Experimental Study of Biodegradation of Ethanol and Toluene Vapors

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CHAPTER SIX – CONCLUSIONS AND RECOMMENDATIONS 6.1 CONCLUSIONS The original contributions of this research are that both high and low solubility VOCs (ethanol and toluene) can readily be captured and bioremediated using a traditional CSTR. The major conclusions are presented in the order of discoveries from mass transfer studies, from bioremediation studies, and from metabolic modeling. Specific discoveries from mass transfer studies include: • Mass transfer studies indicated that ethanol was transferred from a contaminated air stream into the liquid phase of a well-mixed bioreactor completely for gas inlet concentrations up to 95.0 mg/L and air flow rates up to 2 L/min. • Toluene mass transfer studies from contaminated air into the well-mixed bioreactor indicated that the overall mass transfer coefficient increases with agitation speeds from 300 to 600 rpm, reaching a high value of 1.0x10 -3 s -1 . • Oxygen mass transfer studies showed that the presence of ethanol in the liquid phase enhances oxygen overall mass transfer coefficients, with maximum measured values of 0.049 and 0.076 s -1 at an ethanol concentration of 8g/L and agitation speeds of 450 and 600 rpm, respectively. 152
• Air stripping coefficients obtained in this study for toluene were 1000 times higher than for ethanol. The highest measured value for toluene was 12.6 h -1 at air flowrate of 2.1 L/min and agitation speed of 450 rpm. The results from bioremediation studies showed that water soluble VOCs such as ethanol that are readily consumed by bacteria can be continuously captured from contaminated air and biologically treated using a CSTR. This study also demonstrated that using Pseudomonas putida as the biological agent, toluene cannot be biodegraded as sole substrate due to toxicity and inhibition. This study revealed that a traditional CSTR is capable of appreciable removal rates of toluene from a contaminated air stream. A practical strategy to improve the removal efficiency is to use ethanol or benzyl alcohol as co-substrate and to keep the biomass at an appropriate level, resulting in high toluene removal rates. Specific discoveries from batch and continuous bioremediation studies include: • No inhibition effect of ethanol on the growth of P. putida was observed for ethanol initial concentrations up to 5.8 g/L. Growth on ethanol follows the Monod model with a maximum specific growth rate of 0.56 h -1 . • Inhibition effect of benzyl alcohol on the growth of P. putida was observed in the batch growth experiments and was modeled by the inhibition model with a maximum benzyl alcohol concentration of 2.9 g/L above which growth is completely inhibited. 153
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BIOREMEDIATION OF VOLATILE ORGANIC
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ABSTRACT The mass transfer of ethan
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effect on the growth of P. putida.
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ACKNOWLEDGMENT Of the countless peo
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TABLE OF CONTENTS PERMISSION TO USE
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4.3 Batch Growth on Ethanol and Ben
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LIST OF FIGURES Figure 3-1. Schemat
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Figure 5.3 (b) Simulation of ethano
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Figure 5-16. Continuous removal of
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NOMENCLATURE a - Interfacial area,
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CHAPTER ONE - INTRODUCTION 1.1 Air
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esults (van Groenestijn and Hesseli
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experimental results are presented
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Table 2.2 VOC Emissions in the U.S.
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(paint shop effluents, for instance
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combustion provides 70 to 90% air p
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used to degrade ethanol vapours and
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g m -3 . This would suggest that th
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treatment, This excessive biomass f
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The simultaneous degradation of tol
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emoves only water-soluble gases. Wa
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2.2.6 Pseudomonas It is well known
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2.3.2 Growth Models with Inhibition
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where µ is the total specific grow
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2.4.1 Batch Reactor In a batch reac
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discharged from the other end. The
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element solution consisted of (gram
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growth on ethanol, 20-48 hours for
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Gas phase samples of toluene were c
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Inlet sampler Exit sampler To fume
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Once the oxygen meter indicated a s
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centrifuged and the supernatant was
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where k L a is the volumetric mass
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Figure 4-2a shows ethanol liquid co
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coefficient (k L a) in the well-mix
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calculated by dividing the gas volu
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Average bubble diameter, mm 8 7 6 5
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Bioflow III bioreactor. Equation (4
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3.5 y=Ln(S0/S) 3 2.5 2 1.5 1 y = 12
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Ethanol and biomass concentration,
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4.3.2 Batch Growth on Benzyl Alcoho
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Biomass and benzyl alcohol concentr
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ethanol loading was beyond the maxi
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Table 4-2. Comparison of bioremedia
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Biomass, benzyl alcohol and toluene
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4.4.3 Toluene-ethanol Bioremediatio
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Substrate and biomass concentration
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Biomass and benzyl alcohol concentr
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Biomass and benzoic acid concentrat
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ethanol. These results clearly indi
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CHAPTER FIVE - MATHEMATICAL MODELIN
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The stoichiometry of the biomass sy
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synthesis and in the ethanol catabo
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1 max Y ex = − 0.635 + 2δ + K 3
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Biomass Eq.5-18 Benzyl Alcohol Eq.5
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r x r N -1.27 -1 0 1 0 0 -0.2 0 0 2
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φ = −θ b ⋅ν (5-31) φ b = 1.
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The data sets used to evaluate the
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Figures 5.4a and 5.4b present 95% c
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Ethanol and biomass concentration (
Page 121 and 122: Ethanol measured (C-mol/L) 0.3 0.25
Page 123 and 124: Figures 5.5 (a-d) demonstrate the s
Page 125 and 126: Benzyl alcohol and biomass concentr
Page 127 and 128: Benzyl alcohol measured (C-mol/L) 0
Page 129 and 130: x = 5 ∑ i= 1 x N i (5-40) where x
Page 131 and 132: ethanol in a steady state mode is l
Page 133 and 134: where ν 1 , ν 2 , ν 3, ν 4 are
Page 135 and 136: Biomass concentration, g/L 1.5 1 0.
Page 137 and 138: φ T =ν 4 (5-53b) φx = −ν 1 (5
Page 139 and 140: In this study, a metabolic model ha
Page 141 and 142: Equations (5-34) and (5-35) and the
Page 143 and 144: ATP 1 = Y max ATP r x + m ATP ⋅ C
Page 145 and 146: Ethanol, biomass and ammonium conce
Page 147 and 148: Figure 5-13a shows that the lower t
Page 149 and 150: Biomass, substrate concentrations,
Page 151 and 152: C e DKe = (5-63) μ − D m Equatio
Page 153 and 154: corresponds with the value associat
Page 155 and 156: Biomass and ethanol concentrations
Page 157 and 158: than 4.0 mg/L at all dilution rates
Page 159 and 160: Biomass, benzyl alcohol and ammonia
Page 161 and 162: negligible ( y out , e = 0) , and e
Page 163 and 164: Figure 5-17 shows the results at a
Page 165 and 166: Biomass Concentrations, g/L 3.5 3 2
Page 167 and 168: C x ( 1 max Q max = ⋅{ D( Cb0 −
Page 169 and 170: 1.2 g/L, the system could not be op
Page 171: The continuous models can capture a
Page 175 and 176: Toluene acts as an inhibitor on the
Page 177 and 178: Bruining, W. J., G. E. H. Joosten,
Page 179 and 180: Falatko, D. M., and J. T. Novak, 19
Page 181 and 182: Keuning, S., and D. Jager, 1994.
Page 183 and 184: Orshansky, F., and N. Narkis, 1997.
Page 185 and 186: Togna, A. P, M. Singh, 1994. “Bio
Page 187 and 188: APPENDIX A. Important Metabolic Pat
Page 189 and 190: III. Toluene Pathway (Adapted from
Page 191 and 192: Appendix B. Calibration Procedure a
Page 193 and 194: Figure B-2. Pseudomonas putida (ATC
Page 195 and 196: Appendix B-3. Calibration of Chemic
Page 197 and 198: Appendix B-4. Calibration of Toluen
Page 199 and 200: Appendix C. Experimental Results: A
Page 201 and 202: Probe response time, s 12 10 8 6 4
Page 203 and 204: Appendix C-2. Fed-batch Operation B
Page 205 and 206: Appendix D: Mathematical Solutions
Page 207 and 208: The microscopic model allows the fo
Page 209 and 210: 13δ Y o , = 0.585 2 x = (D-24) (8K
Page 211 and 212: 2 σ = −1.3E − 06 (E-11) Y xe Y
Page 213: Biomass, ethanol, and acetic acid c
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Experimental Study of Biodegradation of Ethanol and Toluene Vapors

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