Oscar F. von Meien

A review of recent developments in modeling of microbial growth kinetics and intraparticle phenomena in solid-state fermentation

Mathematical models are important tools for optimizing the design and operation of solid-state fermentation (SSF) bioreactors. Such models must describe the kinetics of microbial growth, how this is affected by the environmental conditions and how this growth affects the environmental conditions. This is done at two levels of sophistication. In many bioreactor models the kinetics are described by simple empirical equations. However, other models that address the interaction of growth with intraparticle diffusion of enzymes, hydrolysis products and O2 with the use of mechanistic equations have also been proposed, and give insights into how these microscale processes can potentially limit the overall performance of a bioreactor. The current article reviews the advances that have been made in both the empirical- and mechanistic-type kinetic models and discusses the insights that have been achieved through the modeling work and the improvements to models that will be necessary in the future.

Recent developments in modeling of solid-state fermentation: heat and mass transfer in bioreactors

Abstract Mathematical models are important tools for optimizing the design and operation of solid-state fermentation (SSF) bioreactors. Such models must describe the transport phenomena within the substrate bed and mass and energy exchanges between the bed and the other subsystems of the bioreactor, such as the bioreactor wall and headspace gases. The sophistication with which this has been done for SSF has improved markedly over the last decade or so. The current article reviews these advances, showing how the various transport phenomena have been modeled. It also discusses the insights that have been achieved through the modeling work and the improvements to models that will be necessary in order to make them even more powerful tools in the optimization of bioreactor performance.

Fast Offshore Wells Model (FOWM): A practical dynamic model for multiphase oil production systems in deepwater and ultra-deepwater scenarios

Abstract This work describes a simplified dynamic model for control and real time applications in offshore deepwater and ultra-deepwater petroleum production systems. Literature about simplified dynamical models, capable of cover the global architecture of an offshore multiphase production system, is scarce. Hence, the proposed model integrates and adapts partial models available in the literature in order to generate a single model of the whole system. The model, designed to represent slugs generated by the casing heading and terrain/riser concomitantly, was evaluated by comparison with a traditional commercial simulator and was also implemented in two actual production systems. As a result, the model showed the capability of capturing complex dynamical behaviors, such as limit cycles, demonstrated to be numerically more stable than similar models in literature, fast enough to be used in real time applications and proved to be adherent to the commercial simulator and actual operating data from Petrobras production systems.

Group II Bioreactors: Forcefully-Aerated Bioreactors Without Mixing

This chapter addresses the design and operation of SSF bioreactors under conditions where forced aeration is used but the substrate bed is not mixed. Typically these bioreactors are referred to as packed-bed bioreactors. This mode of operation is appropriate for those SSF processes in which it is not desirable to mix the substrate bed at all during the fermentation due to deleterious effects on either microbial growth or the physical structure of the final product. The characteristics of this mode of operation also apply to the static phases of forcefully-aerated bioreactors that are mixed once every few hours. The operation of such bioreactors will be discussed in Chap. 10; suffice to say for the moment that during the static phase they will act as packed-bed bioreactors, and therefore the principles developed in the present chapter will apply to this static phase.

The Scale-up Challenge for SSF Bioreactors

Having now seen the various types of bioreactors used in SSF processes (Chap. 3) and the transport phenomena that occur within them (Chap. 4), we now return to the question of how the limitations on the efficiency of the transport phenomena within the bioreactor make it almost impossible to operate large-scale bioreactors in such a manner that the conditions within the substrate bed are maintained throughout the process at the optimum values for growth and product formation. Is it really difficult to design an efficiently operating large-scale SSF bioreactor? In the case of SLF, there are examples of successfully operating bioreactors of hundreds of thousands of liters. Why cannot we do the same for SSF processes? Or can we? The answer is that the challenges in operating a bioreactor of several hundreds of thousands of liters are typically more difficult to overcome in SSF than in SLF, and it is no simple matter to develop efficient large-scale SSF bioreactors. This difficulty, often referred to as “the scale-up problem”, is discussed in the following sections.

Environmental Solid-State Cultivation Processes and Bioreactors

Solid-state cultivation involves the growth of microorganisms in beds of moist solid particles that have a minimum of free water between the particles. The chapter describes environmentally-related solid-state cultivation processes. For example, some processes use substrates that are residues of agriculture, forestry, or food-processing, thereby reducing the environmental impact of the residue. Other processes do not use residues, but produce products that have environmental applications. Still other processes use environmental-friendly biotransformations that have the potential to replace current industrial processes. Finally, some solid-state cultivation processes can be used to remove pollutants from soil or waste streams. Typically, environmental applications of solid-state cultivation involve large-scale processing of organic solids. The current chapter addresses the design and operation of bioreactors for these processes. It shows how the various bioreactor types can be classified according to the aeration strategy, namely whether the bed of solids is forcefully aerated or not, and according to the agitation strategy, namely the frequency of mixing of the bed of solids. It discusses the current state-of-the-art in optimizing the design and operation of the various bioreactor types, showing how mathematical models that combine microbial growth kinetics and heat and mass transfer phenomena are the most powerful tools that we have available for this task. The chapter concludes by highlighting the necessity to convert current mathematical models into user-friendly computer programs that can guide design and operation decisions for large-scale solid-state cultivation bioreactors.

Estimation of Transfer Coefficients for SSF Bioreactors

relatively little attention within SSF bioreactors. At the moment the available information is not sufficient to allow the proposal of general correlations and therefore it will be necessary to determine the coefficients experimentally for each particular bioreactor. In the absence of experimentally determined correlations, correlations for non-SSF systems can be used, although it must be realized that doing this may bring inaccuracies in the model predictions.

Group IVb: Intermittently-Mixed Forcefully-Aerated Bioreactors

Intermittently-mixed, forcefully-aerated bioreactors appear to have some potential, judging by the fact that several processes involving bioreactors that operate in this mode have been demonstrated at a reasonably large scale. They appear to offer some benefits in control of the conditions within the bed, while minimizing the deleterious effects that continuous mixing can have, at least for fungal processes.

A Model of an Intermittently-Mixed Forcefully-Aerated Bioreactor

True packed-bed operation can only be used in those cases where the bed does not dry out to levels that cause water limitations on growth, because water can only be uniformly distributed within a bed of solids while the solids are being agitated. If the organism tolerates some mixing, then the intermittently-mixed mode of operation can be used, in which the bioreactor operates as a packed-bed during the majority of the fermentation period and undergoes infrequent mixing events, during which water can be added to the bed (Chap. 10). In fact, once the intermittentlymixed mode of operation is selected, the use of dry air to promote evaporative cooling is potentially available as an operating strategy. The current chapter presents a model that can be used to investigate the operation of such bioreactors.

Modeling of Heat and Mass Transfer in SSF Bioreactors

This chapter has identified the forms of various terms that may appear within the balance/transport sub-model of a bioreactor model. Several of these will appear in energy and mass balances in the mathematical models of bioreactors presented in Chaps. 22 to 25. These equations contain various parameters that it will be necessary to determine before the model can be solved. Chapters 19 and 20 describe how these and other necessary parameters can be determined.