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ARTICLE IN PRESSG ModelCOENG-3119; No. of Pages 9

Ecological Engineering xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

Ecological Engineering

jou rn al hom ep age: www.elsev ier .com/ locate /eco leng

merging organic contaminant removal in a full-scale hybridonstructed wetland system for wastewater treatment and reuse

ristina Ávilaa, Josep M. Bayonab, Isabel Martínc, Juan José Salasc, Joan Garcíaa,∗

GEMMA – Group of Environmental Engineering and Microbiology, Department of Hydraulic, Maritime and Environmental Engineering, Universitatolitècnica de Catalunya-BarcelonaTech, c/ Jordi Girona, 1-3, Building D1, E-08034 Barcelona, SpainDepartment of Environmental Chemistry, IDAEA-CSIC, c/ Jordi Girona, 18-26, E-08034 Barcelona, SpainFoundation Centre for New Water Technologies (CENTA), Autovía Sevilla-Huelva (A-49), km. 28, Carrión de los Céspedes, E-41820 Seville, Spain

r t i c l e i n f o

rticle history:eceived 12 February 2014eceived in revised form 23 June 2014ccepted 2 July 2014vailable online xxx

eywords:ndocrine disruptorbuprofenathogen removalharmaceuticalsreatment wetland

a b s t r a c t

A full-scale hybrid constructed wetland (CW) system based on three stages of different wetlands configu-rations showed to be a very robust ecotechnology for domestic wastewater treatment and reuse in smallcommunities. It consisted of a 317-m2 vertical subsurface flow (VF), a 229-m2 horizontal subsurface flow(HF), and a 240-m2 free water surface (FWS) CWs operating in series. VF and HF wetlands were plantedwith Phragmites australis and the FWS contained a mixture of plant species. An excellent overall treatmentperformance was exhibited on the elimination of conventional water quality parameters (98–99% averageremoval efficiency for TSS, BOD5 and NH4–N; n = 8), and its final effluent proved to comply with existingSpanish regulations for various reuse applications. The removal of studied emerging contaminants, whichincluded various pharmaceuticals, personal care products and endocrine disruptors, was also very high(above 80% for all compounds), being compound dependent (n = 8). The high rates were achieved dueto high temperatures as well as the differing existing physico-chemical conditions occurring at differentCW configurations, which would allow for the combination and synergy of various abiotic/biotic removal

mechanisms to occur (e.g. biodegradation, sorption, volatilization, hydrolysis, photodegradation). Whileaerobic metabolic pathways and solids retention are enhanced in the VF bed, other removal mechanismssuch as anaerobic biodegradation and sorption would predominate in the HF bed. At last, photodegrada-tion through direct sunlight exposure, and less importantly, sorption onto organic matter, seem to takean active part in organic contaminant removal in the FWS wetland.

ieleaimicdi

. Introduction

The occurrence of emerging organic contaminants (EOCs), suchs pharmaceutical and personal care products (PPCPs), pesticidesr antiseptics in poorly treated wastewater and eventually in otheratercourses constitutes nowadays an increasing concern world-ide due to their possible toxicological effects to the environment

nd living organisms (Cunningham et al., 2006; Daughton, 2005;ümmerer, 2009).

On the other hand, constructed wetlands (CWs) are wastewa-er treatment systems that emphasize the processes happening in

Please cite this article in press as: Ávila, C., et al., Emerging organic csystem for wastewater treatment and reuse. Ecol. Eng. (2014), http://

atural wetlands so as to improve their treatment capacity (Kadlecnd Wallace, 2009). They constitute a cost-effective alternative toonventional wastewater treatment plants (WWTPs), especially

∗ Corresponding author. Tel.: +34 93 4016464; fax: +34 93 4017357.E-mail address: joan.garcia@upc.edu (J. García).

eanM

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ttp://dx.doi.org/10.1016/j.ecoleng.2014.07.056925-8574/© 2014 Elsevier B.V. All rights reserved.

© 2014 Elsevier B.V. All rights reserved.

n the context of small communities with less than 2000 peoplequivalent (Puigagut et al., 2007). Various types of constructed wet-ands have been combined in order to achieve higher treatmentfficiency, especially for nitrogen removal. These hybrid systemsre normally comprised of vertical subsurface flow (VF) and hor-zontal subsurface flow (HF) beds arranged in different possible

anners, including recirculation from one stage to another. Whilen HF wetlands nitrification is not achieved due to their low oxygenontent, in VF aerobic conditions prevail, which provide good con-itions for nitrification, but little to negligible denitrification occurs

n these systems. Thenceforward, the strengths and weaknesses ofach type of system can balance each other out when combined,nd in consequence it is possible to obtain an effluent low in totalitrogen concentrations, as well as other pollutants (Cooper, 1999;

ontaminant removal in a full-scale hybrid constructed wetlanddx.doi.org/10.1016/j.ecoleng.2014.07.056

asi and Martinuzzi, 2007; Vymazal, 2007).Since EOCs are often poorly removed in conventional WWTPs

Heberer, 2002), advanced water reclamation technologies haveeen studied (e.g. advanced oxidation processes (AOPs) such as

ING ModelECOENG-3119; No. of Pages 9

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ARTICLE C. Ávila et al. / Ecological E

hoto-Fenton, ozonitzation) (Klavarioti et al., 2009; Rosal et al.,010). However, these AOPs often require a high level of energy andave high O&M costs, and thus are very unlikely to be implemented

n the context of wastewater treatment of small communities. Tohis regard, several studies have shown a great capacity for EOCemoval of constructed wetland systems at full-scale for domes-ic wastewater treatment of small communities in warm climates.hese studies were conducted at systems consisting of a single wet-and configuration at a time, namely VF, HF (Matamoros et al., 2009)r free water surface (FWS) (Llorens et al., 2009; Matamoros et al.,008b). However, studies which evaluate the contribution to EOCemoval of different wetland types within a hybrid system throughotential synergies in treatment processes are very scarce, and

nclude other types of treatment units (e.g. conventional WWTPs,aste stabilization ponds) as a treatment step prior to CWs (Hijosa-alsero et al., 2010a; Matamoros and Salvadó, 2012). Evaluating

he physicochemical properties and behavior of EOCs in differentonstructed wetland units belonging to hybrid systems remain,hus, a future challenge to be developed. This will help in refiningW design and operation modes, which in turn may increase CWcceptance and implementation as a cost-effective and operationallternative to conventional wastewater treatment technologies inecentralized areas (Imfeld et al., 2009).

In the context of a collaborative project between the Univer-itat Politècnica de Catalunya-BarcelonaTech (Barcelona) and theoundation Center for New Water Technologies-CENTA (Seville),hich aimed at the treatment of domestic wastewater up to qual-

ty standards appropriate for reuse through the sole use of CWs,n experimental meso-scale hybrid constructed wetland systemas constructed. The system combined different CW configura-

ions (VF, HF and FWS) and showed an excellent performance, bothn terms of water quality parameters but also on EOC removal (Ávilat al., 2013a, 2014). Parallely, and in the context of the same collab-ration, a comprehensive approach implemented at pilot full-scaleith identical wetland configuration (VF, HF and FWS) in a Mediter-

anean climate area of south Spain (Seville) proved to be a highlyfficient ecotechnology for an integrated sanitation of small com-unities in warm climates, holding very low O&M requirements

Ávila et al., 2013c). The treatment technology, which receivedombined sewer effluent, exhibited a great performance on solids,rganic matter and total nitrogen removal, and showed to be veryesilient to water flow fluctuations when evaluated during stormyeriods and first-flush events. The final effluent of this proved toe of sufficient quality for its further reuse in various applicationsi.e. silviculture and irrigation of forests and other green areas nonccessible to the public, etc.), according to the quality criteria set-ling in the Royal Decree 1620/2007 establishing the legal regimeor the reuse of treated water in Spain (maximum admitted valuesqual to 1000 CFU/100 mL of Escherichia coli and 35 mg L−1 of TSS).

However, the disposal into the aquatic environment of EOCsue to incomplete wastewater treatment has been of great concernor more than a decade (Cunningham et al., 2006). Additionally, inecent times there is a clear need to include irrigation as an addi-ional exposure route for chemicals in terrestrial ecosystems. As anxample, recent research is being done to explore whether theseontaminants can be incorporated to crops irrigated with reclaimedater (Calderón-Preciado et al., 2013; Matamoros et al., 2012b).lthough concentrations are low, questions have been raised about

he potential impacts of these substances in the environment andnimal and public health after long-term exposure (Matamorost al., 2012b).

Please cite this article in press as: Ávila, C., et al., Emerging organic csystem for wastewater treatment and reuse. Ecol. Eng. (2014), http://

In this scenario, the aim of this study was to evaluate the treat-ent performance of a full-scale hybrid CW system located in aediterranean climate from southern Spain on the elimination

f various EOCs from a combined sewer effluent. The selected

flgwa

PRESSering xxx (2014) xxx–xxx

ompounds consisted of various commonly used pharmaceuticalsnd personal care products (PPCPs), as well as a high-productionhemical widely used in epoxy resins lining food and beverage con-ainers. These were: three non-steroidal anti-inflammatory drugsibuprofen – IB, diclofenac – DCF, acetaminophen – ACE), three per-onal care products (tonalide – AHTN, oxybenzone – OXY, triclosan

TCS) and two endocrine disrupting compounds (bisphenol A –PA and ethinylestradiol – EE2).

. Materials and methods

.1. Plant description

The hybrid treatment system was part of a larger research, inno-ation and development center (R&D&i) Center for wastewaterreatment and reuse (41,000-m2) of the Foundation Center for New

ater Technologies (CENTA) that received the wastewater from500 PE from the municipality of Carrión de los Céspedes (Seville)ogether with the urban runoff collected in a combined sewer sys-em. Average annual rainfall in the area is around 650 mm and theverage temperature is 17.4 ◦C. The center contains a great varietyf both extensive and intensive technologies for wastewater treat-ent and reuse from small rural communities in the Mediterranean

rea (Fadh et al., 2007; Martín et al., 2009a), which are submittedo analysis and validation, and are used for knowledge dissemina-ion and outreach (http://www.centa.es). Pretreatment chambersre common to all technologies and its effluent is diverted towardach of them. Pretreatment consists of screening (3 cm and 3 mm),nd sand and grease removal. After pretreatment, the effluent isonveyed toward a pumping chamber, from which the water isistributed through submersible pumps to the different treatmentechnologies present in the center. The constructed wetland sys-em started operation in 2005, though the treatment line as it isow began to operate in July 2009. In particular, a hybrid systemonsisting of a combination of various CW configurations was setn order to balance out the strengths and weaknesses of each typef system. The treatment line consisted of an Imhoff tank followedy a vertical subsurface flow CW (VF), a horizontal subsurface flowonstructed wetland (HF) and a free-water surface CW (FWS) con-ected in series (Fig. 1).

The VF wetland had a surface area of 317 m2 and was designedor an organic loading rate (OLR) of about 9 g BOD5 m−2 d−1. Notehat this was rather a conservative design because of the lack ofxperience at full-scale in the area. It was fed intermittently atbout 20 pulses d−1 to an average inflow of 14 m3 d−1. The bedonsisted of a top layer of 0.05 m of sand (1–2 mm), followed by a.6 m layer of siliceous gravel (4–12 mm) and an underlying 0.15 miliceous gravel (25–40 mm). Feeding of the VF was done throughve lengthwise pipes (diameter = 125 mm) perforated with 1 cmiameter holes every 1.8 m distance. Five draining pipes were

nstalled lengthwise at the bottom of the wetland within the 15 cm-hick gravel layer. Every draining pipe had three 1 m-tall chimneyso as to provide oxygen transfer into the wetland bed.

The HF unit had a surface area of 229 m2 and consisted of ailiceous gravel bed of 0.4 m depth (4–12 mm), with an inlet andutlet zone of stones (40–80 mm) to facilitate the flow. Feeding ofhe bed was done through a 63 mm diameter polyethylene pipeerforated with 1 cm holes every 1 m distance. The outlet of theetland was done by means of two 125 mm-diameter drainingipes located at the bottom of the stone layer and connected to a

ontaminant removal in a full-scale hybrid constructed wetlanddx.doi.org/10.1016/j.ecoleng.2014.07.056

exible pipe, which held the water level 5 cm below the top of theravel. Theoretical hydraulic retention time (HRT) within this bedas of 2.3 d, unlike the VF bed one which is supposed to be of just

few hours due to the operation regime of this type of wetlands

ARTICLE IN PRESSG ModelECOENG-3119; No. of Pages 9

C. Ávila et al. / Ecological Engineering xxx (2014) xxx–xxx 3

d con

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unsaturated). Both the VF and the HF were planted with Phrag-ites australis. Vegetation was very well developed at the time of

he study.Finally, the FWS had a surface area of 240 m2 and a water depth

f 30 cm. Theoretical HRT was of 5.1 d. A mixture of Typha spp., Scir-us spp., Iris pseudacorus, Carex flacca, Cyperus rutundus and Juncuspp. were planted on a 0.2 m siliceous gravel bed. Since the treat-ent system had been working for several years, it was mature

nd the vegetation was well developed also in this unit. The finalffluent of the treatment line was collected in an open-air waterank with a capacity of 20 m3 so as to store the treated water forts further reuse. Total theoretical HRT throughout the whole CWystem was greater than 7.4 d. Further details on the system can beound in Ávila et al. (2013c).

.2. Sampling procedure

Concentrations of EOCs found at urban wastewaters are oftenery variable, since their disposal and consumption varies a lotepending on the time of the day and period of the year (Nelsont al., 2011; Ort et al., 2010). Therefore, and given the HRT of thereatment systems (which is usually in the range of several days), its challenging – if not impossible – to assess the removal efficiencyf the treatment system at a given moment. In order to minimizehis problem, non flow-dependent 24-h composite samples wereaken at this study. Sampling was performed twice a week insteadf daily so as to minimize variability and to distribute sampling andnalysis efforts overtime.

Sampling was performed twice a week for four consecutiveeeks (n = 8) during May and June 2011. In particular, 24-h com-osite samples of the wastewater influent, as well as the effluentsf the Imhoff tank, VF, HF and FWS were collected by Sigma 900utosamplers (about 500 mL every 1 h; no refrigeration applied).rab samples from the final water tank were also taken so as toeasure the final quality of the stored water, which was exposed

o direct sunlight. Samples for the evaluation of EOCs were trans-orted to the laboratory in 250 mL amber glass bottles and keptefrigerated at 4 ◦C until analysis. The sample holding time wasess than 24 h. Conventional water quality parameters and studiedOCs were analyzed as described in Section 2.4. Moreover, it shoulde noted that no rainfall events were recorded two weeks beforer during the sampling period.

.3. Chemicals

Gas chromatography (GC) grade (Suprasolv) hexane, methanol,thyl acetate and acetone were obtained from Merck (Darm-tadt, Germany) and analytical-grade hydrogen chloride wasupplied by Panreac (Barcelona, Spain). ENR, SMZ, DC, ETM, LIN,B, ACE, DCF, AHTN, OXB, BPA, TCS, EE2 and 2,2′-dinitrophenyl

Please cite this article in press as: Ávila, C., et al., Emerging organic csystem for wastewater treatment and reuse. Ecol. Eng. (2014), http://

ere obtained from Sigma–Aldrich (Steinheim, Germany). 2,4,5-richlorophenoxypropionic acid (2,4,5-TPA) was from Reidel-de-aen (Seelze, Germany). Trimethylsulfonium hydroxide (TMSH)as supplied by Fluka (Buchs, Switzerland). Strata-X polymeric

omiS

structed wetland system.

PE cartridges (200 mg) were purchased from Phenomenex (Tor-ance, CA, USA) and the 0.7 �m glass fiber filters of ø = 47 mm werebtained from Whatman (Maidstone, UK).

.4. Analytical methods

Onsite measurements of dissolved oxygen (DO), redox poten-ial (EH), water temperature, electrical conductivity (EC), pH andurbidity were taken using a Hach HQ 30d oxymeter, a HachensIon i30 multi-meter and a Hach 2100Q turbidity meter, respec-ively. EH values were corrected for the potential of the hydrogenlectrode. Conventional wastewater quality parameters, includingotal suspended solids (TSS) and chemical oxygen demand (COD)ere determined by using Standard Methods (APHA, 2001). Non-

arbonaceous biochemical oxygen demand at 5 days (BOD5) waseasured by using a WTW® OxiTop® BOD Measuring System.

otal nitrogen (TN), total phosphorus (TP), ammonium nitrogenNH4–N), inorganic oxidized nitrogen (NOx–N) and reactive solu-le phosphorus (PO4-P) were determined by using a Bran LuebbeutoAnalyzer 3. Isolation and enumeration of E. coli was made using

Chromogenic Membrane Filtration technique (APHA, 2001). Forntestinal nematode eggs sampling, extraction and determination

as made according the modified Bailinger’s Method (Bouhoumnd Schwartzbrod, 1989).

Determination of EOCs in water samples was carried out afteramples had been filtered and processed as previously describedy Matamoros et al. (2005). The linearity range was from 0.01 to

mg L−1. The correlation coefficients (R2) of the calibration curvesere always higher than 0.99. The limit of detection (LOD) and limit

f quantification (LOQ) were compound dependent in the rangerom 0.009 to 0.08 �g L−1 and 0.02 to 0.27 �g L−1, respectively.

. Results and discussion

.1. Conventional water quality parameters

Table 1 shows concentrations of the studied conventional wateruality parameters along the hybrid CW system. Water temper-tures were fairly high at the time of the study (20–24 ◦C), asxpected for the hot summers of the Mediterranean climate fromouthern Spain. Indeed, EC values showed to increase as waterassed through the FWS and the water tank, which could bexplained by the evapotranspiration taking place in the systems.stimated OLR and hydraulic loading rates (HLRs) entering the VFetland at the time of experiments were about 6 g BOD5/m2 d and

.044 m d−1, respectively.Average overall removal efficiencies achieved in the treatment

ystem up to the water tank were unquestionably high for mostonventional water quality parameters (98% TSS, 89% COD, 99%OD5, 98% NH4–N). These results are in conformity with those

ontaminant removal in a full-scale hybrid constructed wetlanddx.doi.org/10.1016/j.ecoleng.2014.07.056

btained by Ávila et al. (2013c) in this R&D&i center, after a 1.5-yearonitoring period under dry and wet weather conditions, includ-

ng an intensive sampling campaign during a first-flush event.olids entrapment and organic matter removal was very high

ARTICLE IN PRESSG ModelECOENG-3119; No. of Pages 9

4 C. Ávila et al. / Ecological Engineering xxx (2014) xxx–xxx

Table 1Mean concentrations, standard deviations and overall removal efficiency of water quality parameters along the hybrid constructed wetland system and the water reuse tank(n = 8). Individual removal efficiencies (%) are shown in parentheses.

Influent Imhoff tank VF HF FWS Water tank Overall removalefficiency (%)

Temperature (◦C) 24 ± 2 24 ± 2 23 ± 2 22 ± 2 20 ± 2 21 ± 2 n.a.DO (mg L−1) 0.2 ± 0.0 0.2 ± 0.0 2.0 ± 1.7 4.2 ± 0.4 2.7 ± 0.3 3.8 ± 0.6 n.a.EH (mV) +62 ± 8 +2 ± 31 +115 ± 62 +139 ± 44 +129 ± 61 +210 ± 63 n.a.pH 7.8 ± 0.1 7.5 ± 0.5 7.4 ± 0.4 7.5 ± 0.4 7.8 ± 0.1 7.8 ± 0.2 n.a.EC (ms cm−1) 1.5 ± 0.1 1.5 ± 0.08 1.5 ± 0.05 1.5 ± 0.03 1.7 ± 0.09 1.8 ± 0.09 n.a.Turbidity (NTU) 228 ± 33 108 ± 30 22 ± 18 28 ± 13 8 ± 3 4 ± 2 98TSS (mg L−1) 212 ± 59 114 ± 33 (46%) 11 ± 4 (90%) 13 ± 4 (−18%) 6 ± 2 (54%) 3 ± 1 (50%) 98COD (mg L−1) 405 ± 106 258 ± 42 (36%) 44 ± 14 (83%) 29 ± 7 (34%) 47 ± 8 (−62%) 43 ± 8 (8%) 89BOD5 (mg L−1) 320 ± 57 125 ± 7 (61%) 11 ± 8 (91%) 7 ± 2 (36%) 6 ± 2 (14%) 4 ± 3 (33%) 99NH4–N (mg L−1) 25.5 ± 5.4 24.2 ± 6.6 (5%) 8.0 ± 2.2 (67%) 2.5 ± 1.8 (69%) 0.7 ± 0.11 (72%) 0.6 ± 0.1 (14%) 98NOx–N (mg L−1) 0.3 ± 0.3 0.2 ± 0.2 0.8 ± 0.9 0.5 ± 0.2 0.2 ± 0.2 0.1 ± 0.1 n.a.TN (mg L−1) 40.1 ± 8.8 38.5 ± 6.1 (4%) 13.3 ± 3.6 (65%) 3.6 ± 1.4 (73%) 2.4 ± 0.6 (33%) 2.2 ± 0.5 (8%) 94TP (mg L−1) 5.9 ± 1.2 5.9 ± 1.6 (0%) 5.3 ± 1.8 (10%) 4.2 ± 2.0 (21%) 3.1 ± 0.4 (26%) 3.1 ± 0.6 (0%) 47PO -P (mg L−1) 3.2 ± 0.7 3.2 ± 0.6 (0%) 2.9 ± 0.4 (9%) 2.2 ± 0.9 (24%) 2.7 ± 0.3 (−23%) 2.7 ± 0.7 (0%) 16

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ithin the VF wetland (90 and 91% for TSS and BOD5, respectively).heir concentrations remained low along the treatment system.he elimination of NH4–N was also fairly high within the VF (67%),here the high values for TN removal (65%) together with the low

oncentrations of NOx–N suggest once again both nitrification andenitrification processes to take place within this wetland type, dueo the coexistence of aerobic and anoxic sites within the wetlanded (Ávila et al., 2013b; Cooper et al., 1996). Further nitrificationnd denitrification occurred within the HF and FWS wetlands, up ton overall TN removal of 94%. This removal rate is higher than mostalues reported by full-scale hybrid CWs of similar configuration atarm climates, such as the one by Masi and Martinuzzi (2007) at a

ystem consisting of a 160-m2 HF followed by a 180-m2 VF, whichreated the wastewater from a medium scale tourist facility in Italy60% TN removal). To this regard, Ayaz et al. (2012) performed somexperiments at a pilot-system in Turkey consisting of a HF (18 m2)nd a VF (14 m2) in series, and found how recirculation from the VFo the HF enhanced the treatment efficiency, especially in terms ofitrogen removal (up to 79% TN removal). In our study the overallemoval efficiencies of TP and PO4-P were 47 and 16%, respectively.

The hybrid treatment system proved to have a great disinfec-ion capacity, exhibiting overall E. coli removal of about 5 log-units,hich is in conformity with previous long-term microbiologicalathogen evaluations in this system (Ávila et al., 2013c). Withegard to intestinal nematode eggs of interest for human and ani-al parasitology, these were not identified at any of the different

reatment units during the study period, which is in accordanceith results obtained during a 2-year period in the same systems

2007–2009) (Martín et al., 2009b). Final effluent concentrationsomplied with Spanish regulation limits for some water reusepplications (e.g. irrigation of forests and green areas non acces-ible to the public, silviculture, recharge of aquifers by percolationhrough the ground, etc.). The function made by the HF and FWSetlands proved crucial to achieve a water quality appropriate for

ts reuse.

.2. Emerging organic contaminants

.2.1. Occurrence and overall treatment performanceInfluent concentrations of studied EOCs in raw wastewater

anged 13.5–24.5 �g L−1 for IB, 0.4–1.9 �g L−1 for DCF, <LOD –

Please cite this article in press as: Ávila, C., et al., Emerging organic csystem for wastewater treatment and reuse. Ecol. Eng. (2014), http://

.5 �g L−1 for ACE, 0.4–0.9 �g L−1 for AHTN, 0.1–0.2 �g L−1 for TCSnd 1.4–5.7 �g L−1 for BPA (Table 2). Those values were in the rangereviously reported in raw wastewater in other studies (Ávila et al.,013b; Hijosa-Valsero et al., 2010b; Matamoros et al., 2007; Miège

tvop

103 <40 <40 99.999

t al., 2009). The sunscreen agent OXY and the synthetic estrogenE2 were not detected at any of the sampling days. The analgesicaracetamol (ACE) was detected in 50% of the influent samples and

ts concentrations varied significantly. The rest of compounds wereetected at every sample of influent wastewater.

To assess the EOC removal capacity of the CWs, concentrationemoval efficiencies (%) were calculated instead of mass removalates (gr of contaminant m−2 d−1), given that no individual treat-ent unit flow data were available for this full-scale system. Note

herefore that while for the VF bed the inflow could be consideredlmost equal to outflow, for the HF and FWS wetlands evapotran-piration rates could actually influence and in fact underestimatehe actual removal capacity of the system. In general, the hybridonstructed wetland system (up to the effluent of the FWS unit)erformed remarkably well in the removal of EOCs, achieving veryigh overall removal efficiencies for the majority of the studiedompounds (above 80% for all compounds). These rates are ingreement with those reported by Ávila et al. (2014) at an injec-ion experiment conducted at a meso-scale experimental hybridW system consisting of the exact treatment line, although oper-ted under three different HLRs which correspond to OLRs ranging5–93 g BOD5/m2 d, being much higher than the load applied in theurrent system. Removal rates are also similar to those found byijosa-Valsero et al. (2010a) at three full-scale hybrid CW systemsonsisting of different combinations of waste stabilization pondsnd FWS and HF CWs in series. Moreover, Matamoros and Salvadó2012) observed very high removal efficiencies (around 90%) for

ost studied compounds (e.g. IB, DCF, AHTN, TCS) at a full-scaleeclamation pond-FWS wetland system in Girona, Spain, treatingecondary effluent from a conventional WWTP. However, influentoncentrations were much lower than this study.

Final effluent concentrations of target EOCs were very low, beingelow the limit of detection for various contaminants (i.e. ACE,PA). The rest were in the ng L−1 order (20–100), which is in theange of those found in the environment, such as those reportedy Matamoros et al. (2009) in small ponds or lagoons. These con-entrations were also in the range of those obtained in advancedreatment technologies applied at full-scale, such as ozonation or

embrane filtration (Rosal et al., 2010; Snyder et al., 2007).The high removal efficiencies can be explained by differing

xisting physico-chemical conditions at different CW configura-

ontaminant removal in a full-scale hybrid constructed wetlanddx.doi.org/10.1016/j.ecoleng.2014.07.056

ions, which would allow for the combination and synergy ofarious physicochemical and biological removal mechanisms toccur (e.g. biodegradation, sorption, volatilization, hydrolysis, andhotodegradation) and thus achieve improved treatment efficiency

ARTICLE IN PRESSG ModelECOENG-3119; No. of Pages 9

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Table 2Mean values and standard deviations of studied emerging organic contaminants along the hybrid constructed wetland system (n = 8).

Influent Imhoff tank VF HF FWS Water tank Overall removalefficiency (%)

Analgesic-antiinflammatory drugsIbuprofen (�g L−1) 18.66 ± 3.89 14.78 ± 1.53 4.01 ± 1.54 0.52 ± 0.34 0.03 ± 0.02 0.03 ± 0.03 >99Diclofenac (�g L−1) 0.77 ± 0.52 0.74 ± 0.18 0.50 ± 0.18 0.28 ± 0.12 0.10 ± 0.04 0.10 ± 0.03 89Acetaminophen (�g L−1) 3.50 ± 3.42 3.32 ± 2.98 <LOD <LOD <LOD <LOD 99

Personal care productsTonalide (�g L−1) 0.54 ± 0.22 0.33 ± 0.11 0.24 ± 0.07 0.11 ± 0.03 0.05 ± 0.02 0.02 ± 0.00 90Oxybenzone (�g L−1) <LOD <LOD <LOD <LOD <LOD <LOD –Triclosan (�g L−1) 0.15 ± 0.03 0.13 ± 0.03 0.05 ± 0.01 0.05 ± 0.01 0.04 ± 0.01 0.03 ± 0.00 79

Endocrine disrupting compounds33

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Bisphenol A (�g L−1) 4.06 ± 1.19 3.90 ± 1.59 2.12 ± 1.Ethinylestradiol (�g L−1) <LOD <LOD <LOD

f most pollutants (Imfeld et al., 2009). In this sense, while aero-ic metabolic pathways and solids retention are enhanced in VFetlands, other removal mechanisms such as anaerobic biodegra-ation and sorption would predominate in HF beds. At last, the FWSetland would be responsible for potential photodegradation of

ompounds, and less importantly through adsorption onto organicatter and uptake of plant material (Matamoros and Salvadó,

012). However, although the experimental design and analysisnd eventually data were insufficient for the deepening into thelucidation of EOC removal mechanisms occurring within a CW,he purpose of this study was rather to attempt to identify pos-ible removal pathways for different EOCs occurring in differentW configurations, based on their observed experimental behav-

or, together with the support from previous literature. Althoughhese experiments were carried out only in summer season, furtherxperiments should be carried out in colder conditions to evaluateossible reduction in treatment performance.

.2.2. VF performanceFig. 2 shows average removal efficiencies of selected EOCs at

ach stage of the hybrid constructed wetland system. The Imhoffank achieved a good removal of the musk fragrance AHTN (40%),resumably due to a high degree of attachment to the particulateatter. The removal of the biodegradable substance IB was also not

egligible in this tank (20%). The VF bed showed variable removalf EOCs, being compound dependent. It performed best for ACE94%), IB (58%) and TCS (50%), while lower removal efficienciesere achieved for BPA (44%), AHTN (17%) and DCF (36%).

In particular, ACE was completely removed within the VF bed.his analgesic has shown to be readily biodegraded to concen-rations below the limit of detection in all types of wetlandsYamamoto et al., 2009), including HF (Ávila et al., 2013b), VFÁvila et al., 2014) and hybrid treatment wetlands (Ávila et al.,014; Conkle et al., 2008), as well as conventional WWTPs (Mièget al., 2009). Average elimination rates achieved for IB (58%) didot fluctuate much during the sampling campaign and are in agree-ent with the attributed aerobic biodegradation of this compound,

eing oxidizing conditions provided by the unsaturated operation,s well as intermittent feeding, of the VF bed of key importance forn enhanced degradation (Matamoros et al., 2008a; Zwiener andrimmel, 2003). To this regard, Matamoros et al. (2007) showedow removal rates for IB were higher for unsaturated (99 ± 1%)han for saturated (55 ± 1) VF wetlands (5 m2) at an experimen-al pilot plant in Denmark. Similar results were obtained by Ávilat al. (2013b) at an injection experiment at HF CW system com-

Please cite this article in press as: Ávila, C., et al., Emerging organic csystem for wastewater treatment and reuse. Ecol. Eng. (2014), http://

aring permanently saturated operation vs. operation on cycles ofaturation/unsaturation (63 and 85%, respectively). What is more,vila et al. (2014) reported an average of 55% of IB elimination at

wo alternating VF beds (3 m2) at a hybrid system with the same

ceca

1.35 ± 0.52 <LOD <LOD >99<LOD <LOD <LOD –

onfiguration but at experimental scale in Spain, and treatmenterformance in terms of IB removal seemed to be negatively corre-

ated to HLRs. In that particular case, higher HLRs would translatento a higher number of feeding pulses and shorter resting times,esulting in a decrease of aeration into the system and hence aower treatment performance (Torrens et al., 2009). Nevertheless,his compound seems to be quite easily biodegraded, and it isell attenuated also in conventional WWTPs (Lishman et al., 2006;iège et al., 2009).Moreover, the prevailing aerobic conditions of the VF bed also

eemed to be especially important for the elimination of TCS (50%).hese results are in agreement with those by Ávila et al. (2014)n VF wetlands (3 m2), who reported an average removal of 78%nd observed how the operation under higher HLRs decreasedreatment performance (from 85 to 71%). Although sorption ontohe substrate could constitute a relevant removal mechanism forCS, given its hydrophobic characteristics (log Kow = 4.7), a negli-ible removal took place within the HF bed (Fig. 2). While otherubstances, like AHTN, show a great reduction within the HF pre-umably due to sorption processes, results for TCS would exhibitittle sorption capacity. The behavior of TCS within the three dif-erent wetland configurations indicate aerobic biodegradation ashe major removal mechanism involved in the elimination of thisompound (Singer et al., 2002; Ying et al., 2007).

Conversely, the removal of DCF within the VF wetland wasower (36%) and more variable. Although DCF has been reportedo be recalcitrant in activated sludge WWTPs (Heberer, 2002a;

iège et al., 2009), variable (from negligible to very high) removalfficiencies of this substance have been reported at CW sys-ems (Matamoros et al., 2009; Matamoros and Bayona, 2006).

ell-replicated experimental mesoscale studies carried out in HFetlands have demonstrated that higher redox conditions enhance

he removal of this compound, among other EOCs (Ávila et al.,014, 2013b; Hijosa-Valsero et al., 2010b). In this way, Matamorost al. (2007) reported a better elimination in an unsaturated VFed (73%) if compared to a saturated VF (53%). Zhang et al. (2012)ound significantly better performance of experimental mesoscaleF beds operating in pulses than those continuously fed. What isore, Ávila et al. (2014) recently found how DCF was efficiently

emoved within the first stage (VF) of the experimental hybrid CWystem (around 65%), but conversely no removal of DCF occurred athe following HF bed, where degenerated oxygen conditions pre-ailed. Nevertheless, very high (99%) removal rates were found byvila et al. (2010) during a continuous injection experiment in sum-er in an experimental HF CW system operating under anaerobic

ontaminant removal in a full-scale hybrid constructed wetlanddx.doi.org/10.1016/j.ecoleng.2014.07.056

onditions (EH = −123 mV; DO < LOD). The similarly high removalfficiencies achieved in the current study in the HF bed (23%) ifompared to the VF (36%) suggest that various alternative mech-nisms may determine the elimination of this compound, and to

ARTICLE IN PRESSG ModelECOENG-3119; No. of Pages 9

6 C. Ávila et al. / Ecological Engineering xxx (2014) xxx–xxx

nic co

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Fig. 2. Removal efficiencies for the selected emerging orga

hat respect, anaerobic biodegradation through reductive dehalo-enation could constitute a predominant degradation pathway ofCF when anaerobic conditions prevail (Ávila et al., 2010; Hijosa-alsero et al., 2010a; Park et al., 2009). Average removal rate of theusk fragrance AHTN in the VF wetland was lower (17%), than that

ound by Matamoros et al. (2007) in unsaturated and saturated VFetlands (82 and 75%, respectively), and Ávila et al. (2014) (aver-

ge of 69%), which found a dependence of this substance on thepplied HLR, suggesting that decreased entrapment of hydropho-ic compounds onto particulate matter occurred due to reducedontact time at higher HLRs. The removal of this compound occursainly through sorption on the particulate matter, given its high

ydrophobicity (Matamoros et al., 2007). Moreover, the elimina-ion of the endocrine disruptor BPA was significantly higher in thisetland (44%) if compared to the HF wetland (19%), which is in con-

ormity with the previously observed dependence of this substancen aerobic conditions (Ávila et al., 2014). However, the removalf this substance has also been achieved under anaerobic condi-ions of HF wetlands (Ávila et al., 2010) and thus the degradation ofhis substance could be owed to multiple mechanisms which seemo vary significantly in time, including association to the particu-ate matter (Wintgens et al., 2004), and biodegradation (Ávila et al.,010).

The superior treatment performance of the VF over the otherreatment units could be owed to energetically favorable aerobic

icrobial reactions, as well as hydrolysis reactions, taking placeithin this wetland type and provided by its design and operation

trategy, conferring high effluent redox potentials (+115 ± 62 mV)nd dissolved oxygen concentrations (2.0 ± 1.7 mg O2 L−1). Thisetland type is characterized by holding a great oxygen trans-

er capacity due to the unsaturated conditions of the bed, withassive aeration, as well as to the intermittent feeding operation.xygen transfer is achieved mainly by means of convection while

ntermittent loading and diffusion processes occurring betweenoses (Torrens et al., 2009). In fact, significantly higher enzymaticctivities and microbial biomass have been found in the upperayer of the sand of VF wetlands, where there is more substratend nutrient availability, indicating favorable redox conditions for

Please cite this article in press as: Ávila, C., et al., Emerging organic csystem for wastewater treatment and reuse. Ecol. Eng. (2014), http://

erobic metabolism, including carbon, nitrogen and other pollu-ants’ degradation (Imfeld et al., 2009; Tietz et al., 2007; Zhout al., 2005). However, the synergic nitrification–denitrificationctivity observed in the VF bed within this study (Section 3.1)

eill

ntaminants at the different units of the treatment system.

uggest the co-existence of both aerobic and anaerobic environ-ents within this wetland bed, which would allow both processes

o take place. Similarly, this finding indicates that although aerobiciodegradation and sorption onto organic matter may be the majoremoval mechanisms contributing to EOCs reduction in VF wet-ands, alternative processes based on anaerobic metabolism couldimultaneously be occurring at anoxic sites or micropores withinhe wetland bed (i.e. in lower layers) (Ávila et al., 2010; Coopert al., 1996), which contribute to its elimination. Finally, it is worthoting that the large removal rates achieved at this wetland in com-arison to the other wetland units are also influenced by the facthat this bed was the first stage of the system, where the major partf the removal would occur (Ávila et al., 2014; Hijosa-Valsero et al.,010a).

.2.3. HF performanceTarget emerging organic contaminants within the HF bed as a

econd stage of the hybrid CW system exhibited removal efficien-ies, which were best for DCF, AHTN, BPA and IB (Fig. 2). Note thathese were not individual efficiencies in respect to the influent ofhe HF, but the further proportion of elimination in respect to therevious treatment unit (% accum.). The purpose was to ease theomparison of the efficiency of removal within this bed in respecto the other units. The remaining IB was considerably reducedp to average effluent concentrations of 0.5 ± 0.3 �g L−1. The fra-rance AHTN, due to its high hydrophobicity, was moderatelyemoved, presumably by sorption onto the particulate material ofhe gravel matrix (Carballa et al., 2005; Matamoros and Bayona,006). Removal of TCS was extremely poor within this wetlanded, as compared to the VF bed. Similarly low removal efficienciesere obtained at the HF bed of the mesoscale hybrid CW system

valuated by Ávila et al. (2014). Although TCS has been detectedn plant and sediments of a HF CW and its concentration gener-lly decreased from inflow to outflow (Zarate et al., 2012), sorptionnd plant uptake does not appear to constitute a principal mech-nism of TCS removal in constructed wetlands. Otherwise, higheregradation rates would have been expected at the HF beds (Singer

ontaminant removal in a full-scale hybrid constructed wetlanddx.doi.org/10.1016/j.ecoleng.2014.07.056

t al., 2002). The degradation of BPA was only moderate, especiallyf compared to the reduction rates achieved at the VF and particu-arly FWS wetlands. This would be explained by the occurrence ofess energetically-favorable metabolic processes occurring at lower

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ARTICLEC. Ávila et al. / Ecological E

edox conditions, which would result in lower degradation kineticsnd hence lower elimination rates (Ávila et al., 2013b).

In general, HF wetlands have exhibited lower treatment capac-ty on the removal of EOCs than VF beds, which could be attributedo the dependence of their transformation processes on a highedox status of the system (Ávila et al., 2014; Matamoros et al.,009). However, the treatment performance of HF wetlands haseen found to be significantly enhanced in respect to the removalf EOCs (including IB, DCF, or BPA) at experiments at micro, mesond pilot-scale by optimized operation strategies resulting in highedox potentials, such as operating these wetlands in cycles of feednd rest, providing a shallow depth of the water table, or a using

primary treatment based on a conventional settler rather thannaerobic treatments (Ávila et al., 2013b; Matamoros et al., 2005;ong et al., 2009).

.2.4. FWS performanceThe FWS wetland performed especially well for BPA, followed

y DCF. The removal of BPA within this wetland was fairly high ifompared to the HF unit, which could be explained by enhancediodegradation of this substance under higher redox and dissolvedxygen conditions within the water column of the FWS (Ávilat al., 2013b; Liu et al., 2009). Sorption onto particulate matternd photodegradation (Matamoros et al., 2012a) could furtherontribute to BPA removal in FWS wetlands. Moreover, the reduc-ion of DCF was in accordance with elimination rates reportedy Llorens et al. (2009) at a full-scale FWS wetland receivingecondary effluent. The reduction of DCF was also significantlyigh (24% accum.) at a mesoscale FWS (Ávila et al., 2014). Theseesults support photodegradation as a principal removal mecha-ism involved in DCF attenuation in water bodies (Andreozzi et al.,003; Ávila et al., 2014; Buser et al., 1998; Matamoros and Salvadó,012a, 2013), together with less predominant mechanisms (i.e. aer-bic/anaerobic biodegradation, plant uptake) (Ávila et al., 2010).emoval of remaining IB took place in this wetland, presumably dueo biodegradation since low photodegradation rates are expectedor this compound (Szabó et al., 2011; Yamamoto et al., 2009).lthough the removal of TCS was negligible, some more reductionithin the water reuse tank seemed to occur, indicating that pho-

ooxidation processes may constitute a small contribution to itsemoval (Ávila et al., 2014; Matamoros and Salvadó, 2012, 2013;ezcua et al., 2004). Additionally, the further reduction of AHTN

oncentrations within this wetland bed was significant, accumu-ating an overall removal efficiency of 90%. Although the reductionf AHTN concentrations in the FWS could be attributed to sorp-ion onto particulate matter and sediment, further reduction waschieved at the water reuse tank, suggesting photodegradationhrough sunlight exposure as one of the principal mechanismsf AHTN’s removal within this type of wetland configuration.imilarly high removal efficiencies were obtained at other FWSetlands operating as a tertiary treatment step (Ávila et al., 2014;

lorens et al., 2009; Matamoros et al., 2008b; Matamoros andalvadó, 2012).

. Conclusions

A hybrid CW system at full-scale consisting of a combina-ion of CW configurations, which included a vertical subsurfaceow (VF) CW, a horizontal subsurface flow (HF) CW, and a freeater surface (FWS) CWs operating in series, showed to be a very

Please cite this article in press as: Ávila, C., et al., Emerging organic csystem for wastewater treatment and reuse. Ecol. Eng. (2014), http://

obust ecotechnology for wastewater treatment and reuse in smallommunities. Excellent overall treatment performance was exhib-ted on the elimination of conventional water quality parameters98–99% average removal efficiency for TSS, BOD5 and NH4–N), and

Á

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PRESSering xxx (2014) xxx–xxx 7

ts final effluent proved to comply with existing guidelines for itseuse in various applications (e.g. recharge of aquifers by percola-ion through the ground, silviculture and irrigation of forests andther green areas non accessible to the public). The eliminationf emerging organic contaminants, which included various phar-aceuticals, personal care products and endocrine disruptors, was

lso very high (above 80% for all compounds).Most organic matter removal, as well as the major part of EOC

emoval took place in the first stage of the treatment system (VF),here aerobic conditions are expected to prevail. The intermittent

eeding and unsaturation of the bed constitute key practices in thatpproach. However, significant denitrification was also found toccur within this wetland bed, suggesting that although aerobicegradation and sorption onto organic matter might constitute theajor removal mechanisms contributing to EOCs removal in VFs,

lternative processes based on anaerobic microbial metabolismould simultaneously be occurring at anoxic sites or microporesithin the bed, possibly at lower layers. Conversely, lower removal

fficiency was found for the HF bed, where mostly anaerobic degra-ation and sorption onto the gravel matrix are expected to occur.inally, photodegradation through direct sunlight exposure andorption to organic matter seem to take an active part in EOC elim-nation in FWS wetlands.

The combination of different wetland types has shown to opti-ize a number of important treatment processes, achieving an

xcellent overall EOC reduction, as well as removal of conven-ional water quality parameters. This has been possible thanks tohe occurrence of complementary abiotic/biotic removal pathwaysaking place under differing physico-chemical conditions existingt wetlands of different configuration. In this way, the Imhoff tanklays an important role in the reduction of EOCs that get easilyttached to particulate matter. Moreover, while in VF wetlandshere is a great removal of substances that get easily biodegradednder aerobic degradation routes, anaerobic removal pathwaysill predominate in HF wetlands. The effect of photo-oxidation

nd other processes shall finally help in removing EOCs in FWS wet-ands. Nevertheless, further studies should be undertaken in hybridonstructed wetland systems including different constructed wet-and types so as to gain a further insight in the processes involvedn the degradation of these substances.

cknowledgements

This research has been funded by the Spanish Ministry ofnvironment (MMARM) through the Project No. 085/RN08/03.2.uthors are also grateful to the European Commission for the finan-ial support of the SWINGS project (Grant Agreement No.: 308502).s. Cristina Avila kindly acknowledges a predoctoral fellowship

rom the Universitat Politècnica de Catalunya·BarcelonaTech. Theuthors would like to express their gratitude to Ramón Bouza-eano and the rest of the CENTA laboratory staff for their assistancend support during laboratory analyses.

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