Two-phase Partitioning Bioreactor Research Articles

Used tires as the partitioning phase in TPPBs (two phase partitioning bioreactors) applied to xenobiotic removal

Used tires as the partitioning phase in TPPBs (two phase partitioning bioreactors) applied to xenobiotic removal

Application of solid–liquid TPPBs to the production of L‐phenylacetylcarbinol from benzaldehyde using Candida utilis

The biotransformation of benzaldehyde and glucose to L-phenylacetylcarbinol (PAC) using Candida utilis was demonstrated in a solid-liquid two-phase partitioning bioreactor (TPPB) with the aim of reducing substrate, product, and by-product toxicity via sequestration. Previous work in the field had used octanol as the sequestering phase of liquid-liquid TPPBs but was limited by the toxic effects of octanol on C. utilis. To improve solvent selection in any future studies, the critical log P of C. utilis was determined in the current study to be 4.8 and can be used to predict biocompatible solvents. Bioavailability tests showed alkanes and alkenes to be non-bioavailable. As polymers are biocompatible and non-bioavailable, a wide range of commercially available polymers was screened and it was demonstrated that polymer softness plays a key role in absorptive capability. The polymer Hytrel G3548L was selected as the second phase to sequester benzaldehyde, PAC, and benzyl alcohol, with partition coefficients of 35, 7.5, and 10, respectively. With a 9% by volume partitioning phase, 13.6 g/L biomass of C. utilis achieved an overall PAC concentration of 11 g/L, a 1.9-fold improvement over the single-phase case. Benzyl alcohol concentration was 4.5 g/L, a 1.6-fold reduction. The volumetric productivity was 0.85 g/L h, a 1.2-fold improvement over the single-phase system. These results demonstrate a promising starting point for solid-liquid TPPBs for PAC production.

KLa measurement in two‐phase partitioning bioreactors: new insights on potential errors at low power input

AbstractBACKGROUND: Two‐phase partitioning bioreactors (TPPBs) are based on the addition of a non‐aqueous phase (NAP) to a biological process in order to overcome a limited delivery of gaseous substrates to the microorganisms in the case of compounds with low affinity for water. However, the high power input (Pg/V) required to disperse the NAP is often the major limitation for TPPB applications at full scale. Therefore, the accurate determination of the overall mass transfer coefficient (KLa) at low Pg/V values is a critical issue as these operational conditions are more attractive from a scale‐up point of view.RESULTS: NAP addition altered the typical shape of the dissolved oxygen curves used for KLa determination at the lowest Pg/V values tested (70–80 W m−3). Below a threshold Pg/V value of 600 W m−3, the presence of the NAP increased the error in KLa measurements up to 115% relative to controls deprived of NAP.CONCLUSIONS: The error in KLa measurements at low Pg/V values might be related to failures in the fundamental assumption regarding liquid phase homogeneity in the mass transfer model used. Copyright © 2010 Society of Chemical Industry

Medium composition effects on solute partitioning in solid–liquid two‐phase bioreactors

AbstractBiphasic systems such as two‐phase partitioning bioreactors (TPPBs) have been used to alleviate biological inhibition by sequestering inhibitory compounds within an immiscible phase. The use of solid polymer beads as this auxiliary phase provides a fully biocompatible alternative to potentially toxic organic solvents. While guidelines exist for the rational selection of the polymer phase, the effect of the aqueous phase composition on molecular sequestration has not been explored in the literature. This work aims to identify aspects of medium composition that influence the partitioning of target molecules into the sequestering phase. Using benzaldehyde as the target molecule and Hytrel G3548L (DuPont) as the polymer phase, pH, temperature, salt and glucose concentrations, as well as ethanol concentrations, were examined for their effects on the partition coefficient. pH and temperature were observed to have no significant effect on benzaldehyde partitioning. Salt and glucose additions increased the partition coefficient by 173% and 30%, respectively, compared with pure reverse osmosis (RO) water, while increasing ethanol concentration was found to decrease the partition coefficient from 44 ( ± 1.6) to 1 ( ± 0.3). Strategic changes to the aqueous phase can be made to improve affinity of the sequestering phase for target molecules. This provides a simple and cost‐effective method to potentially improve TPPB system performance. Copyright © 2010 Society of Chemical Industry

Biodegradation of VOC mixtures of different hydrophobicities in two‐phase partitioning bioreactors containing tailored polymer mixtures

AbstractBACKGROUND: There is a lack of systematic studies of biodegradation of mixtures of VOCs with different hydrophobicities in two‐phase partitioning bioreactors (TPPBs). The role of tailored mixtures of solid polymers on the biodegradation of MEK (low hydrophobicity), toluene (moderate hydrophobicity) and hexane (high hydrophobicity) was evaluated under steady state operation and transient loading (2‐ and 3.6‐fold 4 h step increase) in TPPBs. Two mixtures of polymer beads (A and B) were selected based on their 2 h partition coefficients for the target VOCs tested, biocompatibility and resistance to microbial attack.RESULTS: The addition of polymer mixture A (20%) into the bioreactor resulted in a severe microbial inhibition, likely due to the leaching of a polymer component, however, the presence of polymer mixture B (20%) supported removal efficiencies (REs) comparable with those recorded in the absence of polymers during steady state operation (hexane, toluene and MEK REs of 7%, 76% and 98%). However, the presence of polymer mixture B supported enhanced MEK REs during the 2‐fold step increase, and increased toluene removal during the 3.6‐fold step increase compared with the system without polymers.CONCLUSIONS: TPPBs with tailored polymer mixtures can improve process performance during VOC transient loadings, however, the interactions between the target VOCs and the solid polymers used should be a key selection criterion in order to avoid microbial inhibition during TPPB operation. Copyright © 2010 Society of Chemical Industry

Bioproduction of benzaldehyde in a solid–liquid two-phase partitioning bioreactor using Pichia pastoris

The bioproduction of benzaldehyde from benzyl alcohol using Pichia pastoris was examined in a solid-liquid two-phase partitioning bioreactor (TPPB) to reduce substrate and product inhibition. Rational polymer selection identified Elvax 40W as an effective sequestering phase, possessing partition coefficients for benzyl alcohol and benzaldehyde of 3.5 and 35.4, respectively. The use of Elvax 40W increased the overall mass of benzaldehyde produced by approx. 300% in a 5l bioreactor, relative to a single phase biotransformation. The two-phase system had a molar yield of 0.99, indicating that only minor losses occurred. These results provide a promising starting point for solid-liquid TPPBs to enhance benzaldehyde production, and suggest that multiple, targeted polymers may provide relief for transformations characterized by multiple inhibitory substrates/product/by-products.

A comparative study of solid and liquid non‐aqueous phases for the biodegradation of hexane in two‐phase partitioning bioreactors

A comparative study of the performance of solid and liquid non-aqueous phases (NAPs) to enhance the mass transfer and biodegradation of hexane by Pseudomonas aeruginosa in two-phase partitioning bioreactors (TPPBs) was undertaken. A preliminary NAP screening was thus carried out among the most common solid and liquid NAPs used in pollutant biodegradation. The polymer Kraton G1657 (solid) and the liquid silicone oils SO20 and SO200 were selected from this screening based on their biocompatibility, resistance to microbial attack, non-volatility and high affinity for hexane (low partition coefficient: K = C(g)/C(NAP), where C(g) and C(NAP) represent the pollutant concentration in the gas phase and NAP, respectively). Despite the three NAPs exhibited a similar affinity for hexane (K approximately 0.0058), SO200 and SO20 showed a superior performance to Kraton G1657 in terms of hexane mass transfer and biodegradation enhancement. The enhanced performance of SO200 and SO20 could be explained by both the low interfacial area of this solid polymer (as a result of the large size of commercial beads) and by the interference of water on hexane transfer (observed in this work). When Kraton G1657 (20%) was tested in a TPPB inoculated with P. aeruginosa, steady state elimination capacities (ECs) of 5.6 +/- 0.6 g m(-3) h(-1) were achieved. These values were similar to those obtained in the absence of a NAP but lower compared to the ECs recorded in the presence of 20% of SO200 (10.6 +/- 0.9 g m(-3) h(-1)). Finally, this study showed that the enhancement in the transfer of hexane supported by SO200 was attenuated by limitations in microbial activity, as shown by the fact that the ECs in biotic systems were far lower than the maximum hexane transfer capacity recorded under abiotic conditions.

Study of mass transfer and biocatalyst stability for the enzymatic degradation of anthracene in a two-phase partitioning bioreactor

In this study the optimal experimental conditions for the degradation of a polycyclic aromatic hydrocarbon in an enzymatic two-phase partitioning bioreactor (TPPB) were investigated. The immiscible organic phase was comprised of silicone oil, acting as a pollutant reservoir for anthracene. This compound underwent degradation by the enzyme versatile peroxidase (VP) produced by the white-rot fungus Bjerkandera adusta. Mass transfer coefficients ( k L a) and enzymatic deactivation constants ( k D) were determined in the TPPB system. The effects of operational parameters such as solvent viscosity (10, 20 and 50 cSt), agitation rate (200, 250 and 300 rpm) and addition of the non-ionic surfactant Triton X-100 (below its critical micelle concentration, CMC) on the mass transfer and enzymatic decay were investigated. It was ascertained that there was superior enzymatic stability at high values of viscosity. The addition of surfactant below CMC displayed the dual benefit of increasing mass transfer of the substrate fivefold from the organic to aqueous phase whilst also creating a protecting effect upon VP. Optimized conditions led to an 88% oxidation of anthracene after 38 h.

Two-Phase Partitioning Bioreactors Operating with Polymers Applied to the Removal of Substituted Phenols

Significant improvement in biodegradation performance has been demonstrated arising from the reduction of cytotoxicity provided by the sequestering of 4-nitrophenol (4NP) within Hytrel polymer beads added to a two-phase partitioning bioreactor (TPPB) operating in sequencing batch reactor (SBR) mode. This reduced toxicity is particularly apparent as the feed substrate concentration is increased; in fact it was shown that at a feed of 1000 mg/L 4NP, the inhibitory effect of the substrate completely prevents degradation from occurring in a single-phase system, whereas at only a 5% polymer loading, rapid and compete biodegradation is achieved. Different polymer/aqueous phase ratios were used to detoxify varying feed concentrations, and degradation rates were enhanced through the use of increased polymer loadings. As demonstrated in oxygen uptake experiments, the addition of polymers also reduces the maximum demand for oxygen, relative to single-phase operation, and smoothes the demand for oxygen throughout the degradation process. Polymer regeneration has also been further characterized by quantifying the number of methanol washes required to achieve satisfactory 4NP residuals, and the addition of a small amount of cosolvent has been shown to dramatically increase the rate of bioregeneration to produce beads ready for reuse.

Development of an original approach to evaluate effects of surfactants, biomass and pollutants on the scaling‐up of a two‐phase partitioning bioreactor

AbstractBACKGROUND: Two‐phase partitioning bioreactors (TPPBs) are considered as a new technology for xenobiotic degradation in gaseous effluents. However, there is still a need for more knowledge on how to design and scale up TPPBs. The partitioning of the two phases remains a misunderstood method of research. In particular, the impact of pollutant (isopropylbenzene), biomass and surfactant extract needs to be better evaluated.RESULTS: An adapted scale‐down apparatus has been developed in order to quantify the speed of phase partitioning (SPP) into a plug flow section. First, it was shown that isopropylbenzene (IPB) does not destabilise the system more significantly. Second, respectively 0.5 g L−1 and 0.05 g L−1 of biomass and surfactant extract, separately or in mixture, were sufficient to ensure the stability of the two‐phase system. Finally, a 100 m3 limit of scaling‐up was suggested on the basis of the circulation time comparison.CONCLUSION: The scaling up of an aqueous–silicone oil TPPB was found to be definitely conceivable when the presence of biotic compounds were considered. However, further considerations are needed to verify our assumptions, in particular by taking into account the velocity field pattern in full‐scale bioreactors and reproduce it in laboratory‐scale apparatus. Copyright © 2010 Society of Chemical Industry

Kinetics of phenol removal from saline solutions by solvent extraction coupled with degradation in a two-phase partitioning bioreactor

A combined process of solvent extraction and two-phase biodegradation was proposed to remove phenol from saline solutions by Pseudomonas putida BCRC (Bioresource Collection Research Center) 14365 at 30 °C, where kerosene was selected as the organic solvent due to its biocompatible and non-biodegradability. The saline solutions contained 100 kg/m 3 NaCl at pH 3.0 and the initial cell concentration in mineral salt medium was fixed at 25 g/m 3. The effect of initial phenol level (320–3000 g/m 3) in saline solutions on phenol removal and cell growth was experimentally studied. A simple model that combined steady mass-transfer equations and dynamic growth kinetics of suspended cells was further proposed to follow the whole process. For the convenience of kinetic modeling, the organic–aqueous interfaces remain quasi-quiescent during the process. Under the conditions studied, phenol could be completely removed from saline solutions and degraded in the aqueous cell medium within 90 h even though the initial phenol level was high up to 1850 g/m 3. It was shown that the proposed model satisfactorily described the process as long as phenol level in the cell medium did not exceed the toxicity limit of suspended cells. This model also allowed us to estimate the optimal partition coefficient for a qualified organic solution.

Bioscrubbing as a treatment for a complex mixture of volatile organic compounds: influence of the absorption column characteristics on performanceThis article is one of a selection of papers published in this Special Issue on Biological Air Treatment.

A semi-industrial bioscrubber was developed to treat a complex mixture of volatile organic compounds (VOCs), including oxygenated, aromatic, and chlorinated compounds. Packed and atomizing columns were used for the bioscrubber. For an applied inlet load of around 850–870 g VOCs·m–3 packing material·h–1, the various performances of the bioscrubber were equivalent (around 50%), regardless of the selected absorption column. Only the removal efficiency of oxygenated compounds was found to be reasonable, close to 80%–85%. For the bioscrubber equipped with an atomizing column, a doubling of the inlet load involved a decrease in the removal efficiency of the VOC mixture (35%) and oxygenated compounds (from 80% to 55%). As the transferred compounds were biodegraded, the limits could be explained by the hydrodynamic characteristics of the atomizing column. Furthermore, these results demonstrate the necessity of optimizing the gas–liquid mass transfer step. Two-phase partitioning bioreactors seem to represent an attractive option, even though knowledge of the transfer of compounds and biodegradation mechanisms is required prior to scale-up and industrial use.

Polymer-solute interactions in solid-liquid two-phase partitioning bioreactors

BACKGROUND: Biphasic systems with immiscible solvents have been studied for in situ product removal, and have shown improvements in bioreactor performance, however, problems associated with solvent biocompatibility, bioavailability and operation have been identified. One alternative is the solid–liquid system in which polymer beads are used, absorbing and removing target compounds from the aqueous phase while maintaining equilibrium conditions. This work aims to identify polymer properties that may be important in polymer selection for selected biotransformation molecules including 2-phenylethanol, cis-1,3-indandiol, iso-butanol, succinic acid and 3-hydroxybutyrolactone. RESULTS: Relatively hydrophobic compounds (e.g. 2-phenylethanol) tend to be absorbed by polymers better than hydrophilic ones (e.g. iso-butanol) based on partition coefficient tests; values as high as 80 were obtained for the former and < 3 for the latter. Owing to the presence of polar functional groups on these compounds, polar polymers such as Hytrel® performed better than non-polar ones such as Kraton®. Crystallinity and intermolecular hydrogen-bonding were also found to be important polymer properties. CONCLUSION: Polymers showed excellent results in absorbing hydrophobic compounds such as aromatic alcohols, and positive results in absorbing hydrophilic compounds but to a lesser extent. Grafting hydrophilic functional groups onto polymers may be a promising approach for extending polymer uptake capabilities and is currently being investigated. Copyright © 2009 Society of Chemical Industry

Model for a solid–liquid stirred tank two-phase partitioning bioscrubber for the treatment of BTEX

A dynamic mathematical model has been developed to predict the performance of a stirred tank, solid–liquid two-phase partitioning bioreactor (SL-TPPB) for the treatment of benzene, toluene, ethylbenzene and o-xylene (BTEX) contaminated gases. The SL-TPPB system consists of an aqueous phase containing a bacterial consortium and a solid phase of silicone rubber beads (10%; v/v) with a high affinity for BTEX compounds. The silicone rubber beads serve to sequester and release BTEX according to thermodynamic equilibrium, which increases mass transfer from the gas phase and reduces aqueous phase concentrations of these toxic compounds during fluctuating inlet loadings. The model was developed from mass balances on BTEX components in the gas, aqueous and polymer phases, and biomass in the aqueous phase. Dynamic experimental data from this system were used to fit model parameters and to assess the accuracy of the model. A detailed estimability analysis of model parameters and initial conditions was completed to identify uncertain parameters that are most influential for the model predictions and to determine the parameters and initial conditions that should be targeted for estimation using the dynamic data. It was found that the developed model, with estimated parameters and initial conditions, has the ability to predict experimental off-gas BTEX concentrations with reasonable accuracy, which are the outputs of greatest importance.

New insights on O2 uptake mechanisms in two-phase partitioning bioreactors

Numerous reports show that both transfer and uptake of poorly-water soluble substrates are significantly enhanced in two-phase partitioning bioreactors (TPPBs). A number of hypotheses have been put forward to explain these enhancements and among them, the occurrence of direct substrate or oxygen uptake from the vector/water interface has been suggested. The objective of this paper was to quantify the direct oxygen uptake from the vector/water interface in a culture of Pseudomonas putida, performed in a stirred tank reactor, using glucose as substrate and silicone oil as vector. Despite of a sufficient dissolved O(2) concentration in the vector phase (17 mg l(-1)) and a significant vector surface area (4,000 m(-1)) no significant direct O(2) uptake from the vector/water interface was observed, compared to O(2) uptake from the aqueous phase. From these results it was concluded that, direct O(2) or substrate uptake from the vector/water interface might not be significant in TPPBs.

Determining the effect of solid and liquid vectors on the gaseous interfacial area and oxygen transfer rates in two-phase partitioning bioreactors

The effect of liquid and solid transfer vectors (silicone oil and Desmopan, respectively) on the gaseous interfacial area (a(g)) was evaluated in a two-phase partitioning bioreactor (TPPB) using fresh mineral salt medium and the cultivation broth of a toluene degradation culture (Pseudomonas putida DOT-T1E cultures continuously cultivated with and without silicone oil at low toluene loading rates). Higher values of a(g) were recorded in the presence of both silicone oil and Desmopan compared to the values obtained in the absence of a vector, regardless of the aqueous medium tested (1.6 and 3 times higher, respectively, using fresh mineral salt medium). These improvements in a(g) were well correlated to the oxygen mass transfer enhancements supported by the vectors (1.3 and 2.5 for liquid and solid vectors, respectively, using fresh medium). In this context, oxygen transfer rates of 2.5 g O(2)L(-1)h(-1) and 1.3 g O(2)L(-1)h(-1) were recorded in the presence of Desmopan and silicone oil, respectively, which are in agreement with previously reported values in literature. These results suggest that mass transfer enhancements in TPPBs might correspond to an increase in a(g) rather than to the establishment of a high-performance gas/vector/water transfer pathway.

Benzene bioremediation using cow dung microflora in two phase partitioning bioreactor

Bioremediation of benzene has been carried out using cow dung microflora in a bioreactor. The bioremediation of benzene under the influence of cow dung microflora was found to be 100% and 67.5%, at initial concentrations of 100 mg/l and 250 mg/l within 72 h and 168 h respectively; where as at higher concentration (500 mg/l), benzene was found to be inhibitory. Hence the two phase partitioning bioreactor (TPPB) has been designed and developed to carryout biodegradation at higher concentration. In TPPB 5000 mg/l benzene was biodegraded up to 50.17% over a period of 168 h. Further the Pseudomonas putida MHF 7109 was isolated from cow dung microflora as potential benzene degrader and its ability to degrade benzene at various concentrations was evaluated. The data indicates 100%, 81% and 65% degradation at the concentrations of 50 mg/l, 100 mg/l, 250 mg/l within the time period of 24 h, 96 h and 168 h respectively. The GC-MS data also shows the presence of catechol and 2-hydroxymuconic semialdehyde, which confirms the established pathway of benzene biodegradation. The present research proves the potential of cow dung microflora as a source of biomass for benzene biodegradation in TPPB.

Two-phase partitioning bioreactors in environmental biotechnology

Two-phase partitioning bioreactors (TPPBs) in environmental biotechnology are based on the addition of a non-aqueous phase (NAP) into a biological process in order to overcome both mass-transfer limitations from the gas to aqueous phase and pollutant-mediated inhibitions. Despite constituting a robust and reliable technology in terms of pollutant biodegradation rates and process stability in wastewater, soil, and gas treatment applications, this superior performance only applies for a restricted number of pollutants or contamination events. Severe limitations such as high energy requirements, high costs of some NAPs, foaming, or pollutant sequestration challenge the full-scale application of this technology. The introduction of solid NAPs into this research field has opened a promising pathway for the future development of TPPBs. Finally, this work reviews fundamental aspects of NAP selection and mass transfer and identifies the niches for future research: low energy-demand bioreactor designs, experimental determination of partial mass transfers, and solid NAP tailoring.

A step-forward in the characterization and potential applications of solid and liquid oxygen transfer vectors

Silicone oil 20 and 200 cSt, a perfluorocarbon (FC40TM), heptamethylnonane, Kraton, Elvax, and Desmopan were evaluated for their ability to enhance oxygen transfer in stirred tank and airlift reactors (STR and ALR, respectively). None of the vectors tested was either toxic or biodegradable and they exhibited a moderate affinity for oxygen (gas/vector partitioning coefficients K(g)/(v) = C(g) times C(v)(-1) ranging from 3 to 5.1). FC40 was highly volatile, while KratonTM and ElvaxTM exhibited a low thermal stability, which constitutes a serious handicap for their implementation in fermentations. Silicone oil 20 cSt and Desmopan supported the highest oxygen transfer rates under abiotic conditions in both STR and ALR designs, with enhancement factors of up to 90% and 250%, respectively, compared to control tests (deprived of vector). The fact that these vectors showed the highest K (g/v) proved that, besides the classical selection criteria, the in situ hydrodynamic behavior (which affects K ( L ) a) must be considered for vector selection. The use of silicone oil 20 cSt and Desmopan in glucose-supplemented Saccharomyces cerevisiae fermentations resulted in a two- and threefold increase in biomass productions, respectively. The better performance of Desmopan in terms of biomass growth enhancement, together with the absence of the operational problems inherent to the use of liquid vectors (such as intensive foaming, high cost, and difficult solvent recovery), make solid vectors a promising and cost-effective alternative in the future developments of two-phase partitioning bioreactors.

A two‐phase partitioning airlift bioreactor for the treatment of BTEX contaminated gases

This investigation characterizes a novel 11 L airlift two-phase partitioning bioreactor (TPPB) for the treatment of gases contaminated with a mixture of benzene, toluene, ethylbenzene, and o-xylene (BTEX). The application of the TPPB technology in an airlift bioreactor configuration provides a novel technology that reduces energy intensity relative to traditional stirred tank TPPB configurations. The addition of a solid second phase of silicone rubber beads (10%, v/v) or of a liquid second phase of silicone oil (10%, v/v) resulted in enhanced performance of the airlift bioreactor relative to the single phase case, with 20% more BTEX being removed from the gas phase during an imposed transient loading. During a 4 h loading step change of three times the nominal loading (60 g m(-3) h(-1)), overall removal efficiencies for the airlift TPPBs containing a liquid or solid phase remained above 75%, whereas the single phase airlift had an overall removal efficiency of 47.1%. The airlift TPPB containing a silicone rubber second phase was further characterized by testing performance during steady-state operation over a range of loadings and inlet gas flow rates in the form of a 3(2) factorial experimental design. Optimal operating conditions that avoid oxygen limitations and that still have a slow enough gas flow rate for sufficient BTEX transfer from the gas phase to the working volume are identified. The novel solid-liquid airlift TPPB reduces energy inputs relative to stirred tank designs while being able to eliminate large amounts of BTEX during both steady-state and fluctuating loading conditions.