Use of hydroponics culture to assess nutrient supply by treated wastewater

Journal of Environmental Management 127 (2013) 162e165

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Use of hydroponics culture to assess nutrient supply by treated wastewater Maria Adrover, Gabriel Moyà, Jaume Vadell* Department of Biology, University of Balearic Islands, 07122 Palma de Mallorca, Spain

a r t i c l e i n f o

a b s t r a c t

Article history: Received 30 September 2009 Received in revised form 22 February 2013 Accepted 20 April 2013 Available online

The use of treated wastewater for irrigation is increasing, especially in those areas where water resources are limited. Treated wastewaters contain nutrients that are useful for plant growth and help to reduce fertilizers needs. Nutrient content of these waters depends on the treatment system. Nutrient supply by a treated wastewater from a conventional treatment plant (CWW) and a lagooned wastewater from the campus of the University of Balearic Islands (LWW) was tested in an experiment in hydroponics conditions. Half-strength Hoagland nutrient solution (HNS) was used as a control. Barley (Hordeum vulgare L.) seedlings were grown in 4 L containers filled with the three types of water. Four weeks after planting, barley was harvested and root and shoot biomass was measured. N, P, K, Ca, Mg, Na and Fe contents were determined in both tissues and heavy metal concentrations were analysed in shoots. N, P and K concentrations were lower in LWW than in CWW, while HNS had the highest nutrient concentration. Dry weight barley production was reduced in CWW and LWW treatments to 49% and 17%, respectively, comparing to HNS. However, to a lesser extent, reduction was found in shoot and root N content. Treated wastewater increased Na content in shoots and roots of barley and Ca and Cr content in shoots. However, heavy metals content was lower than toxic levels in all the cases. Although treated wastewater is an interesting water resource, additional fertilization is needed to maintain a high productivity in barley seedlings. Ó 2013 Elsevier Ltd. All rights reserved.

Keywords: Barley Treated wastewater Hydroponics Mineral content Heavy metals

1. Introduction The reuse of treated wastewater for crop irrigation has been widely recommended for their environmental benefits, especially in those areas with problems of water shortage (Pereira et al., 2002; Qadir et al., 2007). Chemical composition of treated wastewaters depends on their origin and the treatment received. Effluents from non-industrial municipalities that have received at least secondary treatment have generally low concentrations of heavy metals, which do not cause any adverse effects on plant growth and public health (Crook, 1998). However, they contain suspended and dissolved organic and inorganic solids (Pereira et al., 2002). Conventional treatment plants have higher removal efficiency of biological oxygen demand (BOD) but a lower removal efficiency of total nitrogen and total phosphorus than lagooned treatment plants (Muga and Mihelcic, 2007). Several authors reported that treated wastewaters can be used as a fertilizer for wheat, maize and barley in field conditions

* Corresponding author. Tel.: þ34 971173167; fax: þ34 971173184. E-mail address: [email protected] (J. Vadell). 0301-4797/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvman.2013.04.044

(Hussain et al., 1996; Vazquez-Montiel et al., 1996; Rusan et al., 2007). However, soil fertility should be taken into account. Hydroponic cultures have been widely used in studies of plant nutrition (Alam et al., 2001; Crowley et al., 2002) because the root medium is homogeneous (Le Bot et al., 1998) and deficiencies and toxicities are more evident than in soil cultures (Ma et al., 1997). On the other hand, they can be useful for nutrient removal from wastewaters (Ghaly et al., 2005; Vaillant et al., 2003). Snow and Ghaly (2008) showed that hydroponically grown barley was able to reduce significantly the pollution load of aquaculture wastewater. Moreover, the reuse of treated wastewaters in hydroponic cultures to produce commercially valuable plants has been previously evaluated (Rababah and Ashbolt, 2000; Oyama et al., 2005). Recently, treated wastewater has also been considered a feasible source of water to produce barley fodder under hydroponic system (Al Ajmi et al., 2009; Al-Karaki, 2011). A hydroponic culture experiment was established in order to compare the growth response and mineral nutrient status of barley supplied with two different treated wastewaters. The effect of treated wastewaters on heavy metal accumulation was also evaluated. This experiment complements a larger research to study the effects of these two types of treated wastewater on three common Mediterranean soil types sown with barley (Adrover et al., 2012).

M. Adrover et al. / Journal of Environmental Management 127 (2013) 162e165

2. Material and methods Seeds of barley (Hordeum vulgare L. cv. County) were sown in germination cells filled with vermiculite and kept in a germination chamber untill emergence. Once germinated were watered with half-strength Hoagland nutrient solution. One-week seedlings were transplanted to 4 L polyethylene containers filled with three continuously-aerated types of water: half-strength Hoagland nutrient solution (HNS; Hoagland and Arnon, 1950), treated municipal wastewater from a conventional treatment plant (CWW) and treated municipal wastewater from the lagoon system (LWW). The conventional wastewater treatment plant works with the activated sludge system and has a capacity of 5000 equivalent inhabitants with a daily flow of 1000 m3. The water for the experiment was collected from the secondary settling tank. The lagooned wastewater came from a wastewater stabilization pound located at the campus of the University of Balearic Islands, with a capacity of 225 equivalent inhabitants and a daily flow of 50 m3, which was thoroughly described by AmengualMorro et al. (2012). The water for this experiment was collected from the second maturation pond. Water properties are shown in Table 1. Five seedlings were planted in each container and a set of four containers was used for each treatment. Previously, roots were thoroughly washed with distilled water. Seedlinds were supported with a polystyrene disc with the same diameter of the container. These discs also covered the containers to exclude light from the solution and root systems. After two weeks from the transplanting, two plants were removed in each container. Weekly, both treated wastewaters (CWW and LWW) were collected from the treatment plants, nutrient solution (HNS) was prepared and water of the hydroponic culture was changed for the three treatments. Distilled water was added if the volume of the solution decreased during the week, in order to keep the containers full without adding nutrients. Plants were grown in a greenhouse. The experiment was repeated twice. In the first time (culture 1), barley seedlings were transplanted on 24th of March of 2006. The repetition of the experiment (culture 2) started on 12th of April of 2006. Barley plants were harvested after four weeks in both hydroponic cultures. Roots and shoots were separated. Roots were thoroughly washed with distilled water. Plant material was dried in an oven at 60  C for three days and weighed to measure crop production. Plant samples were milled to <1 mm. Contents of N, P, K, Ca, Mg, Na and Fe

in shoots and roots in addition to contents of Cd, Cr, Cu, Mn, Ni, Pb and Zn in shoots were measured. N was analysed by the Kjeldahl method (Bremmer and Mulvaney, 1982). To determine the levels of other elements, 1 g of the sample was dry ashed at 550  C for 3 h and dissolved in 5 ml of 25% nitric acid and 50 ml of double distilled water. After mixing thoroughly and standing for approximately 30 min, the supernatant was filtered through 0.45 mm and analyzed with an inductively coupled plasma spectrophotometer. Crop production and mineral content were analysed by two-way ANOVA, with water treatment and repetition (culture 1 and 2) as main factors. Means were separated by Tukey’s test (p < 0.05) for comparisons. All statistical analyses were performed using SPSS 15.0. 3. Results Both treated wastewaters (CWW and LWW) had low inorganic N contents compared to HNS, which were 15% and 3%, respectively. Ammonia was the predominant form of N in treated wastewaters, in contrast to HNS, where most of N was in nitrate form. Treated wastewaters had also a lower content in P and K than HNS. Concentrations of these two elements were higher in CWW than in LWW. Ca and Mg concentration were lower in treated wastewaters than in HNS but there were less strong differences than in the case of N, P and K. In contrast, Na concentration was higher in CWW, followed by LWW, than in HNS, where the concentration of this element was unappreciable. Another differential characteristic of treated wastewaters, in comparison with HNS, was the presence of suspended solids, which was higher in lagooned wastewater. Moreover, pH was very much higher in treated wastewater, reaching values upper to 9 in LWW (Table 1). The treatment with CWW produced a 57% of shoots and a 51% of roots in culture 1 and a 39% of shoots and a 55% of roots in the culture 2, comparing to HNS. The production of the treatment with LWW was still lower, 22% of shoots and 26% of roots in culture 1 and 11% of shoots and 17% of roots in culture 2, comparing to the treatment with HNS (Fig. 1). The crop production was statistically different in the three water treatments but not statistically significant differences were found between both cultures (Table 2). Mineral content in shoots was statistically significantly different (p < 0.05) between the three water treatments, although no differences were found between both cultures, except for N and Mg. Shoots of barley grown in HNS had higher N, K and Fe content and lower Ca and Na content than those of barley grown in both treated 20

Table 1 Chemical composition of irrigation water. Mean values and range between brackets.

18

HNS

CWW

LWW

16

1.15 6.2 0 113 14 31.0 197 60 28 0 0.5 0.01 0.25 0.03 bdl

1.54 (1.50e1.60) 8.0 (7.9e8.1) 46 (28e64) 3 (0.2e10) 16 (12e18) 2.4 (1.9e2.8) 16 (15e18) 39 (31e50) 12 (11e12) 90 (85e96) bdl bdl bdl bdl bdl

1.00 (0.91e1.11) 9.3 (8.9e9.6) 115 (82e140) 0.2 (0.0e0.6) 3 (1e6) 0.9 (0.7e1.2) 12 (11e13) 24 (21e29) 13 (12e14) 57 (53e64) bdl bdl bdl bdl bdl

14

HNS, Hoagland nutrient solution; CWW, treated wastewater from a conventional treatment plant; LWW, treated wastewater from a lagoon; EC, electrical conductivity; SS, suspended solids; bdl, below detection limit. Detection limit: Fe, 0.001 mg l1; Cu, 0.0004 mg l1; Mn, 0.018 mg l1; Zn, 0.001 mg l1; Cd, 0.0006 mg l1; Cr, 0.01 mg l1; Ni, 0.005 mg l1; Pb, 0.009 mg l1.

Dry weight (g)

EC 25  C (dS m1) pH SS (mg l1) 1 NeNO 3 (mg l ) 1 NeNHþ 4 (mg l ) Total P (mg l1) K (mg l1) Ca (mg l1) Mg (mg l1) Na (mg l1) Fe (mg l1) Cu (mg l1) Mn (mg l1) Zn (mg l1) Cd, Cr, Ni, Pb, (mg l1)

163

a

a

Shoots Roots

12

b

10

bc

8 6

bc

4

c

2 0 HNS 1

HNS 2

CWW 1

CWW 2

LWW 1

LWW 2

Fig. 1. Aboveground (shoots) and belowground (roots) biomass for each treatment in the cultures 1 and 2 (HNS, Hoagland nutrient solution; CWW, treated wastewater from a conventional treatment plant; LWW, treated wastewater from a lagoon). Error bars represent the standard error of the total dry weight. Treatments with different letters are statistically different according to the Tukey test at P < 0.05 for total biomass (roots and shoots).

164

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Table 2 Two-way ANOVA on crop production (CP), expressed as g container1, and mineral content of barley shoots, expressed as g kg1, considering water treatment and culture. CP

N

Water treatment (W) HNS 12.0a 41.1a CWW 5.7b 24.4c LWW 1.9c 31.4b Sig. <0.001 <0.001 Culture 1 2 Sig.

(C) 7.1 6.0 0.242

Interaction W  C 0.609

28.9 35.7 0.001

0.002

P

K

Ca

Mg

Na

Fe

5.9ab 4.0b 8.1a 0.001

55.3a 29.3b 35.8b <0.001

3.0c 5.2b 7.0a <0.001

1.7b 1.7b 3.4a <0.001

0.2b 8.7a 9.2a <0.001

47.5a 43.0ab 30.3b 0.015

5.4 6.6 0.104

0.001

41.3 39.0 0.560

0.001

5.1 5.0 0.902

0.113

1.9 2.6 0.029

0.003

6.0 6.1 0.867

0.611

42.8 37.7 0.265

0.179

For water treatment, values followed by different letters in the same column are statistically different (Tukey test, p < 0.05). HNS, Hoagland Nutrient Solution; CWW, treated wastewater from a conventional treatment plant; LWW, treated wastewater from a lagoon; Sig, significance.

wastewaters (Table 2). Similar results were found in roots (Table 3). Although production was higher in CWW treatment than in LWW treatment (Fig. 1), a higher rate of N content was detected in the shoots of barley treated with LWW, compared with CWW and similar pattern was observed by P, Ca and Mg content (Table 2). Significant interactions were found between water treatment and repetition for N, P, K and Mg in shoots and Mg in roots, indicating significantly different patterns of response in both cultures by the different water treatment examined (Tables 2 and 3). As for heavy metal contents, they were significantly higher in culture 2 than in culture 1, with the exception of Ni and Pb contents. Plants grown with CWW and LWW had significantly lower Cu and Mn contents in their shoots than plants grown with HNS. In contrast, Ni content was significantly higher in shoots from the treatments with CWW and LWW and similar results were found for Cr content. No differences were found among treatments in Pb and Zn contents. Significant interactions between water treatment and repetition were found only for Cd and Cr contents (Table 4). 4. Discussion Half-strength Hoagland nutrient solution (HNS) is considered a complete formulation of all required nutrients and is recommended Table 3 Two-way ANOVA on crop production (CP), expressed as g container1, and mineral content of barley roots, expressed as g kg1, considering water treatment and culture. P

K

Ca

Mg

Na

Fe

Water treatment (W) HNS 3.2a 36.5a CWW 1.7b 24.7c LWW 0.7c 31.2b Sig. <0.001 <0.001

CP

N

6.7 4.8 5.7 0.064

42.1a 21.2b 21.4b <0.001

2.8b 5.7a 3.3b 0.014

1.6b 2.2a 1.7ab 0.027

0.4c 11.6a 6.5b <0.001

136.3ab 178.8a 61.0b 0.004

Culture 1 2 Sig.

(C) 2.1 1.7 0.093

29.8 31.8 0.181

5.1 6.4 0.043

24.7 31.8 0.087

3.3 4.6 0.111

1.5 2.1 0.002

5.5 6.9 0.018

125.8 124.9 0.972

Interaction A  C 0.814

0.441

0.073

0.339

0.276

0.032

0.186

0.584

For water treatment, values followed by different letters in the same column are statistically different (Tukey test, p < 0.05). HNS, Hoagland Nutrient Solution; CWW, treated wastewater from a conventional treatment plant; LWW, treated wastewater from a lagoon; Sig, significance.

Table 4 Two-way ANOVA on heavy metal content of barley shoots, expressed as mg kg1, considering water treatment and culture. Cu

Mn

Ni

Pb

Zn

Water treatment (W) SN 0.04a 0.42b ARC 0.01b 0.91a ARL 0.03a 1.09a Sig. <0.001 <0.001

Cd

Cr

7.1a 4.4b 4.8b 0.016

32.6a 12.3c 24.6b <0.001

0.12c 0.57a 0.32b <0.001

0.12 0.24 0.13 0.118

27.6 33.7 20.9 0.082

Culture (C) 1 0.02 2 0.03 Sig. 0.010

0.67 0.93 0.008

3.7 7.1 <0.001

20.7 25.6 0.049

0.34 0.33 0.784

0.13 0.20 0.194

21.8 33.0 0.018

Interaction AC 0.047

0.003

0.512

0.097

0.343

0.191

0.073

For water treatment, values followed by different letters in the same column are statistically different (Tukey test, p < 0.05). HNS, Hoagland Nutrient Solution; CWW, treated wastewater from a conventional treatment plant; LWW, treated wastewater from a lagoon; Sig, significance.

for general use in hydroponic systems (Epstein and Bloom, 2005). According to Hopper et al. (1997), its formulation satisfies barley needs. Ingestad and Agren (1995) pointed out that plant properties under unlimited conditions can be used as reference values and any deviation from these values is a measure of resource limitation or excess. In this way, the treatment with HNS had the maximum aboveground and belowground productions and they were similar in both cultures, although root biomass was lower in the second culture (Fig. 1). The small biomass produced by LWW was associated to its reduced nutrient supply, lower than HNS and CWW, and the high water pH, which reduces the availability of some elements, such as Fe and Zn, due to precipitation (Kopittke and Menzies, 2004). The aboveground:belowground ratio was higher in the treatments with HNS and CWW than in the treatment with LWW. Nitrogen supply has a larger effect on shoot’s growth than on root’s growth, and that explains the increase of this ratio (Gastal and Lemaire, 2002). In contrast, when nutrients are limited, as in the treatment with LWW, root’s growth is stimulated in comparison to shoot’s growth (Le Bot et al., 1998). The highest contents of N detected in the shoots of barley treated with LWW, compared with CWW were also found in a soil experiment using the same water treatments (Adrover et al., 2012) and were attributed to the effect of concentration/dilution, because plants from CWW treatment accumulated more N than plants from LWW treatments, but LWW had a lower production of dry biomass (Fonseca et al., 2005). The effect of concentration caused by the low growth of plants grown in LWW was observed for most of the studied elements in shoots and roots, although not all of them were statistically significant (Tables 2 and 3). The only elements that were found in a lower concentration in the LWW treatment were Fe and Zn (Tables 2e4), which availability was reduced by the high water pH (Kopittke and Menzies, 2004). P content in shoots was higher comparing to values obtained by Soon (1988) in barley leaves of the same age under field conditions and the values obtained for the same barley cultivar in pot cultures in outdoors conditions (Adrover et al., 2012), which were both about 3 g kg1. However, in all treatments except LWW, it was lower than critical levels calculated by Bolland and Brennan (2005) for 30 day barley (10.9 g kg1). The high P content in shoots of LWW treatment might be attributed to a lower N:P supply ratio (Güsewell, 2004). Values of K content in shoots were all above the levels found under field conditions (Soon, 1988). The highest K content was found in shoots and roots of barley grown in HNS

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(Tables 2 and 3). These values were higher than those found in barley grown in three types of soil, in pot cultures (Adrover et al., 2012). This fact can be explained by luxury consumption (Epstein and Bloom, 2005), as K is more available in a water media. Plants grown with treated wastewaters (CWW and LWW) differed significantly from plants grown in HNS in Na content in shoots and roots (Tables 2 and 3). This is due to a higher Na concentration in treated wastewaters comparing to nutrient solution (Table 1). On the other hand, plant Ca contents were higher in barley grown with treated wastewaters than in barley grown with HNS (Tables 2 and 3), although Ca concentration was lower in treated wastewaters (Table 1). The concentration of Na in treated wastewaters may result in a reduced growth due to the toxicity of the Naþ (Tester and Davenport, 2003). In this case, the K concentration is critical to attenuate Na damage (Chen et al., 2005). Similarly, Ca plays an important role in the mitigation of the negative effects of Na (Liu and Zhu, 1998; Cramer, 2002; Kader and Lindberg, 2010). In fact, in shoots and roots remain relatively high levels of K and Ca (Tables 2 and 3). However, salinity from treated wastewaters (EC: 0.9e1.6 dS m1) does not produce salt stress in barley plants, since barley is a relatively salt-tolerant crop (Tester and Davenport, 2003). Heavy metal contents of the three water treatments were all below the critical levels of toxicity for barley (Davis et al., 1978; Macnicol and Beckett, 1985) and below values found in the pot experiment, except for Zn (Adrover et al., 2012). In fact, the Mn content in plants grown with CWW under hydroponic conditions was in the critical Mn deficiency range of 10e20 mg kg1 (Husted et al., 2005).

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