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
9
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
24
improved HF-CW achieved similar or better percentage abatement than those reported
25
using some hybrid systems.
26
Keywords
27
Aerated domestic wastewater. Blast furnace slag. Horizontal subsurface flow
28
constructed wetland. Mediterranean climate. Reclaimed wastewaters reuse.
29
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
52
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
55
way, Valencia is the area with higher dynamism in wastewater reuse, mainly focused on
56
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
59
Alicante, where in 2006 there were 9225 individual households without access to public
60
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
72
organics abatement (Vymazal, 2007); and also because the traditional HF-CWs filling
73
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
78
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
82
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,
84
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
88
CWs.
89
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
172
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