Modeling Analysis of CO 2 Solubility in Solutions of DEA, MDEA and Their Mixtures Using Kent- Eisenberg and Deshmukh-Mather models

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1 rd Internatonal Conference on Chemcal, Bologcal and Envronment Scences (ICCEBS1) January 89, 1 Kuala Lumpur (Malaysa) Modelng Analyss of Solublty n Solutons of DEA, MDEA and Ther Mxtures Usng Kent Esenberg and DeshmukhMather models Abdelbak Benamor; Abdelwahab Arouss AbstractAmne based solvents are wdely used n the ndustry for the removal of acd gases such as and S from process streams contanng these components. The technque has been proven to be relable and has found wde applcaton n many chemcal ndustres such as ammona producton, coal gasfcaton and natural gas processng. In ths work, solublty data of absorpton n aqueous solutons of sngle and mxed amne was analysed usng two dfferent models;.e, the Kent Esenberg model and the Deshmukh Mather model. loadng data n aqueous solutons of DEA and MDEA at temperatures rangng from K to K and partal pressure from.9 ka to 1 ka obtaned usng a strred cell reactor was ftted to the two models separately to generate the dfferent parameters requred n each model. Usng the generated parameters, the models were appled to predct the loadng n solutons of DEA and MDEA reported n the lterature. In all cases, t was found that both models were found to gve a good predcton of loadng over a wde range of operatng condtons. owever, the Deshmukh Mather model was found to be more accurate compared to the Kent Esenberg model n predctng loadng especally at low partal pressures. Keywords Absorpton, carbon doxde, Dethanolamne, Methyldethanolamne, modelng. I. INTRODUCTION E use of aqueous solutons of alkanoalamne to Tremove from process streams s stll the choce n the ndustres. Alkanolamne s broadly classfed nto prmary, secondary and tertary dependng on the number of alkyl group(s) attached to the ntrogen atom n the molecule structure. Both prmary and secondary amnes generally exhbt low loadngs (mol of captured /mol of amne) and a hgh rate of absorpton. Tertary amne showed the opposte behavour. Another class of amne known as stercally hndered amne shows hgh absorpton rate and hgh maxmum gas loadng. owever, the choce of a partcular amne wll depend not only on the absorpton rate and maxmum loadng that can be acheved, but also on other factors such as regeneraton energy, corroson tendency and the cost of the solvent. Abdelbak Benamor; Abdelwahab Arouss are wth Gas rocessng Center, Faculty of Engneerng, Qatar Unversty, 71 Doha, Qatar. E mal: benamor.abdelbak@qu.edu.qa; Tel: ; Fax: The absorpton of n amne solutons couples physcal absorpton wth chemcal reacton whch fxes the n the soluton as carbonates, bcarbonates and carbamates dependng on the type of amne beng used. The mechansms for these reactons are avalable n the lterature [1]. It s agreed that smlar reacton steps are nvolved for all types of amne ncludng the protonaton of amne as well as the onzaton of dfferent speces n the soluton. owever, for system nvolvng prmary and secondary amnes, an addtonal step, whch s the formaton of carbamate on has been proposed. Ths reacton lmts the maxmum loadng for these classes of amne to.. Several models are avalable to analyse the solublty of n amne solutons and to predct the equlbrum loadng. Among the models whch have been used wdely s that of the electrolytenrtl model [], the Deshmukh and Mather [] model and that of Kent and Esenberg [4]. The NRTL model and that of Deshmukh and Mather were developed based on sound thermodynamc prncples. Non dealtes of soluton are taken nto consderaton by allowng long and short range nteractons between the dfferent speces that are present n the soluton. The NRTL model used a combnaton of Debyeückel theory and the electrolytenrtl equaton to calculate the actvty coeffcents. The Deshmukh and Mather model s much smpler to handle as compared to the prevous model. It employed the Guggenhem equaton to represent actvty coeffcents. The Kent and Esenberg model s the smplest among these models. The nondealtes present n the system are lumped together nto the K values. In ths work, solublty data of absorpton n aqueous solutons of sngle and mxed amne was analysed usng two dfferent models;.e, the Kent Esenberg model and the Deshmukh Mather model. loadng data n aqueous solutons of DEA and MDEA at temperatures rangng from K to K and partal pressure from.9 ka to 1 ka was ftted to the two models separately to generate the dfferent parameters requred n each model. Usng the generated parameters, the models were appled to predct the loadng n solutons of DEA and MDEA reported n the lterature. 8

2 rd Internatonal Conference on Chemcal, Bologcal and Envronment Scences (ICCEBS1) January 89, 1 Kuala Lumpur (Malaysa) II. TEORY An equlbrum soluton of n aqueous amne soluton s governed by the followng set of equatons: K 1 RR N RR N (1) K RR NO O RR N () K O () K 4 (4) K O O () The equlbrum constants for the above equatons are expressed as follows: [RRN] [ ] e RRN e K (6) 1 [RRN ] e RN [RRNO ] [ ] RRNO e e K [RRN] e [ ] e RRN [ ] [ ] e e K [ ] [ ] [ ] e e K 4 [ ] [O ] [ ] e e K (7) e e O a O (8) (9) (1) Where, [J] s the concentraton of the varous speces, and s the actvty coeffcent of each speces. In addton, the followng balances must hold. Amne balance: [RRN] [RRN] [RRN ] [RRNO ] (11) t e e e balance: α [RRN] [ ] [RRNO ] [ ] / (1) t e e e Charge balance: [RRN ] [ ] [RRNO ] [ ] (1) e e e e Where α s the loadng. The concentraton of carbon doxde n the lqud phase can be estmated from enry s law,.e. [ ] (14) II.1. DeshmukhMather Model The model s based on an actvty coeffcent approach accordng to Debyeückel theory []. The actvty coeffcent s calculated by the equaton proposed by Guggenhem and Stokes [6] and Scatchard [7]: AZ I ln β m (1). j j 1 B I Where Z and m j are respectvely the electrcal charges and concentratons of the correspondng speces and I s the onc strength. The value of A s taken as a functon of temperature as proposed by Lews et al. [8] and B equals to 1. as suggested by tzer [9, 1]. The nteracton parameters, β j, between the dfferent speces n the system are represented n the followng form: β a bt j j j (16) Where parameters a j, b j were taken from a prevous work [11], they are summarzed n Tables 1. It should be noted that nteractons between solutes and solvent were excluded. The onc strength, I, of the soluton was calculated by the followng equaton: 1 I m Z (17) j j TABLE I. NSTANTS FOR INTERACTION ARAMETERS USED IN TIS WORK FOR DEA SOLUTIONS Ions/molecules Values for Equaton 16. nteractons [L/mol] a j [L/mol] b j [L.K/mol] 1x1.1x x x x x1 7 x1.1x x x x1 1x1 7 61x1 79x1 DEA DEA DEA DEA DEAO DEA DEADEA DEA DEADEAO DEA DEAO TABLE II. NSTANTS FOR INTERACTION ARAMETERS USED IN TIS WORK FOR MDEA SOLUTIONS Speces nteractons Values for Equaton 16. [L/mol] a j [L/mol] b j [L.K/mol] MDEA MDEA MDEA MDEA MDEA MDEA 17x x x 1.19x1 6 4x1.x1.71x x1.76x1.49x1 7.47x1 4 TABLE III. NSTANTS FOR INTERACTION ARAMETERS USED IN TIS WORK FOR DEAMDEA MIXTURES Ions/molecules Regressed values for Equaton nteractons 16. [L/mol] arj R[L/mol] brj R[L.K/mol] 1 DEA MDEA 18x1.177x1 DEAMDEA DEAMDEA MDEA DEAO MDEADEAO.17x1.44x x1.18x1.17x1.181x

3 rd Internatonal Conference on Chemcal, Bologcal and Envronment Scences (ICCEBS1) January 89, 1 Kuala Lumpur (Malaysa) II.. Modfed KentEsenberg Model The approach consdered here, s that the apparent equlbrum constants, K, for reactons 1 and as defned n terms of the concentraton of the correspondng speces are taken to be depended on the partal pressure of and the amne concentraton n the soluton as prevously shown by ajsulaman et al [1]. Snce the equlbrum constant at nfnte dluton, K, s only a functon of temperature, a factor F s ntroduced to take nto account the effects of partal pressure and amne concentraton. Thus, K K.F (18) Where, F s defned n a general form as: (19) [ ] [ ] f j F exp g ln h k ln RRN m RRN [ RRN] Smlarly, the coeffcents (f, g, h, k, m ) are constants and were taken from a prevous work [1], they are presented n Table 4. For reactons, coeffcents F were set equal to one whch makes equlbrum constants K K. Table IV. arameters used for Equaton (19) arameter f g h j k m F ,DEA F,DEA F 1,MDEA.68 6 III. MATEMATICAL FRAMEWORK III.1. Sngle amne solutons For aqueous solutons of DEA, Equatons (614) were reduced to a sngle polynomal equaton n terms of [ ] and the equlbrum constants as follows: A[ ] B[ ] 4 C[ ] D[ ] E[ ]F () where A 1 [ ] B DEA K 1,DEA e C K K K K 1,DEA,DEA 4 [ ] 1,DEA,DEA e D DEA K K K K 4 E K K K K K K K K K F K1,DEAK,DEAKK4 Consequently, the total loadng, α, can be expressed as: K1,DEA [ DEA] K K e 4 K 4 K 1,DEA 1 K1,DEA α (1) [ DEA] t For MDEA solutons, no stable carbamates are formed. Thus Reacton does not exst n the system. ence, Equaton becomes: [ ] 4 B[ ] C[ ] D[ ]E () Where, A 1 B MDEA K [ ] e 1,MDEA ( ) C K K D KK4 K1,MDEAK K1,MDEAK E K1,MDEAK Fnally the total loadng becomes ( K K ) ([ MDEA ] K e 1,MDEA ) 1 α () [ MDEA] III.. Mxed Amne Solutons For aqueous mxtures of DEA and MDEA, Equatons (6) (14) were reduced to a sngle polynomal equaton of sxth order. In ths case, Equaton 1 s appled twce, once to account for DEA and a second tme to account for MDEA. In addton, Equatons (11) and (1) should be modfed to account for free MDEA and MDEA. Fnally, the reduced equaton n terms of hydrogen ons concentraton, [ ], and the equlbrum constants s gven as follows: 6 4 A[ ] B[ ] C[ ] D[ ] E[ ] F[ ]G (4) Where A 1 B MDEA DEA K K 1,DEA 1,MDEA C K DEA K MDEA K K 1,MDEA 1,DEA K1,DEAK 1,MDEA K1,DEAK t 8

4 rd Internatonal Conference on Chemcal, Bologcal and Envronment Scences (ICCEBS1) January 89, 1 Kuala Lumpur (Malaysa) D K1,DEAK KK 4 K1,DEAKK1,MDEA ( ([ MDEA] [ DEA] ) ) ( K 1,DEA K1,MDEA ) K K [ ] ( 1,MDEA ) E K K K DEA K K K K 1,DEA 1,MDEA 4 1,DEA K K 1,DEA 1,MDEA K1,DEAK K K K K K K K K 4 1,DEA 1,MDEA 1,DEA F K K K K K 1,DEA 1,MDEA G K K K K K 1 4 1,DEA The loadng s gven by: [ ] K DEA KK 4 K [ ] [ ] [ ] [ ] 1 K K 1.DEA [ ] α () ([MDEA][DEA]) Whle carbamate concentraton s gven by: K [MDEA] [ ] [ ] 1 K K 1,DEA [ ] Carbamate (6) ([DEA][MDEA]) III.. Thermodynamc arameters The equlbrum constant, K, as well as the enry s constant,, were expressed as: a lnk ( or ) b lnt c T d (7) T Values of these constants (a d ) were taken from the lterature and are gven n Table. TABLE V. VALUES OF TE NSTANTS USED IN EQUATIONS 7 arameter a b c d Range ( C) Ref [1] K 1,DEA K 1,MDEA [14] K [1] K [16] K [16] K [16] [16] IV. SOURCE OF DATA All data used n the model regresson were expermentally determned n the laboratory n a prevous work. The absorpton experments were conducted usng a strred cell reactor where the amne soluton was exposed to a flowng gas consstng of a mxture of and N of known composton. Detals of the expermental apparatus and procedure are provded by ajsulaman et al [11]. V. RESULTS AND DISCUSSION V.1. Sngle Amne Solutons Usng the regressed parameters, the predcted loadngs for M and 4M aqueous solutons of DEA and MDEA were compared wth expermental loadngs at dfferent temperatures. The results are gven as plots of loadng aganst partal pressure as shown n Fg. 1 and Fg. respectvely. Loadng [mol/mol] Loadng [mol/mol].9 Loadexp K LoadD.M K LoadK.E K Loadexp K.7 LoadD.M K LoadK.E K artal ressure [ka] Fg 1. Comparson between measured and predcted loadng n M DEA solutons at dfferent temperatures..9 Loadexp K LoadD.M K LoadK.E K.7 Loadexp 1K LoadD.M 1K LoadK.E 1K Loadexp K LoadD.M K LoadK.E K artal ressure [ka] Fg. Comparson between measured and predcted loadng n 4M MDEA solutons at dfferent temperatures. In general, wthn the studed range of temperature, pressure and amne concentraton, both predcted and measured data showed a good agreement wth maxmum devatons of about % for DeshmukhMather model. Relatvely larger devatons of about % are obtaned usng the modfed KentEsenberg model. The man reason for the observed dfferences at these two extreme ends of partal pressure s that the data used to regress these constants were those taken wthn the range of.9 and 1 ka partal pressure of. Thus as expected, loadngs outsde ths range could not be predcted wth a hgh degree of accuracy. Smlarly, 8

5 rd Internatonal Conference on Chemcal, Bologcal and Envronment Scences (ICCEBS1) January 89, 1 Kuala Lumpur (Malaysa) predctng loadng at the hgher operatng temperatures whch are beyond those used to regress the constants also ntroduced some errors. For practcal purposes and wthn the range of condtons employed n ths work, t s clear that both models together are able to predct loadngs comparable to the expermental results as shown n Fg1 and Fg.. V.. Mxed Amne Solutons For a soluton contanng a mxture of DEA and MDEA, the system s also descrbed by the set of Equatons (6) (14). In addton, Equaton (1) must be consdered twce, once for MDEA and once for DEA to account for ther effects n the mxture. Usng the same parameters generated from sngle amne experments, and regressng the remanng parameters that do not appear n sngle cases, the predcted loadng and carbamate concentraton are compared wth those obtaned expermentally n ths work as shown n Fg. for total M mxtures of DEAMDEA at varyng ratos and temperatures. Concentraton [mol/mol] Loadexp LoadK.E LoadD.M Carbaexp artal ressure [ka] Fg. Comparson between expermental and predcted loadng and Carbamate concentraton n a soluton of 1.M DEA.M MDEA soluton at K usng both models Over the entre range of nvestgated partal pressure, the models can correlate well both; the total gas loadng that could be acheved and carbamate concentraton n the soluton. A maxmum devaton of about % was reached at hgh pressures. It should be noted that the DeshmukhMather model has a superor ablty to predct loadng and especally carbamate concentraton n the soluton as compared to the one of Kent Esenberg. V.. Comparson wth lterature data To assess the valdty of the models further, comparson was made wth the avalable data reported by Austgen et al.[17] as shown n Fg. 4. The data was obtaned at two dfferent temperatures of 1 and K n 4M mxtures contanng equal proporton of DEA and MDEA. Loadng [mol/mol].9 Loadexp 1K LoadD.M 1K.7 LoadK.E 1K Loadexp K LoadD.M K LoadK.E K artal ressure [ka] Fg 4. Comparson between predcted loadng and the data of Austgen et al. [17] n aqueous 4M DEAMDEA soluton at dfferent temperatures. Overall, a good agreement between expermental and calculated values was obtaned despte the fact that the model parameters were generated from expermental data coverng a small range of operatng condtons. As expected, relatvely larger devatons of about % were observed at low partal pressures (less than.1 ka) and very hgh pressures. Ths can be explaned by the fact that the data used to regress these parameters were taken wthn the range of.9 ka and 11 ka partal pressure of. V.4. Specaton lots The concentratons of the dfferent speces n the system were evaluated usng the models as shown n Fgure. It was found that at low partal pressure and therefore at low loadng, most of the absorbed nto the soluton s n the form of carbamate wth a small amount n the form of bcarbonate. As the loadng ncreases, the trend s reversed where the presence of bcarbonate s most sgnfcant. The formaton of carbamate from DEA s very fast and the equlbrum s reached quckly, ndcatng that at low pressure, s preferentally absorbed nto DEA. owever, due to the stablty of the carbamate the theoretcal stochometrc loadng wth DEA s lmted to.. Speces Concentraton [mol/l] 1.6 Carbaexp CarbaD.M 1.4 DEAD.M DEAD.M 1. MDEAD.M MDEAD.M Loadng [mol/mol] Fg. Speces concentraton profle for aqueous soluton of.m DEA1.M MDEA usng both models at K A slghtly hgher loadng of about.7 could be acheved n practce usng DEA due to the formaton of bcarbonate. As the partal pressure s ncreased, a hgher loadng greater than about.7 s only possble through absorpton nto MDEA, where the s fxed 84

6 rd Internatonal Conference on Chemcal, Bologcal and Envronment Scences (ICCEBS1) January 89, 1 Kuala Lumpur (Malaysa) manly as the bcarbonate. Ths explanaton s n agreement wth the observed expermental data as well as the model correlaton n Fg. that shows the lqud phase concentraton profle for an aqueous mxture of DEA and MDEA. Comparng the carbamate expermental results to those obtaned by both models, shows that the Deshmukh Mather model has a superor ablty to closely correlate the carbamate concentraton n the soluton as compared to the model of KentEsenberg. Furthermore, comparng results obtaned by both models to those obtaned by Austgen et al. [17] usng NRTL model, for the same proporton of DEA /MDEA but hgher total amne concentraton and temperature, an excellent agreement regardng the trend of the concentraton profle exst between the NRTL model and the DeshmukhMather model compared to the results obtaned by Kent Esenberg model. VI. NCLUSION The modfed DeshmukhMather model was used to analyze the solublty of and carbamate concentraton for the absorpton of n aqueous solutons of DEA, MDEA and ther mxtures. Compared to ts orgnal form two new parameters were ncluded n ths model; namely, the expermental value of the equlbrum constant for the formaton of carbamate, and the concentraton of carbamate n case of DEA whch was ftted smultaneously wth loadng to generate the correspondng nteracton parameters. Usng the generated parameters from each case, the model s able to gve generally good correlatons of the total loadng and carbamate concentraton n solutons of sngle and blended amnes. The dfferent nteracton parameters expressng the equlbrum constant n terms of actvty coeffcents whch were generated from experments usng a sngle amne can be used to descrbe the observed data for blended amnes and those publshed n the lterature. The modfed Kent Esenberg model whch takes nto account the effects of partal pressure and total amne concentraton on the apparent equlbrum constant for the protonaton of amne and the formaton of carbamate s able to gve relatvely good predcton of the total loadng n solutons of sngle and blended amnes. The dfferent parameters expressng the equlbrum constant n terms of pressure and amne concentraton whch were generated from experments usng sngle amne can be used to descrbe the observed data for blended amnes and those publshed n the lterature. REFERENCES [1] Danckwerts,. V. and McNel, K. M., 1967, The Absorpton of carbon Doxde nto Aqueous Amne Solutons and the Effects of Catalyss, Trans. Instn. Chem. Engrs, 4:T1 [] Chen, C. C., and Evans, L. B. A., 1986, Local Composton Model for the Excess Gbbs Energy of Aqueous Electrolyte System, AIChE J.,, 444 [] Deshmukh, R. D., and Mather, A. E., 1981, A Mathemetcal Model for Equlbrum Solublty of ydrogen Sulfde and Carbon Doxde n Aqueous Alkanolamne Solutons, Chem. Eng. Scence, 6, [4] Kent, R. L., and Esenberg, B., 1976, Better Data for Amne Treatng, ydrocarbon rocess., (), 87 []. Debye, E. ückel, hys. Z. 4 (19) 186. [6] E. A. Guggenhem, R.. Stokes, Trans. Faraday Soc. 4 (198) [7] G. Scatchard, Chem. Rev. 19 (196) 97. [8] G.N. Lews, M. Randall, K.S. tzer, L. Brewer, Thermodynamcs, nd ed., McGraw ll, [9] K.S. tzer, J. hys. Chem. 77 (197) [1] K.S. tzer, J.J. Km, J. Am. Chem. Soc. 96 (1974) [11] Benamor, A, and Aroua, M. K, Modelng of Solublty and Carbamate Concentraton n DEA, MDEA and Ther Mxtures Usng the DeshmukhMather Model, Flud hase Equlbra Journal, 1 () 1 16 (). [1] aj Sulaman, M. Z., Aroua, M. K. and Benamor, A., Analyss of Equlbrum Data of n Aqueous Solutons of Dethanolamne (DEA), Methyldethanolamne (MDEA) and Ther Mxtures Usng the Modfed Kent Esenberg Model, Trans IChemE. Vol. 76, art A, , November [1] D.D. errn, Dssocaton Constants of Organc Bases n Aqueous Solutons, Butterworths, London, 196. [14] Aroua, M. K., Benamor, A, and aj Sulaman, M. Z., 1997, Temperature Dependency of the Equlbrum Constant for the Formaton of Carbamate from Dethanolamne, J. Chem. Eng. Data, 4, 69 [1] Lttel, J. I., Bos, M. and Knoop, G. J., 199, Dssocaton Constants of Some Alkanolamnes at 9,, 18, and K, J. Chem. Eng. Data.,, 76) [16] Edwards, T. J., Maurer, G., Newman, J. and rausntz, J.M., 1978,VaporLqud Equlbra n Multcomponent Aqueous Solutons of Volatle Weak Electrolytes, AIChEJ., 4, 966 [17] D.M. Austgen, G.T. Rochelle, C.C. Chen, Ind. Eng. Chem. Res. (1991) 4. 8

7 rd Internatonal Conference on Chemcal, Bologcal and Envronment Scences (ICCEBS1) January 89, 1 Kuala Lumpur (Malaysa) Senstvty of freshwater organsms to znc M. ShuhamOthman, N. Yakub, and N.A. Ramle Abstract A study was conducted n the laboratory to determne acute toxcty of heavy metal znc (Zn) to sx speces of freshwater organsms.e. one speces of shrmp (Macrobrachum lanchester), two speces of fsh (Rasbora sumatrana (Seluang) and oecla retculata (guppy), one speces of gastropod (Melanodes tuberculata), one speces of ostracod Stenocyprs major and one speces of mdge (larvae) Chronomus javanus. All organsms were exposed for a fourday perod n the controlled laboratory condton to a range of Zn for 96 hours. Mortalty was assessed and medan lethal concentratons (LC ) were calculated. 96 hours LC for M. lanchester, R. sumatrana,. retculata, M. tuberculata, S. major and C. javanus of Zn were.,.46, 1.,.9, 1.19 and.7 mg/l, respectvely. Ths study ndcated that R. sumatrana was the most senstve to Zn. Keywords Acute, freshwater, heavy metals, senstvty, soft water, toxcty. T I. INTRODUCTION OXICITY testng has been wdely used as a tool to dentfy sutable organsms as a bondcator and to derve water qualty standards for chemcals. Toxcty testng s an essental tool for assessng the effect and fate of toxcants n aquatc ecosystems. Metal contamnaton has been shown to have serous effects on the both envronment and humans. Malaysa, as a developng country, s no excepton and faces metal polluton caused especally by anthropogenc actvtes such as manufacturng, agrculture, sewage and motor vehcle emssons [1], []. Metals such as Zn are released from natural sources as well as human actvty. Despte the adverse effect of metal on the envronment and organsms, Zn s essental to lvng organsms and plays an mportant role as an enzyme carbonc anhydrase. Macronvertebrate and fsh as a test organsms n toxcty tests has several valuable characterstcs such as ts wdespread dstrbuton and common occurrence n freshwater, ts ecologcal mportance and ease of handlng M. ShuhamOthman s wth the School of Envronmental and Natural Resource Scences, Faculty of Scence and Technology, Unverst Kebangsaan Malaysa (UKM), 46 Bang, Selangor, Malaysa (correspondng author phone: ; fax: 689 7; emal: shuham@ukm.my). Y. Nadzfah s wth the School of Envronmental and Natural Resource Scences, Faculty of Scence and Technology, Unverst Kebangsaan Malaysa (UKM), 46 Bang, Selangor, Malaysa (emal: posh_ap41@yahoo.com). N.A. Ramle s wth the School of Envronmental and Natural Resource Scences, Faculty of Scence and Technology, Unverst Kebangsaan Malaysa (UKM), 46 Bang, Selangor, Malaysa (emal: lna_exora84@yahoo.com). durng testng, as well as ts rapd growth, short lfe cycle and senstvty to contamnants [], [4]. Therefore, these organsms have the potental to act as a bondcator of heavy metals polluton n an aquatc envronment and as organsms for toxcty testng. The purpose of ths study was to determne the acute toxcty of Zn to sx local freshwater organsms and to compare the senstvty between them. II. MATERIALS AND METODS A. Organsms and test chemcals In ths study sx local freshwater organsms have been used n toxcty testng.e. a prawn Macrobrachum lanchester, two fsh oecla retculata (guppy, famly oeclldae) and Rasbora sumatrana (famly Cyprndae), a snal (Gastropoda) Melanodes tuberculata (famly Thardae), an ostracod Stenocyprs major, and a mdge larvae Chronomus javanus (Dptera, Chronomdae). M. lanchester and R. sumatrana were obtaned from local pet stores.. retculata and M. tuberculata were collected from the feld. S. major and C. javanus were collected from a fsh pond flter system. ror to toxcty testng, the organsms were acclmatzed for one week under laboratory condtons (8 o C wth 1h lght : 1h darkness) n L stockng tanks usng dechlornated tap water (fltered by several layer of sand and actvated carbon; T.C. Sedment Flter (TK Multtrade, Ser Kembangan, Malaysa)) and aerated through an ar stone. Durng acclmaton the organsms were fed wth commercal fsh food Tetramn (Tetrawerke, Germany). The standard stock soluton (1 mg/l) of Zn was prepared from analytcal grade metallc salts of ZnSO 4.7 O (Merck, Darmstadt, Germany). The stock solutons were prepared wth deonzed water n 1L volumetrc. B. Acute toxcty test Acute Zn toxcty experments were performed for a fourday perod (96h) usng adult anmals or larvae (fourth nstar mdge larvae). Followng a range fndng test, fve Zn concentratons were chosen. Metal solutons were prepared by dluton of a stock soluton wth dechlornated tap water. A control wth dechlornated tap water only was also used. The tests were carred out under statc condtons wth renewal of the soluton every two days. Control and metal treated groups each conssted of two to four replcates of fve randomly allocated organsms. No sgnfcant stress was observed for the organsms n the soluton ndcated by 91% survval 86