A novel bioreactor for the biodegradation of inhibitory aromatic solvents: Experimental results and mathematical analysis

Biodegradation kinetics of tetrahydrofuran, benzene, toluene, and ethylbenzene as multi-substrate by Pseudomonas oleovorans DT4

The biodegradation kinetics of tetrahydrofuran, benzene (B), toluene (T), and ethylbenzene (E) were systematically investigated individually and as mixtures by a series of aerobic batch degradation experiments initiated by Pseudomonas oleovorans DT4. The Andrews model parameters, e.g., maximum specific growth rates (μmax), half saturation, and substrate inhibition constant, were obtained from single-substrate experiments. The interaction parameters in the sum kinetics model (SKIP) were obtained from the dual substrates. The μmax value of 1.01 for tetrahydrofuran indicated that cell growth using tetrahydrofuran as carbon source was faster than the growth on B (μmax, B = 0.39) or T (μmax, T = 0.39). The interactions in the dual-substrate experiments, including genhancement, inhibition, and co-metabolism, in the mixtures of tetrahydrofuran with B or T or E were identified. The degradation of the four compounds existing simultaneously could be predicted by the combination of SKIP and co-metabolism models. This study is the first to quantify the interactions between tetrahydrofuran and BTE.

Monoaromatics removal from polluted water through bioreactors-a review

Water contaminated by oil products is becoming a major problem in water supplies as these organic compounds cause hazards for human health. Different types of aerobic and anaerobic bioreactors have been widely used for water cleanup from organic pollutants such as petroleum hydrocarbons. Many studies report that aerobic biofilm processes are a very efficient method for monoaromatic hydrocarbons removal from contaminated water as they are able to reduce up to 99% of the pollutants from water, but generally these works do not discuss possible pollutant loss through gas stripping. On the other hand, some research is related to the ability of anaerobic bioreactors for monoaromatics treatment and results have shown that anaerobic immobilized reactors are able to remove monoaromatic compounds from water with maximal efficiencies between 95-99%. But here again, no data are found about the amount of volatile organic compounds that can be found in the biogas. Also, the data generated when a solid biomass support (activated carbon, polyurethane, etc.) is present in the medium do not take care about possible solute sorption phenomena. This paper reviews various properties of monoaromatic compounds including benzene, toluene, ethylbenzene and mixture of xylenes. The sources of pollutants, various analytical methods suitable for identification and quantitative measurement of monoaromatics, and knowledge gained on the true removal rates by aerobic and anaerobic bioreactors are reviewed and discussed in this study.

Substrate inhibition kinetics for toluene and benzene degrading pure cultures and a method for collection and analysis of respirometric data for strongly inhibited cultures

We present an evaluation of the qualitative and quantitative effects that high concentrations of benzene and toluene have on the growth rate of several pure cultures that use these compounds as their sole carbon and energy source. The cultures employed were five widely studied environmental isolates: Pseudomonas putida F1, P. putida mt2, P. mendocina KR, Ralstonia pickettii PKO1, and Burkholderia cepacia G4. Three cultures degraded toluene following a pattern consistent with the kinetic model of Wayman and Tseng (1976) while the other two followed a modification of this model introduced by Alagappan and Cowan (2001). The pattern followed for benzene degradation was different than that for toluene degradation for all four capable pure cultures and consistent with that described by the model of Luong (1987). Mechanisms of substrate inhibition and solvent toxicity are discussed, used to conceptually evaluate the reasons for the differences in inhibition behavior, and used to support a call for more widespread use of the empirical, terminal substrate concentration inhibition models employed here. We also present the methodology developed to overcome a limitation commonly encountered when attempting to collect oxygen uptake data for use in quantifying substrate inhibition kinetics. The experimental method was effective for use in the collection of high quality data and the substrate inhibition models most useful in representing the growth of bacteria on these solvents are those that show a complete loss of activity at high concentration rather than the more popular asymptotic inhibition models.

Kinetics of inhibition in the biodegradation of monoaromatic hydrocarbons in presence of heavy metals

The toxicity and inhibitory effects of heavy metals such as cadmium, nickel and zinc on alkylbenzene removal were evaluated with a Bacillus strain. The kinetics of alkylbenzene biodegradation with the different heavy metals at various concentrations were modeled using the Andrews equation which yielded a good fit between model and experimental data. Additional experiments undertaken with a Pseudomonas sp. in presence of nickel confirmed a good fit between experimental data and the Andrews model for this strain as well. The heavy metals inhibition constants (Ki) were calculated for different combinations of volatile organic compounds (VOC) and heavy metals. The present approach provides a method for evaluating and quantifying the inhibition effect of heavy metals on the biodegradtion of pollutants by specific microbial strains.

Biodegradation kinetics of benzene, toluene, and phenol as single and mixed substrates for Pseudomonas putida F1

Although microbial growth on substrate mixtures is commonly encountered in bioremediation, wastewater treatment, and fermentation, mathematical modeling of mixed substrate kinetics has been limited. We report the kinetics of Pseudomonas putida F1 growing on benzene, toluene, phenol, and their mixtures, and compare mathematical models to describe these results. The three aromatics are each able to act as carbon and energy sources for this strain. Biodegradation rates were measured in batch cultivations following a protocol that eliminated mass transfer limitations for the volatile substrates and considered the culture history of the inoculum and the initial substrate to inoculum mass ratio. Toluene and benzene were better growth substrates than phenol, resulting in faster growth and higher yield coefficients. In the concentration ranges tested, toluene and benzene biodegradation kinetics were well described by the Monod model. The Monod model was also used to characterize phenol biodegradation by P. putida F1, although a small degree of substrate inhibition was noted. In mixture experiments, the rate of consumption of one substrate was found to be affected by the presence of the others, although the degree of influence varied widely. The substrates are catabolized by the same enzymatic pathway, but purely competitive enzyme kinetics did not capture the substrate interactions well. Toluene significantly inhibited the biodegradation rate of both of the other substrates, and benzene slowed the consumption of phenol (but not of toluene). Phenol had little effect on the biodegradation of either toluene or benzene. Of the models tested, a sum kinetics with interaction parameters (SKIP) model provided the best description of the paired substrate results. This model, with parameters determined from one- and two-substrate experiments, provided an excellent prediction of the biodegradation kinetics for the three-component mixture.

Biodegradation of benzene, toluene, ethylbenzene, and o-xylene by a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in a fibrous-bed bioreactor

A fibrous-bed bioreactor containing the coculture of Pseudomonas putida and P. fluorescens immobilized in a fibrous matrix was developed to degrade benzene (B), toluene (T), ethylbenzene (E), and o-xylene (X) in synthetic waste streams. The kinetics of BTEX biodegradation by immobilized cells adapted in the fibrous-bed bioreactor and free cells grown in serum bottles were studied. In general, the BTEX biodegradation rate increased with increasing substrate concentration and then decreased after reaching a maximum, showing substrate-inhibition kinetics. However, for immobilized cells, the degradation rate was much higher than that of free cells. Compared to free cells, immobilized cells in the bioreactor tolerated higher concentrations (> 1000 mg l-1) of benzene and toluene, and gave at least 16-fold higher degradation rates for benzene, ethylbenzene, and o-xylene, and a 9-fold higher degradation rate for toluene. Complete and simultaneous degradation of BTEX mixture was achieved in the bioreactor under hypoxic conditions. Cells in the bioreactor were relatively insensitive to benzene toxicity; this insensitivity was attributed to adaptation of the cells in the bioreactor. Compared to the original seeding culture, the adapted cells from the fibrous-bed bioreactor had higher specific growth rate, benzene degradation rate, and cell yield when the benzene concentration was higher than 100 mg l-1. Cells in the fibrous bed had a long, slim morphology, which is different from the normal short-rod shape found for suspended cells in solution.

Production of L-DOPA(3,4-dihydroxyphenyl-L-alanine) from benzene by using a hybrid pathway

As an alternative approach to the production of L-DOPA from a cheap raw material, we constructed a hybrid pathway consisting of toluene dioxygenase, toluene cis-glycol dehydrogenase, and tyrosine phenol-lyase. In this pathway, catechol is formed from benzene through the sequential action of toluene dioxygenase and toluene cis-glycol dehydrogenase, and L-DOPA is synthesized from the resulting catechol in the presence of pyruvate and ammonia by tyrosine phenol-lyase cloned from Citrobacter freundii. When the hybrid pathway was expressed in E. coli, production of L-DOPA was as low as 3 mM in 4 h due to the toxic effect of benzene on the cells. In order to reduce lysis of cells, Pseudomonas aeruginosa was employed as an alternative, which resulted in accumulation of about 14 mM L-DOPA in 9 h, showing a stronger resistance to benzene.