Removal of emerging contaminants from wastewater using nanofiltration for its subsequent reuse: Full–scale pilot plant

Journal of Cleaner Production 214 (2019) 514e523

Contents lists available at ScienceDirect

Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro

Removal of emerging contaminants from wastewater using nanofiltration for its subsequent reuse: Fullescale pilot plant
rrez Ruiz b, Jose
María Quiroga Alonso a Agata Egea-Corbacho a, *, Santiago Gutie a b


diz, Spain Department of Environmental Technologies, Faculty of Marine and Environmental Sciences, University of Cadiz. 11510, Puerto Real, Ca
diz, Spain PhD Science for the University of Ca

a r t i c l e i n f o

a b s t r a c t

Article history: Received 6 July 2018 Received in revised form 21 December 2018 Accepted 29 December 2018 Available online 4 January 2019

Effluents from wastewater treatment plants (WWTPs) are widely recognized as the main source of emerging contaminants (including stimulants and antibiotics) in natural water courses. The problem is aggravated in those regions where water is scarce and its reuse is necessary. With the aim of avoiding these problems, the present paper reports the results obtained by installing a nanofiltration membrane at the outlet of the secondary decanter at the WWTP situated in the municipality of Medina Sidonia (SW Spain). Permeate samples were taken over a period of 72 h while the membranes were operating. Contaminants belonging to the aforementioned families (caffeine, theobromine, theophylline, amoxicillin and penicillin G) were analysed by means of liquid chromatography with mass spectrometry (UPLC-MS). The results indicate that nanofiltration removed these contaminants from the wastewater turning the treated water as suitable to be reused for all the uses included in the Spanish Royal Decree 1620/2007 on water regeneration and reuse. © 2018 Elsevier Ltd. All rights reserved.

Keywords: Emerging contaminants (EC) Nanofiltration Wastewater and reuse

1. Introduction Earth is continually being polluted with numerous chemical substances of natural and anthropogenic origin. The exponential growth of the population and the rise in the use of these substances has led to an increase in their concentrations in wastewater, hence in the environment (Sarkar et al., 2018). Many of these pollutants have not been subjected to a suitable assessment of the potential environmental risks and impacts that they may have on ecosystems and living beings, including their effects on human health (Riva et al., 2018a). Among the substances detected in WWTP effluents it is possible to detect antibiotics (amoxicillin and penicillin G). Antibiotics may have a considerable environmental impact even at low concentrations, as they can cause resistance in bacteria and other microorganisms (Lu et al., 2016), including Streptococcus pneumoniae, which is classified as “penicillin-non-susceptible” in the World Health Organization (WHO) list of priority pathogens for R&D (WHO, 2017). Caffeine, theobromine and theophylline, which belong to the family of stimulants, have also been detected in quite

* Corresponding author. E-mail address: [email protected] (A. Egea-Corbacho). https://doi.org/10.1016/j.jclepro.2018.12.297 0959-6526/© 2018 Elsevier Ltd. All rights reserved.

significant concentrations in both wastewater and receiving waters (Buchberger, 2011; Senta et al., 2015), especially in some Mediterranean river basins where WWTP effluents (Rabiet et al, 2006) constitute a high percentage of the total river flow, especially in €ck-Schulmeyer et al., 2011). periods of drought (Ko Different types of treatments are currently being tested to effectively remove these emerging contaminants (EC) from wastewater, with the lowest possible economic cost, before being discharged into ecosystems. The technologies that are currently being used include membrane processes, in particular, nanofiltration and reverse osmosis. Both technologies have been very effective in the removal of different organic compounds (Kim et al., 2018), as they even permit the respective separation of divalent and monovalent ions from wastewater. Besides, the scarcity of water in certain areas of the world (Mediterranean countries among them) leads to the need to regenerate and reuse water from secondary effluents. European landfill regulations (Directive 91/271/EEC) regulate the organic load that WWTP effluents must have, but guides about their possible reuse are missing. There is no specific legislation in Europe on the reuse of treated water. In Spain, the quality of reclaimed water is regulated by Royal Decree 1620/2007, of 7 December, establishing the legal framework for the reuse of treated water. In order to reuse reclaimed water, Spanish legislation requires that quality water

A. Egea-Corbacho et al. / Journal of Cleaner Production 214 (2019) 514e523

obtained at the WWTP have to be in accordance with its intended use. However, the legislation on discharges and reuse do not takes into consideration emerging contaminants, as they are not among the priority substances in the field of water policy (Directive, 2013/ 39/EU). These substances will be probably included in the pertinent legislation in the future. For all these reasons, to avoid the problems that they may cause in the meantime and taking into account the effectiveness and relative low cost of nanofiltration membranes, they were chosen. Previous studies demonstrated that nanofiltration as tertiary treatment is a viable method for removing trace pharmaceutically (García-Ivars et al., 2017), but it is necessary to know at higher concentrations of emerging contaminants, real wastewater in pilot plant and more time than those studied. The present study shows an open circuit (72 h) with high concentrations of the chosen contaminants. The removal of emerging contaminants belonging to the family of stimulants (caffeine, theobromine and theophylline) and the family of antibiotics (amoxicillin and penicillin G) present in municipal wastewater via the use of nanofiltration as a tertiary treatment at a WWTP was studied in this work, in order to test the effectiveness of this technology for the reuse of the effluent. 2. Materials and methods 2.1. Equipment used - Medina Sidonia WWTP The plant chosen to carry out the experiments was located in the town of Medina Sidonia, a municipality in Southern Spain, in the
diz, Andalusia. It currently has a popcentre of the province of Ca ulation of 11.741 inhabitants. Its WWTP is equipped to treat the wastewater from a population centre of 17.599 hab-eq and can achieve a flow rate of 2.223 m3$day
1. There are two treatment lines: water and sludge. As at the majority of the existing WWTPs in Spain, the water line of the plant consists of primary and secondary treatment made up of the following units: - Primary treatment with a coarse and fine screening unit and a de-gritting and degreasing system. - The secondary treatment consists in an extended aeration biological reactor and secondary settling. The effluent from Medina Sidonia WWTP complies with European regulations (Directive 91/271/EEC) and its transposition into Spanish law (Royal Decree-Law 11/1995), which establishes the regulations applicable to the treatment of municipal wastewater. In the sludge line, the sludge is first thickened and then dehydrated until reaching dryness higher than 60%. It also has a deodorization system employing active carbon filtration. For the purposes of this study, part of the effluent from the plant was subjected to tertiary treatment which is the technology under study in this paper, and is described in the following section. - Membrane technology: nanofiltration Water from the secondary settling tank was sent to a 400 L mixing tank by means of the secondary settler pressure pumps at the WWTP. Prior to entering this tank, the water is pre-treated by means of a 200 mm self-cleaning filter, manufactured by COPERSA (model 85102M-p-DC). The tank, which is equipped with a stirring system, is used to mix and prepare the dissolution of the wastewater with the added contaminants (stimulants and antibiotics). The water from this tank, containing a known concentration of

515

pharmaceuticals, is conveyed to the feed tank of regeneration plant by means of a peristaltic pump which provides a flow rate of 5 L h
1. The feed tank has a continuous inflow of 700e730 L h
1 water from the secondary decanter. In this phase is where the mixture with the drugs that will give rise to the study feeding water is created. The plant consists of a Sea Recovery Aqua Frame™ desalination system, employing an NF270-2540 nanofiltration membrane and additionally equipped with a series of instruments for automated tracking of the main control parameters at the plant. The feed line from the feed tank to the membrane unit is equipped with a pre-filter consisting of a 5 mm mesh size polypropylene wire cartridge, which ensures that the water has sufficient quality before entering the nanofiltration unit. The water from the feed tank is introduced into the nanofiltration membrane by a 1.68 CV centrifugal pump. The operating conditions were those recommended by the manufacturer in the technical specifications. Control of the feed stream is carried out by means of a flowmeter installed in the inlet pipes to the feed tank. This tank is equipped with a heat exchanger connected to an external cryostat, which allows the control of the temperature of the feed water in the experiments. The membrane container is made of stainless steel for 2540 inch membranes with a spiral configuration. The DOW FILMTEC company supplied the nanofiltration membrane (Table 1). The chosen model was an NF270-2540, which operated at a pressure of 4.8 bar. A system of pipes equipped with three-way valves for sampling purposes was used to convey the water along the three lines (feed, reject and permeate). 2.2. Experimental procedure Some of the pollutants under study were not found in the wastewater, while other pollutants were detected in such low concentrations that it was difficult to quantify them. Therefore, additional quantities of each contaminant were added to the mixing tank (56 g of each pollutant in 400 L of wastewater) to study. This high concentration in the mixing tank ensured that by means of the small pumping, 5 L h
1 of the peristaltic pump, that there was always a CE concentration useful for the study in the feed tank. This feeding tank was responsible for supplying the study water to the membrane and had a much higher flow rate (700e730 L h
1, varying according to the pressure groups of the WWTP). The water in the feed tank came directly from the WWTP effluent. It worked in open circuit (removing the rejection and the permeate) during the 72 h that lasted in the trial. Samples were taken at 1, 2, 4, 12, 24, 48 and 72 h. Fig. 1 shows a flow chart for the experimental procedure. The concentration of each contaminant in the influent mixture to the nanofiltration unit varied, ranging from 0.562 to 1.255 mg L
1 for caffeine, 0.420e0.724 mg L
1 for theobromine,
1 0.396e0.814 mg L for theophylline, 0.164e0.173 mg L
1 for

Table 1 Characteristics of the NF membrane. Membrane Type

Polyamide Thin-Film Composite

Active Area Maximum Operating Temperature Maximum Operating Pressure Maximum Feed Flow Rate Maximum Pressure Drop - tape wrapped - fiberglassed pH Range, Continuous Operation pH Range, Short-Term Cleaning (30 min) Stabilized Salt Rejection Maximum Feed Silt Density Index Free Chlorine Tolerance

2.6 m2 (28 ft2) 45  C (113  F) 41 bar (600 psi) 1.4 m3 h
1 (6 gpm) 0.9 bar (13 psig) 1.0 bar (15 psig) 2e11 1e12 >97.0 (%) SDI 5 <0.1 mg L
1

516

A. Egea-Corbacho et al. / Journal of Cleaner Production 214 (2019) 514e523

2.5. Instruments and analytical techniques

Fig. 1. Flow chart for the experimental procedure.

amoxicillin and 0.109e0.270 mg L
1 for penicillin G. These amounts close to 1 mg L
1 for the family of stimulants, are in accordance with the maximum concentrations recorded for caffeine in water (Luo et al., 2014). After carrying out the experiments, an autopsy of the membrane was performed to determine its integrity, the accumulated fouling and the contaminants that may had been retained in it. 2.3. Reagents and chemical products used The emerging contaminants used in this study were caffeine, theobromine, theophylline, amoxicillin and penicillin G (>99% purity), all supplied by Sigma Aldrich The UPLC/HPLC-grade methanol and water used as solvents for chromatographic analysis were provided by Scharlau. Formic acid (98%) was purchased from Sigma Aldrich. The mini-columns used for solid-phase extraction (SPE) were supplied by Waters (Oasis HLB cartridges, Waters Corp., Milford, MA). The solutions of the emerging contaminants were prepared in each use in ultrapure water. 2.4. Solid-phase extraction (SPE) Given the low concentrations of the studied contaminants in the influent, effluent and permeate, it was necessary to concentrate them by means of solid phase extraction. Several experiments were thus carried out to optimize the operating conditions of the SPE mini-columns, following the procedures reported in the bibliography (Baena-Nogueras et al., 2016a). Acetonitrile (ACN) and methanol (MeOH) were tested as eluting agents. Optimal results were obtained with methanol and the following extraction conditions: the column (mini-column equipped with 60 mg solid phase Oasis HLB cartridges, supplied by Waters) was activated with 10 mL methanol and 10 mL water. Then, 100 mL of sample was passed through the mini-column, which retains the studied compounds. Finally, these compounds were desorbed and eluted using 10 mL of methanol. The extract was evaporated with liquid nitrogen and the dry residue dissolved in 1 mL water. The resulting solution was then filtered through a 0.22 mm filter. The recovery efficiencies of the mini-columns using methanol for activation and as the eluent were respectively 49%, 43% and 42% for caffeine, theobromine and theophylline, and 10% and 82% for amoxicillin and penicillin G. Although these values are low, except for penicillin G, the results coincide with those obtained by the authors of the method that served as a reference (Baena-Nogueras et al., 2016a).

Analysis of the compounds was carried out by ultraperformance liquid chromatography time-of-flight mass spectrometry was used for the identification and quantification of analytes (Xevo, Waters Synapt G2). Identification of analytes was based on comparing retention times and accurate mass measurements (allowing an error of less than 5 mg L
1) to those for commercially available pure standards. All the data were processed using the MassLynx 4.1 software. The noise type selected was root mean square (RMS). Limits of detection were calculated for the quantifier transition. Instrumental limits of detection (iLOD) and quantitation (iLOQ) for each target compound were calculated based on the signal to noise ratio of 3 (iLODs) and a signal-to-noise ratio of 10 (iLOQs) near the target peak by using the lowest standard solution. Quantification of target compounds was performed using calibration curves (from 1$10
3 to 1 mg L
1), prepared in water in 1 mL vials. A dilution factor 1:2 of the greatest concentration samples was performed to calculate the levels of the analytes. The reproducibility and repeatability of the methods were evaluated by performing three successive extractions and injections of the same sample and by re-analyzing a batch of standards two weeks after its first analysis. The mass spectrometer equipped with a 50 mm BEH C18 column and 1.7 mm pore size, both from Waters (Milford, MA). A volume of 10 mL was injected into the column, using methanol as the eluent. The mass spectrum ranged from 50 to 1200 amu. Positive and negative electrosprays (ESI þ/
) were used to identify the peaks representing the studied contaminants (Table 2). The aqueous phase consisted of a 0.1% solution of formic acid (A) and methanol (B) as organic solvent. The flow rate was 0.40 mL min
1. The best results were obtained in ESI þ mode (Table 2), with an operating gradient that began with a 70/30% mix of water/methanol for 3 min; the water concentration was then decreased until 4:20 min until obtaining a ratio of 10% A/90% B; subsequently returning to the initial conditions (70/30) at 4:50 min, and maintaining this ratio until 5 min (overall run time ¼ 5 min). Visualization of the deposits accumulated on the membrane was performed using a Nova NanoSEM 450 scanning electron microscope (SEM). Microanalysis of the majority chemical elements present in the fouling of the membrane was also carried out by means of the energy-dispersive spectrometers (EDS) with which the SEM is equipped. The concentrations of cations and anions in the fouling were measured by means of a Thermo Elemental IRIS Intrepid ICP-AES spectrophotometer. Merck 0.2 mm syringe filters were used for the injections of the total organic carbon (TOC) and total nitrogen (TN) chromatography and analyser samples. TOC and TN were measured on a Shimadzu TOC-L (CPH) analyser with an ASI-L autosampler and a TN unit. Determination of the other parameters was carried out in accordance with the Standard Methods for the Examination of Waters and Wastewater (Standard Method, 2017). Samples were

Table 2 UPLC-MS/MS parameters (ionization mode, retention time and mass). COMPONENTS

ELECTROSPRAY

TR(min)

MASS

Caffeine Theobromine Theophylline Amoxicillin Penicillin G

þ þ þ þ þ

0.68 0.44 0.56 0.42 3.38

195.0882 181.0726 181.0726 366.1124 357.0890

A. Egea-Corbacho et al. / Journal of Cleaner Production 214 (2019) 514e523

analysed in duplicate or triplicate, having a maximum standard deviation (samples not UPLC-MS) of 10%. 3. Results and discussion 3.1. Characterization of the influent and effluent at Medina Sidonia WWTP The influent and effluent at Medina Sidonia WWTP were characterized between January 2017 and January 2018. Table 3 shows the average, minimum and maximum values of the different parameters for the 12 samplings performed, as well as their standard deviations. In general, the characterization of the influent wastewater reaching the plant indicates that it is comparable to mediumpolluted municipal wastewater (Egea-Corbacho, 2019). Some parameters (Chemical Oxygen Demand (COD), turbidity, (Biological Oxygen Demand (BOD5), hardness) had a high standard deviation, which shows the variability of these parameters in wastewater. The cause is most likely the fact that it is a town whose population varies considerably depending on the time of seasonal. The salts (chlorides and hardness) have an average concentration in the influent of 268.2 and 591 mg L
1, respectively, values that can be considered lower than those found in other wastewaters (Li et al., 2013). The standard deviations show that the concentration of chlorides in the wastewater presents variability over the studied months of ±58.1 mg L
1 for the influent and ±219 mg L
1 for the hardness in the influent. The nematode eggs parameter was never detected, besides, as the historical analysis carried out verified the absence of nematode eggs in the WWTP wastewater. Caffeine, amoxicillin and penicillin G were not detected in the influent in any of the samples. However, theobromine and theophylline were detected in all the samples. The average concentrations detected in some of the samples of the influent vary from 20.15, 20.26 and 17.08 mg L
1 of caffeine, theobromine and theophylline, respectively, to 1.07 and < LOQs of amoxicillin and penicillin G. These values found for caffeine are similar to those reported in the literature for studies conducted in different parts of the world. For example, concentrations of 17 and 20 mg L
1 have been documented for caffeine in Montevideo and Rome,

517

respectively (Senta et al., 2015). The concentrations observed in this study for the antibiotics were slightly lower than those reported in the literature (Kulkarni et al., 2017). These contaminants are not considered either in landfill legislation or in reuse legislation. They are not among the priority substances in the field of water policy (Directive, 2013/39/EU) despite the risk they can pose to the environment, as stated in the list (WHO, 2017). In the effluent (Table 3), the average values for COD, BOD5 and TSS were 85, 7 and 12 mg L
1, respectively. The values for the family of stimulants were respectively 11.15, 7.40 and 4.34 mg L
1 for caffeine, theobromine and theophylline, while for the antibiotics, they were
Table 3 Characterization of medina sidonia WWTP (January 2017eJanuary 2018). INFLUENT

COD (mgO2$L
1) BOD5 (mgO2$L
1) TOTAL SUSPENDED SOLIDS (mg$L
1) TURBIDITY (NTU) TOTAL NITROGEN (mg N$L
1) NITRATES (mg$L
1) TOTAL PHOSPHOROUS (mgP$L
1) E. COLI (CFU 100 mL (u.log10)) TOTAL COLIFORMS (CFU 100 mL (u.log10)) pH (pH units) CONDUCTIVITY (mScm
1)
1 Þ) PHOSPHATES (mgPO
4 3 $L CHLORIDES (mg Cl
$L
1)
1 HARDNESS (mgCaCO3$L ) TOC (mgC$L
1)
1 AMMONIUM (mgNH þ 4 $L Þ TEMPERATURE ( C) CAFFEINE [mg$L
1] THEOBROMINE [mg$L
1] THEOPHYLLINE [mg$L
1] AMOXICILLIN [mg$L
1] PENICILLIN G [mg$L
1]

EFFLUENT

MIN

MAX

AVERAGE

S.D.

MIN

MAX

AVERAGE

S.D.

360 230 164 153.80 56.66 0.34 35.43 6.03 6.17 1.66 1875 5.27

479 435 341 408.75 80.21 12.71 44.07 8.40 9.52 8.93 2655 10.41

434 329 215 277.51 70.06 8.16 38.51 6.91 7.88 6.95 2090 7.58

53 103 84 115 10 5.40 3.91 1.05 1.60 3.53 378 2.47

27 2 1 12.23 6.01 20.47 15.24 3.63 4.21 6.52 1310 2.13

196 14 22 23.43 8.6 32.90 27.67 5.36 6.23 8.61 1536 2.68

85 7 12 16.36 7.04 24.36 18.78 4.27 5.36 7.68 1451 2.42

79 5 9 4.90 1.17 5.78 5.96 0.78 0.94 1.04 98 0.24

223.6 345 40.93 62.82

353.0 1030 95.56 123.45

268.2 591 76.38 82.87

58.1 219 24.21 27.48

214.6 375 7.43 0.039

238 610 10.47 1.87

227.1 458 9.10 0.657

10.8 104 1.28 1.05

15.64
21.49 26.11 39.28 49.05 3.14
17.945 20.15 20.26 17.08 1.07
2.51 9.64 13.22 11.75 1.03 e

11.18
20.75 30.36 14.77 9.06
16.72 11.15 7.40 4.34
4.02 9.87 5.23 3.81 e e

518

A. Egea-Corbacho et al. / Journal of Cleaner Production 214 (2019) 514e523

Table 4 Summary of Spanish Royal Decree 1620/2007. USES

MUNICIPAL AGRICULTURAL

INDUSTRIAL

RECREATIONAL ENVIRONMENTAL

MAXIMUM ADMISSIBLE VALUE (MAV) QUALITY

INTESTINAL NEMATODES (Eggs$10L
1)

1.1 1.2 2.1 2.2 2.3 3.1 A and B 3.1. C 3.2 4.1 4.2 5.1 5.2 5.3 5.4

1 0 1 2.3 1 2 1 3 1 4 Not established 4 1 3 1 Absence 1 2.3 Not established 4 Not established 3 1 Absence Not established Not established The required minimum quality is to be studied case by case

comply with reuse legislation and the emerging contaminants are not removed by the conventional treatments employed at the plant, more specific technologies need to be applied for their treatment with the aim to reuse this water. 3.2. Removal of pharmaceutical drugs and stimulants by nanofiltration 3.2.1. QA/QC (quality assurance/quality control) The intra-day variation was evaluated by continuously injecting two replicates within a day (differences observed ranged from 1 to 8%), whereas the inter-day variation was performed by analysing some replicates on different days (differences observed were between 3% and 10%). The MS response of all compounds was linear between 1$10
3 to 1 mg L
1 and coefficients of determination (R2) for calibration curves were always above 0.9 for target compounds. The limits of detection (LODs) ranged were 0.001, 0.0003, 0.001, 0.001 y 0.0006 mg L
1 to caffeine, theobromine theophylline, amoxicillin and penicillin G, respectively, and limits of quantitation (LOQs) were 0.004, 0.001, 0.004, 0.0014 and 0.002 mg L
1 respectively. 3.2.2. Pharmaceutical drug and stimulant removal experiments Once the wastewater had been adulterated with the emerging contaminants studied here, as reported before (Section 2.2.), and before starting the experiments in the nanofiltration unit, it was necessary to verify if these contaminants were undergoing processes of degradation during their residence time in the mixing tank (72 h) due to the presence of microorganisms in the wastewater (biodegradation) or to any other process (photo-oxidation, adsorption to the walls of the tank, etc.). Two types of experiments were performed. In the first, a solution of the 5 contaminants under study was prepared in ultrapure water at a concentration of 1 mg L
1 each. This solution was left in the room where the tests were carried out in a covered amber glass flask to ensure complete darkness. The second experiment consisted in the addition of the necessary amount of each antibiotic and stimulant to the 400 L of wastewater present in the mixing tank so that the concentration of each of these contaminants was 1 mg L
1. A sample was collected and analysed once a day for three days. The temperature in the glass flask varied between 15 and 25  C, while the measured temperature in the mixing tank ranged between 10 and 25  C. The results are given in Table 5, which shows the degradation rates of the emerging contaminants with respect to the first day. In general, it was verified for both experiments that the degradation

E. COLI (CFU 100 mL
1 (u.log10))

TSS (mg$L
1)

TURBIDITY (NTU)

10 20 20 35 35 35 35 5 20 35 35 10 35

2 10 10 Not Not 15 Not 1 10 Not Not 2 Not

established established established

established established established

rate of the emerging contaminants varies with increasing residence time, both in the mixing tank and in the glass flask with ultrapure water. Theophylline is degraded only 7% in the two tests (glass flask and mixing tank). The concentrations of caffeine and theobromine vary slightly over the course of the tests (around 20% in both cases). This may be because theophylline is a metabolite of caffeine, so a decrease in the concentration of caffeine may increase the concentration of theophylline (Wang et al., 2013). For the family of antibiotics, the degradation rates of the samples in the glass flask with ultrapure water were 46% and 37% for amoxicillin and penicillin G, respectively. When the matrix is wastewater, the values obtained in the mixing tank indicate that the antibiotics begin to degrade right from the first contact with the wastewater, with degradation rates of 89% and 70% in the case of amoxicillin and penicillin G, respectively. This may be due to processes of hydrolysis of the drug itself or to processes of adsorption to the solids in the wastewater or to the walls of the tank, etc. (Li et al., 2008). Taking into account these results, the studied antibiotics could be degraded during the processes employed at the WWTP if a sufficient hydraulic retention time was maintained in the biological reactor. However, this would not ensure the complete mineralization of these compounds and would also result in higher energy consumption. The implementation of advanced treatment systems could provide the solution for the removal of these contaminants  a
mkova
and Diaz-SosaWanner, 2018). from wastewater (Sr Once the degradation tests had been carried out, the performance of the nanofiltration membranes was studied using wastewater from Medina Sidonia WWTP previously adulterated with the compounds under study. The filtration mechanism of the membranes is the classic process of controlled diffusion in which the mass transfer of ions through the membranes (AWWARF, 1998). Separation occurs not as in classical filtration processes, but by the diffusion of water molecules through the active layer of the membrane. In the case of the emerging contaminants under study, the formation of hydrogen bridges between the components of the membrane and the water molecules is not possible, so they are rejected and do not pass through the membrane as proved by the experiments carried out and whose results are shown in Table 6. First, it can be seen that the feed concentration of each contaminant to the membrane varies from hour to hour in the experiment. This is due to the fact that when the contaminants dissolve in wastewater, a series of processes take place (adsorption to the suspended solids present, their hydrolysis, biodegradation,

A. Egea-Corbacho et al. / Journal of Cleaner Production 214 (2019) 514e523

519

Table 5 Decrease in the concentration (mg$L
1) of the emerging contaminants at room temperature and the mixing tank. Standard solution at room temperature in solution Time [h] Caffeine Theobromine Theophylline Amoxicillin Penicillin G

day 0 0.90 0.76 0.75 0.74 0.79

day 1 4% 7% 7% 32% 8%

day 2 7% 9% 9% 36% 14%

day 3 23% 24% 23% 46% 37%

day 0 1.11 0.77 1.22 0.73 1.25

day 1 5% 4% 2% 52% 46%

day 2 1% 21% 0% 82% 64%

day 3 20% 18% 7% 89% 70%

Standard solution added to the mixing tank Time [h] Caffeine Theobromine Theophylline Amoxicillin Penicillin G

Table 6 Evolution of the concentration of the studied contaminants (test with a mixture of contaminants). Caffeine [mg·L
1] Time [h]

1

2

4

12

24

48

72

Feed Reject Permeate

0.725 0.929 0.037

0.562 0.720 0.030

0.834 0.896 0.033

1.175 1.715 0.046

1.065 0.979 0.029

0.708 0.837 0.010

1.255 1.713 0.043

1 0.42 0.642 0.004

2 0.43 0.624 0.005

4 0.524 0.514 0.005

12 0.545 0.846 0.006

24 0.724 0.633 0.006

48 0.423 0.42 0.002

72 0.727 1.125 0.004

1 0.461 0.665 0.057

2 0.396 0.658 0.056

4 0.532 0.54 0.069

12 0.814 1.013 0.083

24 0.616 0.648 0.066

48 0.45 0.471 0.012

72 0.715 0.873 0.083

1 0.164 0.18
2 0.165 0.166
4 0.165 0.165
12 0.173 0.169
24 0.167 0.17
48 0.164 0.166
72 0.165 0.169
1 0.155 0.235 0.012

2 0.109 0.268
4 0.177 0.193
12 0.27 0.374
24 0.226 0.217
48 0.144 0.166
72 0.214 0.557
Theobromine [mg·L
1] Time [h] Feed Reject Permeate Theophylline [mg·L
1] Time [h] Feed Reject Permeate Amoxicillin [mg·L
1] Time [h] Feed Reject Permeate Penicillin G [mg·L
1] Time [h] Feed Reject Permeate

etc.), which rapidly decreases the concentration of the compound in the water, as verified in the experiments carried out and described. Regarding the operation of the NF270-2540 nanofiltration membranes with respect to the family of stimulants, the concentration of each of these in each sample of the permeate is very low (Table 6), with a highly concentrated reject fraction that is greater or equal to the concentration in the feed stream in the majority of cases. This indicates the proper functioning of the nanofiltration membrane as regards their removal. It performs similarly with the family of antibiotics, amoxicillin and penicillin G, which were not detected in the permeate (Table 6). This demonstrates the effectiveness of the applied treatment for compounds of this kind. A concentration in the permeate of 0.012 mg L
1 of penicillin G was detected only in the first hour of operation. These results indicate that it is possible to eliminate these high amounts of pollutants that can be found in large WWTP (Baena-

Nogeras, 2016), in effluents from hospitals (Ajo et al, 2018), pharmaceutical effluents or even in continental waters (Luo et al., 2014) through nanofiltration technology, even if we subject them to a chronic situation during the 72 h that the study lasted. 3.3. Regeneration and reuse of the wastewater Parallel to the study of the performance of the membranes in the removal of the studied stimulants and antibiotics and as these contaminants are not included in the regulation on water reuse (RD 1620/2007), the parameters required by the regulations were analysed to allow the reuse of this water in any of the permitted uses (Table 4). Other parameters of interest for the use of wastewater were also taken into account. The evolution of these parameters in the feed, reject and permeate streams during the 72 h that the experiment lasted are shown in Fig. 2 and Fig. 3. For the BOD5, COD and TSS parameters (Fig. 2A, B and 2C), the concentrations in the reject stream are equal or greater than that in

A. Egea-Corbacho et al. / Journal of Cleaner Production 214 (2019) 514e523

150

-1

6

(B) COD (mgO2·L )

8

-1

(A) BOD5 (mgO2·L )

520

4

2

100

50

0

0

(C) 8

-1

Phosphates (mg·L )

(D) 2

-1

TSS (mg·L )

6

4

2

(F) 25

0 3

-1

Nitrates (mg·L )

0 20

-1

Ammonium (mg·L )

(E)

1

2

1

15 10 5 0

0

(H) 20

15

15 -1

TP (mg·L )

-1

TN (mg·L )

(G) 20

10

5

0

1

2

4

12 24 t (h)

48

72

10

5

0

1

2

4

12

t (h)

24

48

72

Fig. 2. Concentration in the feed, reject and permeate streams applying nanofiltration. BOD5 (A), COD (B), TSS (C), phosphates (D), ammonium (E), nitrates (F), TN (G), TP (H). Key: Feed CReject :Permeate.

▪

the feed stream. This supposes a high percentage of removal in all cases (69%, 63% and 85% for BOD5, COD and TSS, respectively, calculated using the average values of these parameters in the feed and permeate streams). The removal efficiency following the tertiary treatment complies with discharge requirements (Directive 91/271/EEC) and the reuse requirement that establishes a maximum value of 5 mg L
1 for all these parameters. It can thus be stated that, with respect to these three parameters, the effluent could be adequate to any use. Depending on the intended use of the reclaimed water, it is necessary to know the membrane's ability to separate nutrients. Phosphates were practically removed in their entirety (Fig. 2D), with an average removal rate of 99%. However, a removal rate of 55% was obtained for total phosphorus (Fig. 2H). The differences in removal rates (99% for phosphates and 55% for total phosphorus) may be due to the existence of inorganic forms of phosphorus (polyphosphates from cleaning agents, orthophosphate, pyrophosphate, triphosphate and polyphosphate anions) which the

membrane is not able to retain diffusing through the unit with the permeate. For the case of nitrogen in its ammonium form, an average removal rate of 30% was obtained (Fig. 2E), but at 4 and 12 h of testing, the value of the permeate with respect to the feed presents a negative yield. According to some authors, nitrates, which are monovalent compounds, are not rejected by nanofiltration membranes, subsequently passing to the permeate stream (Epsztein et al., 2015). The analytical results for nitrate confirm this statement (Fig. 2F). The removal rate for total nitrogen (Fig. 2G) is around 28%. As nitrates are not removed, it may be stated that any nitrogen removal that takes place is due to nitrogen in its ammonium form. The turbidity in the permeate stream varies from not detected to 0.27 NTU, being the removal rate 99% (Fig. 3A). This value is well below the minimum required by regulations, so the effluent could be suitable for any use according to Spanish regulations in this respect. Likewise, there is a practically complete removal of organic

A. Egea-Corbacho et al. / Journal of Cleaner Production 214 (2019) 514e523

(B) 25

(A) 20

TOC (mg·L )

-1

E. coli (UFC 100 mL (u. log10))

5

0 4

2

4

2

0

(F)

400

-1

Hardness (mg·L )

-1

Chlorides (mg·L )

5 0

0

200

100

3.4. Membrane autopsy

300 200 100

0

(H)

10

pH (u. pH)

0

(G)2000 -1

10

(D)

(E) 300

Conductivity (mS·cm )

15

Total coliforms (UFC 100 mL (u. log10))

Turbidity (NTU)

10

(C)

legislation (TSS, turbidity and E. Coli), it may be stated that the water obtained by nanofiltration using the NF270 membrane could be reused in any of the specified uses, obtaining the minimum required values in the permeate water for all parameters at all times. The efficiency of the technology is also corroborated when the permeate is analysed (Table 6 and Figs. 2 and 3), in which a high removal performance of the contaminants is observed. Comparing it with authors who carried out similar studies (Palma et al., 2016), the effectiveness of this treatment for the elimination of emerging pollutants in wastewater and its possibility of later reuse is observed. Palma (Palma et al., 2016) obtained elimination data for chlorides of 55%, NT 34%, COD and BOD5 of 77.7% nitrates 20% and CT ranging from 62 to 75.8%. These values are very similar to those obtained in this study.

20

15

8

1500

1000

6

500

0

521

1

2

4

12

t (h)

24

48

72

4

1

2

4

12

t (h)

24

48

72

Fig. 3. Concentration in the feed, reject and permeate streams applying nanofiltration. Turbidity (A), TOC (B), E. Coli (C), total coliforms (D), chlorides (E), hardness (F), conductivity (G), pH (H). Key: Feed C Reject : Permeate.

▪

carbon (99%) in the permeate (Fig. 3B), obtaining concentrations ranging from 0.74 to 1.32 mg L
1 in the reclaimed water. E. coli and total coliforms show 100% removal rates (Fig. 3C and D) and no colony-forming unit was detected during the entire duration of the experiment. This result means that the effluent is suitable for any use permitted by current Spanish regulations in this respect. As to the chloride ion, the NF270-2540 nanofiltration membrane presents a 39% of removal rate (Fig. 3E), well below the value obtained with the use of reverse osmosis membranes, with which virtually 100% removal is achieved (Haidari et al., 2018). Some authors have shown that nanofiltration using the NF270 membrane removes the main hardness fraction (calcium and magnesium) of groundwater (Van der Bruggen et al., 2003). In the present study, the average values obtained for hardness in the permeate (Fig. 3F) was 80% removal with respect to the feed. This value is lower than the 97% retention of salts stated by the manufacturer (DOW FILMTEC) in the specifications of the membrane. The average value obtained for conductivity for the feed and permeate streams was 1439 and 570 mS cm
1, respectively (Fig. 3G). The average removal rate during the 72 h that the experiment lasted was 60%. This performance can be considered adequate due to the fact that the nanofiltration membranes were not designed for the removal of ions that contribute to increasing conductivity, in contrast to what occurs in the case of reverse osmosis membranes (Warsinger et al., 2018). The pH does not vary in any of the three water streams (feed, reject or permeate), presenting average values of 8.45, 7.98 and 8.49 pH units, respectively (Fig. 3H). If we take into account only the parameters set by Spanish reuse

The detailed study of fouled membranes allows the causes that originated said fouling to be determined. It is thus possible to study how to avoid fouling and determine the best products and condi
n-Facundo et al., tions for cleaning and disinfecting the facility (Luja 2017). Accordingly, an autopsy of the membrane used in the experiments was carried out. The scheme followed was based on that
rrez, 2011), starting with an reported by other authors (Gutie external inspection, followed by an internal one, assessment of the membrane and assessment of the deposits (chemical analysis of the deposits and other analyses such as SEM, EDS and EDX). For the external inspection, the physical integrity of the housing, as well as that of the permeate collector tube and the inlet ring were verified. There was no telescope effect or dirt on the inlet and outlet membrane. After cutting and unrolling the membrane, the integrity of the sheets, support and glue lines were analysed. The existence of a thin layer of homogeneously distributed fouling was observed. Fragments of fouled membrane were taken and some of the fouling accumulated in the sheets was scratched off for analysis. The fouled membrane fragments were studied under a scanning electron microscope (SEM) and an elemental composition of the fouling was performed by energy dispersive spectrometry (EDS) analysis. In the microscopic view below, clusters of matter due to salt incrustations as well as several types of diatoms were observed (Fig. 4). The priority compounds found in the fouling were organic matter (carbon and oxygen), in addition to sodium, magnesium, silica, phosphorus, sulphur and calcium salts. Metals such as iron and nickel were also detected (Fig. 5). An analysis of the accumulated fouling was carried out including the following parameters: - Moisture content of the sample (loss at 105  C). After submitting the sample to 105  C for 24 h, it presented a moisture content of 18.9 mg L
1. - Organic matter (loss at 450  C). After submitting the sample to 450  C, a loss of organic matter of 18.0 mg L
1 was detected. - Cations: Sodium, Ammonium, Potassium, Calcium and Magnesium. Values of 32 mg L
1 for sodium and 17 mg L
1 for calcium

Fig. 4. Diatoms and clusters of matter.

522

A. Egea-Corbacho et al. / Journal of Cleaner Production 214 (2019) 514e523

Si Mg 0.20% 0.29%

P 0.38%

S 0.44%

Ca 0.11%

Fe 0.39%

Ni 0.24%

Na 0.47%

C N Na Mg

N 40.21%

areas or street cleaning), agricultural (e.g. irrigation, aquaculture), industrial (e.g. cooling towers, process and cleaning water), recreational (e.g. golf) to environmental uses (e.g. aquifer recharge). Applying this tertiary treatment in a WWTP, it can be ensured that the water gets an optimum quality for its reuse, without the risks associated to these emerging contaminants in receiving waters and in water for human consumption.

Si C 57.27%

P S Ca Fe

Acknowledgments We thank WWTP's technician of Medina Sidonia, Juan Carlos, for all his work and we also thank the Global Medina company for the facilities.

Ni

Atomic % Fig. 5. Elemental composition of the fouling.

were observed, which demonstrates the viability of the membrane to reject bivalent cations. Magnesium presents a lower rejection value of 3.58 mg L
1. For monovalent cations such as ammonium and potassium, the results also showed a reject, with values of 4 and 5 mg L
1, respectively. - Anions: Nitrites, bromide and nitrate were not detected in the fouling, which shows that the membrane is not very effective in removing these contaminants, as was found in the previous point. Likewise, there is a high rejection of chloride, sulphates and phosphates and the presence of fluorides (35, 14, 9 and 0.026 mg L
1, respectively). - Emerging contaminants: caffeine, theobromine, theophylline were detected but could not be quantified in the membrane fouling. Amoxicillin and penicillin G were not detected. Once the experiments were finished, and although the permeate flow remained constant, an autopsy was carried out on the membrane in order to check the soiling of the membranes. The results obtained are shown in Fig. 5 and Table 6. Given the low degree of fouling that has occurred during the study time, membranes with the same characteristics could be reused for longer periods of time until a degree of fouling was reached. This degree of fouling is observed when the pressure loss through it decreases, decreasing the permeate flow and leading to the need for an increase in the working pressure. After the membrane autopsy, it can be observed that the membrane is not saturated yet; it could be used for a longer period of time before applying a first cleaning. The evaluation of the efficiencies of chemical cleaning solutions for NF270 is well studied by other authors (Aguiar et al., 2018). The autopsy results obtained also demonstrate the efficacy of the technology used to eliminate both the emerging contaminants and the different parameters analysed, as shown in the analysis of the elemental composition of fouling (Fig. 5), where the elements that constitute the molecules of the contaminants studied appear.

4. Conclusions The study of tertiary treatment by nanofiltration for the removal of stimulants and antibiotics in a pilot plant was found to be both satisfactory and highly promising, achieving complete removal of the contaminants under study. Likewise, the viability of the nanofiltration in obtaining a permeate water with suitable quality to be put to all possible reuses has been demonstrated. These reuses may vary from residential or urban irrigation (e.g. irrigation of green

References Aguiar, A., Andrade, L., Grossi, L., Pires, W., Amaral, M., 2018. Acid mine drainage treatment by nanofiltration: a study of membrane fouling, chemical cleaning, and membrane ageing. Separ. Purif. Technol. 192, 185e195. https://doi.org/10. 1016/j.seppur.2017.09.043. €ntta €ri, M., Kallioinen, M., Louhi-Kultanen, M., 2018. Ajo, P., Preis, S., Vornamo, T., Ma Hospital wastewater treatment with pilot-scale pulsed corona discharge for removal of pharmaceutical residues. J of Environ Chem Eng 6 (Issue 2), 1569e1577. https://doi.org/10.1016/j.jece.2018.02.007. AMERICAN WATER WORKS ASSOCIATION RESEARCH FOUNDATION, 1998. Water Treatment Membrane Processes. McGraw-Hill Inc. ISBN: 84-481-1206-7. Andreozzi, R., Canterino, M., Marotta, R., Paxeus, N., 2005. Antibiotic removal from wastewaters: the ozonation of amoxicillin. J. Hazard Mater. 122, 243e250. https://doi.org/10.1016/j.jhazmat.2005.03.004.
n y comportamiento ambiental de proBaena-Nogueras, R.M., 2016. Determinacio
uticos y de cuidado personal en ambientes acua
ticos (PhD ductor farmace
diz, C
~ a. Thesis). Universidad de Ca adiz, Espan
lez-Mazo, E., Lara-Martin, P.A., Baena-Nogueras, R.M., Pintado-Herrera, M.G., Gonza 2016a. Determination of pharmaceuticals in coastal systems using solid phase extraction (SPE) followed by ultra performance liquid chromatography e tandem mass spectrometry (UPLC- MS/MS). Curr. Anal. Chem. 12, 0e0. Buchberger, W.W., 2011. Current approaches to trace analysis of pharmaceuticals and personal care products in the environment. J. Chromatogr. A 1218, 603e618. Council Directive 91/271/EEC. Concerning Urban Waste Water Treatment. Directive 2013/39/EU Of the European Parliament and of the Council Amending Directives 2000/60/EC and 2008/105/EC as Regards Priority Substances in the Field of Water Policy..
rrez, S., Quiroga, J.M., 2019. Removal of emerging conEgea-Corbacho, A., Gutie taminants from wastewater through pilot plants using intermittent sand/coke filters for its subsequent reuse. Sci. Total Environ. 646, 1232e1240. https://doi. org/10.1016/j.scitotenv.2018.07.399. Epsztein, R., Nir, O., Lahav, O., Green, M., 2015. Selective nitrate removal from groundwater using a hybrid nanofiltrationereverse osmosis filtration scheme. Chem. Eng. J. 279, 372e378. https://doi.org/10.1016/j.cej.2015.05.010. García-Ivars, J., Martella, L., Massella, M., Carbonell-Alcaia, C., Alcaina-Miranda, M.I., Iborra-Clar, M.I., 2017. Nanofiltration as tertiary treatment method for removing trace pharmaceutically active compounds in wastewater from wastewater treatment plants. Water Res. 125, 360e373. https://doi.org/10.1016/j.watres. 2017.08.070.
rrez, S., 2011. Desalacio
n de aguas de mar mediante o
smosis inversa. Estudio Gutie de los mecanismos de ensuciamiento y limpieza. PhD Tesis. Universidad de
diz. C
adiz. Ca Haidari, A.H., Heihman, S.G.j., van der Meer, G.J., 2018. Optimal design of spacers in reverse osmosis. Separ. Purif. Technol. 192, 441e456. https://doi.org/10.1016/j. seppur.2017.10.042. Kim, S., Chu, K.,H., Hamadani, Al, Y.A.J, Park, C.M., Jag, M., Kim, D.H., Yu, M., Heo, J., Yoon, Y., 2018. Removal of contaminants of emerging concern by membranes in water and wastewater: a review. Chem. Eng. J. 335, 896e914. https://doi.org/10. 1016/j.cej.2017.11.044. €ck-Schulmeter, M., Ginebrada, A., Postigo, C., Lo
pez-Serna, R., Pe
rez, S., Briz, R., Ko
pez de Alda, M., Petrovi

, A., Tirapu, L., Barcelo
, D., Llorca, M., Lo c, M., Munne 2011. Wastewater reuse in Mediterranean semi-arid areas: the impact of discharges of tertiary treated sewage on the load of polar micro pollutants in the Llobregat River (NE Spain). Chemosphere 82 (5), 670e678. https://doi.org/10. 1016/j.supflu.2017.05.013. Kulkarni, P., Olson, N.D., Raspanti, G.A., Rosenberg, R.E., Gibbs, S.G., Sapkota, A., Sapkota, A.M., 2017. Antibiotic concentrations decrease during wastewater treatment but persist at low levels in reclaimed water. Int. J. Environ. Res. Publ. Health 14 (6), 668. https://doi.org/10.3390/ijerph14060668. Li, D., Yang, M., Hu, J., Zhang, Y., Chang, Hong, Jin, F., 2008. Determination of penicillin G and 17 its degradation products in a penicillin production wastewater treatment plant and the receiving river. Water Res. 42 (1e2), 307e317. Li, X., Wang, C., Qian, Y., Wang, Y., Zhang, L., 2013. Simultaneous removal of chemical oxygen demand, turbidity and hardness from biologically treated citric acid

A. Egea-Corbacho et al. / Journal of Cleaner Production 214 (2019) 514e523 wastewater by electrochemical oxidation for reuse. Separ. Purif. Technol. 107, 281e288. https://doi.org/10.1016/j.seppur.2013.01.008. Lu, H., Zou, W., Chai, P., Wang, J., Bazinet, L., 2016. Feasibility of antibiotic and sulfate ions separation from wastewater using electrodialysis with ultrafiltration membrane. J. Clean. Prod. 112 (Part 4), 3097e3105. https://doi.org/10.1016/j. jclepro.2015.09.091.

n-Facundo, M.J., Mendoza-Roca, J.A., Cuartas-Uribe, B., Alvarez-Blanco, Luja S., 2017. Membrane fouling in whey processing and subsequent cleaning with ultrasounds for a more sustainable process. J. Clean. Prod. 143, 804e813. https://doi. org/10.1016/j.jclepro.2016.12.043. Luo, Y., Guo, W., Ngo, H., Nghiem, D., Hai, F., Zhang, J., Liang, S., Wang, X.C., 2014. A review on the occurrence of micropollutants in the aquatic environment and their fate and removal during wastewater treatment. Sci. Total Environ. 473e474, 619e641. Machado, K.C., Grassi, M.T., Vidal, C., Pescara, I.C., Jardim, W.F., Fernandes, A.N.,
, F.F., Almeida, F.V., Santana, J.S., Canela, M.C., Nunes, C.R.O., Bichinho, K.M., Sodre Severa, F.J.R., 2016. A preliminary nationwide survey of the presence of emerging contaminants in drinking and source waters in Brazil. Sci. Total Environ. 572 (1 December 2016), 138e146. https://doi.org/10.1016/j.scitotenv. 2016.07.210.
s, T., Palma, G., Cavaco, C., gomes, R., Palma, P., Fialho, S., Alvarenga, P., Santos, C., Bra Neves, L.A., 2016. Membranes technology used in water treatment: chemical, microbiological and ecotoxicological analysis. Sci. Total Environ. 568, 998e1009. https://doi.org/10.1016/j.scitotenv.2016.04.208. Rabiet, M., Togola, A., Brissaud, F., Seidel, J.L., Budziniski, H., Ebaz-Poulichet, F., 2006. Consequences of treated water recycling as regards pharmaceuticals and drugs in surface and ground waters of a medium-sized mediterranean catchment. Environ. Sci. Technol. 40, 5282e5288. https://doi.org/10.1021/es060528p. Riva, F., Zuccato, E., Davoli, E., Fattore, E., Castiglioni, S., 2018a. Risk assessment of a mixture of emerging contaminants in surface water in a highly urbanized area in Italy. J. Hazard Mater. Available online 2 August 2018. (in press), Accepted Manuscript https://doi.org/10.1016/j.jhazmat.2018.07.099. Riva, F., Castiglioni, S., Fattore, E., Manenti, A., Davoli, E., Zuccato, E., 2018b. Monitoring emerging contaminants in the drinking water of Milan and assessment of the human risk. Int. J. Hyg Environ. Health 221 (3), 451e457. https://doi.org/10. 1016/j.ijheh.2018.01.008.

523

Royal Decree 1620/2007 of December 7, Which Establishes the Legal Regime for the Reuse of Treated Water. Royal Decree-law 11/1995, of December 28, by Which the Applicable Norms for the Treatment of Urban Wastewater Are Established. Sarkar, B., Mandal, S., Tsang, Y.F., Kumar, P., Kim, K., Ok, Y., 2018. Designer carbon nanotubes for contaminant removal in water and wastewater: a critical review. Sci. Total Environ. 612, 561e581. https://doi.org/10.1016/j.scitotenv.2017.08.132. Senta, I., Gracia Lor, E., Borsotti, A., Zuccato, E., Castiglioni, S., 2015. Wastewater analysis to monitor use of caffeine and nicotine and evaluation of their metabolites as biomarkers for population size assessment. Water Res. 74, 23e33. https://doi.org/10.1016/j.watres.2015.02.002.  a
mkova
, M.V., Diaz-Sosa, V., Wanner, J., 2018. Experimental verification of tertiary Sr treatment process in achieving effluent quality required by wastewater reuse standards. Journal of Water Process Engineering 22, 41e45. Standard methods for the examination of water and wastewater, 2017, 23st ed. American Public Health Association/American Water Works Association/Water Environment Federation, Washington DC, USA. Stavbar, S., Hrn ci c, M.K., Premzl, K., Kolar, M., Turk, S.S., 2017. Sub- and super-critical water oxidation of wastewater containing amoxicillin and ciprofloxacin. J. Supercrit. Fluids 128, 73e78. https://doi.org/10.1016/j.supflu.2017.05.013. Van der Bruggen, B., Vandecasteele, C., 2003. Removal of pollutants from surface water and groundwater by nanofiltration: overview of possible applications in the drinking water industry. Chem. Eng. J. 279, 372e378. https://doi.org/10. 1016/S0269-7491(02)00308-1. Wang, R., Kang, X., Wang, R., Wang, R., Dou, H., Wu, J., Song, C., Chang, J., 2013. Comparative study of the binding of trypsin to caffeine and theophylline by spectrofluorimetry. J. Lumin. 138, 258e266. https://doi.org/10.1016/j.jlumin. 2013.02.021. Warsinger, D.M., Tow, E.W., Maswadeh, L.A., Connors, G., Swaminathan, J., Lienhard V, J.H., 2018. Inorganic fouling mitigation by salinity cycling in batch reverse osmosis. Water Res. Available online 5 February 2018. (in press), Accepted Manuscript https://doi.org/10.1016/j.watres.2018.01.060. WHO (World Health Organization), 2017. Global Priority List of Antibiotic-resistant Bacteria to Guide Research, Discovery, and Development of New Antibiotics. Geneva.