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Pham Thi Thuy 1 Nguyen Viet Anh 2 Bart van der Bruggen 1 1 Laboratory for Applied Physical Chemistry and Environment Technology, Department of Chemical Engineering, K.U. Leuven, Belgium 2 Institute of Environmental Science and Engineering, Hanoi University of Civil Engineering, Hanoi, Viet Nam Research Article Evaluation of Two Low-Cost–High-Performance Adsorbent Materials in the Waste-to-Product Approach for the Removal of Pesticides from Drinking
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  Pham Thi Thuy 1 Nguyen Viet Anh 2 Bart van der Bruggen 1 1 Laboratory for Applied PhysicalChemistry and EnvironmentTechnology, Department of ChemicalEngineering, K.U. Leuven, Belgium 2 Institute of Environmental Scienceand Engineering, Hanoi University ofCivil Engineering, Hanoi, Viet Nam Research Article Evaluation of Two Low-Cost–High-PerformanceAdsorbent Materials in the Waste-to-ProductApproach for the Removal of Pesticides fromDrinking Water  This study evaluates the performance of two low cost and high performance adsorptionmaterials, i.e., activated carbon produced from two natural waste products: Bamboo andcoconut shell, inthe removal ofthree pesticides fromdrinkingwatersources. Due tothefact that bamboo and coconut shell are abundant and inexpensive materials in many partsoftheworld,theyrespondtothe‘‘low-cost’’aspect.Theadsorptioncapacitiesoftwolocal adsorbents have been compared with commercial activated carbon to explore theirpotential to respond to the ‘‘high quality’’ aspect. Two pesticides were selected, namely dieldrin and chlorpyrifos, because they are commonly used in agriculture activities, andmay remain inhighconcentrations in surface water used as drinking water sources. Theresults indicate that the adsorption of pesticides on activated carbons is influenced by physico-chemical properties of the activated carbon and the pesticides such as thepresence of an aromatic ring, and their molar mass. The activated carbon producedfrom bamboo can be employed as low-cost and high performance adsorbent, alternativeto commercial activated carbon for the removal of pesticides during drinking waterproduction. The performance of activated carbon from bamboo was better due to itsrelatively large macroporosity and planar surface. The effect of adsorbent and pesticidecharacteristics on the performance was derived from batch experiments in which theadsorption behavior was studied on the basis of Freundlich isotherms. Keywords:  Activated carbon; Adsorption; Biomass; Surface water Received:   April 27, 2011;  revised:   August 10, 2011;  accepted:   September 20, 2011 DOI:  10.1002/clen.201100209 1 Introduction Because water is the basis of the development of any society, theMillennium Development Goals (MDGs), set for 2015, include Target10 of Goal 7, which aims to ‘‘halve,by 2015,the proportion of people without sustainable access to safe drinking water and basic sani-tation’’ [1]. Nevertheless, millions of people worldwide are sufferingfrom shortage of fresh and clean water. Causes of water supply problems in urbanized regions (especially in developing countries),as described by van der Bruggen et al. [2] are to be found in the highrate of population growth, lack of economical resources, and suit-able infrastructure. In addition, surface water resources nowadaysare becoming polluted with many toxic compounds because of untreated or partially treated industrial effluents and agriculturalrun-off, which are difficult to remove by conventional treatmentmethods [3]. Pesticides, which have adverse effects on human healthatlow concentrationsandoftenremaininwaterfora long time[4–6],are a group of such hazardous materials found in surface water bodies as a result of agricultural wash out [7]. Standards for pesti-cides in drinking water were sharpened following the introductionof WHO drinking water standards 2006 [8]. The concentration of asingle pesticide in drinking water cannot exceed 0.1 m g/L while thesum of all pesticide concentrations cannot exceed 0.5 and 1–3 m g/L[9]. Consequently there is a need to intensify drinking water treat-ment and additionally, special attention should be given to theremoval of organic compounds, including pesticides [10, 11].Conventional drinking water treatment, which is widely applied in watertreatmentplants,requiresimprovementsbecauseoftheincreas-ingly poor quality of water sources in many parts of the world [10]. Inparticular,watertreatmentplantsindevelopingcountriesoftenmakeuse of basic technologies providing inadequate purification (e.g.,coagulation–flocculation). Several methods areavailablefor pesticidesremoval such as photocatalytic degradation [12, 13], combined photo-Fenton and biological oxidation [14, 15],advanced oxidation processes[16], nanofiltration [17], ozonation [18, 19], and adsorption [20–22]. Adsorption processes were studied intensively using a wide rangeof adsorption materials and emerged as one of the most promisingtechniques [23] due to their low investment cost, ease of operation,and efficiency for the removal organic and inorganic micropollu-tants including pesticides [24–26]. Adsorption on activated carbon isthe most widespread technology used for purification of watercontaminated by pesticides [11]. Activated carbon is a very efficientadsorbent for removing varieties of pesticides from drinking water Correspondence:  Dr. P. T. Thuy, Laboratory for Applied PhysicalChemistry and Environment Technology, Department of ChemicalEngineering, K.U. Leuven, W. de Croylaan 46, B-3001 Leuven, Belgium E-mail:  thithuy.pham@cit.kuleuven.be  Abbreviations: ACBC,  activated carbon made from bituminous coal;  ACCS,  activated carbon made from coconut shell;  ACB,  activated carbonmade from bamboo;  SEM,  scanning electron microscopy  Clean – Soil, Air, Water 2011,  00   (0), 1–8 1  2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com  and wastewater due to its high surface area, porosity, and physico-chemical characteristics [27]; however, its use is limited due to itshigh cost and low selectivity. Recently, some agricultural wasteproducts,biomass,andvarioussolidsubstanceshavebeendevelopedas alternative cheap adsorbents to removal pesticides. Materialsinvestigatedas adsorbentsforpesticidesinclude:charcoalfromagro waste [28–30], straw [31, 32], date and olive stones [33], wood chips/corn cob [32], lignocellulosic substrate from agro-industry [34], bark [35], chestnut shells [36], watermelon peels [25], bagasse fly ash [37,38], coal fly ash [39, 40], strawberry leave [41], tamarind fruit shell[42],ricehusk[43],andseaweed[44].Theselow-costmaterialshavebeenreported as inexpensive and effective adsorbents for removal of con-taminants in water and wastewater treatment [45]. However, reportedlow-cost adsorbents have cellulose, hemicellulose, lignin, waxes,pectines, etc., as their constituents. The presence of waxes, pectines,and other impurities adds to the hydrophobic character of these adsorbents; furthermore, waxes and impurities also can usesurface area of the adsorbent, causing an overalldecrease in the activesurface area and a negative effect to the efficiency of these adsorbents[46]. The efficiency of low-cost adsorbents depends on the character-istics and particle size of the adsorbent, and the characteristics andconcentrationoftheadsorbate[45].Therefore,‘‘unprocessed’’materialsmentioned above show a relatively poor removal of pollutants fromeffluents compared to activated carbon [46]. Thus, unprocessedmaterials appear not to be a good option particularly for safe drinking water treatment. Activated carbon, produced from renewable andcheap raw materials, can be considered as a low-cost and high per-formance adsorbent. Moreover, the cost of biomaterials is negligible when compared to the cost of commercial activated carbon [47–49].Bamboo is a large, woody-grasses member of the sub-family Bambusoidae of the family Poaceae (Graminae) [50, 51]. Approximately 1500 commercial applications of bamboo have beenidentified mostly in Asia [50, 51]. Bamboo is an abundant naturalresource in many countries in South-East Asia and elsewhere, because it takes only a few months to grow up and has beentraditionally used to construct various living facilities, tools, andhandicraft [51, 52]. Bamboo also has been used as the structuralmaterial for steps at construction sites in Viet Nam, China, India,Malaysia, and other countries because of its properties such asstrong, tough, and low-cost material. The waste of bamboo can beconverted to a value-added product such as activated carbon [51, 53].Coconutshellisthemesocarpofcoconutandacoconutconsistsof 33–35%ofshell[54].CoconutisabundantlygrowninSouth-EastAsia,e.g., in Viet Nam, about 180000ha of land in the Mekong Delta andthe Central coast area is used for coconut plantation[55]. At present,coconut shells are used as a domestic fuel, as fuel for coconutprocessing, and also as a source of fiber for rope and mats [54, 56].It is proposedto convertcoconutshellinto activatedcarbontomake better use of this cheap and abundant agricultural waste [54].Conversion of coconut husk and bamboo to activated carbon willserve a double purpose [54]. Firstly, unwanted agricultural waste andindustrial waste are converted to useful, value-added adsorbent andsecondly,theuseofagriculturalandindustrialby-productsrepresentsapotentialsourceofadsorbents,whichwillcontributetosolvingpartof the water and wastewater treatment problem [54]. Several studiesonremoval ofCr(VI), nitrate–nitrogen, and cadmium(II)ionsreportedeffective adsorption capacity of coconut shell [57, 58] and bamboocharcoal [59, 60]. Hence, the activated carbon based on coconut shelland bamboo can be also employed as potential low-cost and highperformance adsorbent in the removal of pesticides. The purpose of this work is not only to use a low-cost method, butalso to evaluate the high-performance adsorption capacity of coco-nut shell and bamboo – based activated carbon to remove pesticidesduringdrinkingwaterproduction.Duetothefactthatcoconutshelland bamboo are abundant and inexpensive materials, they respondto the ‘‘low-cost’’ aspect. They will be compared with the adsorptionperformance of commercial activated carbon, which is a high-per-formance adsorbent to explore their potential to respond to the‘‘high quality’’ aspect. Two pesticides were selected, namely dieldrinand chlorpyrifos, because they are commonly used in agricultureactivities, and may remain in high concentrations in surface waterused as drinking water sources. 2 Materials and methods 2.1 Materials 2.1.1 Activated carbon  The granulated activated carbons were selected from different raw materials: Activated carbon made from bituminous coal (ACBC)(DesotecActivatedcarbonCo.,Belgium);activatedcarbonmadefrom bamboo (ACB) (Ha Bac Activated Carbon Co., Hoa Binh, Viet Nam),and activated carbon made from coconut shell ((ACCS); Tra Bac Activated Carbon Co., Ben Tre, Viet Nam). The commercial activatedcarbon, made from bituminous coal, was used as a reference incomparison with the two local activated carbons. Bamboo and coco-nut shell were obtained from local traditional bamboo handicraft villages and coconut processing factories in Viet Nam as waste afterproducing goods. The preparation method of bamboo and coconutshell activated carbon was physical activation. Raw materials werecut into pieces (1–3cm), dried in an oven at 75 8 C for three days,crushed and screened to a particle size of 1–4mm. Raw materials werefirstcarbonizationunderaflowofnitrogengasat600 8 Cfor2h. The resulting chars were secondarily activated under flow of vaporsteam to the range of 800–1000 8 C for 2h. Finally, the materials were washed and cooled to room temperature by nitrogen. For betterunderstanding the surface properties, characterization of all theadsorbents were examined using scanning electron microscopy (SEM). A Philips XL 30 FEG SEM has been used to study surfacemorphology of the adsorbents at 10keV.Before the batch experiments, the carbon was washed with dis-tilled water to make sure that fines and impurities in carbon wereremoved, oven dried at 110 8 C for 6h and stored in plastic containersfor further use. These activated carbons were analyzed for molasses number andMethylene Blue number by using CEFIC standards [61], and iodinenumber by using ASTM D4607-94 [62]. 2.1.2 Pesticides  Two pesticides commonly used in agriculture activities, which may remain in high concentrations in surface water sources, wereselected: dieldrin and chlorpyrifos. Dieldrin and chlorpyrifos has been commonly used in agriculture for control of soil insects andplant pests in rice, coffee and maize which are the main crops andtheir products are also main source of income for a lot of farmers inSouth-East Asia [63]. The pesticides (Pestanal) were purchased fromRiedeldeHae¨n(Sigma–Aldrich,Bornem,Belgium).Theformulasandsome properties of pesticides in this study are shown in Tab. 1. 2 P. T. Thuy et al. Clean – Soil, Air, Water 2011,  00   (0), 1–8  2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com   The concentrations of pesticides added to the water samplesranged from 1 to 100 m g/L, to simulate actual concentrations insurface water up to extreme circumstances [6, 63]. 2.2 Determination of adsorption isotherms  The basis of batch experiments adsorption isotherms of the pesti-cidesontheactivatedcarbonsusedinthisstudyweredeterminedonthe basis of batch experiments [64, 65]. Adsorption tests were per-formedinvesselsof1L,whichcontainedaqueoussolutionsprepared by spiking both surface water and distilled water [6, 65]. Someparameters of surface water in this study were as follows:COD ¼ 40mg/L (chemical oxygen demand), SS ¼ 13mg/L (suspendedsolid),turbidity  ¼ 53NTU,DOC ¼ 6.7mg/L(dissolvedorganiccarbon),pH ¼ 7.2. The experiments were carried out at different initial con-centrations and adsorbent dose. An amount of 100, 200, and 300mgof the activated carbons was added into each vessel where 1L of selected pesticides solutionswith initialconcentrations of 1, 10, and100 m g/L. The vessels were then placed in a jar test shaker withagitation speed of 120rpm in 2h to reach equilibrium at roomtemperature. All samples were filtered prior to analysis in orderto minimize interference of carbon fines with the analysis.Each experiment was duplicated. The concentrations of the pes-ticides in the solution before and after adsorption were determinedusingGCwithanelectroncapturedetector(ECD)(PerkinElmer8500,Perkin Elmer, Zaventem, Belgium). The column used was CP-Sil 8CB(Chrompack, Antwerp, Belgium). Before analysis, the samples werepreconcentrated using liquid–liquid extraction with dichlorome-thane solvent [6]. The pesticide concentration retained in the adsor- bent phase and was calculated using Eq. (1): q e  ¼ð C  o  C  e Þ V W   (1) where C  o and C  e arethepesticideconcentrationmeasuredbeforeandafter adsorption (mg/L),  V   the volume of aqueous solution (L), and  W  is dry weight of the adsorbent (g). Two replicates per sample weredone and the average results were used.By knowing the pesticide concentration before and after adsorp-tion,theefficiencyofadsorptionofpesticidebyactivatedcarboncan be calculated by using Eq. (2): Adsorption ð % Þ¼ C  o  C  e C  o  100 (2) 3 Results and discussion 3.1 Surface characterization  Adsorption of reference compounds on bituminous coal, bamboo,and coconut shell activated carbons) in standard condition is sum-marizedinTab.2.Inthistable,theiodinenumberisameasureofthemicroporecontent(upto2nm),themolassesnumberisameasureof the macropore content ( > 5nm) and the Methylene Blue number is ameasure of the mesopore (between 2 and 5nm) [27]. The iodinenumber of ACB was found to be the lowest (690mg/g), while thecorresponding value was higher for ACCS (800mg/g) and for ACBC(960mg/g). The molasses number and Methylene Blue number wasthe highest for ACBC, followed by ACB and much lower for ACCS. These results confirm that the commercial activated carbon (ACBC)had higher mesopore, medium pore, and micropore content thanthe two local activated carbons (ACCS and ACB). However, theobserved values are still in the same order of magnitude than forclassical activated carbon, at much lower cost. Therefore, bothmaterials have a potential to be used as ‘‘low-cost, high-performance’’materials. Furthermore, ACCS had higher micropore content andlower mesopore and medium pore than ACB.Due to the difference in raw materials used in production, thestructure of the activated carbons may be different. The SEM imagesofthreeactivatedcarbonsareshowninFigs.1–3.ExaminationoftheSEM micrograph of ACBC (see Fig. 1) showed rough areas with longridges. This shows the morphology of highly porous, spongy, and branched particle. The SEM image of ACB (see Fig. 2) also showsthe expected spongy and porous structure. Some white dots wereobserved on the surface of bamboo activated carbon. This image Table 1.  Physical–chemical properties of pesticides considered in thisstudy Chlorpyrifos DieldrinStructureMolecular weight(g/mol)350.59 380.91Solubility in waterat 20 8 C (mg/L)1.398 0.1–0.25log  K  ow   4.96 5.45 Table 2.  Some physical properties of GAC consider in this study  ACBC ACB ACCSGrain size (mm) 2–3 2–4 1.5–3Molasses number (mg/g) 260 136 81Methylene Blue number (mg/g) 260 190 150Iodine number (mg/g) 960 690 800 ACBC,activatedcarbonfrombituminouscoal;ACB,activatedcarbonfrom bamboo; ACCS, activated carbon from coconut shell. Figure 1.  SEM image of bituminous coal activated carbon (Magnification:2000  ).Clean – Soil, Air, Water 2011,  00   (0), 1–8 Evaluation of Two Low-Cost–High-Performance 3  2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com  obtained with backscattered electrons clearly shows an irregulardistribution of the inorganic particles on the surface carbon piece. This irregular distribution was mainly due to the anisotropic struc-ture of bamboo. The SEM image of ACCS (see Fig. 3) proves that thesurface of ACCS contains well-developed pores. Many large pores with a honey comb shape were clearly observed on the surface. The ACCS was mesoporous with relatively large and plane surface area[54]. The SEM images show that all three activated carbons had high well-developed pores in surface, which shows a potential possibility for pesticides to be adsorbed [66]. 3.2 Removal efficiency in distilled water and riverwater  The removal efficiency of pesticides using selected activated carbonsusing 100mg activated carbons in distilled water and river water isshown in Tab. 3. The percentage of pesticides removal was found to decrease withincrease of the initial concentration of pesticides, and to decrease with a decrease in the amount of activated carbon dosages in dis-tilled water and river water. This is also what should be expected based on adsorption theory [64]. In most cases, the percentageremoval of pesticides in distilled water was higher than in river water confirms that the substances present in river water (e.g.,natural organic matters) interact with the adsorbents and decreasethe adsorbents’ surface areas available for adsorption [6]. In accor-dance with the results given in Tab. 3, the removal efficiency of low initialpesticidesconcentration(1 m g/L)isnearlythesameindistilled water and river water. This indicates that at low initial concen-tration, the surface area and the availability of adsorption sites wererelative high in adsorbents. At low initial concentration of twopesticides in river water and distilled water, the removal efficiency of the two local activated carbons studied were found to be nearly equal to ACBC. This confirms that the structure of the pores of thetwolocalactivatedcarbonsiswellsuitedforadsorptionofpesticides,similar to commercial activated carbon. The removal efficiency of dieldrin was higher than of chlorpyrifosindistilledwaterandriverwater.Thestructureofthepesticideplaysan important role for the adsorption capacity [65]. Thus, the higheradsorption capacity observed for dieldrin in most cases is probably due to theabsence of an aromaticring of chlorpyrifos. The branchedsubstituent of aromatic ring of chlorpyrifos causes the rate andextent of adsorption of this pesticide to be the highest by providinghydrophobicity to the structure [65]. The removal of pesticides by ACCS (from 68.6 to 90.5% with chlor-pyrifos and 71.1 to 92.1% with dieldrin in distilled water) is thelowest, followed by ACB (from 71 to 93.1% with chlorpyrifos and76 to 94% with dieldrin in distilled water) and the highest for ACBC(from 74.5 to 93.9% with chlorpyrifos and 79.5 to 94.1% with dieldrinin distilled water. The two local activated carbons have a goodadsorption capacity for pesticides, as is clearly from the results withdistilled water; they were evidently found to have adsorptioncapacity almost equal to commercial activated carbon, especially  Figure2. SEMimage ofbambooactivated carbon(Magnification:2000  ).  Figure 3.  SEM image of coconut shell activated carbon (Magnification:2000  ). Table 3.  The removal efficiency of pesticides using 100mg selected activated carbons in distilled water and river water Conc. ( m g/L) ACBC ACB ACCSChlorpyrifos Dieldrin Chlorpyrifos Dieldrin Chlorpyrifos DieldrinDW RW DW RW DW RW DW RW DW RW DW RW 1 93.9 93.2 94.1 94.1 93.1 92.5 94.0 93.0 90.5 89.0 92.1 91.110 80.6 77.7 87.9 85.4 85.1 79.5 84.7 83.7 79.2 71.5 81.6 72.6100 74.5 68.6 79.5 74.6 71.0 66.1 76.0 71.2 68.6 64.3 71.1 69.5 ACBC, activated carbon from bituminous coal; ACB, activated carbon from bamboo; ACCS, activated carbon from coconut shell; Conc.,concentration; DW, distilled water; RW, river water. 4 P. T. Thuy et al. Clean – Soil, Air, Water 2011,  00   (0), 1–8  2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com

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