Adsorption of Phenol from Aqueous Solution by Avocado Seed Activated Carbon: Equilibrium, Kinetic, and Full Factorial Design Analysis

Transcription

1 61 Adsorption of Phnol from Aquous Solution by Avocado Sd Activatd Carbon: Equilibrium, Kintic, and Full Factorial Dsign Analysis Muluh, S.N. 1*, Ghogomu, J.N., Alongamo, A.A.B. 3, Ajifack, D.L. 4 1,,3,4 Dpartmnt of Chmistry, Faculty of Scinc, Univrsity of Dschang, Camroon *Corrsponding author: nkngsvrin@yahoo.co.uk; Tl.: ABSTRACT Activatd carbon from avocado (Prsa Amricana) sds, obtaind by chmical activation using H 3 PO 4 acid i.. avocado sd activatd carbon (ASAC) was usd for th rmoval of phnol from aquous solution. Sampls wr charactrizd by FTIR, Bohm, phpzc, iodin numbr, surfac ara, and proximat analysis. Batch adsorption studis wr prformd in ordr to valuat th maximum adsorption capacity of phnol by ASAC at 7 o C. optimal conditions from quilibrium studis stood at: adsorbnt dos of 1g, ph of 7 and contact tim of 1 min for all th diffrnt initial concntrations of adsorbat usd. Th Langmuir isothrm modl bst rprsntd th quilibrium data with monolayr adsorption capacitis of 7.94 mg/g, mg/g, and mg/g rspctivly for 1ppm, ppm, and 3ppm initial adsorbat concntrations. Kintic studis rvald that th adsorption procss followd a psudo-scond ordr modl and th mchanism of th sorption procss is controlld by film diffusion of th adsorbat into th adsorbnt. In ordr to xamin th main factors (ph, adsorbnt dosag and contact tim) and thir intractions for th uptak of phnol, a 3 full factorial dsign was usd. Th optimization of factors to obtain maximum adsorption was carrid out by using main factors and thir intractions, normal probability plot, Analysis of Varianc (ANOVA) and Parto chart. Kywords Activatd Carbon, Factorial Exprimntal Dsign, Optimization, Prsa Amricana, Phnol 1. INTRODUCTION Organic pollution is th trm usd whn organic compounds contaminat th nvironmnt. It originats from domstic swag, urban run-off, industrial fflunts, agricultural wastwatr, pulp and papr making and swag tratmnt plants. Organic pollutants includ psticids, frtilizrs, hydrocarbons, pharmacuticals, biphnyls, plasticizrs, phnol tc. [1]. Among th diffrnt pollutants, phnol and phnolics ar considrd as priority pollutants sinc thy ar harmful to plants, animals, and humans, vn at low concntration and can b toxic whn prsnt at lvatd lvls []. Chronic toxic ffcts du to phnol pollution in human includ kidny and livr damag, anorxia, hadach, vomiting, difficulty in swallowing, fainting and phnol is suspctd to b carcinognic [3]. Du to th toxic natur of phnol, svral rgulatory bodis lik World Halth Organization (WHO) and US Environmntal Protction Agncy (USEPA) tc. hav listd phnol and phnolic compounds on th priority pollutant list. WHO has givn a maximum prmissibl limit of. mg/l and. mg/l for chlorophnol and phnol rspctivly in drinking watr [1, 4]. Phnol dcomposition is difficult, primarily du to its stability and its solubility in watr. Svral tchniqus for th squstration of toxic organic compounds from wastwatr hav bn studid xtnsivly by diffrnt rsarchrs. Tchniqus such as coagulation, filtration with coagulation, prcipitation, ion xchang, rvrs osmosis, advancd oxidation procsss and adsorption hav bn usd for th dcontamination of pollutd watr and wastwatr. Som of ths mthods hav bn found to b limitd sinc th oprational cost involv is using high [5]. Amongst th possibl wastwatr tratmnts tchniqus, adsorption using activatd carbon has shown grat potntials as on of th most fficint tratmnt mthods for th uptak of organic contaminants from wastwatr [6, 7]. Activatd carbons ar th most widly usd adsorbnt for rmoving pollutants from gasous, aquous and non-aquous strams du to thir uniqu powrful adsorption proprtis and th ability to radily modify thir surfac chmistry [8]. Activatd carbons ar amorphous solid adsorbnts that can b producd from almost all carbon-rich matrials, including avocado sd. It's uniqu adsorption proprtis rsult from its larg surfac ara, adquat por siz distribution and a broad rang of surfac functional groups. Ths uniqu charactristics ar rsponsibl for its adsorption proprtis [9]. Commrcial activatd carbon is vry costly. In rcnt yars, th sarch for radily availabl and low-cost matrials for activatd carbon production has bn intnsifid. Matrials locally availabl such as natural matrials and agricultural wast can b usd as low-cost adsorbnts. Activatd carbon producd from ths matrials can b usd as an adsorbnt for watr and wastwatr tratmnt [1]. Avocado (Prsa Amricana) is a fruit cultivatd in almost vry tropical ara. Aftr fruit consumption, th sds ar discardd as thy ar not dibl. Thus, avocado sds ar availabl fr and ar considrd as wast mattr in th nvironmnt. Lik othr agricultural rsidus, th avocado sd is mainly composd of cllulos, hmicllulos, and lignin. This composition maks avocado sd a good prcursor for th production of th nw low-cost adsorbnt for watr tratmnt procsss. In th prsnt study, th main objctiv is to prpar, charactriz and valuat th possibility of using drid avocado sd activatd carbon (ASAC) to study its application in rmoving phnol from aquous mdia. Systmatic valuation of th diffrnt xprimntal factors such as ph, initial phnol concntration, adsorbnt dos and contact tim wr carrid out. In addition, quilibrium, kintic and procss optimization using full factorial dsign analysis wr prformd in ordr to stablish th adsorption capacity of ASAC.

2 611. MATERIALS AND METHODS.1 Sampl Collction and Prtratmnt A collction of frsh rip avocados (Prsa Amricana) was bought from th Bamnda food markt in th North Wst Rgion of Camroon. Th avocados wr all washd and th flsh rmovd to gt th sds. Th sds wr cut into small pics using a knif thn washd thoroughly with distilld watr and sundry for tn days. Th drid sampls wr crushd into powdr using a high powr lctric blndr and scrnd through a st of sivs to obtain a particl siz of 1 m. Th rsulting powdr was ovn drid for 4 hours at 15 o C.. Prparation of Activatd Carbon 5 g of avocado sd powdr was imprgnatd using H 3 PO 4 at a 1:1 (W:V) imprgnation ratio. Th imprgnation was carrid out at 15 o C in a hot air ovn for 4h to achiv good pntration of th chmical into th intrior of th prcursor matrial. Th imprgnatd sampl was thn drid at 15 o C in an ovn for 1h. Th drid imprgnatd sampl was transfrrd into a porclain crucibl with lid. Th crucibl was placd insid an lctric Muffl furnac and th sampl carbonizd at 4 o C for 1h, in th absnc of air. Th carbonizd sampl was thn coold to room tmpratur and washd with distilld watr until th ph valu of th rinsd watr was nutral. Th washd activatd carbon was thn drid in th ovn at 15 o C for 5 hours. Th sampl was furthr pulvrizd and packd in cllulos papr packts for xprimntal work. Th adsorbnt prpard by H 3 PO 4 was dnotd as ASAC throughout this study..3 Stock Solution of Phnol (C 6 H 5 OH, 99.5%, Mrck-Aldrich) was prpard by dissolving 1. g of th salt in 1 Litr of distilld watr to giv a concntration of 1 ppm. Srial dilutions for working solutions wr mad by diluting th stock solution in accurat proportions..4 ph Adjustmnt Solutions ph adjustmnt solutions wr prpard using hydrochloric acid (.1M, 6%, Ridl-d-Han) and sodium hydroxid (.1 M of 98%, Fluka) solutions rspctivly..5 Batch Adsorption Exprimnts Th batch adsorption xprimnts for th uptak of phnol by avocado sd activatd carbon wr carrid out in a shakr (Edmund Bühlr SM 3) maintaind at 5 o C. All th xprimnts (xcpt th study of th ffct of ph) wr carrid out at a ph of 7. For ach xprimnt (xcpt othrwis statd), 1 g of adsorbnt was masurd and put into a 5-mL conical flask containing 1 ml of th phnol solution at th dsird concntration that rangd btwn 1 and in this study. Aftr stirring th solution for a prdtrmind tim intrval (1-18 minuts), sampls wr thn filtrd, th filtrat was analyzd spctrophotomtrically to dtrmin th concntration of th rsidual phnol using a UV-Visibl spctrophotomtr (JENWAY) at max = 7 nm. Adsorption data obtaind from quilibrium studis (contact tim and initiation concntration ffcts) wr mployd in th kintic studis and th applicability of diffrnt adsorption isothrms to phnol. Th amount of phnol adsorbd pr unit mass was calculatd using th following quation [11]: C - C V o q (mg/g) = (1) M Whr q is th amount of phnol adsorbd on th adsorbnt (mg/g), C o and C (mg/l) ar th initial and quilibrium liquid-phas concntrations of phnol (mg/g), rspctivly. V (L) is th volum of phnol solution and m (g) is th amount of th adsorbnt usd. Th rmoval fficincy was dfind as [11] C - C o % R = 1 () C o.6 Adsorption Isothrm Modls.6.1 Langmuir Isothrm Th Langmuir isothrm assums monolayr adsorption onto a surfac containing a finit numbr of idntical adsorption sits [1]. Langmuir thory is basd on two assumptions that th adsorbd layr is unimolcular and th forcs of intraction btwn sorbd molculs ar ngligibl [13]. Adsorption is assumd to tak plac at spcific homognous sits on th adsorbnt. Onc a phnol molcul occupis a sit, no furthr adsorption can tak plac at that sit. Th linar form of Langmuir isothrm quation is rprsntd as (3) [14] C 1 C q K q q = + (3) L m m

3 61 Whr q m (mg/g) and k L (L/mg) ar Langmuir constants rlatd to maximum adsorption capacity and rat of adsorption, rspctivly. Also, q (mg/g) is th amount of phnol adsorbd pr unit wight of adsorbnt, C (mg/l) is th concntration of th phnol solution at quilibrium. q m and K L valus ar obtaind from th slop and intrcpt of th linar plot (C /q is plottd against C ). Th fficincy of th Langmuir adsorption procss is furthr assssd by (4): 1 R L = (4) 1 + K C L o.6. Frundlich Isothrm Th Frundlich isothrm assums htrognous surfac nrgis on th adsorbnt surfac [15], in which th nrgy trm in Langmuir quation varis as a function of th surfac covrag. A linar form of th Frundlich quation is drivd by [16] 1 log q = log K F + log C (5) n Whr K F (mg/g(l/mg) 1/n ) and n ar th Frundlich adsorption constant and htrognity factor, rspctivly. K F is rlatd to th bonding nrgy and 1/n valu is rlatd to th adsorption intnsity. Th intrcpt K F and th slop 1/n ar obtaind by plotting log q vrsus log C..7 Sorption Kintic Modls To lucidat th possibl mchanism of th adsorption of phnol onto ASAC, th psudo-first-ordr, psudo-scond-ordr, intra-particl diffusion and Boyd kintic modls wr tstd by using th data obtaind from adsorption kintic xprimnts. Th psudo-first-ordr kintic modl of Lagrgrn is xtnsivly studid and dfind as [17]: K1 log q - q t = log q + t (6).33 Whr K 1 is th rat constant of psudo-first-ordr adsorption (1/min), t is th contact tim (min), q and q t (mg/g) ar th amounts of phnol adsorbd at quilibrium and at tim t (min), rspctivly. By using this linar quation and drawing a plot of log(q q t ) vrsus t, K 1 and q can b obtaind from th slop and th intrcpt. Th psudo-scond-ordr modl stimats th bhavior ovr th whol rang adsorption and this modl is also basd on th adsorption capacity of th solid phas. Th psudo-scond-ordr modl has a supposition that th sorption procss involvs chmisorption mchanism and is dfind as [18]: t 1 1 = + t (7) q K q q t Whr K is th rat constant of psudo-scond-ordr adsorption (g/mg.min), t is th contact tim (min), and q and q t (mg/g) ar th amounts of phnol adsorbd at quilibrium and at tim t (min), rspctivly. If th psudo-scond-ordr kintic quation is suitabl, q and K can b dtrmind xprimntally from th slop and intrcpt of plot t/q t vrsus t. Th basic assumption of th Wbr and Morris or intra-particl diffusion modl is that film diffusion is ngligibl and intraparticl diffusion is th rat controlling stp. According to Wbr and Morris (1963) [19], if th rat limiting stp is intra- particl diffusion, thn th amount of adsorbat adsorbd at any tim t should b dirctly proportional to th squar root of contact tim (t). This is dfind mathmatically as: q = K t + C (8) t.5 id Whr q t (mg/g) is th amount of phnol adsorbd onto th adsorbnt at tim t (min), K id (mg/g. min) is th intra-particl diffusion rat constant. Th valu of C xplains th thicknss of th boundary layr, th largr th intrcpt th gratr th boundary layr ffct. A plot of q t vrsus t.5 should giv a linar graph if intraparticl diffusion is involvd in th sorption procss and if th plot passs through th origin thn intraparticl diffusion is said to b th sol rat-limiting stp. Howvr, q t vrsus t.5 could giv a multilinar plot which suggsts that two or mor stps govrn th sorption procss [19]. If both film diffusion and intra-particl diffusion occur in th adsorption procss, Boyd's modl is oftn usd to dtrmin th actual rat limiting stp involvd in th procss. Th Boyd's kintic xprssion [] is givn by quations (9-11) as follows: 6 1 z Dt F(t) = 1 - xp (9) z1 z r whr F(t) =q t /q is th fractional attainmnt of quilibrium at tim t, D is th ffctiv diffusion cofficint of phnol in th adsorbnt phas (cm /s), r is th radius of th adsorbnt particls assum to b sphrical and z is an intgr. Fitting quation (9) to th whol rang < F(t) < 1, for adsorption on sphrical particls.

4 613 Dt Ft 1xp (1) r This quation could b furthr simplifid to covr most of th data points for calculating th ffctiv particl diffusivity. 1 Dt ln (11) 1 F t r Thus, th slop of th plot of ln[1/(1-f(t))] vrsus t would giv D. 1.8 Statistical Dsign of Exprimnts Th statistical optimization tchniqu using th full factorial dsign of xprimnts is gnrally applid to dtrmin th boundary conditions, which allows for th maximum output of th dsird products. Using a propr dsign matrix, on can obtain a rgrssion quation, which highlights th ffct of individual paramtrs and thir rlativ importanc in a givn opration/procss. Th intractional ffcts of two or mor variabls can also b known, this is not possibl in a classical on factor at a tim (OFAT) xprimnt [1]. Th principal stps of statistically dsignd xprimnts ar a dtrmination of rspons variabls, factors and factor lvls; choic of th xprimntal dsign; and statistical analysis of th data. Today, th most widly usd xprimntal dsign to stimat main ffcts, as wll as intraction ffcts, is th k factorial dsign, whr ach variabl is invstigatd at two lvls. Rsarch can b dsignd for multipl factors and tratmnts, but data analysis and tratmnt stablishmnt bcoms mor complx and tim-consuming as th numbr of factors and tratmnts incras []. In ordr to xamin th main ffcts and intractions btwn factors for th uptak of phnol by ASAC at initial phnol concntration of 3ppm, a factorial of typ 3 was usd. Th xprimntal dsign involvd thr factors at two lvls (i.. low and high) as spcifid in TABLE 1. Exprimnts for th full factorial dsign wr conductd in a st of ragnt bottls containing 1mL phnol solution of known ph, concntration, and adsorbnt dos for 1 h at 7 o C until quilibrium was rachd. Aftr on hour of contact, th suspnsions wr filtrd and phnol concntrations in th suprnatant solutions wr masurd using a UV- Vis Spctrophotomtr. A total of 8 xprimnts wr carrid out, th ordr in which th xprimnts wr prformd was randomizd to avoid systmatic rrors [3]. Th rsults of th xprimntal dsign wr analyzd using Dsign-Exprt softwar vrsion 7. (Stat-Eas, Inc. Minnapolis USA). Tabl 1: High and low lvls of factors Factors Codd symbols Low lvl (-1) High lvl (+1) ph A 1 Adsorbnt dosag (g) B.1 Contact tim (min) C RESULTS AND DISCUSSION 3.1 Charactrization Physicochmical/Proximat Analysis Th physicochmical charactristics of avocado sd activatd carbon (ASAC) ar summarizd in TABLE. Tabl : Physicochmical and proximat analysis of ASAC ph pzc Moistur contnt Proximat Analysis Volatil mattr Ash contnt Bohm titration (mmol/g) Fixd carbon Carboxylic Lactonic phnolic Total basic Iodin numbr (m /g) S BET(m /g) FTIR Spctra Analysis Figur 1: FTIR spctrum of ASAC

5 614 Th FTIR spctrum of ASAC is givn in Fig. 1. it can b obsrvd that th functional groups rsponsibl for adsorption on th surfac of th adsorbnt ar, a hydroxyl group at 3415 cm -1, unsymmtrical aliphatic C H strtching at 916 cm -1 and C=C strtching of aromatic rings at 1563 cm -1. Th band at 1149 cm -1 on th surfac of ASAC can b attributd to C O strtching in alcohol or thr and th band at 876 cm -1 can b ascribd to symmtrical vibration in a chain of P-O-P and to P-C phosphoruscontaining compound. 3. Effcts of Procss Paramtrs 3..1 Effct of Adsorbnt Dos Fig. a shows th ffct of adsorbnt dos on th rmoval of phnol for diffrnt initial phnol concntrations (1-3) ppm. Th rsults show that th prcntag rmoval of phnol incrass with th incras in adsorbnt dosag. This can b attributd to incrasing in adsorbnt surfac ara and availability of mor adsorption sits as th mass of adsorbnt is incrasd. Similar rsults wr obtaind by [3, 4]. Th rsults also clarly show that th rmoval fficincy incrass up to th maximum adsorbnt dosag of 1g byond which th rmoval fficincy is ngligibl % Rmoval 6 4 % Rmoval 6 4 % Rmoval Adsorbnt dos (g) ph Contact tim (min.) Figur : Effcts of procss paramtrs on th adsorption of phnol onto ASAC (a) Adsorbnt dosag (b) ph and (c) contact tim 3.. Effct of ph Solution ph is on of th most important paramtrs that affct th adsorption proprty of an adsorbnt and adsorbat. Functional groups prsnt on both adsorbnt and adsorbat ar affctd by th ph of th solution. Th surfac charg of th adsorbnt and th dgr of ionization of th adsorbat ar qually affctd by ph of th solution. Th rsults of th adsorption of phnol as a function of ph ar prsntd in Fig. b. From th rsults, it can b obsrvd that th rmoval fficincy of phnol incrass with th incras in ph from to 7, thn dcras sharply byond ph 7. In gnral, phnol uptak is low at low and high ph valus. At low ph valus (ph<), th uptak of phnol is small du to xcss H + ions in solution compting with phnol for th sorption sits of th adsorbnt. Also, th xcss H + ions supprss th ionization of phnol and hnc its uptak by polar adsorbnts is rducd. At high ph (>7), phnol form salts which ar radily ionizd laving th ngativ charg on th phnolic group. At th sam tim, th prsnc of OH - ions on th adsorbnt surfac prvnt th uptak of phnolat ions. Similar rsults wr rportd by [4] Effct of Contact Tim Th ffct of contact tim on th rat of phnol rmoval was invstigatd at diffrnt initial concntrations (1, and 3) ppm as shown in Fig. c. Th rsults indicat that th rmoval fficincy of phnol incrass with incrasing contact tim and quilibrium is rachd at approximatly 1 min for all th xprimnts. Byond this priod, th prcntag rmoval of phnol is fairly constant. Equally, from th rsults, it can b obsrvd that th sorption procss is vry fast with th first 4 mins of th procss, bcaus of th availability of a larg numbr of vacant sits on th adsorbnt surfac at this initial stag. 3.3 Adsorption Isothrm Modl In ordr to find th most appropriat modl for phnol adsorption, th data wr fittd to ach isothrm modl. Th paramtrs of th diffrnt modls ar prsntd in TABLE 3 and only th Langmuir isothrm modl (R =.9967,.9959 and.997 for 1ppm, ppm and 3ppm rspctivly) rprsntd on Fig. 3a bst fittd th xprimntal data. Th homognous monolayr adsorption capacity of phnol adsorption at 5 o C was found to b qual to 7.94 mg/g, mg/g and mg/g for 1ppm, ppm, and 3ppm initial phnol concntration rspctivly. Th dimnsionlss constant sparation trm (R L ) was usd to invstigat th shap of th Langmuir isothrm. In this invstigation, th quilibrium paramtr was found to b in th rang < R L < 1 as shown in TABLE 3. This indicats that th sorption procss was vry favorabl and that th adsorbnt mployd xhibits good adsorption potntials.

6 615 Tabl 3: Langmuir and Frundlich isothrm paramtrs Conc. (ppm) q, xp (mg/g) Langmuir isothrm Frundlich Isothrm q m (mg/g) K L (L/mg) R L R n K F R Y = X; R = Y = X; R = Y = X; R = C /q (g/l) log q X; R = X; R = X; R = C (mg/l) log C Figur 3: Isothrm modls for th adsorption of phnol onto ASAC (a) Langmuir isothrm and (b) Frundlich isothrm rprsntation. 3.4 Adsorption Kintic Modl Th rsults of th kintic studis ar prsntd in Fig. 4. Th paramtrs of th diffrnt kintic modls valuatd in this study ar rprsntd in TABLE 4. From TABLE 4, it can b noticd that th corrlation cofficint (R 1 ) (.988,.9545 and.9384 rspctivly for 1, and initial concntrations) for th psudo-first ordr kintic modl ar corrspondingly lss than th corrlation cofficint (R ) (.9991,.998 and.9983 rspctivly for 1ppm, ppm and 3ppm initial concntrations) for th psudo-scond ordr kintic modl. Equally, from TABLE 4, it can b obsrv that th calculatd q valus (q,cal ) for th psudo-first ordr modl for th diffrnt initial concntrations ar significantly diffrnt from th xprimntal q valus (q,xp ) manwhil th q,cal valus for th psudo-scond ordr modl ar consistnt with th q,xp valus. Ths findings suggst that th adsorption of phnol onto ASAC is bst dscribd by th psudo-scond ordr kintic modl Y = X; R = Y = X; R = Y = X; R = Y = X; R =.9983 log (q -q t ).5. Y = X; R = Y = X; R = t/q t t (min) t (min) 5 4 q t (mg/g) t 1/ (min 1/ ) In[1/1-F(t)] 3 Y = X; R = Y = X; R = Y = X; R = tim (min) Figur 4: Kintic modls for th adsorption of phnol onto ASAC (a) Psudo-first ordr (b) Psudo-scond ordr (c) intraparticl diffusion and (d) Boyd modl plot.

7 616 Tabl 4: kintic paramtrs for th adsorption of phnol onto ASAC for diffrnt initial concntration Concntration (ppm) Kintic Modls Paramtrs 1 3 Psudo-first ordr modl Psudo-scond ordr modl Intraparticl diffusion modl Boyd modl q, xp (mg/g) q, cal (mg/g) K 1 (1/min) R q, cal (mg/g) K (mg/g.min) R K id (mg/g.min) First lin sgmnt C R K id (mg/g.min) Scond lin sgmnt C R B(slop) Intrcpt D i (m /s) 11.x x x1-1 R From Fig. 4c, th two linar portions of th intraparticl diffusion plot suggst that th adsorption procss procds by film diffusion and intraparticl diffusion. As obsrvd in TABLE 4, th Y-intrcpt of th two linar portions (C valus) is a masur of th thicknss of th boundary layr. Th largr th valu of C, th gratr is th boundary ffct. In ordr to stablish th rat-limiting stp, th kintic data wr furthr analyzd using Boyd s modl Fig. 4d. From th rsults, it is noticd that th straight lins do not pass through th origin, this is indicativ that th adsorption procss is controlld by film diffusion or chmical raction. From TABLE 4, valus of th ffctiv diffusion cofficint (D i ) which li in th rang (1-1 to 1-1 m /s) provid an indication that film diffusion is th rat-limiting stp in th adsorption of phnol onto ASAC. Similar rsults wr rportd by [5]. Th uptak of phnol on avocado sd activatd carbon is vry comparabl to othr low-cost adsorbnts as wll as to commrcial activatd carbon prviously studid [6-9] as shown in TABLE 5. Tabl 5: Comparison of th maximum monolayr adsorption capacitis of phnol onto various adsorbnts Adsorbnt q m (mg/g) Rfrncs 9.7 ASAC 17.6 Prsnt study.8 Kaolinit 5.4 [] Swag Sludg Basd Adsorbnt 6. [6] Coal fly ash 17.1 [7] Bagass fly ash 3.8 [8] Commrcial Activatd Carbon 9.4 [9] 3.5 Full Factorial Dsign of Exprimnt Factors that influnc th quantity of phnol adsorbd by ASAC wr valuatd by using factorial plots: main ffct, intraction ffct, normal probability plot and th Parto chart. ANOVA, F, and P-valus wr usd to chck th significanc of th ffcts on th rspons. Th factorial dsign matrix and th rsponss (% rmoval fficincy), masurd in ach xprimnt is prsntd in TABLE 6. Run Ordr Tabl 6: Dsign Matrix for Phnol Adsorption Variabl valus Rmoval Efficincy (%) ph Dosag (g) Contact tim (min) Obsrvd Prdictd Rsidual

8 ANOVA Analysis of Varianc is a statistical mthod that partition th total variation into its componnt parts [3]. TABLE 7 prsnts th rsults of ANOVA for th adsorption of phnol by ASAC using th factorial dsign. From th rsults, th factors that influnc th uptak of phnol wr valuatd using th Fishr s F-ratios (dfind as th ratio of th man squar ffct and th man squar rror) and P-valus (dfind as th lvl of significanc lading to th rjction of th null hypothsis). A high F- valu and low P-valu (P <.5) indicat that such main ffct and/or intractions ar significant at 95% confidnc intrval [31]. It can b infrrd from th rsults in TABLE 7 that F-valus of 438.7, 5.18,835. and , all having P-valus lss than.5 indicat that, th modl, th main ffcts (A and C) and th intraction ffct (AC) ar significant. Modl trms with P-valus gratr than.1, indicating that th trms ar not significant. Thus, th main ffct (B) with P-valu of.13 is not significant. Tabl 7: Analysis of Varianc (ANOVA) for adsorption of phnol Sourc Sum of Dgr of Man P-valu F-valu Squars frdom squar Prob>F Commnts Modl significant A-pH significant B-Adsorbnt Dosag C-Contact Tim <.1 significant AC-pH * Contact tim significant Rsidual Cor Total R-Sq =.9983 R-Sq (adj) =.996 R-Sq (prd) =.9877 Tabl 8: Estimatd Rgrssion Cofficints for th rmoval of phnol Factor Cofficint Estimat Dgr of frdom Standard Error 95% CI Low 95% CI High VIF Intrcpt A-pH B-Adsorbnt Dosag C-Contact Tim AC-pH x Contact Tim Th Main and Intraction Effcts Th rsults of th main and intraction ffcts on th rmoval fficincy ar shown in Fig 5. Th ffct of a factor is th chang in rspons producd by a chang in th lvl of th factor. Th main and intraction ffct plots wr gnratd to rprsnt th rsults of th rgrssion analysis. From TABLE 8, it can b obsrvd that th stimatd cofficints of th main factors that ar significant to th rspons ar positiv (A=16. and C=.66). This implis that th rmoval fficincy incrass as th factors chang from low to high lvls. In contrast, th stimatd cofficint for th intraction ffct is ngativ (AC = ), indicating a rduction in th rmoval fficincy as th factor changs from low to high lvls [3]. It should qually b pointd out that, th statistical significanc of a factor is dirctly rlatd to th slop of th ffct lin. If th slop of th ffct lin is clos to zro, thn th siz of th ffct on th rspons is small, whil a stpr ffct lin slop indicats that th siz of th ffct on th rspons would b larg [33]. Thus from Fig. 5, it can b infrrd that th main ffcts A and C with stpr slops contribut significantly to th rmoval fficincy of phnol. Whil th main ffct B whos slop is clos to zro is insignificant to th rmoval fficincy. Th fit of th modl was chckd using th corrlation cofficints (R ). Th prdictd corrlation cofficint (prd R ) of.9877 was in good agrmnt with th modl s corrlation cofficint of.9983 and th adjustd corrlation cofficint (R adj) of.996. Th polynomial quation dscribing th modl in trms of th codd factors is xprssd as quation (1). It should b notd that th insignificant ffcts wr nglctd in quation (1) Rmoval Efficincy (%) = A +.66C AC (1)

9 618 Figur 5: Main ffct and intraction ffct plots for rmoval fficincy of phnol Th Parto Chart Th Parto chart was also usd to visualiz th rlativ importanc of th main ffcts and thir intractions as shown in Fig. 6. A studnt's t-tst was usd to dtrmin whthr th calculatd ffcts wr significantly diffrnt from zro. For th 95% confidnc intrval, th t-valu is.78 and is rprsntd on th Parto chart as a horizontal lin. Th ffcts that xcd th t- valu lin ar considrd significant and thos which ar blow th lin ar considrd insignificant [34]. According to Fig 6, th main ffcts (A and C), and th intraction (AC) ar significant. 1.5 C Parto Chart Normal Plot 99 A t-valu of Effct AC Bonfrroni Limit Normal % Probability AC A C t-valu Limit Rank Standardizd Effct Figur 6: Parto chart of th standardizd ffcts Figur 7: Normal probability plot of ffcts Th Normal Probability Plot A normal probability plot is qually usd to choos significant ffcts. On point on th plot is assignd to an ffct. According to th plot, points situatd at th cntr rprsnt thos ffcts that hav littl or no significanc on th rspons whil

10 619 point far away from th cntr st of points rprsnts significant factors [35]. Fig. 7, shows th normal probability plot of standardizd ffcts. From th plot, it can b obsrvd that th main factors (A and C) and th intraction AC, ar vry far away from th cntr st of points and thrfor ar considrd to b significant. Th intraction AC is situatd to th lft of th lin indicating that it has a ngativ ffct whras, A and C ar situatd to th right of th lin indicating thy hav a positiv ffct on th rspons. Ths rsults, confirm prvious Parto chart analysis, ANOVA rsults and th valus in TABLE CONCLUSION From th statistical analysis, it was found that ph and contact tim had a positiv ffct on phnol rmoval by adsorption. On th othr hand, th intraction btwn ph and contact tim though ngativ, was a significant factor in phnol rmoval. Maximum phnol rmoval was obtaind at ph 7, adsorbnt dos of 1 g and contact tim of 1 min. Th Langmuir isothrm modl obyd th quilibrium data bttr than th Frundlich modl as vidnt from th valus of th rgrssion cofficints. Rsults of kintic studis indicat that th psudo-scond ordr kintic modl controlld th adsorption procss with film diffusion as th rat limiting stp in th mchanism. Du to th rsults obtaind, Avocado Sd Activatd Carbon (ASAC) producd by chmical activation using phosphoric acid could b mployd as an ffctiv low-cost adsorbnt and an altrnativ to commrcial activatd carbon, for th rmoval of phnol from aquous solution. REFERENCES [1] A.A.M. Akl, M.B. Dawy, A.A. Srag, Efficint rmoval of phnol from watr sampls using sugarcan Bagass basd activatd carbon, Journal of Analytical and Bioanalytical Tchniqus, 5(), 14, 1-1 [] J.N. Ghogomu, D.T. Noufam, E.B.N. Tamungang, D.L. Ajifack, J.N. Ndi and J.M. Ktcha, Adsorption of phnol from aquous solution onto natural and thrmal modifid kaolinitic matrials. Intrnational Journal of Biological and Chmical Scincs, 8(5), 14, [3] O.A. Ekpt, M. Horsfall, A.I. Spiff, Rmoval of chlorophnol from aquous solution using flutd pumpkin and commrcial activatd carbon, Asian Journal of Natural and Applid Scincs, 1(1), 1, [4] I. Ali, M. Asim, T.A. Khan, low-cost adsorbnt for th rmoval of organic pollutants from wastwatr, Journal of nvironmntal managmnt, 113, 1, [5] C.A. Tols and W.E. Marshall, Coppr ion rmoval by almond shll carbons and commrcial carbons: batch and column studis, Sparation Scinc and Tchnology, 37,, [6] K. Nakagawa, A. Namba, S.R. Mukai, H. Tamon, Ariyadjwanich, Adsorption of phnol and ractiv dy from aquous solution on activatd carbons drivd from solid wasts, Watr Rsourcs 38, 4, [7] A.E. Navarro, N.A. Cuizano, J.C. Lazo, M.R. Sun-Kou, B.P. Llanos, comparativ study of th rmoval of phnolic compounds by biological and non-biological adsorbnts, Journal of Hazardous Matrials, 164, 9, [8] R.M.A. Roqu-marlbrb, adsorption and diffusion in non porous matrial, CRC prss, USA, 7, [9] D.M. Ruthvn, Encyclopadia of sparation tchiniqus (USA): A Wily-Intrscinc Publication, vol.1, 1985, 7-13 [1] L.J. knndy, J.J. Vijaya, G. Skaran, Effct of two-stag procss on th prparation and charactrization of porous carbons composit from ric husk by phosphoric acid activattion, Industrial and Enginring Chmistry Rsarch, 43, 4, [11] J.N. Ghogomu, S.N. Muluh, D.L. Ajifack, A.A.B. Alongamo and D.T. Noufam, Adsorption of lad (II) from aquous solution using activatd carbon prpard from raffia palm (raphia hookri) fruit picarps, IOSR Journal of Applid Chmistry (IOSR-JAC). 9(5), 16, [1] Z.-Y. Zhong, Q. Yang, X.-M. Li, K. Luo, Y. Liu, and G.-M.Zng, Prparation of panut hull-basd activatd carbon bymicrowav-inducd phosphoric acid activation and its application in Rmazol Brilliant Blu R adsorption, Industrial Crops and Products, 37(1), 1, [13] K. Y. Foo and B. H. Hamd, Prparation and charactrization of activatd carbon from sunflowr sd oil rsidu via microwav assistd K CO 3 activation, Biorsourc Tchnology, 1(), 11, [14] M. F. Elkady, A. M. Ibrahim, and M.M. A. El-Latif, Assssmnt of th adsorption kintics, quilibrium and thrmodynamic for th potntial rmoval of ractiv rd dy using ggshll biocomposit bads, Dsalination, 78(1 3), 11, [15] P. Sathishkumar, M. Arulkumar, and T. Palvannan, Utilization of agro-industrial wast Jatropha curcas pods as an activatd carbon for th adsorption of ractiv dy Rmazol Brilliant Blu R (RBBR), Journal of Clanr Production, (1), 1, [16] M. Jain, V. K. Garg, and K. Kadirvlu, Equilibrium and kintic studis for squstration of Cr(VI) from simulatd wastwatr using sunflowrwast biomass, Journal of Hazardous Matrials, 171(1 3), 9, [17] S.Y. Lagrgrn, About th thory of so-calld adsorption of solubl substancs, Handlingar. 4, 1898, 1-39 [18] Y. Ho and G. Mckay, Psudo-scond ordr modl for sorption procsss, Procss Biochmistry. 34, 1994, [19] W.J. Wbr and J.C. Morris, Kintics of adsorption on carbon from solution, Journal of Sanitary Enginring Division: procdings of ASCE. 59, 1963, [] G.E. Boyd, A.W. Adamson and L.S. Myrs, Th xchang adsorption of ions from aquous solutions by organic zolits, Journal of th Amrican Chmical Socity, 69, 1947, [1] B. P. Singh, L. Bsra, S. Bhattacharj, Factorial dsign of xprimnts on th ffct of surfac chargs on stability of aquous colloidal cramic suspnsion. Colloids and Surfacs A Physicochmical and Enginring Aspcts, 4,, [] D.C. Montgomry, Dsign and Analysis of Exprimnts, (USA: John Wily & Sons, 1997) 1-7 [3] B.B. Kar, Y.V. Swamy, B.V.R. Murthy, Dsign of xprimnts to study th xtraction of nickl from latritic or by sulphatization using sulphuric acid, Hydromtallurgy. 56,,

11 6 [4] A.Zari, E.Bazrafshan, H.Faridi, R.Khaksfidi and M.Alizadh, Th valuation of rmoval fficincy of phnol from aquous solution using Moringa Prgrina tr shll ash. Iranian Journal of Halth Scincs, 1(1), 13, [5] A.I. Okoy, P.M. Ejikm and O.D. Onukwuli, Lad rmoval from wastwatr using flutd pumpkin sd shll activatd carbon: Adsorption modling and kintics. Intrnational Journal of Environmntal Scincs and Tchnology, 7(4), 1, [6] S. Bousba, A.H. Mniai, Rmoval of phnol from watr by adsorption onto swag sludg basd adsorbnt, Chmical Enginring Transactions, 4, 14, 35-4 [7] M. Sarkar, P.K. Acharya, Us of fly ash for th rmoval of phnol and its analogus from contaminatd watr. Wast Managmnt, 6, 6, [8] V.C Srivastava, M.M. Swamy, I.D. Mall, B. Prasad, I.M. Mishra, Adsorptiv rmoval of phnol by bagass fly ash and activatd carbon: quilibrium, kintics and thrmodynamics. Colloids Surfac A:Physicochmical and Enginring Aspcts, 7, 6, [9] V. Srihari, A. Das, Adsorption of phnol from aquous mdia by an agrowast (Hmidsmus indicus) basd activatd carbon. Appl. Ecol. Environ. Rs. 7, 9, [3] Y. Safa and H.N. Bhatti, Adsorptiv rmoval of dirct txtil dys by low cost agricultural wast. Application of factorial dsign analysis. Chmical Enginring Journal, 167(1), 11, [31] M. Musah, J. Yisa, A. Mann, M.A.T. Suliman and M. Auta, Application of factorial dsign to th adsorption of Cd(II) ions from aquous solution onto chmically modifid Bombax Buonopozns calyx. Journal of Scintific and Enginring Rsarch, 3(3), 16, [3] D. Bingol, N. Tkin and M. Alkan, Brilliant yllow dy adsorption onto spiolit using full factorial dsign. Applid Clay Scinc, 5, 1, [33] N. Özbay, A.Ş. Yargiç, R.Z. Yarbay-Şahin and E. Önal, Full factorial xprimntal dsign analysis of ractiv dy rmoval by carbon adsorption. Journal of Chmistry, Vol. 13, [34] A. Rgti, A. El Kassimi, M.R. Laamariand M. El Haddad, Comptitiv adsorption and optimization of binary mixtur of txtil dys: A factorial dsign analysis. Journal of th Association of Arab Univrsitis for Basic and Applid Scincs. 16, 1-9. [35] K. Palanikumar and J.P. Dawim, Assssmnt of som factors influncing tool war on th machining of glass-rinforcd plastics by coatd cmntd carbid tools. Journal of Matrial Procssing Tchnology, 9, 9,