Domestic wastewaters reuse reclaimed by an improved horizontal subsurface-flow constructed wetland: A case study in the southeast of Spain

Accepted Manuscript Case Study Domestic wastewaters reuse reclaimed by an improved horizontal subsurfaceflow constructed wetland: a case study in the southeast of Spain Pedro Andreo-Martíneza, Nuria García-Martínez, Joaquín Quesada-Medina, Luis Almela PII: DOI: Reference:

S0960-8524(17)30252-3 http://dx.doi.org/10.1016/j.biortech.2017.02.123 BITE 17695

To appear in:

Bioresource Technology

Received Date: Revised Date: Accepted Date:

6 February 2017 23 February 2017 26 February 2017

Please cite this article as: Andreo-Martíneza, P., García-Martínez, N., Quesada-Medina, J., Almela, L., Domestic wastewaters reuse reclaimed by an improved horizontal subsurface-flow constructed wetland: a case study in the southeast of Spain, Bioresource Technology (2017), doi: http://dx.doi.org/10.1016/j.biortech.2017.02.123

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1

Title

2

Domestic wastewaters reuse reclaimed by an improved horizontal subsurface-flow

3

constructed wetland: a case study in the southeast of Spain.

4

Authors

5

Pedro Andreo-Martínezaa, Nuria García-Martíneza, Joaquín Quesada-Medinab, Luis

6

Almelaa*.

7

Affiliations

8

a

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Campus of Espinardo, 30100 Murcia, (Spain).

10

Department of Agricultural Chemistry, Faculty of Chemistry, University of Murcia.

b

Department of Chemical Engineering, Faculty of Chemistry, University of Murcia,

11

Campus of Espinardo, 30100 Murcia, (Spain).

12

Abstract

13

The aim of this case study was to assess the performance of a horizontal subsurface

14

flow constructed wetland (HF-CW) located in southeastern Spain, filled with blast

15

furnace slags (BFS), planted with Phragmites australis and designed to treat artificially

16

aerated domestic wastewater to produce effluents suitable for agriculture reuse. The

17

water quality parameters, included in the Spanish regulations for reclaimed wastewater

18

reuse as agricultural quality 2.1, were monitored for one year. Data for all studied

19

parameters, except electrical conductivity (EC) and sodium absorption rate (SAR), met

20

the Spanish standards for reclaimed wastewater reuse due to the high evapotranspiration

21

(ET) during the summer. The introduced improvements were effective for turbidity,

22

total suspended solids (TSS), total nitrogen (TN), Escherichia coli (E. coli) and,

23

specially, for total phosphorus (TP) with an average abatement of 96.9 ± 1.7%. The

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improved HF-CW achieved similar or better percentage abatement than those reported

25

using some hybrid systems.

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Keywords

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Aerated domestic wastewater. Blast furnace slag. Horizontal subsurface flow

28

constructed wetland. Mediterranean climate. Reclaimed wastewaters reuse.

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1. Introduction

30

One of the most important challenges of any civilization is the proper sustainable

31

management and conservation of water resources. This challenge is accentuated in arid

32

and semiarid regions of the globe mainly due to water shortage problems presented by

33

these regions. Many regions under water scarcity suffer severe pressure on local water

34

resources caused mainly by a strong urban and tourist population growth and

35

agricultural or industrial development. Furthermore, it is expected that climate change

36

will compromise the quality and availability of water for further supply, as well as the

37

functioning of aquatic ecosystems, which increases the need to find sustainable

38

solutions to this problem (Garcia and Pargament, 2015; Sowers et al., 2011).

39

One possible solution for the sustainable management and conservation of water

40

resources is the reuse of reclaimed wastewaters which has been recognized as a

41

promising solution for addressing the problem of water scarcity worldwide. Thus, the

42

adoption of the principles of Integrated Water Resources Management will ensure that

43

the implementation of wastewater reuse projects will take into account all stakeholders

44

affected and also the external costs and benefits of the decision to reuse (Garcia and

45

Pargament, 2015). In regard, Spain developed specific legislation (Decree, 2007) which

46

regulates the reuse of reclaimed wastewater from waste water treatment plants (WWTP)

47

which must be equipped with a regenerative water station to meet the physicochemical

48

and microbiological parameters required by such legislation.

49

In Spain, the future of reclaimed wastewater reuse is essentially focused on the coastal

50

areas of the Mediterranean, South-Atlantic Arc and the Balearic and Canary Islands.

51

The Spanish area where most reclaimed wastewater is reused is located in the

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Mediterranean Arc, due to the difficulty of obtaining additional resources, the depletion

53

and deterioration of traditional supply sources, the progressive salinization of aquifers,

54

and the frequent droughts that affect these areas severely (Iglesias et al., 2010). In this

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way, Valencia is the area with higher dynamism in wastewater reuse, mainly focused on

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agricultural use (71%) (Iglesias et al., 2010). However, there are still areas in Valencia

57

where the practice of reuse is not possible because they do not have public sewage

58

systems yet. An example of these areas is the countryside of Elche, located south of

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Alicante, where in 2006 there were 9225 individual households without access to public

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sewers (Ruiz-Arnáiz, 2006) and it has not been built yet.

61

Constructed wetlands (CWs) are an interesting solution for improving the quality of

62

wastewater before disposal into the environment or reuse for irrigation (Akratos and

63

Tsihrintzis, 2007). Indeed, CWs have proven to be efficient in abating the main

64

chemicals (organic substances, metals and metalloids, etc.) and biological organisms

65

(bacteria, viruses, parasites, etc.) from municipal and domestic wastewater (Ayaz et al.,

66

2015; Gross et al., 2007; Morari and Giardini, 2009; Zhang et al., 2014). On the other

67

hand, it has been reported that horizontal subsurface-flow constructed wetlands (HF-

68

CWs), the CWs type most commonly used in Spain (Puigagut et al., 2007), present

69

limitations with regard to abating some pollutants such as nitrogen, organic matter and

70

phosphorus. This fact is mainly because HF-CWs are considered as anoxic systems and

71

an insufficient amount of dissolved oxygen (DO) in water can decrease nitrogen or

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organics abatement (Vymazal, 2007); and also because the traditional HF-CWs filling

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materials are not suitable enough to abate phosphorus as they lack sufficient Ca, Mg, Fe

74

or Al ions (Vohla et al., 2011). In this sense, some solutions such as HF-CW bed

75

aeration (Fan et al., 2013; Nivala et al., 2007) and influent wastewater aeration

76

(Rossmann et al., 2012; Rossmann et al., 2013), to complement the natural aeration

77

processes, and various bed filling materials such as blast furnace slags (BFS) or heated

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opoka (natural material from south-eastern Poland composed by 50% of CaCO3, 40% of

79

SiO2 and, 10% of Al, Fe and other oxides), to improve the HF-CW bed adsorption

80

properties (Vohla et al., 2011), have been proposed recently.

81

Therefore, the implementation of HF-CWs could be a solution for the treatment of

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domestic wastewater from the isolated houses in the Elche countryside. In fact, given

83

the need for adequate treatment of domestic wastewaters generated by such houses,

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logic itself tells us that these reclaimed wastewaters should be used for different

85

applications such as irrigation of crops, discharge of bathrooms, watering green zones

86

or similar. Besides, in this area, home gardens of fruits and vegetables for familiar

87

consumption are very common, which could be irrigated by reclaimed wastewater by

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CWs.

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Although CWs are listed in the Spanish reuse law (Decree, 2007) as adequate systems

90

to maintain the quality of reclaimed wastewater during storage, they are not considered

91

as suitable systems for secondary or tertiary treatment for further reuse. Conversely,

92

specific national guidelines of other countries such as China and Mexico, permit the use

93

of municipal wastewater treated with CWs for crop irrigation (Belmont et al., 2004;

94

Wang et al., 2005). In Spain, the only study developed in this field was conducted in

95

"Carrión de los Céspedes" (Seville), where urban wastewater was treated by a hybrid

96

CW system; the results showed that the effluents were suitable for some reuse

97

applications (Ávila et al., 2013).

98

This work is derived from a previously published case study in the same area where an

99

over-sized HF-CW treating domestic wastewater for discharge suitability was studied

100

and a new theoretical design was proposed (Andreo-Martínez et al., 2016). The focus of

101

interest of this case study was to provide more information and data about the potential

102

of HF-CWs in terms of domestic wastewaters treatment and its reuse in areas with water

103

shortages, like the Mediterranean arc. For this purpose, the quality of the domestic

104

wastewaters, from an isolated house located in the countryside of Elche (southeastern

105

Spain) reclaimed by a HF-CW fed with artificially aerated influent and filled with BFS,

106

were evaluated. The parameters were those set by the Spanish legislation for reusing

107

reclaimed wastewaters destined to agricultural use quality 2.1 (Decree, 2007).

108

2. Materials and methods

109

2.1 Constructed wetland and pretreatment design

110

The HF-CW system was located in the Southeast of Spain, in an isolated house of La

111

Marina -Elche- (Alicante, Spain) (38° 09' 23.5" N 0° 39' 54.6" W), with an altitude of

112

29.7 m above sea level. The climate of the area is typically dry Mediterranean with

113

mean annual temperature, rainfall and reference evapotranspiration (ETO) of 17.5 ± 1.4

114

°C, 240.0 ± 87.1 mm and 1138.6 ± 122.7 mm/m2, respectively, from 1999 until 2015

115

(IVIA, 2016).

116

Figure 1 shows a comprehensive section drawing of the improved HF-CW. The CW

117

consists of a pretreatment system and a HF-CW. The pretreatment system was a

118

decanter tank of 1000 l (Remosa, Barcelona, Spain). The HF-CW was fed through a 75

119

mm diameter PVC pipe. Feeding water was aerated intermittently (15 min every 60

120

min) through an air vent tube (21 mm diameter) placed inside the feeding pipe, with an

121

air flow of 50 l/min supplied by a SECOH SLL-40 air pump (Bibus, Pontevedra, Spain).

122

The HF-CW was designed to achieve 15 mg/l total nitrogen (TN) effluents, according to

123

Reed’s method (Reed et al., 1995). The effective area and depth were 8 m2 and 0.6 m,

124

respectively. The plant species used was native Phragmites australis (Cav.) Trin. ex

125

Steud with a density of 4 plants/m2. Volumetric flow meters were located in both inlet

126

and outlet of the HF-CW.

127

The filler material involved a 15 cm layer of BFS (2 cm particle size), obtained from a

128

nearby cement company and composed by 40% of CaO, 35% of SiO2, 8% of MgO,

129

12% of Al2O3, and less than 1% of other compounds such as S, FeO, MnO or TiO2, at

130

the bottom of the HF-CW. This layer was followed by a 45 cm layer of construction

131

sand (5 mm particle size) composed by ~80% of SiO, ~6% of CaO, ~5% of Al2O3, ~2%

132

of MgO and less than 1% of other compounds such as FeO, Fe2O3, Na2O or TiO2, as the

133

upper layer. The inlet and outlet structure were composed by gravel (5 cm particle size)

134

and BFS (1:1 volume ratio). The final effluent was collected in a storage tank for further

135

transport to WWTP.

136

Figure 1

137

138

139

2.2 Water sampling and monitoring

140

Wastewater samples were collected from the manholes located at inlet and outlet of the

141

HF-CW and analyzed in triplicate for a year. The parameters analyzed and sampling

142

frequencies are shown in Table 1. This corresponds to a 2.1 quality reclaimed

143

wastewater according to Decree (2007), which can be used to irrigate crops with water

144

application systems that allow direct reclaimed wastewater contact with edible parts of

145

plants for direct human consumption. In addition, temperature (T), pH, termotolerant

146

coliforms (TC), DO and redox potential (Eh) were also sampled weekly.

147

Table 1 (Decree, 2007)

148

2.2.1 Physicochemical analysis

149

Electrical conductivity (EC) and T were measured in situ with the multiparameter meter

150

HANNA HI 9835 (Hanna Instrument, Bedfordshire, UK). Dissolved oxygen was

151

measured using a portable dissolved oxygen meter HANNA HI 9146N (Hanna

152

Instrument, Bedfordshire, UK). Redox potential was measured with a CRISON

153

MICROpH 2000 ion meter using a platinum electrode CRISON 5057 (Hach Lange

154

Spain, L’Hospitalet de Llobregat, Spain). Total suspended solids (TSS) determination

155

followed the APHA 1989 method. A pH-meter CRISON-GLP21 (Hach Lange Spain,

156

L’Hospitalet de Llobregat, Spain) was used to measure pH. Biochemical oxygen

157

demand after five days (BOD5), chemical oxygen demand (COD), TN and total

158

phosphorus (TP) were determined using a photometer NANOCOLOR® 500D and the

159

rapid kits: 985 822, 985 029, 985 064 and 985 080, respectively (Macherey-Nagel

160

GmbH, Düren, Germany). Turbidity was measured following the ISO-7027 method,

161

using a turbidimeter Lovibond® model TurbiCheck (Tintometer GmbH, Dortmund,

162

Germany).

163

Metals and metalloids (B, As, Be, Cd, Co, Cr, Cu, Mn, Mo, Ni, Se and V) were

164

analyzed by inductively coupled plasma mass spectrometry using an Agilent 7500 a

165

device (Agilent Technologies, Santa Clara, CA, USA), following the USEPA-6020A

166

method. Inductively coupled plasma optical emission spectrometry was used to analyze

167

Na, Ca and Mg, following the USEPA-6010C method.

168

To calculate the sodium absorption ratio (SAR) value Richards equation (equation 1)

169

was used (Richards, 1954).

170

 meq  SAR  =  L 

[Na ] [Ca ]+ [Mg ] +

2+

(1)

2+

2

171

2.2.2 Microbiological analysis

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Escherichia coli (E. coli) and thermotolerant coliforms (TC) were determined using the

173

selective culture medium Rose-Gal BCIG (5-5-bromo-4-chloro-3-indolyl-β-D-

174

galactoside) (Bioser S.A., Barcelona, Spain), with incubation T of 44 ± 1 ºC for 24 ± 2 h

175

following the ISO-9308:1 method. E. coli was confirmed by means of the biochemical

176

identification test “Gallery EnteroPluri-Test” (Liofilmchem® S.r.l., Roseto degli

177

Abruzzi, Italy).

178

Detection and confirmation of Salmonella species was performed by polymerase chain

179

reaction technique (PCR) using a “PCR Applied Biosystems® 7500 Fast Real-Time”

180

device (Life Technologies S.A., Madrid, Spain) supplied with the “RapidFinderTM”

181

software. The kit used was prepSEQ® Rapid Spin Sample and microSEQ® Salmonella

182

species. Detection and enumeration of Legionella species was performed following the

183

ISO-11731-2 method. Finally, intestinal nematode eggs were identified by the modified

184

Bailenger method.

185

2.2.3 Pollutant percentage abatements, water balance and crop coefficient

186

The pollutant percentage abatements were evaluated according to equation 2 (Białowiec

187

et al., 2014):

188

Percentage abatement (%) =

(Cin x Qin ) − (C ef x Qef ) (Cin x Qin )

× 100

(2)

189

where Cin and Cef are the influent and the effluent concentration of a given pollutant

190

(mg/l, ppb or meq/l); Qin and Qef are the influent and the effluent flow (l).

191

The percentage abatements for turbidity and EC were evaluated according to equation 3

192

(Białowiec et al., 2014) as they lack volume units:

193

Percentage abatement (%) =

Pin − Pef Pin

×100

(3)

194

where Pin and Pef are the influent and the effluent value of a given parameter

195

(nephelometric turbidity units (NTU) or µS/cm).

196

Microorganism efficiency abatements were calculated following equation 4:

197

 CFU in Efficiency abatement = log10   CFU ef 

   

(4)

198

where CFUin and CFUef are the influent and the effluent microorganism counts (colony

199

forming units expresses as log10 CFU/100 ml).

200

HF-CW water balance was evaluated according to equation 5 (Headley et al., 2012) and

201

meteorological data were obtained from an agro-climatic weather station (IVIA, 2016)

202

located at about 5 Km from the HF-CW location.

203

ETCW = Qin + P − Qef

204

where ETcw is constructed wetland evapotranspiration (mm/m2·month); Qin is influent

205

flow (m3/month); P is precipitation (mm/m2·month) and Qef is effluent flow (m3/month).

206

HF-CW plant coefficient was obtained using equation 6 (Allen et al., 1998):

207

KCW =

208

where Kcw is constructed wetland crop coefficient (dimensionless).

209

3. Results and discussion

210

The HF-CW average daily influent flow rate was 0.21 m3 with a calculated hydraulic

211

retention time (HRT) of 8.70 days and a hydraulic loading rate (HLR) of 2.62 cm/day

212

(assuming a CW bed media porosity of 0.38).

213

The influent aeration conditions were the optimal to keep an average DO and Eh of 9.1

214

± 0.9 mg/l and 125 ± 36 mV, respectively. Average DO in the effluents was 0.25 ± 0.1

215

mg/l with Eh of -168 ± 51 mV. These conditions provided temporal/spatial aerobic and

216

anaerobic conditions in the same environment.

217

It is noteworthy that the percentage abatement calculated in this case study are higher

218

than the others reported in the literature because it has been proven that percentage

ETCW ETO

(5)

(6)

219

abatement calculated by comparison between initial and final concentration is

220

significantly lower than the those calculated by mass balance (Białowiec et al., 2014).

221

3.1. Organic matter abatement

222

BOD5 and COD concentration values in HF-CW influents and effluents as well as their

223

legal limits are shown in Fig. 2. The average percentage abatements were 97.8 ± 1.2%

224

for BOD5 and 92.7 ± 3.7% for COD, with a minimum of 96.3 ± 1.9% and 87.8 ± 2.6%

225

in November 2014, respectively. The maximum BOD5 and COD percentage abatement

226

were 99.7 ± 1.5% and 99.1 ± 1.4% in July 2014, respectively.

227

Average concentration values in the effluent for BOD5 and COD were 16.5 ± 3.3 mg/l

228

and 100.3 ± 12.6 mg/l, respectively. BOD5 and COD concentration values in June 2014

229

were higher than their legal limit values (see Fig. 2) however, their percentage

230

abatements, above 75%, allowed these two parameters to meet the Spanish legal

231

requirements for reclaimed wastewaters reuse.

232

Figure 2

233

These high effluent values may be due to the fact that during the beginning of the HF-

234

CW activity, the biofilm, largely responsible for the organic matter abatement

235

processes, was not yet fully developed. A way to promote biofilm development can be

236

the use of a systems fed with aerated influents because the long organic matter chains

237

can be partially or fully hydrolyzed before entry into the system (Rossmann et al.,

238

2013).

239

As expected, BOD5 and COD percentage abatements found in this case study were very

240

high, in line with previously reported results for the same area and also for other

241

Mediterranean areas (Andreo-Martínez et al., 2016). This fact shows that these systems

242

do not present major problems regarding organic matter abatement under these climate

243

conditions. On the other hand, Rossmann et al. (2013) reported that aerated influents did

244

not affect organic matter abatement efficiencies when they studied a HF-CW feed with

245

aerated coffee processing wastewater.

246

BOD5/COD mean ratio decreased from 0.53 in the influent to 0.16 in the effluents. This

247

fact proves that HRT utilized (8.7 d) was enough to abate both parameters because

248

organic matter was longer exposed to bacterial community and their enzymes together

249

with the physical processes of sedimentation and filtration (Rossmann et al., 2013).

250

3.2. Particulate matter abatement

251

Fig. 3 shows the evolution of TSS and turbidity values for both influent and effluent and

252

also their legal limits. The TSS average percentage abatement was 97.5 ± 1.3%. The

253

maximum TSS percentage abatement of 99.8 ± 1.7% was reached in July 2014 (week 3

254

and 4); while the minimum (94.9 ± 1.5%) was found in January 2015 (week 3). The

255

average turbidity percentage abatement was 99.5 ± 0.3%. The maximum turbidity

256

percentage abatement of 99.8% was found 6 times: August 2014 (week 1 to 3),

257

September 2014 (week 1), October 2014 (week 1) and January 2015 (week 1); while the

258

minimum of 98.4 ± 0.4% was found in June 2014 (week 1).

259

Figure 3

260

The first 5-6 samples (June-July 2014) for TSS and turbidity showed higher values in

261

the effluents than the rest of the samples (see Fig. 3), as it happened with organic

262

matter. This fact can be explained by the bed filler media washing which produced the

263

appearance of particulate matter in the effluent during this stage. Nevertheless, these

264

values did not prevent the compliance with the Spanish legislation for reclaimed

265

wastewater reuse.

266

Turbidity and TSS abatement in HF-CWs occur mostly through physical mechanisms

267

like filtration and sedimentation. These processes, in turn, increase their effectiveness

268

with increasing HRT. In this way, both macrophyte roots and substrate, by reducing the

269

water speed, promotes these processes and reach high percentage abatements (> 90%),

270

just like the results obtained in this case study and those of other authors (Andreo-

271

Martínez et al., 2016; Ávila et al., 2013). As in the case of organic matter, HF-CW does

272

not present major problems regarding particulate matter abatement under Mediterranean

273

climate conditions.

274

Artificial influent aeration can also improve TSS and turbidity abatement in HF-CW

275

since aerobic conditions allow the development of a protozoan community. Protozoa,

276

particularly ciliated protozoa, have been documented to reduce turbidity in water by

277

heavily grazing suspended unicellular bacteria (Tunçsiper et al., 2015). In this sense,

278

Rossmann et al. (2013) reported that turbidity values in non-aerated influents were 31%

279

greater than those of aerated ones.

280

3.3 Water balance of the system

281

Table 2 shows the HF-CW water balance and crop coefficients throughout the case

282

study. Because 37.1% of influent domestic wastewater (30.8 m3) was lost by

283

evapotranspiration (ET), 62.9% of reclaimed domestic wastewater (52.2 m3) could have

284

been destined for reuse. Phragmites australis KCW showed higher values in summer

285

months than in winter months.

286

Table 2

287

These data are about half of those reported for other CWs planted within Phragmites

288

australis with a density of 8 plants/m2 under dry Mediterranean areas (Sicily) (Borin et

289

al., 2011; Milani and Toscano, 2013). Milani and Toscano (2013) reported a high

290

correlation between KCW, total leaves and stem density indicating interdependency

291

between the crop coefficient and leaf area index, hence, our planting density (4

292

plants/m2) can be the explanation for KCW values found in this case study. On the other

293

hand, Qef values found in July and August of 2014 were 0.36 and 0.74 m3, respectively.

294

This indicated that ET and KCW are parameters that should be taken into account for

295

HF-CW design in dry climates to avoid bed desiccation episodes, as reported by

296

Andreo-Martínez et al. (2016) when they studied an over-sized HF-CW of 27 m2 in the

297

same area.

298

3.4 Electrical conductivity and sodium adsorption ratio abatement.

299

Fig. 4 shows EC and SAR values in influent and effluent wastewaters of HF-CW and

300

their legal limit values. Effluents showed higher EC and SAR values than influents and,

301

therefore, negative percentage abatements were achieved for EC parameters (calculated

302

by comparison between initial and final concentration). However, percentage

303

abatements for SAR were positive because they were calculated by mass balance.

304

Besides, values for EC and SAR above legal limit for reuse in July and August 2014

305

were found. This fact may be caused by the high ETcw as discussed before. Effluent EC

306

increase in arid or semi-arid climates has also been reported by several authors (Ammari

307

et al., 2014; Andreo-Martínez et al., 2016; Freedman et al., 2014). The process of ET

308

reduces the volume of water and increases the concentration of salt in the water, mainly

309

responsible for EC and SAR increase. In this sense, Freedman et al. (2014) reported that

310

in arid and semi-arid climates, excess salinity poses an additional problem to the

311

common concerns of nutrients and pathogens, which all need to be addressed during the

312

treatment. The decrease of HRT could eliminate the problems of salinity and

313

concentration derived from ET but good percentage abatements obtained for other

314

parameters would be affected. On the other hand, a HF-CW with higher HRT (12 d),

315

located in southeastern Brazil (altitude tropical climate), achieved lower EC in the

316

effluents than in the influents due to the precipitation of salts and their absorption by

317

plants and microorganisms (Rossmann et al., 2013).

318

Figure 4

319

Further, HF-CW influents already presented high average EC (2481 ± 67 µS/cm)

320

leaving little scope for ET effect that does not increase effluent conductivity above the

321

legal limit (3000 µS/cm). The solution to this problem is complicated considering that

322

the average EC of water supply was 1500 ± 55 µS/cm and EC reduction in water supply

323

can help to solve the problem of high EC in influent wastewater. The water supply

324

company is working in this sense by mixing drinking water from different sources. In

325

any case, further research is needed in this regard as the use of macrophytes and/or

326

halophytes with lower KCW (Liang et al., 2017).

327

3.5 Nutrients abatement

328

3.5.1 Total Nitrogen abatement

329

Fig. 5a shows TN values in HF-CW influents and effluents and its legal limit value.

330

Total nitrogen average percentage abatement was 91.5 ± 5.3%. The legal limit (15 mg/l)

331

was exceeded on several occasions but the percentage abatements remained above 75%,

332

in all cases, provided effluents consistent with the Spanish law.

333

Figure 5

334

Some seasonality was also observed which can be due to the fact that P. australis is a

335

perennial macrophyte that usually shows a distinct seasonal cycle (Saeed and Sun,

336

2012). Other authors have also reported this effect (Akratos and Tsihrintzis, 2007;

337

Zhang et al., 2017). In addition, P. australis provides oxygen to the HF-CW bed,

338

allowing the more active and diverse biofilm development near the rhizosphere and

339

improving the aerobic/anaerobic condition for TN abatement (Rossmann et al., 2012).

340

Besides plants, microorganisms responsible for TN abatement optimally function at T

341

above 15 °C (Saeed and Sun, 2012). This T was exceeded in all cases in the effluents

342

except in December 2014 (13.4 °C). November 2014 (15.5 °C) and January 2015 (15.0

343

°C) showed T near to 15 °C, therefore microbial activity can also be affected in winter.

344

With respect to pH, there should not be problems to carry out TN abatement reactions;

345

for example ammonification requires a pH range between 6.5 and 8.5 (Saeed and Sun,

346

2012) and the average pH in effluents was 7.6 ± 0.2. Further, the average influent C/N

347

ratio of 6.7, (> 5.0), allowed enough organic carbon source for denitrification process

348

(He et al., 2016; Li et al., 2014).

349

Aerated influent together with plant effect and large HRT appears to be an effective

350

method to improve TN abatement by providing alternate aerobic (influent and close to

351

HF-CW rhizosphere) and anaerobic (HF-CW bed far from rhizosphere) conditions and

352

also enough wastewater-HF-CW bed contact time for the simultaneously occurring

353

nitrification and denitrification processes, as reported by Rossmann et al. (2012). Those

354

same authors reported a lower average TN abatement value (69.1 ± 4.6%), using a

355

higher HRT (12 d), than the achieved in this case study. This fact can be explained by

356

the different meteorology between Brazil and Spain, as discussed in section 3.4.

357

On the other hand, with regard to system size, the average TN concentration in the

358

effluents was 16.1 ± 3.3 mg/l while the HF-CW was designed to obtain 15 mg/l TN

359

effluents. This fact provided an acceptable design of HF-CW for Mediterranean

360

climates following Reed’s method (Reed et al., 1995) combined with influent aeration.

361

3.5.2 Total Phosphorus abatement

362

Fig. 5b shows TP concentration values in HF-CW influents and effluents and its legal

363

limit value. Total phosphorus average percentage abatement was 96.9 ± 1.7% and TP

364

effluent values were below Spanish legal limit (2 mg/l).

365

Total phosphorus abatement includes chemical mechanisms (absorption, complex

366

formation with Ca and Mg ions, precipitation with Fe, Al and Ca ions), and biological

367

mechanisms such as microbial and plant assimilation. In this sense, the aerated influent

368

can help the development of microorganisms responsible for phosphorus

369

immobilization (Rossmann et al., 2012) and the BFS and, as has a great amount of the

370

aforementioned ions, it can also improve phosphorus immobilization. Further,

371

according to Vohla et al. (2011) the mean effluent pH found in this case study (7.6 ±

372

0.2) was optimal for phosphorus abatement.

373

The average effluent values found in this case study were very low (1.0 ± 0.1 mg/l),

374

proves the effectiveness of both BFS and aerated influent to abate TP. Andreo-Martínez

375

et al. (2016) reported that a 27 m2 HF-CW with a HRT of 22.6 d, located in the same

376

area, achieved higher TP effluent values (3.2 ± 0.4 mg/l) during the first year of study.

377

Rossmann et al. (2012) found an average TP abatement of 72.1 ± 9.5% in a HF-CW fed

378

with aerated influent and a HRT of 12 d. Further, an hybrid system composed by a

379

vertical flow CW followed by a HF-CW and a free water surface CW, studied in Seville

380

(Spain), achieved TP effluents values similar to those found in this case study using

381

only one HF-CW, but with a lower percentage abatement (57.1%) (Ávila et al., 2013).

382

On the other hand, if TP abatement would have been the criteria used to calculate the

383

HF-CW surface it would have resulted in a surface of 20.4 m2, 2.5 times greater than

384

that obtained considering TN abatement. This implies an increase in the price of

385

building the system and a risk related with desiccation of HF-CW bed in summer (Table

386

2). Therefore, the choice of sizing the system taking into account TN abatement rather

387

than TP abatement is preferable, in view of the good results obtained in this case study.

388

3.6 Metals and metalloids abatement

389

Table 3 shows metals and metalloids average values in the influents and the effluents

390

and their percentage abatements. It is noteworthy that the metals and metalloids

391

concentrations found in the influents, except for boron in certain samples, were below

392

the limits set by Spanish law for reuse (Table 1). Boron may appear in domestic

393

wastewaters from detergents, cleaning products or soaps (Türker et al., 2014). Selenium

394

and beryllium were not detected. In general, metals and metalloids do not constitute a

395

major problem in wastewaters from scattered houses or small villages without industrial

396

activity (Vymazal, 2005).

397

Table 3

398

The concentrations of all metals and metalloids in the effluents were lower than the

399

legal limit values. Percentage abatements varied between 100.0 ± 0.0% for Cd and 52.7

400

± 28.0% for Co during the case study. There are not many experimental data regarding

401

metals and metalloids abatement in domestic wastewaters because, as discussed above,

402

the concentrations are so low that they do not represent a significant risk factor.

403

Nevertheless, CWs also have been effective, as phytoremediation, for the treatment of

404

wastewater from very contaminant activities such as mining, having reached percentage

405

abatements up to 100% for Al, Cd, Cu, Mn, Pb or Zn (Sheoran and Sheoran, 2006).

406

3.7 Microorganisms abatement

407

3.7.1 Escherichia coli and thermotolerant coliforms abatement

408

Escherichia coli and TC count values in the influents and the effluents as well as the E.

409

coli legal limit value are shown in Fig. 6. Thermotolerant coliforms counts showed

410

mean values in the influents and the effluents of 6.4 ± 0.1 and 2.9 ± 0.1 log10 CFU/100

411

ml, respectively, with an average efficiency abatement of 3.5 ± 0.2 log10 CFU/100 ml.

412

Thermotolerant coliforms counts are not set by Spanish law for reclaimed wastewater

413

reuse but the good percentage abatement obtained, similar to those reported by Tanner

414

et al. (1995), also demonstrated the HF-CWs ability to abate pathogenic

415

microorganisms.

416

Escherichia coli counts showed a mean value of 5.1 ± 0.1 log10 CFU/100 ml in the

417

influents, but the effluents were free of E. coli from the first operation month; and even

418

the legally established values were achieved from the second week.

419

In scientific literature there are not many systems that achieve total E. coli abatement

420

without using external chemical agents or the application of other disinfectants such as

421

ultraviolet light (Azaizeh et al., 2013). Nevertheless, Baeder-Bederski et al. (2005)

422

achieved an efficiency abatement of 5 log10 CFU/100 ml for E. coli in a hybrid system

423

(HF-CW followed by vertical flow CW) and Ávila et al. (2013) also reported the same

424

efficiency abatement for E. coli in a different hybrid system configuration

425

aforementioned. These results are similar to those found in this case study using only an

426

improved HF-CW.

427

Figure 6

428

With respect to artificial aeration, it appears to be a promising approach since Headley

429

et al. (2013) reported efficiency abatements of 3.3 log10 CFU/100 ml for E. coli in an

430

artificially aerated HF-CW whereas for non-aerated systems efficiency abatements of

431

1.4 log10 CFU/100 ml were reported. This may have originated in that, apart from the

432

physical E. coli abatement processes in HF-CWs, biological processes exist such as

433

bacterial predation or competition with other microorganisms such as bacteria and

434

protozoa. In this sense, artificial aeration can create the optimum conditions for the

435

growth of bacteria and protozoa to exercise effective competition against E. coli.

436

3.7.2 Salmonella, intestinal nematode eggs and Legionella abatements

437

The results for Salmonella and intestinal nematode eggs in the influents were negative

438

and, therefore, were also negative in the effluents. This fact provided suitable effluents

439

for reuse. With respect to these two pathogens behavior in HF-CW, the abatement

440

mechanisms for Salmonella must be the same as for E. coli, achieving efficiency

441

abatements of 3.2 log10 CFU/100 ml (Hench et al., 2003). The abatement mechanisms

442

of intestinal nematode eggs are filtering through the substrate and adhesion with the

443

macrophyte roots, usually being eliminated in the first quarter of the HF-CW (Stott et

444

al., 1999).

445

As Legionella may appear in the water supply with counts ranging from 1 to 3.8 log10

446

CFU/1000 ml (Rodríguez-Martínez et al., 2015), water supply sampling was also

447

performed. Legionella in water supply was found in summer months with an average

448

count of 2.0 ± 0.1 log10 CFU/1000 ml. However, Legionella counts in the influents and

449

the effluents throughout this case study were negative, providing suitable effluents for

450

reuse. Birks et al. (2004) reported Legionella pneumophila counts between 3.2 and 3.9

451

log10 CFU/1000 ml in grey water (GW) of Thames water recycling plant (London).

452

Interestingly, they did not detect it again in GW from another location (Birks and Hills,

453

2007). On the other hand, Blanky et al. (2015) found Legionella count of 5.1 log10

454

CFU/1000 ml in GW using an adjusted ISO-11731-2 based protocol developed by them.

455

Constructed wetlands ability to abate Legionella has been little studied. Legionella

456

species life cycle is complex and it is capable of existing in water with varied T (from

457

20 to 50 °C), pH levels and oxygen contents. In water, Legionella survives

458

planktonically and in biofilms it lives and replicates within protozoa (its natural host)

459

(Blanky et al., 2015). In this sense, assisted aeration influent can help to develop

460

protozoa and, hence, Legionella development can be affected positively. On the other

461

hand, assisted aeration can also help to develop other bacterial species like

462

Pseudomonas aeruginosa (Blanky et al., 2015) and Legionella counts in CWs can be

463

affected negatively by bacterial competition. In any case, due to Legionella colonies

464

absence in both influents and effluents HF-CW and the lack of Pseudomonas analysis in

465

this case study, further studies on Legionella occurrence in CWs world-wide are

466

needed.

467

4. Conclusions

468

In this case study it was shown that an improved HF-CW located in Mediterranean

469

climate, fed with aerated domestic wastewater and filled with BFS, produced effluents

470

consistent with Spanish law for reclaimed wastewater reuse, as agricultural quality 2.1,

471

except for EC and SAR in summer due to the high evapotranspiration. Decreasing EC in

472

water supply or using macrophytes with lower water uptake can solve this problem.

473

Artificial aeration provided enhancements with respect to turbidity, TSS, TN and E. coli

474

abatement while BFS and aeration improved TP abatement. The improved HF-CW

475

effectiveness was similar or better than some hybrid systems.

476

Acknowledgments

477

The authors would to thank the company Biogxido S.L. since this work is derived from

478

a consultancy on “Water purification system by a combined phytodepuration-

479

fitoevapotranspiración” under contract for technology support and/or counseling from

480

the University of Murcia and the company Biogxido S.L. The authors also would like to

481

thank Ms. Seonaid McNabb for her English revision.

482

Conflict of Interest

483

The authors declare that they have no conflict of interest.

484

References

485 486 487 488 489 490 491 492 493 494 495 496 497

1. Akratos, C.S., Tsihrintzis, V.A., 2007. Effect of temperature, HRT, vegetation and porous media on removal efficiency of pilot-scale horizontal subsurface flow constructed wetlands. Ecol. Eng., 29 (2), 173-191. 2. Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration Guidelines for computing crop water requirements. FAO Irrigation and drainage paper 56. Food and Agriculture Organization of the United Nations, Rome. 3. Ammari, T.G., Al-Zu’bi, Y., Al-Balawneh, A., Tahhan, R., Al-Dabbas, M., Ta’any, R.A., Abu-Harb, R., 2014. An evaluation of the re-circulated vertical flow bioreactor to recycle rural greywater for irrigation under arid Mediterranean bioclimate. Ecol. Eng., 70, 16-24. 4. Andreo-Martínez, P., García-Martínez, N., Almela, L., 2016. Domestic Wastewater Depuration Using a Horizontal Subsurface Flow Constructed

498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545

Wetland and Theoretical Surface Optimization: A Case Study under Dry Mediterranean Climate. Water, 8 (10), 434. 5. Ávila, C., Salas, J.J., Martín, I., Aragón, C., García, J., 2013. Integrated treatment of combined sewer wastewater and stormwater in a hybrid constructed wetland system in southern Spain and its further reuse. Ecol. Eng., 50 (0), 13-20. 6. Ayaz, S.Ç., Aktaş, Ö., Akça, L., Fındık, N., 2015. Effluent quality and reuse potential of domestic wastewater treated in a pilot-scale hybrid constructed wetland system. J. Environ. Manage., 156, 115-120. 7. Azaizeh, H., Linden, K.G., Barstow, C., Kalbouneh, S., Tellawi, A., Albalawneh, A., Gerchman, Y., 2013. Constructed wetlands combined with UV disinfection systems for removal of enteric pathogens and wastewater contaminants. Water Sci. Technol., 67 (3), 651-7. 8. Baeder-Bederski, O., Dürr, M., Borneff-Lipp, M., Kuschk, P., Netter, R., Daeschlein, G., Mosig, P., Müller, R.A., 2005. Retention of Escherichia coli in municipal sewage by means of planted soil filters in two-stage pilot plant systems. Water Sci. Technol., 51 (9), 205-12. 9. Belmont, M.A., Cantellano, E., Thompson, S., Williamson, M., Sánchez, A., Metcalfe, C.D., 2004. Treatment of domestic wastewater in a pilot-scale natural treatment system in central Mexico. Ecol. Eng., 23 (4-5), 299-311. 10. Białowiec, A., Albuquerque, A., Randerson, P.F., 2014. The influence of evapotranspiration on vertical flow subsurface constructed wetland performance. Ecol. Eng., 67, 89-94. 11. Birks, R., Colbourne, J., Hills, S., Hobson, R., 2004. Microbiological water quality in a large in-building, water recycling facility. Water Sci. Technol., 50 (2), 165-72. 12. Birks, R., Hills, S., 2007. Characterisation of indicator organisms and pathogens in domestic greywater for recycling. Environ. Monit. Assess., 129 (1-3), 61-9. 13. Blanky, M., Rodríguez-Martínez, S., Halpern, M., Friedler, E., 2015. Legionella pneumophila: From potable water to treated greywater; quantification and removal during treatment. Sci. Total Environ., 533, 557-565. 14. Borin, M., Milani, M., Salvato, M., Toscano, A., 2011. Evaluation of Phragmites australis (Cav.) Trin. evapotranspiration in Northern and Southern Italy. Ecol. Eng., 37 (5), 721-728. 15. Decree, R., 2007. Royal Decree 1620/2007, of 7 December, which set the legal framework for the reuse of treated wastewater. BOE num. 294. Madrid, Spain. http://www.boe.es/boe/dias/2007/12/08/pdfs/A50639-50661.pdf (in Spanish). 16. Fan, J., Zhang, B., Zhang, J., Ngo, H.H., Guo, W., Liu, F., Guo, Y., Wu, H., 2013. Intermittent aeration strategy to enhance organics and nitrogen removal in subsurface flow constructed wetlands. Bioresour. Technol., 141, 117-122. 17. Freedman, A., Gross, A., Shelef, O., Rachmilevitch, S., Arnon, S., 2014. Salt uptake and evapotranspiration under arid conditions in horizontal subsurface flow constructed wetland planted with halophytes. Ecol. Eng., 70, 282-286. 18. Garcia, X., Pargament, D., 2015. Reusing wastewater to cope with water scarcity: Economic, social and environmental considerations for decisionmaking. Resour. Conserv. Recycl., 101, 154-166. 19. Gross, A., Shmueli, O., Ronen, Z., Raveh, E., 2007. Recycled vertical flow constructed wetland (RVFCW)-a novel method of recycling greywater for irrigation in small communities and households. Chemosphere, 66 (5), 916-923.

546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593

20. He, Y., Wang, Y., Song, X., 2016. High-effective denitrification of low C/N wastewater by combined constructed wetland and biofilm-electrode reactor (CW–BER). Bioresour. Technol., 203, 245-251. 21. Headley, T., Nivala, J., Kassa, K., Olsson, L., Wallace, S., Brix, H., van Afferden, M., Müller, R., 2013. Escherichia coli removal and internal dynamics in subsurface flow ecotechnologies: Effects of design and plants. Ecol. Eng., 61, Part B, 564-574. 22. Headley, T.R., Davison, L., Huett, D.O., Müller, R., 2012. Evapotranspiration from subsurface horizontal flow wetlands planted with Phragmites australis in sub-tropical Australia. Water Res., 46 (2), 345-354. 23. Hench, K.R., Bissonnette, G.K., Sexstone, A.J., Coleman, J.G., Garbutt, K., Skousen, J.G., 2003. Fate of physical, chemical, and microbial contaminants in domestic wastewater following treatment by small constructed wetlands. Water Res., 37 (4), 921-927. 24. Iglesias, R., Ortega, E., Batanero, G., Quintas, L., 2010. Water reuse in Spain: Data overview and costs estimation of suitable treatment trains. Desalination, 263 (1–3), 1-10. 25. IVIA, 2016. IVIA irrigation, metereological data. http://riegos.ivia.es/datosmeteorologicos. Accessed: 19.03.2016 (in Spanish). 26. Li, F., Lu, L., Zheng, X., Ngo, H.H., Liang, S., Guo, W., Zhang, X., 2014. Enhanced nitrogen removal in constructed wetlands: Effects of dissolved oxygen and step-feeding. Bioresour. Technol., 169, 395-402. 27. Liang, Y., Zhu, H., Bañuelos, G., Yan, B., Zhou, Q., Yu, X., Cheng, X., 2017. Constructed wetlands for saline wastewater treatment: A review. Ecol. Eng., 98, 275-285. 28. Milani, M., Toscano, A., 2013. Evapotranspiration from pilot-scale constructed wetlands planted with Phragmites australis in a Mediterranean environment. J. Environ. Sci. Health, Pt. A: Toxic/Hazard. Subst. Environ. Eng., 48 (5), 568580. 29. Morari, F., Giardini, L., 2009. Municipal wastewater treatment with vertical flow constructed wetlands for irrigation reuse. Ecol. Eng., 35 (5), 643-653. 30. Nivala, J., Hoos, M.B., Cross, C., Wallace, S., Parkin, G., 2007. Treatment of landfill leachate using an aerated, horizontal subsurface-flow constructed wetland. Sci. Total Environ., 380 (1–3), 19-27. 31. Puigagut, J., Villaseñor, J., Salas, J.J., Bécares, E., García, J., 2007. Subsurfaceflow constructed wetlands in Spain for the sanitation of small communities: A comparative study. Ecol. Eng., 30 (4), 312-319. 32. Reed, S.C., Crites, R.W., Middlebrooks, E.J., 1995. Natural systems for waste management and treatment, 2nd Ed. McGraw-Hill, New York, USA. 33. Richards, L.R.S.L., 1954. Diagnosis and improvement of saline and alkali soils. U.S.G.P.O., Washington DC, USA. 34. Rodríguez-Martínez, S., Sharaby, Y., Pecellín, M., Brettar, I., Höfle, M., Halpern, M., 2015. Spatial distribution of Legionella pneumophila MLVAgenotypes in a drinking water system. Water Res., 77, 119-132. 35. Rossmann, M., de Matos, A.T., Abreu, E.C., e Silva, F.F., Borges, A.C., 2012. Performance of constructed wetlands in the treatment of aerated coffee processing wastewater: Removal of nutrients and phenolic compounds. Ecol. Eng., 49, 264-269.

594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639

36. Rossmann, M., Matos, A.T., Abreu, E.C., Silva, F.F., Borges, A.C., 2013. Effect of influent aeration on removal of organic matter from coffee processing wastewater in constructed wetlands. J. Environ. Manage., 128, 912-919. 37. Ruiz-Arnáiz, G., 2006. Régimen urbanístico del suelo rústico: en especial, la construcción de viviendas. La Ley S.A., Madrid, Spain. 38. Saeed, T., Sun, G., 2012. A review on nitrogen and organics removal mechanisms in subsurface flow constructed wetlands: Dependency on environmental parameters, operating conditions and supporting media. J. Environ. Manage., 112 (0), 429-448. 39. Sheoran, A.S., Sheoran, V., 2006. Heavy metal removal mechanism of acid mine drainage in wetlands: A critical review. Miner. Eng., 19 (2), 105-116. 40. Sowers, J., Vengosh, A., Weinthal, E., 2011. Climate change, water resources, and the politics of adaptation in the Middle East and North Africa. Clim. Change, 104 (3-4), 599-627. 41. Stott, R., Jenkins, T., Bahgat, M., Shalaby, I., 1999. Capacity of constructed wetlands to remove parasite eggs from wastewaters in Egypt. Water Sci. Technol., 40 (3), 117-123. 42. Tanner, C.C., Clayton, J.S., Upsdell, M.P., 1995. Effect of loading rate and planting on treatment of dairy farm wastewaters in constructed wetlands—I. Removal of oxygen demand, suspended solids and faecal coliforms. Water Res., 29 (1), 17-26. 43. Tunçsiper, B., Drizo, A., Twohig, E., 2015. Constructed wetlands as a potential management practice for cold climate dairy effluent treatment — VT, USA. CATENA, 135, 184-192. 44. Türker, O.C., Vymazal, J., Türe, C., 2014. Constructed wetlands for boron removal: A review. Ecol. Eng., 64 (0), 350-359. 45. Vohla, C., Kõiv, M., Bavor, H.J., Chazarenc, F., Mander, Ü., 2011. Filter materials for phosphorus removal from wastewater in treatment wetlands—A review. Ecol. Eng., 37 (1), 70-89. 46. Vymazal, J., 2005. Removal of heavy metals in a horizontal sub-surface flow constructed wetland. J Environ Sci Health A Tox Hazard Subst Environ Eng, 40 (6-7), 1369-79. 47. Vymazal, J., 2007. Removal of nutrients in various types of constructed wetlands. Sci. Total Environ., 380 (1–3), 48-65. 48. Wang, X., Bai, X., Qiu, J., Wang, B., 2005. Municipal wastewater treatment with pond-constructed wetland system: A case study. Water Sci. Technol., 51 (12), 325-329. 49. Zhang, D.Q., Jinadasa, K.B.S.N., Gersberg, R.M., Liu, Y., Ng, W.J., Tan, S.K., 2014. Application of constructed wetlands for wastewater treatment in developing countries – A review of recent developments (2000–2013). J. Environ. Manage., 141, 116-131. 50. Zhang, J., Sun, H., Wang, W., Hu, Z., Yin, X., Ngo, H.H., Guo, W., Fan, J., 2017. Enhancement of surface flow constructed wetlands performance at low temperature through seasonal plant collocation. Bioresour. Technol., 224, 222228.

640

Figure Captions

641

Fig. 1 Section drawing of the improved horizontal subsurface flow constructed wetland

642

(HF-CW).

643

Fig. 2 (a) Evolution of biological oxygen demand after five days (BOD5) in the

644

influents (left ordinates axis) and the effluents (right ordinates axis) of the horizontal

645

subsurface flow constructed wetland (HF-CW) and its legal limit; (b) Evolution of

646

chemical oxygen demand (COD) in the influents (left ordinates axis) and the effluents

647

(right ordinates axis) of the HF-CW and its legal limit.

648

Fig. 3 (a) Evolution of total suspended solids (TSS) in the influents (left ordinates axis)

649

and the effluents (right ordinates axis) of the horizontal subsurface flow constructed

650

wetland (HF-CW) and its legal limit; (b) Evolution of turbidity in the influents (left

651

ordinates axis) and the effluents (right ordinates axis) of the HF-CW and its legal limit.

652

Fig. 4 (a) Evolution of electrical conductivity (EC) in the influents (left ordinates axis)

653

and the effluents (right ordinates axis) of the horizontal subsurface flow constructed

654

wetland (HF-CW) and its legal limit; (b) Evolution of sodium absorption rate (SAR) in

655

the influents (left ordinates axis) and the effluents (right ordinates axis) of the HF-CW

656

and its legal limit.

657

Fig. 5 (a) Evolution of total nitrogen (TN) in the influents (left ordinates axis) and the

658

effluents (right ordinates axis) of the horizontal subsurface flow constructed wetland

659

(HF-CW) and its legal limit; (b) Evolution of total phosphorus (TP) in the influents (left

660

ordinates axis) and the effluents (right ordinates axis) of the HF-CW and its legal limit.

661

Fig. 6 Evolution of Escherichia coli (E. coli) and thermotolerant coliforms (TC) in the

662

influents and the effluents of the horizontal subsurface flow constructed wetland (HF-

663

CW) and E. coli legal limit.

664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683

684

Tables and Figures

685

Table 1

686 687

Spanish guidelines for reclaimed wastewater reuse as agricultural quality 2.1(Decree, 2007) Parameters

Sampling Frequency

Legal limit

Intestinal nematode eggs (eggs/10 l)

fortnightly

1

Escherichia coli (CFU/100 ml)

weekly

100

Total suspended solids (mg/l)

weekly

20

Turbidity (NTU)

weekly

10

Legionella (log CFU/l)

monthly

3

Salmonella (Presence/Absence)

monthly

Absence

Electrical conductivity (µS/cm)

monthly

3000

Sodium adsorption ratio (meq/l)

monthly

6

Metals and metalloids

Monthly

Boron (µg/l)

500

Arsenic (µg/l)

100

Beryllium (µg/l)

100

Cadmium (µg/l)

10

Cobalt (µg/l)

50

Chrome (µg/l)

100

Copper (µg/l)

200

Manganese (µg/l)

200

Molybdenum (µg/l)

10

Nickel (µg/l)

200

Selenium (µg/l)

20

Vanadium (µg/l)

100

% Abatement

70

Other parameters included for agricultural use quality 2.1 in sensitive areas

688 689 690 691 692

BOD5 (mg/l)

Monthly

25

75

COD (mg/l)

Monthly

125

75

Total Nitrogen (mg/l)

Monthly

15

70

Total phosphorus (mg/l)

Monthly

2

80

693

Table 2

694

Monthly HF-CW water balance and crop coefficient. Year Month 2014 June July August September October November December 2015 January February March April May June

Qin (m3) 6.36 6.55 6.58 6.33 6.48 6.25 6.45 6.51 5.89 6.47 6.24 6.54 6.41

Qef (m3) 2.43 0.36 0.74 3.68 5.02 5.86 6.36 6.12 5.30 5.77 4.88 3.55 1.97

P (mm/m2) 3.90 0.00 0.70 35.7 9.90 24.6 36.00 8.40 5.10 19.9 3.20 0.50 2.30

ETCW (mm/m2) 494.74 773.43 730.76 367.44 192.43 72.99 46.81 57.60 79.01 107.63 173.42 373.89 543.15

ETO (mm/m2 ) 163.82 184.59 162.03 118.53 82.59 48.02 39.01 48.81 64.76 86.10 109.76 161.16 179.85

KCW 3.02 4.19 4.51 3.10 2.33 1.52 1.20 1.18 1.22 1.25 1.58 2.32 3.10

695

696 697

Table 3

698 699

HF-CW metals and metalloids concentrations in the influent and the effluent, percentage abatements and legal limit value.

700

Metals and metalloids

Influent (µg/l)

Effluent (µg/l)

% Abatement

B

521.2 ± 76.8

370.6 ± 62.8

55.2 ± 22.6

As

3.0 ± 0.4

1.9 ± 0.6

57.0 ± 22.4

Be

nd*

nd*

Cd

0.4 ± 0.3

nd*

100.0 ± 0.0

Co

1.3 ± 0.2

1.0 ± 0.3

52.7 ± 28.0

Cr

18.0 ± 10.6

8.0 ± 5.3

71.1 ± 18.7

Cu

2.9 ± 0.9

2.0 ± 0.4

55.9 ± 23.2

Mn

54.0 ± 10.9

26.7 ± 10.0

68.6 ± 18.1

Mo

2.0 ± 0.4

1.4 ± 0.3

55.1 ± 27.1

Ni

16.8 ± 5.8

8.3 ± 4.4

68.4 ± 18.1

Se

nd*

nd*

V

4.2 ± 2.1

1.3 ± 0.4

*nd: not detected

74.2 ± 20.8

701 702

703 704 705 706 707 708 709 710 711 712 713

Fig. 1

714

Fig. 2

715

(a)

716

(b)

717 718

719 720

721

Fig. 3

722

(a)

723 724

(b)

725 726 727

728

Fig. 4

729

(a)

730

(b)

731 732 733 734 735

736

Fig. 5

737

(a)

738 739

740 741

742 743

744 745

746 747 748 749 750 751 752 753 754 755 756

Fig. 6

Graphical Abstract