Specific Growth Rate Constant Research Articles

High cell density culture of microalgae in horizontal thin-layer algal reactor: Modeling of light attenuation and cell growth kinetics

This study delved into the light intensity effects and light attenuation modeling in high cell density culture (HCDC) of green alga Neochloris oleoabundans. The research primarily focused on how different light intensities influence cell growth in terms of cell division and cell mass, and the biochemical composition within the cells. Recognizing the need to avoid overestimating light path by excluding data point in the data zone where the light intensity was zero, we proposed and verified a novel modified Beer-Lambert model, which was superb in fitting experimental data and predicting light attenuation in both low and high cell density cultures. Taking advantage of the prediction power of the modified Beer-Lambert model, we devised an approach to maintain constant mean light intensity (Imean) and by adjusting the incident light intensity (I0). The results indicate that at an Imean of approximately 66.67 μmol/m2/s and 6 mm culture thickness, maximum volumetric and areal biomass productivities of 2.72 g/L/day and 16.32 g/m2/day, respectively, were achieved. Whereas the highest biomass concentration of 28.20 g/L was produced in 20 days at Imean 50 μmol/m2/s. Photoinhibition to cell division become evident at I0 750 μmol/m2/s and above. Using the data generated at constant Imean in the constant specific growth rate range, superb fitting to the Monod model with a R2 of 0.9910 was demonstrated, highlighting the importance of generating reliable data for the modelling of the kinetics of photoautotrophic growth of microalgae, which had considered to be challenging.

Comparison of the bioaccumulation and biosorption of copper ions by Rhizopus delemar and Candida lipolytica

In this study, the bioaccumulation of Cu(II) ion by Rhizopus delemar and Candida lipolytica was investigated and the bioaccumulation and biosorption of Cu(II) ions by Candida lipolytica compared. The specific growth rate and the maximum microorganism concentration of both microorganisms increased with increasing initial molasses concentration whereas decreased with increasing initial Cu(II) ion concentrations up to 250 mg/L. Accoding to Monod equation, the maximum specific growth rate and saturation constant for C. lipolytica and R. delemar were determined as 0.335 h−1-32.330 g/L and 0.406 h−1-24.182 g/L, respectively. The bioaccumulation efficiencies of R. delemar and C. lipolytica were determined as 74.18% and 67.30% in the presence of 50 mg/L Cu(II), respectively. At pH 4.0, the maximum biosorption rate (4.72 mg/g min) and the biosorbed Cu(II) ion concentration (49.0 mg/L) were obtained for C. lipolytica and these values increased with increasing Cu(II) concentration. Cu(II) biosorption by C. lipolytica fitted well to the Langmuir isotherm model and pseudo-second-order kinetic model and maximum adsorption capacity was found as 114.942 mg/g. The bioaccumulated Cu(II) was found to be 21.5 mg/g whereas the amounts of biosorbed Cu(II) were calculated as 53 mg/g by C. lipolytica at a concentration of 100 mg/L of Cu(II).

Growth kinetics of lead resistant Bacillus infantis isolated from battery industry waste

The current investigation presents an innovative approach to address the challenge of removing heavy metal lead from industrial waste through advanced biological remediation techniques. By amalgamating theoretical insights with empirically acquired data, this research endeavours to develop efficient bioreactor strategies suitable for large-scale applications. Initially, bacteria naturally endowed with lead resistance has been isolated from a native source. Extensive microbiological assessments, including a 16S rDNA study, verified the identity of the lead-resistant bacterial cells as Bacillus infantis 4352-1T. In order to evaluate the efficacy of Bacillus infantis 4352-1T for lead removal an attempt has been made to study the growth dynamics of Bacillus infantis 4352-1T cells in batch mode, using lead amended selective media. It has been observed that Monod's equation effectively defined the cell growth behaviour within the lead concentration range of 0.05–0.25 kg lead/m3. Notably, the experiment was also facilitated the derivation of essential intrinsic kinetic parameters, such as the maximum specific cell growth rate (0.0237 h−1) and substrate saturation constant (0.018 kg/m3). Beyond lead concentrations of 0.25 kg lead/m3, up to 0.43 kg lead/m3, it has also been observed the pronounced influence of substrate inhibition which is quantitatively elucidated by the Haldane equation.

Synergistic effect of process parameters and nanoparticles on spent lubricant oil waste biodegradation by UV-exposed Scenedesmus vacuolatus: Process modelling, kinetics and degradation pathways

The study examines the impact of process parameters and nanoparticles (NPs) on the degradation of spent coolant waste (SCW) by UV-exposed S. vacuolatus. The model was experimentally optimized using response surface methodology (RSM) with high coefficient of determination (R2) >0.99. Upon validation of the model, total petroleum hydrocarbon (TPH) degradation of 100 % was obtained after 15 days under the optimized conditions of 25 °C temperature, 10 % (v/v) substrate concentration and 10 % (v/v) inoculum concentration. Moreover, the sensitivity of the process parameters on the degradation process assessed using artificial neural network (ANN) revealed high sensitivity of the degradation process to operational temperature. Metabolites obtained provide strong evidence for terminal oxidation and subterminal oxidation metabolic pathways in SCW degradation. In addition, the incorporation of NPs in the SCW degradation significantly enhanced the biodegradation efficiency of UV-exposed S. vacuolatus resulting in shortened degradation period from 15 to 12 days. Likewise, the inclusion of NPs substantially improved UV-exposed S. vacuolatus affinity (1/Ks) for SCW, growth constant (Kg) and maximum specific growth rate (μmax). The degradation kinetics followed the second-order reaction with degradation rate constant (K) in the range of 0.029 to 0.288 m−1 t−1 for monoaromatics and 0.972 to 4.130 m−1 t−1 for PAHs, at half-life (T1/2) ranges of 0.75 to 1.52 day−1 and 0.08 to 0.23 day−1, respectively. This knowledge will enhance the design of waste pollutant degradation towards sustainable green environment.

Evaluation of Bio-Friendly Formulations from Siderophore-Producing Fluorescent Pseudomonas as Biocontrol Agents for the Management of Soil-Borne Fungi, Fusarium oxysporum and Rhizoctonia solani

Secretion of siderophores by Pseudomonas aeruginosa F2 and P. fluorescens JY3 was evaluated on chrome azurol S (CAS) agar plates and their inhibitory effect was inspected against Fusarium oxysporum and Rhizoctonia solani. Production of siderophores as biocontrol agents from F2 and JY3 was accomplished in two optimized media. Afterward, cell-free supernatants of the bacterial cultures containing siderophores were used for the preparation of two bio-friendly formulations for the management of F. oxysporum and R. solani under greenhouse conditions. The investigated bacterial isolates, F2 and JY3, showed antagonistic activity in vitro against F. oxysporum and R. solani and produced siderophores in optimized media with high efficiency. Colonies of both bacterial isolates were grown exponentially with a constant specific growth rate of 0.07 h−1 and 0.27 h−1, correspondingly. Siderophores estimated in 10 µL reached their highest value of 16.95% at 47 h and 19.5% at 48 h for isolate F2 and JY3, respectively. Formulations of siderophore-generating F2 and JY3 reduced damping-off caused by F. oxysporum by 40% and 80%, while the reduction percentage of damping-off caused by R. solani reached 87.5% and 62.5%, correspondingly. Moreover, both formulations encouraged the growing of wheat plants where the fresh and dry weight of shoots and roots were increased compared to the treatment with each fungus. In conclusion, bio-friendly formulations resulting from this investigation can play an active role in managing soil-borne diseases.

Developing a metabolic model‐based fed‐batch feeding strategy for Pichia pastoris fermentation through fine‐tuning of the methanol utilization pathway

Pichia pastoris is a commonly used microbial host for recombinant protein production. It is mostly cultivated in fed-batch mode, in which the environment of the cell is continuously changing. Hence, it is vital to understand the influence of feeding strategy parameters on the intracellular reaction network to fine-tune bioreactor performance. This study used dynamic flux balance analysis (DFBA) integrated with transcriptomics data to simulate the recombinant P. pastoris (Muts ) growth during the induction phase for three fed-batch strategies, conducted at constant specific growth rates (μ-stat). The induction phase was split into equal time intervals, and the correlated reactions with protein yield were identified in the three fed-batch strategies using the Pearson correlation coefficient. Subsequently, principal component analysis (PCA) was applied to cluster induction phase time intervals and identify the role of correlated reactions on metabolic differentiation of time intervals. It was found that increasing fluxes through the methanol dissimilation pathway increased protein yield. By adding a methanol assimilation pathway inhibitor (HgCl2 ) to the shake flask medium growing on glycerol: methanol mixture (10%: 90%, v/v), the protein titre increased by 60%. As per DFBA, the higher the methanol to biomass flux ratio (Rmeoh/Δx ), the higher the protein yield. Finally, a novel feeding strategy was developed to increase the amount of Rmeoh/Δx compared to the three feeding strategies. The concentration of recombinant human growth hormone (rhGH), used as the model protein, increased by 16% compared to the optimal culture result obtained previously (800 mg L-1 to 928 mg L-1 ), while production yield improved by 85% (24.8 mg gDCW -1 to 46 mg gDCW -1 ).

Modelling Nannochloropsis gaditana Growth in Reactors with Different Geometries, Determination of Kinetic Parameters and Biochemical Analysis in Response to Light Intensity

Microalgae are unicellular and photosynthetic microorganisms which grow thanks to inorganic salts, CO2 and light, and find applications in several fields thanks to their variety. The industrial application of microalgae has not often been fully exploited because of a lack of information about how microalgae respond to inputs and to different growth environments. In the present work a model able to predict the microalgae growth in reactors with different geometries was developed. We combined a Monod-like model for the specific growth rate with the Lambert-Beer law of homogeneous light distribution in thick photobioreactors. Kinetic parameters related to the cultivation of the microalga Nannochloropsis gaditana were obtained, for the first time through batch cultivation under different photon flux densities inside a quasi-isoactinic photobioreactor, in order to obtain a practically homogeneous light distribution. The maximum specific growth rate and saturation constant resulted, respectively as µmax = 0.0256 h−1 and Ik = 15.28 µE s−1m−2. These parameters were applied to the model to obtain data on microalgae growth in different geometries. Model simulation results are presented and discussed. Furthermore, biochemical analysis was performed on the biomass obtained at the end of each batch cultivation, grown both under different light intensities and in reactors with different configurations. Results indicated that lipid content increases with increasing average photon flux density. The fatty acid and carotenoids profiles markedly shift when the average light intensity varies: the PUFA content decreases and the SFA content increases when the average light intensity rises, and an accumulation of carotenoids at lower photon flux densities is observed. In conclusion, the model resulted in a useful tool, able to predict the growth of the microalga Nannochloropsis gaditana in reactors with different configurations.

Kinetic study of thermophilic anaerobic digestion of sugarcane vinasse in a single-stage continuous stirred tank reactor

Vinasse, the liquid waste from the bottom of a bioethanol distillation column, is a potential feedstock for biogas production due to its high organic content. Vinasse is discharged at a high temperature, i.e., 60–80 °C. Therefore, thermophilic anaerobic digestion is more efficient to directly treat the vinasse at a high organic loading rate (OLR). This study investigated the performance of thermophilic anaerobic digestion on sugarcane vinasse inoculated with acclimated digested cow manure (DCM). The experiment was run at varied OLRs (1,2; 1.8 and 2.4 gCOD.L−1.day−1). The process was carried out in a continuous stirred tank reactor (CSTR) with controlled pH (7 ± 0.5) and oxidation-reduction potential/ORP (−500 ± 10 mV). During the 111 days of the experiment, we monitored the volatile fatty acids (VFA), total chemical oxygen demand (tCOD), and soluble chemical oxygen demand (sCOD), as well as methane and biogas production rates, to evaluate the reactor performance. The experimental data were fitted on the Anaerobic Digestion Model 1 (ADM 1) using the AQUASIM® software. The data were categorized in three process stages observed in this study: stabilization, enrichment, and steady-state. The kinetic parameters, i.e., the coefficient of affinity (KS,ac, KS,pro) and the specific growth rate (km,ac and km, pro), were obtained from the data fitting. The good fit of ADM 1 to the data highlighted the flexibility of ADM 1 to represent a dynamic system of a thermophilic anaerobic digestion system with simultaneous changes in both process variables and microbial composition. The data fitting gave consistently low Ks values in the lower OLR of 0.2 gCOD. L−1.day−1 up to the higher OLR of 2.4 gCOD. L−1.day−1. The Ks values, which were less than 1/1000 of the specific growth rate constants (km), indicated that the combined effects of the thermophilic condition and vinasse composition increased the microbial-substrate affinity (showed by KS) more essentially than the microbial growth rate (addressed by km). In addition, inhibitory effects were not observed with all OLR values tested in this study.

Dynamic Optimization Approach to Estimate Kinetic Parameters of Monod-Based Microalgae Growth Models.

The biomass concentration of microalgae growth in photobioreactor was predicted using the Monod-based growth models. Kinetic parameters such as maximum specific growth rate and saturation constant of light intensity were evaluated by nonlinear least squares methods that focused on minimizing the sum of squares error (SSE). The importance of good initial guess for the nonlinear least squares method was also discussed. The optimal control problem of the microalgae growth model was determined based on parameter sensitivity. Therefore, a dynamic optimization approach was used where an optimal input design method was formulated to obtain a control function of a problem. The dynamic state equations, additional state equations, cost function, and Hamiltonian function were used to establish a control function of microalgae growth in a photobioreactor. Hence, the biomass production of microalgae can be predicted using numerical methods such as the Taylor series method.

Biodegradation of acid red 3BN dye in sequential batch reactor: parameters and kinetics studies

Abstract Textile and dye industries generate wastewater which is considered as highly polluted and carcinogenic. Due to this, treatment of wastewater is required earlier to discharge or recycle. In the present studies, treatment of dye bearing water (DBW) has been explored. The treatment was performed using activated sludge (mixed culture) for aerobic process in sequential batch reactor (SBR). The fill volume (V F) and fill time (t F) variation in the treatment of DBW was taken place. The initial value of dye concentration, chemical oxygen demand (COD), sludge, and hydraulic retention time (HRT) were found to play important role in the treatment. At optimum condition (HRT = 2.5 d), the 86.84% COD reduction of 190 mg/L COD, and 92.33% dye reduction of 339 mg/L dye were achieved. These values are equal to overall 94.85% dye reduction of 500 mg/L, and 93.15% COD reduction of 380 mg/L. As a result, 500 mg/L dye was reduced to 26 mg/L, and 380 mg/L COD was reduced to 25 mg/L. The biodegradation fitted to Monod kinetics, for which kinetics parameter values of specific growth rate constant of biomass µ = 0.0047 h−1, yield coefficient (Y) = 1.059, and substrate utilization rate (q) = 0.0044 h−1 were evaluated at HRT = 2.5 d. The results show, this process can be applied to treat Acid Red 3BN Dye Water (AR3BNDW).

A novel relationship for the maximum specific growth rate of a microbial guild

One of the major parameters that characterizes the kinetics of microbial processes is the maximum specific growth rate. The maximum specific growth rate for a single microorganism (${\mu _{max}}$) is fairly constant. However, a certain microbial process is typically catalyzed by a group of microorganisms (guild) that have various ${\mu _{max}}$ values. In many occasions, it is not feasible to breakdown a guild into its constituent microorganisms. Therefore, it is a common practice to assume a constant maximum specific growth rate for the guild ($\acute{\mu}_{max}$) and determine its value by fitting experimental data. This assumption is valid for natural environments, where microbial guilds are stabilized and dominated by microorganisms that grow optimally in those environments' conditions. However, a change in an environment's conditions will trigger a community shift by favoring some of the microorganisms. This shift leads to a variable ${\acute{\mu}_{max}}$ as long as substrate availability is significantly higher than substrate affinity constant. In this work, it is illustrated that the assumption of constant ${\acute{\mu}_{max}}$ may underestimate or overestimate microbial growth. To circumvent this, a novel relationship that characterizes changes in ${\acute{\mu}_{max}}$ under abundant nutrient availability is proposed. The proposed relationship is evaluated for various random microbial guilds in batch experiments.

Buried Kex2 Sites in Glargine Precursor Aggregates Prevent Its Intracellular Processing in Pichia pastoris Muts Strains and the Effect of Methanol-Feeding Strategy and Induction Temperature on Glargine Precursor Production Parameters.

Glargine is a long-acting insulin analog with less hypoglycemia risk. Like human insulin, glargine is a globular protein composed of two polypeptide chains linked by two disulfide bonds. Pichia pastoris KM71 Muts strains were engineered to produce and secrete insulin glargine through the cleavage of two Kex2 sites. Nevertheless, the recombinant product was the single-chain insulin glargine (glargine precursor) instead of the expected double-chain glargine. Molecular model analysis of the dimeric and hexameric forms of the single-chain glargine showed buried Kex2 sites that prevent intracellular glargine precursor processing. The effect of the methanol-feeding strategy (methanol limited fed-batch vs. methanol non-limited fed-batch) and the induction temperature (28 °C vs. 24 °C) on the cell growth and production parameters in bioreactor cultures was also evaluated. Exponential growth at a constant specific growth rate was observed in all the cultures. The volumetric productivities and specific substrate consumption rates were directly proportional to the specific growth rate. The lower temperature led to increased metabolic activity of the yeast cells, which increased the specific growth rate. The methanol non-limited fed-batch culture at 24 °C showed the highest values for the process parameters. After 75 h of induction, 0.122 g/L of glargine precursor was obtained from the culture medium.

Acidogenic mixed consortium isolated from soil of agricultural field: acid production behaviour and growth kinetics under the influence of pretreatment hydrolysate of rice straw (RS)

ABSTRACT The present study was conducted to assess the possibilities of biofuel production through volatile fatty acid (VFA) platform using mixed consortia isolated from a natural source (soil of rice cultivation field). The acid production potential of the isolated acidogenic mixed consortium UACJUChE1, using pretreatment hydrolysate of rice straw as the carbohydrate source, was assessed. Growth kinetic parameters i.e. maximum specific growth rate (μ max) and substrate saturation constant (KS ) of UACJUChE1 have been determined separately for both glucose and hydrolysate in the Reinforced Clostridial Medium (RCM). A summative type growth model has been observed to be valid when the combination of glucose and RS-hydrolysate (RSH) is used as the carbon sources. The summative model has been validated by successful comparison of model predictions with the experimental data. The presence of VFAs in the culture broth of the consortium grown on glucose, RS-hydrolysate and their combination (Glc:RSH: 2:3; 1:4 (w/w)) has been established. The survival and growth of solventogenic Clostridium acetobutylicum in a growth medium amended with the effluent of these batch cultures of UACJUChE1 have been ascertained. This indicates a strong potential of UACJUChE1 in the hybridisation of the VFA platform and conventional sugar platform for the generation of butanol from RS.

Ethanol fed-batch bioreactor operation to enhance therapeutic protein production in Pichia pastoris under hybrid-architectured ADH2 promoter

ABSTRACT We presented ethanol fed-batch bioreactor operations (FBBOs) designed for enhanced recombinant human growth hormone (rhGH) production in Pichia pastoris constructed with novel hybrid-architectured ADH2 promoter, PADH2-Cat8-L2. The parameters in the fed-batch fermentation of ethanol were investigated, and the boundaries of the production domain in terms of the design parameters were determined. Two FBBO design methods were used, and a platform aiming to adjust cellular metabolism for the generation of constant specific growth rate (μ) and substrate concentration (CEtOH) was established. The highest overall productivity (rP,ov) was generated with model-based continuous feed-stream (CFS) design with μpreD = 0.035 h-1 up to tmax ≤ 9 h as rP,ov = 3.0 mg L-1 h-1 and CrhGH = 34 mg L-1. The ethanol-stat FBBO at CEtOH,set = 0.5 g L-1 allowed increased product titer with high productivity and the highest CrhGH =90.1 mg L-1 at tmax = 24 h. The effect of CEtOH on specific rates for cell reactions was represented by the Haldane model in which the cell generation and rhGH production were simulated with low mean relative errors of 6.5 and 16%, respectively. The results indicate the need for an upgraded CFS design model with kinetic expressions involving substrate inhibition. We conclude that a two-step hybrid fed-batch design strategy to be started (i) with the initial-period of the model-based FBBO, in turn, proceeded (ii) with the controlled feeding with ethanol-stat FBBO enables a gradual approach to the hypothetical performance of FBBOs.

Impact of decreasing hydraulic retention times on the specific affinity of methanogens and their community structures in an anaerobic membrane bioreactor process treating low strength wastewater

Maximum specific growth rate (μmax) and substrate saturation constant (Ks) are widely used in determining the growth of microorganisms. The ratio (μmax/Ks), also referred to as specific affinity, aA0, is a better parameter to assess the advantage in competition for substrates by bridging microbial growth and the kinetics of enzymatic substrate uptake, but is not well studied. This study investigated the effect of hydraulic retention time (HRT) on the aA0 of anaerobic sludge from an anaerobic membrane bioreactor (AnMBR), associated microbial communities and the overall wastewater treatment performance. The AnMBR was fed with acetate wastewater (~500 mg COD/L) and operated at fixed solids retention time (45 d) while HRT continued to decrease. There was no significant difference in Ks (ranging from 170 to 243 mg COD/L) at different HRTs. However, aA0 increased from (4.0 ± 0.2) × 10−4 to (4.9 ± 0.2) × 10−4 and to (6.5 ± 0.1) × 10−4 L/mg COD/d as HRT decreased from 24 h to 12 h and further to 6 h, respectively. This was accompanied by the increase in acetoclastic methanogens (mainly Methanosaeta) from 3.85 × 1010, 8.82 × 1010 to 1.05 × 1011 cells/L, respectively. The fraction of Methanosaeta in the anaerobic biomass increased from 33.67% to 61.08% as HRT decreased from 24 h to 6 h. Correspondingly, effluent quality was improved, as evidenced from the COD concentrations of 32 ± 6, 21 ± 4, and 13 ± 5 mg/L at the HRTs of 24 h, 12 h, and 6 h, respectively. The results confirm that microorganisms are able to adapt to growth conditions by adjusting their kinetic properties and suggest that short HRTs in the AnMBR favor the growth and accumulation of Methanosaeta with high specific affinity likely because they can compete for acetate at low concentrations by increasing substrate uptake rate and thus specific microbial growth rate.

Evaluation of assays for screening polycyclic aromatic hydrocarbon-degrading potential of bacteria

Within a 30-day incubation laboratory study, the polycyclic aromatic hydrocarbon (PAH) degradation profile of two bacteria, Planomicrobium sp. RNP01 and Rhodococcus sp. RNP05 were studied by three microtiter plate assays to reveal the combination of certain biological and biochemical characteristics which are reliable indicators in evaluation of bacterial biodegradation abilities. The three assays, which are hydrocarbon growth assay, 2,6-DCPIP assay and dehydrogenase activity assay revealed that Rhodococcus sp. RNP05 exhibited better potential for PAH degradation than Planomicrobium sp. RNP01. Differences between initial and final optical density and specific growth rate constants were significantly higher (r = 0.995, P < 0.05) in case of Rhodococcus sp. RNP05 on all tested substrates, as compared to Planomicrobium sp. RNP01. This was confirmed by GC-FID analyses. Dehydrogenase activity of Rhodococcus sp. RNP05 was higher (r = 0.9995, P < 0.05) than Planomicrobium sp. RNP01 and correlated positively with the hydrocarbon growth assay (r = 0.999, P < 0.05, for Rhodococcus sp. RNP05, r = 0.986, P < 0.05 for Planomicrobium sp. RNP01). This study has shown that the combination of these assays could be used for determining the bioremediation potential of PAHs in petroleum contaminated soil with the ability of screening a large number of bacterial strains.

Reactive Transport of Nutrients and Bioclogging During Dynamic Disconnection Process of Stream and Groundwater

AbstractBiofilm‐induced dynamic evolution of streambed permeability commonly concurs with the transition from connection to disconnection between surface water and groundwater in arid regions. However, in most previous studies, static streambeds were assumed to examine the evolution of disconnection, or despite dynamic streambeds being considered, the feedbacks between nutrients transport and microbial growth were ignored. In this study, we developed an innovative coupled variably saturated flow, microbial growth, biogeochemical reactions, and bioclogging model. We applied this model to investigate the feedbacks between nutrients transport and microbial growth and their controls on infiltration evolution. Our results showed that a new clogging layer can naturally develop due to these feedbacks and does not require prior clogging. The development of the new clogging layer promotes the occurrence of disconnection. These results illustrate that as bioclogging is a dominant process, previous static disconnection conditions cannot be used as criteria to predict whether disconnection can occur in a stream‐aquifer system. Furthermore, different from the previous assumption of constant specific microbial growth rates, biomass growth, and streambed permeability evolution are self‐limiting. Accordingly, due to initial low growth rate, infiltration increases when the water table declines, and it then decreases and reaches a minimum while a stable biofilm is developed. These trends coincide with the infiltration variations reported in previous field investigations. After reaching the minimum, infiltration increases again with decline of the water table until achieving a constant at the moment of disconnection. This stage was missing in previous studies because constant specific growth rates were assumed.

Liquid state bioconversion continuous bioreactor of sewage sludge treatment: Determination and evaluation of mixed fungi growth kinetics

Abstract Liquid state bioconversion (LSB), a bioremediation and biodewatering process was applied for sewage sludge treatment in this study. The LSB process is a non-hazardous, safer and environmentally friendlier method for ultimate sludge management and disposal compared to the other available technologies. The system presented in this study was developed by using mixed fungi of Aspergillus niger and Penicillium corylophilum to treat sewage sludge in a LSB bioreactor. This research was conducted in order to study the LSB process on continuous system in terms of kinetic coefficients determination. For the continuous LSB process, a mathematical model was developed from the basic principles of material balance based on Monod equation. By investigating the kinetics of substrate utilisation and biomass growth, the kinetic coefficients of growth yield coefficient (Y), specific microorganism decay rate (Kd), half saturation constant (Ks) and maximum specific growth rate (μmax) were found to be 0.79 g VSS g COD−1, 0.012 day−1, 1.78 g COD L−1 and 0.357 day−1, respectively.

Mathematical modelling of flat plate biofilm photobioreactors with circular and rectangular configurations

Flat plate photobioreactors (FPPBRs) using bacterial biofilm have gained much recent attention due to operational ease, improved light conversion efficiency and reduction of process cost, particularly in hydrogen production. In this study, two comprehensive mathematical models, one explaining the dynamics of a batch type FPPBR used for the development of biofilm and the other a deterministic model (both temporal and spatial) to predict the performance of a continuous FPPBR using Rhodopseudomonas sp. have been developed for both circular and rectangular configurations. The system equations have been solved using MATLAB 2013. From batch studies, the maximum specific growth rate and half saturation constant for the microorganism have been determined to be 0.07 h−1 and 1.946 g l−1 respectively. An “Instantaneous attachment and proliferation” mechanism has been proposed to explain the behaviour of biofilm right from the early stage of attachment to the reversal from attached to planktonic state. The flow patterns of substrate medium through the biofilm have been generated using COMSOL Multiphysics software. From the perspective of the hydrogen yield, the models predict that the FPPBR geometry plays a crucial role by demonstrating the superior performance of the circular reactor in comparison to the rectangular counterpart. It is expected that the mathematical models developed here will help in the design, scale-up and control of FPPBRs to be used particularly for hydrogen production using suitable microorganisms.

Production and cleavage of a fusion protein of porcine trypsinogen and enhanced green fluorescent protein (EGFP) in Pichia pastoris.

Pharmaceutical grade trypsin is in ever-increasing demand for medical and industrial applications. Improving the efficiency of existing biotechnological manufacturing processes is therefore paramount. When produced biotechnologically, trypsinogen-the inactive precursor of trypsin-is advantageous, since active trypsin would impair cell viability. To study factors affecting cell physiology and the production of trypsinogen in fed-batch cultures, we built a fusion protein of porcine trypsinogen and enhanced green fluorescent protein (EGFP) in Pichia pastoris. The experiments were performed with two different pH values (5.0 and 5.9) and two constant specific growth rates (0.02 and 0.04 1/h), maintained using exponential addition of methanol. All the productivity data presented rely on an active determination of trypsin obtained by proteolysis of the trypsinogen produced. The pH of the medium did not affect cell growth, but significantly influenced specific production of trypsinogen: A 1.7-fold higher concentration of trypsinogen was achieved at pH5.9 (64mg/L at 0.02 1/h) compared to pH5.0. EGFP was primarily used to facilitate detection of intracellular protein over the biosynthetic time course. Using flow cytometry with fluorescence detection, cell disruption was avoided, and protein extraction and purification prior to analysis were unnecessary. However, Western blot and SDS-PAGE showed that cleavage of EGFP-trypsinogen fusion protein occurred, probably caused by Pichia-endogenous proteases. The fluorescence analysis did therefore not accurately represent the actual trypsinogen concentration. However, we gained new experimentally-relevant insights, which can be used to avoid misinterpretation of tracking and quantifying as well as online-monitoring of proteins with the frequently used fluorescent tags.