KINETICS OF HYDROGEN PRODUCTION FROM CONDENSED MOLASSES FERMENTATION SOLUBLES USING SEWAGE SLUDGE IN A CONTINUOUS STIRRED TANK REACTOR

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1 Sustan. Envron. Res., 1(), (11) 117 (Formerly, J. Envron. Eng. Manage.) KINETICS OF HYDROGEN PRODUCTION FROM CONDENSED MOLASSES FERMENTATION SOLUBLES USING SEWAGE SLUDGE IN A CONTINUOUS STIRRED TANK REACTOR Chn-Chao Chen, 1, * Jou-Hsen Wu, Chy-How Lay, Bswarup Sen 3 and Jo-Shu Chang 4 1 Department of Landscape Archtecture Chungchou Insttute of Technology Changhwa 51, Tawan Department of Envronmental Engneerng and Scence Feng Cha Unversty Tachung 474, Tawan 3 Mcrobal Scences Dvson Agharkar Research Insttute Pune 411 4, Inda 4 Department of Chemcal Engneerng Natonal Cheng Kung Unversty Tanan 71, Tawan Key Words: Knetcs, hydrogen producton, contnuous strred tank reactor(cstr), condensed molasses, soluble mcrobal products ABSTRACT The hydrogen producton process from condensed molasses fermentaton solubles (CMS) n a contnuous strred tank reactor usng both expermental and modelng approaches were evaluated. Seeded sludge was acclmated to enhance H producton and operaton strateges were developed. Knetc models were derved to explan and predct the knetc propertes of the hydrogen and metabolte producton. The maxmum specfc growth rate, Monod constant and yeld coeffcent for cell growth were estmated to be.33 h -1, 77 mg COD L -1, and.4 g g -1, respectvely. Knetc analyss revealed good smulaton by the model for H and metabolte productons. The major volatle fatty acds produced were butyrc acd (HBu), followed by acetc acd and proponc acd. Ethanol produced represented only 1% of HBu concentraton whch clearly ndcated that the metabolc flow durng anaerobc fermentaton favored H producton. These results ndcate that ths knetc model could be used to descrbe the balance of hydrogen yeld and process desgn for effcent hydrogen producton from CMS wastewater. INTRODUCTION Hydrogen producton va dark fermentaton s consdered one of the most effcent routes, and economcally more sutable for commercalzaton of hydrogen energy technology. The major beneft of hydrogen s that t s clean renewable energy source havng hgh specfc heat of combuston, does not contrbute to the green house effect [1,]. Use of sewage sludge to convert hexose nto hydrogen has been reported [3-6], but the cost of those substrates s expensve, and t s unrealstc to scale-up such technologes to the ndustral scale for energy producton. Therefore, some researchers have focused on the actual wastewaters,.e. saccharferous wastewater, sugar beet wastewater, bean curd wastewater, brewery wastewater, beans waste and ktchen waste to produce bohydrogen va dark fermentaton usng anaerobc mcroorgansms [7-13]. Condensed molasses fermentaton solubles (CMS) s a saccharferous wastewater whch contans some nutrent elements that are necessary for bacteral growth, mcrobal proten, amno acds, organc acds, vtamns, and coenzymes [6]. Thus, CMS s an deal substrate for producng hydrogen va dark fermentaton. Indeed, t s mportant to evaluate the knetcs of hydrogen-producton usng a contnuous strred tank reactor (CSTR) from CMS to determne the reactor *Correspondng author Emal: ccchen@dragon.ccut.edu.tw

2 118 Sustan. Envron. Res., 1(), (11) desgn crtera and descrbe the progress of contnuous dark fermentatve process. Moreover, a comprehensve knetc model may become a useful tool to assst the dentfcaton of rate-determnng factors n anaerobc hydrogen producton. H fermentaton usng carbohydrates such as dsacchardes or polysacchardes has been studed wth a knetc model earler developed by Chen et al. [14]. The model proposed was able to nterpret the expermental data and could estmate the knetc constants and suggested a lnear relatonshp of product formaton and bomass concentraton n a contnuous hydrogen producng reactor [14]. Dluton rate (D) s an mportant reactor parameter n CSTR systems. It has been found that D hgher than a crtcal value leads to bomass washout and loss of hydrogen producton [14]. However, ths crtcal value s substrate dependent and t s therefore essental to evaluate the effect of dfferent Ds on hydrogen producton performance durng dark fermentaton of CMS. The objectve of ths study was to nvestgate the effect of dfferent Ds on hydrogen yeld and soluble metabolte producton, and evaluate the knetc model proposed wth the expermental data of hydrogen producton from CMS n a CSTR for knetc constants. To our knowledge there s no report whch evaluated a knetc model to descrbe the balance of hydrogen yeld and process desgn for effcent hydrogen producton from CMS. Ths study reports both the expermental and theoretcal results for hydrogen producton from CMS n a CSTR. 1. Substrate MATERIALS AND METHODS The seed sludge was acclmated wth 4 g COD L -1 CMS (3 35 g COD L -1 d -1 ) from Vedan Corporaton Tawan. CMS s a by-product from the mcrobal fermentaton of molasses. Ths molasses wastewater contaned varous nutrents and other fermentaton products such as mcrobal proten, amno acds, organc acds, vtamns, and coenzymes [6]. No extra nutrents were added n ths experment.. Seed Sludge The seed sludge was collected from L-Mng Muncpal Sewage Treatment Plant n Tachung, Tawan. The collected sewage sludge was heated at 1 C for 45 mn to nhbt methanogenc actvty. The ph, volatle suspended solds (VSS) and total solds (TS) concentratons of the seed sludge were 6.9, 46.3 g L -1 and 7.1 g L -1, respectvely. 3. Reactor Operaton The hydrogen fermentaton was conducted n a 4 L reactor. Detals for startng-up the reactor s descrbed n the prevous work [15]. The reactor was constantly mxed at 5 rpm wth a flow level controller. The reactor was operated to reach steady state condtons at hydraulc retenton tmes (HRTs) 4-3 h (correspondng to D of.4 to.333 h -1 ). The reactor was operated at a temperature of 35 C, and the ph was controlled at 5.5. The ph value, alkalnty, gas producton and composton, volatle fatty acd (VFA) dstrbuton and solds concentraton were montored at regular ntervals. The gas volumes were corrected to standard temperature and pressure (73 K; 11 kpa). 4. Analyss Hydrogen gas was determned wth a Shmadzu (Japan) GC-14A gas chromatography equpped wth a thermal conductvty detector and an ntegrator (Shmadzu C-R3A Chromatopac). The temperatures at stanless column and njecton were 55 and 9 C, respectvely. The carrer gas used was Ar and the column was packed wth Porapak Q (8/1 mesh, Waters., USA). Detecton of VFA and ethanol were also done wth gas chromatography (Shmadzu GC-14A) usng a flame onzaton detector. The temperatures at glass column and njecton were 145 and 175 C, respectvely. The carrer gas was N and the packng materal was FON (Shmadzu, Japan). Alkalnty and VSS were measured accordng to the procedures descrbed n Standard Methods [16]. 5. Knetc s Knetc models based upon materal balances for the process components of the H producng boreactor were constructed to descrbe the steady-state behavor of organc substrate, bomass and products (H, VFA and solvents) of the sewage sludge adapted for H producton [14]. In the prevous study, a knetc model (Eqs. 1-) was reported to study the steadystate expressons for ntal substrate concentraton (S, mg COD L -1 ), D (h -1 ), bomass (X, mg L -1 ), the lqudphase (P L,I, mg COD L -1 ) and gaseous-phase products (P G,I, M) n the contnuous reactor. DKS S = (1) μ - D X = Y max S P L, P L, DKS μ max - D X/S o () = α X (3) P G, α P G, = X (4) Where P L, s the metabolc byproduct wth yeld coeffcent (α L, ) and P G, s the gaseous product wth yeld coeffcent ( α P G, ). The expermental data were used for numercal

3 Chen et al.: H Producton from CMS 119 smulatons to estmate the unknown knetc constants for cell growth (maxmum specfc growth rate, μ max, h -1 ; Monod constant, K S, mg COD L -1 ; and yeld coeffcent, Y x/s, g g -1 ) and product formaton ( αp L, andα P ). G, RESULTS AND DISCUSSION 1. Knetc Analyss of Hydrogen Producton from Condensed Molasses Solubles The expermental data from the hydrogenproducng boreactor obtaned at D = h -1 were selected to estmate the unknown knetc constants for cell growth (μ max, K S, and Y x/s ). The expermental results showed that the peak hydrogen producton rate of 39 mm H d -1 occurred at an organc loadng rate of 3 g COD L -1 d -1 correspondng to a HRT of 3 h (D =.333 h -1 ). The hydrogen producton yeld, whch s defned as the hydrogen producton per g consumed CMS COD (mol-h g -1 COD), at an HRT of 3 h was found to be 1. mmol-h g -1 COD (.9 mol-h mol -1 hexose). The parameters for growth knetcs were estmated (R =.91) as.33 h -1, 77 mg COD L -1, and.4 g g -1 for μ max, K S, and Y x/s, respectvely. The value of μ max.33 h -1 s qute smlar to the expermental data (.333 h -1 ) of ths study and the result from H fermentaton wth glucose (.345 h -1 ) [17], but lower than the μ max obtaned wth sucrose (.17 h -1 ) [14]. Strateges lke acd/heat pretreatment of actvated sludge and addton of methanogeness nhbtors have been reported to ncrease H producton and yeld. However, our results show that shfts n Ds to hgher values can also ncrease the H producton and yeld. The knetc constants can be used to shorten the HRT to 3 h, n ths study, step by step for enhancng the anaerobc hydrogen producton effcency from CMS.. Knetc analyss of yeld coeffcent of hydrogen and soluble metabolc products The major metabolc products durng the anaerobc hydrogen fermentaton of CMS were acetate (HAc), proponate (HPr), butyrate (HBu) and ethanol. A comparson of smulaton and expermental results of VFA s shown n Fg. 1. The optmal knetc constants for product formaton are lsted n Table. 1. The correlaton coeffcent values (R ) show that the knetc models were able to descrbe the expermental data satsfactorly, except for devatons n the predcton of n-hbu. The apparent yeld coeffcent, whch s estmated for gas (hydrogen) or lqud products (volatle fatty acds and solvents), s reported n terms of mol-h or mg COD g -1 CMS substrate consumed. In the present study for H the apparent yeld coeffcent ( α H ) was estmated as mol-h g -1 bomass. The yeld coeffcent ( α P L, ) for HBu was hgher than that of HAc, HPr and ethanol. Ths shows PL,I (mg COD L -1 ) HAc (model) HPr (model) Ethanol (model) n-hbu (model) HAc (data) HPr (data) Ethanol (data) n-hbu (data) D (h -1 ) Fg. 1. Effect of dfferent dluton rates (D) on soluble metaboltes producton durng fermentaton of condensed molasses solubles. Table 1. Estmated yeld coeffcents and substrate-based yelds for products resultng from H fermentaton of CMS (mg COD). Product (P L, a : mg COD L -1 ; P H b : M) Yeld coeffcent of products (α L, : mg COD g -1 bomass; α' H : mol g -1 bomass) R Substrate-base yeld (Y L, : mg COD g -1 hexose; Y H : mol-h mol -1 hexose) HAc c * HPr * n-hbu * Ethanol * H ** a P L, α L and Y L : product, yeld coeffcent and substrate-base yeld n lqud phase. b P H, α H and Y H: product, yeld coeffcent and substrate-base yeld for H. c HAc, acetc acd; HPr, proponc acd; n-hbu, normal butyrc acd.; *Y L, = α L, Y x/s **Y H = α' H Y x/s = α H η Y x/s (η = 38 ± 318)

4 1 Sustan. Envron. Res., 1(), (11) that HBu was the domnant VFA product formed durng fermentaton of CMS. Moreover, acdogenc pathway domnated the metabolc flow nstead of solventogenc pathway whch s a good ndcaton of hydrogen producng fermentatve process [18]. The rato of ethanol/total soluble metabolte was qute smaller than total VFA/total soluble metabolte n our study (data not shown). The α P L, values can be converted to substrate-based yelds ( Y P L, ) by multplyng them wth Y x/s (Table 1) [14]. Smlarly, the substrate-based yeld of the gaseous product H ( Y H ) could be obtaned by multplyng Y x/s wth the ntrnsc yeld co- effcent ( α H ), nstead of the apparent yeld coeffcent ( α H ) estmated from the model (.e., Y H = α H Y x/s ). The αh can be converted from α H f the rato (η) of gas-phase and lqud-phase dluton rate s known. When the boreactor was operated at D = h -1, the η value was relatvely stable (η = 38 ± 318), resultng n an average α H value of mol H g -1 hexose. Thus, Y H can be calculated as 1. mol H mol -1 hexose. Ths value s smlar to the Y H from H fermentaton utlzng glucose as substrate (1.8 mol-h mol -1 glucose [17]), but qute lower from sucrose (3.47 mol H mol -1 sucrose [14]). It s very remarkable that Y H from CMS s smlar to Y H from glucose, and can thus replace glucose for hydrogen producton at the ndustral scale. Ths further ensures cost reducton n runnng boreactors at large scale wth a much cheaper resource lke CMS that s abundantly and easly avalable. Estmaton of knetc constants can therefore gve an dea of the potentalty of waste resources to generate hydrogen wth hgher yeld. 3. Relatonshp between and Expermental The relatonshp between the results from knetc analyss and expermental data for dfferent dluton rates (D =.15,.167 and.5 h -1 ) s shown n Fg.. The results show the model predcton for hydrogen producton yeld at D =.15,.167 and.5 h -1 was reasonable, wth almost 9% accuracy. Contrary to the our prevous studes wth glucose and sucrose as substrate, ths study usng CMS showed less dfference n relatve concentratons of soluble metabolc products obtaned from model and experment wth ncrease of D. At D =.5 h -1, we found a good model ft of the expermental data (Fg. ) for both soluble metabolc products and H. Based on model predcton and expermental data, a lnear D-dependent relatonshp for H usng CMS wastewater was obtaned. The knetc analyss showed good smulaton of the H and lqud products formed n the boreactor. These results ndcate that ths knetc model could be used to descrbe the balance of hydrogen yeld and process desgn for eff- Relatve concentraton (%) Relatve concentraton (%) Relatve concentraton (%) (a) (b) (c) HAc HPr n-hbu Ethanol TVFA SMP H rh Fg.. Relatonshp between the knetc analyss and expermental data for soluble metaboltes formed n the boreactor fed wth condensed molasses soluble at dluton rate (a).15 h -1, (b).167 h -1 and (c).5 h -1. cent hydrogen producton from CMS wastewater. CONCLUSIONS Developed knetc model was used to ft and predct the expermental results obtaned from the H - producng CSTR operated usng acclmatzed sewage sludge and CMS as substrate. The knetcs can well smulate the H and soluble metabolte productons. The parameters for growth knetcs were estmated as.33 h -1, 77 mg COD L -1, and.4 g g -1 for μ max, K S, and Y x/s, respectvely. The correlaton coeffcent values (R >.9) show that the knetc models were able to descrbe the expermental data satsfactorly, except for devatons n the predcton of n-hbu. The model results for hydrogen producton yeld at D =.15,.167 and.5 h -1 was reasonable, wth almost 9% accuracy. In contrast to prevous results wth glucose and sucrose as substrate, ths study showed that at hgher Ds the model behaved well and gave good predcton of reactor products formed durng the anaerobc fermentaton of CMS. The knetc constants obtaned n ths study can be useful as desgn parameters for varous confguratons of boreactors producng bohydrogen from CMS and could possbly be ex-

5 Chen et al.: H Producton from CMS 11 tended to other complex waste resources also. ACKNOWLEDGMENTS The authors gratefully acknowledge the fnancal support by Tawan s Bureau of Energy (grant no. 99- D4-3) and Tawan s Natonal Scence Councl (Grants NSC 93-ET ET, E-6-6, 94-ET ET, 95-ET ET and 96-1-E MY3) and Feng Cha Unversty (9G71). REFERENCES 1. Lenssen, N. and C. Flavn, Sustanable energy for tomorrow's world: The case for an optmstc vew of the future. Energ. Polcy, 4(9), (1996).. Akano, T., Y. Mura, K. Fukatsu, H. Myasaka, Y. Ikuta, H. Matsumoto, A. Hamasak, N. Shoj, T. Mzoguch, K. Yag and I. Maeda, Hydrogen producton by photosynthetc mcroorgansms. Appl. Bochem. Bot., 57-58(1), (1996). 3. Ln, C.Y. and R.C. Chang, Hydrogen producton durng the anaerobc acdogenc converson of glucose. J. Chem. Technol. Bot., 74(6), (1999). 4. Nakamura, M., H. Kanbe and J. Matsumoto, Fundamental studes on hydrogen producton n the acd-formng phase and ts bactera n anaerobc treatment processes - The effects of solds retenton tme. Water Sc. Technol., 8(7), (1993). 5. Ln, C.Y., C.C. Chang and C.H. Hung, Fermentatve hydrogen producton from starch usng natural mxed cultures. Int. J. Hydrogen Energy, 33(1), (8) 6. Lay, C.H., J.H. Wu, C.L. Hsao, J.J. Chang, C.C. Chen and C.Y. Ln, Bohydrogen producton from soluble condensed molasses fermentaton usng anaerobc fermentaton. Int. J. Hydrogen Energy, 35 (4), (1). 7. Zhu, H., T. Suzuk, A.A. Tsygankov, Y. Asada and J. Myake, Hydrogen producton from tofu wastewater by Rhodobacter sphaerodes mmoblzed n agar gels. Int. J. Hydrogen Energy, 4(4), (1999). 8. Noke, T. and O. Mzuno, Hydrogen fermentaton of organc muncpal wastes. Water Sc. Technol., 4(1), (). 9. Ueno, Y., S. Haruta, M. Ish and Y. Igarash, Mcrobal communty n anaerobc hydrogenproducng mcroflora enrched from sludge compost. Appl. Mcrobal Bot., 57(4), (1). 1. Fang, H.H.P., H. Lu and T. Zhang, Characterzaton of a hydrogen-producng granular sludge. Botechnol. Boeng., 78(1), 44-5 (). 11. Yu, H., Z. Zhua, W. Hu and H. Zhang, Hydrogen producton from rce wnery wastewater n an upflow anaerobc reactor by usng mxed anaerobc cultures. Int. J. Hydrogen Energy, 7(11-1), (). 1. Shn, H.S. and J.H. Youn, Converson of food waste nto hydrogen by thermophlc acdogeness. Bodegradaton, 16(1), (5). 13. Hussy, I., F.R. Hawkes, R. Dnsdale and D.L. Hawkes, Contnuous fermentatve hydrogen producton from sucrose and sugar beet. Int. J. Hydrogen Energy, 3(5), (5). 14. Chen, C.C., C.Y. Ln and J.S. Chang, Knetcs of hydrogen producton wth contnuous anaerobc cultures utlzng sucrose as the lmtng substrate. Appl. Mcrobol. Bot., 57(1-), (1). 15. Wu, J.H. and C.Y. Ln, Bohydrogen producton by mesophlc fermentaton of food wastewater. Water Sc. Technol., 49(5), 3-8 (4). 16. APHA. Standard Methods for the Examnaton of Water and Wastewater. 19th Ed., Amercan Publc Health Assocaton (APHA), New York (1995). 17. Chen, C.C. and C.Y. Ln, Knetcs characterstcs of hydrogen producton wth contnuous anaerobc cultures utlzng glucose as the lmtng substrate. Asan Waterqual 3. Bangkok, Thaland, October -, pp. 46 (3). 18. Yan, R.T., Zhu C.X., Golembosk C. and J.S. Chen, Expresson of solvent-formng enzymes and onset of solvent producton n batch culture of Clostrdum butyrcum. Appl. Envron. Mcrobol., 54(3), (1988). Dscussons of ths paper may appear n the dscusson secton of a future ssue. All dscussons should be submtted to the Edtor-n-Chef wthn sx months of publcaton. Manuscrpt Receved: Aprl 3, 1 Revson Receved: August 1, 1 and Accepted: August 18, 1