Pramod Agrawal

Glutamine decomposition in DMEM: Effect of pH and serum concentration

SummaryThe pH and serum dependence of the glutamine decomposition rate constant, Kgln, in Dulbeccos Modified Eagles Medium, DMEM, was determined. The findings indicate that Kgln increases with increase in pH and fetal calf serum (FCS) concentration in DMEM. At a constant pH of 7.25, Kgln increases from 5.7×10−4 to 13.2×10−4 h−1 as FCS content of the medium increases from 0.0 to 10.0 (% v/v). Moreover, at a constant FCS of 10 (% v/v), Kgln increases from 11.5×10−4 to 33.6×10−4 h−1 as pH of the medium increases from 7.2 to 7.6.

The effect of CO2 ventilation on kinetics and yields of cell-mass and ethanol in batch cultures ofZymomonas mobilis

SummaryThe effect of CO2 removal by continuous sparging of N2 in batch cultures ofZymomonas mobilis (ATCC10988) was examined. N2 sparging considerably reduces lag times in batch cultures, possibly because of continuous removal of CO2 from the culture media. Ventilation of CO2 from culture media results in an increase of about 15% in the average specific growth rate and about 12% in the cell-mass yield with no noticeable trend in the average specific glucose uptake and ethanol production rates. The overall ethanol yield on glucose, however, decreases slightly by 5%. Analysis of ventilated experiments show that the CO2 production is directly coupled with the ethanol formation but not necessarily with the cell-mass production, indicating a decoupling of growth from ethanol production. Further, comparison of ventilated and non-ventilated experiments rules out the possibility of CO2 accumulation in the culture media as a factor responsible for increasing growth inhibition and decoupling of growth from ethanol fermentation at increasing initial glucose concentrations in batch cultures.

An experimental study of acid production rate controlled operations of a continuous fermentor

The efficacy of acid production rate (APR) controlled operations of a continuous fermentor supporting the growth of a methylotroph, L3, was experimentally examined. Direct digital control of pH at a constant value allowed for on-line estimation of APR during the fermentation. Two types of APR controlled operations were studied. In the first type of operation, the APR was controlled at a constant value according to a predetermined program by manipulating the feed flow rate to the fermentor. Such an operation effectively stabilized the cell mass productivity of a continuous fermentor subjected to disturbances in the feed nutrient concentration. It resulted in a near complete conversion of methanol to yield a cell mass product with very low amounts of unutilized methanol at both steady state and transient fermentation situations. In the second type of operation, the feed flow rate was manipulated to optimize the steady state value of APR during the fermentation. This method shows promise for on-line steady state optimization of cell mass productivity in a continuous fermentor.

Non-linear adaptive control of fermentation processes utilizing a priori modelling knowledge

Abstract This paper describes both SISO and MIMO adaptive versions of non-linear generic model control (GMC) applied to a bakers yeast fermentation. A mechanistic non-linear model is used whose structure can represent a wide range of different fermentation systems and operating conditions. This a priori representation of process knowledge is then combined with a simple and effective adaptation scheme to yield optimal flexibility of the model. Only a few parameters which appear linearly in the model need to be estimated on-line, resulting in very fast and potentially offset-free tracking of the process by the model-based controller. Simulations demonstrate that an adaptive MIMO version of GMC is superior to the corresponding non-adaptive version when faced with modelling errors. Experiments with a bench-scale yeast fermentation system demonstrate for the SISO case the applicability of adaptive non-linear control methods to an actual process and compare adaptive GMC performance with that of a conventional PI controller.

Nonlinear adaptive optimization of biomass productivity in continuous bioreactors

A novel on-line adaptive optimization algorithm is developed and applied to continuous biological reactors. The algorithm makes use of a simple nonlinear estimation model that relates either the cell-mass productivity or the cell-mass concentration to the dilution rate. On-line estimation is used to recursively identify the parameters in the nonlinear process model and to periodically calculate and steer the bioreactor to the dilution rate that yields optimum cell-mass productivity. Thus, the algorithm does not require an accurate process model, locates the optimum dilution rate online, and maintains the bioreactors at this optimum condition at all times. The features of the proposed new algorithm are compared with those of other adaptive optimization techniques presented in the literature [1–5]. A detailed simulation study using three different microbial system models [3, 6–7] was conducted to illustrate the performance of the optimization algorithm.

An experimental study of a modified turbidostat

The efficacy of a modified turbidostat scheme for control of a continuous fermentor supporting substrate - inhibited growth of a methylotroph, L3, was experimentally examined. The control was based on continuous measure of optical density of fermentation broth. The experimental results illustrate the feasibility of the control scheme for effective startup as well as stabilization of a continuous fermentor under the influence of a load disturbance.