Substrate Loading Research Articles

Nitrile Synthesis with Aldoxime Dehydratases: A Biocatalytic Platform with Applications in Asymmetric Synthesis, Bulk Chemicals, and Biorefineries

Nitriles comprise a broad group of chemicals that are currently being industrially produced and used in fine chemicals and pharmaceuticals, as well as in bulk applications, polymer chemistry, solvents, etc. Aldoxime dehydratases catalyze the cyanide-free synthesis of nitriles starting from aldoximes under mild conditions, holding potential to become sustainable alternatives for industrial processes. Different aldoxime dehydratases accept a broad range of aldoximes with impressive high substrate loadings of up to >1 Kg L−1 and can efficiently catalyze the reaction in aqueous media as well as in non-aqueous systems, such as organic solvents and solvent-free (neat substrates). This paper provides an overview of the recent developments in this field with emphasis on strategies that may be of relevance for industry and sustainability. When possible, potential links to biorefineries and to the use of biogenic raw materials are discussed.

Large-scale ratcheting in a bacterial DEAH/RHA-type RNA helicase that modulates antibiotics susceptibility

Many bacteria harbor RNA-dependent nucleoside-triphosphatases of the DEAH/RHA family, whose molecular mechanisms and cellular functions are poorly understood. Here, we show that the Escherichia coli DEAH/RHA protein, HrpA, is an ATP-dependent 3 to 5' RNA helicase and that the RNA helicase activity of HrpA influences bacterial survival under antibiotics treatment. Limited proteolysis, crystal structure analysis, and functional assays showed that HrpA contains an N-terminal DEAH/RHA helicase cassette preceded by a unique N-terminal domain and followed by a large C-terminal region that modulates the helicase activity. Structures of an expanded HrpA helicase cassette in the apo and RNA-bound states in combination with cross-linking/mass spectrometry revealed ratchet-like domain movements upon RNA engagement, much more pronounced than hitherto observed in related eukaryotic DEAH/RHA enzymes. Structure-based functional analyses delineated transient interdomain contact sites that support substrate loading and unwinding, suggesting that similar conformational changes support RNA translocation. Consistently, modeling studies showed that analogous dynamic intramolecular contacts are not possible in the related but helicase-inactive RNA-dependent nucleoside-triphosphatase, HrpB. Our results indicate that HrpA may be an interesting target to interfere with bacterial tolerance toward certain antibiotics and suggest possible interfering strategies.

Enzymatic Hydrolysis and Fermentation of Banana Pseudostem Hydrolysate to Produce Bioethanol.

Banana pseudostem (BPS) is an agricultural waste with a high holocellulose content, which, upon hydrolysis, releases fermentable sugars that can be used for bioethanol production. Different pretreatment methods, namely, 3% (w/v) NaOH, 5% (v/v) H2SO4, and liquid hot water, applied on the BPS resulted in the availability of 52%, 48%, and 25% cellulose after treatment, respectively. Saccharification of the pretreated BPS with 10 FPU/g dry solids (29.3 mg protein/g d.s) crude enzyme from Trichoderma harzianum LMLBP07 13-5 at 50°C and a substrate loading of 10 to 15% released 3.8 to 21.8 g/L and from T. longibrachiatum LMLSAUL 14-1 released 5.4 to 43.5 g/L glucose to the biomass. Ethanol was produced through separate hydrolysis and fermentation (SHF) of alkaline pretreated BPS hydrolysate using Saccharomyces cerevisiae UL01 at 30°C and 100 rpm. Highest ethanol produced was 17.6 g/L. Banana pseudostem was shown as a potentially cheap substrate for bioethanol production.

High metabolic substrate load induces mitochondrial dysfunction in rat skeletal muscle microvascular endothelial cells.

The influence of glucose and palmitic acid (PA) on mitochondrial respiration and emission of hydrogen peroxide (H2O2) was determined in skeletal muscle‐derived microvascular endothelial cells. Measurements were assessed in intact and permeabilized (cells treated with 0.025% saponin) low passage endothelial cells with acute‐or prolonged (3 days) incubation with regular (1.7 mM) or elevated (2.2 mM) PA concentrations and regular (5 mM) or elevated (11 mM) glucose concentrations. In intact cells, acute incubation with 1.7 mM PA alone or with 1.7 mM PA + 5 mM glucose (p < .001) led to a lower mitochondrial respiration (p < 0.01) and markedly higher H2O2/O2 emission (p < 0.05) than with 5 mM glucose alone. Prolonged incubation of intact cells with 1.7 mM PA +5 mM glucose led to 34% (p < 0.05) lower respiration and 2.5‐fold higher H2O2/O2 emission (p < 0.01) than incubation with 5 mM glucose alone. Prolonged incubation of intact cells with elevated glucose led to 60% lower (p < 0.05) mitochondrial respiration and 4.6‐fold higher H2O2/O2 production than incubation with 5 mM glucose in intact cells (p < 0.001). All effects observed in intact cells were present also in permeabilized cells (State 2). In conclusion, our results show that acute and prolonged lipid availability, as well as prolonged hyperglycemia, induces mitochondrial dysfunction as evidenced by lower mitochondrial respiration and enhanced H2O2/O2 emission. Elevated plasma substrate availability may lead to microvascular dysfunction in skeletal muscle by impairing endothelial mitochondrial function.

Purification and Characterization of Nit phym , a Robust Thermostable Nitrilase From Paraburkholderia phymatum.

Despite the success of some nitrilases in industrial applications, there is a constant demand to broaden the catalog of these hydrolases, especially robust ones with high operational stability. By using the criteria of thermoresistance to screen a collection of candidate enzymes heterologously expressed in Escherichia coli, the enzyme Nitphym from the mesophilic organism Paraburkholderia phymatum was selected and further characterized. Its quick and efficient purification by heat treatment is of major interest for large-scale applications. The purified nitrilase displayed a high thermostability with 90% of remaining activity after 2 days at 30°C and a half-life of 18 h at 60°C, together with a broad pH range of 5.5–8.5. Its high resistance to various miscible cosolvents and tolerance to high substrate loadings enabled the quantitative conversion of 65.5 g⋅L–1 of 3-phenylpropionitrile into 3-phenylpropionic acid at 50°C in 8 h at low enzyme loadings of 0.5 g⋅L–1, with an isolated yield of 90%. This study highlights that thermophilic organisms are not the only source of industrially relevant thermostable enzymes and extends the scope of efficient nitrilases for the hydrolysis of a wide range of nitriles, especially trans-cinnamonitrile, terephthalonitrile, cyanopyridines, and 3-phenylpropionitrile.

Phase field study on the effect of substrate elasticity on tip-force-induced domain switching in ferroelectric thin films

Tip-force-induced domain switching in ferroelectrics has recently attracted extensive interest as it provides an alternative switching strategy that might ease the problems brought by electrical switching. From the viewpoint of mechanics, substrate elasticity can largely modify the tip-induced deformation of ferroelectric thin films. However, so far, discussions on the influence of substrate elastic properties on such domain switching still remain exclusive. Here, a phase-field model is employed to study the influence of substrate stiffness on the domain switching in BaTiO3 (BTO) thin films, with the strain and stress distributions in BTO thin films and substrates solved by the finite element method. The results demonstrate that the substrate stiffness and loading modes (i.e., pressing and sliding) have a great influence on the symmetry of strain and stress distributions. The switched domain size is highly dependent on the substrate stiffness and loading modes. The switching is more efficient for thin films on a softer substrate. Moreover, the domain could be switched more effectively by the sliding mode under relatively large forces. Our study thus provides a strategy to increase the mechanical switching efficiency of ferroelectric thin films via tuning the substrate elasticity.

Front Cover: Transacylation Kinetics in Fatty Acid and Polyketide Synthases and its Sensitivity to Point Mutations (ChemCatChem 12/2021)

The Front Cover shows an example of polyketide synthases, producing complex products from simple substrates, in which the acyl transferase (AT) selects substrates from the bulk cytoplasm. Subsequently, the substrates are transferred by the acyl carrier protein (ACP) robotic arm to the catalytic domains KS, KR, DH, ER forcondensation and processing. Secondary metabolite biosynthetic pathways often proceed separately from the housekeeping functions of a cell. Compartmentalization is achieved by enzyme kinetic phenomena that may rely on dedicated protein architecture and physical proximity. The substrates and cofactors for secondary metabolite biosynthetic pathways are at least partly shared with primary metabolism, and questions remain how resources are distributed among primary and secondary metabolisms. In their Full Paper, F. Stegemann and M. Grininger analyze the process of substrate loading in enzyme kinetic detail, in its substrate selectivity and in its protein-protein interaction. More information can be found in the Full Paper by F. Stegemann and M. Grininger.

Anaerobic Digestion of Industrial Tempeh Wastewater with Sludge from Cow Manure Biogas Digester as Inoculum: Effect of F/M Ratio on the Methane Production

Industrial tempeh wastewater contains high organic compounds that will negatively affect the water ecosystem's quality whenever discharged without proper treatments. Biological treatment, in particular, anaerobic digestion, is the potential to be an effective solution for eliminating that contaminant. Considering its advantages, especially to produce methane gas, a study to evaluate the anaerobic digestion process's performance to reduce the organic substances in industrial tempeh wastewater was conducted. Sludge from cow manure biogas digester was used as inoculum to foster an anaerobic decomposition process. Hence the particular focus was given to elaborate the effect of F/M ratio on methane production. With a practical volume of 4L each, controlled batch reactors were employed with several operational parameters (pH, COD, VFAs) to be monitored to understand the process. Results elucidated that methane production was closely related to the composition of the substrate to microorganism. The maximum methane production (8720 mL) followed by the highest organic reduction (67.7%) were found in F/M = 1.12. The measured operational parameters informed a sequence of the process involved in the complete anaerobic decomposition. Accumulation of VFAs, because of higher substrate loading, tended to hamper methanogens metabolism resulted in low methane production. In addition to that, inoculum from biogas digester of cow manure was proved to play a significant role in the anaerobic decomposition for industrial tempeh wastewater. This finding is essential for arranging an effective yet low-cost wastewater treatment for tempeh producers, which is a basis for further study.

Directional Selection of Microbial Community Reduces Propionate Accumulation in Glycerol and Glucose Anaerobic Bioconversion Under Elevated pCO2.

Volatile fatty acid accumulation is a sign of digester perturbation. Previous work showed the thermodynamic limitations of hydrogen and CO2 in syntrophic propionate oxidation under elevated partial pressure of CO2 (pCO2). Here we study the effect of directional selection under increasing substrate load as a strategy to restructure the microbial community and induce cross-protection mechanisms to improve glucose and glycerol conversion performance under elevated pCO2. After an adaptive laboratory evolution (ALE) process, viable cell density increased and predominant microbial groups were modified: an increase in Methanosaeta and syntrophic propionate oxidizing bacteria (SPOB) associated with the Smithella genus was found with glycerol as the substrate. A modest increase in SPOB along with a shift in the predominance of Methanobacterium toward Methanosaeta was observed with glucose as the substrate. The evolved inoculum showed affected diversity within archaeal spp. under 5 bar initial pCO2; however, higher CH4 yield resulted from enhanced propionate conversion linked to the community shifts and biomass adaptation during the ALE process. Moreover, the evolved inoculum attained increased cell viability with glucose and a marginal decrease with glycerol as the substrate. Results showed differences in terms of carbon flux distribution using the evolved inoculum under elevated pCO2: glucose conversion resulted in a higher cell density and viability, whereas glycerol conversion led to higher propionate production whose enabled conversion reflected in increased CH4 yield. Our results highlight that limited propionate conversion at elevated pCO2 resulted from decreased cell viability and low abundance of syntrophic partners. This limitation can be mitigated by promoting alternative and more resilient SPOB and building up biomass adaptation to environmental conditions via directional selection of microbial community.

Interactions between calcium carbonate and ammonium polyphosphate in low‐borate concentration hydrocarbon intumescent coatings

SummaryFor high performance of hydrocarbon intumescent coatings, interactions between the acid source ammonium polyphosphate (APP) and inorganic fillers can be critical. In the present work, low‐borate concentration (ie, 1 wt% zinc borate) intumescent coatings with different concentration ratios of CaCO3 to APP were studied in an attempt to map the reaction mechanisms. The analysis of the coating performance was conducted using thermal insulation assessment according to the UL1709 fire curve (disregarding substrate load, geometrical diversity, and other full‐scale implications of the complete standard), rheological measurements, thermogravimetric analyses, attenuated total reflection‐Fourier transform infrared spectrometer (ATR‐FTIR), and X‐ray diffraction. Results show that a coating with a CaCO3/APP mass ratio of 0.3 gives the best performance (ie, the longest critical time of steel substrates to reach both 400 and 550°C in the thermal insulation assessment). The dependency on the CaCO3/APP ratio of the dynamic viscosity minimum points to significant interactions between CaCO3 and APP during the softening state (ie, the intumescence process) of the coating. Due to an enhanced anti‐oxidation property, the degradation zone of the intumescent char and the residual weight of the coating after exposure were both improved when increasing the CaCO3/APP ratio. The compositional development of the intumescent char showed that CaCO3 and APP react to form a new polymeric phase, calcium catena‐polyphosphate (CaP2O6). This polyphosphate may contribute to the formation of a compact phase in the intumescent char and benefit the thermal insulation performance of low‐borate concentration hydrocarbon intumescent coatings.

Optimization of sugar production from Durian seeds via alkaline hydrolysis for second-generation bioethanol production

Abstract As one way to eliminate the issues found in the preceding generation, feedstock exploration in second-generation bioethanol production remains an issue, especially for a tropical country such as Indonesia. From exotic fruit by-products, durian holds a promising perspective that rests on its abundance, superb carbohydrate content and limited usage until now. This work presents the first-ever utilization of durian seeds for sugar production under optimized conditions through alkaline hydrolysis. A simple form of sugar was extracted by varying four parameters, namely substrate loading, NaOH concentration, hydrolysis time and hydrolysis temperature. Response surface methodology based on the Box-Behnken design was employed to outline the most optimum parameter values. Analysis of variance revealed that the quadratic model fit the data appropriately with the order of significance as substrate loading &amp;gt; hydrolysis time &amp;gt; NaOH concentration &amp;gt; hydrolysis temperature. The optimized conditions for reducing sugar yield, as high as 2.140 g/L, corresponded to &amp;lt;50 g/L substrate loading, 0.522 M NaOH, 60 minutes of hydrolysis time and 80oC hydrolysis temperature. The possible ethanol content of 1.094 g/L was also expected under optimized conditions, demonstrating great potential in second-generation bioethanol production. Second-generation bioethanol production from a non-edible feedstock (durian seeds) is optimized by varying key parameters in the alkaline hydrolysis process, showing high yields of fermentable sugars.

Effect of molecular structure of cation and anions of ionic liquids and co-solvents on selectivity of 5-hydroxymethylfurfural from sugars, cellulose and real biomass

The concept of biorefinery still requires advancements in process development for energy and materials. Ionic liquids have been successfully used for several biorefinery applications including high yield synthesis of biofuels and value added platform chemicals. Designing suitable ionic liquid that is efficient in terms of cost as well as product selectivity is still highly needed. This study is carried out to check the effect of different anions of Bronsted acidic ionic liquids (BAILs), Bronsted Lewis acidic ionic liquids (BLAILs), Lewis acidic ionic liquids (LAILs) as well as organic electrolyte solutions (OES) for 5-HMF selectivities from monosaccharides, polysaccharides as well as lignocellulosic composite. Different variables and parameters such as Lewis acidity of anions, alkyl side chain of ionic liquid, metal chloride type and loading, time, temperature, substrate loading, polar protic and aprotic solvents are thoroughly studied for process optimization. Polar protic solvents added in [C1C4SO3HPy] based ionic liquids with CH3COO− and Cl− anions yielded 94 and 80% 5-HMF from fructose and glucose respectively in the presence of AlCl3 as Lewis acid. C4SO3H side chain yielding high from fructose and glucose is inefficient for conversion of cellulose and lignocellulose. High product selectivity from these biopolymers is achieved using butyl side chain with 3-methylpyridinium cation and chlorochromate anion.

Integration of natural deep-eutectic solvent and surfactant for efficient synthesis of chiral aromatic alcohol mediated by Cyberlindnera saturnus whole cells

Efficiency of whole-cell biocatalysis in aqueous buffer solution is mainly limited by the low cellular membrane permeability and poor solubility of hydrophobic non-natural substrate. In this study, highly efficient bioreduction of 3,5-bis(trifluoromethyl)acetophenone (BTAP) to (S)-1-[3,5-bis(trifluoromethyl)phenyl]ethanol ((S)-BTPE) with excellent enantioselectivity (> 99.9 % ee) by a novel yeast isolate Cyberlindnera saturnus ZJPH1807 was achieved via a integrated strategy of natural deep-eutectic solvent (NADES) and surfactant. The introduction of L-carnitine: lysine (C:Lys, molar ratio 1:2) in the reaction medium improved cell membrane permeability effectively and relieved BTAP toxicity to the cells. The Tween-80 addition further accelerated catalytic yield by increasing solubility of BTAP for 7.6-fold compared with neat aqueous buffer solution. After the optimization of key reaction parameters, a 81.0 % yield within 24 h under 500 mM substrate loading was achieved in the established C:Lys/Tween-80-containing system, compared with a 76.4 % yield for 30 h in aqueous buffer system under 200 mM BTAP concentration. This biocatalytic process was also feasible at 500 mL preparation scale with a 79.7 % (S)-BTPE yield under 500 mM BTAP. The developed combinational strategy of NADES with surfactant is an effective approach for enhancing bioreductive efficiency of hydrophobic substrates mediated by whole-cell catalyst, and has great potential in biocatalysis.

Effect of solid loading on the behaviour of pectin-degrading enzymes

BackgroundPectin plays a role in the recalcitrance of plant biomass by affecting the accessibility of other cell wall components to enzymatic degradation. Elimination of pectin consequently has a positive impact on the saccharification of pectin-rich biomass. This work thus focused on the behaviour of different pectin-degrading enzymes in the presence of low (5%) to high (35%) solid loading of lemon peel.ResultsHigh solid loading of lemon peel affected pectin solubilisation differently depending on the pectinase used. Pectin lyase was less sensitive to a reduction of water content than was a mixture of endopolygalacturonase and pectin methylesterase, regardless of whether or not the latter's mode of action is processive or not. Marked changes in water mobility were observed along with enzymatic degradation depending on the enzyme used. However, the pectin lyase resulted in less pronounced shifts in water distribution than polygalacturonase–pectin methylesterase mixtures. At similar pectin concentration, pectin solutions hindered the diffusion of hydrolases more than the solid substrate. This can be attributed to the high viscosity of the highly concentrated pectin solutions while the solid substrate may provide continuous diffusion paths through pores.ConclusionsThe increase in solid substrate loading reduced the efficiency of pectin-degrading enzymes catalysing hydrolysis more significantly than those catalysing β-elimination. LF-NMR experiments highlighted the impact of solid loading on water mobility. Compared to other enzymes and whatever the solid loading, pectin lyase led to longer relaxation times linked with the most destructuration of the solid substrate. This new information could benefit the biorefinery processing of pectin-rich plant material when enzymes are used in the treatment.

Anaerobic co-digester microbiome during food waste valorization reveals Methanosaeta mediated methanogenesis with improved carbohydrate and lipid metabolism

This study determines the optimum food waste (FW) loading in an anaerobic digester for methane production. Interrelation between the degradation mechanism and microbial community composition was assessed through in-depth metabolic pathway analysis and gene quantification. Higher methane production and short lag phase were observed in the FW reactors with low substrate loadings (<4% v/v) while extended lag phase and incomplete substrate utilization were observed in the reactors fed with higher substrates (>6% v/v). The long-chain fatty acids (LCFAs) degradation was influenced by initial FW loading, and up to 99% LCFA degradation occurred at 4% FW reactor. The addition of 8 to 10% FW substrate inhibited methanogenesis due to the accumulation of volatile fatty acids (VFA) and low LCFA degradation. Under optimal conditions of substrate loading, Methanosaeta and Methanosarcina were abundant, indicating their role in methanogenesis and syntrophic acetogenesis, along with enhanced metabolic pathways specific for carbohydrate and lipid metabolism.

High-titer bio-succinic acid production from sequential alkalic and metal salt pretreated empty fruit bunch via simultaneous saccharification and fermentation

Bio-succinic acid is produced from inorganic salt pretreated oil palm empty fruit bunch (OPEFB) for the first time through simultaneous saccharification and fermentation (SSF). OPEFB is an agriculture waste that can be converted into succinic acid (SA) which is a high value added product sought after in the chemical industry. In this study OPEFB is pretreated using sequential inorganic salt (sodium phosphate dodecahydrate and zinc chloride) before undergoing SSF using Actinobacillus succinogenes ATCC 55618. Parameters that influenced the SA production such as substrate loading, inoculum size and enzyme loading are investigated using design of experiments. The results revealed that biomass loading and enzyme loading have significant impact in SA yield. Under condition of 100 g/L biomass, 5% inoculum and cellulase enzyme 40 FPU/g OPEFB, maximum concentration of SA (65.2 g/L) and yield (0.65 g/g OPEFB) are obtained. Subsequently the model developed for predicting SA production has been successfully validated.

High-solid digestion from cellulosic ethanol stillage with activated sludge of simultaneous propionate degradation and methanogenesis

High solid anaerobic digestion (HSAD) was an emerging bioconversion technology which had the advantages of small digester, less digestate and low heating energy. A one-stage anaerobic system in CSTR by inoculating activated sludge of simultaneous propionate degradation and methanogenesis was proposed to improve the high-solid digestion performance and to stabilize the reaction process. Semi-continuous mode was successfully used to perform HSAD from cellulosic ethanol whole stillage at an initial substrate loading of 15.4% (w/w) dry matter content with different OLRs from 1.5 to 5.0 gVS·L−1 d−1 at an HRT of 30 days. The average methane yield during whole digestion reached 349.9 mL⋅gVS−1 with a total VS removal rate of 61.3%. The acclimation mechanism of multifunctional activated sludge was also explored by analyzing the functional property, physiological activity and microbial community structure. The results indicated the feasibility and efficiency of multifunctional activated sludge in a semi-continuous high-solid stirred tank reactor system.

Box–Behnken experimental design for the optimization of enzymatic saccharification of wheat bran

Lignocellulosic raw materials have been widely studied for obtaining bioproducts. Pretreatments for delignification, uncertainties in feedstock composition, long hydrolysis times, and large quantities of expensive enzymes are factors that limit fermentable sugar production. Statistical optimization can help adjust these limiting factors and variables of enzymatic saccharification. This study aimed to optimize conditions for fermentable sugar production using wheat bran, Botrytis ricini URM 5627 endoglucanase, and Box–Behnken experimental design, a response surface methodology. A zymographic assay in polyacrylamide gel was stained with Congo red after hydrolysis. Enzymatic activity measurements indicated enzyme stability at different temperatures (− 20 °C and 6 °C) and periods (up to 120 days). Wheat bran was characterized using Fourier transform infrared spectroscopy (FTIR) before and after enzymatic saccharification. Saccharification time, substrate load, and enzyme load were optimized using the Box–Behnken design. The zymogram demonstrated a single activity band around 39 kDa, the molecular weight of B. ricini URM5627 endoglucanase. Enzyme activity was preserved at 78.78% and 86.08% after storage for 120 days at − 20 °C and 6 °C, respectively. FTIR analyses showed cellulose delignification and loosening after enzymatic action. Maximum production of reducing sugars (116.93 mg g−1) occurred when conditions were maintained at the central point of planning (8 h, 2% substrate load, and 4% enzyme load). The enzyme isolated from B. ricini was stable in solid medium and in stored form, and could saccharify wheat bran without pretreatments. High yield of reducing sugars and proximity between predicted and real values demonstrated effectiveness of statistical optimization in saccharification of lignocellulosic biomass.

Effect of substrate load on anaerobic fermentation of rice straw with rumen liquid as inoculum: Hydrolysis and acidogenesis efficiency, enzymatic activities and rumen bacterial community structure

Rumen liquid is excellent to effectively degrade lignocellulose. In this study, the suitable rice straw load during anaerobic fermentation of rice straw with rumen liquid as inoculum was explored to improve volatile fatty acid (VFA) production. At 10.0% rice straw load, the highest VFA concentration reached 10821.4 mg/L, and acetic acid and propionic acid were the main components. In 10.0% rice straw load system, high concentration of soluble chemical oxygen demand (SCOD) was also observed, and the enzymatic activities at 48 h were higher than those at other rice straw loads. At 10.0% rice straw load, lower diversity and richness of rumen bacteria were found than those at other rice straw loads. Bacteroides, Prevotella, and Ruminococcus were the main rumen bacteria during rice straw degradation, and the rumen bacteria might secret effective lignocellulolytic enzymes to enhance the hydrolysis and acidogenesis of rice straw. The determination of suitable rice straw load will be beneficial to the application of rumen liquid as inoculum in actual production.

Dynamical simulation of a continuous stirred tank bioreactor with the use of cellular automata for the biofilm description

The paper concerns mathematical modeling and simulation of a continuous-flow stirred tank bioreactor (CSTBR) in which heterogeneous biofilm forms on its walls. The mathematical model couples a 2D cellular-automata biofilm model with differential equations describing the liquid phase in the bioreactor. Double-substrate aerobic phenol biodegradation by Pseudomonas putida bacteria was chosen as a process example. The influence of key process parameters on the dynamical characteristics of the bioreactor and the biofilm structure evolution during the process was investigated. Such an analysis has not been previously performed. It was shown that cell death strongly affects both biofilm heterogeneity and the technological properties of the bioreactor. Neglecting this phenomenon leads to improper design of the bioreactor. The influence of substrate load on the heterogeneity of the biofilm was evaluated in the process limited by two substrates. So far only a single substrate limitation has been evaluated in this regard. Even for large carbonaceous substrate concentrations, the biofilm growth and its structure are influenced by oxygen depletion. It was shown that an increased detachment rate increases bioreactor productivity.