Kinetics of soluble microbial product formation in substrate-sufficient batch culture of activated sludge

The kinetics of soluble microbial product (SMP) formation under substrate-sufficient conditions appear to exhibit different patterns from substrate-limited cultures. However, energy spilling-associated SMP formation is not taken into account in the existing kinetic models and classification of SMP. Based on the concepts of growth yield and energy uncoupling, a kinetic model describing energy spilling-associated SMP formation in relation to the ratio of initial substrate concentration to initial biomass concentration (S ₀/X ₀) was developed for substrate-sufficient batch culture of activated sludge, and was verified by experimental data. The specific rate of energy spilling-associated SMP formation showed an increasing trend with the S ₀/X ₀ ratio up to its maximum value. The SMP productivity coefficient (α _p/e) was defined from the model on the basis of energy spilling-associated substrate consumption. Results revealed that less than 5% of energy spilling-associated substrate consumption was converted into SMP. Electronic Publication     

The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in batch cultures

The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in batch cultures was examined, using on-line off-gas analyses to measure the oxygen and carbon dioxide consumption rates continuously. A cell suspension from continuous cultures at steady state was used as the inoculum. It was observed that a dynamic phase occurred in the initial phase of the experiment. In this phase the bacterial ferrous iron oxidation and growth were uncoupled. After about 16 h the bacteria were adapted and achieved a pseudo-steady state, in which the specific growth rate and oxygen consumption rate were coupled and their relationship was described by the Pirt equation. In pseudo-steady state, the growth and oxidation kinetics were accurately described by the rate equation for competitive product inhibition. Bacterial substrate consumption is regarded as the primary process, which is described by the equation for competitive product inhibition. Subsequently the kinetic equation for the specific growth rate, μ, is derived by applying the Pirt equation for bacterial substrate consumption and growth. The maximum specific growth rate, μ _max, measured in the batch culture agrees with the dilution rate at which washout occurs in continuous cultures. The maximum oxygen consumption rate, q _O2,max, of the cell suspension in the batch culture was determined by respiration measurements in a biological oxygen monitor at excess ferrous iron, and showed changes of up to 20% during the course of the experiment. The kinetic constants determined in the batch culture slightly differ from those in continuous cultures, such that, at equal ferric to ferrous iron concentration ratios, biomass-specific rates are up to 1.3 times higher in continuous cultures. Received: 8 February 1999 / Accepted: 17 February 1999     

Effect of phosphate and oxygen concentrations on alginate production and stoichiometry of metabolism of Azotobacter vinelandii under microaerobic conditions

Alginate production by Azotobacter vinelandii was studied in batch and continuous cultures under microaerobic conditions. In batch culture at a pO₂ of 2–3% (air saturation) alginate production was enhanced by decreasing the PO³⁻ ₄ level in the medium. Alginate yield from biomass (Y _P/X) reached the highest value of 0.66 g/g at the lowest phosphate level (100 mg/l), compared to 0.40 g/g and 0.25 g/g at higher phosphate levels (200 mg/l and 400 mg/l, respectively). In contrast, biomass formation behaved differently and the growth yield (Y _X/S) decreased with decreasing PO₄ ³⁻ concentrations. Moreover, the respiratory quotient (RQ) of the culture was dependent on the initial phosphate concentration, especially in the phosphate-limited phase of growth. As the initial phosphate level decreased from 400 mg/l to 100 mg/l, the average RQ value of the culture declined from 1.46 to 0.89. The low RQ value is very close to the theoretical optimum RQ, calculated to be 0.8 on the basis of the stoichiometry of the metabolic pathways for alginate formation from sucrose. This optimum RQ was also confirmed in continuous culture at different dilution rates. Independent of the dilution rate, a pO₂ value of 2–5% (air saturation) was found to be optimal for alginate production, the corresponding RQ values being 0.80–0.84. In addition, the molecular mass and composition of alginate were also found to be affected by both phosphate and oxygen concentrations. In conclusion, the RQ appears to be a useful parameter for optimum control of alginate production with this microorganism. Received: 31 March 1999 / Received revision: 2 July 1999 / Accepted: 5 July 1999     

The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in continuous cultures

The oxidation and growth kinetics of ferrous iron with Thiobacillus ferrooxidans in continuous cultures was examined at several total iron concentrations. On-line off-gas analyses of O₂ and CO₂ were used to measure the oxygen and carbon dioxide consumption rates in the culture. Off-line respiration measurements in a biological oxygen monitor (BOM) were used to measure directly the maximum specific oxygen consumption rate, qO₂,max, of cells grown in continuous culture. It was shown that these reproducibly measured values of qO₂,max vary with the dilution rate. The biomass-specific oxygen consumption rate, qO₂, is dependent on the ratio of the ferric and ferrous iron concentrations in the culture. The oxidation kinetics was accurately described with a rate equation for competitive ferric iron inhibition, using the value of qO₂,max measured in the BOM. Accordingly, only the kinetic constant Ks/K _i needed to be fitted from the measurements. A new method was introduced to determine the steady-state kinetics of a cell suspension in a batch culture that only takes a few hours. The batch culture was set up by terminating the feeding of a continuous culture at its steady state. The kinetic constant K _s/K _i determined in this batch culture agreed with the value determined in continuous cultures at various steady states. Received: 8 February 1999 / Accepted: 17 February 1999     

Kinetic models for astaxanthin production by high cell density mixotrophic culture of the microalga Haematococcus pluvialis

High cell density cultivation of Haematococcus pluvialis for astaxanthin production was carried out in batch and fed-batch modes in 3.7-L bioreactors with stepwise increased light intensity control mode. A high cell density of 2.65 g L⁻¹ (batch culture) or 2.74 g L⁻¹ (fed-batch culture) was obtained, and total astaxanthin production in the fed-batch culture (64.36 mg L⁻¹) was about 20.5% higher than in the batch culture (53.43 mg L⁻¹). An unstructured kinetic model to describe the microalga culture system including cell growth, astaxanthin formation, as well as sodium acetate consumption was proposed. Good agreement was found between the model predictions and experimental data. The models demonstrated that the optimal light intensity for mixotrophic growth of H. pluvialis in batch or fed-batch cultures in a 3.7-L bioreactor was 90–360 μmol m⁻² s⁻¹, and that the stepwise increased light intensity mode could be replaced by a constant light intensity mode. Received 24 December 1998/ Accepted in revised form 23 April 1999     

Degradation of 4-chlorophenol by enriched mixed cultures utilizing phenol and glucose as added growth substrate

Two mixed cultures, phenol-oxidizing (PO) and glucose-oxidizing (GO), were cultivated in two parallel chemostat reactors. The PO culture was enriched on phenol, and the GO culture was enriched on glucose. Batch biodegradation experiments were conducted to examine the degradation of 4-chlorophenol (4-CP) under various substrate conditions. The results indicate that in the absence of added growth substrate, 4-CP transformation by PO culture was complete at S _c ^o /X _o (initial 4-CP concentration/initial biomass concentration) 0.27 and that by GO culture was complete at S _c ^o /X _o = 0.09. In the presence of 5–500 mg phenol/l, the phenol dosage required to achieve the complete transformation of 4-CP was 60 mg/l at S _c ^o /X _o = 1, increasing to 120 mg/l at S _c ^o /X _o = 2, and to 180 mg/l at S _c ^o /X _o = 5. As glucose was added to the GO culture at a concentration of over 5–500 mg chemical oxygen demand (COD)/l, 4-CP was not completely transformed at S _c ^o /X _o = 5 [S _c ^o = 50 mg/l, X _o = 10 mg/l volatile suspended solids (VSS)]. These two cultures in utilizing added growth substrate were easily switched between glucose and phenol. Overall, the capacity of PO culture to degrade 4-CP, expressed as T _c (4-CP mass consumed /biomass inactivated, having unit of mg 4-CP/mg VSS), was 0.15–0.80, which compares with T _c values of 0.05–0.26 for GO culture. This work shows that adding phenol as a growth substrate is preferable over adding glucose, as it enhances 4-CP transformation, but a final choice should take into account both degradation efficiency and the risk of phenol toxicity.     

Pentachlorophenol biodegradation kinetics of an oligotrophic fluidized-bed enrichment culture

A fluidized-bed reactor (FBR) was used to enrich an aerobic chlorophenol-degrading microbial culture. Long-term continuous-flow operation with low effluent concentrations selected oligotrophic microorganisms producing good-quality effluent for pentachlorophenol(PCP)-contaminated water. PCP biodegradation kinetics was studied using this FBR enrichment culture. The results from FBR batch experiments were modeled using a modified Haldane equation, which resulted in the following kinetic constants: q _max = 0.41 mg PCP mg protein⁻¹ day⁻¹, K _S = 16 μg l⁻¹, K _i = 5.3 mg l⁻¹, and n = 3.5. These results show that the culture has a high affinity for PCP but is also inhibited by relatively low PCP concentrations (above 1.1 mg PCP l⁻¹). This enrichment culture was maintained over 1 year of continuous-flow operation with PCP as the sole source of carbon and energy. During continuous-flow operation, effluent concentrations below 2 μg l⁻¹ were achieved at 268 min hydraulic retention time (t _HR) and 2.5 mg PCP l⁻¹ feed concentration. An increase in loading rate by decreasing t _HR did not significantly deteriorate the effluent quality until a t _HR decrease from 30 min to 21 min resulted in process failure. Recovery from process failure was slow. Decreasing the feed PCP concentration and increasing t _HR resulted in an improved process recovery. Received: 10 October 1996 / Received revision: 21 January 1997 / Accepted: 24 January 1997     

Determination of the kinetic parameters during continuous cultivation of the lipase-producing thermophile Bacillus sp. IHI-91 on olive oil

A thermostable lipase was produced in continuous cultivation of a newly isolated thermophilic Bacillus sp. strain IHI-91 growing optimally at 65 °C. Lipase activity decreased with increasing dilution rate while lipase productivity showed a maximum of 340 U l⁻¹ h⁻¹ at a dilution rate of 0.4 h⁻¹. Lipase productivity was increased by 50% compared to data from batch fermentations. Up to 70% of the total lipase activity measured was associated to cells and by-products or residual substrate. Kinetic and stoichiometric parameters for the utilisation of olive oil were determined. The maximal biomass output method led to a saturation constant K _S of 0.88 g/l. Both batch growth data and a washout experiment yielded a maximal specific growth rate, μ_max, of 1.0 h⁻¹. Oxygen uptake rates of up to 2.9 g l⁻¹h⁻¹ were calculated and the yield coefficient, Y _X/O, was determined to be 0.29 g dry cell weight/g O₂. From an overall material balance the yield coefficient, Y _X/S, was estimated to be 0.60 g dry cell weight/g olive oil. Received: 8 January 1997 / Received revision: 30 April 1997 / Accepted: 4 May 1997     

An unstructured kinetic model to study NaCl effect on volatile ester fermentation by <Emphasis Type="Italic">Candida etchellsii</Emphasis> for soy sauce production

Salt-tolerant aromatic yeast is an important microorganism arising from the solid state fermentation of soy sauce. The fermentation kinetics of volatile esters by Candida etchellsii was studied in a batch system. The data obtained from the fermentation were used for determining the kinetic parameters of the model. Batch experimental results at four NaCl levels (180, 200, 220, and 240 g/L) were used to formulate the parameter estimation model. The kinetic parameters of the model were optimized by specifically designed Runge-Kutta Genetic Algorithms (GA). The resulting mathematical model for volatile ester production, cell growth and glucose consumption simulates the experimental data well. The resulting new model was capable of explaining the behavior of volatile ester fermentation. The optimized parameters (μ_o, X _max, K _i, α, β, Y _X/S, m, and Y _P/S) were characterized by a correlation of functions assuming salinity dependence. The kinetic models optimized by GA describe the batch fermentation process adequately, as demonstrated by our experimental results.     

Comparison of relative rates of BTEX biodegradation using respirometry

Biodegradation of BTEX by a microbial consortium isolated from a closed municipal landfill was studied using respirometric techniques. The kinetics of biodegradation were estimated from experimental oxygen uptake data using a nonlinear parameter estimation technique. All of the six compounds were rapidly degraded by the microbial culture and no substrate inhibition was observed at the concentration levels examined (200 mg L⁻¹ as COD). Microbial growth and contaminant degradation were adequately described by the Monod equation. Considerable differences were observed in the rates of BTEX biodegradation as seen from the estimates of the kinetic parameters. A three-fold variation was seen in the values of the maximum specific growth rate, μ_max. The highest value of μ_max was 0.389 h⁻¹ for p-xylene while o-xylene was characterized by a μ_max value of 0.14 h⁻¹, the lowest observed in this study. The half saturation coefficient, K _s, and the yield coefficient, Y, varied between 1.288–4.681 mg L⁻¹ and 0.272–0.645 mg mg⁻¹, respectively. Benzene and o-xylene exhibited higher resistance to biodegradation while toluene and p-xylene were rapidly degraded. Ethylbenzene and m-xylene were degraded at intermediate rates. In biodegradation experiments with a multiple substrate matrix, substrate depletion was slower than in single substrate experiments, suggesting an inhibitory nature of substrate interaction. Received 15 February 1998/ Accepted in revised form 5 July 1998     

Kinetic models for phycocyanin production by high cell density mixotrophic culture of the microalga Spirulina platensis

Phycocyanin production by high cell density cultivation of Spirulina platensis in batch and fed-batch modes in 3.7-L bioreactors with a programmed stepwise increase in light intensity program was investigated. The results showed that the cell density in fed-batch culture (10.2 g L⁻¹) was 4.29-fold that in batch culture (2.38 g L⁻¹), and the total phycocyanin production in the fed-batch culture (0.795 g L⁻¹) was 3.05-fold that in the batch culture (0.261 g L⁻¹). An unstructured kinetic model to describe the microalga culture system including cell growth, phycocyanin formation, as well as glucose consumption was proposed. The data fitted the models well (r ² > 0.99). Furthermore, based on the kinetic models, the potential effects of light limitation and photoinhibition on cell growth and phycocyanin formation can be examined in depth. The models demonstrated that the optimal light intensity for mixotrophic growth of Spirulina platensis in batch or fed-batch cultures using a 3.7-L bioreactor was 80160 μE m⁻² s⁻¹, and the stepwise increase in light intensity can be replaced by a constant light intensity mode. Received 28 July 1998/ Accepted in revised form 8 October 1998     

Preparation of stearoyl lactic acid ester catalyzed by lipases from Rhizomucor miehei and porcine pancreas optimization using response surface methodology

The esterification reaction between stearic acid and lactic acid using Rhizomucor miehei lipase and porcine pancreas lipase was optimized for maximum esterification using response surface methodology. The formation of the ester was found to depend on three parameters namely enzyme/substrate ratio, lactic acid (stearic acid) concentration and incubation period. The maximum esterification predicted by theoretical equations for both lipases matched well with the observed experimental values. In the case of R. miehei lipase, stearoyl lactic acid ester formation was found to increase with incubation period and lactic acid (stearic acid) concentrations with maximum esterification of 26.9% at an enzyme/substrate (E/S) ratio of 125 g mol⁻¹. In the case of porcine pancreas lipase, esterification showed a steady increase with increase in incubation period and lactic acid (stearic acid) concentration independent of the E/S ratios employed. In the case of PPL, a maximum esterification of 18.9% was observed at an E/S ratio of 25 g mol⁻¹ at a lactic acid (stearic acid) concentration of 0.09 M after an incubation period of 72 h. Received: 12 February 1999 / Received revision: 31 May 1999 / Accepted: 4 June 1999     

Cometabolic biodegradation of methyl t-butyl ether by Pseudomonas aeruginosa grown on pentane

A bacterial strain identified as Pseudomonas aeruginosa was isolated from a soil consortium able to mineralize pentane. P. aeruginosa could metabolize methyl t-butyl ether (MTBE) in the presence of pentane as the sole carbon and energy source. The carbon balance for this strain, grown on pentane, was established in order to determine the fate of pentane and the growth yield (0.9 g biomass/g pentane). An inhibition model for P. aeruginosa grown on pentane was proposed. Pentane had an inhibitory effect on growth of P. aeruginosa, even at a concentration as low as 85 μg/l. This resulted in the calculation of the following kinetic parameters (μ_max = 0.19 h⁻¹, K _s = 2.9 μg/l, K _i = 3.5 mg/l). Finally a simple model of MTBE degradation was derived in order to predict the quantity of MTBE able to be degraded in batch culture in the presence of pentane. This model depends only on two parameters: the concentrations of pentane and MTBE. Received: 16 July 1998 / Received revision: 11 November 1998 / Accepted 31 November 1998     

Repeated batch cultivation of the microalga Spirulina platensis

Summary The cultivation of photosynthetic microorganisms such as the microalga Spirulina platensis can provide an alternative source of food. The water in Mangueira Lagoon (Rio Grande do Sul state, southern Brazil) has several required nutrients for the growth of Spirulina and could be added to culture medium to reduce the cost of producing S. platensis. Although little studied, repeated batch cultivation is a very useful technique because it has a better cost–benefit ratio than other cultivation methods. In a series of runs, we studied the influence of cell concentration, renewal rate and strain on the specific growth rate and biomass productivity of S. platensis during repeated batch cultivation, the runs taking place in 2-l Erlenmeyer flasks for 2160 h at 30 °C and a light intensity of 2500 lux under a 12 h photoperiod. The three factors studied had a significant (P < 0.05) effect on the results (specific growth rate and productivity). Using Zarrouk’s medium, the highest specific growth rate (μ_X) was 0.111 day⁻¹ while the biomass productivity (P _X) was 0.0423 g l⁻¹ day⁻¹, while Mangueira Lagoon water supplemented with 10% Zarrouk’s medium gave μ_X = 0.113 day⁻¹ and a productivity P _X = 0.0467 g l⁻¹ day⁻¹. These values were two to three times higher than the results obtained in batch cultivation, indicating that the repeated batch cultivation of S. platensis is attractive and convenient.     

A novel method for characterisation of microbial growth kinetics on volatile organic compounds

A novel method for the determination of microbial growth kinetics on hydrophobic volatile organic compounds (VOC) has been developed. A stirred tank reactor was operated as a fed-batch system to which the VOC was continuously fed via the gas phase, assuring a constant VOC concentration in the mineral medium. A flow of air was saturated with the VOC, and then mixed with a further flow of air, to obtain a predetermined VOC concentration. Thus, different VOC concentrations in the mineral medium could be obtained by altering the VOC concentration in the feed gas. The growth kinetics of Xanthobacter autotrophicus GJ10 on 1,2-dichloroethane (DCE) and of Pseudomonas sp. strain JS150 on MonoChloroBenzene (MCB) were assessed using this method. The growth of strain JS150 was strongly inhibited at MCB concentrations higher than 160 mg l⁻¹, and the results were fitted using a piecewise function. The growth kinetics of strain GJ10 were described by the Luong model where maximum growth rate μ_max = 0.12 h⁻¹, substrate saturation constant K _S = 7.8 mg l⁻¹, and maximum substrate concentration S _m (above which growth is completely inhibited) = 1080 mg l⁻¹. Varying nitrogen and oxygen flows enabled the effect of oxygen concentration on the growth kinetics of Pseudomonas JS150 to be determined. Received: 30 November 1998 / Received revision: 19 March 1999 / Accepted: 20 March 1999     

Fast remediation of coal-tar-related compounds in biofilm bioreactors

The biological degradation of complex mixtures of recalcitrant substances is still a major challenge in environmental biotechnology and the remediation of coal-tar constitutes one such problem area. Biofilm bioreactors offer many advantages and may be successfully used for this purpose. Two stirred-tank reactors and one packed-bed reactor were tested in a continuous mode. Continuous cultivation allows microbial selection to take place whilst adhesive growth provides a high degradation capacity and process stability. The reactors were inoculated with mixed microbial populations to favour complete metabolism and to prevent metabolite accumulation and substrate inhibition effects. Phenol, o-cresol, quinoline, dibenzofuran, acenaphthene and phenanthrene were used as model contaminants and constituted the sole energy and carbon sources. The hydraulic retention time (HRT) was initially set to 2.5 days for a period of several months to allow the establishment of a stable biofilm and was then gradually decreased. All the compounds were found to be degraded by more than 90% at HRT of 3 h or more. Neither substrate inhibition nor metabolite accumulation effects were observed. The stirred-tank configuration was found to be the most efficient for use with high loads. No improvement in the degradation capacity could be achieved by increasing the biofilm surface in these reactors, illustrating that the limiting factor may be the mass transfer limitations rather than the availability of the biofilm surface. Finally, anaerobic treatment was successfully achieved, confirming the potential for remediation of contaminated sites under anaerobic conditions, providing that alternative electron acceptors are present. Received: 16 March 1999 / Received revision: 3 May 1999 / Accepted: 7 May 1999     

Physiology and kinetics of trimethylamine conversion by two methylotrophic strains in continuous cultivation systems

The change of dilution rate (D) on both Methylophilus methylotrophus NCIMB11348 and Methylobacterium sp. RXM CCMI908 growing in trimethylamine (TMA) chemostat cultures was studied in order to assess their ability to remove odours in fish processing plants. M. methylotrophus NCIMB11348 was grown at dilution rates of 0.012–0.084 h⁻¹ and the biomass level slightly increased up to values of D around 0.07 h⁻¹. The maximum cell production rate was obtained at 0.07 h⁻¹ corresponding to a maximum conversion of carbon into cell mass (35%). The highest rate of TMA consumption was 3.04 mM h⁻¹ occurring at D=0.076 h⁻¹. Methylobacterium sp. RXM CCMI908 was grown under similar conditions. The biomass increased in a more steep manner up to values of D around 0.06 h⁻¹. The maximum cell production rate (0.058 g l⁻¹h⁻¹) was obtained in the region close to 0.06 h⁻¹ where a maximum conversion of the carbon into cell mass (40%) was observed. The maximum TMA consumption was 2.33 mM h⁻¹ at D=0.075 h⁻¹. The flux of carbon from TMA towards cell synthesis and carbon dioxide in both strains indicates that the cell is not excreting products but directing most of the carbon source to growth. Carbon recovery levels of approximately 100% show that the cultures are carbon-limited. Values for theoretical maximum yields and maintenance coefficients are presented along with a kinetic assessment based on the determination of the substrate saturation constant and maximum growth rate for each organism. Received: 25 February 1999 / Received revision: 14 May 1999 / Accepted: 17 May 1999     

Microbial production, purification, and characterization of (S)-specific N-acetyl-2-amino-1-phenyl-4-pentene amidohydrolase from Rhodococcus globerulus K1/1

Rhodococcus globerulus K1/1 was found to express an inducible (S)-specific N-acetyl-2-amino-1-phenyl-4-pentene amidohydrolase. Optimal bacterial growth and amidohydrolase expression were both observed at about pH 6.5. Purification of the enzyme to a single band in a Coomassie blue-stained SDS-PAGE gel was achieved by nucleic acid and ammonium sulfate precipitation of Rhodococcus globerulus K1/1 crude extract and column chromatography on TSK Butyl-650(S) Fractogel and Superose 12HR. The amidohydrolase was purified to a homogeneity leading to a tenfold increase of the specific activity with a recovery rate of 65%. At pH 7.0 and 23 °C the enzyme showed no loss of activity after 30 days incubation. The amidohydrolase was stable up to 55 °C. The enzyme was inhibited strongly only by 10 mM Zn²⁺ among the tested metal cations and was inhibited 100% by 0.01 mM phenylmethanesulfonyl fluoride. The molecular weight of the native enzyme was estimated to be 92 kDa by gel filtration and 55 kDa by SDS-PAGE, suggesting a homodimeric structure. Received: 8 February 1999 / Received revision: 3 May 1999 / Accepted: 7 May 1999     

Phenol inhibition kinetics for growth of Acetobacter aceti on ethanol

Acetobacter aceti have been grown on ethanol under inhibitory conditions created by high concentrations of phenol. A defined medium with no vitamin or amino acid supplements has been used such that ethanol was the sole carbon substrate. The culture temperature was maintained at 30 °C while the pH was manually controlled to fall within the range 4.5–6.0 during ethanol consumption. Growth on ethanol at a few thousand milligrams per litre (below the known inhibitory level) resulted in a maximum specific growth rate of 0.16 h⁻¹ with a 95% yield of acetic acid, followed immediately by acetic acid consumption at a growth rate of 0.037 h⁻¹. Phenol was found to inhibit growth by decreasing both the specific growth rate and the biomass yield during ethanol consumption. On the other hand, the yield of acetic acid during ethanol consumption and the yield of biomass during acetic acid consumption remained constant, independent of phenol inhibition. A model is presented and is shown to represent the phenol-inhibited growth behaviour of A. aceti during both ethanol and acetic acid consumption. Received: 6 November 1998 / Received revision: 8 February 1999 / Accepted: 12 February 1999     

BTEX catabolism interactions in a toluene-acclimatized biofilter

BTEX substrate interactions for a toluene-acclimatized biofilter consortium were investigated. Benzene, ethylbenzene, o-xylene, m-xylene and p-xylene removal efficiencies were determined at a loading rate of 18.07 g m⁻³h⁻¹ and retention times of 0.5–3.0 min. This was also repeated for toluene in a 1:1 (m/m) ratio mixture (toluene: benzene, ethylbenzene, or xylene ) with each of the other compounds individually to obtain a final total loading of 18.07 g m⁻³h⁻¹. The results obtained were modelled using Michaelis–Menten kinetics and an explicit finite difference scheme to generate v _max and K _m parameters. The v _max/K _m ratio (a measure of the catalytic efficiency, or biodegradation capacity, of the reactor) was used to quantify substrate interactions occurring within the biofilter reactor without the need for free-cell suspended and monoculture experimentation. Toluene was found to enhance the catalytic efficiency of the reactor for p-xylene, while catabolism of all the other compounds was inhibited competitively by the presence of toluene. The toluene-acclimatized biofilter was also able to degrade all of the other BTEX compounds, even in the absence of toluene. The catalytic efficiency of the reactor for compounds other than toluene was in the order: ethylbenzene>benzene>o-xylene>m-xylene>p-xylene. The catalytic efficiency for toluene was reduced by the presence of all other tested BTEX compounds, with the greatest inhibitory effect being caused by the presence of benzene, while o-xylene and p-xylene caused the least inhibitory effect. This work illustrated that substrate interactions can be determined directly from biofilter reactor results without the need for free-cell and monoculture experimentation. Received: 13 April 2000 / Received revision: 20 July 2000 / Accepted: 27 July 2000