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Ecological Engineering 61 (2013) 496–500

Contents lists available at ScienceDirect

Ecological Engineering

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ffect of aeration on hydrocarbon phytoremediation capability inilot sub-surface flow constructed wetland operation

sraa Abdulwahab Al-Baldawia,d,∗, Siti Rozaimah Sheikh Abdullaha, Fatihah Sujab,urina Anuara, Idris Mushrifahc

Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Selangor, MalaysiaDepartment of Civil and Structural Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Selangor, MalaysiaTasik Chini Reasearch Centre, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Selangor, MalaysiaDepartment of Biochemical Engineering, Al-khwarizmi College of Engineering, University of Baghdad, Baghdad, Iraq

r t i c l e i n f o

rticle history:eceived 10 June 2013eceived in revised form 6 October 2013ccepted 15 October 2013vailable online 9 November 2013

a b s t r a c t

This study consisted of an experiment with 12 wetland reactors, operating at different diesel concen-trations of 0%, 0.1%, 0.175% and 0.25% (Vdiesel/Vwater) and aeration rates (0, 1 and 2 L/min) and aimed toevaluate the effect of aeration supply on a pilot treatment performance during 72 days of operation. Thesub-surface flow constructed wetland (SSFCW) was planted with the native Malaysian plant of Scirpusgrossus. The best removal of total petroleum hydrocarbon (TPH) from diesel contaminated water in the

eywords:hytoremediationcirpus grossuseration

SSFCW reactors was found to be 84.1%, 86.3% and 88.3% for 0.1%, 0.175% and 0.25% diesel concentrations,respectively, with 1 L/min aeration treatment. Aeration supply can also improve the plant growth andbacterial population, indicating that combining plants and bacteria together with aeration representsbetter treatment for water contaminated with diesel. According to statistical analyses, 1 L/min aeration

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. Introduction

Constructed wetlands (CWs) are currently a well-acceptedriendly ecosystem for wastewater treatment technology pro-esses due to the lower cost of operation and easier maintenanceAl-Baldawi et al., 2013a; Wu et al., 2013). In constructed wet-ands, contamination is removed through filtration beds vialant–bacteria degradation and by physicochemical processes insystem of aerobic, anoxic, anaerobic zones, with aerobic zones

imited to the areas close to the roots, where oxygen leaks to theubstrate (Vymazal, 2010). The main sources of oxygen transfern sub-surface flow constructed wetland (SSFCW) treatment aretmospheric diffusion via plant aerenchyma and the convectiveow of air within the porous medium (Kadlec and Wallace, 2009;anner and Kadlec, 2003).

Aerobic processes are usually preferred for the treatment of

ydrocarbons in soil or underground water, because they causeore contaminants to be degraded more rapidly. Vieira et al. (2009)

ompared biodegradation of diesel oil and gasoline processes under

∗ Corresponding author at: Department of Chemical and Process Engineering,aculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia,elangor, Malaysia. Tel.: +60 3 89216407; fax: +60 3 89216148.

E-mail addresses: israaukm@gmail.com, israabal@eng.ukm.my (I.A. Al-Baldawi),ozaimah@eng.ukm.my (S.R.S. Abdullah).

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925-8574/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.ecoleng.2013.10.017

rameter for TPH removal in diesel-contaminated water using S. grossus.© 2013 Elsevier B.V. All rights reserved.

onstant aeration, without aeration, or with intermittent aerationonditions and found that the latter treatment resulted in greaterPH removal after 22 days of operation. Zhang et al. (2010) stud-ed the effect of limited artificial aeration on domestic wastewaterreatment in CWs and found that it is an efficient and cost-ffective method for pollutant removal. In addition, Butterwortht al. (2013) compared between aerated and non-aerated horizon-al flow constructed wetlands for tertiary nitrification treatmentnd concluded that aeration enhanced nitrification in the aerateded with 99% mass removal.

The aim of this study was to examine and compare the perfor-ance of a pilot SSFCW using bulrush Scirpus grossus plants for the

reatment of diesel contaminated water in terms of total petroleumydrocarbon (TPH) removal from water. To date, no study has beenerformed to see the affect of different aeration rates on dieselemoval in SSFCW using S. grossus. In addition, the effect of aera-ion on plant–microbe growth in constructed wetland reactors willlso be discussed.

. Materials and methods

.1. Design of sub-surface flow constructed wetlands

Twelve parallel pilot SSFCW reactors without aeration (0 L/min)nd with aeration (1 or 2 L/min), and 0%, 0.1%, 0.175% or 0.25%

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Vdiesel/Vwater) diesel concentrations, were constructed, to study thereatment of wastewater containing diesel. The wetland reactorsere located in a greenhouse at Universiti Kebangsaan Malaysia.

he wetland reactors were made of fibreglass, with dimensions of80 cm (L) × 90 cm (W) × 90 cm (H), and 0.5 cm thickness. Each wet-

and reactor was sequentially filled from the bottom to top with aayer of medium gravel (˚ 1–5 mm) to 15 cm height; a layer of fineravel (˚ 10–20 mm) to a further 15 cm height; and a layer of fineand (˚ 1–2 mm) of 20 cm in height. Additional water was addednce a week to the reactors to maintain the water level at the sameevel as that of the surface sand bed.

In the aerated wetland reactor, supplementary aeration wasocated 20 cm below the bed surface, via five air distribution pipessing an air compressor of 2 HP (ORIMAS HP2, Malaysia). When theompressor was switched on, the bubbles were observed cominghrough sand layer and along the tank. Each SSFCW reactor waslanted with 50 plants of one-month old at a depth of 2–10 cm inhe sand. After planting, the wetland reactors were fed with mixedynthetic wastewater contaminated with diesel through the inletoint at the midpoint of the sand bed. All wetland reactors wereperated batchwise in single exposure.

.2. Analysis of physical parameters

Water samples were collected to evaluate the physical param-ters of temperature, T (◦C); pH; dissolved oxygen, DO (mg/L);nd oxidation reduction potential, ORP (mV). Water samples wereaken from three points inside each reactor at different heightsrom the bottom of the reactor: upper point (20 cm); middle point10 cm); and lower point (5 cm) to minimise sampling errors. Thehysical parameters were measured using a multi-probe IQ 150 (I.Qcientific Instruments, U.K.) for pH, ORP and temperature measure-ents, and a dissolved oxygen sensor (GLI International, Model 63,.S.A.) for DO.

.3. Analysis of TPH content

Water samples from the outlet taps were collected and analysedo examine the TPH removal efficiency of the wetland reactors.he TPH content was analysed through the liquid–liquid extractionethod with dichloromethane and gas chromatography (Lohi et al.,

008). The method followed the Environmental Protection AgencyEPA) Method 3510C (USEPA, 2011). The samples were analysedy a GC–FID using a capillary column (Agilent Technologies, Model890A, GC system, U.K.) with a HP-5, 5% phenyl methyl siloxaneolumn (30 m × 0.32 mm i.d × 0.25 �m) with helium as the carrieras. The column temperature was programmed to remain at 50 ◦Cor 1 min, and then ramp at 15 ◦C per min to 320 ◦C for 10 min.

.4. Bulrush growth parameters

Morphological data of the plants were monitored throughouthe experiment. At each sampling time (0, 14, 28, 42 and 72 days),lant growth parameters of wet and dry weight were recorded.hree replicate samples of S. grossus were randomly collected fromach SSFCW reactor, washed with tap water, dried with tissueaper and stem height and root length were then measured. Weteight was recorded before the bulrush was dried at 70 ◦C for 72 h

nd reweighed to obtain the dry weight (Ji et al., 2007).

.5. Bacteria plate-counts

Bacterial populations during the phytoremediation processere analysed by the plate-counting method (Prescott et al., 2002;l-Baldawi et al., 2013b). Total bacterial number was estimated

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ineering 61 (2013) 496–500 497

sing sterile plates containing nutrient agar medium (tryptic soyagar, TSA) (Zhang et al., 2012).

.6. Statistical analysis

Statistical analysis was conducted with Statistical Product andervice Solutions (SPSS) 16.0 for Windows. Physical parametersere analysed according to one-way analysis of variance (ANOVA)

nd Pearson linear correlation to determine any significant effectf the aeration rates on the physical parameters. To comparePH removal, plant growth and bacterial populations with aer-tion, retention time and diesel concentration, the data werenalysed using two-way ANOVA. Duncan’s multiple range testsere used to evaluate statistical differences of all the parameters

t the 0.05 probability level unless otherwise stated. The sam-lings were performed in triplicate and the results are presenteds means ± standard deviation.

. Results and discussion

.1. Physical profile along the media bed

Temperature is generally ranged between 23.2 and 29.1 ◦Cith the three different aeration rates and diesel concentrations,epending on the greenhouse temperature of 23–30 ◦C and thereere not significantly correlated with aeration rates (r = −0.082,> 0.01). Huang et al. (2013) showed that temperature wereositively correlated with micro-environment, plant growth anditrogen removal in SSCWs. The pH is an essential factor for wateruality and greatly influences the aquatic system. The pH of thehree aeration rates and different diesel concentrations rangedetween 5.1 and 8.9 with significant negative correlation with aer-tion rate (r = −0.478, p < 0.01). In contrast, Ji et al. (2007) showedhat pH was not affected by SSFCW in oil-contaminated water treat-

ents.According to IWA (2000), the prevailing conditions in the SSFCW

reatment beds were anoxic. Based on DO and ORP monitoring inhis study, it was observed that anoxic conditions dominated in theon-aerated and aerated wetlands. Oxygen is an important envi-onmental parameter that control organics biodegradation. MeanO concentrations in SSCWs ranged from 1.12 to 3.9 and 1.03 to.55 mg/L with aerations (1 and 2 L/min) and without aeration,espectively (Table 1). Aeration rates showed a positive correla-ion (r = 0.262, p < 0.01) with DO because in SSFCW oxygen is lowue to the difficulty of surface diffusion into their pore water (Chent al., 2012). However, DO was not statistically different betweeneration rates of 1 and 2 L/min (p = 0.691). In the wetland reac-ors with aeration, the ORP was in the range of −35.4 to 60 mV,ut was −108.4 to 53.1 mV in without aeration reactor at differ-nt diesel concentrations and significantly correlated with aerationates (r = 0.179, p < 0.01). The ORP have no significant differenceetween aeration rate of 0 and 1 L/min (p = 0.699) while it was sig-ificantly different with 2 L/min aeration rate (p < 0.05). An increase

n DO and decrease in ORP with increasing aeration was observedlong the SSFCW beds, indicating the development of anoxic condi-ions in the whole medium bed. Thus, supplementary aeration ratef 1 L/min is enough and effectively for a better performance of the2 SSFCW to increase oxygen transfer in the wetland treatmentystems.

.2. TPH removal from water in wetland reactors

The effect of aeration on TPH removal efficiency was analysedith two-way analysis of variance (ANOVA). Removal of TPH fromater differed significantly between aeration rates and retention

498 I.A. Al-Baldawi et al. / Ecological Engineering 61 (2013) 496–500

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ig. 1. TPH removal in the phytoremediation of water contaminated with diesel eetters A and B represent statistically significant differences in TPH removal on a spp < 0.05).

ime (p < 0.05), but did not differ significantly between diesel con-entrations (p = 0.409).

TPH removal in the wetland reactor without aeration was about1.5%, 71.4% and 66.6%, whereas it was about 84.1%, 86.3% and8.3% or 81.3%, 84.5% and 90.7% with diesel concentrations of.1%, 0.175% and 0.25% diesel and aeration of 1 or 2 L/min, respec-ively. Removal of TPH from water was significantly higher with 1r 2 L/min aeration compared with no aeration after 72 days ofbservation (Fig. 1) for 0.175% and 0.25% diesel concentrations.mong all aeration rates with different diesel concentrations, areater TPH removal efficiency was observed at a diesel concen-ration of 0.25%, and aeration of 1 or 2 L/min, which exceeded8.3% and 90.7%, respectively (Fig. 1). The performance of wetlandeactors was clearly better with aeration. This result is consistentith the findings of Rossmann et al. (2012), showing that aera-

ion resulted in an improved efficiency of the removal of pollutants

uch as nitrogen (N), phosphorus (P) and phenolic compounds. Theemoval in wetland reactors is due to physical, chemical and bio-ogical mechanism such as volatilisation, adsorption, photolysis,hemical oxidation and microbial degradation (Lors et al., 2012).

able 1ean values of physical parameters obtained during the monitoring period.

Parameter Without aeration(0 L/min)

With aeration(1 L/min)

With aeration(2 L/min)

Temperature (◦C)Mean 25.69a 26.36b 25.48a

SD (n) 0.86 (60) 0.91 (60) 1.20 (60)Min 23.90 23.70 23.20Max 27.70 27.80 29.10

pHMean 7.07a 6.35b 6.09c

SD (n) 1.18 (60) 0.37 (60) 0.26 (60)Min 5.10 5.50 5.32Max 8.90 7.00 6.60

DO (mg/L)Mean 1.93a 2.41b 2.37b

SD (n) 0.65 (60) 0.65 (60) 0.66 (60)Min 1.03 1.12 1.19Max 3.55 3.83 3.90

ORP (mV)Mean −4.62a −6.57a 6.59b

SD (n) 32.87 (60) 21.3 (60) 18.67 (60)Min −108.4 −35.4 −25.90Max 53.1 60 55.00

D: standard deviation; n: sample number; different letters (a and b) in row showsignificantly different by Duncan’s (p < 0.05).

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with or without aeration. Data are presented as means ± standard deviation (SD).day when compared with different aeration rates within one diesel concentration

mong them, biodegradation is the primary pathway of the highPH removal efficiency with availability of aeration.

This comparison shows that a supply of 1 L/min aeration wasuitable to enhance TPH removal efficiency by wetland reactors,ecause there was no significant difference between aeration ratesf 1 and 2 L/min, thus 1 L/min aeration is a more cost-effectiveption. Aeration contributes to aerobic conditions within the wet-and substrate and consequently to an enhancement of the dieselegradation process by bacteria (Stefanakis and Tsihrintzis, 2012).

.3. Plant biomass propagation

S. grossus was able to grow in diesel-contaminated water andnaffected by all diesel concentrations with aeration, but slightly

nhibited at diesel concentrations without aeration, compared withhe corresponding control (0% diesel). Statistically analysis showed

significant effect of wet weight with aeration 1 and 2 L/minompared to without aeration (p < 0.05) (Fig. 2a). However, notatistically significant difference was found for dry weight, com-aring treatment without aeration with those with 1and 2 L/mineration (p > 0.05) (Fig. 2b).

A negative effect of diesel contamination on growth was clearlybserved in the no aeration treatment with a diesel concentra-ion of 0.175% or 0.25%. However, S. grossus can grow better withncreased aeration in contaminated water in all diesel concentra-ions (0.1%, 0.175% and 0.25%). Thus, S. grossus has the potential tohytoremediate water contaminated with diesel up to 0.25% withn aeration supply of 1 L/min, for optimum TPH degradation withost savings in terms of electric power.

.4. Effects of aeration on bacterial population

In this study, we evaluated the effects of aeration on bacte-ial populations by comparing the difference between without andith aerations of 1 and 2 L/min (Fig. 3). Statistical analysis of the

acterial population by two-way ANOVA showed significant dif-erences among retention time, diesel concentration and aerationp < 0.05). There was a highly significant difference in most bacterialopulations of beds with 1 and 2 L/min aerations compared withithout aeration. For all diesel concentrations, the bacterial popu-

ation in SSFCW reactors without aeration decreased significantlyp < 0.05) from 5.5 × 106 to 7.5 × 104 CUF/mL. However, it increased

ignificantly (p < 0.05) with 1 and 2 L/min aeration from 7.2 × 104

o 4.5 × 105 and from 4.65 × 104 to 9 × 105 CUF/mL respectively.ccording to Dong et al. (2012), supplementary aeration in SSFCWeactors can enhance the variety and activity of the bacterial popu-

I.A. Al-Baldawi et al. / Ecological Engineering 61 (2013) 496–500 499

Fig. 2. The effect of aeration on S. grossus growth parameters: (a) wet weight, (b) dry weight. Letters A and B represent statistically significant differences on a specific daywhen compared with different aeration rates within one diesel concentration (p < 0.05).

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ig. 3. Effects of aeration on the bacterial population in the phytoremediation of wignificant differences on a specific day when compared with different aeration rate

ations improving the removal of contaminants. Indeed providinghe aeration in the wetland bed has led to a more biodegradationf diesel contamination (Fan et al., 2013).

With all the factors investigated (physical parameters, TPHemoval, plant growth, bacteria population), we found that a lowereration of 1 L/min is the best condition for an optimum per-ormance of the wetland reactors. A higher aeration does notive a better performance of the TPH removal. In terms of the

anagement of the environmental problems, using CWs with a

ower aeration can give a cost-effective method to treat diesel-ontaminated water.

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contaminated with diesel in SSFCWs. Letters A, B and C represent the statisticallyhin one diesel concentration (p < 0.05).

. Conclusions

The SSFCW reactors with an aeration of 1 and 2 L/min performedore effectively than without aeration for higher diesel concentra-

ions (0.175% and 0.25% Vdiesel/Vwater). The 1 and 2 L/min aerationates resulted in greater TPH removal after 72 days compared toreatment without aeration. Since there was no significant differ-nce between 1 and 2 L/min aeration on TPH removal, an aeration

ate of 1 L/min represents a more cost-saving operation. In addition,upplementary aeration has enhanced plant growth of S. grossusnd bacterial populations compared to without aeration contribut-ng to higher TPH removal.

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cknowledgments

The authors would like to thank Malaysian Ministry of EducationFRGS/1/2013/TK07/UKM/02/7), Universiti Kebangsaan Malaysiand the Tasik Chini Research Centre for supporting this researchroject. They also acknowledge with thanks to the Iraqi Ministry ofigher Education and Scientific Research for providing a doctoral

cholarship for the first author.

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