REMOVAL OF HIGH CONCENTRATIONS OF PHOSPHATE FROM AQUEOUS SOLUTION USING ARAGONITE

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1 Procdings of th 13 th Intrnational Confrnc of Environmntal Scinc and Tchnology Athns, Grc, 57 Sptmbr 2013 REMOVAL OF HIGH CONCENTRATIONS OF PHOSPHATE FROM AQUEOUS SOLUTION USING ARAGONITE NADIRA NAJIB 1, CHRISTOS CHRISTODOULATOS 1, MAHMOUD WAZNE 2 and SANTHI JAGUPILLA 3 1 Stvns Institut of Tchnology, Dpartmnt of Environmntal, Civil, and Ocan Enginring Nadira Najib and Christos Christodoulatos, 2 Lbans Amrican Univrsity, School of Enginring, Zakhm Enginring Hall, Mahmoud Wazn, 3 TRC Companis, Inc. nnajib@stvns.du Christos.Christodoulatos@stvns.du EXTENDED ABSTRACT High loadings of nutrints such as phosphorus (P) ar a major sourc of utrophication that is thratning natural watr quality worldwid. Th xcssiv concntrations of P prsnt in watr bodis originat in agricultural and wastwatr fflunts, storm watr runoff, tc. Th disruption of th trrstrial P cycl by anthropognic activitis along with a growing awarnss that P is a limitd rsourc call for ffctiv mthods to rmov and rtain P bfor it rachs natural watrs. This study invstigats th rmoval of orthophosphat spcis ( P) by adsorption onto aragonit as a natural adsorbnt undr a wid rang of nvironmntal conditions. Aragonit is a rnwabl and conomical matrial; it can b usd jointly with any bstmanagmnt practics or as a postscondary tratmnt in a wastwatr tratmnt plant to nhanc th phosphorus rmoval and consquntly mitigat utrophication in surfac watrs. Morovr, th aragonitadsorbd P product can b usd dirctly as a frtilizr for soils or as a fd matrial for frtilizr production. Batch xprimnts wr usd in this study to xamin th adsorption bhavior of P on aragonit as a function of solidtoliquid ratio, P concntrations, and ph. Th rsults showd that solution ph gratly affcts th P rmoval mchanism. Th ffct of ph on phosphat rmoval can b attributd to th natur of P spcis in solution as wll as to hydrolysis ractions on th aragonit surfac. Ztapotntial masurmnts suggstd that th uptak is drivn by spcific adsorption of P onto th aragonit surfac. Isothrm studis showd a maximum P rmoval of th ordr of 60 mg/g for a solidtoliquid ratio of 1 g/l. Th data ar bst dscribd by th Langmuir modl, which indicats that adsorption of P on aragonit occurs most likly via a monolayr mchanism. A column tst prmating an aquous phosphat solution of 10 g/l through an aragonitpackd bd was studid. Th rsults showd that phosphat brakthrough occurrd aftr approximatly 20 por volums. This study showd that aragonit fficintly rmovs phosphat from aquous solutions. Th lctrokintic rsults suggst that orthophosphat spcis ar chmically adsorbd onto aragonit ovr th ph rang xamind in this study. Kywords: Phosphat, Adsorbnts, Aragonit, Adsorption, Phosphorus, Rmoval, Eutrophication 1. INTRODUCTION Nutrint contamination is bcoming a major problm facing surfac watr worldwid. Nutrint contamination coms primarily from municipal wastwatr discharg and agricultural runoff, with th lattr bing th lading sourc of pollution. Phosphorus has

2 bn dmonstratd to b th limiting nutrint in frsh watrs (S.R Carpntr t.al, 1998 and Aldridg and Ganf 2003). Excss of phosphorus stimulats th growth of alga, lading to blooms which consum larg amounts of dissolvd oxygn, suffocating fish and othr marin lif and crating dad zons. Th disruption of th trrstrial phosphorus cycl by anthropognic activitis and a growing awarnss that phosphorus is a limiting rsourc, call for ffctiv tchniqus to rmov and rtain/rcycl/rus phosphat bfor it rachs natural watrs. For nonpoint sourc pollution, th EPA, in coopration with its stat countrparts, has adoptd tools such as bst managmnt practics (BMPs) to protct watr rsourcs. Th most common nvironmntal systms usd as BMPs ar wtlands and wt ponds. Ths hav shown rlativly ffctiv rmoval rats of P, but hav provn to b highly dlicat constructs that can frquntly and asily b damagd by pollutant ovrloads (J.N.Carlton t al 2001). For pointsourc pollution, thr ar thr main catgoris of tratmnt tchnologis availabl for phosphorus rmoval: physical, chmical and biological. In all cass, phosphorus is convrtd into a solid fraction. This fraction can b an insolubl prcipitat salt, a microbial mass in activatd sludg, or a plant biomass in constructd wtlands. Of all ths mthods, adsorption has shown to b th most ffctiv mchanism for phosphat rmoval. Mtal salts hav also bn shown to b ffctiv for th rmoval of phosphat compounds. Howvr, mtal salts ar xpnsiv, and th final product of prcipitation is a mtal phosphat sludg which is unrcovrabl for possibl industrial procssing (Donnrt and Salckr, 1999). Studis hav xamind th adsorption of phosphats onto calcium carbonat matrials such as calcit and monohydrocalcit. K. Karagorgiou t al. hav shown that high rmoval of orthophosphat spcis rmoval from aquous solutions can b achivd by adsorption onto calcit. Th purpos of this rsarch is to invstigat th fasibility of phosphat rmoval using aragonit as a natural adsorbnt. Aragonit is a naturally occurring minral prcipitating from ocan watr. It is a rnwabl and conomical matrial that can b usd jointly with any BMPs or as a postscondary tratmnt in wastwatr tratmnt plants to nhanc th rmoval and rcycling of phosphorus as calcium phosphat, and consquntly mitigat utrophication in surfac watrs. Morovr, th aragonitwithadsorbdphosphat product can b also usd as a slowrlas soil frtilizr or a fd matrial for frtilizr production. 2. MATERIALS AND METHODS 2.1. Matrials All chmical ragnts usd in this study wr of A.C.S. grad or bttr. Synthtic orthophosphat solutions wr prpard to conduct adsorption tsts. A stock solution of P was prpard by dissolving a st amount of Na 2H.H 2O in dionizd watr. An aliquot of th stock solution was addd to a crtain volum of dionizd (DI) watr to prpar th dsird phosphatbaring solutions. Aragonit was obtaind from CaCO 3 Aragonit Products, Inc. A fixd amount of aragonit was siftd to rtain 20 (d=0.85 mm) and 200 (d=0.075 mm) mshs. Th rst was micronizd to obtain grain siz lss than 0.01 mm Batch xprimnts All tsts, including isothrm tsts, wr carrid out with batch xprimnts at room tmpratur. A prdtrmind amount of aragonit was addd to a st volum of a phosphat solution of known concntration in 30 ml polypropyln bottls. Th bottls wr thn sald and placd in a tumblr for 24 hours. Th rang of P concntrations was from 20 to 320 mg/l. Aftr mixing, th suspnsion was filtratd using a Millipor vacuumopratd systm using 0.45 μm mmbran filtrs. P concntrations in th filtrat wr dtrmind using Hach DR/2010 portabl data logging spctrophotomtr according to PhosVr3 (Ascorbic Acid) Mthod.

3 Th valus for initial and final P concntrations wr usd to calculat th P rmoval capacity (mg/g) as th amount of P rmovd at quilibrium pr volum of sampl as follow: Whr; q= uptak of P (mg/g), C 0= initial P concntration of th solution (mg/l), V = volum of solution (L), and m =mass of sorbnt (g) Column xprimnts: A column tst was prformd to valuat th phosphat rmoval capacity by aragonit in a continuous systm at room tmpratur. Th Konts Flxcolumn column (Thrmo Fishr Scintific Inc., Waltham, MA) usd in this xprimnt was 18 cm long and had an innr diamtr of 1.8 cm. Th column was prmatd with a phosphat solution up to 100 por volums (PVs). Th aragonit sampl was washd with DI watr, and thn packd moist into th column to avoid th formation of air bubbls. Th dry wight of aragonit packd into th column was g, which yildd a porosity of 0.6 (spcific gravity = 2.95). A pic of 20 µm filtr papr was placd at ach nd of th packd aragonit mdia to prvnt migration of fin aragonit particls through th column. Tubing mad of inrt Tygon (Nalgn, Rochstr, NY) was usd for all xtrnal piping ntworks. Th laching procss was conductd in a continuous upflow mod to promot saturatd flow conditions and to mitigat shortcircuiting of flow. An avrag flow rat of 0.1 L/hr was chosn for this study, which yildd an avrag column rtntion tim of approximatly 16 minuts. Th initial concntration of phosphat ( P) was 10 mg/l. Th influnt solution was mixd continuously using a magntic stirrr. A MastrFlx pristaltic pump was usd to introduc th aquous phosphat solution into th column. Th fflunt solution was sampld at prst tim intrvals, and th total volums of th prmatd solutions wr rcordd Zta potntial Ztapotntial masurmnts wr carrid out using 1 g/l of micronizd aragonit suspnsions in th prsnc and absnc of 100 mg/l P solution. Th suspnsions wr prpard in 30 ml bottls and placd on a rotator for 24h at 25 C. Aftr mixing, th quilibrium ph of th sampls was masurd, and th aliquots wr filtrd through 11 μm filtr papr (Whatman No 1), thn thy wr disprsd by a thrmostatd shakr bath for 15 minuts. On ml of ach filtrat was introducd into a polystyrn cuvtt and Zta potntial was masurd using a Ztasizr Nano sris instrumnt (Malvrn, Worcstrshir, UK) using dynamic light scattring (DLS). Th Hlmholtz Smoluchowski quation was applid to convrt masurd lctrophortic mobilitis to ζ potntial. All sampls wr prpard in duplicats. Th filtr por siz was slctd basd on th Malvrn Ztasizr particlsiz rang limitation for Zta potntial masurmnt btwn 5 nm and 10 μm. 3. RESULTS AND DISCUSSION 3.1. Effct of Solidtoliquid Ratio and Grain Siz on P Rmoval Th rmoval capacity of aragonit, with diffrnt grain sizs, was dtrmind by batch xprimnts. Two solidtoliquid ratios, 10 g/l and 1 g/l, wr usd, with an initial P concntration of 100 ppm. Th rsults ar givn in Figurs 1 and 2. It is obsrvd that incrasing th solidtoliquid ratio from 1 g to 10 g pr 1 litr solution for diffrnt grain sizs incrasd th rmoval prcntag of P for all diffrnt grain sizs. Dcrasing th grain siz from 0.85 mm to and 0.01 mm significantly incrasd th P rmoval capacity. Howvr, thr was no diffrnc on th P rmoval capacity btwn and 0.01 grain sizs.

4 Figur 1: Effct of grain siz on P uptak P with 1g/L aragonit Figur 2: Effct of grain siz on uptak using 10g/L aragonit Effct of ph on th Adsorption Mchanism of Phosphat Th ffct of ph on th rmoval of phosphats with micronizd aragonit was invstigatd at room tmpratur. Th initial ph of th xprimnt was pradjustd to diffrnt valus btwn 5 and 13 with 1 M NaOH solution. Th tsts wr carrid out with an initial P concntration of 100 ppm and a solidtoliquid ratio of 1 g/l. From Figur 3, it sms that th adsorption procss of phosphat onto aragonit is ph dpndnt. At initial ph rang btwn 5 and 7 (th final ph from 7.6 to 8.2), P rmoval was btwn 59 and 77 mg/g. Howvr, as th initial ph incrasd from 7 to 12 (th final ph 8.2 to 11.6), th P rmoval dcrasd. Th rmoval fficincy thn incrasd with th incras of ph from 12 to 13 (final 11.6 to 12.4). From Figur 4, it can b obsrvd that whn 100 ppm P is addd to aragonit suspnsions, th charg on th surfac of aragonit drops in th ph rang btwn 6 and 12. Th lctrokintic rsults suggst that orthophosphat spcis ar chmically adsorbd onto aragonit for th ph rang xamind in this study. Th ffct of ph on P rmoval can b attributd to th natur of phosphat spcis in th solution as wll as th hydrolysis ractions on aragonit surfac as shown in Figur 3. In watr, th ractions of phosphat spcis ar as follows (Snoyink and Jnkins, 1983): + H 2O = H + OH, pk 1 = 1.68 H +H 2O = H 2 +OH, pk 2 = 6.79 H 2 + H 2O = H 3 +OH, pk 3 = H 2O = H + + OH, pk w =14

5 Th hydrolysis ractions for th cationic and anionic spcis on aragonit surfac ar dscribd by th following ractions (Karagorgiou t al and Liu t al.): CaCO 3 = Ca 2+ + CO 3, pk S = 3.25 CO 3 +H 2O = HCO 3 +OH, pk = 3.67 Ca 2+ + HCO 3 = CaHCO 3+, pk = 0.82 Ca 2+ +OH = CaOH +, pk = 1.4 From th spciation diagram for phosphat (Figur 4), in th ph rgion from 7.6 to 8.2, phosphorus spcis ar mainly in th form of H 2. At ph btwn 8.2 and 11.6, H spcis prdominat ovr, whil at ph highr than 11.6, is th main P spcis. Basd on th aformntiond ractions, th rmoval procss could b dscribd through th following ractions: Ca 2+ + H 2 = CaH 2+, pk = 1.08 Ca 2+ + H2 = CaH, pk = 7.0 Ca 2+ + = Ca, pk = 6.5 3Ca = Ca 3() 2, pk = 26 3Ca 2+ + H + HCO 3 = Ca 2HCO 3 + H +, pk =1.33 Ca 2HCO 3 = Ca 2CO3 + H +, pk =8.3 10CaCO 3 +2H + +6H +2H 2O = Ca 10(PO4)6(OH) 2+ 10HCO, pk = 32 Figur 3: Effct of ph on P adsorption onto aragonit Figur 4: Distribution diagram for phosphat as a function of ph

6 Figur 5: Zta potntial of aragonit with and without phosphat as a function of ph 3.3. Isothrm Rsults: An adsorption isothrm was constructd for th phosphat rmoval by aragonit. Th P rmoval vrsus quilibrium P concntrations in solution was plottd as shown in Figur 4. Frundlich and Langmuir modls wr attmptd to dscrib th quilibrium uptak data. Figur 6: Adsorption Isothrm for P sorption onto aragonit Th Langmuir modl assums a uniform adsorption nrgy among adsorption sits on a homognous surfac. Th Langmuir modl (Langmuir 1918) is givn by quation (1) q q max whr q (mg/g) is th Langmuir monolayr sorption capacity and C (mg/l) is th quilibrium concntration of P in th solid and liquid phas, rspctivly. q max (mg/g) is th Langmuir monolayr sorption capacity KL is th Langmuir cofficint rlating to adsorption intnsity (l/mg). Th Frundlich isothrm is an mpirical rlationship mployd to dscrib htrognous systms. This isothrm dos not prdict any saturation; thus, infinit surfac covrag is prdictd mathmatically, indicating a multilayr adsorption on th surfac of th adsorbnt. Th Frundlich modl (Frundlich 1926) is dscribd by th following quation (2): K L c 1 K q K F c L c 1/ n

7 Whr; K F [mg/g(l/mg) 1/n ] is th rlativ sorption capacity and 1/n is th intnsity of sorption.nonlinar rgrssion procdurs wr usd to stimat th paramtrs for th two adsorption isothrm modls in th rmoval of P. Tabl 1 summarizs th stimatd paramtrs for both Langmuir and Frundlich modls. Basd on th highr valus of corrlation cofficints (R 2 ) for th Langmuir modl compard to th Frundlich modl, th adsorption data ar bttr dscribd by th Langmuir modl. This indicats that th adsorption mchanism of P is most likly a monolayr adsorption mchanism onto th surfac of aragonit. Tabl 1: Isothrm paramtrs for adsorption of P Langmuir Frundlich q max(mg/g) K L (mg/l) R 2 SSE K F 1/n R 2 SSE Elctrokintic Rsults Th ffct of addition of P and th ffct of ph on th surfac charg of aragonit wr invstigatd using aragonit suspnsions in th prsnc and absnc of 100 mg/l of P. Th rsults ar prsntd in Figur 5. Th Ztapotntial valus for aragonit suspnsions in th absnc of P wr gratr than thos in th prsnc of P ovr a ph rang from 6.5 to Th lctrokintic rsults show that th addition of P into th aragonit suspnsions rsultd in a dcras in th surfac charg of aragonit. Th lctrokintic rsults suggst that P spcis ar chmically adsorbd onto aragonit for th ph rang xamind in this study Column Tst Rsult Th rsults for th phosphat column ar summarizd in Tabl 2. Figur 1 prsnts th fflunt P concntrations from th aragonit column at diffrnt por volums. Th tst rsults show that P brakthrough occurrd aftr approximatly 20 por volums. Howvr, complt brakthrough (C/Co = 1) was not achivd during th tst duration of 100 por volums. Por Volums (mg/l) Por Volums (Continud) (mg/l) Tabl 2. Column Laching Rsults

8 4. CONCLUSION Th sorption bhavior of phosphat onto aragonit as a natural adsorbnt was xamind as a function of solid toliquid ratio, phosphat loadings, and ph. Aragonit with a grain siz lss than mm showd a rmoval capacity gratr than 75% with a solidvolum ratio of 1 g/l. This study showd that phosphat rmoval dpnds on th solution ph. Th ffct of ph on phosphat rmoval can b attributd to th natur of phosphorus spcis in th solution, as wll as to hydrolysis ractions on th aragonit surfac. Th lctrokintic rsults suggst that orthophosphat spcis ar chmically adsorbd onto aragonit ovr th ph rang xamind in this study. Finally, th column study indicatd that phosphat brakthrough occurrd aftr approximatly 20 por volums. REFERENCES 1. A.P Sincro and G.A Sincro 2003Physicalchmical tratmnt of watr and wastwatr. 2. Carlton, J.T Introducd Spcis in U.S. Coastal Watrs: Environmntal Impacts and Managmnt Prioritis. Prpard for th Pw Ocans Commission, Arlington, VAContrasting Macrophyts: Implications for Phosphorus Adsorption/Dsorption. Marin & Frshwatr Rsarch, 54 (1): p D.Donnrt and M.Salckr, "Elimination of phosphorus from municipal and industrial wast watr." Watr Scinc and Tchnology, 40(45), Frundlich.H (1926) Colloid and Capillary Chmistry, Mthun & Co., London. 5. K. Karagorgiou t.al. Rmoval of phosphat spcis from solution by adsorption onto calcit usd as natural adsorbnt. Journal of Hazardous Matrials A139 (2007) L.E. DBashan and Y. Bashan 2004, Rcnt advancs in rmoving phosphorus from wastwatr and its futur us as frtilizr ( ), Watr Rs. 38 pp Langmuir.I (1918), th adsorption of gass on plan surfacs of glass, mica and platinum. J Am Chm Soc 40: Mtcalf & Eddy wastwatr tratmnt plants 4 th dition, PhosVER3 (Ascorbic Acid) Mthod, HACH DR/4000 procdur, S.R Carpntr t.al, 1998, Nonpoint Pollution of Surfac Watrs with Phosphorus and Nitrogn. Ecological Applications.Vol. 8, No. 3 : Watr Chmistry Vrnon L. Snoyink (Author), David Jnkin, Y. Liu t.al, Rmoval of high concntration phosphat by calcit: Effct of Sulfat and ph. Dsalination 289 (2012) 667