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Fitorremediacion en aguas y suelos contaminados con hidrocarburos del petroleo.

ENVIRONMENTAL & SANITARY ENGINEERING

Phytoremediation of Water and Soils Contaminated by Petroleum Hydrocarbons

1. Introduction

The increase in the demand for fuels, in combination with the opening of new gas stations in Colombia, has positioned the petroleum derivates in the highest ranks of public interest for their environmental and public health consequences because of their toxic, mutagenic, and cancer producing effects, aside from their known recalcitrant and bioaccumulant characteristics (Haritash & Kaushik, 2009). The hydrocarbon derivates (gasoline, kerosene, oils, fuels, paraffines, and asphalt among many others) are generally of common use in human activities that somehow allow their permeation into the environment because of the accidents in industrial, domestic, and transportation processes in combination with the spills and escapes as a result of drilling, pumping, conduction, and storage of the substances. The disposal of waters mixed with fuels as a result of the daily activities of the gas stations (through disposition or runoff) has not only impacted the surface layer of the soil and the surface water sources, but also has penetrated the ground waters.

The wastewater fuels are generally characterized by their contents of oils and greases, hydrocarbons, suspended solids and variable metal concentrations that on the soil block the atmospheric gas exchange, thus initiating a series of simultaneous physic-chemical processes, such as evaporation and penetration, that according to the type of hydrocarbon, temperature, humidity, soil texture, and amount disposed, may cause an increased resistance to their degradation. The hydrocarbons disposed of on the water tend to float because of the density difference and block the penetration of light and the gas exchange, thus promoting the solubilization of materials that affect the different populations: Plankton, microinvertebrate and benthos (macroinvertebrate) that live in the bottom of rivers and quagmires (Bento et al, 2003).

The complexity of the hydrocarbons has forced the implementation of a variety of different treatment technologies in-situ and ex-situ in order to assess their effectiveness when removing them. The use of phytochemical processes employing activated carbon, microorganisms, chemical substances, air and other compounds imply relative high investment and operation costs that make their application difficult (Susarla et al, 2002; Sangabriel et al, 2006). This is the reason why the interest has shifted to phytoremediation which represents a natural technique where the plants and their interaction with the microorganisms located on the rhizosphere can remove, abduce and/or degrade the organic contaminants into less toxic compounds or even to C[O.sub.2] y [H.sub.2]O (Guendy, 2008). This technological alternative has limitations for its application on a large scale or when the contaminant is toxic for the plants (Glick, 2003), but the advantages when compared to other conventional technologies that include physical or chemical removal are evident because i) it represents a lower cost-effectiveness, ii) it captures the greenhouse gases, iii) improves the surroundings from a aesthetical perspective, and iv) its principal source of energy is the solar radiation (Guendy, 2008). In this review article the authors are focused on introducing the advantages of phytoremediation on the treatment and recovery of waters and contaminated soils by organic and inorganic compounds of complex degradation, specificallythrough constructed wetland systems.

2. Petroleum hydrocarbons

The hydrocarbons are classified according to the API degrees (density) that they possess and they have a characteristic look where some are of a clear appearance and easily evaporate, and some others are dense and obscure liquids that do not evaporate (ATSDR, 1999). The hydrocarbons are usually divided in three different groups: Acyclic with open chains, saturated cyclic with open chains, and non-saturated aromatic hydrocarbons (Kamath et al., 2004), with the benzene ring as structural base like the BTEX (benzene, toluene, etilbenzene, and xylene that are monoaromatic) or the PAHs (Naphthalene, Phenanthrene, and Anthracene that are polyaromatic) (Gabriel et al., 2004).

The BTEX are more soluble in water (low [K.sub.OW]: 1.8-3.2) than the cyclic compounds of heavy molecular weight, this the reason for their easiness in displacement on aqueous environments and the easy biodegradation in aerobic conditions (USEPA, 1999); furthermore, they may be easily removed through volatilization due to their nature, highlighting the use of superficial flow wetlands as a good alternative for the task (Kadlec & Wallace, 2009). The PAHs belong to a wide group of hydrocarbons made up of 2-7 benzene rings that are characterized by their low solubility in water (log [K.sub.OW] > 4) and low volatility; these may achieve a mean life that goes from weeks to several years in the environment (Sverdrup et al., 2003). Those with low molecular weight (2 -3 benzene rings) may be easily degraded through biological processes, but the ones with high molecular weight may be resistant to the microbial biodegradation (Sun et al, 2010).

3. Phytoremediation mechanisms on waters and soils contaminated with hydrocarbons

Phytoremedition is defined as a low cost environmental friendly technological alternative developed to bring remedy to the affected resources with different types of contaminants (Khan et al., 2013). This is based on the use of plants and their interaction with the microorganisms located in the rhizosphere in order to remove, isolate or degrade the contaminant substances present in the soil, sediments, surface waters, ground waters, and the air (Meagher, 2000; Susarla et al., 2002; Ali et al., 2012; Kabra et al., 2012). This alternative may be used to remove metals, pesticides, solvents, explosives, oils derived from petroleum, hydrocarbons derived from petroleum, chlorinated compounds, lixiviated compounds, and volatile compounds in the air (Meagher, 2000; Newman & Reynolds, 2004; Imfeld et al., 2009). The use of the phytoremediation depends on the type of affected resource, on the objectives of the remediation (type of contaminant), on the type of preferable outcome process: Stabilization, Isolation, Reduction, Degradation, Metabolization and/or Mineralization.

In agreement with some authors like Susarla et al. (2002) and Zhang et al. (2012), the plants play a major determinant role in the remediation of soils and contaminated waters through several processes that diminish the toxicity grade of the contaminant compounds by modifying the physicochemical properties of the contaminated system and the ratio of exudate--roots in order to increase the organic carbon and the ventilation of the radicular area.

Phytoremediation has been widely researched in the recent years in order to understand the sorption and metabolic processes of organic and inorganic compounds by the plants (Bock et al, 2002). Pena et al. (2006) establish that the plants render an important function on the phytoremediation of organic compounds like the hydrocarbons because i) The rhizosphere improves the properties of the soil through the injection of air and the introduction of nutrients that encourage microbial diversity, ii) the interaction between the plant and the microorganisms promotes the cometabolism of the contaminants that forces the activation of several metabolic options, and iii) the transportation of water to the superior areas of the plant works in favor of the degradation or immobilization of the contaminant in order to produce a degradation in the interior and exterior of the plant.

It has been demonstrated that the plants can metabolize or immobilize the petroleum hydrocarbons through several processes, such as the metabolic oxidation or the co-oxidation, in agreement with the levels of concentration of the hydrocarbons. This is why upon low toxicity levels the rhizospheric system supplies favorable nutritional and ventilation conditions in order to increase the population and diversity of the flora, while on high toxicity levels the exudation of sugars, the growing factors, and the organic acids may be affected jointly with a break in the rhizospheric equilibrium, the decrease in microorganisms (fungi and bacteria), and the decrease of nitrogen assimilating and atmospheric nitrogen fixation bacteria (Perez et al., 2002).

3.1 Principal mechanisms of phytoremediation

In phytoremediation several mechanism are present and they are classified according to the place where the process takes place (Figure 1): Phytoextraction, Rhizodegradation, Phytostabilization, Phytodegradation, and Phytovolatilization (Imfeld et al., 2009; Jain et al., 2011).

Phytoextraction This refers to the sorption of the contaminantby the root of the plant, also known as phytoaccumulation, because of its capacity to accumulate different compounds on its reaping parts, and tissues of leaves and stems (Glick, 2003; Carpena & Bernal, 2007), mainly when they are not completely or quickly degraded. This mechanism may be affected by the lipophilic nature of the compound, measured under the octanol-water partition coefficient ([K.sub.OW]) (Kamath et al., 2004). Several studies (Schnnor, 1997; O'Niell & Nzengung, 2004; Wallace & Kadlec, 2005; Boonsaner et al., 2011) show that phytoaccumulation is an efficient mechanism in order to remove BTEX, chlorinated solvents, and aliphatic hydrocarbons of short chain because its K varies between 1, 0-3, 5. The compounds that have a [K.sub.OW] > 4 are hydrophobic compounds and, therefore, cannot be easily incorporated to the roots of the plant (Khan et al., 2013), those that are soluble water have log [K.sub.OW] < 1, 0 values.

The plants destined to a Phytoextraction process are characterized for their high tolerance and effectiviness on accumulating the contaminant and they are also easy to harvest (Vangronsveld et al., 2009). The principal advantage of this process lays on its low cost implementation if compared to other remediation techniques, and, among its disadvantages, it must be handled in low or moderated contaminant concentrations that require high accumulation times (Spaczynski et al., 2012).

Rhizodegradation In this phytoremediation technique the degradation of the organic contaminants takes place close to the roots of the plant through microorganisms (fungi and bacteria) that are stimulated by the liberated enzymes from the plant. This is the reason why it is also called phytoestimulation because the plants do not directly degrade the contaminant but in turn generate the proteins and enzymes that guarantee the growth of fungi and bacteria that degrade it (Van Deeps, 2006; Cameselle et al, 2013; Khan et al, 2013).

The Rhizodegradation in the case of soils, aside from having a low maintenance and investment cost if compared with conventional technologies as excavation, improves soil quality and texture, delivering stability and mitigating the erosion generated by the wind and water (Gerhard et al., 2009). It, however, presents disadvantages in the face of traditional technologies because of the low rate of bioremediation and stressing environmental factors in temperature, precipitation, nutrients, pathogenic plants, herbivores, and the competence of weeds that may hinder or diminish the growth of the plants (Nedunuri et al., 2000).

Phytostabilization This refers to the use of plants in order to reduce the bioavailability of the organic and inorganic contaminants by immobilizing them through the addition of amendments to the soil, the absorption or the roots of the plants or soil particles, and the precipitation in the area of the root in order to hinder their migration and the decrease of erosion, the runoff, and the lixiviation (Van Deeps, 2006; Kumpiene et al., 2007). This mechanism is mainly applied to metallic contaminants because sometimes is advisable to immobilize the compound due to its difficult or incomplete biodegradation (Cameselle et al, 2013). This phytoremediation technique, Schwitzguebel et al. (2011), promotes the restoration and the biodiversity of the ecosystems that represent ecological benefits for the production of industrial harvests. It is also advised the use of endemic plant species, adapted to the soils and weather of the areas to remedy, in order to avoid adaptation and invasion problems.

Phytodegradation This mechanism, also known as phytotransformation, allows the absorption of contaminants and transforms them into more simple molecules such as C[O.sub.2] y [H.sub.2]O to later incorporate them to the plant tissues and help in its growth (Conesa et al., 2012; Spaczynski et al., 2012). This process is catalyzed by the enzymes and proteins from the plants in order to generate a break up in the contaminant molecules (de-Bashan et al., 2012). The Phytodegradation takes place in three steps: i) conversion through oxidation-reduction reaction, ii) amino acid and sugar conjugation, and iii) the incorporation of the contaminant to the plant through its organelles (vacuole and cell wall) (Dietz & Schnoor, 2001). Spaczynski et al. (2012) point out that in spite that inthe vegetal cells a complete degradationof organic compounds generally does not take place, the plants use the products of biotransformation in other forms such as the amino acid synthesis.

The Phytodegradation associated with certain microorganism has presented efficient results on the degradation of organic compounds such as the petroleum derivates through a cooperation process named rhizo-phytodegradation, where the potential and biodiversity of the secondary metabolism of the plants is used (Vangronsveld et al., 2009; Schwitzguebel et al., 2011).

Phytovolatilization This phytoremediation process is based on the absorption of the contaminant compound that is generally of a low molecular weight on the part of the plants in order to achieve its posterior volatilization to the atmosphere through the leaves (Glick, 2003; O'Niell & Nzengung, 2004; Gerhardt et al., 2009; Conesa et al., 2012). The phytovolatization has been mainly used for the elimination of heavy metals such as mercury which is transformed into its most elemental form that is less toxic than the organic or inorganic one, but this technique, however, has the disadvantage that the liberated metal into the atmosphere may return to the ecosystems through precipitation and be deposited again (Ghosh & Singh, 2005).

3.2 Environmental factors and nutritional needs in the phytoremediation of hydrocarbons

Among the determinant factors in the process of phytoremediation pointed by several authors (Frick et al., 1999; Glick, 2003; Petenello & Feldman, 2012) the following are found: i) the concentration of microorganisms around the roots of the plants, ii) the regime of rains, iii) the type of roots, iv) the adaptation capacity of the plant to the contaminants, v) the temperature and solar radiation, vi) the concentration of the contaminant, and vii) the temperature. Aside from these, Gerhardt et al. (2009) indicate that relevant environmental factors for the phytoremediation on soils are: i) structure, ii) organic matter contained, iii) pH, iv) humidity contained, and v) microbial activity.

The increase in the concentration of carbon due to the hydrocarbons can create hydrogen and phosphorus deficiencies because of the immobilization caused by microbial processes and the nutritional requirements of the microorganisms and the plants for their metabolism and the remediation of the affected area (Kirkpatrick et al., 2006; Guendy, 2008). Pardo et al. (2004) and Ramirez et al. (2009) indicate that the proportion C: N: P (100:10:1) must be adjusted through the addition of any type of fertilizer to stimulate the remediation whenscarce nutrient availability is present. If, on the other hand, the content of nitrogen is excessive, it may become an inhibitory factor because of the toxic effect provoked by the accumulation of nitrates and nitrogen oxide generated by the processes of denitrification under anaerobic conditions and low pH values (Chaineau et al., 2005; Ramirez et al., 2009).

The assimilation of nutrients by the plants takes place thanks to the transformation of nitrogen in organic form to organic compounds that are good for cell formation and new tissue; this is why the potential of nutrient intake by the macrophytes is limited to its growth rate and the concentration of nutrients in their tissues (Vymazal, 2007). The capacity of nutrient intake by the emerging plants is between 1000 to 2500 Kg N/Ha-year according to Vanier & Dahab (2001), and the ammonium ion found in the wetlands is the nitrogen form that can be taken by the plants through their radicular area or by the anaerobic microorganisms that turn it back into organic matter (Zhu et al., 2010). These mechanisms are dependent on biotic and abiotic factors like pH, redox potential, availability and presence of microorganisms (Jones et al., 2004).

4. Phytoremediation application on hydrocarbon contaminated waters through constructed wetlands

The constructed wetlands are engineering systems that have been designed and built in different parts of the world since the 1950's with the purpose of a controlled environment reproduction of the processes that take place in the natural wetlands, taking advantage of the interactions between the vegetation, the soils, and the microbial communities in order to treat wastewaters (Brix, 1994; Verhoeven & Meuleman, 1999; Vymazal, 2007; Haarstad et al., 2012). The constructed wetlands may be classified in agreement with the type of growth or life form of the predominant macrophytes and with the flow regime (Brix, 1994; Mahmood et al., 2013). The first classification is divided in systems based on macrophytes i) free floating, ii) submerged, and iii) emerging roots (Vymazal et al., 1998). In the second classification, meanwhile, the constructed wetlands may be characterized as a function of the incoming water flow direction into the system; this can be in horizontal, surface, subsurface, or vertical flow (Kivaisi, 2001; Kuschk et al., 2012).

The constructed wetlands have had different successful applications since their first implementations, from the most developed treatment of domestic wastewaters to the draining of mines, wastewater from swine farms, leachates, residues from the food industry, waters contaminated by pesticides, liquid residues from the textile industry, from the pulp and paper, sugar and distillation industries, dumping from the military and explosive industry (Haberl et al, 2003; Paredes et al., 2007; Rani et al., 2011; Vymazal, 2011). The constructed wetlands have been used in some countries, like China, for the treatment of lakes and contaminated rivers (Zhang et al., 2012). The principal steps for the removal of hydrocarbons through wetlands are the volatilization, the biological or microbial degradation, the photochemical oxidation, the sedimentation, the absorption, and the chemical filtration and precipitation (Kadlec & Wallace, 2009). Zhang et al. (2010) indicate, however, that these compounds may generate morphological damages in the plants, such as reduction in the growth of the roots and stems, deficiencies in the growth of radicular hair, and delays in floration and white dots appearance. At the cellular and tissue level, simultaneously, the plants may suffer an oxidant stress that reduces their effectiveness in the nutrient and water intake which inhibits the photosynthesis and the electron transportation. Table 1 presents a summary of the research where phytoremediation was used through constructed wetlands for the treatment of contaminated waters with different species of hydrocarbons.

This research confirms the advantages of the constructed wetlands for the treatment of hydrocarbons derivated from petroleum where removals from 67% to 90% and beyond are present. As a general rule, no evidence of predominant mechanisms of phytoremediation are present because the behavior chosen by the plants mainly lays on factors such as the partition coefficient of the contaminant hydrocarbon, volatility, the flow regime, and the type of plants used in the constructed wetlands. The studies present, regarding the use of plants, a vegetal species that is commonly used in research; the Phragmites australis has been the vegetal species largely used on the treatment of wastewaters and specifically on constructed wetlands because it has proven that the chemical demand for oxygen, the nutrients (dissolved and in particles), and some heavy metals are reduced when this type of plant is used in these waters (Chambers et al., 1999), and, additionally, the hydraulic conductivity is improved on the beds of the wetlands to insure the subsurface flow of the waters (Brix et al., 2007). This is backed up with the use of the P. australis for the removal of compounds derivated from petroleum through studies where there is coincidence about the fact that the substances secreted by the roots stimulate the degradation of the studied compounds, and their interaction with microorganisms such as the Mycobacterium spp accelerate this degradation thus increasing its use possibilities on the treatment of compounds with high molecular weight (Jouanneau et al., 2005; Toyama et al., 2011). It is evident, however, that a great deal of the research is carried out on a pilot and lab scale, but there is the need for great scale studies to contribute to the establishment of implementation criteria on this type of systems in order to test their effectiveness on the treatment of great volumes of contaminated water by different hydrocarbons.

5. Phytoremediation used on the treatment of soils contaminated with hydrocarbons

Aside from its ecological and economic efficiency on the treatment for great soil areas and low contaminant concentration; otheradvantages offered to contaminated soils by the phytoremediation are the increase in microbial activity, render help in erosion reduction, and protection against the direct radiation of the sun (Cameselle et al, 2013). Soil phytoremediation is generally based on planting selected vegetal species on contaminated soils where the action of the plants is initiated. Kathi & Khan (2011) introduce several studies with a wide selection of vegetal species for the treatment of contaminated soils by hydrocarbons, such as trees, plants, and shrubs among others. There are a wide number of experiences about the effectiveness of phytoremediation on contaminated locations by petroleum derivates. Table 2 introduces a review on the research carried out on remediation of soils contaminated by hydrocarbons derivated from petroleum, and a summary of the principal findings is given with the species used for each case. There is a difference between the removal presented in the treatment of the wetland waters and the efficiency of plants that remove the hydrocarbon compounds on the soil, the later have an efficiency that varies in a wide range between 40-97% for the reported studies. A common vegetal species is neither present on the reported studies, there is a wide variety of used species on them. The authors, however, coincide in the fact that the mayor removals are introduced when grass and leguminous plants are present. It is more frequent to find real scale experiences for the removal of hydrocarbons on soils; however, the common denominator is that these experiences require at least three years to obtain adequate results (Macci et al., 2013). The used vegetal species on soil phytoremediation generally present tolerance to hydrocarbonated compounds of up to 10000 mg/ Kg, and, additionally, in some species the presence of contaminant compounds favor their growth and development.

6. Conclusions

This document confirms the potential of the wetland systems in the removal of the total petroleum hydrocarbons. This treatment alternative becomes a promising solution in order to reduce the effects caused by the contamination through these compounds with the clear application advantage that it may be used in or ex situ.

It is important to know the physiological and morphological characteristics of the plants to be used in order to remove the hydrocarbons from the wetlands. This will lead to the employment of macrophytes with a positive response towards the tolerance of the compounds in order to understand the involved removal and interaction processes between plants-environment-microorganisms that allow to transform and/or reduce the hydrocarbon concentration. It is also important to inquire about the microbial activity that takes place in the interior of the wetlands through biochemical and molecular tests that allow the identification of the associated microorganisms to the process of the hydrocarbon removal.

In spite of the different phytoremediation research projects done worldwide, several gaps still remain that hinder the full understanding on how the technology functions because many of the experiments have taken place on a lab scale where a great deal of the factors have been controlled and this reducesthe possibility to interpret the system effectiveness in real conditions where the weather conditions may also influence the degradation of the hydrocarbons. The application of phytoremediation must be evaluated on a real scale in order to estimate the efficiency of this technology in the application of specific organic compounds because the hydrocarbon family is very wide and their reactions with the water, soil, and plants change from one species to another.

7. Acknowledgement

The authors wish to express their thanks to the Administrative Department of Science, Technology and Innovation--Colciencias and to the Universidad Tecnologica de Pereira, especially to the Water and Sanitation Research Group of the Faculty of Environmental Sciences for their support during this research.

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Janneth Cubillos * ([seccion]), Pilar Pulgarin *, Johnatan Gutierrez *, Diego Paredes *

* Water and Sanitation Research Group, Faculty of Environmental Sciences, Universidad Tecnologica de Pereira, Colombia.

([seccion]) jacubillos@utp.edu.co, pilarpulgarin@utp.edu.co, johnguti@utp.edu.co, diparede@utp.edu.co

(Recibido: 19 de septiembre de 2012--Aceptado: 18 de noviembre de 2013)

Table 1. Research done on the use of constructed wetlands
for the treatment of hydrocarbons in waters

Type of                 Plant(s) Used      Configuration
contaminant                                    of the
                                             plantation

Subsurface water       Salix babylonica          HF
contaminated with
gasoline-ethanol

Wastewaters            Typha latifolia          HFSS
contaminated with       - Lemna minor
diesel                    (Control)

Subsurface waters       Ceratophyllum           HFS
with hydrocarbons        demersum and
and cyanide            Potamageton spp

Effluents from        Salix, Phragmites,     HFSS aired
BTEX refinery          Schoenoplectus,     and non-aired
process                   Juncus and
                           Cornus.

Subsurface waters     Salix, Phragmites,     Aired HFV
with BTEX and          Scirpus, Juncus,
diesel                      Cornus

Waster waters             Phragmites            HFV
contaminated with         australis
benzene

AR effluent of a          Phragmites         HFS, HFSS
primary treatment       australis and        and gravel
with PAHs and            Arudo donax           filter
equilbenzene

Subsurfacewaters          Phragmites           HFHSS
contaminated with         australis
benzene and MTBE

Runoff waters with        Phragmites            HFV
hydrocarbons from         australis
vehicle exhaust
pipesand heavy
metals

Subsurface waters         Phragmites        HF (1); HFSS
contaminated with         australis.       (2) (planted &
benzene and MTBE                            non-planted)

Synthetic              Scirpus grossus          HFSS
wastewaters with
diesel.

Refinery effluents      Ceratophyllum           ---
                           demersum

Type of                          Findings                   Ref
contaminant

Subsurface water        Reduction of ethanol and          Corseuil
contaminated with     benzene >90%. Toxic compounds       & Moreno
gasoline-ethanol           for macrophytes in              (2001)
                      concentrations over 2000 mg/L.

Wastewaters           Removal efficiencies between        Omari et
contaminated with     80, 78 y 72% on the surface,       al. (2003)
diesel                medium and bottom sections of
                           the planted wetland.

Subsurface waters      Removal of 67% of gasoline      Gessner et al.
with hydrocarbons              and diesel.                 (2005)
and cyanide

Effluents from        Research done on the pilot and     Wallace &
BTEX refinery           real scales; the greatest      Kadlec (2005)
process                 removal efficiencies were
                       found in aired wetlands; the
                      removals of BTEX reached 94%.

Subsurface waters     Removal of up to 88% of BTEX;     Bedessem et
with BTEX and           benzene reduction between        al. (2007)
diesel                           13-21%.

Waster waters            Benzene removal of 85%;        Eke & Scholz
contaminated with     in wetlands with biomass, the        (2008)
benzene               removal took half of the time
                         to that of the wetlands
                          without biomass; the
                      predominant removal mechanism
                         was Phytovolatilization.

AR effluent of a        The HFSS presented better       Fountoulakis
primary treatment      efficiencies tan the other      et al. (2009)
with PAHs and            evaluated systems; the
equilbenzene            Phytodegradation mechanism
                             was predominant.

Subsurfacewaters      Compared wetland systems with    Seeger et al.
contaminated with        gravel and planted. The           (2011)
benzene and MTBE      greatest removal efficiencies
                       were on the planted wetland.

Runoff waters with    Removalefficiencies of 90-95%.    Tromp et al.
hydrocarbons from      Widely satisfied the Dutch,         (2012)
vehicle exhaust          European, and American
pipesand heavy        standards for surface waters
metals                and shallow subsurface waters.

Subsurface waters        The HF jointly with the        Chen et al.
contaminated with     planted HFSS presented similar       (2012)
benzene and MTBE          removal efficiencies.

Synthetic                 Toxic concentrations         Al-Baldawi et
wastewaters with         > 17400 mg/L of diesel;         al. (2013)
diesel.                removal of 91,5%. Growth on
                       the microbial concentration
                       on the rhizosphere with the
                       increase on the hydrocarbon
                             concentrations.

Refinery effluents         The plant presented          Alwan et al.
                           efficiencies > 80%.             (2013)
                          The principal removal
                      mechanismwas Phytoextraction.

HFS: Wetland of Superficial flow; HFSS: Wetland of
Subsurface Flow; HFHSS: Wetlands of Subsurface horizontal
Flow; HFV: Wetland of Vertical Flow; HF: Floating Wetland

Table 2. Research done on the use of constructed wetlands
for the treatment of hydrocarbons on soils

Contaminant          Vegetal species used
on the soil

Soil with HTP         Loliummultiflorum

PAHs                   Medicago sativa
                       Panicumvirgatum
                    Schizachyriumscoparium

PAHs on              Spartinaalterniflora
marine
sediment

Accidental                Leguminous
spill of fueloil      (Clitoriaternatea,
on the soil.         Phaseoluscoccineus y
                       Cicerarietinum)
                    Gramineae (Brachiaria
                     hibrido y brizanthay
                       Panicum maximum)

Hydrocarbons           Six gramineae--
on soils            Principally, Medicago
                            sativa

Phenanthrene            Echinogalus y
and Pyrene          Astragalusmembranaceus

Hydrocarbons          Mirabilis jalapa L
from
petroleum
fields

Sediments            Rizophora mangle and
from                 Avicenniaschaueriana
mangrove
areas
contaminated
with total
hydrocarbons

Soil                   Canna generalis
contaminated
with BTEX

Soil with           Trees (P. nigra and P.
hydrocarbons              tomentosa)
and heavy           Shrub (C. scoparius.)
metals

Soil                   Pinusdensiflora,
contaminated       Populustomentiglandulosa
with diesel oil        Thujaorientalis

Contaminant                    Findings                     Ref
on the soil

Soil with HTP        Removal efficiencies > 97%        Gunter et al.
                   in total hydrocarbons; greater         (1996)
                    presence of microorganisms if
                    compared with soils unplanted.

PAHs               These plantation showed removal    Prahand et al.
                         efficiencies of 50%              (1998)
                            in six months

PAHs on             The greatest concentration of      Weatherly et
marine             contaminant was found in roots        al.(2006)
sediment           and stems in two and three order
                   of magnitude respectively, below
                    the concentration of the soil.
                     Principally present adhered
                     to the surface of the root.

Accidental          The gramineae easily tolerated     Sangabriel et
spill of fueloil    the compound The predominant        al. (2006)
on the soil.                mechanism was
                        rhizovolatilization.
                     The Brizhanta got the best
                        compound degradation..

Hydrocarbons        Removals > 50% were obtained.     Phillips et al.
on soils           The Alfalfa presented a dominant       (2006)
                   effect over the microorganisms,
                         stimulating growth.

Phenanthrene        The studied compounds are not       Lee et al.
and Pyrene             toxic for the mentioned            (2008)
                   leguminous. This degradation on
                      the part of the plants is
                    attributed to the increase of
                   microorganism in the rhizosphere
                    and their microbial activity.

Hydrocarbons         Removals between 40-60% and        Peng et al.
from               19-37% in natural and greenhouse       (2009)
petroleum          conditions respectively. Toxic
fields             for the plants from 10000 mg/Kg.

Sediments          The phytoremediation presented     Moreira et al.
from                   greater efficiencies of         (2011; 2012)
mangrove            contaminant removal (87%) tan
areas                the bioremediation and the
contaminated         plants presented a greater
with total         growth in compared to the white
hydrocarbons        units. The predominant removal
                   mechanism was Rhizodegradation.

Soil                The plant can achieve removal      Boonsaner et
contaminated            of l 80% of BTEX. Its           al. (2011)
with BTEX           predominant removal mechanism
                         is Phytoextraction.
                   Consideration to the soil water
                    content must be taken because
                   it affects the phytoremediation
                              mechanism.

Soil with               Real scale (10000m2).          Macci et al.
hydrocarbons        The reduction of hydrocarbons         (2013)
and heavy            reached 40% in three years.
metals                Increase of dehydrogenase
                    indicating microbial activity.

Soil               The evaluated species tolerated     Jagtap et al.
contaminated        concentrations of 6000 mg/Kg.         (2014)
with diesel oil    The microbial consortia and the
                   addition of fertilizers improved
                       the process efficiency..
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Title Annotation:articulo en ingles
Author:Cubillos, Janneth; Pulgarin, Pilar; Gutierrez, Johnatan; Paredes, Diego
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Date:Jun 1, 2014
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