No abstract

A model-based analysis of a three-phase continuously operated fluidized bed bioreactor is developed in order to determine the multi-objective optimal feeding policy of the immobilized biomass used for removing mercury ions from wastewater. The analysis is focus on finding the optimal feeding policy of alginate porous beads of known particle size containing immobilized biomass (Pseudomonas putida bacteria) to minimize the biomass consumption, while keeping a quasi-constant high conversion. The extended bioreactor model is accounting for the biomass growth, biodegradation, and its partial leakage and washout. Bioreactor dynamics prediction has been generated by using a simple Michaelis-Menten kinetic model adopted from literature. The resulted optimal feeding policy of the bioreactor points out the importance of the adoption of an extended and adequate process/reactor model able to solve engineering operation problems by quickly adjusting the feeding conditions according to the time-varying characteristics of the biomass culture and to the limited possibilities to control the process during the wastewater residence time in the bioreactor.Production of penicillin, [42] secreted recombinant proteins, [47] microbial growth, [56] acetic acid, [51] lactic acid from whey lactose, [52] citric acid, [53,57] polysaccharide pullulan by fungi Aureobasidium pullulans [58] and so on Asia-Pacific Journal of Chemical Engineering BIOREACTOR OPTIMIZATION FOR MERCURY UPTAKE FROM WASTEWATERS 723 Footnote: A Hg = 200.59 atom-g, mercury atomic mass; c XL, inlet,100 = inlet concentration of the immobilized biomass for the running time arc 0 ≤ t ≤ 100 min (ref. to the reactor liquid); c XL, inlet,200 = inlet concentration of the immobilized biomass for running time arc 100 ≤ t ≤ 200 min (ref. to the reactor liquid); c XL, inlet,300 = inlet concentration of the immobilized biomass for running time arc 200≤ t ≤ 300 min (ref. to the reactor liquid);G-L mass transfer on the liquid side: k L a L = 0.022 s À1 (experimental [19] ). L-S mass transfer on the liquid side: k s = Sh × D L /d p (for Hg 2þ L ; with Sh correlated with the operating conditions [37] ) a s = (6ε s )/d p (spherical particles); k s a s = 0.0114 s À1 (experimental [19] )Asia-Pacific Journal of Chemical Engineering BIOREACTOR OPTIMIZATION FOR MERCURY UPTAKE FROM WASTEWATERS 729

No abstract

No abstract

Genetic regulatory circuits (GRCs) including switches, oscillators, signal amplifiers or filters, and signalling circuits are responsible for the control of cell metabolism. Modelling such complex GRCs is a difficult task due to high complexity of the the process (partly known) and the structural, functional and temporal hierarchical organisation of the cell system. Modular lumped representation, grouping some reactions/components and including different types of variables, is a promising alternative allowing individual module characterisation and elaboration of extended simulation platforms for representing the GRC dynamic properties and designing new cell functions. Such models allow to in-silico design modified micro-organisms with desirable properties for practical applications in bioprocess engineering and biotechnology. In the present work, the analysis of a designed bistable switch formed by two gene expression modules is performed in a variable-volume and whole-cell modelling framework, by mimicking the Escherichia coli cell growth. The advantages but also limitations of such a new approach are investigated, by using a Hill-type kinetics combined with few elementary steps, with the aim of better representing the adjustable levels of key intermediates tuning the GRC regulatory properties in terms of stability strength, species connectivity, responsiveness, and regulatory efficiency under stationary and dynamic perturbations. 

No abstract

Autonomous oscillations of species levels in the glycolysis express the self-control of this essential cellular pathway belonging to the central carbon metabolism (CCM), and this phenomenon takes place in a large number of bacteria. Oscillations of glycolytic intermediates in living cells occur according to the environmental conditions and to the cell characteristics, especially the adenosine triphosphate (ATP) recovery system. Determining the conditions that lead to the occurrence and maintenance of the glycolytic oscillations can present immediate practical applications. Such a model-based analysis allows in silico (model-based) design of genetically modified microorganisms (GMO) with certain characteristics of interest for the biosynthesis industry, medicine, etc. Based on our kinetic model validated in previous works, this paper aims to in silico identify operating parameters and cell factors leading to the occurrence of stable glycolytic oscillations in the Escherichia coli cells. As long as most of the glycolytic intermediates are involved in various cellular metabolic pathways belonging to the CCM, evaluation of the dynamics and average level of its intermediates is of high importance for further applicative analyses. As an example, by using a lumped kinetic model for tryptophan (TRP) synthesis from literature, and its own kinetic model for the oscillatory glycolysis, this paper highlights the influence of glycolytic oscillations on the oscillatory TRP synthesis through the PEP (phosphoenolpyruvate) glycolytic node shared by the two oscillatory processes. The numerical analysis allows further TRP production maximization in a fed-batch bioreactor (FBR).

No abstract