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Three pilot-scale bioreactors were started up and operated under salinity-amended urban wastewater feeding. The bioreactors were configured as membrane bioreactor and two different hybrid, moving bed biofilm reactor-membrane bioreactor and operated with a hydraulic retention time of 9.5 h, a solid residence time of 11.75 days and a total solids concentration of 2500 mg L-1 . The three systems showed excellent performance in suspended solids, BOD5 , and COD removal (values of 96-100%, 97-99%, and 88-90%, respectively), but poor nitrogen removal (values of 20-30%). The bacterial community structure during the start-up phase and the stabilization phase were different, as showed by β-diversity analyses. The differences between aerobic and anoxic biomass-and between suspended and attached biomass-were higher at the start-up phase than at the stabilization phase. The start-up phase showed high abundances of Chiayiivirga (mean values around 3-12% relative abundance) and Luteimonas (5-8%), but in the stabilization phase, the domination belonged to Thermomonas (3-14%), Nitrobacter (3-7%), Ottowia (3-11.5%), and Comamonas (2-6%), among others. Multivariate redundancy analyses showed that Thermomonas and Nitrosomonas were positively correlated with fast autotrophic kinetics, while Caulobacter and Ottowia were positively correlated with fast heterotrophic kinetics. Nitrobacter, Rhodanobacter, and Comamonas were positively correlated with fast autotrophic and heterotrophic kinetics. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1483-1495, 2017.

Scale-up of bioprocesses is hampered by open questions, mostly related to poor mixing and mass transfer limitations. Concentration gradients of substrate, carbon dioxide, and oxygen in time and space, especially in large-scale high-cell density fed-batch processes, are likely induced as the mixing time of the fermentor is usually longer than the relevant cellular reaction time. Cells in the fermentor are therefore repeatedly exposed to dynamic environments or perturbations. As a consequence, the heterogeneity in industrial practices often decreases either yield, titer, or productivity, or combinations thereof and increases by-product formation as compared to well-mixed small-scale bioreactors, which is summarized as scale-up effects. Identification of response mechanisms of the microorganism to various external perturbations is of great importance for pinpointing metabolic bottlenecks and targets for metabolic engineering. In this review, pulse response experimentation is proposed as an ideal way of obtaining kinetic information in combination with scale-down approaches for in-depth understanding of dynamic response mechanisms. As an emerging tool, computational fluid dynamics is able to draw a holistic picture of the fluid flow and concentration fields in the fermentor and finds its use in the optimization of fermentor design and process strategy. In the future, directed strain improvement and fermentor redesign are expected to largely depend on models, in which both microbial kinetics and fluid dynamics are thoroughly integrated.

Microbiological and modeling (combined heat transfer and microbial kinetic equations [HTMK] model) approaches were used to determine the location of microorganisms within cucumber. The total number of aerobes found within/on cucumbers varied from 10 5 to 10 7 colony-forming units (CFU)/g. The highest and the least amount of microbiota were respectively found at the blossom end and middle part of the cucumbers and were within the 1st 6 mm of the cucumber surface. A comparison of the calculated thermal death time from the HTMK model with the values obtained from experimental data showed that total aerobic microorganisms were located within 0.65 mm of the fruit surface.

Context:In this review, we discuss empirical and stoichiometric models, which have been developed recently in SSF processes and the influence of environmental conditions on the variables of these models. Additionally, new studies on modeling of product formation are also mentioned. Evidence Acquisition:Solid-state fermentation (SSF) is recognized as a cheap process for producing many valuable products like industrial enzymes and bioethanol. To develop, optimize, and scale-up this process, mathematical models are required. In this review, we collected all the papers regarding microbial growth and product formation modeling in SSF. The pros and cons of each model and confirmation with experimental data were also discussed. We discussed here the simple empirical growth kinetics models and the effect of environmental conditions on these models parameters, stoichiometric models and product formation models. Results:Simple empirical models are used widely in the kinetic modeling of SSF processes due to their simplicity and ease of use. However, more studies should be done in this field to make them more accurate, especially; the effect of environmental conditions, like temperature and moisture, on key variables of the model must be considered. Robust modeling methods, like stoichiometric models, are in their early stages in SSF processes and require more studies. Developing models in which transport phenomena models are coupled with the growth kinetics models can help better SSF bioreactor designing. On the other hand, to use SSF for producing valuable products, product formation models, which are not developed well in SSF processes, are necessary. Conclusions:To use SSF for producing valuable metabolites in large scales, more attention is required for modeling the SSF processes, especially for product formation models and using modern methods like stoichiometric models.

Anaerobic sequencing batch reactors (ANSBRs) typically have not been used to treat wastewater, possibly because of the potential rapid acidification that may occur with batch feeding of an anaerobic reactor. To investigate ANSBR capabilities, a simulation model was developed and experimentally validated. The model explicitly considers different microbial populations in an anaerobic community, predicts formation and consumption of intermediate products as a function of hydrogen partial pressure, predicts system pH, and considers inhibition caused by pH and hydrogen partial pressure. Simulation model results agreed well with experimental results from three separate tests using a laboratory-scale ANSBR receiving glucose. Experimental and simulation results indicated that, for the same organic loading rate, reactor performance improved with a slower fill cycle. The model may be used to rapidly identify other opportunities to improve the capability of ANSBRs to treat a variety of wastewater types.

The object of the present article is the characterization of mixing processes in small pilot plant bioreactors used in our laboratory for studies of the microbial kinetics of Penicillium chrysogenum and Aspergillus oryzae. The characterization is based on injection of the radioactive isotope 1 13m In, followed by measurement of the radioactivity at different positions in the tank using scintillation counters placed outside the bioreactor

It is conventional to describe the relationship between the specific rate of microbial growth and the concentration of the inhibitory substrate in terms of the Andrews–Edwards equation. A novel method for establishing the constants of this equation is presented. The equation is transformed to a polynomial and the empirical data are approximated by a quadratic polynomial. The results obtained for the biodegradation of phenol in a mixed culture (activated sludge) are discussed.

Biodegradability testing is examined and the many factors affecting extrapolation of laboratory biodegradation results to microbial degradation in the environment are discussed. Recent advances in the understanding of the effects of the concentration and nature of various nutrients and organic substrates and modeling the microbial kinetics of degradation are reviewed. The advantages and disadvantages of screening methods and grab sample testing are discussed. The importance of groundwater biodegradation is also examined. Research needs are identified and guidelines are given to select various testing procedures to model diverse environmental situations.

Microbial kinetics and energetics are discussed in connection with the formulation of unstructured growth models. The development of microbial energetics and the use of macroscopic methods in the study of microbial growth are briefly evaluated. The general approach to the modelling of microbial growth has been critically discussed and a strategy for the formulation of unstructured models is presented. A simple unstructured model based on Monod kinetics and the linear relation for substrate consumption is evaluated with reference to extensive experimental and simulation data obtained in batch, fed-batch, and continuous cultivation modes. Choice for a kinetic expression is discussed and has been shown not to be critical in most situations. It is shown that during growth in batch mode, the behavior of the system is rigidly fixed by the kinetic parameter: the maximum specific growth rate. The energetic parameters have minimal influence. In continuous cultivation the behavior is fixed by the energetic parameters: the maximum yield and the coefficient of maintenance. Implications of these observations have also been discussed. The linear relation for substrate consumption is tested with continuous culture data. It is shown that significant deviations at low growth rates cannot be fully accounted by the loss of viability. The situations where unstructured models will be adequate or not for system description, are evaluated and checked experimentally. Influence of an environmental factor, the temperature, on the unstructured model parameters is also quantitatively described. It is concluded that the art of unstructured model building has already reached its maturity and that now much effort should be channelled into the development and verification of structured models.

The effect of the dynamics of the mixing process in mechanically stirred bioreactors upon their performance has been investigated by using a circulation-model for flow of fluid and a two-environment-model to account for the extent of micromixing in the vessel. With the help of an empirical kinetic model to depict the oxidative and the fermentative growth of bakers' yeast, experimentally observed effects of initial sugar concentrations upon critical dilution rates in continuous cultures of this system could be explained. Effect of different scales of operation upon productivities of fed-batch cultures of bakers' yeast could also be satisfactorily predicted. A discrete simulation procedure was found to be a convenient tool in coupling the two-environment circulation-model of mixing with kinetics of microbial reactions. On a etudie l'effet de la dynamique du processus de melange, dans les bioreacteurs agites mecaniquement, sur leurs performances; on a employe a cette fin un modele de circulation pour l'ecoulement du fluide et un modele comportant deux milieux pour representer le degre de micromelange dans le recipient. On a pu expliquer, grǎce a l'emploi d'un modele cinetique empirique de la croissance de la levure de boulangerie par oxydation et fermentation, les effets observes de la concentration initiale du sucre sur les vitesses de dilution critiques dans les cultures continues du systeme en question. On a pu aussi prevoir d'une maniere satisfaisante l'effet de l'operation a differentes echelles, sur les productivites des cultures de levure de boulangerie alimentees de maniere discontinue. On a trouve qu'une procedure de simulation discrete constituait un moyen approprie pour associer le modele de melange impliquant deux milieux, a la cinetique des reactions microbiennes.

The primary reactor type currently used in the production of microorganisms or microbial products is the stirred tank reactor (STR). If operated on a continuous flow basis (CFSTR) they become similar in performance to the primary reactor configuration used in most of the chemical industry. In this work, microbial kinetics are considered in the design of CFSTRs in series. An equation is derived to predict the minimum possible total residence time to achieve any desired substrate conversion. The equation permits the use of a wide variety of growth kinetic models and is applied here to Monod, substrate inhibition and product inhibition cases. For the majority of cases, it is found that three optimally designed CFSTRs in series provide close to the minimum possible residence time for any desired substrate conversion. A comparison to the use of a PFR is made for cases of both no-recycle and biomass recycle to the CFSTR train. It is found that three CFSTRs, which are not equi-volume, provide the same required total mean residence time as a PFR for Monod kinetics, but are significantly superior (i.e., less total volume required) to a PFR for substrate-inhibited growth. Le type de reacteur primaire habituellement utilise dans la production de microorganismes ou de produits microbiens est le reacteur agite (STR). En mode continu (CFSTR), la performance de ces reacteurs se compare a celle des reacteurs primaires utilises le plus souvent dans l'industrie chimique. On considere dans ce travail des cinetiques microbiennes pour la conception de reacteurs agites continus en serie. Une equation est etablie pour predire le temps de sejour total possible minimum pour obtenir les conversions voulues de substrat. Cette equation permet l'utilisation d'un large eventail de modeles cinetiques de croissance et est appliquee ici aux cas de Monod, de l'inhibition de substrat et de l'inhibition de produit. Dans la majorite des cas, on a trouve que trois reacteurs agites continus en serie concus de maniere optimale permettent de se rapprocher du temps de sejour possible minimum pour toute conversion de substrat desiree. On a effectue une comparaison entre ce type de reacteur et un PFR pour les cas d'un non-recyclage et d'un recyclage de biomasse dans la serie de reacteurs agites continus. On a trouve que trois reacteurs agites continus, qui n'ont pas le měme volume, donnent le měme temps de sejour moyen total requis qu'un PFR pour la cinetique de Monod, mais ils sont nettement plus performants (par exemple volume total requis moins important) que les PFR pour la croissance inhibee par le substrat.