Simultaneous removal of ammonium and phosphate by zeolite synthesized from coal fly ash as influence

WHIRIILENAvailableonlineatwww.sciencedirect.comURNAL OFScience DirectTALJoumal of Environmental Sciences 19(2007)540-545Simultaneous removal of ammonium and phosphate by zeolite synthesizedfrom coal fy ash as influenced by acid treatmentZHANG Bao-hua, WU De-yi, WANG Chong, HE Sheng-bingZHANG Zhen-jia, KONG Hai-nanSchoolofEmvironmentalScienceandEngineering,ShanghaiJiaoTongUniversityShanghai200240,China.E-mail:scidusr@sjtu.edu.cnReceived 22 May 2006; revised 4 August 2006: accepted 21 August 2006abstractZeolite synthesized from fly ash(zFA) without modification is not efficient for the purification of NH4* and phosphate at lowconcentrations that occur in real effluents, despite the high potential removal capacity. To develop an effective technique to enhance theremoval efficiency of ammonium and phosphate at low concentrations, ZFA was modified with acid treatment and the simultaneousremoval of ammonium and phosphate in a wide range of concentration was investigated. It was seen that when compared withuntreated ZFA, only the treatment by 0.01 molL of H2SO4 significantly improved the removal efficiency of ammonium at low initialconcentrations. The behavior was well explained by the pH effect. Treatment by more concentrated H2SO4 led to the deterioration ofthe ZFA structure and a decrease in the cation exchange capacity. Treatment by 0.01 molL H2SO4 improved the removal efficiencyof phosphate by ZFA at all initial P concentrations, while the treatment by concentrated H2SO4(> 0.9 moVL)resulted in a limitedmaximum phosphate immobilization capacity(PIC). It was concluded that through a previous mild acid treatment(e. g 0.01 molL ofH2SO4), ZFA can be used in the simultaneous removal of nH,* and P at low concentrations in simulating real effluent.Key words: zeolite; fy ash; acid treatment; ammonium; phosphate; removalIntroductionone material has been rarely reported hitherto. The meritof using only one material to simultaneously eliminateThe accumulation of nitrogen and phosphorus in rel- ammonium and phosphate from wastewater is obviousatively stagnant water is usually the leading cause of Generally, two kinds of reagents must be applied for theeutrophication. Therefore, removal of nitrogen and phos- removal of NHA* and PO43. For example, the comlphorus from domestic and agro-industrial wastewater prior tion of a cation exchanger and an anion exchanger, or ato discharge, as well as from eutrophicated natural water cation exchanger and an inorganic cohesion precipitant aris obligatory. The application of efficient solid materials, considered. In any case, the cost is high, and the counterinvolving natural materials, synthesized materials, and anion such as CI" and SO42-remains in the treated water.solid wastes, in ammonium and phosphate removal from In the previous studies(Wu et aL., 2005, 2006a, 2006baqueous solutions has been widely investigated in recent Chen et aL, 2006, 2007; Zhao et aL, 2006), it was reportedyears.Natural clays, especially zeolites, were proved to that both the CEC(cation exchange capacity)value and thebe efficient for ammonium removal( Booker et al., 1996; phosphate immobilization capacity(PIC)value of zeoliteKomarowski and Yu, 1997; Rozic et al., 2000; Sarioglu, synthesized from fly ash(ZFA) were improved greatly2005), while a variety of materials such as blast fur- when compared with the corresponding raw fly ash. Itnace slag, activated alumina, fly ash, aluminum oxide was noted that ZFA may be a promising material for thehydroxide, synthetic iron oxide-gypsum compound, and simultaneous removal of ammonium and phosphate fromother materials were investigated for their ability to treat wastewaterphosphate-laden wastes(Neufeld and Thodos, 1969; Baker Unfortunately, the preliminary study found that1999; Drizo ef al., 1999: Cheung and Venkitachalam, phate at low concentrations s wing real eftucns hos.2000; Johansson and Gustafsson, 2000; Tanada et aL., quite中国煤化工 aximum potential ofAlthough both ammonium and phosphate have to be rialCNMH Gremoval capacity andavenged from wastewater, the simultaneous removal by a high removal efficiency at low nutrients concentration.se Ministry of Science and Technologwhich occurs in most real wastesFunding(No. 2002AA601013) *CorrespondIn an attempt to improve the treatability especially atE-mail:dywu@sjtu.edu.cnlow nutrient concentrations, the simultaneous removal ofSimultaneous removal of ammonium and phosphate by zeolite synthesized from coal fly ash as influenced by acid treatment.541ammonium and phosphate by ZFA that received acid pre- to be associated with the phosphate removal, are listed intreatments was investigated. A wide range of ammonium Table 1and phosphate concentration, with the nutrients co-existingThe zeolitic phase(s)in the products were identified byin aqueous solution, was employed so as to evaluate the the powder X-ray diffraction method on a D8 ADVANCEeffectiveness of the acid pretreatment on the potential X-ray diffractometer using Ni filtered Cu-ka radiation(40removal capacity and the treatability at low nutrients kV, 40 mA)concentration. It was concluded that through a previousmild acid treatment, ZFA can be used in the simultaneous 1.2 Batch immobilization studiesremoval of NH4 and P at low concentrations simulating An original stock solution(A)containing 5000 mgN/Lreal effluentand 1000 mgP/L, and a stock solution(B)containing10000 gN/L and 5000 mgP/L1 Materials and methodsanhydrous(NH4)2HPO4 and anhydrous NH Cl. Batchequilibration experiments were conducted using aqueouslI Materialssolutions containing both ammonium and phosphate withA fly ash sample was supplied by the second electricthe combinations of initial ammonium and phosphateconcentration as shown in Table 2. The initial ammoniumpower station of wujing, Shanghai, China. Fifteen grams and phosphate concentration ranged from 2.5 to 1200of fly ash were placed in a flask, mixed with 150 ml of mgN/L and from 0.5 to 1000 mgP/L, respectively. Since2.0 moy/L NaOH solution, and boiled with reflux for 48 h. the concentrations of ammonium and phosphate presentAt the end of the synthesis process, the solid phase was in domestic wastewater in China typically have the N/Pseparated by centrifugation, washed with re-distilled water ratio of 5, the combinations with P concentration 12three times and with ethanol twice, and dried in an ovenat 45C. For acid treatments ZFA was mixed with 0.01, to simulate real sewage, while the combinations with p0.9, and1.8 molL H2 SO4 using a liquid/ solid ratio concentration >25 mg/L were prepared from the originalof 6, and boiled with reflux for 6 h. The suspensions were stock solution(B). For the batch equilibration experiments,separated by centrifugation, washed with re-distilled water 40 ml of the aqueous solutions were added to centrifugeand ethanol, and dried in a similar manner. The obtained tubes containing 0.4 g of the sample. The tubes were thenproducts were finally ground to pass an 80-mesh sieve shaken for 24 h at room temperature(24 h was found to beprior to isufficient for ammonium and phosphate to achieve equilib-The methods for chemical analysis, CEC (cation ex- rium in the pre-experiments). After 24 h, the suspensionshange capacity), PlC, and fractionation of immobilizedphosphorus were the same as in the previous articles( Chen were centrifuged and the supernatants were determined forphosphate by the molybdenum-blue ascorbic acid methodet.,2006; Wu et al., 2006b). The CEC value and the total (APHA, 1995)and for ammonium by the Nessler methodamount of Si, Al, Fe, Ca, and Mg, which were believed (APHA, 1995)using a Unico spectrophotometer(modelTable 1 Some chemical composition of ZFA untreated and treated by H2S04SO2(%)Al2O3(%)Ca0(%)Mgo(%)Fe?O3(%)CEC (cmol kg)Untreated213H2SO4(0.01 molL)35.318418.6H2SO4(0.9 molL)14.86.4H2SO4(1.8 moyLTable 2 pH values in equilibrium solutions containing ammonium, phosphate, and ZFA untreated and treated by H2SO4Initial concentrationpH in equilibrium solutionN(mgL) P(mg/L) No ZFA Untreated H2SO4(0.01 mol/ L) H2SO4(0. 1 molL) H2SO4(0.9 molL) H2SO4(1.8 moUL)006.02l14510.459.193.99l.2410.569.173.9810114410.06152.05.31l1410.085.2511. 4010.ll8.8211.091005869120529.848.5510025.62009中国煤化工200.0I000933CNMHG6004.729204.5887.15L,OI4.467.474.1010000498728pH values of solutions containing ammonium and phosphate without the addition of ZFA KH2 POa solution.542ZHANG Bao-hua etUV-2102PCS), respectively. Ammonium and phosphate 0.1 molLimmobilized from the solution were calculated from thdifference between the initial and the final concentrations2.2 Removal efficiency of ammonium1.3 Effect of pH on ammonium removalThe removal efficiency of ammonium as a function ofthe initial concentration is shown in Fig. 2. A logarithmicOne gram of untreated ZFA was placed in flasks con- scale was used for the horizontal axis so that the resultstaining 100 ml re-distilled water. The suspensions were at low concentrations can be clearly presented. The readjusted to the desired ph levels by adding 2 mol/L HCI sults in Fig. 2 indicated that ZFA treated with 0.01 molLor NaoH. Appropriate volume of re-distilled water was H2SO4 had the highest removal efficiency at all initialupplemented for some flasks so that all suspensions with concentrations. Although ZFA without acid treatment haddifferent pH values contained the same volume of water. removal efficiency compatible with the 0.01 mol/L H2SO4After being shaken for 24 h, the pH was monitored using a treated one at high initial concentrations(> 200 mg/L),Hach 51910 pH meter. The immobilization studies were the removal efficiency at low initial NH4* concentrationscarried out using an initial ammonium concentration of (<40 mg/L) was very low(< 20%6). When comparedabout 25 mgN/L by adding 0.5 ml of the original stock with untreated ZFA, treatments with 0. 1 and 0.9 molLH2S04 slightly improved the removal efficiency at lowinitial concentrations, but lowered the removal eficiency at2 Results and discussionhigh initial concentrations. On the other hand, the removalefficiency by ZFA treated with 1.8 molL H2SO4 was2. 1 Characterization of zFa with and without acid very low at all initial concentrations. Given that both themaximum removal capacity and the removal efficiency atThe XRD patterns of ZFA with and without acidlow ammonium concentration that exist in real effluent areimportant in practical usage, the obtained results suggesttreatment are illustrated in Fig. 1. Following the alka- that the treatment of zfA by dilute H2S04(0.01 molL)isline activation process, monomineral of NaPl zeolite the most advantageous(Na6 Al SinoO32 12H2O, Si/Al=1.73)was produced. Smallamounts of quartz, mullite, and calcite remained in ZFANaPl is a low-silica zeolite, which is known to deteriorateinder acid conditions. with the treatment of 0.01 molLH2SO4, the crystallinity of NaPl dropped slightly. Theproduction of a new crystal phase(gypsum)with d valuesof 7.59 and 3. 07 initiated at the concentration of 0. 1 molLwhile the crystallinity of NaPl was destroyed entirely, andypsum and anhydrite were formed upon treatment with0.9 mol/L H2SOThough the CEC value decreased obviously followinghe treatment by 0.01 and 0.I molL H2SO4(Table 1),itwas still considerably high. a drastic decrease in the CECvalue occurred when the H2SO4 concentration exceededInitial N concentration in solution(mg/L)Fig 2 Ammonium removal efficiency by ZFA untreated and treatedby H2SO4 with different concentrations as a function of the initialammonium concentratonUntreated2.3 Effect of plH on ammonium removalTo probe into the reasons accounting for the influence0.01 mol/Lof the acid treatment on ammonium sequestration, theremoval of ammonium as a function of the ph value wasinvestigated and the results are shown in Fig 3. It canbe seen that favorable elimination of ammonium by ZFAproduced from fy ash occurred within the pH range of5.5-10.5. The decrease in ammonium elimination at the al0.9 molL GGka中国煤化工 lained by the fact thataiC MH Gabate the sequestrationof ammonium ion. Although it was expected that theFig. I XRD patternsvolatilization of NH3 could contribute to the eliminationdifferent concentrations.(P)NaPl zeolite; (Q) quartz:(M) mullite;(C) of ammonium at alkaline pH values, the data obtained bycalcite;(A)anhydrite;(G) gypsumrepeated experiments indicated that only about 5% of theSimultaneous removal of ammonium and phosphate by zeolite synthesized from coal fly ash as influenced by acid treatmentconcentrations for untreated zFA can be also explained bythe change in the pH value( to be below 10.5)2. 4 PIC of ZFA and fractionation of immobilized phoshorusThe Pic values of ZFA with and without acid treatmentare shown in Table 3. The treatment by dilute acid (0.01and 0.1 molL H2SO4)resulted in a significant increase inthe PIC value, while the treatment by more concentratedH2SO4 carin the pic valueformer behavior cannot be explained by the change in thetotal chemical composition(Table 1), and was presumablybecause of the change in the Ca ingredient from sparinglyig. 3 NH4* immobilization at an initial concentration of 25 mgN/L as a soluble CaCO3(calcite, see Fig. 1)to relatively solublefunction of pH in equilibrium suspensionCaso4(gypsum and anhydrite, see Fig. 1), which wouldfavor the calcium phosphate precipitation. The sharp de-added ammonium was lost by volatilization for a solution crease in the removal capacity of phosphate by relatively(without ZFA) having an ammonium concentration of 25 concentrated H2SO4(0.9 or 1.8 mol/L)was clearly asso-mgN/L and a pH value of 11.4 in the experimental con- ciated with the loss of Fe, Al, Ca, and Mg, which wasditions. The negligible removal by volatilization process believed to be involved in phosphate fixation (Table 1)was probably attributed to the facts that the concentration To understand the mechanism of phosphate removalof ammounium was low, and the removal experiment fractionation of phosphorus immobilized from solutionwas done in capped centrifuge tubes. On the other hand, with an initial P concentration of 1000 mg/L was conduct-ammonium may compete with other cations including ed and the results are shown in Table 3. The percentage ofthe hydrogen ion for the exchangeable site at pH<5.0, residual phosphorus was very low For ZFA untreated andresulting in the reduction of ammonium removalThe ph values in equilibrium solutions are given in P fraction was either Ca+Mg-P(treated with 0.01 or 0.1Table 2. The data in the third row of Table 2 indicates mol/L H2 SO4 )or LB-P(untreated), though Fe+Al-P alsothat the addition of untreated Zfa to distilled water results accounted for a considerable part of the total immobilizedin an increase of the pH value, probably because of the P. It is speculated that LB-Pis principally a part of Ca+Mhydrolysis and the dissolution of alkali and alkaline earth P(probably di-calcium phosphate di-hydrate which canmetal oxides in ZFA (Rozic et aL, 2000). The acid treat- relatively easily re-dissolve into solution. Further, the lowment causes the decrease in the pH value: the higher the, Mgo content implies that immobilized phosphate wasconcentration of H2SO4, the lower the pH value. However, bound mainly to calcium components. It is considered that,the addition of (NH4)2HPO4 and NH CI into the aqueous for untreated and dilute(0.01 or 0. 1 molL) H2SO4-treasuspension of ZFA leads to the decrease in the equilibrium ZFA, the formation of calcium phosphate precipitatespH values for the untreated, 0.01 and 0.1 molL H2 SO4- be the predominant mechanism for phosphate removaltreated ZFA, while the pH values for 0.9 and 1.8 mol/LZFA treated with 0.9or 1.8 moVL H2SO4 had an equilib-H2SO -treated ZFA remain almost unchangedrium pH of 4.36 and 3.60, respectively (Table 2). Since ironIt can be seen from Table 2, and Figs. 2 and 3 that when and aluminum based crystalline and amorphous phasescompared with untreated ZFA, the treatment by 0.o1 mol/L will become positively charged and through the ligandH2SO4 lowered the pH value of the equilibrium solution at exchange mechanism, their adsorption capabilities willlow initial NH4* concentrations to be below 10.5, resulting increase at such acidic pH values(Parfitt, 1978; Geelhoedin the increase of the ammonium removal efficiency. How- et al, 1997), Fe+Al-P predominated in immobilized Pever, since the treatment by more concentrated H2sO4 led whereas CatMg-P was negligible. It thus suggests that,to the deterioration of the zeolite structure, this probably for ZFA treated by 0.9 or 1.8 mol/L H2SO4,immobilizeddecreased the ammonium removal efficiency. The increase phosphate was bound mainly to Fe and Al related compo-in the ammonium removal efficiency at high initial NH4* nentsTable 3 Fractionation of phosphorus immobilized by ZFA with and without acid treatment(values of P fractions in mgP/g dw)LB-P Fe+Al-PRes.-PPercentage in PIC (%中国煤化工Res, -PUntreated38.2618.808.69106127.73042H2SO4001(molL)62.7717.62CNMHG 46.98H2SO4 0.1(molL)44.34HSO4 0.9(molL)194077.94N DH2 SO4 1.8(molL)0.910.4429.3147.6423.04LB-P: loosely bound phosphorus; Ca+Mg-P: calcium and magnesium bound phosphorus; Fe+Al-P: iron and aluminum bound phosphorus and Res.P:residual phosphorus544ZHANG Bao-hua et almild acid treatment caused no significant decrease in the8-8mt0.01 molL0 1 mol/Lpotential immobilization capacity (CEC) for ammonium,but resulted in a significant increase in PIC. However, thetreatment by more concentrated H2SO4 caused a sharpdecrease in the CEC and PIC values though it improvedthe removability of P and NH4* at low concentrationsTherefore, mild acid treatment is the most advantageousto improve the simultaneous removal efficiency of NH4and P from wastewater at low nutrients concentration byZFAReferencesInitial P concentration in solution(mg/APHA(American Public Health Association), 1995. Standardmethods for the examination of water and wastewater [S]Fig. 4 Phosphate removal efficiency by ZFA untreated and treated by19th ed. Washington, D. C: APHA.H2SO4 with different concentrations as a function of the initial P Baker m], Blowes D W. Ptacek CJ, 1998. Laboratory de-concentrationvelopment of permeable reactive mixtures for the removalof phosphorus from onsite wastewater disposal systems[J]2.5 Removal eficiency of phosphateEnviron Sci Technol. 32: 2308-2316The removal efficiency of phosphate as a function of the Bastin O, Janssens F, Dufey Jet al,1999. Phosphorus removal byinitial concentration is illustrated in Fig 4. A logarithmica synthetic iron oxide-gypsum compoundg]. Ecolog Enginscale was used for the horizontal axis so that the results12:339351at low concentrations can be clearly presented. At lowBooker N A, Cooney EL, Priesrley A J, 1996. Ammonia removalinitial concentrations, ZFA treated with 0.9 and 1.8 molLfrom sewage using natural Australian zeolite[]. Wat SciTech,34:17-24.H2SO4 showed the greatest affinity for phosphate. This was Chen J G, Kong H N, Wu dY et al,2006.Removal ofexplained by the fact that the adsorption mechanism ofphosphate from aqueous solution by zeolite synthesizedphosphate was primarily associated with Fe and al throughfrom fly ash[J]. J Colloid Interface Sci, 300: 491-45ligand exchange at acidic pH levels, and it is known that the Chen J G, Kong HN,Wu d Y et al, 2007. Phosphate immo-dsorption by this mechanism takes place even at dilutebilization from aqueous solution by fly ashes in relation tophosphate concentration(Parfitt, 1978; Geelhoed et altheir composition]. J Hazard Mater. 139: 293-3001997). However, the removal efficiency quickly declined asCheung K C, Venkitachalam T H, 2000. Improving phosphatee initial P concentration increased because of the limitedremoval of sand infiltration system using alkaline fly ashU]immobilization capacity. At all initial P concentrations,Chemosphere, 41: 243-249ZFA treated with 0.01 and 0.1 moI/L H2 SO4 showed Drizo A, Frost C A, Grace J et al, 1999. Physico-chemicalstrates for use in con-notably higher removal efficiency than the untreatedtructed wetland systems]. Wat Res, 33: 3595-3602Treatment by H2SO4 can cause the transformation of Geelhoed J S, Hiemstra T, Van RiemsdijkVH, 1997. PhosphateCaCO3(K甲=29×10° into more soluble calcium phaseand sulfate adsorption on goethite: single anion and com-such as gypsum(Ksp=9.1x10)and anhydrite(Fig. 1),titive adsorption[J]. Geochimica et Cosmochimica Acta,thus favoring the dissolution of Ca and precipitation61:23892396of calcium phosphate. The removal efficiency initially Johansson L, Gustafsson JP, 2000. Phosphate removal using blastincreased linearly at low concentration in solution, andfurnace slags and opoka-mechanisms[]. Wat Res, 34: 259-reached the maximum at intermediate concentration Thisis because of the fact that the P concentration needs to Komarowski S, Yu Q, 1997. Ammonium ion removal fromincrease above a certain level(the precipitation limit)towastewater using Australian natural zeolite: batch equilibrum and kinetic studies[]. Environ Technol, 18: 1085-1097precipitate phosphate, depending on the concentration of Koutsoukos P. Amjad Z, Tomson MB et al, 1980. crystallizationalcium(Koutsoukos et aL., 1980; Baker et al., 1998).of calcium phosphates. A constant composition study[J].JHowever, the removal efficiency finally declined at high PAm Chem Soc. 102: 1553-1107oncentration with the amount of immobilized P approach- Neufeld R D, Thodos G, 1969. Removal of orthophosphate froming the maximum immobilization capacity.aqueous solution with activated alumina[J]. Environ SciTechnol. 3: 661-667.3 ConclusionsParfittR L, 1978. 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