Phytoremediation of the pisciculture wastewater, using Typha domingensis in constructed wetlands system
Marcos Vinícius Teles Gomesa,*, Roberto Rodrigues de Souzab, Vinícius Silva Telesb, Érica Araújo Mendesa
a
Centro Integrado de Recursos Pesqueiros e Aquicultura de Três Marias - CODEVASF; Av. Geraldo Rodrigues dos Santos, s/n, Satélite, CEP 39.205-000, CP 11, Três Marias/MG
b
Departamento de Engenharia Química, Universidade Federal de Sergipe; Av. Marechal Rondon, s/n, Jardim Rosa Elza, CEP 49.100-000, São Cristovão/SE
* Corresponding author. Tel.: +55-38-3754-1422.
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Abstract
This actual study offers information of an experiment accomplished in pilot scale and projected to evaluate the aquatic macrophytes Typha domingensis in constructed wetland systems with subsurface flow in order to have the phytoremediation of wastewater of piscicultures. It is considerable important to understand the dynamics of the abiotic parameters variation, showing that the increasing of the pH, EC, TDS and total alkalinity, in addition of the reduction of DO, total nitrogen and total phosphorus oscillated in function of the exposure time and the density of the macrophyte, suggesting being those the preponderant factors in the constructed wetlands cultivated with Typha domingensis. After 120 h of exposure time, the treatment with 50 shoots per m² showed a total nitrogen removal efficiency 217% higher than the control line (machrophyte free), showing the Typha domingensis is, essential to the nitrogen phytoremediation. For the total phosphorus, the removal efficiency was 26% higher than the control line, possibly for being present in the particulate matter, and this, has been retained predominantly by filtration and sedimentation. The total nitrogen and phosphorus removal efficiency were about 90%. The results showed the great potential of the aquatic macrophyte Typha domingensis for the phytoremediation of the wastewater of pisciculture.
Keywords: pisciculture, phytoremediation, constructed wetlands, Typha domingensis, nutrients.
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INTRODUCTION
Nowadays, the world demand for animal protein has enhanced the aquaculture productivity, increasing the generation of waste, usually released in the water bodies without proper treatment which could use efficient biotechnological processes. There are a small amount of piscicultures that have wastewater treatment systems, especially for the removal of the nitrogen and phosphorus constituents. The fish excretion, ration and fertilizer, they are capable of provoking the eutrophication of the water, where are present many times in the particulate matter. Studies show that the phosphorous nutrients are some of the main responsible for the eutrophication of aquatic environments, and are often the limiting factor for such a process (Salas et al., 1991; Esteves, 1998).
As alternative to a bioprocess, the constructed wetland systems cultivated with aquatic macrophytes, has showed efficiency in the phytoremediation of the wastewaters with high load of organic matter (Vymazal and Kröpfelová, 2009), and in the removal of the macronutrients of effluents from pisciculture tanks (Hussar et al., 2004). Such systems work as biological filter, and occur the sedimentation of great part of the particulate matter, in which aerobic and anaerobic microorganisms are the main responsible for the decomposition of organic matter, with consequent assimilation of part of the metabolic by plant.
The phytoremediation consists in a group of technologies based on the use of natural occurrence or genetically modified plants to reduce, remove, degrade or immobilize pollutants, as alternative to conventional wastewater treatment methods (Lasat, 2002), due to its sustainability, low maintenance and energy costs (Maine et al., 2006).
Among the main actions of the plant under the pollutants, stand out: the rhizofiltration with removal of pollutants of an aqueous environment through the
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absorption, concentration and/or precipitation through roots (Dushenkov et al., 1995); the phytoextraction, that involves the removal by roots, with subsequent transport to the aerial part of the plant (Salt et al., 1998), when occurs the degradation or volatilization of the pollutant; the phytodegradation, where the plant, from intern or secreted enzymes, via roots or associated microflora, degrade the pollutants, converting them in substances with low toxicity (Suresh and Ravishankar, 2004); and the phytoestabilization, when the pollutant stays retained or inactive in the vegetal tissue (Wenzel, 2009; Sun et al., 2010).
The aquatic macrophytes perform important function in the maintenance and balance of the aquatic environments (Rodella et al., 2006), contributing into physical, chemical transformations and in the microbiological process of nutrients removal (Sipaúba-Tavares et al., 2003). The process partially reduces the metabolic load from the cultivation of aquatic organisms, substantially improving the quality of the water (Sipaúba-Tavares et al., 2002).
Studies indicate the species of the Typha spp. type, as plants that show high capacity to tolerate and eliminate contaminants present in water or soil (Dordio et al., 2009; Park et al., 2009; Dordio et al., 2010). A great variety of aquatic macrophytes may be used in the treatment of wastewaters in constructed wetlands systems. But its choice must be associated to the capacity of tolerate the flooding conditions and the high pollutant concentrations. Native plants must be considered, once they are adapted to the local weather, bugs and diseases.
Typha is a cosmopolitan type out of eleven species of floriferous plants from
Typhaceae family (Akkol et al., 2011). It has fast growth, and the majority shows high evapotranspiration rates (Glenn et al., 1995).
The Typha domingensis is an emergent aquatic macrophyte plant that grows in all regions with tropical, hot and temperate climates (Eid et al., 2012), and it is commonly used in constructed wetlands to improve the water quality in treatment
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Brazil, it is known as “Taboa” (Bove, 2010), and occurs in the Caatinga, Cerrado, Rainforest and Swamp (Pott and Pott, 1997), spontaneously growing in flooded lowlands, marsh, dams and draining channels.
In pilot scale, the present study was projected to evaluate the potential of the aquatic macrophyte Typha domingensis (Typhaceae), in a constructed wetland system (Constructed Wetland – CW) with subsurface flow, for the phytoremediation of wastewater of pisciculture. The specific objectives were to determine the variation of abiotic parameters (pH, electrical conductivity, dissolved oxygen, total dissolute solids, total alkalinity, total nitrogen and total phosphorus), and the efficiency on the removal of phosphorus and nitrogen nutrients, according to exposure time.
MATERIAL AND METHODS
Construction and conception of constructed wetlands
A constructed wetland system with subsurface flow was built in triplicate in the Três Marias Integrated Center for Fishing Resources and Aquaculture (1ª/CIT), Três Marias city, state of Minas Gerais, Brazil. The system operated by treating wastewaters from a polyculture pond (23K 0473273, UTM 7987393), which was provided with water from the Três Marias reservoir (23K 0473273, UTM 7987393). The reservoir situated at Alto São Francisco was formed in 1961 by the impoundment of the São Francisco River, having an water volume of 21 billion per m³, and occupying an area of 1040 km². Among the fishes present in the polyculture pond, the most abundant species were the following: curimatã pacu (Prochilodus argenteus), curimatã pioa (Prochilodus
costatus), matrinxã (Brycon orthotaenia), piau verdadeiro (Leporinus obtusidens),
pacamã (Lophiosilurus alexandri) and surubim (Pseudoplatystoma corruscans).
The construction of the system (Fig. 1) was started in the summer, on January 11th, during the rain period, when the air temperature average oscillated between 18 and 30°C. In a region of natural wetlands located close to where the experiment was made,
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shoots were collected from young and apparently healthy plants of the Typha
domingensis species. Immediately transplanted, they were cultivated with densities of
10, 20, 30, 40 and 50 shoots per m² (E10, E20, E30, E40 e E50 respectively), over a period of 160 days, time enough to reach 136 ± 16 cm high. During the plants acclimation and growth, the system was loaded with water from the Três Marias reservoir, exclusively.
The treatment system (Figure 1) was formed by a recipient of 3000 liters that was loaded by pumping the wastewater from the polyculture pond, and then, distributing it by gravity to six other recipients of 1000 liters each. Initially, they were filled ¼ with gravel 2 (30 mm mesh), granulometry varying between 19 and 25 mm, and ¼ with gravel 0 (12 mm mesh), granulometry between 4.8 and 9.5 mm. In five of the smaller recipients (constructed wetland), were cultivated shoots of the Typha
domingensis. The exposure time varied between zero to five days. The draining, made
through the gravity action in the lower part of the system, allowed the direct contact of the wastewater with the gravel and with the plants’ roots. The sixth recipient - plants free, was used as control line.
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Sampling and Chemical analysis
The system was evaluated for 5 (five) days during drought period (August 11th), when the average of air temperature varied between 12 and 27°C. Operating in batch, the supply with wastewater from the polyculture pond occurred only once.
Water samples were collected in the treatments output (constructed wetlands and control line) every 24h, and preserved in polyethylene flasks previously decontaminated.
In order to determine the pH, electrical conductivity (EC), dissolved oxygen (DO), and total dissolved solids (TDS), was used a Horiba mulitparameter probe, model W22XD. The calibration of the equipment was made according to the manufacturer’s recommendations (Horiba, 2007), and after performing three readings per sample. To determine the total alkalinity, the potentiometric method was used (ABNT NBR 13736, 1996). The total nitrogen and phosphorus concentrations were determined according to the method written by Valderrama (1981).
RESULTS AND DISCUSSION
On the beginning of the experiment, the wastewater that supplied the system showed pH of 7.13 ± 0.11, EC of 116 ± 3 µS cm-1, DO of 6.91 ± 0.04 mg L-1, TDS of 76 ± 2 mg L-1, total alkalinity of de 29.37 ± 0.26 mg L-1, total nitrogen of 826.05 ± 17.43 µg L-1, and total phosphorus of 101.80 ± 3.71 µg L-1.
The CONAMA 357/05 Resolution states the classification of water bodies and environmental guidelines for their framework as well as establishes the conditions and standards for effluent release. For class 2 water, the pH must be in between 6 and 9, DO greater than 5 mg L-1, TDS less than 500 mg L-1, total nitrogen less than 2180 µg L-1, and total phosphorus less than 100 µg L-1. At the beginning of the experiment, only the
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total phosphorus values presented was greater than those established by CONAMA 357/05.
In all treatments occurred a pH variation (Figure 2) already in the first 24 h. In the end of the experiment, the control line presented the highest value (7.46 ± 0.09), and the E40 treatment the lowest (6.97± 0.06). The presence of Typha domingensis kept the pH close to neutral, fact that has not occurred with the line control, where there has been in basicity increase that may be associated to the degradation of the organic matter and consequent formation of metabolic, in addition to denitrification.
Figure 2 PH variation depending on exposure time and density of the macrophyte.
0 20 40 60 80 100 120 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0 pH
Exposure time (hours)
Shoots per square meter: 0 10 20 30 40 50
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After 120 h of exposure time, the minimum EC was of 179 ± 3 µS cm-1 has been found in the control line (Figure 3), and maximum of 488 ± 5 µS cm-1, in E40 treatment. In the presence of the macrophyte occurred a strong increase of the EC in all treatments, suggesting its effective participation in the particulate matter degradation and consequent cycling of the nutrients, releasing them in the dissolved form. After 48 h of exposure time, occurs a reduction of electrical conductivity in the E50 treatment, possibly due to the great absorption of dissolved form arising from the higher density of macrophytes.
Figure 3 Variation of electric conductivity (EC) depending on exposure time and density of the macrophyte.
0 20 40 60 80 100 120 50 100 150 200 250 300 350 400 450 500 E C ( µ S cm -1 )
Exposure time (hours)
Shoots per square meter: 0 10 20 30 40 50
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In all treatments, including the control line, occurred a strong DO reduction within the exposure time of 48 h (Figure 4). In the end of the experiment, the lowest concentration was found in the E50 treatment (2.41 ± 0.03 mg L-1), probably influenced by the increase of the microbial activity over the degradation of the organic matter.
Figure 4 Variation of dissolved oxygen (DO) depending on exposure time and density of the macrophyte.
After 120 h of exposure time, the minimal TDS value (Figure 5) was of 117 ± 1 mg L-1, found in the control line (Figure 5), and maximum of 313 ± 2 mg L-1, in the E40 treatment. In the presence of the macrophyte occurred a strong increase of the TDS
0 20 40 60 80 100 120 2 3 4 5 6 7 8 9 D O ( mg L -1 )
Exposure time (hours)
Shoots per square meter: 0 10 20 30 40 50
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suggests a bigger degradation of the particulate matter retained in the fixed bed (gravel) and in the roots of the Typha domingensis, releasing them in the dissolved form, and absorbed with greater intensity in the E50 treatment, possibly due to the higher density of macrophyte.
Figure 5 Variation of total dissolved solids (TDS) depending on exposure time and density of the macrophyte.
In the end of the experiment, with 120 h of exposure time, the minimal total alkalinity value (Figure 6) was of 71.12 ± 0.40 mg L-1, found in the control line (Figure 6), and maximum of 169.62 ± 0.23 mg L-1, in the E50 treatment. The elevation of the total alkalinity varied directly in function of the exposure time and the density of the
0 20 40 60 80 100 120 0 50 100 150 200 250 300 350 T D S ( m g L -1 )
Exposure time (hours)
Shoots per square meter: 0 10 20 30 40 50
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macrophyte, possibly caused by the increase of the metabolic dissolved in the water, also responsible for the pH increase.
Figure 6 Variation of total alkalinity depending on exposure time and density of the macrophyte.
In the beginning of the experiment, the wastewater that loaded the system presented an initial total nitrogen concentration of 826.05 ± 17.43 µg L-1. In all treatments there was a strong reduction of the values until 48 h, probably because of the retention of part of the particle material in the fixed bed (gravel) and in the roots of the
Typha domingensis. When reaching 120 h of exposure time, the control line showed
0 20 40 60 80 100 120 20 40 60 80 100 120 140 160 180 200 T o ta l a lk a lin it y ( m g L -1 )
Exposure time (hours)
Shoots per square meter: 0 10 20 30 40 50
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treatment, corresponding to a removal efficiency (Figure 8) of 28.34 ± 0.05% and 89.11 ± 10.50%, respectively.
Figure 7 Variation of total nitrogen depending on exposure time and density of the macrophyte. 0 20 40 60 80 100 120 0 200 400 600 800 1000 Tot al nit ro ge n (µg L -1 )
Exposure time (hours)
Shoots per square meter: 0 10 20 30 40 50
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Figure 8 Variation of total nitrogen removal efficiency depending on exposure time and density of the macrophyte.
The wastewater that provided the system presented an initial concentration of total phosphorus of 101.80 ± 3.71 µg L-1. Similarly to the occurred for the total nitrogen, in all treatments there was a strong reduction in the total phosphorus values within 48 h. In the end of the experiment, the control line showed concentration (Figure 9) of 27.84 ± 3.85 µg L-1, and 8.56 ± 1.45 µg L-1 for the E50 treatment, corresponding to a removal efficiency (Figure 10) of 72.65 ± 2.61% and 91.60 ± 5.24%, respectively. At the end of the experiment, in all treatments the total phosphorus concentration showed values within the limits established by CONAMA 357/05, which is 100 µg L-1.
0 20 40 60 80 100 120 0 20 40 60 80 100 T o ta l ni tr o g e n r e m o v a l e ff ic ie nc y ( %)
Exposure time (hours)
Shoots per square meter: 0 10 20 30 40 50
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Figure 9 Variation of total phosphorus depending on exposure time and density of the macrophyte. 0 20 40 60 80 100 120 0 20 40 60 80 100 T o ta l ph o sph o ru s (µ g L -1 )
Exposure time (hours)
Shoots per square meter: 0 10 20 30 40 50
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Figure 10 Variation of total phosphorus removal efficiency depending on exposure time and density of the macrophyte.
At the end of the experiment, in all treatments, the abiotic parameters studied showed values within the limits for effluent release, according to CONAMA 357/05.
After 120 h of exposure time, the E50 presented a removal efficiency of total nitrogen 217% higher than the control line, showing that the Typha domingensis is essential to the phytoremediation of nitrogen. The transformations of the nitrogen forms in constructed wetlands usually are variable and uncertain, due to the nitrification/denitrification processes, absorption by plants and storage in sediment
0 20 40 60 80 100 120 0 20 40 60 80 100 T o ta l ph o sph o r us r e m o v a l e ff ic ie nc y ( %)
Exposure time (hours)
Shoots per square meter: 0 10 20 30 40 50
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degradation of the organic matter, both for microbial aerobic and anaerobic process, as for sedimentation and filtration of the particles of organic matter (Vymazal, 2007).
Regarding the total phosphorus, the removal efficiency in the E50 was 26% higher than the control line, possibly for being present in the particle matter, and being retained predominantly by filtration and sedimentation. Studies made in Germany for the treatment of effluents for creation of a trout species (Sindilariu et al., 2007) obtained mechanical phosphorus removal efficiency between 84 and 95%, but the leaching and microbial degradation may release it as dissolved phosphorus, reducing the final removal rate.
According to Vymazal (2002), in constructed wetland systems with subsurface flow, the nutrient removal efficiency based on the input and output concentrations of the wastewaters, has been of 60.1 to 64.8% for the total nitrogen, and 26.7 to 65.0% for the total phosphorus.
The study showed that the removal efficacy of the total phosphorus and nitrogen were near to 90%. The results are similar to the ones obtained by Sovik and Mørkved (2008) acquire nitrogen removal efficiency of over 90%. A study made by Stewart (2005) using Gynerium sagittatum, obtained a removal efficiency of 95% of total nitrogen, and 97% of total phosphorus.
In constructed wetland systems, the particulate matter is predominantly retained by filtration and sedimentation and the removal efficiency is usually very high (Vymazal, 2010). Furthermore, the retained material may be degraded by a bacteria present in the rhizosphere (Brix, 1994), being then, absorbed by the roots. The removal of great quantities of nitrogen occurs mainly by the denitrification mechanism (Vymazal, 2007).
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CONCLUSIONS
This study became important for the understanding of the dynamic variation of the abiotic parameters showing that the increase of pH, EC, TDS, and total alkalinity, and reduction of OD, total nitrogen, and total phosphorus, oscilated in function of the exposure time and the macrophyte’s density, suggesting that these are preponderant factors in the constructed wetlands system cultivated with Typha domingensis.
After 120 h of exposure time, the E50 treatment showed a total nitrogen removal efficiency of 217% higher than the control line, showing that the Typha domingensis, is essential for phytoremediation of nitrogen. For total phosphorus, the efficiency of the E50 treatment was 26% higher than the control line, possibly for being present in the particle matter, and this being predominantly retained by sedimentation and filtration.
The study showed that the removal efficiency of total nitrogen and phosphorus were of about 90% similar or higher than the obtained in other studies.
The results showed the great potential of the aquatic macrophyte Typha
domingensis in constructed wetlands system with subsurface flow, for the
phytoremediation of the wastewater of the pisciculture.
ACKNOWLEDGEMENTS
The authors thank the Três Marias Integrated Center for fishing Resources and Aquaculture – 1ª CIT / CODEVASF and the Northeast Network of Biotechnology – RENORBIO.
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