caov

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ya, M

11 November 2013Accepted 18 November 2013Available online 8 December 2013

Keywords:

that is extremely rich in organic content needs to be properly treated to minimize environmental hazards

Malaysia currently accounts for 39% of world palm oil produc-

also generates large amounts of waste in the form of empty fruitbunch (EFB) (23%), mesocarp ber (12%), shell (5%), and POME(60%) for every ton of fresh fruit bunch (FFB) processed in the mills

high chemical oxygen demand (COD), biochemical oxygen demandworth mentioningrocessing (Zahrim

terest from manyrated in the mills,e minimization ofinly oil and fattyh that reduces itssuitable approach

for its treatment (Azhari et al., 2010). Many technologies have beenstudied and applied for treating raw POME and biologically treatedPOME such as biological digestion (Chotwattanasak andPuetpaiboon, 2011), membrane technology (Ahmad et al., 2006),coagulation and occulation (Saifuddin and Dinara, 2011),adsorption (Igwe et al., 2010b), tertiary treatment (Shakila, 2008),and Fenton oxidation (Ooi, 2006) systems. A good review oftreating POME is presented by Yeong et al. (2010). Every treatmenthas its own advantages and disadvantages. Membrane technology

* Corresponding author. Department of Chemical Industries, Mosul TechnicalInstitute, Al-Majmoaa Al-Thaqaya, Mosul, Iraq. Tel.: 964 7701622984.

E-mail addresses: rae59.che@gmail.com, rafaa59@yahoo.com (R.

Contents lists availab

Journal of Environm

journal homepage: www.els

Journal of Environmental Management 132 (2014) 237e249R. Mohammed).tion and 44% of world exports. The oil palm planted area in 2011reached 5.00 million hectares, an increase of 3.0% against 4.85million hectares recorded in the previous year. Crude palm oil(CPO) production in 2011 increased by 11.3% to reach a record of18.91million tons (MPOC, 2013), which produced 30million tons ofPalm Oil Mill Efuent (POME) (Tengku et al., 2012). Palm oil pro-cessing is carried out in palm oil mills, where oil is extracted from apalm oil fruit bunch, and about 50% of the waste that results isPOME. Despite high economical returns to the country, the industry

(BOD), phenol, and color concentrations. It isthat no chemical is added during palm oil mill pet al., 2009).

Thus, the treatment of POME has gained inresearchers due to the abundant amount geneand this treatment is an important issue for thwater pollution. The high organic content, maacids, enables POME to support bacterial growtpolluting strength. Anaerobic process is the mostpollutes the environment if discharged directly into rivers due to itsPalm Oil Mill EfuentAdsorptionBiosorbentBanana peel

1. Introduction0301-4797/$ e see front matter 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jenvman.2013.11.031natural, chemically and thermally modied banana peel as sorbent for the treatment of biologicallytreated POME. Characteristics of these sorbents were analyzed with BET surface area and SEM. Batchadsorption studies were carried out to remove color, total suspended solids (TSS), chemical oxygendemand (COD), tannin and lignin, and biological oxygen demand (BOD) onto natural banana peel (NBP),methylated banana peel (MBP), and banana peel activated carbon (BPAC) respectively. The variables ofpH, adsorbent dosage, and contact time were investigated in this study. Maximum percentage removal ofcolor, TSS, COD, BOD, and tannin and lignin (95.96%, 100%, 100%, 97.41%, and 76.74% respectively) on BPACwere obtained at optimized pH of 2, contact time of 30 h and adsorbent dosage of 30 g/100 ml. Theisotherm data were well described by the RedlichePeterson isotherm model with correlation coefcientof more than 0.99. Kinetic of adsorption was examined by Langergren pseudo rst order, pseudo secondorder, and second order. The pseudo second order was identied to be the governing mechanism withhigh correlation coefcient of more than 0.99.

2013 Elsevier Ltd. All rights reserved.

(Azhari et al., 2010). POME is a highly polluting wastewater thatReceived 27 June 2013Received in revised form before it is released into watercourses. The main aim of this work is to evaluate the potential of applyingArticle history: Palm Oil Mill Efuent (POME) treatment has always been a topic of research in Malaysia. This efuentTreatment and decolorization of biologiEfuent (POME) using banana peel as n

Rae Rushdy Mohammed a,b,*, Mei Fong Chong a

aDepartment of Chemical and Environmental Engineering, Faculty of Engineering, UniveMalaysiabDepartment of Chemical Industries, Mosul Technical Institute, Al-Majmoaa Al-Thaqa

a r t i c l e i n f o a b s t r a c tAll rights reserved.lly treated Palm Oil Millel biosorbent

of Nottingham Malaysia campus, 43500 Semenyih, Selangor,

osul, Iraq

le at ScienceDirect

ental Management

evier .com/locate/ jenvman

sphere in a tubular furnace (Carbolite CTF 12/100/900, UnitedKingdom) and then was left to cool to room temperature. Thecarbonized material was then subjected to potassium hydroxide(KOH) activation. The material was agitated by using (cermaicstirring; IKA 3581000; Vernon Hills, IL, USA) in KOH (45% aqueoussolution) at a ratio of 1:4 carbonized material to KOH weight byweight basis. After 12 h of agitation, the carbonized slurry was leftfor 24 h at room temperature. The sample was then dried at 110 Cfor another 24 h. The dried sample was then activated in nitrogenatmosphere using (Carbolite CTF 12/100/900, United Kingdom)with temperature maintained at 700 C for 1 h before cooling. Aftercooling for 12 h, the activated carbon was washed 3 times with0.2 N hydrochloric acid (HCl). The washing was completed with hot

vironhas the highest removal efciency in COD but the treatment is verycostly. As for carbon based adsorption, despite of its prolic use,granular activated carbon (GAC) is considered an expensive mate-rial. While many studies have been conducted about the use ofactivated carbon in treating various types of contaminants, therehas been limited reporting of its application in treating POME. Also,there is little information in the eld about using biosorbents oractivated carbon made from waste materials to treat POME. Thisstudy intends to ll the existing knowledge gaps.

POME retains its color even after biological treatment, bothaerobic and anaerobic. The color of the efuent is due to plantconstituents such as lignin and phenolic compounds as well as re-polymerization of coloring compounds after anaerobic treatment(Chanida and Poonsuk, 2011). The removal of color from efuents isone of the major environmental problems. In this concern,adsorption process has been found to be a more effective methodfor the treatment of dye containing wastewater. The most efcientand commonly used adsorbent is commercially available activatedcarbon which is expensive and has regeneration problems. Recentinvestigations focused on effectiveness of low cost adsorbents likepearl millet husk, neam leaf powder, coconut husk, wheat straw,wood, peat, banana pith, and agricultural waste in the removal ofdyes fromwastewater efuent (Verma andMishra, 2010). However,there is still scarcity of information in the literature on the use oflow cost adsorbents for decolorization of POME.

As one of the most consumed fruits in the world, banana is avery common fruit. Themain banana residue is the fruit peel, whichaccounts for 30e40% of the total fruit weight. Preliminary in-vestigations show that several tons of banana peels are produceddaily in marketplaces and household garbage, creating an envi-ronmental nuisance and disposal problem. Various chemicalgroups exist on the banana peel surface, including carboxyl, hy-droxyl and amide groups, which have been extensively proven toplay a critical role in the biosorption processes (e.g. enhancingbiosorption capacity and shortening stable time) (Cong et al., 2012).

In this study, efciencies of removal of color, TSS, tannin andlignin, BOD, and COD from the nal biologically treated POME wereinvestigated using 3 types of adsorbents: natural banana peel(NBP), methylated banana peel (MBP), and banana peel activatedcarbon (BPAC). The effects of various parameters such as agitationtime, pH, and adsorbent dosage were investigated in batch exper-iments. Equilibrium isotherms were analyzed by using the Lang-muir, Freundlich, Redlich, and Sips models. The adsorption kineticwas determined by tting with pseudo-rst-order, pseudo secondorder, and second order adsorption kinetic models. Determinationof the isotherm and kinetic concepts provided a sound basis for theprocess of designing an adsorption unit for POME nal polishing toachieve optimal treatment results. Thus, banana peel can be used inremoving color from biologically treated POME as the nal pol-ishing step before discharge.

2. Materials and methods

2.1. Biologically treated POME

The efuent was collected in plastic containers from the nalpond efuent of a palm oil mill in Dengkil, Selangor, Malaysia. Thecontainers were properly washed and rinsed with the efuentbefore collection to avoid contamination and dilution. Containerswere then brought back to laboratory and stored in refrigerator attemperature of 4 C for tests and analysis. COD, pH, TSS, tannin andlignin, BOD, and color units were determined. The characteristics ofthe biological POME sample obtained are summarized in Table 1.

It has been observed that the biologically treated POME excee-

R.R. Mohammed, M.F. Chong / Journal of En238ded the standard discharge limit of Environmental Quality Act(EQA) 1974, Department of Environment (DOE), Malaysia(Saifuddin and Dinara, 2011). The nal treated efuent still con-tained high concentrations of COD, color, BOD and TSS. On the otherhand, the pH indicated that the efuent was alkaline.

All chemicals used in this study were of analytical grade sup-plied by Aldrich Chemicals. All solutions used in this study werediluted with distilled water as required.

2.2. Collection and preparation of adsorbents

2.2.1. Natural banana peel (NBP)Mature banana with yellow peel was collected as solid waste.

The collected material was thenwashed three times with tap waterand three times with distilled water to remove external dirt. Thewashed material was cut into small pieces (1e2 cm) then dried in ahot air oven (Memmert Universal oven Model UFE 600 - Germany)at 80 C until it reached a constant weight, which was accom-plished after 48 h. In the nal stage, the material was grounded byusing Retsch Cutting Mill SM 100 (Germany) with mesh size 0.2,and screened by using ELE international laboratory sieve shaker(USA) with mesh size of 300e425 mm.

2.2.2. Methylated banana peel (MBP)Modication of the carbonyl groups on the surface of the banana

peel (esterication) was achieved by using acidic methanol. 9 gfrom the previously prepared NBP was suspended in 633 ml of99.9% methanol to which 5.4 ml of concentrated hydrochloric acid37% was added to give a nal concentration of 0.1 M. Then thesolution was heated at 60 C and stirred continuously for 48 h byusing digital orbital shaker (Heidolph unimax 1010, Germany). Thesolid material was then separated and washed three times withdeionized water at (20 C) in order to halt the esterication reac-tion. The material was then dried in the oven at 100 C for a periodof 8 h (Jamil et al., 2008).

2.2.3. Banana peel activated carbon (BPAC)The NBP was used for BPAC preparation. It was prepared by a

carbonized temperature of 500 C for 1 h under a nitrogen atmo-

Table 1Properties of biologically treated POME.

Property Values Standard discharge limits(Saifuddin and Dinara, 2011)

Units

pH 8.4 5e9Color 9900 e PtCo/lTSS 1800 400 mg/lCOD 4700 mg/lBOD5 1350 100 mg/lTannin and lignin 215 e mg/l

mental Management 132 (2014) 237e249water until the pH became neutral, and nally with cold water to

vironremove the excess KOH compounds. The washed samples weredried at 110 C for 8 h to get the nal product (Mopoung, 2008).

2.3. Adsorption isotherm experiments

Adsorption isotherm experiments were carried out in 250 mlconical asks into which 15 g of adsorbent and 100 ml of biologi-cally treated POME were added with different concentrationsrespectively. The desired concentrations were achieved by dilutingthe biologically treated POME with distilled water. The sampleswere then shaken at 200 rpm for 40 h by using digital orbital shaker(Heidolph unimax 1010, Germany). At the end of the adsorptionperiod, the solution was centrifuged for 5 min at 3000 rpm andthen the concentrations of the residual color, TSS, and COD weredetermined.

The adsorption capacity of these parameters on the adsorbentwas calculated from the mass balance equation as follows

qe Co CeV=M (1)

where qe is the amount of constituent adsorbed per unit mass ofadsorbent at equilibrium (mg/g), Co and Ce are the initial andequilibrium liquid-phase concentrations of solution (mg/L)respectively, V is the volume of efuent solution (L), and M is themass of adsorbent sample used (g).

2.4. Adsorption experiment

In each adsorption experiment, 100 ml of efuent solution wasadded to different amounts of adsorbent (5, 10, 15, 20, 25 and 30 g)respectively in closed asks and the samples were stirred at200 rpm in a rotary orbital shaker (Cermaic Stirring; IKA 3581000;Vernon Hills, IL, USA) at room temperature for a period of timeranging from 2 to 36 h. Shaking step was done after noting downthe initial pH of the solutions (2, 5, 7, 8.4, and 12). The initial pH ofeach solution was adjusted to the required value by adding either1 M HCl or 1 M sodium hydroxide (NaOH) solution. Samples werewithdrawn from each of the asks at predetermined time intervals.The adsorbents were separated from the solution by centrifugation(Eppendorf 5430, Hamberg, Germany) at 3000 rpm for 5min. Color,TSS, COD, BOD, and tannin and lignin were measured to determinethe concentration of the residue.

The percentage of removal (%R) of each parameter and theamounts adsorbed by the adsorbents were calculated by thefollowing equations:

%R fCo Ct=Cog 100 (2)

qt Co CtV=M (3)Here, Ct is the concentration of the solution at any time (mg/L)

and qt is the amount adsorbed at any time for each parameterinvestigated (mg/g).

Three repeatable experiments were tested and the averagevalues with their standard deviations were recorded and used fordiscussion.

2.5. Analytical methods

COD measurement was carried by APHA Standard method 8000using the colorimetric method. 2 ml of sample was added into CODvial (HR 20e1500 mg/L) and digested for 2 h by using HACHdigester (DRB200, Loveland, CO). The COD concentration was thenmeasured with a HACH spectrophotometer (DR2800, Loveland,

R.R. Mohammed, M.F. Chong / Journal of EnCO). Total suspended solids were also measured by following theAPHA Standard method 8006 using HACH spectrophotometer (DR2800, Loveland, CO) by placing 10 ml of sample in a speciallydesigned square quartz sample cell. The color analysis was carriedout by following platinum-cobalt standard method 8025 and thecolor was detected at a wavelength of 455 nm using HACH spec-trophotometer (DR 2800, Loveland, CO) by placing 10 ml of samplein the same previous sample cell. Tyrosine method 8193 was usedwith the aid of HACH spectrophotometer (DR 2800, Loveland, CO)to measure the concentration of tannin and lignin in the sample.After adding 0.5 ml of tannin-lignin reagent and 5.0 ml of sodiumcarbonate solution to 25 ml of the sample, 10 ml of the mixture waspoured into square sample cell and themeasured result was inmg/ltannins. The BOD tests were carried out using standard procedureAPHA Standard method with a dissolved oxygen (DO) probe (YSImodel 5100, USA). Seeds and nutrient buffer pillows were added tothe samples (1.5e3.5 ml). Samples were diluted 15 times followedby aeration tomake sure enough dissolved oxygenwill remain afterve days of incubation. 300 ml standard BOD bottles were used inthese tests which were incubated at 20 C in a dark incubator(Memmert Model IN110 e Germany). After ve days, the differ-ences in oxygen consumption were measured by using a DO meter(YSI model 5100, USA) to estimate BOD5. Solutions pH weremeasured with a HACH sension1 pH meter using a combined glasselectrode. Finally, surface morphology and BET surface areas of NBP,MBP and BPAC were studied using Quanta 400 Field EmissionScanning Electron Microscope (FESEM), and N2 adsorptionisotherm by Nano Porosity System (Micrometrics ASAP 2020, USA)respectively.

3. Results and discussion

In this study, the adsorption behavior of biologically treatedPOME onto 3 different types of biosorbents, namely NBP, MBP andBPAC prepared from banana peel was investigated. The BET surfacearea of NBP was found to be 24.2572 m2/g. This BET surface areawas higher than that of chitosan akes and pine bark (Ngah andFatinathan, 2006; Vzquez et al., 2007) but lower than that ofpalm oil fruit shell (Hossain et al., 2012). On the other hand, thesurface areawas low compared to chemically (MBP), (168.3648m2/g), and thermally (BPAC), (875.2914 m2/g), treated banana peel.Nevertheless, it could be considered a good alternative as it wasproduced from non-treated, low cost material using a simple pro-cess. It is evident that specic surface area of banana peel bio-sorbent is fully dependent on the preparation method.

In general, acidic methylation and alkali treatment of the NBP toproduce MBP and BPAC respectively could alter its lattice structureeffectively compared to the raw material. These treatments led toremarkable increase in the specic area and the major changeachieved in the materials structure promoted considerably its ca-pacity for all contaminants removal compared to original untreatedpeel.

3.1. Performance study

In the present study the adsorption performance is measured onthe basis of the percentage of removal for the parameters of color,TSS, and COD from biologically treated POME as in Equation (2). Theinuence of operating parameters in terms of biosorbent dosage,contact time, and initial pH on the adsorption performance wasinvestigated for all types of biosorbents. Fig. 1 shows the effect ofadsorbent dosage at room temperature (25 C) by varying thesorbent amounts from 5 to 30 g with varying contact times. Fig. 1shows the effects of NBP, MBP and BPAC dosage on the percent-age of removal of color, TSS, and COD. It is obvious that, regardless

mental Management 132 (2014) 237e249 239of the type of biosorbent used, the percentage of removal increases

Fig. 1. Effect of dosage on the percentage removal of (i) color, (ii) TSS, and (iii) COD for (a) NBP, (b) MBP and (c) BPAC respectively with varying contact time at pH 8.4.

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rapidly with increase in the amount of adsorbent due to greateravailability of surface area for adsorption. This leads to the intro-duction of more binding sites for adsorption. A signicant increasein uptake was observed when the dosage was increased from 5 to25 g/100 ml. Any further addition of adsorbent beyond this amountdid not cause signicant change in adsorption performance. Thismay be due to the overlapping of adsorption sites as a result ofovercrowding of adsorbent particles (Goud et al., 2005; Verma andMishra, 2008). For all types of biosorbents, maximum removal of allstudied contaminations was obtained at the adsorbent dosage of30 g/100 ml.

It can be seen from Figs. 1 and 2 that by increasing the contacttime from 2 h to 36 h the removal percentage increases untiladsorption equilibrium is reached. It also illustrates that thecontaminant removal was rapid in the rst 24 h during whichnearly 70e80% of the total uptake appeared to have been adsorbeddepending upon the adsorption ability of different biosorbents.This can be attributed to the availability of sites for the sorbate. Inaddition, a very high adsorption driving force at the beginningresulted in a higher adsorption rate. After the initial period, sloweradsorption may be attributed to the slower diffusion of moleculesinto the interior pores of the adsorbent (Shavandi et al., 2012), andthe molecules subsequently occupy the positions within theadsorbent framework. This observation is in support of the ndingsreported by several authors (Goud et al., 2005; Shavandi et al.,2012; Zahangir et al., 2009).

ChiSq. 0.145292E00, Red. ChiSq. 0.363231E-01 > P(Red.ChiSq.) 0.997 and Average absolute residual 0.138289E00).This correlation may offer a basis for the estimation of colorremoval as a function of total suspended solids and tannin andlignin removal from POME. This correlation is also indicates thatTSS and tannin and lignin contents of POME are responsible for itscolor.

The effect of variation of pH on adsorption performance in termsof color, TSS, and COD onto MBP at constant time of 24 h andadsorbent dosage of 30 g/100 ml are shown in Fig. 3. As otherbiosorbents of NBP and BPAC follow a similar trend as that in Fig. 3

Table 2Comparison of biosorption capacity of color, TSS and COD on NBP, MBP and BPACadsorbent dose (5e30 g/100 ml), contact time (2e36 h) and pH (2e12).

Parameters (% removal) Biosorbent

NBP MBP BPAC

Min. Max. Min. Max. Min. Max.

Color 18.182 61.111 41.414 73.737 64.646 96.464TSS 5.556 90.278 5.556 91.667 50.000 w100

R.R. Mohammed, M.F. Chong / Journal of Environmental Management 132 (2014) 237e249 241Fig. 2. Effect of contact time on the percentage removal of (a) tannin and lignin with

varying dosage and (b) BOD with the dosage of 5 g/100 ml on BPAC with constant pH of8.4.Suspended and dissolved particles in water inuence color.Dissolved organic matter, such as humus, peat, or decaying plantmatter can produce a yellow or brown color. Concentrations ofnaturally dissolved organic acids such as tannins and lignins mayalso have an effect by giving water a tea color. Tannins that areyellow to black are the most abundant kind found in POME and canhave a great inuence on its color, as well as a musty smell. Thebrown coloring comes from tannins leaching into runoff water fromthe manufacturing process of palm oil (Clean Water team, 2013).From the previous facts, it is obvious that color removal is stronglydependent on the removal of total suspended solids and tannin andlignin. This is revealed by Fig. 1(i), (ii), and 2(a). LAB Fit curve ttingsoftware V7.2.48 was used to establish a new correlation betweenthe adsorption capacities of color with TSS and tannin and lignin onBPAC. This correlation is represented by:

Y 37:18X1*X20:0468 (4)

where Y, X1 and X2 are the adsorption capacity of color, TSS andtannin and lignin respectively. The statistical data for the predictedcorrelation are (Correlation Coefcient: R2 0.9938680E00,

Fig. 3. Effect of pH on the percentage removal of color, TSS and COD on 30 g/100 mlMBP adsorbent at 24 h.COD 70.213 99.468 80.850 w100 84.04 w100

at different levels of intensity, the removal efciency at minimumandmaximumpercentages for various contaminants is tabulated inTable 2. The maximum percentages of removal in Table 2 are for30 g/100 ml adsorbent dose, 30 h contact time and pH 2. Theminimum values are for 5 g/100 ml, 2 h contact time and pH 12. Adeterioration of adsorption performance as pH increased wasobserved for all types of biosorbent with the maximum percentageof removal recorded at pH 2. The same trend for NBP was found inanother study where Khan et al. (2012) found that banana peel

adsorbent was effective in the adsorption of Reactive Yellow 15from aqueous solution and maximum adsorption occurred at pH 2.The most possible explanation may be related to the presence ofexcess H ions accelerating the removal of the contaminants withthe anion OH- in the solution. It is also possible that the surfaceproperties of the adsorbent depend on the pH of the solution.Higher uptakes obtained at lower pH may be due to the electro-static attractions between negatively charged functional groupslocated on the contaminants and positively charged adsorbentsurface. Hydrogen ion also acts as a bridging ligand between the

R.R. Mohammed, M.F. Chong / Journal of Environmental Management 132 (2014) 237e249242Fig. 4. Adsorption isotherm of (a) color, (b) TSS, and (c) COD on NBP. Fig. 5. Adsorption isotherm of (a) color, (b) TSS, and (c) COD on MBP.

adsorbent wall and the contaminants molecules (Zawani et al.,2009). Malik (2004) and Mohamed (2003) reported that at lowpH region the surface of the sorbent will be largely protonated. Thepositive ions (H) provide an electrostatic attraction between thebers surface and the contaminants molecules leading tomaximum adsorption. On the other hand, at pH above 2 (i.e., pHrange of 3e12) the degree of protonation of the surface of the berswill be less, which results in a decrease in diffusion and adsorptiondue to electrostatic repulsion. Furthermore, lower adsorption of thecontaminants in alkaline medium can also be attributed to the

R.R. Mohammed, M.F. Chong / Journal of EnvironFig. 6. Adsorption isotherm of (a) color, (b) TSS, and (c) COD on BPAC.competition between excess hydroxide ions (OH) and the anioniccontaminant molecules for the adsorption sites (Khan et al., 2012).

In all, it is clear that NBP, MBP, and BPAC were capable ofreducing the concentrations of color, TSS, COD, BOD, and tannin andlignin from biologically treated (POME). The adsorptive removal ofthese contaminants could be explained based on the modes ofsorption of materials or contaminants on biosorbents.

The adsorptive removal of contaminants may be attributed totwo main terms; intrinsic adsorption and coulombic interaction.The coulombic term results from the electrostatic energy of in-teractions between the adsorbents and adsorbates. It can also beobserved in the adsorption of cationic species versus anionic spe-cies on adsorbents. The intrinsic adsorption of the materials isdetermined by their surface areas. Moreover, both factors caninteract, thereby inuencing the adsorption capacity. It has beenreported that the surface area has a great effect on the sorptioncapacities of adsorbents (Igwe et al., 2010a). Thus, increase in sur-face area increases sorption capacity. The trend of this sorptioncapacity can be put as COD> BOD> TSS> tannin and lignin> color(Figs. 1 and 2 and Table 2). This trend can be explained based onsolubility and diffusion processes. COD and BOD are dened as theamount of dissolved oxygen needed to break down the carbona-ceous component of the waste (Igwe et al., 2010a). This means thatboth COD and BOD involve dissolved components of the efuent.Also, color is a consequence of dissolved components and TSS of theefuent. Diffusion takes place before adsorption of the contami-nants because dissolved contaminants diffuse faster than sus-pended particles, hence they will be more adsorbed. Therefore, inour opinion, this is the reason for the sorption trend observed. ThepH could be considered as resulting from the interactions of theother parameters. That is, changes in pH of the efuent aredependent on the changes in the hydrogen ion concentrationwhichin turn is dependent on the dissolved components of the efuent.

It was found that BPAC biosorbent exhibited the highest per-formance in terms of color, TSS, COD, BOD, and tannin and ligninremoval efciency followed by MBP and NBP. This may be attrib-uted to the carbonization followed by chemical (KOH) activation ofthe banana peel. Chemical activation of carbons is a very commonmethod for obtaining activated carbons with very high surfaceareas. KOH is one of the most effective agents employed for organicmaterials. KOH may be more selective in the activation process,causing a more localized reaction with the carbon precursor and ismore effective for highly ordered materials (Mopoung, 2008). Theeffectiveness of KOH activation relative to either physical activationmethods or activation by other chemical agents can be attributed tothe ability of potassium (K) to easily form intercalation compoundswith carbon. In addition, the potassium oxide (K2O) formed duringthe process of KOH activation, in-situ, can easily inltrate into thepores. K2O is reduced to K by carbon resulting in carbon gasicationwith a subsequent emission of carbon dioxide (CO2) leading to theformation of pores. Also K atoms that intercalate into the lamella ofthe carbon crystallites widen the space between the adjacent car-bon layers (intercalation phenomenon), resulting in an increase inthe value of specic surface area (Yong et al., 2007). The carboxylgroups on banana surface are responsible to some extent for thebinding of sorbate ions. This means that increasing the number ofcarboxylate ligands in the biomass can enhance the sorbate bindingcapacity. Some groups from cellulose, pectin, and hemicelluloses,which are major constituents of banana peel, can be modied tocarboxylate ligands by treating the biomass with KOH, therebyincreasing the sorbate-binding ability of the biomass (Baig et al.,1999).

In general, acidic methylation, alkali, and thermal treatment ofthe NBP to produce MBP and BPAC respectively could alter their

mental Management 132 (2014) 237e249 243lattice structure more effectively compared to the raw material.

r La

2

2

5

2

4

vironThese treatments led to remarkable increase in the specic area,and the major change achieved in the materials structure consid-erably promoted its capacity for all contaminants removalcompared to the original untreated peel.

3.2. Equilibrium isotherms

In this study equilibrium isotherm equations are used todescribe the experimental sorption data. The equation parametersand the underlying thermodynamic assumptions of these equilib-

Table 3Adsorption isotherm parameters, correlation coefcient and relative average error foand COD using NBP, MBP and BPAC.

Biosorbent NBP MBP

Parameter Color TSS COD Color

Langmuir isothermqm (mg/g) 49.751 28.409 67.563 87.719b (L/mg) 3.559 104 1.983 103 9.113 104 3 104R2 98.84 102 91.19 102 96.71 102 98.04 10Relative av. error 0.027004 0.087318 0.033989 0.132826RL 22.1 102 21.9 102 18,9 102 25 102Freundlich isothermKf 28.5 102 46.2 102 39.1 102 46.7 102n 1.805 1.85 1.578 1.745R2 0.9624 0.937 0.9939 0.9776Relative av. error 0.062819 0.088169 0.025039 0.048738RedlichePeterson IsothermKRP 1.408 102 39.27 102 12.16 102 2.555 10aRP 1.500 105 53.42 102 6.312 102 1.899 10b 1.321 52.07 102 55.28 102 1.279R2 0.9945 0.9750 0.9933 0.9950Relative av. error 0.017747 0.086435 0.022765 0.04144Sips IsothermKS 3.489 103 53.07 102 24.88 102 1.754 10bS 1.234 52.01 102 73.11 102 1.081aS 8.083 105 1.248 104 1.502 103 1.802 10R2 0.9927 0.9449 0.9914 0.9939Relative av. error 0.020385 0.090476 0.023493 0.045303

R.R. Mohammed, M.F. Chong / Journal of En244rium models often provide some insight into the sorption mecha-nism and the surface properties as well as afnity of the sorbent.Themost common isotherms applied in solid/liquid systems are thetheoretical equilibrium isotherm, the Langmuir, which is the bestknown and most often used isotherm for the sorption of a solutefrom a liquid solution; the Freundlich, which is the earliest knownrelationship describing the adsorption equation; the RedlichePeterson and the Sips, which are the isotherms containing threeparameters. These equilibrium isotherm models were used toanalyze the adsorption behavior in this study. Table S1 supple-mentary data shows a summary of the models used. The equilib-rium isotherm data were tted with Langmuir and Freundlichmodels by using linear regression method. Non-linear regressionwas used for data tting on RedlichePeterson and Sips models withthe aid of Graphpad Prism version 6 package. The degree of tnessfor all models was determined by least squares error analysis.

From Table S1 supplementary data, qm is the maximum uptakecapacity under the given conditions (mg/g), b is the equilibriumconstant related to free energy of adsorption (L/mg), Kf (mg/g)(L/mg)1/n and n are the Freundlich constants characteristic of thesystem and the indicators of the adsorption capacity and adsorp-tion intensity respectively, KRP (L/g) and aRP (L/mg)(1/b) are RedlichePeterson isotherm constants, Ks (mg/g)(L/mg)bs and as (L/mg)bs areSips isotherm constants, b and bs are the isotherm exponents.

The comparison of the experimental and estimated data byLangmuir, Freundlich, RedlichePeterson, and Sips models for theparameters of color, TSS, and COD with different biosorbents ofNBP, MBP and BPAC at 25 C are presented in Figs. 4e6 with thecorresponding goodness of t in Table 3. Generally, both two-parameter and three-parameter models show good tness withexperimental data for adsorption of most parameters. This can beattributed to the presence of both heterogenous and homogenoussurfaces on the banana peel (Febrianto et al., 2009). However, basedon values of mean residual square (R2) and relative average error ascriteria for goodness of t, RedlichePeterson isotherm provides abetter correlation between the theoretical and experimental datafor the whole concentration range for all types of biosorbentcompared to the other models. This is expected as the form of the

ngmuir, Freundlich, RedlichePeterson and Sips isotherm for adsorption of Color, TSS

BPAC

TSS COD Color TSS COD

47.17 147.059 135.135 62.893 2001.206 103 3.717 104 1.675 103 3.721 103 1.91 10389.72 102 87.43 102 99.7 102 98.3 102 92.6 1020.122038 0.039245 0.03911 0.055281 0.10241831.5 102 36.4 102 5.69 102 13 102 1 101

50.5 102 16.3 102 662.7 102 110.6 102 187.1 1021.7 1.26 2.837 1.719 1.6130.9908 0.9975 0.9532 0.9602 0.99350.035662 0.022178 0.062763 0.074782 0.029085

133.5 987.6 26.70 102 19.94 102 85.74 102286.6 6970 3.352 103 8.486 104 11.38 10239.98 102 18.63 102 93.94 102 1.197 57.07 1020.9979 0.9980 0.9986 0.9994 0.99820.034923 0.020235 0.036194 0.043963 0.023811

37.14 102 18.26 102 57.15 102 7.565 102 1.35464.67 102 76.67 102 84.31 102 1.251 71.65 1021.107 103 3.253 104 3.948 103 1.438 103 3.988 1030.9939 0.9981 0.9952 0.9969 0.99510.03716 0.019674 0.038162 0.047905 0.025001

mental Management 132 (2014) 237e249RedlichePeterson equation includes features of the Langmuir andFreundlich isotherms. So it may be used to represent adsorptionequilibrium over a wide concentration range of adsorbate.

The values of adsorption capacity qm for adsorption of color, TSSand COD onto BPAC are higher than for both MBP and NBP. Thehigher adsorption capacity for all parameters for the BPAC incomparison to the other studied adsorbents may be attributed tothe higher pore fraction capable of adsorbing the contaminationmolecules and is in-line with the trend observed from the previoussection of performance study. However, heterogeneity of the car-bon surface and the wide range of pore sizes and surface propertiesextremely complicate analysis of the observed behavior.

3.3. Adsorption kinetics

The experimental sorbate uptake rates onto the biosorbentswere investigated by using kinetic models in this study. The ki-netics of adsorption based on the overall adsorption rate by theadsorbents were analyzed by the Pseudo-rst-order, pseudo-sec-ond-order, and second order kinetic models as shown in Table S2supplementary data.

In Table S2 supplementary data, qt is the amount adsorbed attime t (mg/g); K1 is the rate constant of rst order adsorption (L/min), K2 and K are the rate constants of pseudo second order andsecond order-adsorption respectively (g/mg.hr).

Figs. 7e9 show that for the pseudo rst order kinetic modelthere is a deviation from the experimental data and the data weretted with a poor correlation coefcient and high relative average

error for most parameters (Table 4). This indicates that the rate ofremoval of color, TSS, and COD onto banana peel does not follow thepseudo-rst-order sorption rate expression of Lagergren.

The pseudo-second-order equation is based on the sorptioncapacity of the solid phase. It predicts the behavior over the wholerange of data. Furthermore, it is in agreement with chemisorptionbeing the rate controlling step. Model parameters K2 and qe values

were determined from the slope and intercept of the plots of t/qtagainst t. The values of the parameters, correlation coefcients andrelative average errors are also presented in Table 4. The correlationcoefcients of all examined data were found to be very high(R2 > 0.99) and the relative average errors were very low. Also thecalculated values of equilibrium sorption capacity, qe, are verymuch in agreement with experimental data for all studied systems.This shows that the model can be applied for the entire adsorptionprocess and conrms that the sorption of color, TSS, COD, BOD, and

R.R. Mohammed, M.F. Chong / Journal of Environmental Management 132 (2014) 237e249 245Fig. 7. Comparison of different kinetic models for (a) color, (b)TSS and (c) COD on NBPbiosorbent.Fig. 8. Comparison of different kinetic models for (a) color, (b)TSS and (c) COD on MBPbiosorbent.

tannin and lignin onto NBP, MBP and BPAC follow the pseudo-second-order kinetic mechanism.

Figs. 7e9 also show the kinetic modeling of color, TSS, and CODadsorption by the second order model equation. Correlation co-efcients, relative average errors and the second order model rate Kfor all studied systems are listed in Table 4. The correlation co-efcients, R2, of the second-order kinetic were found to be rela-tively low compared to the pseudo second order model, but stillbetter than those of the rst order kinetic model. Relative average

R.R. Mohammed, M.F. Chong / Journal of Environ246Fig. 9. Comparison of different kinetic models for (a) color, (b)TSS and (c) COD on BPACbiosorbent.errors were higher than that of the pseudo second-ordermodel, butstill lower than those of the pseudo rst-order model.

The kinetics of sorption processes are concerned with forcesbetween sites and adsorbate molecules, and this forms an impor-tant area of surface chemistry. Banana peel surface is cellulosebased and contains carboxylic and amine groups. Also the esteri-cation process of the banana peel introduces specic functionalgroups on the bril surface by which signicant improvement ofhydrophobicity may be obtained. On contact with water anddepending on pH, these groups become negatively charged and arelikely sites for chemical reaction to take place on the banana peelsurface. According to Ho and McKay (1999), pseudo-second ordermodel is based on the assumption that the rate-limiting step maybe chemical sorption or chemisorption involving valency forcesthrough sharing or exchange of electrons between sorbent andsorbate. The adsorption system obeys the pseudo second-orderkinetic model for the entire adsorption period and thus supportsthe assumption behind the model that the adsorption is due tochemisorption.

3.4. Scanning Electron Microscopy (SEM)

The surface physical morphology of NBP, MBP, and BPAC asobserved in Fig. 10 show progressive changes in the surface of theparticles. Fig. 10(a) reveals that microporous structures, heteroge-nous, rough surface with crater-like pores exist in banana peel. TheNBP particles are of irregular shape and their surface exhibits amicro-rough texture, which can promote the adherence ofadsorbates.

Fig. 10(b) shows that the treatment with methanol and acid haschanged the surface morphology of NBP. The surface of MBP hasmore irregular and porous structure than that of NBP, and thereforeexplains the higher BET surface area with higher adsorption ca-pacity. Fig. 10(b) also shows that the pores within the particles aremore homogenous. Also, this slightly rough surface provides suit-able binding sites for adsorbate molecules.

It is obvious from Fig. 10(C1) that the BPAC activated by KOH lostits original cellular structure and looked broken. The KOH reagent isa strong base. It is able to interact with carbon atoms and thuscatalyze the dehydrogenation and oxidation reactions, leading tothe increment of tar evolution and development of porosity (Hsuand Teng, 2000).

White spheres and some uffy materials can be seen in thepores of BPAC (Fig. 10(C2)). The white spheres and uffy materialsmay be due to the presence of K2O, potassium carbonate (K2CO3), orK residues. It may be argued that during the KOH activation process,various reactions can take place with such products as hydrogengas (H2), K, K2CO3, and K2O (Babel and Jurewicz, 2004). At highactivation temperature, the formation of K2O is thermodynamicallythemost stable. The high KOH ratio of 4 to 1 in samples containing alarge amount of Kmay cause the production of more K2CO3 and K2Oduring pyrolysis. It appears that larger amounts of K2CO3 causelarger pore size and structural deformation (Fig. 10(C3)). This pro-posed mechanism causes BPAC to have a higher performance thanNBP andMBP (Yupeng et al., 2002). These ndings are in agreementwith the ndings of Mopoung (2008).

3.5. Optimum conditions for treatment and decolorization ofbiologically treated POME

Treatment of POME requires a sound and efcient system to facethe current challenges. With the present situation where there aresome mills still failing to comply with the DOE standard dischargelimit even after they have applied the available treatment system, it

mental Management 132 (2014) 237e249is believed that adsorption technology will be able to further polish

ed b

Ps

r K2

6.2.113919476.2326904.

vironthe biologically treated POME in a more benecial way. For allstudied biosorbents, the optimum condition was found at contacttime of 24 h, dosage of 30 g/100 ml, and pH of 2. The BPAC wasfound to be the optimum biosorbent as compared to NBP and MBP.Under optimum conditions, the color of biologically treated POME(dark brown) was signicantly different after adsorption process.The color after adsorption by NBP and MBP turned to light and verylight yellow respectively. The color degree of biologically treatedPOME after undergoing BPAC adsorption treatment was furtherreduced, asmore than 96.46% of its initial valuewas removed, and itwas found to be colorless to the naked eye. The nal color con-centration at the optimum conditions of this work was 350 PtCo/Lafter treatment with BPAC adsorption compared to a nal colorconcentration of 1350 PtCo/L found by Kutty et al. (2011) aftertreating POME with microwave incinerated rice husk ashadsorption.

The test results for TSS removal showed that the maximumextent of removal was approximately 90% after treating with NBP.This is equivalent to a residual concentration of 180 mg/L which ismuch lower than the standard discharge limit. This removal per-centage is slightly higher when treating with MBP where it reaches91.667% of the initial value, while the nal TSS concentration afterBPAC adsorption treatment was close to 0 mg/L.

COD shows a reduction by 99% after adsorption with NBP. TheMBP and BPAC treatments brought down the COD value nearly to0 mg/L from the original COD value of biologically treated POME.For BOD reduction, a similar trend to the COD reduction was ob-tained from each type of biosorbent. However, it can be seen thatNBP treatment process reduced the BOD percentage by more than90%, which is well below the allowable limit set by the Malaysian

Table 4Parameters, correlation coefcient and relative average error of kinetic models obtainon NBP, MBP and BPAC.

Adsorbent Adsorbate qe(exp.) (mg/g) Pseudo rst-order model

K1 (1/hr) R2 Relative av. Erro

NBP Color 65.0 0.2633 0.9550 0.056534TSS 19.0 0.1275 0.9960 0.06474COD 85.0 0.2829 0.6710 0.102363

MBP Color 94.0 0.4505 0.9150 0.073979TSS 13.0 0.2195 0.9710 0.114048COD 85.0 0.4501 0.8090 0.074324

BPAC Colour 176.0 0.2183 0.7742 0.148375TSS 28.5 0.1854 0.7166 0.153404COD 91.5 0.2472 0.7920 0.15139Tannin & lignin 1.4 0.1153 0.9788 0.17692BOD 27.0 0.1257 0.9674 0.10591

R.R. Mohammed, M.F. Chong / Journal of EnDepartment of Environment, which is 100 mg/L. Similarly, a BODreduction to near 0 mg/L was observed for both MBP and BPACtreatment processes.

Adsorption processes were expected to reduce tannin and lignincontent of biologically treated POME effectively. Results revealedthat BPAC adsorption processes were capable of reducing tanninand lignin by up to 76.744% (as compared to initial level). Due to thefact that there is no chemical addition during palm oil processing,the color of this efuent is due to plant constituents such as ligninand phenolics as well as repolymerizsation of coloring compoundsafter anaerobic treatment (Zahrim et al., 2009). Considering theresults of this research, it is believed that decolorization of bio-logically treated POME is a function of its TSS and tannin and ligninconcentrations.

In addition, with the nal pH adjustment to 7, the resultingbiologically treated POME using this technology is in compliancewith standard discharge regulations and the resulting high-qualitytreated water can be recycled back to the plant to be reused.4. Conclusion

Research was carried out to explore banana peels as a high ca-pacity, economically viable and low cost adsorbent for treatingbiologically treated POME. The experimental results showed thatNBP has the ability to reduce the concentrations of biologicallytreated POME to meet the POME discharge standard. Resultsshowed that modication of NBP by acidied methanol or KOH andthermal treatment can further improve the sorption removal forcolor, TSS, and COD. The optimum adsorption capacity of NBP wasfound at 97 mg/g for color, 25 mg/g for TSS, and 90.5 mg/g for CODremovals respectively. The MBP has optimum adsorption capacityof 137.5 mg/g, 28.5 mg/g and 93 mg/g for color, TSS, and COD re-movals respectively, while BPAC has 184.5 mg/g, 34.5 mg/g, 94 mg/g, 26.76 mg/g and 1.4 mg/g for color, TSS, COD, BOD, and tannin andlignin removals respectively. In the present study, the optimumadsorption conditions were found at dosage of 30 g of adsorbent/100 ml of sample and after 24 h contact time. The pH played anobvious effect on the sorbate adsorption capacity onto all types ofbanana peel biosorbents. The decrease in the solution pH led to asignicant increase in the adsorption capacities of all parameterson the banana peel biosorbents withmaximum adsorption capacityoccurring at acidic pH of 2, although, the adsorption efciency isstill high at the original efuent pH (8.4).

Four adsorption isotherm models were studied. The sorptiondata of color, TSS, and COD on banana peel biosorbents tted intotwo-parameter isotherm models (Langmuir and Freundlich) andthree-parameter isotherm models (RedlichePeterson and Sips). Anexcellent prediction in all the studied concentration range can beobtained by the three-parameter equations. Among all the tested

y using the linear methods for adsorption of color, TSS, COD, Tannin & lignin and BOD

eudo second-order model Second-order model

(g/mg/hr) R2 Relative av. Error K (g/mg/hr) R2 Relative av. Error

762 103 0.9983 0.033199 0.0314 0.9265 0.145756913 103 0.9940 0.027864 0.0190 0.9709 0.339175.710 103 0.9996 0.016083 0.0156 0.9931 0.021715.400 103 w1 0.006587 0.0911 0.9327 0.023886.700 103 0.9940 0.050348 0.0910 0.9568 0.304766.200 103 w1 0.00709 0.8810 0.9523 0.038508436 103 0.9999 0.012703 0.0663 0.9034 0.087279.600 103 0.9988 0.035884 0.0871 0.9135 0.097595.400 103 0.9995 0.018225 0.0861 0.8577 0.027888.400 103 0.9988 0.010357 0.4209 0.9664 0.07071965 103 0.9991 0.070284 0.0609 0.7092 0. 09533

mental Management 132 (2014) 237e249 247equations, an excellent and perfect representation of the experi-mental results is obtained using the RedlichePeterson model. andthe mechanism of adsorption is a hybrid unique and does notfollow ideal monolayer adsorption.

Kinetic study showed that sorption behavior of color, TSS, COD,BOD, and tannin and lignin onto banana peel biosorbents had abetter t with the pseudo second order equation than the Lagerg-ren rst order and second order equations. Following the pseudosecond-order kinetics indicates that the biosorption process oper-ates through chemisorption mechanism. Chemical sorption canoccur by the active functional groups of biosorbents as chemicalbonding agents.

The addition of KOH raised the pore size and porosity of BPACwhich is due to the aggressive action on the cellular structure,indicating that carbon gasicationwas enhanced by the addition ofKOH which led to widened pores.

The present work reveals that the waste banana peel is apromising material for the treatment of biologically treated POME.

vironR.R. Mohammed, M.F. Chong / Journal of En248Acknowledgment

This work has been carried out during sabbatical leave grantedto the author (Rae R. Mohammed) from Mosul Technical Instituteduring the academic year 2012, so the author thanks Ministry ofHigher Education/Iraq, and Foundation of Technical Education/Iraq, for their support. Authors would like to acknowledge andextend their heartfelt gratitude to Dr. Vasanthi Sethu who hasmade the completion of this research possible. We are deeply

Fig. 10. Surface images of (a) NBP, (b) MBP, (C1) BPAC, (C2) BPAC with thmental Management 132 (2014) 237e249indebted to Andrew, Y.S., Farahwahida B.M., and Filza M.F. for theirtechnical assistance. This research has been supported by theUniversity of Nottingham/Malaysia Campus as a research scholarfellowship.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.jenvman.2013.11.031

e white spheres and uffy materials and (C3) BPAC with large pores.

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Treatment and decolorization of biologically treated Palm Oil Mill Effluent (POME) using banana peel as novel biosorbent1 Introduction2 Materials and methods2.1 Biologically treated POME2.2 Collection and preparation of adsorbents2.2.1 Natural banana peel (NBP)2.2.2 Methylated banana peel (MBP)2.2.3 Banana peel activated carbon (BPAC)

2.3 Adsorption isotherm experiments2.4 Adsorption experiment2.5 Analytical methods

3 Results and discussion3.1 Performance study3.2 Equilibrium isotherms3.3 Adsorption kinetics3.4 Scanning Electron Microscopy (SEM)3.5 Optimum conditions for treatment and decolorization of biologically treated POME

4 ConclusionAcknowledgmentAppendix A Supplementary dataReferences