˆ 2). J. Qian et al. Ecotoxicology and Environmental Safety 270 (2024) 115915 4 However, benzotriazole was abundant in the particle phase (RE‡AS particles), and the concentration of benzotriazole even increased by 10 - 25% in the particle phase (RE‡AS particles) after ozonation at an ozone dose of 0.5 gO3/gDOC in WWTP-A and WWTP-B (Fig. S2 and Fig. S3). Part of the soluble benzotriazole seemed to turn into the particle phase after ozonation. Studies have proven that ozonation at low doses ( 0.5 gO3/gDOC) can destabilize organic particles and dissolved organic matter and promote aggregation of particles (Chandrakanth and Amy, 1996; Zucker et al., 2015). The aggregation of organic matter induced by ozonation was, to a large extent, due to the presence of metal cations (Chandrakanth and Amy, 1996). Since benzotriazole can chelate metal ions (Hart et al., 2004; Kusnierz, 2018), and ozonation causes precipi- tation of metal-DOM complexes (Reckhow et al., 1992; Chandrakanth and Amy, 1996), the authors hypothesize that benzotriazole may co-precipitate with the metal-DOM complexes. However, more detailed studies shall be carried out to investigate these phenomena. Distribution of OMPs in aqueous and particle phases The partition of OMPs in the aqueous and particle phase was calculated as a ratio between the amount of OMPs in the aqueous phase [µg/L] and the amount of OMPs in the particle phase per liter effluent sample [µg/L]. Fig. 3 demonstrates that OMP distribution in the aqueous and particle phase had a minor change after ozonation in RE samples from WWTP-B. The aqueous concentrations of carbamazepine, diclofe- nac, and sulfamethoxazole were below the detection limit after ozona- tion at the dose of 0.5 gO3/gDOC, and the corresponding data points are not displayed in Fig. 3. The load of candesartan and diclofenac in the aqueous phase was three orders of magnitude higher than in the particle phase (Fig. 3). At the same time, carbamazepine, methyl-benzotriazole, and benzotriazole display the lowest ratio between the aqueous and the particle phases. The results in WWTP-A display similar results (Fig. S4 in the Supplementary Information). Candesartan displays poor affinition to effluent particles, probably due to its negative charge and low logDow value (logDOW ˆ 1.04 at pH ˆ 7). To be mentioned, candesartan is considered as a substance with variable or low PAC affinity (Decrey et al., 2020; Atallah Al-Asad et al., 2022). Although irbesartan is also negatively charged at pH ˆ 7, this substance shows relatively high abundance in the effluent particles, probably due to its high hydro- phobicity (logDOW ˆ 4.46 at pH ˆ 7). Carbamazepine, on the other hand, shows a very good affinity to particles due to its neutral charge and high logDOW value (logDOW ˆ 2.77 at pH ˆ 7) (Sbardella et al., 2018). According to the literature, the lipophilicity and acidity of OMPs correlate to their sorption to sludge (Carballa et al., 2005; Carballa et al., 2008; Vieno and Sillanpaa, 2014). When studying the DOM-organic pollutant interactions, the polarity and aromaticity of DOM are critical parameters (Caupos et al., 2015; Gauthier et al., 1987; Chiou et al., 1986; Zietzschmann et al., 2015). This study suggests that high logDOW and low polarity are critical to the high distribution of OMPs to effluent particles. This study reveals that OMPs in the aqueous phase were one to three orders of magnitude higher than that in the particle phase, and ozone treats OMPs in both aqueous and particle phases. However, discharging treated wastewater may still lead to the accumulation of OMPs, such as carbamazepine and benzotriazole, via effluent particles in receiving water bodies. 3.3. UVA254 abatement Fig. 4 shows that UVA254 abatement correlates well with the ozone doses at all three TSS concentrations: Filtrate (TSS ˆ 0), RE (native TSS concentration, 1,6 - 4,7 mg/L), and RE‡AS (TSS between 22 - 26 mg/L). The presence of effluent particles and activated sludge displayed a minor effect at lower ozone doses (< 0.4 gO3/gDOC). At the doses higher than 0.5 gO3/gDOC, a negative correlation between UVA254 abatement and TSS concentration was observed. The UVA254 abatement at the ozone dose of 0.75 gO3/gDOC decreased from 49% (Filtrate) to 47% (RE) and Fig. 2. Removal of OMPs in the aqueous and particle phases from RE samples of WWTP-B at ozone dose of (a) 0.2 gO3/gDOC and (b) 0.5 gO3/gDOC. Error bars indicate standard deviations based on double measurements (n ˆ 2). Fig. 3. OMP distribution in aqueous and particle phase from RE samples of WWTP-B before and after ozonation at ozone dose of 0.2 gO3/gDOC and 0.5 gO3/gDOC. Error bars indicate standard deviations based on double measure- ments (n ˆ 2). J. Qian et al. Ecotoxicology and Environmental Safety 270 (2024) 115915 5 42% (RE‡AS) (Fig. 4). Zucker et al. also reported an adverse effect of particles on the reduction of the effluent UVA254 at a dose of 0.93 gO3/ gDOC (Zucker et al., 2015), as the UVA254 abatement reduced from ca. 57% in the 0.45 µm-filtrated water samples to ca. 46% in unfiltered samples. In this study, the lowered UVA254 abatement at 0.75 gO3/gDOC may have resulted from two mechanisms. Firstly, particles react with ozone and OH and depleted part of the reactive oxygen species. Therefore, less ozone and OH were available for the oxidation of the DOM. Sec- ondly, ozone transforms suspended particles into dissolved organic matter, contributing to UVA254. The rise of DOC after the ozone disin- tegration of sludge has been observed at ozone doses from 0.005 to 0.08 gO3/gTSS in literature (Meng et al., 2015; Fatoorehchi, 2016). This was due to cell lysis and the release of intracellular organic matter (Meng et al., 2015; Zhang et al., 2009; Gu et al., 2020) and the transformation of non-soluble EPS into soluble DOM after sludge disintegration (Li et al., 2021). Compared to the literature study, this study examined the UVA254 abatement at six ozone doses as well as the impact of both effluent particles and AS particles. This study reveals that particles had only a minor impact at ozone doses lower than 0.4 gO3/gDOC on UVA254 abatement. This is caused by the preferential reactions between ozone and dissolved substances at low ozone doses (Dietrich et al., 2007) and Fig. 4. Abatement of UVA at 254 nm at different ozone doses and TSS con- centrations. Error bars indicate standard deviations based on double measure- ments (n ˆ 2). Fig. 5. Removal of the fast-reacting OMPs in effluents with different TSS concentrations in WWTP-A and WWTP-B. (a) and (d): the removal of carbamazepine; (b) and (e): the removal of diclofenac; and (c) and (f): the removal of sulfamethoxazole. Error bars indicate standard deviations based on double measurements (n ˆ 2). J. Qian et al. Ecotoxicology and Environmental Safety 270 (2024) 115915 6 the low reaction rate between ozone and particles. In the sludge parti- cles, the bacterial cells make up a minor part (5 - 20% according to different methods) of the organic material, and the largest remaining part are EPS (Nielsen et al., 2004). EPS have been reported to be resis- tant to antimicrobial agents such as chlorine and ozone (Brown and Gilbert, 1993; De Beer et al., 1994). A biofilm chlorination experiment shows that chlorine concentrations measured 10 µm deep in the biofilms were typically only 20% or less of the concentration in the bulk liquid after 1–2 h of chlorine treatment (De Beer et al., 1994), indicating the resistance of biofilm and EPS to disinfectants. 3.4. OMP removal in the water phase with different particle concentrations The removal of fast-reacting OMPs such as carbamazepine, diclofe- nac, and sulfamethoxazole at different ozone doses and particle con- centrations in samples from two WWTPs was investigated. Fig. 5 shows that a particle concentration of up to 30 mg/L had a minor impact on removing these compounds. Like the fast-reacting substances, the moderately-reacting substances including benzotriazole, candesartan and metoprolol were similarly removed in the presence or the absence of particles (Fig. S1 in the Supplementary Information). Therefore, results indicate that the effluent particles and AS particles have negligible impact on removing fast- and moderately-reacting OMPs in the water phase via ozonation till a concentration of 30 mg/L TSS. This finding is consistent with the previous evidence reported by Huber et al., who studied the removal of OMPs in raw effluent or effluent spiked with 15 mg/L AS (Huber et al., 2005). Minor effects of the addition of AS on OMP removal were observed (Huber et al., 2005). On the other side, Juarez et al. reported that suspended solids (mainly from 50 - 200 mg/L) had a negative effect on OMP removal (Juarez et al., 2021). If a linear correlation between the TSS concentrations and reduced OMP removals was assumed, the impact of TSS at common effluent concentrations (<10 mg/L) was between 1.6% and 3.7% in the study of Juarez et al. (Juarez et al., 2021), which is among the mea- surement uncertainty of the experiments. This study suggests that the neglectable impact of particles up to 30 mg/L on ozonation was owing to the low distribution of OMPs in the particle phase compared to the water phase as shown in Sections 3.1 and 3.2. No critical reaction competition thus occurred between the OMPs in water and particle phases. Another argument is the relatively low re- action rate between ozone and the components of particles, such as EPS. A previous study has proposed that the low ozone transfer (0.4%) across the boundary layer surrounding the particle was the mechanism of the minor effect of particles during effluent ozonation (Huber et al., 2005). In their study, a particle surface area of 2.4 m2/gTSS was estimated with the assumption of a spherical particle/floc (50 µm) to evaluate the ozone transfer to particles (Huber et al., 2005). This study demonstrates that OMPs sorbed on particles were comparably removed during ozonation compared to OMPs in the aqueous phase. This implies that ozone transfer from bulk to the particle surface didn’t noticeably hinder the ozonation of the particles. Andreadakis reported that the specific surface areas of sludge flocs (porous structure) were measured to be typically 100 - 200 m2/g dry sludge, which was one to two orders of magnitude higher than the corresponding geometric floc surface areas (Andreada- kis, 1993). Therefore the ozone diffusion to particle surface was prob- ably underestimated by Huber et al. (Huber et al., 2005). However, more studies are necessary to investigate the ozone transfer and reactions within the porous structure of the sludge particles. 3.5. OH and ozone exposure 3.5.1. OH exposure The abatement of an OMP can be predicted by a second-order kinetic equation (Eq. 1). Based on Eq. 1, para-chlorobenzoic acid (pCBA, kOH ˆ 5 109 M 1s 1) is usually used as a probe compound to calculate OH exposure. This study uses the removal of irbesartan to determine the OH exposure, because irbesartan mainly reacts with OH (kO3 ˆ 23 M 1s 1, kOH ˆ 1010 M 1s 1) (Bourgin et al., 2018). A pre- liminary study revealed that irbesartan removal was well predicted by Fig. 6. (a) OH exposure (a) and (b) ozone exposure determined for waste- water samples with different particle concentrations of WWTP-B. Inset of (a): Exponential regression of the same data points of three wastewater types. In Figure (b), the filled points were determined with the removal of sulfameth- oxazole (SMX), and the hollow points were determined with the removal of metoprolol (MTP). Error bars indicate standard deviations based on double measurements (n ˆ 2). J. Qian et al. Ecotoxicology and Environmental Safety 270 (2024) 115915 7 the removal of pCBA (data not shown). Fig. 6(a) displays the correlation between OH exposure and ozone doses ranging from 0.05 to 0.8 gO3/gDOC in wastewater samples with different particle concentrations in WWTP-B. Only a minor difference was observed between the three water types: filtrate, RE, and RE‡AS. Furthermore, the correlation between OH exposure and ozone doses can be fit into two linear phases (main figure) or be described as an exponential regression (inset of Fig. 6(a)). Lee et al. (2014) reported a two-phase linear regression of OH exposure with the first phase from 0.0 - 0.6 gO3/gDOC and the second phase from 0.6 - 1.5 gO3/gDOC, which is comparable to this study (Lee et al., 2014). 3.5.2. Ozone exposure The ozone exposure as a function of the ozone doses for water samples from WWTP-B is demonstrated in Fig. 6(b). For the ozone doses from 0.05 to 0.3 gO3/gDOC, the ozone exposure was calculated based on the removal of sulfamethoxazole (kO3 ˆ 5:7 10 5 M 1s 1, kOH ˆ 5: 5 109 M 1s 1). For the ozone doses from 0.4 to 0.75 gO3/gDOC, the removal of metoprolol (kO3 ˆ 2 10 3 M 1s 1, kOH ˆ 7:3 109 M 1s 1) was applied to determine the ozone exposure. Metoprolol was not used for doses lower than 0.4 gO3/gDOC, because metoprolol elimination was low at these doses ( 20%) and was mainly removed by OH. These two substances were chosen due to their abundance in the wastewater effluent samples and their reaction rate with ozone: sulfa- methoxazole as a fast-reacting substance and metoprolol as a moderately-reacting substance. Ozone exposure increased exponentially, ranging from 10 7 to 10 3 (M s) as a function of the ozone doses. Similar results have been reported by Lee et al. (2014), who have also determined similar ozone exposure ranging from 10 7 to 10 3 (M s) in hospital wastewater at similar ozone doses. It can be seen that there was a jump in the ozone exposure when the substance for exposure calculation was changed from sulfamethox- azole to metoprolol (Fig. 6(b)). This may be because the OH and ozone rate constants chosen from the literature (listed in Table S5 in Supple- mentary Information) don’t align with the real rate constants during ozonation in this study. 3.6. Prediction of micropollutant removal efficiency Fig. 7 shows the calculated and measured OMP removal for all samples of both WWTPs. The calculated removal was assessed based on the OH and ozone exposure reported in 3.5, the ozone and OH rate constants of these compounds (Table S5 in the Supplementary Infor- mation), and Eq. 1. It can be seen that using irbesartan for the deter- mination of OH exposure as well as sulfamethoxazole and metoprolol for the calculation of the ozone exposure resulted in a good prediction of the other OMPs. The data points in Fig. 7 are scattered above or under the line y ˆ x for benzotriazole and methyl-benzotriazole. The slight inconsistency of these substances between the measured and calculated removal can result from measurement uncertainty of the OMPs. Moreover, the con- centrations of carbamazepine were generally overpredicted, and the concentrations of diclofenac were generally underestimated. The two reaction constants were determined in Milli-Q water in literature (Table S5) and may deviate from the actual rate constants in wastewater in this study. In this case, the ozone rate constant for carbamazepine applied in the calculation was underestimated. The impact of TSS concentration on the prediction of the OMP con- centrations has also been assessed (Fig. S6). Results show that the TSS concentration up to 30 mg/L didn’t play a role in predicting the OMP concentrations. 4. Conclusions This study investigated the impact of effluent particles and secondary sludge up to a TSS concentration of 30 mg/L on removing organic micropollutants during wastewater effluent ozonation. In order to evaluate the impact of OMPs in the particle phase on the OMP removal in the aqueous phase, particle-bound OMPs were extracted and analyzed before and after ozonation. It was determined that OMP sorption in effluent particles was 2 - 5 times higher than that in sludge particles. The OMPs in the particle phase were 1 - 3 orders of magnitude lower than that in the aqueous phase. During ozonation, OMPs sorbed on particles were removed comparably to OMPs in the aqueous phase. The particle concentrations within common secondary effluent ranges had a minor effect on the removal of OMPs in the aqueous phase, probably due to the low distribution of OMPs in the particle phase and low reaction rate between ozone and the components of particles, such as EPS, in the investigated ozone concentrations. The reduction of UVA254 during ozonation was not affected by particles (TSS  30 mg/L) when the ozone dose was lower than 0.4 gO3/gDOC. However, the reduction of UVA254 was negatively affected by particles at higher ozone doses. It suggests that UVA254 abatement was more sensitive to the presence of particles compared to OMP removal. Moreover, the calculated ozone and OH exposure at different TSS concentrations and two WWTP effluents can reliably predict the elimi- nation of other OMPs analyzed in this study. CRediT authorship contribution statement Jueying Qian: Conceptualization, Methodology, Investigation, Data Curation, Writing, Review and Editing; Hana Atallah Al-asad: Conceptualization, Review; Janna Parniske: Conceptualization, Re- view; Andrea Brandl: Methodology, Investigation; Monika Degen- hardt: Methodology, Investigation; Tobias Morck: Conceptualization, Methodology, Validation, Supervision, Writing, Review and Editing Declaration of Competing Interest The authors declare the following financial interests/personal re- lationships which may be considered as potential competing interests: Janna Parniske, Hana Atallah Al-asad, Jueying Qian reports financial Fig. 7. Calculated and measured OMP concentrations after ozonation of wastewater samples from WWTP-A and WWTP-B at ozone doses from 0.05 to 0.8 gO3/gDOC. J. Qian et al. Ecotoxicology and Environmental Safety 270 (2024) 115915 8 support was provided by Federal Ministry of Education and Research Bonn Office Library. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data availability Data will be made available on request. Acknowledgement The authors thank the German Federal Ministry of Education and Research for funding the project 02WDG1592A. We are very grateful to all involved persons of WWTP-A and WWTP-B for providing support and cooperation. Thank you to Luca Brauer and Dennis Peupelmann for making available a part of the data from their master theses at University of Kassel and in addition to Lukas Hoft (University of Kassel) for all the sampling rides. Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at doi:10.1016/j.ecoenv.2023.115915. References Alsager, Omar A., Alnajrani, Mohammed N., Abuelizz, Hatem A., Aldaghmani, Ibrahim A., 2018. Removal of antibiotics from water and waste milk by ozonation: kinetics, byproducts, and antimicrobial activity. Ecotoxicol. Environ. Saf. 158, 114–122. https://doi.org/10.1016/j.ecoenv.2018.04.024. Andreadakis, Andreas D., 1993. Physical and chemical properties of activated sludge floc. Water Res. 27 (12), 1707–1714. https://doi.org/10.1016/0043-1354(93) 90107-S. Asimakopoulos, Alexandros G., Ajibola, Akinranti, Kannan, Kurunthachalam, Thomaidis, Nikolaos S., 2013. Occurrence and removal efficiencies of benzotriazoles and benzothiazoles in a wastewater treatment plant in Greece. Sci. Total Environ. 163–171. https://doi.org/10.1016/j.scitotenv.2013.02.041. Atallah Al-Asad, Hana, Parniske, Janna, Qian, Jueying, Alex, Jens, Ramaswami, Sreenivasan, Kaetzl, Korbinian, Morck, Tobias, 2022. Development and application of a predictive model for advanced wastewater treatment by adsorption onto powdered activated carbon. Water Res. 217, 118427 https://doi.org/10.1016/ j.watres.2022.118427. Bader, H., Hoigne, J., 1981. Determination of ozone in water by the indigo method. Water Res. 15 (4), 449–456. https://doi.org/10.1016/0043-1354(81)90054-3. Boix, C., Iba~nez, M., Fabregat-Safont, D., Morales, E., Pastor, L., Sancho, J.V., et al., 2016. Analytical methodologies based on LC-MS/MS for monitoring selected emerging compounds in liquid and solid phases of the sewage sludge. MethodsX 3, 333–342. https://doi.org/10.1016/j.mex.2016.04.010. Bourgin, Marc, Beck, Birgit, Boehler, Marc, Borowska, Ewa, Fleiner, Julian, Salhi, Elisabeth, et al., 2018. Evaluation of a full-scale wastewater treatment plant upgraded with ozonation and biological post-treatments: abatement of micropollutants, formation of transformation products and oxidation by-products. Water Res. 129, 486–498. https://doi.org/10.1016/j.watres.2017.10.036. Brown, M.R., Gilbert, P., 1993. Sensitivity of biofilms to antimicrobial agents. Suppl, 87S–97S J. Appl. Bacteriol. 74. https://doi.org/10.1111/j.1365-2672.1993.tb04345.x. Carballa, Marta, Omil, Francisco, Lema, Juan M., 2005. Removal of cosmetic ingredients and pharmaceuticals in sewage primary treatment. Water Res. 39 (19), 4790–4796. https://doi.org/10.1016/j.watres.2005.09.018. Carballa, Marta, Fink, Guido, Omil, Francisco, Lema, Juan M., Ternes, Thomas, 2008. Determination of the solid-water distribution coefficient (Kd) for pharmaceuticals, estrogens and musk fragrances in digested sludge. Water Res. 42 (1-2), 287–295. https://doi.org/10.1016/j.watres.2007.07.012. Caupos, Emilie, Touffet, Arnaud, Mazellier, Patrick, Croue, Jean-Philippe, 2015. Partitioning of the pesticide trifluralin between dissolved organic matter and water using automated SPME-GC/MS. Environ. Sci. Pollut. Res. Int. 22 (6), 4201–4212. https://doi.org/10.1007/s11356-014-3614-0. Chandrakanth, Mysore S., Amy, Gary L., 1996. Effects of ozone on the colloidal stability and aggregation of particles coated with natural organic matter. Environ. Sci. Technol. 30 (2), 431–443. https://doi.org/10.1021/es9500567. Chiou, C.T., Malcolm, R.L., Brinton, T.I., Kile, D.E., 1986. Water solubility enhancement of some organic pollutants and pesticides by dissolved humic and fulvic acids. Environ. Sci. Technol. 20 (5), 502–508. https://doi.org/10.1021/es00147a010. De Beer, D., Srinivasan, R., Stewart, P.S., 1994. Direct measurement of chlorine penetration into biofilms during disinfection. Appl. Environ. Microbiol. 60 (12), 4339–4344. https://doi.org/10.1128/aem.60.12.4339-4344.1994. Decrey, Loïc, Bonvin, Florence, Bonvin, Christophe, Bonvin, Emmanuel, Kohn, Tamar, 2020. Removal of trace organic contaminants from wastewater by superfine powdered activated carbon (SPAC) is neither affected by SPAC dispersal nor coagulation. Water Res. 185 https://doi.org/10.1016/j.watres.2020.116302. Dietrich, Joseph P., Loge, Frank J., Ginn, Timothy R., Bas¸agaoglu, Hakan, 2007. Inactivation of particle-associated microorganisms in wastewater disinfection: modeling of ozone and chlorine reactive diffusive transport in polydispersed suspensions. Water Res. 41 (10), 2189–2201. https://doi.org/10.1016/j. watres.2007.01.038. envilab (2021): Clarifications regarding the suitability of the ozonation process - Work instructions for carrying out the clarifications (in German: Abklarungen Verfahrenseignung Ozonung - Arbeitsanweisung zur Durchführung der Abklarungen), pp. 1–39. Available online at https://micropoll.ch/Mediathek/ testverfahren-zur-beurteilung-der-behandelbarkeit-von-abwasser-mit-ozon- anleitung/, checked on 12/7/2023. Fatoorehchi, Elham (2016): Sludge disintegration techniques - assessment of their impacts on solubilization of organic carbon and methane production. Dissertation. Gauthier, T.D., Seitz, W.R., Grant, C.L., 1987. Effects of structural and compositional variations of dissolved humic materials on pyrene Koc values. Environ. Sci. Technol. 21 (3), 243–248. https://doi.org/10.1021/es00157a003. Gonzales, Sarah, Pe~na, Andria, Rosario-Ortiz, Fernando L., 2012. Examining the role of effluent organic matter components on the decomposition of ozone and formation of hydroxyl radicals in wastewater. Ozone. Sci. Eng. 34 (1), 42–48. https://doi.org/ 10.1080/01919512.2011.637387. Gonzalez-Gil, L., Papa, M., Feretti, D., Ceretti, E., Mazzoleni, G., Steimberg, N., et al., 2016. Is anaerobic digestion effective for the removal of organic micropollutants and biological activities from sewage sludge? Water Res. 102, 211–220. https://doi.org/ 10.1016/j.watres.2016.06.025. Gu, Lipeng; Tang, Xin; Sun, Ying; Kou, Huijuan (2020): Bioavailability of dissolved organic matter in biogas slurry enhanced by catalytic ozonation combined with membrane separation. In Ecotoxicology and environmental safety 196, p. 110547. DOI: 10.1016/j.ecoenv.2020.110547. Guo, Yang, Yu, Gang, Gunten, Urs von, Wang, Yujue, 2023. Evaluation of the role of superoxide radical as chain carrier for the formation of hydroxyl radical during ozonation. Water Res. 242 https://doi.org/10.1016/j.watres.2023.120158. Hart, D.S., Davis, L.C., Erickson, L.E., Callender, T.M., 2004. Sorption and partitioning parameters of benzotriazole compounds. Microchem. J. 77 (1), 9–17. https://doi. org/10.1016/j.microc.2003.08.005. Hoigne, J., Bader, H., Haag, W.R., Staehelin, J., 1985. Rate constants of reactions of ozone with organic and inorganic compounds in water-III. Inorganic compounds and radicals. Water Res. 19 (8), 993–1004. Huang, Yu, Li, Wentao, Qin, Long, Xie, Xianchuan, Gao, Bin, Sun, Jie, Li, Aimin, 2019. Distribution of endocrine-disrupting chemicals in colloidal and soluble phases in municipal secondary effluents and their removal by different advanced treatment processes. Chemosphere 219, 730–739. https://doi.org/10.1016/j. chemosphere.2018.11.201. Huber, Marc M., Gobel, Anke, Joss, Adriano, Hermann, Nadine, Loffler, Dirk, McArdell, Christa S., et al., 2005. Oxidation of pharmaceuticals during ozonation of municipal wastewater effluents: a pilot study. Environ. Sci. Technol. 39 (11), 4290–4299. https://doi.org/10.1021/es048396s. Juarez, Ruben, Karlsson, Stina, Falås, Per, Davidsson, Åsa, Bester, Kai, Cimbritz, Michael, 2021. Integrating dissolved and particulate matter into a prediction tool for ozonation of organic micropollutants in wastewater, 148711 Sci. Total Environ. 795. https://doi.org/10.1016/j.scitotenv.2021.148711. Khanam, Taslima, Syuhada, Wan Ata, Wan, Nur, Rashedi, Ahmad, 2016. Particle size measurement in waste water influent and effluent using particle size analyzer and quantitative image analysis technique. AMR 1133, 571–575. https://doi.org/ 10.4028/www.scientific.net/AMR.1133.571. Kusnierz, Magdalena, 2018. Scale of small particle population in activated sludge flocs. Water Air Soil Pollut. 229 (10), 327. https://doi.org/10.1007/s11270-018-3979-7. Lajeunesse, A., Smyth, S.A., Barclay, K., Sauve, S., Gagnon, C., 2012. Distribution of antidepressant residues in wastewater and biosolids following different treatment processes by municipal wastewater treatment plants in Canada. Water Res. 46 (17), 5600–5612. https://doi.org/10.1016/j.watres.2012.07.042. Lee, Yunho, Gunten, Urs von, 2010. Oxidative transformation of micropollutants during municipal wastewater treatment: comparison of kinetic aspects of selective (chlorine, chlorine dioxide, ferrate VI, and ozone) and non-selective oxidants (hydroxyl radical). Water Res. 44 (2), 555–566. https://doi.org/10.1016/j. watres.2009.11.045. Lee, Yunho, Gerrity, Daniel, Lee, Minju, Bogeat, Angel Encinas, Salhi, Elisabeth, Gamage, Sujanie, et al., 2013. Prediction of micropollutant elimination during ozonation of municipal wastewater effluents: use of kinetic and water specific information. Environ. Sci. Technol. 47 (11), 5872–5881. https://doi.org/10.1021/ es400781r. Lee, Yunho, Kovalova, Lubomira, McArdell, Christa S., Gunten, Urs von, 2014. Prediction of micropollutant elimination during ozonation of a hospital wastewater effluent. Water Res. 64, 134–148. https://doi.org/10.1016/j.watres.2014.06.027. Li, Dahong, Ganczarczyk, Jerzy, 1991. Size distribution of activated sludge flocs. J. Water Pollut. Control Fed. 63 (5), 806–814. Li, Wenhao, Li, Chao, Zhu, Nanwen, Yuan, Haiping, Shen, Yanwen, 2021. The extent of sludge solubilization allows to estimate the efficacy of ozonation for removal of polycyclic aromatic hydrocarbons (PAHs) in municipal sewage sludge. J. Hazard. Mater. 413 https://doi.org/10.1016/j.jhazmat.2021.125404. Ma, Jun, Graham, Nigel J.D., 1999. Degradation of atrazine by manganese-catalysed ozonation: Influence of humic substances. Water Res. 33 (3), 785–793. https://doi. org/10.1016/S0043-1354(98)00266-8. J. Qian et al. Ecotoxicology and Environmental Safety 270 (2024) 115915 9 Mailler, R., Gasperi, J., Chebbo, G., Rocher, V., 2014. Priority and emerging pollutants in sewage sludge and fate during sludge treatment. Waste Manag. 34 (7), 1217–1226. https://doi.org/10.1016/j.wasman.2014.03.028. Mathon, B., Coquery, M., Liu, Z., Penru, Y., Guillon, A., Esperanza, M., et al., 2021. Ozonation of 47 organic micropollutants in secondary treated municipal effluents: Direct and indirect kinetic reaction rates and modelling. Chemosphere 262. https:// doi.org/10.1016/j.chemosphere.2020.127969. Meng, Xianrong, Liu, Dongfang, Frigon, Matthew, 2015. The process of activated sludge ozonation: effect of ozone on cells, flocs, macromolecules and nutrient release. Water Sci. Technol. 71 (7), 1026–1032. https://doi.org/10.2166/wst.2015.066. Mittelman, M.W., 1998. Structure and functional characteristics of bacterial biofilms in fluid processing operations. J. Dairy Sci. 81 (10), 2760–2764. https://doi.org/ 10.3168/jds.S0022-0302(98)75833-3. Nielsen, P.H., Thomsen, T.R., Nielsen, J.L., 2004. Bacterial composition of activated sludge - importance for floc and sludge properties. Water Sci. Technol. 49 (10), 51–58. https://doi.org/10.2166/wst.2004.0606. Pocostales, J. Pablo, Sein, Myint M., Knolle, Wolfgang, Sonntag, Clemens von, Schmidt, Torsten C., 2010. Degradation of ozone-refractory organic phosphates in wastewater by ozone and ozone/hydrogen peroxide (peroxone): the role of ozone consumption by dissolved organic matter. Environ. Sci. Technol. 44 (21), 8248–8253. https://doi.org/10.1021/es1018288. Puig-Bargues, J., Arbat, G., Barragan, J., Ramírez de Cartagena, F., 2005. Effluent particle removal by microirrigation system filters. Span. J. Agric. Res 3 (2), 182. https://doi.org/10.5424/sjar/2005032-139. Reckhow, D.A.; Edzwald, J.K.; Tobiason, J.E. (1992): Use of Ozone as an aid to Coagulation/Filtration; Final Project Report to AW-WARF. Sauter, Daniel, Dąbrowska, Agata, Bloch, Robert, Stapf, Michael, Miehe, Ulf, Sperlich, Alexander, et al., 2021. Deep-bed filters as post-treatment for ozonation in tertiary municipal wastewater treatment: impact of design and operation on treatment goals. Environ. Sci. Water Res. Technol. 7 (1), 197–211. https://doi.org/ 10.1039/D0EW00684J. Sbardella, Luca, Comas, Joaquim, Fenu, Alessio, Rodriguez-Roda, Ignasi, Weemaes, Marjoleine, 2018. Advanced biological activated carbon filter for removing pharmaceutically active compounds from treated wastewater. Sci. Total Environ. 636, 519–529. https://doi.org/10.1016/j.scitotenv.2018.04.214. Staehelin, Johannes, Hoigne, Juerg, Staehelin, J., Hoigne, J., 1985. Decomposition of ozone in water in the presence of organic solutes acting as promoters and inhibitors of radical chain reactions. Environ. Sci. Technol. 19 (12), 1206–1213. https://doi. org/10.1021/es00142a012. Stasinakis, Athanasios S., Thomaidis, Nikolaos S., Arvaniti, Olga S., Asimakopoulos, Alexandros G., Samaras, Vasilios G., Ajibola, Akinranti, et al., 2013. Contribution of primary and secondary treatment on the removal of benzothiazoles, benzotriazoles, endocrine disruptors, pharmaceuticals and perfluorinated compounds in a sewage treatment plant. Sci. Total Environ. 463-464, 1067–1075. https://doi.org/10.1016/j.scitotenv.2013.06.087. Staudt, C., Horn, H., Hempel, D.C., Neu, T.R., 2004. Volumetric measurements of bacterial cells and extracellular polymeric substance glycoconjugates in biofilms. Biotechnol. Bioeng. 88 (5), 585–592. https://doi.org/10.1002/bit.20241. Svahn, Ola, Bjorklund, Erland, 2015. Describing sorption of pharmaceuticals to lake and river sediments, and sewage sludge from UNESCO Biosphere Reserve Kristianstads Vattenrike by chromatographic asymmetry factors and recovery measurements. J. Chromatogr. A 1415, 73–82. https://doi.org/10.1016/j.chroma.2015.08.061. Ternes, Thomas A., Andersen, Henrik, Gilberg, Daniel, Bonerz, Matthias, 2002. Determination of estrogens in sludge and sediments by liquid extraction and GC/ MS/MS. Anal. Chem. 74 (14), 3498–3504. https://doi.org/10.1021/ac015717z. Vieno, Niina, Sillanpaa, Mika, 2014. Fate of diclofenac in municipal wastewater treatment plant – a review. Environ. Int. 69, 28–39. https://doi.org/10.1016/j. envint.2014.03.021. von Sonntag, C.; von Gunten, Urs (2012): Chemistry of ozone in water and wastewater treatment. From basic principles to applications / Clemens von Sonntag and Urs von Gunten. London: IWA Pub. Wagner, Michael, Ivleva, Natalia P., Haisch, Christoph, Niessner, Reinhard, Horn, Harald, 2009. Combined use of confocal laser scanning microscopy (CLSM) and Raman microscopy (RM): investigations on EPS-Matrix. Water Res. 43 (1), 63–76. https://doi.org/10.1016/j.watres.2008.10.034. Wert, Eric C., Rosario-Ortiz, Fernando L., Snyder, Shane A., 2009. Effect of ozone exposure on the oxidation of trace organic contaminants in wastewater. Water Res. 43 (4), 1005–1014. https://doi.org/10.1016/j.watres.2008.11.050. Xiao, Keke, Abbt-Braun, Gudrun, Borowska, Ewa, Thomagkini, Xanthippi, Horn, Harald, 2022. Solid–liquid distribution of ciprofloxacin during sludge dewatering after Fe (II)-activated peroxymonosulfate treatment: focusing on the role of dissolved organic components. EST Eng. 2 (5), 863–873. https://doi.org/10.1021/acsestengg.1c00402. Zhang, Guangming, Yang, Jing, Liu, Huanzhi, Zhang, Jie, 2009. Sludge ozonation: disintegration, supernatant changes and mechanisms. Bioresour. Technol. 100 (3), 1505–1509. https://doi.org/10.1016/j.biortech.2008.08.041. Zietzschmann, F., Mitchell, R.-L., Jekel, M., 2015. Impacts of ozonation on the competition between organic micro-pollutants and effluent organic matter in powdered activated carbon adsorption. Water Res. 84, 153–160. https://doi.org/ 10.1016/j.watres.2015.07.031. Zucker, Ines, Lester, Yaal, Avisar, Dror, Hübner, Uwe, Jekel, Martin, Weinberger, Yigal, Mamane, Hadas, 2015. Influence of wastewater particles on ozone degradation of trace organic contaminants. Environ. Sci. Technol. 49 (1), 301–308. https://doi.org/ 10.1021/es504314t. J. Qian et al.