Naphthalene Mass Transfer from a Non-Aqueous Phase Liquid (NAPL) in Rotating Baffled and Bead Mill Bioreactors

Abstract

Rotating bead mill and baffled bioreactors have earlier been shown to provide excellent mass transfer and bioremediation rates for naphthalene particulates. In this study, the mass transfer rates of naphthalene and methylnaphthalenes from NAPL into water in both the bead mill and baffled bioreactors are reported. The values of K_La ranged between 1.0 h^?1 and 42 h^?1, similar to values observed with suspended PAH particulates, increasing with bead loadings up to 50% by volume, bead size up to 5.0 mm, rotation rate up to 50 RPM, oil loading up to 72 mL (7.2% volume fraction) and naphthalene loading up to 1000 mg/L (based on the water phase). Baffled bioreactors provided similar volumetric mass transfer coefficients as bead mill bioreactors, but without the loss of working volume due to the presence of solid beads.     

Mass Transfer and Bioremediation of Naphthalene and Methyl Naphthalenes in Baffled and Bead Mill Bioreactors

Mass transfer and bioremediation of naphthalene, 2‐methylnaphthalene and 1,5‐dimethylnaphthalene have been studied in a rotating bioreactor modified with the addition of baffles and beads. Mass transfer rates of these low solubility organic particles dissolving in water (based on the working volume of the bioreactor) were highest in the bioreactor that combined beads and baffles, with the overall mass transfer coefficient (K_La) reaching up to 25 h^?1. Based on its capacity to hold the largest volume of polluted media, the simple baffled bioreactor was considered to be the optimum roller bioreactor design. Using Pseudomonas putida, the bioremediation rate of naphthalene reached 61 mg/l‐h in this vessel and using mixed substrates, the bioremediation rate of 2‐methylnaphthalene reached 30 mg/l‐h. The dissolution rates for hydrophobic particles into the culture media during the bioremediation process were up to four times higher compared to mass transfer rates into abiotic controls, which was likely due to the production of biosurfactants by P. putida.     

Bioremediation of toluene‐contaminated air using an external loop airlift bioreactor

An external loop airlift bioreactor (ELAB) has been used to capture and degrade toluene from a contaminated air stream. Using a spinning sparger, the toluene could be transferred from small, uniform bubbles into the aqueous culture media with an overall mass transfer coefficient as high as 1.1 h^?1. Due to the very volatile nature of toluene, Pseudomonas putida (ATCC 23973) was cultured and maintained on benzyl alcohol, the first intermediate compound in the metabolic degradation pathway for toluene. Consequently, before successful continuous operation of the ELAB with toluene‐contaminated air, Pseudomonas putida was acclimatized to toluene by using 30 min intermittent sparging of contaminated air into the bioreactor. Continuous sparging of toluene‐contaminated air could then be successfully carried out with 100% capture and biodegradation efficiency at a contaminated air concentration of 15 mg dm^?3 and a loading rate of 35 mg dm^?3 h^?1. Higher concentrations and loading rates were only partially degraded. Although this capture matches only the low rates reported earlier using biofilters to remediate toluene, the ELAB operates using submerged culture and requires no packing which can plug during biofilter operation. In this study, Pseudomonas putida grew on toluene at a maximum specific growth rate of only 0.05 h^?1. © 2003 Society of Chemical Industry     

BTEX removal from contaminated groundwater by a co‐culture of Pseudomonas putida and Pseudomonas fluorescens immobilized in a continuous fibrous‐bed bioreactor

A fibrous‐bed bioreactor with immobilized cells of Pseudomonas putida and Pseudomonas fluorescens was used to treat groundwater contaminated with benzene, toluene, ethylbenzene, and xylenes (collectively know as BTEX). The kinetics of BTEX biodegradation in the fibrous‐bed bioreactor operated under continuous well‐mixed conditions was studied at room temperature. Aeration was not used in the process fed with groundwater samples with an average total BTEX concentration of 2.75 mg dm^?3. All BTEX compounds present in the groundwater feed were concurrently and completely biodegraded even under oxygen‐limited or hypoxic conditions. Nearly 100% removal efficiency was obtained when the retention time was greater than 1 h. BTEX removal efficiency decreased with decreasing the retention time, with p‐ and o‐xylenes showed up first in the treated groundwater, followed by benzene and then other BTEX compounds. Biodegradation rates of BTEX generally increased with increasing BTEX concentration and loading rate. The maximum BTEX biodegradation rate was 5.76 mg h^?1 dm^?3 at the loading rate of 6.54 mg dm^?3 h^?1. The bioreactor had a stable performance, maintaining its ability for efficient BTEX degradation without requiring additional nutrients for more than 1 month. The good performance of the fibrous‐bed bioreactor was attributed to the high cell density (～15 g dm^?3 reactor volume) in the fibrous matrix. © 2002 Society of Chemical Industry     

Biodegradation of diesel oil in a baffled roller bioreactor

BACKGROUND: Ex situ bioremediation is a feasible and economical way to remove petroleum pollutants from contaminated soil or water. A baffled roller bioreactor was shown to be effective for biodegradation of diesel oil as a model petroleum pollutant. Microorganisms enriched from an industrially contaminated soil with heavy hydrocarbons were shown to be the best inoculum source for diesel biodegradation. RESULTS: The baffled roller bioreactor demonstrated better performance than control (roller bioreactor without baffles) or bead mill roller (control bioreactor filled partially with spherical beads) bioreactors. Biodegradation consisted of both fast and slow stages for degradation of light and heavy compounds, respectively. Among the tested temperatures ranging from 15 to 35 °C, room temperature (23 °C) was found to be the optimum temperature for biodegradation. The values of maximum specific growth rate and substrate yield (µ_max and Y_XS) for the indigenous microorganisms in the baffled roller bioreactor at room temperature were found to be 0.72 ± 0.08 h^?1 and (7.0 ± 1.0) × 10⁷ cells mg^?1 diesel, respectively. Biodegradation of diesel concentrations up to 200 g L^?1 was achieved with the highest biodegradation rate of 266 mg L^?1 h^?1 at the highest rotation rate of 45 rpm in the baffled roller bioreactor. CONCLUSION: Using indigenous bacteria enriched from industrial contaminated soil at room temperature, a baffled roller bioreactor is able to biodegrade high diesel oil concentrations at high biodegradation rates. Copyright © 2008 Society of Chemical Industry     

Improvement of antibiotic production by increased oxygen solubility through the addition of perfluorodecalin

A perfluorocarbon (PFC), namely perfluorodecalin, was added to fermentation medium to increase the medium's oxygen solubility. The antibiotic concentration obtained in the absence of PFC was 45 mg dm^?3, whereas it was 90 mg dm^?3 in the presence of 10% (v/v) PFC. On the other hand, biomass concentration decreased from 5.7 kg m^?3 to 2.9 kg m^?3 by adding 10% PFC. The use of PFC in the fermentation medium also reduced the formation of mycelial pellets. The values of the mass transfer coefficient, k_La, measured in the medium with PFC were found to be in the range of 122–175 h^?1 during the active growth phase which were two to three times higher than those in the medium containing no PFC. Furthermore, the maximum oxygen uptake rates obtained at the stationary phase with and without PFC were 7 mmol dm^?3 h^?1 and 4.9 mmol dm^?3 h^?1, respectively. The actual effect of PFC on actinorhodin fermentation was demonstrated by applying different operational strategies to the system. © 2001 Society of Chemical Industry     

Maximizing the production of acetone—butanol in an alginate bead fluidized bed reactor using clostridium acetobutylicum

Low volumetric solvent productivities are one of the characteristics of an acetone-butanol fermentation by C. acetobutylicum. A calcium alginate immobilized continuous culture was used in a novel gas-sparged reactor to strip the solvents from the aqueous phase and reduce their toxicity. A dilution rate of 0.07 h^?1 was found to give maximum solvent productivity at 0.58 g dm^?3 h^?1, although at 0.12 h^?1 the productivity was slightly lower. In order to increase glucose uptake by the culture, feed glucose concentrations were increased over time to attempt to acclimatize the culture. This resulted in a productivity as high as 0.72 g dm^?3 h^?1 although this production rate was found to be unstable.     

Continuous ethanol production from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor

The continuous production of ethanol from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor has been investigated. At a substrate concentration of 150 g dm^?3, maximum ethanol productivity of 16 g dm^?3 h^?1 was obtained at D = 0·4 h^?1 with 62·3% of theoretical yield and 83·6% sugars′ utilization. At a dilution rate of 0·1 h^?1, optimal ethanol productivity was achieved in the pH range 3·5–5·5, temperature range 30–35·C and initial sugar concentration of 200 g dm^?3. Maximum ethanol productivity of 24·5 g dm^?3 h^?1 was obtained at D = 0·5 h^?1 with 58·8% of theoretical yield and 85% sugars′ utilization when non-sterilized carob pod extract containing 200 g dm^?3 total sugars was used as feed material. The bioreactor system was operated at a constant dilution rate of 0·5 h^?1 for 30 days without loss of the original immobilized yeast activity. In this case, the average ethanol productivity, ethanol yield (% of theoretical) and sugars′ utilization were 25 g dm^?3 h^?1, 58·8% and 85·5%, respectively.     

The effect of a surfactant on mixer—settler operation

A single stage mixer—settler was used to investigate the effect of surfactant on the mass transfer rate in the system water—HNO₃—30 vol.% TBP/dodecane. The interfacial tension of this system first falls then rises with increasing sodium lauryl sulphate (SLS) concentration. The addition of SLS makes the stage efficiency, which is closely related to k_ha, the product of the individual mass transfer coefficient of HNO₃ in the aqueous phase, and average interfacial area per unit volume of mixing chamber, to increase significantly due to an increase in the value of a. A maximum k_ha value of 0.53 litres^?1, a minimum value of interfacial tension, and phase inversion which converted the aqueous phase from continuous to dispersed were observed at around the critical micellar concentration (100 parts 10^?6) of SLS in the system of an aqueous to organic phase ratio of 0.2.     

Kinetic modelling of lactic acid production from whey by Lactobacillus casei (NRRL B‐441)

The biomass growth, lactic acid production and lactose utilisation kinetics of lactic acid production from whey by Lactobacillus casei was studied. Batch fermentation experiments were performed at controlled pH and temperature with six different initial whey lactose concentrations (9‐77 g dm^?3) in a 3 dm³ working volume bioreactor. Biomass growth was well described by the logistic equation with a product inhibition term. In addition, biomass and product inhibition effects were defined with corresponding power terms, which enabled adjustment of the model for low‐ and high‐substrate conditions. The Luedeking‐Piret equation defined the product formation kinetics. Substrate consumption was explained by production rate and maintenance requirements. A maximum productivity of 2.5 g dm^?3 h^?1 was attained with an initial lactose concentration of 35.5 g dm^?3. Copyright © 2006 Society of Chemical Industry     

Anaerobic biodegradation of phenol in sulfide‐rich media

In the refinery industry, the washing processes of middle‐distillates using caustic solutions generate phenol‐ and sulfide‐containing waste streams. The spent caustic liquors generated contain phenols at concentrations higher than 60 g dm^?3(638.3 mmol dm^?3). For sulfur compounds, the average sulfide concentration was 48 g dm^?3(1500 mmol dm^?3) in these streams. The goal of this study was to evaluate the specific impact of phenol and sulfide concentrations towards the phenol‐biodegradation activity of a phenol‐acclimated anaerobic granular sludge. An inhibition model was used to calculate the phenol and sulfide inhibitory concentrations that completely stopped the phenol‐biodegradation activity (IC100). A maximum phenol‐biodegradation activity of 83 µmol g^?1 VSS h^?1 was assessed and the IC100 values were 21.8 mmol dm^?3 and 13.4 mmol dm^?3 for phenol and sulfide respectively. The limitation of the phenol biodegradation flow by phenol inhibition seemed to be related to the more important sensitivity of phenol‐degrading bacteria. The up‐flow anaerobic sludge bed reactor operating in a non‐phenol‐dependent inhibition condition did not present any sensitivity to sulfide concentrations below 9.6 mmol dm^?3. At this residual concentration, the pH and bisulfide ions' concentration might be responsible for the general collapsing of the reactor activity. Copyright © 2004 Society of Chemical Industry     

The dynamics of anaerobic phenol biodegradation in lower greensand

The anaerobic biodegradation of phenol in the unsaturated zone beneath landfill sites has been simulated by percolating an artificial landfill leachate containing phenol through columns of disturbed Lower Greensand. The columns were inoculated with microbes from a laboratory-scale landfill simulator. Phenol degradation was observed at concentrations up to 8.2 g dm^?3 but decomposition was increasingly inhibited above 3.0 g dm^?3. Maximum rates of decomposition were observed at concentrations between 1.5 and 3.0 g dm^?3. The V_max value at a flow rate of 0.5 cm³ h^?1 was 1.05 g dm^?3h^?1 and the K_m value was 450 mg phenol dm_?3. Zero- (r₀) and first-order (r₁) rate constants increased with increasing flow rate. The data are used to calculate the rates of phenol degradation which might be obtained in real landfill.     

High‐level production of recombinant His‐tagged rhamnulose 1‐phosphate aldolase in Escherichia coli

An expression system based on Escherichia coli and the T5 promoter allowed the overproduction of a his‐tagged rhamnulose‐1‐phosphate aldolase (RhuA; EC 4.1.2.19), an enzyme with applications in the production of deoxyazasugars and deoxysugars compounds. Shake flask and bioreactor cultivation with E coli M15 (pQErham) were performed under different media and inducing conditions for RhuA expression. A Defined Medium (DM) with glucose as carbon source gave a high volumetric and enzyme productivity (3460 AU dm^?3 and 288 AU dm^?3 h^?1 respectively) compared with Luria–Bertoni (LB) medium (2292 AU dm^? 3 and 255 AU dm^?3 h^?1). The minimum quantity of (isopropyl‐β‐D ‐thiogalactoside) IPTG for optimal induction was estimated in 18–20 µmol IPTG gDCW^?1. The highest volumetric production of RhuA (8333 AU dm^?3) was obtained when IPTG was added in the late log‐phase. No significant differences were found in specific RhuA activity for induction temperatures of 30 and 37 °C. An effective two‐step purification process comprising affinity chromatography and gel permeation has been developed (overall recovery 66.5%). These studies provide the basis for the further development of an integrated process for recombinant RhuA production suitable for biotransformation applications. Copyright © 2003 Society of Chemical Industry     

Enhancement of the overall volumetric oxygen transfer coefficient in a stirred tank bioreactor using ethanol

Ethanol was observed to improve the oxygen mass transfer rate into a well‐mixed bioreactor. The effects of impeller speed and ethanol concentration on the oxygen transfer from air to the water phase and on the average bubble diameter in a stirred tank bioreactor are reported and modelled. The results show that the oxygen mass transfer coefficient (kLa) increases from 0.002 to 0.017 s^?1 (for distilled water) due to the increase of impeller speed from 135 to 600 rpm. With increasing ethanol concentration from 0 to 8 g/L, the oxygen mass transfer coefficients increase from 0.015 to 0.049 s^?1 and from 0.017 to 0.076 s^?1, for impeller speeds of 450 and 600 rpm, respectively. The average bubble diameter decreased from 7.0 mm to 1.7 mm in pure distilled water as the impeller speed was increased from 135 to 600 rpm. When ethanol was present in the aqueous phase, the bubble diameter fell from 6.0 mm to 0.6 mm as the impeller speed was similarly increased.     

Kinetics of toluene and sulfur compounds removal by means of an integrated process involving the coupling of absorption and biodegradation

BACKGROUND: Scrubbing using an organic solution instead of an aqueous solution could be a useful way to improve the removal of hydrophobic compounds. Absorption of toluene, dimethyldisulfide (DMDS) and dimethylsulfide (DMS) in an organic solution (di‐2‐ethylhexyladipate—DEHA), followed by biodegradation by activated sludge was considered, with particular attention to kinetic aspects. DEHA was selected for its relevance in terms of absorption capacity and absorption velocity of the selected volatile organic compounds (VOCs). After the biodegradation step and owing to its cost, recycling of the VOC‐free solvent should be considered. RESULTS: Enhancement of VOC mass transfer from the organic to the aqueous phase due to bacterial activity was highlighted and the main driving force was found to be biosurfactant production rather than biodegradation reaction. However, the mass transfer rate between the two phases was shown to be lower than VOC biodegradation rate; hence, significant biodegradation of DMDS and toluene was recorded in a few days during batch experiments, 0.10 and 0.09 mmol respectively. Toluene showed higher biodegradation rates (about 0.05 and 0.10 mg h^?1 for DMDS and toluene), leading to higher growth rates. Contrarily, owing to its high volatility, important DMS losses were observed. CONCLUSION: The relevance of the proposed integrated process was shown for hydrophobic VOC removal, at least for toluene and DMDS. Unfortunately, the absorbent phase was also degraded, proved by detection of by‐products during analyses of the aqueous phase headspace. The comparison of DEHA with other solvents or solid polymers available for multiphase bioreactor applications may be a reliable option to continue this work. Copyright © 2010 Society of Chemical Industry     

Aeration and mixing in vortex fermenters

The overall apparent volumetric gas—liquid mass transfer coefficient (k₉₅a) and the mixing time (t₉₅) were determined in a 240 dm³ vortex aerated fermenter over stirrer speed and air flow ranges of 300–800 rpm and 10–45 normal dm³ min^?1, respectively. The mass transfer data obtained in an aqueous salt solution (2.5 kg m^?3 NaCl in water) compared well with the measurements in a fermentation medium used in culture of certain microaerophilic bacteria. Over the ranges examined, the gas-liquid mass transfer coefficient depended only on air flow rate; the dependence was linear with flow. Mixing time declined with increasing agitation according to a power-law relationship. The mixing and mass transfer characteristics of the vortex aerated system were compared with that of a ‘standard’ stirred tank fermenter (27 dm³). The mixing time variations with respect to agitation rate were remarkably similar for the two types of fermenters examined.     

A comparison between the performance of continuously stirred-tank bioreactors and a TORUS bioreactor with respect to highly viscous culture broths

Two different designs of stirred-tank bioreactor, the ‘conventional’ continuously stirred-tank bioreactor (CSTR, 42 dm³ and 300 dm³) and a horizontal-loop bioreactor (TORUS, 114 dm³) were used for the cultivation of Xanthomonas campestris, and their performances with respect to oxygen-transfer rates and xanthan production were compared. The strictly aerobic yeast Trichosporon cutaneum was also cultivated in the TORUS bioreactor in a synthetic medium with up to 3% (w/v) xanthan added. Xanthan solutions are pseudoplastic and therefore an apparent viscosity at a shear rate (y) of 28.8 s^?1 was used to compare the rheological behavior of the different test media. Maximal apparent viscosities of 1100mPa s were measured with xanthan concentrations between 20 and 25 g dm^?3. With apparent viscosities of up to 800 mPa s, the performance of the TORUS bioreactor was found to be equivalent to the performance of the CSTR bioreactor in terms of oxygen transfer and xanthan production rates. However, the amount of glucose converted to xanthan was greater in the TORUS bioreactor. Since the power consumption for the TORUS is lower compared to that for the CSTR, this new design is an interesting alternative to the CSTR for the production of xanthan.     

Modelling Oxygen Transfer and Aerobic Growth in Shake Flasks and Well‐Mixed Bioreactors

Oxygen transfer is an important aspect of aerobic metabolism. In this work, microbial growth on glucose (fast metabolism) and phenol (slow metabolism) have been studied using Pseudomonas putida in shake flasks and a mixed bioreactor considering both substrate and oxygen depletion. Under typical operating conditions, the highest mass transfer coefficient (K_La) for the aerated well‐mixed bioreactor was found to be 50.8 h^?1, while the maximum non‐aerated shake flask K_La was 21.1 h^?1. The presence of media and/or dead cells did not have significant effect on measured values of K_La. A new equation for prediction of K_La in shake flasks with an absolute average deviation of 11.1% is introduced, and a combined model for oxygen mass transfer and microbial growth is shown to fit experimental data during growth on glucose and phenol in both shake flasks and the mixed bioreactor with an absolute average deviation of 19.3%.     

Oxidation of ethanol vapors in a spiral bioreactor

A fixed film spiral bioreactor containing immobilized activated sludge microorganisms has been used to degrade ethanol vapors. The effect of air flow rate, and ethanol feed concentration on elimination capacity has been investigated. Air flow rate is varied in the range from 2?34 to 40?0 dm³ min^?1. Ethanol feed concentration is varied in the range from 600 to 7000 ppmv. In the concentration range studied, the elimination capacity increased proportionately with an increase in feed concentration. However, the elimination capacity decreased significantly at flow rates greater than 20 dm³ min^?1 owing to insulfficient residence time. The maximum elimination capacity observed was 185 g ethanol h^?1 m^?3 of reactor volume. Critical ethanol loading, defined as the maximum loading to achieve greater than 99% elimination at various residence times have been determined. These data are extremely useful in designing bioreactor for large scale applications.     

RDX biodegradation column study: influence of ubiquitous electron acceptors on anaerobic biotransformation of RDX

A series of column studies, with aquifer material from the former Nebraska Ordinance Plant (NOP), were performed to explore the phenomenon of electron competition from ubiquitous inorganic electron acceptors (nitrate and sulfate) present in contaminated groundwater. Acetate was used as a source of readily biodegradable carbon in all of the treatment‐column systems. Influent hexahydro‐1, 3, 5‐trinitro‐1, 3, 5‐triazine (RDX) concentrations (1–1.8 mg dm^?3) were completely removed to below detection levels of 20 µg dm^?3 in all treatment‐column systems without any nitroso‐metabolites. In the control‐column system (with no carbon amendment) significant levels (～30% of the inlet molar RDX) of nitroso‐substituted RDX derivates were observed in the effluent stream. The estimated first‐order biodegradation rate coefficient for RDX was highest (0.79 h^?1) in the treatment‐column system where acetate was the only amendment, about 52 times higher than the rate coefficient (0.015 h^?1) obtained in the control‐column system. The presence of sulfate (100 mg dm^?3) in influent groundwater temporarily delayed the onset of RDX biotransformation without any adverse effects on overall RDX biotransformation. Coexistence of low (100 mg dm^?3) nitrate levels in the influent feed water reduced the first‐order biodegradation rate coefficient obtained in the absence of nitrate by about 80% to 0.16 h^?1. These nitrate levels, however, were low to halt the RDX biodegradation probably because the available carbon levels were high enough to exceed the demands for nitrate reduction. High levels of nitrate (500 mg dm^?3) initially halted RDX removal, and significantly reduced the rate of RDX biotransformation by about 98% to 0.02 h^?1, thereby increasing the half‐life from 0.9 h in the absence of nitrate to about 32 h, with noticeable levels of untreated RDX in the effluent stream. Contrary to the expectations, the presence of ammonium in conjunction with acetate resulted in a lower (0.09 h^?1) biodegradation rate coefficient as compared with the one obtained in the absence of ammonium. Copyright © 2003 Society of Chemical Industry