Simplified modeling of fed-batch alcoholic fermentation of sugarcane blackstrap molasses

THE EFFECT OF THE INTENSITY OF AERATING THE MEDIUM ON THE METABOLIC ACTIVITY OF ALCOHOL YEAST

The article presents the results of investigating how the intensity of aerating the medium effects on the cultivation process and the metabolic activity of alcoholic yeast Saccharomyces cerevisiae, strain U-563, in the modern technology of alcohol and baking yeast from molasses. The chemical and technological parameters of media at the aerobic and anaerobic stages of the process, the level of accumulation of the major and secondary products of yeast metabolism, and their enzymatic activity have been determined by methods commonly employed in science and in the practice of alcohol biotechnology. The objects of research were the yeast Saccharomyces cerevisiae, molasses wort, the medium in the process of yeast cultivation, and fermented wash. It has been established that two factors are the most important in the accumulation of alcoholic yeast biomass: the intensity of aerating the medium, and the staged introduction of the substrate during biomass cultivation. The more aerated the medium, the more intensively secondary metabolites of yeast Saccharomyces cerevisiae are formed (glycerol, aldehydes, higher alcohols, volatile acids, and esters) – both at the yeast generation stage and during anaerobic fermentation. When yeast Saccharomyces cerevisiae is grown in a gradient-continuous manner in a battery of series-connected apparatuses, with undiluted substrate (molasses) added by degrees, yeast biosynthesis is significantly enhanced compared to the traditional homogeneous-continuous method. The results obtained indicate the active metabolism of carbohydrates in the Krebs cycle, when the medium is intensively aerated. Besides, the results reveal the high reactivity of aldehydes and esters that results in their transformation into other compounds, and in a great decrease in their amount at the anaerobic stage of the process. However, a progressive increase is observed in glycerol, higher alcohols, and volatile acids, starting from the first yeast generator and up to the last fermentation apparatus, irrespective of the level of aerating the medium during yeast cultivation. These findings can be effectively used to manufacture food, technical, and fuel ethanol industrially from sugar-based raw materials in the course of co-production of alcohol and baking yeast.

Enhanced ethanol production at commercial scale from molasses using high gravity technology by mutant S. cerevisiae

Very high gravity (VHG) technology was employed on industrial scale to produce ethanol from molasses (fermented) as well as by-products formation estimation. The effect of different Brix° (32, 36 and 40) air-flow rates (0.00, 0.20, 0.40, and 0.60 vvm) was studied on ethanol production. The maximum ethanol production was recorded to be 12.2% (v/v) at 40 Brix° with 0.2 vvm air-flow rate. At optimum level aeration and 40 Brix° VHG, the residual sugar level was recorded in the range of 12.5–18.5 g/L, whereas the viable cell count remained constant up to 50 h of fermentation and dry matter production increased with fermentation time. Both water and steam consumption reduced significantly under optimum conditions of Brix° and aeration rate with compromising the ethanol production. Results revealed VHG with continuous air flow is viable technique to reduce the ethanol production cost form molasses at commercial scale.

Alcoholic fermentation with flocculant Saccharomyces cerevisiae in fed-batch process

Studies have been conducted on selecting yeast strains for use in fermentation for ethanol production to improve the performance of industrial plants and decrease production costs. In this paper, we study alcoholic fermentation in a fed-batch process using a Saccharomyces cerevisiae yeast strain with flocculant characteristics. Central composite design (CCD) was used to determine the optimal combination of the variables involved, with the sucrose concentration of 170 g/L, a cellular concentration in the inoculum of 40% (v/v), and a filling time of 6 h, which resulted in a 92.20% yield relative to the theoretical maximum yield, a productivity of 6.01 g/L h and a residual sucrose concentration of 44.33 g/L. With some changes in the process such as recirculation of medium during the fermentation process and increase in cellular concentration in the inoculum after use of the CCD was possible to reduce the residual sucrose concentration to 2.8 g/L in 9 h of fermentation and increase yield and productivity for 92.75% and 9.26 g/L h, respectively. A model was developed to describe the inhibition of alcoholic fermentation kinetics by the substrate and the product. The maximum specific growth rate was 0.103 h(-1), with K(I) and K(s) values of 109.86 and 30.24 g/L, respectively. The experimental results from the fed-batch reactor show a good fit with the proposed model, resulting in a maximum growth rate of 0.080 h(-1).

A novel full recycling process through two-stage anaerobic treatment of distillery wastewater for bioethanol production from cassava

In the present study, a novel full recycling process for bioethanol production was investigated, where three mathematical models were established to simulate the accumulation of major soluble inhibitory substances, including organic compounds, total ions, volatile fatty acids (VFAs) and colorants. These inhibitory substances in the reused water reached a relative steady state after 3-7 batches of anaerobic treatment and recycling process, which coincided with the results of mathematical models. There were no negative effects of these inhibitory substances on ethanol fermentation and the final ethanol yield, fermentation time, starch utilization ratio were very close to that of the conventional process using tap water. However, approximately 7.54% (w/w) of water was lost during each circulation, which was replenished in subsequent circulations, to assure consistent fermentation broth volume. This novel process was confirmed to have a stable operation over 13 recycles. It is concluded the stable states of the inhibitory substances in the reused water can assure this recycling process will run successfully.

Optimization of Fed-Batch Saccharomyces cerevisiae Fermentation Using Dynamic Flux Balance Models

We developed a dynamic flux balance model for fed-batch Saccharomyces cerevisiae fermentation that couples a detailed steady-state description of primary carbon metabolism with dynamic mass balances on key extracellular species. Model-based dynamic optimization is performed to determine fed-batch operating policies that maximize ethanol productivity and/or ethanol yield on glucose. The initial volume and glucose concentrations, the feed flow rate and dissolved oxygen concentration profiles, and the final batch time are treated as decision variables in the dynamic optimization problem. Optimal solutions are generated to analyze the tradeoff between maximal productivity and yield objectives. We find that for both cases the prediction of a microaerobic region is significant. The optimization results are sensitive to network model parameters for the growth associated maintenance and P/O ratio. The results of our computational study motivate continued development of dynamic flux balance models and further exploration of their application to productivity optimization in biochemical reactors.

Fuel ethanol production: process design trends and integration opportunities

Current fuel ethanol research and development deals with process engineering trends for improving biotechnological production of ethanol. In this work, the key role that process design plays during the development of cost-effective technologies is recognized through the analysis of major trends in process synthesis, modeling, simulation and optimization related to ethanol production. Main directions in techno-economical evaluation of fuel ethanol processes are described as well as some prospecting configurations. The most promising alternatives for compensating ethanol production costs by the generation of valuable co-products are analyzed. Opportunities for integration of fuel ethanol production processes and their implications are underlined. Main ways of process intensification through reaction-reaction, reaction-separation and separation-separation processes are analyzed in the case of bioethanol production. Some examples of energy integration during ethanol production are also highlighted. Finally, some concluding considerations on current and future research tendencies in fuel ethanol production regarding process design and integration are presented.