Use of constructed wetland for the removal of heavy metals from industrial wastewater

Use of constructed wetland for the removal of heavy metals from industrial wastewaterSardar Khan a ,*,Irshad Ahmad b ,M.Tahir Shah b ,Shafiqur Rehman a ,Abdul Khaliq caDepartment of Environmental Science,University of Peshawar,Peshawar 25120,Pakistan bNational Center of Excellence in Geology,University of Peshawar,Pakistan cAtomic Energy Commission,REO-Peshawar,PO Box No.734,University of Peshawar,Pakistana r t i c l e i n f oArticle history:Received 14October 2008Received in revised form 24April 2009Accepted 22May 2009Available online 17June 2009Keywords:Industrial wastewater EfficiencyConstructed wetland Hydrophytes Treatmenta b s t r a c tThis study was conducted to investigate the effectiveness of a continuous free surface flow wetland for removal of heavy metals from industrial wastewater,in Gadoon Amazai Industrial Estate (GAIE),Swabi,Pakistan.Industrial wastewater samples were collected from the in-let,out-let and all cells of the con-structed wetland (CW)and analyzed for heavy metals such as lead (Pb),cadmium (Cd),iron (Fe),nickel (Ni),chromium (Cr)and copper (Cu)using standard methods.Similarly,samples of aquatic macrophytes and sediments were also analyzed for selected heavy metals.Results indicate that the removal effi-ciencies of the CW for Pb,Cd,Fe,Ni,Cr,and Cu were 50%,91.9%,74.1%,40.9%,89%,and 48.3%,respectively.Furthermore,the performance of the CW was efficient enough to remove the heavy metals,particularly Cd,Fe,and Cu,from the industrial wastewater fed to it.However,it is suggested that the metal removal efficiency of the CW can be further enhanced by using proper management of vegetation and area expansion of the present CW.Ó2009Elsevier Ltd.All rights reserved.1.IntroductionConstructed wetland (CW)is a biogeochemical and highly effi-cient system to treat wastewater generating from different sources such as domestic,highways,mining and industrial sectors (Moshiri,1993;Kadlec and Knight,1996;Vymazal et al.,1998;Kadlec et al.,2000).CW offers an effective alternative for traditional wastewater treatment systems.From the last few decades,the application of this technology has gained the popularity (IWA,2000)throughout the world including America,China,Argentina,Czech Republic,Greece,The Netherlands and Europe (Whitney et al.,2003;Chen et al.,2006;Lesage et al.,2007;Vymazal et al.,2007).However,the industrial sector has focused a great deal of attention on CWs for removing heavy metals (HMs)from its wastewater (Hadad et al.,2006;Maine et al.,2006;Jayaweera et al.,2008).The CW system contains natural processes of aquatic macrophytes that not only accumulate pollutants directly into their tissues but also act as catalysts for purification reactions usually occur in the rhizosphere of the plants (Jenssen et al.,1993).In rhizosphere,physicochemical and biological processes are induced by the interaction of plants,microorganisms and soil/sediments,to remove HMs fromwastewater (Stottmeister et al.,2003).Numerous factors including pH of water and sediment,mobilization and uptake from the soil,compartmentalization and sequestration within the root,efficiency of xylem loading and transport (transfer factors),distribution between metal sinks in the aerial parts,sequestration and storage in leaf cells,and plant growing and transpiration rates can also effect the remediation processes of the contaminated sites (Hadad et al.,2006;Khan et al.,2006).Industrialization has contaminated the environments with HMs,particularly,in developing countries of the world,where advance treatment technologies are neither available nor affordable.The CW,therefore,presents a cost effective and promising alternative for the treatment of industrial effluents.Previously,numerous studies have demonstrated that CW has effectively removed HMs from wastewater (Mays and Edwards,2001;Chen et al.,2006;Hadad et al.,2006).However,the use and practice of CW in Pakistan remains largely unreported.Keeping in view the appropriateness and low-cost effectiveness of this technology,the availability of native aquatic plants and favorable climatic condition,a CW is the first choice in Pakistan for the treatment of industrial effluents.A CW was established in Gadoon Amazai Industrial Estate (GAIE),which is one of the largest industrial estates in the country.It has textile,chemicals,ghee and cooking oil,marble,steel,plastic,soap and detergent industries.Considering the environmental pollution caused by industrial wastewater,it is important to treat it*Corresponding author.Tel./fax:þ92919216742.E-mail address:sardar.khan2008@ (S.Khan).Contents lists available at ScienceDirectJournal of Environmental Managementjournal homepage:/locate/jenvman0301-4797/$–see front matter Ó2009Elsevier Ltd.All rights reserved.doi:10.1016/j.jenvman.2009.05.026Journal of Environmental Management 90(2009)3451–3457before dumping into environment using CW.The main objective of this study was to evaluate the efficiency of CW for removal of pollutants present in industrial effluent.This paper,therefore, describes the pollutant load in different cells containing plants and sediments and the role of macrophytes for removal of HMs present in industrial effluent.2.Materials and methods2.1.Site descriptionThe study area is situated in district Swabi,Pakistan(Fig.1). Across the eastern hills,the famous Tarbella dam occurs along the river Indus.Topographically,the study area is consisting offlood deposits,uneven ground and natural drains.It contains extensive gravel deposits with shingle beds,silt and clay stratifications, generallyflat in the south and west of the industrial estate.The industrial effluents were discharged into environment without any treatment that led to pollute the surrounding environment including soil and surface and subsurface water.2.2.Wetland designFree surfaceflow wetland having7cells was constructed in GAIE with a total area of4145.71m2,total storage capacity of1305.58m3 and the overall retention time of wastewater from in-let to out-let was40h.A diagrammatic representation of the CW is given in Fig.2.The complete profile of individual cell(area,depth and storage)is given in Table1.A variety of native plant seedlings were transplanted and cultivated on about45%area of the CW.The plants were selected on the basis of their characteristics(e.g.,fast growing,hyperaccumulation of HMs and high tolerance towards HM toxicities),investigated during treatability studies.The detailed information of the plant species is given in Table2.2.3.SamplingSamples of wastewater were collected from main in-let,out-let and centre of each cell of CW,in polyethylene bottles properly washed with de-ionized water in both fall and spring of2003–2004.Samples were acidified with5%HNO3,and stored at4 C for HM analysis.Aquatic plant samples(at the age of13-weeks)were also randomly collected from each cell and divided into aerial and root components.Moreover,sediment samples(0–10cm)were also collected in polythene bags from the centre of each cell.2.4.Sample preparation and analysesWater samples were analyzed for HMs including lead(Pb), cadmium(Cd),iron(Fe),nickel(Ni),chromium(Cr)and copper(Cu) using atomic absorption spectrophotometer(AA-6601,Shimadzu), following APHA(1992)procedures in the laboratory of Environ-mental Protection Agency,Peshawar.Plant samples were properly washed to remove clay and sand particles and dried in oven at70 C for48h to a constant weight.The dry weights were determined and the dried samples were powdered,and stored for further analyses.Sub-samples were subsequently digested with5mL concentrated HNO3at160 C till colorless solution was obtained. After cooling,the suspensions werefiltered andfiltrate was adjusted to50mL with double deionised water.Similarly,sedi-ments/clay samples were treated with double acids(HNO3and HClO4)and the HM concentrations were measured.All the samples of plants and sediments were analyzed for selected HMs including Cd,Cr,Cu,Ni,Fe,and Pb using AAS(AA-6601,Shimadzu).ReagentFig.1.Location map of GAIE,Swabi,Pakistan.S.Khan et al./Journal of Environmental Management90(2009)3451–34573452blank,reference plant and soil materials were included to verify the accuracy and precision of the digestion procedure and subsequent analysis.2.5.Data analysisResults (HMs in in-let,out-let and sediment samples)were statistically analyzed using SPSS 11.5(SPSS USA)and statistical significance was computed by analysis of variance (ANOVA)at P <0.01.Treatment efficiency for removal of various HMs was determined by the retention equation,as used by Heal and Salt (1999)and Solano et al.(2004).R ¼1ÀC eC iÂ100Where as R,C e and C i are the removal efficiency,the effluent and influent concentrations of various HMs,respectively.In the field environment,root concentration factor (RCF)and aerial tissue concentration factor (ACF)in the samples of wastewater and plants on the basis of dry weight,were measured.The RCF and ACF were calculated as follows:RCF ¼C root C w :waterand SCF ¼C aerial parts C w :waterwhere C root ,C aerial parts and C w.water represent the heavy metal concentration in roots,aerial parts (on dry weight basis)and wastewater,respectively.3.Results and discussions 3.1.LeadTable 3summarizes the concentrations of Pb in the wastewater samples collected from in-let,out-let and different cells of CW.In the wastewater samples,Pb concentrations ranged from 0.78to 1.56mg/L and exceeded the permissible limit (0.5mg/L)set for industrial and sewage wastewater (Pak-EPA,2000).The ANOVA analyses showed that the concentration of Pb in the out-let wastewater samples was significantly lower (P <0.001)than in-let of the CW,indicating that the wetland has efficiently removed Pb from the wastewater.Pb concentrations ranged from 1.0to 2.9mg/kg in the sediment samples (Table 4).In the sediment samples,Pb concentrations were decreased as the distance increased from the in-let and the interaction between concentrations and distance was significant (P <0.01)only for in-let and out-let samples.A strong decrease in Pb concentrations in the sediments was also reported by Lesage et al.(2007).The removal performance of the CW was different for all selected HMs.The Pb removal efficiency of the CW was 50%,higher than those (33%)reported in the literature (Ter-zakis et al.,2008).In the study conducted by Lesage et al.(2007),Pb removal efficiency of a CW was 81%.This can be attributed to the difference in type of wastewater (domestic)and its basic charac-teristics,including high concentrations of nutrients.Pb concen-tration was 3folds higher in the in-let samples and reduced to 0.78mg/L,slightly above from the permissible limit set for indus-trial wastewater in Pakistan.The macrophytes used forindustrialTable 3Mean concentrations (mg/L)of HMs in the wastewater samples collected from CW and indicate the significant decrease between in-let and out-let in HMs at level of P <0.001,and P <0.01,respectively.NEQS c National Environmental Quality Standards,PakistanEPA-2000.yout of CW atGAIE.Table 1Table 2S.Khan et al./Journal of Environmental Management 90(2009)3451–34573453wastewater treatment,showed variable degrees of uptake and accumulation of Pb.As CW is a bioremediation mechanism based system,its metal removal efficiency depending on phytoaccumu-lation,sedimentation,microbial accumulation,and the nature of the plant species (Kadlec and Knight,1996).Plants (Echornia cras-sipes )are helping to prevent precipitation to the bottom and metals are sorbed by macrophytes (Maine et al.,2009).Furthermore,emergent plants contribute to reclamation of wastewater through a variety of physical,chemical and biochemical processes which enhance metal retention by the sediment (Brix,1997;Kadlec et al.,2000).Plant uptake and accumulation of Pb varied from species to species and metal concentration in plant tissue was higher in roots than in aerial parts (Table 5).Concentrations of Pb ranged from 3.8to 7.2mg/kg in the root tissues,while varied from 1.5to 3.2mg/kg in the aerial tissues.These results are generally comparable with those previously reported in the literature (Vymazal et al.,2007).The highest Pb concentration (root þaerial tissues)was found in the Pistia stratiotes species with RCF and ACF of 4.8and 2.2,respectively (Table 6).This plant species is assumed to be hyper-accumulator for Pb,therefore,can be use for removal of Pb from wastewater.The trends of Pb uptake and accumulation in different plant species were in the order of P.stratiotes >Ceratophyllum demersum >Lemna gibba L.>Carex aquatitis >Typha lat-ifolia >Juncus articulatus >E.cressipes >Scirpus cypernius >Alisma plantago -aquatica >Polygonum glabrum >Phragmites australis .3.2.CadmiumCd concentrations (0.19–0.62mg/L)in wastewater samples collected from in-let to cell-5,exceeded the permissible limit (0.1mg/L)set for industrial and sewage wastewater (Pak-EPA,2000),while its concentrations (0.05–0.09mg/L)in the samples from cells 6and 7and out-let met the permissible limit (Table 3).Furthermore,Cd concentrations in the out-let wastewater samples were significantly lower (P <0.01)than in-let of the CW,indicating that the CW has effectively removed the Cd from the wastewater.Inthe sediment samples,the Cd concentrations (0.7–1.8mg/kg)decreased as the distance increased from the in-let towards out-let,as shown in Table 4.This interaction between concentrations and distance was significant (P <0.01)only for in-let and out-let samples.Like Pb,a strong decrease in Cd concentration in the sediments was also reported by Lesage et al.(2007).Mass balance suggested that retained metals were stored mainly in sediments and hydrophytes of the CW.This is a common feature and also observed by earlier researchers (Mays and Edwards,2001;Hadad et al.,2006).Cd removal performance of CW was 91.9%(Table 3).In general,this value agreed with the findings of the previous studies (Yang et al.,2006;Kanagy et al.,2008).Cd concentration was 12folds high in the in-let samples and reduced to guideline limit before entering to cell-6.Interestingly,Cd removal efficiency was highest as compared to other HMs and this could be related with high mobilization of Cd and further uptake of plants.However,Singh et al.(2004)proposed that high accumulation of metals by plants (Helianthus annuus )particularly in the root tissues might have resulted from complexation of the metals with sulfhydryl groups.Plant uptake and accumulation of Cd varied from one species to another and high concentrations (2.3–5.2mg/kg)were found in root tissues as compared to aerial tissues (0.9–2.5mg/kg)as given in Table 5.These findings are generally comparable with those reported by Lesage et al.(2007)and Vymazal et al.(2007).In this study,the highest Cd concentration was found in the J.articulatus species followed by P.stratiotes and C.aquatitis .Similarly,different plant species have shown different RCF and ACF values (Table 6).The RCF for J.articulatus ,P.stratiotes and C.aquatitis were 5.3,4.4and 4.9,respectively,while ACF for J.articulatus ,P.stratiotes and C.aquatitis were 2.3,2.5and 2.0,respectively.All these plant species can be cultivated for effective removal of Cd from wastewater.3.3.IronTable 3shows the Fe concentrations (0.07–0.27mg/L)in wastewater samples collected from in-let,all cells and out-let of the CW and found within the permissible limit (2.0mg/L)set for industrial and sewage wastewater (Pak-EPA,2000).However,the Fe concentrations in the out-let wastewater samples were signifi-cantly lower (P <0.01)than in-let of the CW,indicating that the CW has been also effectively removed Fe from the wastewater.These findings are consistent with those observed by Maine et al.(2009).In sediment samples,the concentrations of Fe ranged from 1.0to 1.7mg/kg and significantly (P <0.01)decreased as the distance increased from in-let towards out-let of CW.Fe concentration was 3–4folds high in the in-let samples as compared to out-let.Like Pb and Cd,the interaction between concentrations and distance was significant for in-let and out-let samples.The Fe removalefficiencyTable 4Indicates the significant decrease between first and last cell of the CW in HMs at the level of P <0.01.Table 5S.Khan et al./Journal of Environmental Management 90(2009)3451–34573454of the CW was 74.1%,higher than those (47%)reported by Jayaweera et al.(2008)and consistent with those reported by Maine et al.(2009).It means that the CW was very effective in the removal of Fe from wastewater.In general,these findings are in agreement with those of Ye et al.(2001a,b)and O’Sullivan et al.(2004)but in contrast with those reported by Lesage et al.(2007).Table 5summarizes the uptake and accumulation of Fe by plants and their concentrations varied from species to species.The Fe concentrations in aerial and root tissues were ranged from 1.0to 2.8mg/kg and 2.7to 5.7mg/kg,respectively.These values are lower than those reported by Lesage et al.(2007)in the plants collected from CW treating domestic wastewater in Flanders,Belgium.This may be due to the lower initial Fe concentrations and other phys-iochemical properties of wastewater treated in that CW.The highest Fe concentration was found in the C.aquatitis ,tifolia and C.demersum species with RCF 4.6,4.6and 4.4,respectively,and ACF 2.5,1.9and 2.3,respectively (Table 6).These plant species can be used for phytoremediation of Fe contaminated wastewater.Earlier study conducted by Jayaweera et al.(2008)indicated that chemical precipitation and rhizofilteration are the key mechanisms to remove Fe from Fe-rich wastewater.3.4.NickelIn the wastewater samples,Ni concentrations ranged from 1.63to 2.76mg/L (Table 3)and exceeded the permissible limit (1.0mg/L)set by Pak-EPA (2000).The ANOVA analyses indicated that the concentration of Ni in the out-let wastewater samples was significantly lower (P <0.001)than in the in-let of the CW.It means that Ni was efficiently removed from the wastewater.Unlikely other metals,the Ni concentrations (2.2–2.9mg/kg)in the sediment samples were not significantly reduced as the distance increased from the in-let towards out-let.These results are comparable with those previously reported in literature (Mays and Edwards,2001;Lesage et al.,2007;Terzakis et al.,2008).The lowest removal efficiency (40.9%)was observed for Ni,as compared to other studied metals.Ni removal efficiency of the present CW was lower than those reported by Hadad et al.(2006)and Maine et al.(2007),but was consistent with those (37.4%)reported by Chandra et al.(2008).Furthermore,this CW was unable to reduce the Ni concentrations up to permissible limit set for industrial wastewater in Pakistan.Like other metals,the uptake and accumulation of Ni by plants varied from species to species as shown in the Table 5.Concentrations of Ni ranged from 1.8to 4.0mg/kg in the aerial tissues and 4.3to 7.6mg/kg in the root tissues.These results are generally comparable with those previously reported by Vymazal et al.(2007).Among all the studied plants,the tifolia species contained the highest Ni concentration with RCF and ACF of 3.0and 1.6,respectively(Table 6).Fascinatingly,higher uptake rates and tolerance towards metal toxicity were observed in tifolia as compared to other macrophytes.These findings are also consistent with the previous studies conducted by Cardwell et al.(2002)and Maine et al.(2007).It means that this plant species can be used for removal of Ni from wastewater.The trends of Ni uptake and accumulation in different plant species were in the order of tifolia >L.gibba L.>P.glabrum >S.cypernius >E.cressipes >P.australis >P.stratiotes >A.plantago -aquatica >J.articulatus >C.aquatilis >C.demersum .However,bio-transformation of metallic complexes is responsible for removal of heavy metals from wastewater in a CW,because of enzymatic action that made the metals more easily bioavailable to the plants (Preeti and Anir-uddha,2006).3.5.ChromiumCr concentrations in wastewater samples ranged from 0.07to 0.35mg/L (Table 3).In the samples from in-let to cell-3,Cr concentrations were exceeded the permissible limit (0.1mg/L)set for industrial and sewage wastewater (Pak-EPA,2000),while its concentrations in the samples from cells 4–7and out-let were within the permissible limit.Furthermore,Cr concentrations in the out-let wastewater samples was significantly lower (P <0.001)than in in-let of the CW,indicating that the CW has effectively removed the Cr from wastewater.Cr concentrations ranged from 0.4to 1.3mg/kg in the sediment samples (Table 4).Like other metals,Cr concentrations were also shown decreasing trend as the distance increased from the in-let towards out-let.These results are comparable with those reported by Lesage et al.(2007)and are contrary with those reported by Mays and Edwards (2001).The Cr removal performance of the CW was 89%(Table 3),which is consistent with the findings (82%)of Hadad et al.(2006).The Cr concentrations were 5folds high in the in-let samples as compared to out-let and reduced to permissible limits before entering in to cell-3.Plant uptake and accumulation of Cr varied from species to species,as given in Table 5.Cr concentrations ranged from 0.4to 1.2mg/kg in aerial tissues and from 1.4to 2.3mg/kg in root tissues.The highest Cr concentration was found in the A.plantago-aquatica species with RCF and ACF of 3.5and 2.0,respectively (Table 6).On the basis of Cr hyperaccumulation,this plant species along with other hyperaccumulators can be used for phytoremediation of Cr-rich wastewater.3.6.CopperTable 3shows the Cu concentrations in wastewater samples collected from in-let,all cells and out-let of the CW.The Cu concentrations were ranged from 0.75to 1.45mg/L anditsTable 6S.Khan et al./Journal of Environmental Management 90(2009)3451–34573455concentrations were exceeded the permissible limit(1.0mg/L)in the wastewater samples collected from in-let to cell-5.The ANOVA analysis showed that the Cu concentrations in the out-let wastewater samples were significantly lower(P<0.01)than in-let of the CW,indicating that the CW has effectively removed the Cu from the wastewater.The Cu concentrations were ranged from1.8 to2.7mg/kg in the sediment samples(Table4).The Cu concen-trations were not regularly decreased as the distance increased from in-let.Thesefindings are in agreement with those reported by Mays and Edwards(2001).The interaction between concen-trations and distance was significant for in-let and out-let samples.This CW has shown48.3%removal efficiency for Cu, which is lower than thefindings(98.8%and99.3%for saline and hypersaline water,respectively)of Kanagy et al.(2008).On other hand,thesefindings are in agreement with those obtained from CW treating highway runoff in the central Mediterranean region (Terzakis et al.,2008).Table5summarizes the plant uptake and accumulation of Cu and its concentrations varied from species to species.Cu concentrations ranged from1.3to2.7mg/kg in aerial tissues and from4.0to5.6mg/kg in root tissues.Thesefindings are compa-rable with those reported in the literature(Campbell et al.,1988; Bernard and Lauve,1995;Lesage et al.,2007).The highest Cu concentration was found in the P.australis followed by C.aquatilis and tifolia.These plant species can be used for phytor-emediation of Cu contaminated wastewater.The RCF and ACF values for different plant species are given in Table6.Previous studies have shown that the rhizofilteration is one of the main mechanisms to remove Cu from wastewater(Lesage et al.,2007; Jayaweera et al.,2008).4.ConclusionsThe CW was very effective in the removal of HMs from industrial wastewater and its removal performance was in order of Cd>Cr>Fe>Pb>Cu>Ni.The studied metal concentrations, except Pb and Ni,were reduced to their specific permissible limits set for wastewater in Pakistan.No significant relationship between plant species and removal efficiency was obtained because of a mix cultivation of macrophytes in all cells of CW.However,it was observed that tifolia,P.stratiotes,P.australis,C.aquatilis and A. plantago-aquatica were more efficient in removal of HMs from wastewater.Finally,it was observed that CW is cost-effective and environmental friendly technology and can be used for reclamation of wastewater.AcknowledgementWe acknowledge thefinancial support provided by the Director, National Center of Excellence in Geology,University of Peshawar,to conduct this research.Dr.Hussain Ahmad,Director,EPA-Peshawar, is thanked for providing facility for sample analyses.We thank the anonymous reviewers for their excellent comments and 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