Specific Growth Rate Constant Research Articles

MODELING OF MIXED LIQUOR VOLATILE SUSPENDED SOLIDS AND PERFORMANCE EVALUATION FOR A SEQUENCING BATCH REACTOR

This study examined carbon, nitrogen and phosphorous removal from municipal wastewater in a sequencing batch reactor and biokinetic coefficients were evaluated according to results of BOD and COD. Furthermore, the MLVSS in the aeration reactor was modeled by using multilayer perceptron and radial basis function artificial neural networks (MLPANN and RBFANN). The experiments were performed so that the cell retention time, filling time and intensity of aeration were (5, 10 and 15 d), (1, 2 and 3 h) and (weak, medium and strong) respectively. The result indicated that with cell retention time of 15 d, filling time of 1 h, aeration time of 6 h and settling time of 3 h the HRT is optimized at 10 h. The BOD5, COD, TP, TN and removal efficiencies were 97.13%, 94.58%, 94.27%, 89.7% and 92.75% respectively. The yield coefficient (Y), decay coefficient (Kd), maximum specific growth rate (K) and saturation constant (Ks) were 6.22 mgVSS/mgCOD, 0.002 1/d, 0.029 1/d and 20 mg COD/L according to COD experimental data. The values of the biokinetic coefficients were found to be as follows: Y = 10.45 mgVSS/mgBOD, Kd = 0.01 1/d, 0.014 1/d and 3.38 mgBOD/L according to BOD5 experimental data. The training procedures for simulation of MLVSS were highly collaborated for both RBFANN and MLPANN. The train and test models for both MLPANN and RBFANN demonstrated perfectly matched results between the experimental and the simulated values of MLVSS. The values of RMSE for train and test (verification) models obtained by MLPANN were 31.82 and 40.25 mg/L respectively, and the value of R2 was 0.99 for both models. The values of RMSE for train and test models obtained by MLPANN were 69.04 and 43.87 mg/L respectively, and the value of R2 was 0.99 for both models. It was observed that the MLPANN has stronger approximation and generalization ability than the RBFANN with regard to our experimental data for MLVSS.

Divergent utilization patterns of grass fructan, inulin, and other nonfiber carbohydrates by ruminal microbes

Fructans are an important nonfiber carbohydrate in cool season grasses. Their fermentation by ruminal microbes is not well described, though such information is needed to understand their nutritional value to ruminants. Our objective was to compare kinetics and product formation of orchardgrass fructan (phlein; PHL) to other nonfiber carbohydrates when fermented in vitro with mixed or pure culture ruminal microbes. Studies were carried out as randomized complete block designs. All rates given are first-order rate constants. With mixed ruminal microbes, rate of substrate disappearance tended to be greater for glucose (GLC) than for PHL and chicory fructan (inulin; INU), which tended to differ from each other (0.74, 0.62, and 0.33h−1, respectively). Disappearance of GLC had almost no lag time (0.04h), whereas the fructans had lags of 1.4h. The maximum microbial N accumulation, a proxy for cell growth, tended to be 20% greater for PHL and INU than for GLC. The N accumulation rate for GLC (1.31h−1) was greater than for PHL (0.75h−1) and INU (0.26h−1), which also differed. More microbial glycogen (+57%) was accumulated from GLC than from PHL, though accumulation rates did not differ (1.95 and 1.44h−1, respectively); little glycogen accumulated from INU. Rates of organic acid formation were 0.80, 0.28, and 0.80h−1 for GLC, INU, and PHL, respectively, with PHL tending to be greater than INU. Lactic acid production was more than 7-fold greater for GLC than for the fructans. The ratio of microbial cell carbon to organic acid carbon tended to be greater for PHL (0.90) and INU (0.86) than for GLC (0.69), indicating a greater yield of cell mass per amount of substrate fermented with fructans. Reduced microbial yield for GLC may relate to the greater glycogen production that requires ATP, and lactate production that yields less ATP; together, these processes could have reduced ATP available for cell growth. Acetate molar proportion was less for GLC than for fructans, and less for PHL than for INU. In studies with pure cultures, all microbes evaluated showed differences in specific growth rate constants (μ) for GLC, fructose, sucrose, maltose, and PHL. Selenomonas ruminantium and Streptococcus bovis showed the highest μ for PHL (0.55 and 0.67h−1, respectively), which were 50 to 60% of the μ achieved for GLC. The 10 other species tested had μ between 0.01 and 0.11h−1 with PHL. Ruminal microbes use PHL differently than they do GLC or INU.

Analysis of reaction kinetics during chemostat cultivation of Saccharomyces cerevisiae using a multiphase microreactor

This paper presents the determination of reaction kinetic parameters and the kinetic analysis of a chemostat cultivation performed using a multiphase microreactor (mMR). Saccharomyces cerevisiae was cultivated aerobically in continuous chemostat mode using an mMR. Steady-state biomass, substrate and ethanol concentrations were determined at dilution rates between 0.14≤D≤0.42h−1 with a glucose-feed concentration of 10gL−1. Modelling the aerobic chemostat culture was based on stationary balance equations. Maximal specific growth rate and Monod constant were determined using different linearization methods. The aerobic yeast metabolism was considered using two validity ranges of the model: (a) with purely oxidative metabolism in which glucose was converted into biomass or was used for maintenance metabolism, and no ethanol was generated; (b) with oxido-reductive metabolism employing an active Crabtree effect, in which ethanol was generated at the expense of biomass production. The different yield coefficients could be determined using the plots of the specific substrate consumption rate qS=f(D) and the specific product formation rate qP=f(D), respectively. Using this model, the reaction kinetic parameters were determined from the stationary concentrations of the biomass, glucose and ethanol that were determined during aerobic cultivation in the mMR. Finally, the kinetic parameters were compared with those reported in the literature that had been obtained using laboratory-scale reactors.

Kinetics and modelling of batch fermentation for the production of organic solvent tolerant and thermostable lipase by recombinant E. coli / Organik çözücü toleranslı ve ısıya dayanıklı rekombinan E. coli lipaz üretiminin kinetiği ve grup fermentasyonu modellemesi

Abstract Objective: Kinetics of organic solvent tolerant and thermostable lipase production by recombinant E. coli in shake flask level and 2 L stirred tank bioreactor level was studied to observe the variations of important kinetic parameters at two different levels of bioprocess. Methods: Unstructured models based on Monod equation for growth and Luedeking-Piret equation for lipase production and glucose consumption were used to predict cell growth, lipase production and glucose utilization. The shake flask fermentation experiments were carried out at different initial glucose and yeast extract concentrations using recombinant bacterial strain E. coli BL21. Lipase production was also carried out using 2L stirred tank bioreactor for comparison. Results: In all cases, the data fitted well to the proposed models. The highest growth and lipase activity were obtained at 25 g/L glucose and 25 g/L yeast extract. Cell growth (6.42 g/L) and lipase production (65.32 IU/mL) in 2 L stirred tank bioreactor was comparable to those obtained in shake flask fermentations. The calculated value of growth associated constant (9.874 IU/g/h) was much higher than that of non-growth associated constant (0.022 IU/g/h) in bioreactor as well as in shake flasks. The values of maximum specific growth rate (μm) and glucose saturation constant (KS) for shake flask fermentations, calculated from Monod equation, were 0.476 h-1 and 5.237 g/L respectively. Conclusion: From the modelling exercise, it was concluded that the lipase production is dominantly growth associated process. The kinetic parameter values for fermentations in shake flask and 2L stirred tank bioreactor were comparable, indicating that the bioprocess could be transferred into larger scale.

Modeling of Activated Sludge with ASM1 Model, Case Study on Wastewater Treatment Plant of South of Isfahan

ASM1 model is one of the most widely used models of activated sludge process which is the interest of researchers. This model was first proposed in 1987 by the IAWQ group and it is the first formal model of activated sludge. In this research, to evaluate the consistent of model's result with the reality, the data of wastewater treatment plant of south of Isfahan was used. This treatment plant covers a population about 800000 people, and the activated sludge method is used for treating municipal wastewater. The components of ASM1 mode such as fast biodegradable substrate parameters (Ss) and slow biodegradable (Xs) and the concentration of total COD, total nitrogen, suspended solids, nitrate nitrogen and Kjeldahl nitrogen were measured within 68 days and were included in the model. For modeling, the STOAT software was used where the ASM1 model was implemented. To calibrate the model, four cases from bio-kinetic coefficients of ASM1 model was obtained based on the results and the model was corrected in the default values. These coefficients include maximum specific growth rate (µm), decay coefficient (Kd), yield coefficient(Y), and saturation constant (Ks). The model results were consistent with the reality‎.

Modeling of oxygen uptake rate evolution in pig manure–wheat straw aerobic composting process

A revised oxygen uptake rate model that considers the specific characteristics of the substrate and the temperature dependence of microbial growth for pig manure–wheat straw aerobic composting was established. The model validation results showed good agreement with experimental data. The model’s accuracy, in terms of a lower relative error and fewer deviations of the oxygen uptake rate, was improved, but the oxidation of the remaining carbon requires further study. Sensitivity analyses were performed to simulate different composting processes and to explore potential engineering applications to the improvement of composting. The specific growth rate constant of the composting mixture was 0.42h−1. Enhanced aeration in the thermophilic phase is suggested for a soluble-rich substrate. Reducing insoluble substrate will help shorten composting period and improve the product’s stability. The smaller the particle size, the better the composting efficiency when air permeability is guaranteed. The optimal ambient temperature of the compost was 21–35°C. These findings provide a theoretical basis that can inform the design of an economical operation strategy for aerobic composting.

Mechanistic insight into ultrasound induced enhancement of simultaneous saccharification and fermentation of Parthenium hysterophorus for ethanol production

This paper presents investigations into mechanism of ultrasound assisted bioethanol synthesis using Parthenium hysterophorus biomass through simultaneous saccharification and fermentation (SSF) mode. Approach of coupling experimental results to mathematical model for SSF using Genetic Algorithm based optimization has been adopted. Comparison of model parameters for experiments with mechanical shaking and sonication (10% duty cycle) give an interesting mechanistic account of influence of ultrasound on SSF system. A 4-fold rise in ethanol and cell mass productivity is seen with ultrasound. The analysis reveals following facets of influence of ultrasound on SSF: increase in Monod constant for glucose for cell growth, maximal specific growth rate and inhibition constant of cell growth by glucose and reduction in specific cell death rate. Values of inhibition constant of cell growth by ethanol (K3E), and constants for growth associated (a) and non-growth associated (b) ethanol production remained unaltered with sonication. Beneficial effects of ultrasound are attributed to enhanced cellulose hydrolysis, enhanced trans-membrane transport of substrate and products as well as dilution of the toxic substances due to micro-convection induced by ultrasound. Intrinsic physiological functioning of cells remained unaffected by ultrasound as indicated by unaltered values of K3E, a and b.

Design, Construction, and Validation of an Internally Lit Air-Lift Photobioreactor for Growing Algae

A novel 28 L photobioreactor for growing algae was developed from a previous bubble column system. The proposed design uses the air lift principle to enhance the culture circulation and induce light/dark cycles to the microorganisms. Optical fibers were used to distribute photons inside the culture media providing an opportunity to control both light cycle and intensity. The fibers were coupled to an artificial light source, however the development of this approach aims for the future use of natural light collected through parabolic solar collectors. This idea could also allow the use of non-clear materials for photobioreactor construction significantly reducing costs and increasing durability. Internal light levels were determined in dry conditions and were maintained above 80 µmol/(s•m2). The hydrodynamic equations of the air lift phenomena were explored and used to define the geometric characteristics of the unit. The reactor was inoculated with the algae strain Chlorella sp. and sparged with air. The reactor was operated under batch mode and daily monitored for biomass concentration. The specific growth rate constant of the novel device was determined to be 0.011 h-1, similar to other reactor designs reported in the literature, suggesting the proposed design can be effectively and economically used in carbon dioxide mitigation technologies and in the production of algal biomass for biofuel and other bioproducts.

Dynamics in bioprocess development for Pichia pastoris

Pichia pastoris is a widely used host organism for the recombinant production of proteins. It is attracting increasing interest for the production of biopharmaceuticals, due to its capability of performing posttranslational modifications. Traditionally, production processes with P. pastoris describe fed-batch processes based on feed forward regimes with a constant specific growth rate. However, this strategy does not consider physiological changes of the organism, bearing the risk of overfeeding and thus harming the cells. Recently, we introduced the specific substrate uptake rate as a novel physiological parameter to design fed-batch strategies for P. pastoris. We showed that by doing dynamic batch experiments strain specific parameters, which are needed to set up respective feeding profiles, can be easily determined. Furthermore we proved that dynamics during feeding directly affects productivity and product purity. Here, we sum up our findings regarding dynamics in bioprocess development for P. pastoris.

Bioprocess and downstream optimization of recombinant bovine chymosin B in Pichia (Komagataella) pastoris under methanol-inducible AOXI promoter

A clone of the methylotrophic yeast Pichia pastoris strain GS115 transformed with the bovine prochymosin B gene was used to optimize the production and downstream of recombinant bovine chymosin expressed under the methanol-inducible AOXI promoter. Cell growth and recombinant chymosin production were analyzed in flask cultures containing basal salts medium with biodiesel-byproduct glycerol as the carbon source, obtaining values of biomass level and milk-clotting activity similar to those achieved with analytical glycerol. The effect of biomass level at the beginning of methanol-induction phase on cell growth and chymosin expression was evaluated, determining that a high concentration of cells at the start of such period generated an increase in the production of chymosin. The impact of the specific growth rate on chymosin expression was studied throughout the induction stage by methanol exponential feeding fermentations in a lab-scale stirred bioreactor, achieving the highest production of heterologous chymosin with a constant specific growth rate of 0.01h−1. By gel filtration chromatography performed at a semi-preparative scale, recombinant chymosin was purified from exponential fed-batch fermentation cultures, obtaining a specific milk-clotting activity of 6400IMCU/mg of chymosin and a purity level of 95%. The effect of temperature and pH on milk-clotting activity was analyzed, establishing that the optimal temperature and pH values for the purified recombinant chymosin are 37°C and 5.5, respectively. This study reported the features of a sustainable bioprocess for the production of recombinant bovine chymosin in P. pastoris by fermentation in stirred-tank bioreactors using biodiesel-derived glycerol as a low-cost carbon source.

Enhanced Biomass Recovery During Phycoremediation of Cr(VI) Using Cyanobacteria and Prospect of Biofuel Production

Utilization of cyanobacteria for remediation of pollutants and thereby large production of microalgae for sustainable biofuel production is a practicable option. In the present study, a cyanobacterial consortium of Oscillatoria subbrevis and Gloeocapsa atrata, collected from East Kolkata Wetland, a “Wetland of International Importance”, has been used for removal of Cr(VI) from simulated wastewater and the effect of Cr(VI) on biomass production was investigated. The Monod model has been used to depict growth kinetics of the cyanobacterial consortium in pure media. Maximum specific growth rate and saturation constant have been found to be 0.1562 day–1 and 0.024 g/L, respectively. The kinetic study on Cr(VI) removal shows that biomass and lipid production are more when the cyanobacterial consortium have been cultured in wastewater containing Cr(VI) than in pure media. The growth of the cyanobacterial consortium in relation to Cr(VI) removal as well as lipid production has been optimized using response surface methodology. Optimum metal removal has been achieved when initial Cr(VI) concentration, pH, inoculum size, and time are 11.08 ppm, 9.0, 0.39 g, and 9 days, respectively.

Assessment of methane biodegradation kinetics in two-phase partitioning bioreactors by pulse respirometry

Biological methane biodegradation is a promising treatment alternative when the methane produced in waste management facilities cannot be used for energy generation. Two-phase partitioning bioreactors (TPPBs), provided with a non-aqueous phase (NAP) with high affinity for the target pollutant, are particularly suitable for the treatment of poorly water-soluble compounds such as methane. Nevertheless, little is known about the influence of the presence of the NAP on the resulting biodegradation kinetics in TPPBs. In this study, an experimental framework based on the in situ pulse respirometry technique was developed to assess the impact of NAP addition on the methane biodegradation kinetics using Methylosinus sporium as a model methane-degrading microorganism. A comprehensive mass transfer characterization was performed in order to avoid mass transfer limiting scenarios and ensure a correct kinetic parameter characterization. The presence of the NAP mediated significant changes in the apparent kinetic parameters of M. sporium during methane biodegradation, with variations of 60, 120, and 150% in the maximum oxygen uptake rate, half-saturation constant and maximum specific growth rate, respectively, compared with the intrinsic kinetic parameters retrieved from a control without NAP. These significant changes in the kinetic parameters mediated by the NAP must be considered for the design, operation and modeling of TPPBs devoted to air pollution control.

Fatty acid content and profile of the aerial microalga Coccomyxa sp. isolated from dry environments.

Aerial algae are considered to be highly tolerant of and adaptable to severe conditions including radiation, desiccation, high temperatures, and nutrient deficiency, compared with those from aquatic habitats. There are considerable variations in the fatty acid (FA) composition of aerial microalgae from dry environments. A new species with a high lipid level was found on concrete surfaces and was identified as Coccomyxa sp. KGU-D001 (Trebouxiophyceae). This study characterized its FA content and profile in a bath culture. The alga showed a constant specific growth rate (0.26 day(-1)) ranging in light intensity from 20 to 80 μmol photons m(-2) s(-1). The algal cells started to form oil bodies in the early stationary phase of growth, and oil bodies occupied most of the cells during the late stationary phase when the cells accumulated 27 % total fatty acids (TFA). The process of lipid body formation accumulating large amounts of triacylglycerols (TAG) appeared to be very unusual in response to stress conditions persisting for a relatively long culture time (50 days). This study could indicate that aerial microalgae will be a candidate for biodiesel production when a new cultivation method is developed using extreme stresses such as nutritional deficiency and/or desiccation.

Signals of aging associated with lower growth rates in Kluyveromyces lactis cultures under nitrogen limitation.

The effects of aging on the specific growth rate of Kluyveromyces lactis cultures, as a function of (NH4)2SO4 concentration, were evaluated. The growth kinetic parameters maximum specific growth rate and saturation constant for (NH4)2SO4 were calculated to be 0.44 h(-1) and 0.15 mmol·L(-1), respectively. Batch cultures were allowed to age for 16 days without influence of cell density or starvation. The specific growth rates of these cultures were determined each day and decreased as the population aged at different nitrogen concentrations. Aging signals (N-acetylglucosamine content of the cell wall, cell dimensions, and apoptosis markers) were measured. Apoptosis markers were detected after 5 days at limiting (NH4)2SO4 concentrations (0.57, 3.80, and 7.60 mmol·L(-1)) but only after 8 days at a nonlimiting (NH4)2SO4 concentration (38.0 mmol·L(-1)). Similarly, continuous cultures of K. lactis performed under nitrogen limitation and, at lower dilution rates, accumulated cells exhibiting aging signals. The results demonstrate that aging affects growth rate and raise the question of whether nitrogen limitation accelerates aging. Because aging is correlated with growth rate, and each dilution rate of the continuous cultures tends to select and accumulate cells with a respective age, cultures growing at lower growth rates can be useful to investigate yeast physiological responses, including aging.

Kinetic Studies on Fermentative Production of Biofuel from Synthesis Gas UsingClostridium ljungdahlii

The intrinsic growth, substrate uptake, and product formation biokinetic parameters were obtained for the anaerobic bacterium, Clostridium ljungdahlii, grown on synthesis gas in various pressurized batch bioreactors. A dual-substrate growth kinetic model using Luong for CO and Monod for H2 was used to describe the growth kinetics of the bacterium on these substrates. The maximum specific growth rate (μ max = 0.195 h−1) and Monod constants for CO (K s,CO = 0.855 atm) and H2 (K s,H2 = 0.412 atm) were obtained. This model also accommodated the CO inhibitory effects on cell growth at high CO partial pressures, where no growth was apparent at high dissolved CO tensions (P CO ∗ > 0.743 atm). The Volterra model, Andrews, and modified Gompertz were, respectively, adopted to describe the cell growth, substrate uptake rate, and product formation. The maximum specific CO uptake rate (q max = 34.364 mmol/gcell/h), CO inhibition constant (K I = 0.601 atm), and maximum rate of ethanol (R max = 0.172 mmol/L/h at P CO = 0.598 atm) and acetate (R max = 0.096 mmol/L/h at P CO = 0.539 atm) production were determined from the applied models.

New ammonia lyases and amine transaminases: Standardization of production process and preparation of immobilized biocatalysts

Background: New enzymes for biotransformations can be obtained by different approaches including directed mutagenesis and in vitro evolution. These mutants have to be efficiently produced for laboratory research on bioreactions as well as for process development. In the framework of a European ERA-IB project, two different types of enzymes (ammonia lyases and aminotransferases) have been selected as biocatalysts for the synthesis of industrially relevant amines. New mutant enzymes have been obtained: a) aspartases able to recognize β-amino acids; b) ω-transaminases with improved activity. The objectives are to find out a common operational strategy applicable to different mutants expressed in E. coli with the same initial genetic background, the development of an integrated process for production and the preparation of stable useful biocatalysts. Results: Mutant enzymes were expressed in E. coli BL21 under the control of isopropylthiogalactoside (IPTG) inducible promoter. The microorganisms were grown in a formulated defined medium and a high-cell density culture process was set up. Fed-batch operation at constant specific growth rate, employing an exponential addition profile allowed high biomass concentrations. The same operational strategy was applied for different mutants of both aspartase and transaminase enzymes, and the results have shown a common area of satisfactory operation for maximum production at low inducer concentration, around 2 μmol IPTG/g DCW. The operational strategy was validated with new mutants and high-cell density cultures were performed for efficient production. Suitable biocatalysts were prepared after recovery of the enzymes. The obtained aspartase was immobilized by covalent attachment on MANA-agarose, while ω-transaminase biocatalysts were prepared by entrapping whole cells and partially purified enzyme onto Lentikats (polyvinyl alcohol gel lens-shaped particles). Conclusions: The possibility of expressing different mutant enzymes under similar operation conditions has been demonstrated. The process was standardized for production of new aspartases with β-amino acid selectivity and new ω-transaminases with improved substrate acceptance. A whole process including production, cell disruption and partial purification was set up. The partially purified enzymes were immobilized and employed as stable biocatalysts in the synthesis of chiral amines.

From laboratory to pilot plant E. coli fed-batch cultures: optimizing the cellular environment for protein maximization

For recombinant protein production in E. coli fed-batch cultures, post-induction conditions have great influence in the quantity and quality of the product. The present paper covers the effect of different factors affecting the cellular environment in recombinant aldolase (rhamnulose-1-phosphate aldolase, RhuA) production. An operational mode employing an exponential addition profile for constant specific growth rate has been analyzed, in order to understand and define possible modifications with influence on post-induction cellular behavior. A constant addition profile has been demonstrated to render higher specific aldolase production than the exponential addition profile, probably due to a more constant environment for the cells. On the other hand, amino acid (leucine) supplementation has proven to increase protein quality in terms of activity units (U) per unit mass of RhuA (Umg(-1)RhuA), alleviating metabolic overload. Based on the above, a production process was set up and scaled up to pilot plant. Resulting production was double that of a standard laboratory operation, 45,000UL(-1), and almost all the protein retained the 6xHis-tag with the highest quality, 11.3Umg(-1) RhuA.

Batch studies with Exiguobacterium aurantiacum degrading structurally diverse organic compounds and its potential for treatment of biomass gasification wastewater

Biomass gasification wastewater primarily consists of phenolics, nitrogen-heterocyclics and polynuclear aromatic hydrocarbons (PAHs). Biodegradation of these compounds present individually as sole substrate is studied in batch cultures in presence of Exiguobacterium aurantiacum. It demonstrated good potential for degrading phenol, pyridine, quinoline, benzene and naphthalene present at initial concentration (Cin) of 500 mg l−1. E. aurantiacum could also utilize 3- and 4-ring PAHs, phenanthrene, fluoranthene and pyrene as sole substrate present at 100 mg l−1 (Cin). While significant increase in absorbance was observed on 3 and 4-ring PAHs, the increase in number concentration of viable cells and extent of degradation was relatively low. E. aurantiacum could effectively degrade a synthetic biomass gasifier wastewater comprised of these compounds with a total COD of 1326 mg l−1 and biokinetic studies revealed applicability of Monod's kinetics for culture growth on gasifier wastewater. The half velocity constant (Ks) and maximum specific growth rate (μmax) were 651 mg l−1 and 1.86 d−1, respectively. All components in the wastewater were degraded simultaneously and compounds with comparable concentration depicted comparable degradation rates. E. aurantiacum could degrade the organics in biomass gasification wastewater even when the ammoniacal-nitrogen concentration was increased up to 1000 mg l−1. Bioaugmentation with E. aurantiacum can significantly enhance biological treatment of biomass gasification wastewater.

Effect of Temperature on Kinetic Constants in Anaerobic Bio-digestion

Chen Hashimoto Model has been used to evaluate the maximum specific growth rate and kinetic constants, significant parameters in anaerobic digestion of vegetable wastes, at various temperatures. The linear approximation and the limitations of their applicability have been described. The samples of vegetable wastes as collected from local market have been taken in an anaerobic semi batch digester. The ultimate methane yield (B 0 ), maximum specific growth rate (µ m ), and kinetic constant (K) have been estimated using Chen Hasimoto model. The maximum values of these coefficients are 0.032 m 3 /Kg DM at 46

Characteristics of cured and wild strains of Enterobacter cloacae IIT-BT 08 for the improvement of biohydrogen production

Enterobacter cloacae IIT-BT 08 was found to harbor multiple endogenous plasmids. The plasmids were successfully cured by the combined action of SDS and mitomycin C. The cured strain exhibited an altered pattern of antibiotic and metal resistance. The effect of plasmid curing on biohydrogen production was determined. LP model showed that hydrogen was a growth associated product for both the wild type and the cured strain. However, modified Gompertz equation showed that the productivity of the cured strain was comparable to the wild type. Further, comparative kinetic parameter analysis showed that the maximum specific growth rate (μmax) and saturation constant (Ks) were 1.26 and 2.2 times higher respectively, for the cured strain as compared to the wild type. Similarly, maintenance coefficient (m) was determined to be function of fermentation time and was lower for the cured strain. This was related to the decrease in plasmid load in the cured strain.