BIOTRANSFORMATION OF TERTIARY BUTYL MERCAPTAN IN SOIL MICROCOSMS

Transcription

1 BIOTRANSFORMATION OF TERTIARY BUTYL MERCAPTAN IN SOIL MICROCOSMS S. Kalanesan 1, L.E. Erckson 1, S. L. L. Hutchnson 2 and R. Karthkeyan 2 Department of Chemcal Engneerng 1 Department of Bologcal and Agrcultural Engneerng 2 Kansas State Unversty Manhattan, KS ABSTRACT Tertary butyl mercaptan (TBM) s a malodorant that s added to natural gas n small quanttes to ad n ts detecton. The objectve of ths study s to nvestgate the bodegradaton of TBM n sol under aerobc condtons. Sol mcrocosms were set up usng two dfferent sols and ther headspace was sampled durng a 62-day perod of study. In the frst set contanng sol from Fort Rley, there was sgnfcantly greater reducton n TBM and producton of carbon doxde n the treatments compared to the sterlzed controls. Further t was observed that there was more carbon doxde producton n the mcrocosms wthout TBM rather than those wth TBM. In the second set of experments usng sol-contanng methyl tertary butyl ether degradng mcroorgansms, the reducton n TBM level was almost equal n the treatments and the sterlzed controls. In ths sol, there was more carbon doxde n the treatments wth TBM compared to those wthout TBM. The sterlzed controls showed mnmum carbon doxde producton. In both sets of experments, an ntermedate product d-tertary-butyl dsulfde was dentfed. The dsulfde producton was observed to be greater n the treatments than n the sterlzed controls. The expermental results show that TBM appears to be bodegradable n sol-water systems under aerobc condtons and may be consdered for approprate uses wth approprate envronmental management. INTRODUCTION A revew of the publshed lterature was made to determne the bodegradaton characterstcs of tertary butyl mercaptan (TBM). As no expermental studes were found, two sets of mcrocosm studes were carred out followng the methods that have been used n other studes (2, 3, 7). In addton the value of Henry s constant for TBM was estmated expermentally. Usng the Henry s constant value, solublty of TBM n water was also estmated. EXPERIMENT I: BIODEGRADATION OF TBM IN SOIL MICROCOSMS Introducton The frst set of experments used sol from Fort Rley for bodegradaton studes. The mcrocosms for the frst set of experments were set up usng 160 ml serum bottle consstng of 10 g sol, 10 ml water and 10 µl TBM each. The mcrocosms were set up for a 62-day perod. They conssted of treatments, sterlzed controls and carbon doxde controls. The

2 volume of the serum bottles where chosen such that the headspace n the mcrocosms was suffcent for aerobc bodegradaton. Sol Characterstcs The Fort Rley sol was from the feld ste where sedments from the vehcle wash water sedmentaton basn had been deposted for a phytoremedaton feld study (5, 6). The organc content of the sol ncluded resdual petroleum hydrocarbons; however, these were a small fracton (less than 3%) of the organc matter n the sol. Table 1*. Sol Analyss Results for Experment I Sample ph Organc Matter % Sand % Texture Slt % Clay % Total N % Total C % 1 a b c a. Sol taken from the treatments that contaned unamended sol and TBM b. Sol taken from the carbon doxde controls that contaned unamended sol and no TBM. c. Unamended sol *Sol analyss results obtaned from sol testng laboratory, Kansas State Unversty. Expermental Setup Treatments Treatments were set up to montor the reducton of tertary butyl mercaptan (TBM) n sol water system due to bodegradaton. The treatments consst of 160 ml serum bottles sealed wth a Teflon lned septum, contanng 10 gram sol and 10 ml water. After the bottle was closed wth the septum and crmped, 10 µl TBM was njected through the septum. The treatments were setup on Day 0 on Sep 22, Three replcates of each treatment were setup for samplng on days 1, 4, 6, 8, 12, 16, 20, 26 and 33. Treatments set up for day 1 were sampled on days 0, 1, 49 and 62. The remanng sets of bottles were sampled only once on one of the days mentoned above. Controls Controls help to establsh that reducton n TBM s prmarly due to bodegradaton. In the absence of mcroorgansms there should be no sgnfcant reducton n the level of TBM.

3 The controls conssted of the same sol as treatments but n ths case t was sterlzed. Sterlzaton of sol was done as follows: the requred amount of sol was packed n an alumnum fol and placed n an autoclave at 250 F for 50 mnutes. The sol packed n the alumnum fol was allowed to cool. It was then ncubated at 30 C for 2 hrs. Then the sol was agan autoclaved as before. Ths process was repeated three tmes to ensure maxmum destructon of mcroorgansms. Sterlzed serum bottles were used for these controls and any nstrument used for settng up the controls such as spatula, ppettes, beakers etc., were also sterlzed. The controls were set up usng 10 g sterlzed sol (sterlzed as mentoned above), 10 ml de-onzed water and 10 µl TBM n 160 ml serum bottle. The de-onzed water was not sterlzed before addng to the controls. Controls were setup and sampled on the same days as the treatments. CO 2 Controls The carbon doxde controls were setup to see the extent of mcrobal actvty n the absence of TBM. They helped to dentfy f TBM ncreased or decreased the mcrobal actvty. The CO 2 controls conssted of 10 g of the sol and 10 ml water n 160 ml serum bottle. No TBM was added to these CO 2 controls whch were set up for analyss on days 4, 12, 26 and 62. EXPERIMENT II: BIODEGRADATION OF TBM IN SOIL MICROCOSMS CONTAINING MTBE DEGRADING MICROORGANISMS Introducton In the second set of mcrocosms, expermental sol contanng methyl tertary butyl ether (MTBE) degradng mcroorgansms was used. Ths sol had been used n earler expermental work to nvestgate MTBE bodegradaton (10). Mcrocosms were set up usng 26 ml serum bottles consstng of 1 g sol, 50 µl water and 2 µl TBM each. Mcrocosms ncluded treatments, sterlzed controls and carbon doxde controls and they were set up for a 78-day perod. The expermental setup was desgned for aerobc bodegradaton. Sol Characterstcs The sol used n ths study was a mxture of sol taken from dfferent sol strata. The characterstcs of the sol used n the experment are tabulated below:

4 Table 2*. Characterstcs of Each Sol Stratum Features Top sol Mddle Sol Bottom Sol Depths at Actual Ste Surface sol cm Below 40 cm Representatve Depths n Channel (cm) Sand Content (%) Slt Content (%) Organc Carbon Content (%) Ntrate Level (ppm) Phosphate Level(ppm) Potash Level (ppm) *Table adapted from Muraldharan, Table 3*. Gravmetrc Water Content Values (g water / g dry sol) Chamber Depth (cm) Dstance Along the Length of the Channel from the Inlet (cm) * Table adapted from Muraldharan, 1994.

5 Expermental Setup Treatments As n the prevous study, treatments were set up to montor the reducton of tertary butyl mercaptan (TBM) n sol water system, due to bodegradaton. The treatments conssted of 26 ml serum bottles sealed wth a Teflon lned septum, contanng 1 g sol and 50 µl water. After the bottle was closed wth the septum and crmped, 2 µl TBM was njected through the septum. The treatments were setup on Day 0 on Feb 2, Sx sets of treatments wth three replcates each were set up. The frst set consstng of three replcates were sampled on days 2 and 20, second set was sampled on days 4 and 26, thrd set was sampled on days 6 and 33, fourth set was sampled on days 8 and 49, ffth set was sampled on days 12 and 62 and the sxth set was sampled on days 16 and 78. Controls Controls help to establsh that reducton n TBM s prmarly due to mneralzaton. The controls conssted of the same sol as treatments but n ths case t was sterlzed; hence, there should be no sgnfcant reducton of TBM due to bodegradaton n the controls. Sterlzaton of sol was done as follows: the requred amount of sol was packed n an alumnum fol and placed n an autoclave at 250 F for 50 mnutes. The sol packed n the alumnum fol was allowed to cool. It was then ncubated at 30 C for 2 hrs. Then the sol was agan autoclaved as before. Ths process was repeated three tmes to ensure maxmum destructon of mcroorgansms. Sterlzed serum bottles were used for these controls and any nstrument used for settng up the controls such as spatula, ppettes, beakers etc., were also sterlzed. The controls were set up usng 1 gm sterlzed sol (sterlzed as mentoned above), 50 µl deonzed water and 2 µl TBM n 26 ml serum bottle. The de-onzed water was not sterlzed before addng to the controls. Controls were setup and sampled on the same days as treatments. CO 2 Controls The carbon doxde controls were setup to determne the extent of mcrobal actvty n the absence of TBM. They helped to dentfy whether the presence of TBM enhanced or decreased the mcrobal actvty. The CO 2 controls conssted of 1 gm sol (the same sol as used n the treatments and controls) and 50 µl water n 26 ml serum bottle. No TBM was added to these mcrocosms. Two sets of CO 2 controls were set up wth three replcates n each set. Frst set was sampled on days 4, 20, 33 and 62 and the second set was sampled on days 12, 26, 49 and 78. IDENTIFICATION OF TBM AND CO 2 PEAKS Headspace from the mcrocosms was analyzed for TBM usng a 5890 Seres II gas chromatograph (Hewlett-Packard, Avondale, PA) wth Chemstaton ntegraton software. The GC was equpped wth a flame onzaton detector. The column used was HP1 (J & W Scentfc, Folsom, CA) mega bore column wth a length of 30 m, nternal dameter 0.53 mm and 5 µm flm thckness. The fuel and carrer gas was H 2 (99.999%), the make up gas was N 2

6 (99.999%) and the support gas was zero-grade dry ar. The column head gauge pressure was mantaned at 0.34 atm (5 ps). The temperature program began at 50 C for 2 mnutes, ramped at 10 C / mn to 150 C and was then held at 150 C for 3 mnutes. The njecton port and detector temperatures were at 150 C and 280 C respectvely. TBM was analyzed by njectng 10 µl (splt less) of headspace gas from the serum bottle manually usng a gas tght Hamlton syrnge. The chromatogram obtaned showed a TBM peak appearng at about 2 mn. The peak areas were obtaned through automatc ntegraton. CO 2 was measured usng a Shmadzu gas chromatograph wth a thermal conductvty detector. A sample contanng 0.5 ml of gas phase was njected and the carbon doxde peak appeared around 0.6 mnutes. The peak area was calculated automatcally. DISULFIDE DETECTION Durng the analyss of headspace gas on the GC, another sgnfcant peak appeared around 12 mn, n addton to the TBM peak. Analyzng sulfur chemstry suggested that TBM oxdzes to form d-tertary-butyl dsulfde. As the mcrocosms were desgned for aerobc bodegradaton, the second peak was expected to be d-tertary-butyl dsulfde, an ntermedate product of degradaton. Mass spectrometer was used to analyze the GC results and the peak that appeared at 12 mn was confrmed to be d-tertary-butyl dsulfde. Another undentfed peak appeared around 4 mnutes. Though ths peak could not be exactly dentfed usng GC/MS t may be a trsulfde or one of the oxdaton products of TBM. ESTIMATION OF HENRY S CONSTANT Henry s Law and Henry s Constant When a vapor mxture and lqud soluton exst n equlbrum at a temperature T and pressure P, the relatonshp for vapor-lqud equlbrum of a pure speces s gven by (9): - Where, v l f = f f v y = φ P f l = x γ f f v l f s the fugacty of speces n vapor mxture. s the fugacty of speces n lqud soluton. y s the mole fracton of speces n vapor. φ s the fugacty coeffcent of speces (equal to unty f vapor phase behaves as deal gas). P s the total system pressure. x s the mole fracton of speces n lqud. γ s the actvty coeffcent of speces (equal to unty for an deal soluton). f s the standard state fugacty of speces.

7 If v f f l = y φ P= x γ f Assumng deal vapor and lqud phases Or, Also, yp= xf f f f = yp x f = = γ x yp = = x f x f x The standard state f must be chosen based upon the lqud phase composton of the system. Henry s law behavor arses when the lqud mxture of nterest s very dlute n component and a drect proportonalty s observed between the fugacty of the speces and ts mole fracton n the lqud phase. Then f becomes equal to the Henry s constant, H whch may be expressed as below (4, 9): - yp f H = lm = lm x 0 x x 0 x The above equaton s the statement of Henry s law as t apples to real solutons (Smth and Van Ness, 1987). The Henry s constant s the partal pressure n the gas phase dvded by the concentraton n the lqud phase. Method of Estmaton of Henry s Constant Standards were prepared by addng 10, 20, 30, 40 and 50 µl TBM nto 160 ml serum bottles contanng 100 ml deonzed water each. The standards were allowed to come to equlbrum. Then the headspace gas and the lqud phase from each bottle were analyzed for TBM usng a gas chromatograph. The njecton volume was 10 µl for headspace gas analyss and 1 µl for lqud phase analyss. The analyss results obtaned n terms of peak areas are as tabulated below:

8 Table 4. Headspace Analyss of Standards for TBM Concentraton of TBM µl/100 ml Water Peak Area Table 5. Lqud Phase Analyss of Standards for TBM Concentraton of TBM µl/100 ml Water Peak Area From the standards prepared, let us consder the standard where 30 µl TBM was added to 100 ml water. At equlbrum 30 µl TBM added would have parttoned nto 100 ml aqueous phase and 60 ml headspace. Assumng that: - Gram moles of TBM n 100 ml water = M w Gram moles of TBM n 60 ml head space = M v From analyss by Gas Chromatograph, Peak area obtaned for (aqueous phase) 1 µl njecton = Peak area obtaned for (head space) 10 µl njecton = For the evaluaton of Henry s constant we use the prncple that the same amount of TBM njected nto the gas chromatograph should result n a peak wth the same peak area.

9 M w 100X10 ( Peakarea µ L) ( Peakarea µ L) gmoles µ L = M 60X10 v 3 3 gmoles µ L M M M M w v w v = = X100 X10 X X 60 X ( 1) Total volume of TBM = 30 µl 3 Mass of TBM = 30X10 ( ml) X ( g/ ml) = g Moles of TBM = = X10 4 gmoles M w 4 + M = X10 gmoles... ( 2) Solvng equatons (1) and (2) we get v 5 M v = 411. X 10 gmoles 4 M = 223. X 10 gmoles w 5 nrt X 10 ( gmol) X 1( atm) X 22400( ml) X 297( K) * P = = V 60( ml) X 273( K) X 1( gmol) * P = ( atm) H P * ( atm) = = C X 10 gmoles X m H = 749. X atm m gmole Smlarly the Henry s constant value was calculated usng vapor and aqueous phase peak areas obtaned from the analyss of standards 20 µl / 100 ml water and 10 µl / 100 ml water.

10 Table 6. Henry s Constant Evaluaton Standard Concentraton Henry s Constant (µl TBM / 100 ml Water) (atm m 3 / gmol) X X X 10-3 The average Henry s constant value calculated usng the above three values of Henry s constant s: H = 719. X 10 3 ( atm m 3 / gmol) The above value of Henry s constant was evaluated at 24 C. It may be notced that the calbraton for the gas phase concentraton of TBM s very close to lnear but n the case of lqud phase we see that there s a talng off of the peak area wth ncrease n concentraton and the results are not as lnear as n the case of gas phase concentraton. Hence for the estmaton of Henry s constant only the lower part of the calbraton curve, whch s more lnear, has been consdered. The value of Henry s constant appears to be n the lower range of 6.77x10-3 to 7.31x10-3, as the calbraton s hghly lnear n ths range. Ths expermental value s compared to predcted values from the publshed lterature n Table 7. Table 7. Comparson of Estmated Henry s Constant Value wth Lterature Values S.No Henry s Constant atm m 3 / gmole 1* 7.19 x 24 C 2** 6.11 x 25 C 3*** 5.12 x 25 C * Estmated value of Henry s constant from ths experment ** Henry s constant value from EPI Sute estmaton software (bond estmate), Syracuse Research Center, Syracuse, New York. *** Henry s constant value from lterature (Yaws et al., 2003). Henry s Constant and Solublty The estmated value of Henry s constant as explaned above was 7.19x10-3 atm m 3 / gmole at 24 C. To evaluate the value of Henry s constant at 20 C we use the data n Table 8.

11 Table 8. Vapor Pressure of TBM at Dfferent Temperatures Vapor Pressure Mm mercury Log(Vapor Pressure) Temperature K 1/T 1/K 181 a x b x c x10-3 a - value from EPI Sute Estmaton Software, Syracuse Research Center, Syracuse, New York. b - value from Atofna Chemcals Inc., Tertary Butyl Mercaptan MSDS, c - value from lterature (Yaws et al., 2003). Usng a plot of log (vapor pressure) vs. 1/T the value of vapor pressure at 293 K was evaluated to be approxmately mm mercury. Then assumng solublty to be constant, Henry s constant at 20 C was estmated to be 5.74 x 10-3 atm m 3 / gmole. As the bodegradaton studes were carred out at 20 C, ths estmate was used for the calculatons. Usng the above estmate of Henry s constant the solublty of TBM n water was calculated from the equaton: S = P / H Where, S s the solublty n mg/l P s the vapor pressure n atmospheres H s the Henry s constant n atm L / mg The solublty of TBM was thus estmated to be 2988 mg/l at 20 C. RESULTS AND DISCUSSION Experment I TBM Dsappearance wth Tme In the frst set of TBM bodegradaton studes t was seen that the concentraton of TBM n the treatments decreased more rapdly than that n the controls. Fgure 1 shows the behavor of TBM durng a 62-day perod for the controls and treatments. It may be seen from Fgure 14, that TBM reducton n the treatments s much hgher than the controls, whch had sterlzed sol. The controls have sterlzed sol and hence deally there should have been no reducton of TBM n the controls. But the graph shows that there was some reducton n TBM n the controls. Ths may be due to the fact that the contents mght not have been sterlzed completely. There mght have been some form of bacteral contamnaton that led to the reducton n TBM n the controls. Nevertheless, reducton of TBM s more n the case of treatments than n the controls. So there s some evdence of bodegradaton. There s also a possblty that the loss of TBM may be partly due to chemcal reacton. There was no evdence of a lag perod for the reducton of TBM n the unsterlzed sol. For these treatments more than 99% of the TBM dsappeared durng the frst 33 days of the experment.

12 TBM Concentraton ( g / ml) TREATMENTS CONTROLS Date Fgure 1. Gas Phase Concentraton of TBM n the Headspace for the Treatments and the Controls CO 2 Producton wth Reducton n TBM Fgure 2 shows carbon doxde producton n treatments, controls and carbon doxde controls from day 0 to day 62. It may be seen that there s sgnfcantly more carbon doxde produced n the treatments than n the sterlzed controls. The producton of CO 2 n the controls and treatments may result from the bodegradaton of TBM, from the mneralzaton of organc carbon content n the sol, or from chemcal converson of TBM. For the unsterlzed treatments, the headspace concentraton of carbon doxde was about 17 gm /L after 62 days. Ths accounts for about 16 percent of carbon that was suppled as TBM. Gas Phase Concentraton of CO 2 ( ηg / ml headspace) TREATMENTS CONTROLS CO2 CONTROL Date Fgure 2. Gas Phase Concentratons of CO 2 n the headspace of the Treatments, Controls and CO 2 Controls.

13 Dsulfde Producton Fgure 3 shows dsulfde producton n the controls and treatments. It may be seen from Fgure 16 that there s more dsulfde producton n the treatments than n the sterlzed controls. Whle ths provdes some evdence n favor of boconverson of TBM to dsulfde, dsulfde producton may also be due to the chemcal converson of TBM TREATMENTS CONTROL Peak Area Day Fgure 3. Gas Phase Concentraton of D-terary-butyl Dsulphde Produced from TBM, for the Treatments and the Controls It was seen earler by testng that the Teflon lned septum could wthstand multple punctures wth neglgble leakage. Also the treatments, sterlzed controls and CO 2 controls were placed n dark locatons away from any lght. Hence the reducton n TBM due to photo degradaton or leakage s neglgble. Knetcs and Frst Order Rate Constant The natural logarthm of the gas phase concentraton of TBM dvded by the ntal gas phase concentraton of TBM was plotted versus tme n order to determne the reacton rate

14 constant for TBM decay n the treatments and the controls. The slope of the straght lne ftted to the data n the above mentoned plot gave the negatve of the frst order rate constant. Ln(gas phase TBM concentraton/ ntal gas phase TBM concentraton) 1 Days y = x -2 R 2 = Fgure 4. Determnaton of Frst Order Rate Constant for the Dsappearance of TBM n the Treatments n Experment I The frst order rate constant thus estmated was found to be day --1 for the sterlzed controls and day -1 for the treatments. It may be seen that frst order rate constant for the treatments s greater than that for the controls. No lag perod s observed n the case of Experment I. The half lfe, whch s the tme taken for TBM to reduce to half ts ntal concentraton was found to be 5.1 days for the treatments and 18.1 days for the controls. Ln(gas phase TBM concentraton/ ntal gas phase TBM concentraton) Days y = x R 2 = 0.97 Fgure 5. Determnaton of Frst Order Rate Constant for the Dsappearance of TBM n the Controls n Experment I

15 Experment II TBM Dsappearance wth Tme In the second set of TBM bodegradaton studes t was seen that the concentraton of TBM n the treatments and controls decreased at almost the same rate. 25 TBM Concentraton n Headspace ( g/ml) Treatments Controls Day Fgure 6. Gas Phase Concentraton of TBM n the Headspace for the Treatments and Controls from Day 2 to Day 78 Fgure 6 shows the behavor of TBM durng a 78-day perod for the sterlzed controls and the treatments. Ideally there should have been no reducton of TBM n the sterlzed controls, but we fnd TBM reducng at the same rate n the treatments and controls. Though some reducton of TBM n the sterlzed controls can be attrbuted to the lack of effectveness of the sterlzaton, the reason for reducton of TBM n the sterlzed controls, at the same rate as the treatments, s not very clear. Hence there s a possblty that chemcal reacton may also be causng TBM dsappearance n addton to bodegradaton. CO 2 Producton wth Reducton n TBM Fgure 7 shows the producton of CO 2 n the sol mcrocosms from day 0 to day 78. CO 2 may be produced due to bodegradaton of TBM, due to mneralzaton of the organc carbon content n the sol or due to chemcal reacton. It can be seen from fgure 7 that the producton of CO 2 n the sterlzed controls s much less than that produced n the treatments, whch leads us to beleve that the sterlzaton was effectve to a certan extent n destroyng the mcroorgansms. It may also be seen from fgure 18 that more carbon doxde was produced by the treatments than the CO 2 controls whch had no TBM n them. Ths shows that the actvty of the mcroorgansms s enhanced by the presence of TBM and hence we can also say that there s some evdence of bodegradaton of TBM.

16 18 Concentraton of CO 2 In Headspace gm / ml Treatments Controls CO2 control Day Fgure 7. Gas Phase Concentraton of CO 2 n the Headspace for the Treatments, Controls and CO 2 Controls from Day 0 to Day 78 For the unsterlzed treatments, the headspace concentraton of carbon doxde was mg TBM/L after 78 days. Ths accounts for about 13 percent of carbon that was suppled as TBM. Dsulfde Producton Treatment s Controls Dsulfde Peak Area Day Fgure 8. Producton of Dsulfde n the Treatments and Sterlzed Controls from Day 2 to Day 78 As n the case of Experment I dsulfde producton was notced n the second set of experments. Fgure 8 shows dsulfde producton n the controls and treatments. It may be

17 seen from Fgure 8 that there s more dsulfde producton n the treatments than n the sterlzed controls. In the case of Experment II about 80% of the TBM dsappeared n 33 days and about 96% TBM dsappeared n 78 days. Knetcs and Frst Order Rate Constant The natural logarthm of the gas phase concentraton of TBM dvded by the ntal gas phase concentraton of TBM was plotted versus tme n order to determne the reacton rate constant for TBM decay n the treatments and the controls. The slope of the straght lne ftted to the data n the above mentoned plot gave the negatve of the frst order rate constant. 0.5 Ln(gas phase TBM concentraton/ ntal gas phase TBM concentraton) Day y = x R 2 = Fgure 9. Determnaton of Frst Order Knetc Parameter for the Decrease n TBM n the Headspace of the Controls n Experment II The frst order rate constant thus estmated was found to be day --1 for the sterlzed controls and day -1 for the treatments. It may be seen that frst order rate constant for the treatments s greater than that for the controls. An ntal lag perod was observed n the case of Experment II, whch was greater for the treatments than the controls. The half lfe, whch s the tme taken for TBM to reduce to half ts ntal concentraton was found to be 15.9 days for the treatments and 19.0 days for the controls.

18 Ln(gas phase TBM concentraton/ ntal gas phase TBM concentraton) Day y = x R 2 = Fgure 10. Determnaton of Frst Order Knetc Parameter for the Decrease n TBM n the Head Space of the Treatments n Experment II ERROR BARS Three replcates (each from a dfferent mcrocosm set up at the same tme) were made for each set of treatment, control and CO 2 control sampled on a partcular day. The average values of the three replcates are plotted n the Fgures 1, 2, 3, 6, 7 and 8. The error bars show one standard devaton of the replcate values n the postve and negatve drecton from the average value. CONCLUSIONS AND RECOMMENDATIONS Conclusons Usng measured peak areas for both gas phase and lqud phase TBM, the value of Henry s constant was estmated to be 7.19x10-3 atm m 3 / gmole at 24 C. Ths value s n good agreement wth predcted values. From both sets of bodegradaton studes t was found that TBM appears to be bodegradable n sol and may be used approprately wth approprate envronmental management. In the frst set of bodegradaton studes, more than 99% of TBM dsappeared n 33 days, whch may be due to bodegradaton or chemcal reacton. In the second set of bodegradaton studes, more than 96% of TBM dsappeared n 78 days. In experment I there was no evdence of any lag phase. In both cases carbon doxde was produced and a dsulfde ntermedate was also produced. It was also observed that the sol contanng MTBE bodegradng organsms showed hgher respraton than mcrocosms wthout TBM. Ths shows

19 that the actvty of MTBE degradng mcroorgansms s enhanced by the presence of TBM and that they thrve well n the presence of TBM. Recommendatons The bodegradaton studes conducted gave some sgnfcant results on the bodegradaton of TBM. But the experment was performed n small mcrocosms usng small quanttes of TBM. Smlar study could be conducted on a large scale to understand the bodegradaton of TBM better. More effectve methods of sterlzaton of the controls could be used to confrm that only mcrobal degradaton s responsble for TBM bodegradaton n the system. Also, mcrobal plate counts can be done at the end of the study to understand the actvty of mcrobes n the sol. The mcroorgansms that showed the capacty to bodegrade TBM can be solated and further experments can be conducted to see f the same mcroorgansms are capable of bodegradng other compounds wth tertary butyl group. D-tertary-butyl dsulfde was dentfed as an ntermedate n the bodegradaton experments that were conducted. Further work can be carred to understand the pathways of degradaton of TBM and the tertary butyl group n general. LITERATURE CITED References 1. Atofna Chemcals Inc., Materal Safety Data Sheet of Tertary butyl mercaptan, Phladelpha, PA, USA, (2002). 2. Cookson, J. T., Boremedaton Engneerng, McGraw-Hll, New York (1995). 3. Ewes, J. B., S. J. Ergas, D. P. Y. Chang, and E. D. Schroeder, Boremedaton Prncples, WCB/McGraw-Hll, New York (1998). 4. Howe, G.B., M.E. Mullns, and T.N. Rogers, Evaluaton and Predcton of Henry's Law Constants and Aqueous Solubltes for Solvents and Hydrocarbon Fuel Components: Vol. I: Techncal Dscusson, Research Trangle Insttute, Tyndall Ar Force Base, Florda (1987).

20 5. Karthkeyan, R., P. Kulakow, and L. E. Erckson, Vegetated Treatment of Vehcle Wash Sedments, Proceedngs of the 28th Annual Bochemcal Engneerng Symposum [Relly, P., Edtor]. Iowa State Unversty, IA., (1998). 6. Karthkeyan, R., P. Kulakow, B. Leven, G. Perzynsk, and L. E. Erckson. Vegetated Treatment of Vehcle Wash Sedments: A Feld Demonstraton, Proceedngs of the 2000 Conference on Hazardous Waste Research [Erckson, L. E. and M. M. Rankn, Edtors]. GP/RM Hazardous Substance Research Center, 101 Ward Hall, Manhattan, KS., (2000). 7. Knox, R. C., D. A. Sabatn, and L. W. Canter, Subsurface Transport and Fate Process, Lews Publshers, Florda (1993). 8. Muraldharan, N., Envronmental and Modelng Studes on Boremedaton of Organc Contamnants n the Presence of Alfalfa Plants, M.S. Thess, Kansas State Unversty, Smth, J. M., and H. C. Van Ness, Introducton to Chemcal Engneerng Thermodynamcs, 4th ed., McGraw-Hll, New York (1987). 10. Wnnke-McMllan, S. K., Q. Zhang, L. C. Davs, L. E. Erckson, and J. L. Schnoor, Phytoremedaton of Methyl Tertary-Butyl Ether, Phytoremedaton: Transformaton and Control of Contamnants [McCutcheon, S. C. and J. L. Schnoor (Edtors)], Wley, New York, (2003). 11. Yaws, C. L., P. Bajaj, and R. W. Pke, Solublty and Henry s Law Constants for Sulfur Compounds n Water, Chemcal Engneerng, 110(8), (2003). Web Resources A. Syracuse Research Center., EPI Sute Estmaton Software, Syracuse, New York, USA.