Anaerobic Batch Fermentation Research Articles

Conversion of furfural in aerobic and anaerobic batch fermentation of glucose by Saccharomyces cerevisiae

The effect of furfural on aerobic and anaerobic batch cultures of Saccharomyces cerevisiae CBS 8066 growing on glucose was investigated. Furfural was found to decrease both the specific growth rate and ethanol production rate after pulse additions in both anaerobic and aerobic batch cultures. The specific growth rate remained low until the furfural had been completely consumed, and then increased somewhat, but not to the initial value. The CO 2 evolution rate decreased to about 35% of the value before the addition of 4 g · l −1 furfural, in both aerobic and anaerobic fermentations. The decrease of the CO 2 evolution rate was rapid at first, and then a more gradual decrease was observed. The furfural was converted mainly to furfuryl alcohol, with a specific conversion rate of 0.6 (±0.03) g (furfural)· g −1 (biomass)· h −1 by exponentially growing cells. However, the conversion rate of furfural by cells in the stationary phase was much lower. A previously unidentified compound was detected during the conversion of furfural. This compound was characterized by mass spectrometry and it is suggested that it is formed from furfural and pyruvate.

Balancing phosphine in manure fermentation

The evolution of phosphine gas during the anaerobic batch fermentation of fresh swine manure was detected and correlated to the production of methane and hydrogen sulphide. A close temporal relationship between phosphine liberation and methane formation was found. However, the gaseous phosphine released from manure during fermentation only represents a tiny fraction of the overall phosphine balance. The majority of phosphine is captured in solid manure constituents. This matrix‐bound phosphine is eliminated by more than 50% during anaerobic batch‐fermentation. Seasonally determined phosphine concentrations in biogas and manure from two large‐scale manure treatment plants also revealed net losses of phosphine in fermentation. Consequently, manure has to be considered more as a sink of phosphine rather than a phosphine‐generating medium. Furthermore, a close relationship between phosphine in the feed of swine and manure of these swine was observed, implying that phosphine residues in the feed (possibly as a result of grain fumigation) represent an important source of phosphine in manure technologies that is relevant before the faecals of swine enter manure treatment plants.

Kinetic studies on glycerol production from molasses and akalona hydrolyzate

A mathematical model for the kinetics of substrate utilization and glycerol production during anaerobic batch fermentation of molasses and Akalona hydrolyzate, as a waste material, was developed. The kinetic study covered also glucose as a standard substrate for the yeast Saccharomyces cerevisae which is to be used in the course of the reaction. It was found that substrate utilization follows first order kinetics with a rate constant k equal to 0.0192, 0.0119 and 0.0085 for glucose, molasses and Akalona hydrolyzate, respectively. A new model was investigated to estimate the specific glycerol production rate during the exponential phase only, which is independent of substrate utilization rate and the specific growth rate of the microbial cells. Thus, it simplified the calculation of the kinetic parameters. The new model was found to simulate glycerol production from the three substrates very well. Also, the kinetic model for glycerol production was tested and the kinetic parameters were calculated.

The effects of pantothenate deficiency and acetate addition on anaerobic batch fermentation of glucose by Saccharomyces cerevisiae.

Physiological effects of deficiency of pantothenate, a necessary precursor in the synthesis of coenzyme A, were studied using the yeast strain Saccharomyces cerevisiae CBS 8066. Cells were grown on defined media in anaerobic batch cultures with glucose (50 g/l) as the carbon and energy source. Batch cultures containing more than 60 micrograms/l pantothenate showed no significant differences with respect to growth rates and product yields. However, with an initial pantothenate concentration at 30 micrograms/l, the average glucose consumption rate was 50% lower than in rich medium and, at even lower concentration of pantothenate, the culture did not consume all the glucose in the medium. Furthermore, pantothenate deficiency caused the acetate and pyruvate yields to increase and the biomass yield to decrease, compared to the yields in pantothenate-rich medium. The increased acetate formation could be counteracted by initial addition of acetate to the medium, and thereby the glycerol yield could be decreased. An initial addition of acetate of 1.6 g/l to pantothenate-deficient medium (30 micrograms/l) caused a 35% decrease in glycerol yield and a 6% increase in ethanol yield. Furthermore, the time required for complete conversion of the glucose decreased by 40%. Acetate addition affected the acetate and glycerol yields in a similar way in pantothenate-rich medium (1000 micrograms/l) also.

Process kinetics and digestion efficiency of anaerobic batch fermentation of brewer's spent grains (BSG)

The process kinetics of optimized anaerobic batch digestion of brewer's spent grains (BSG) reveal that biomethanation is essentially a first order reaction interrupted intermittently by mixed order reactions. An apparent cellulose degradation efficiency of approximately 60% and a lignin degradation efficiency of about 40% was observed in the optimized process. Using the Ken and Hashimoto model, the operational efficiency of the digester was determined to be 26%.

Production of ethanol from pulp mill hardwood and softwood spent sulfite liquors by genetically engineered E. coli.

Although lignocellulosic biomass and wastes are targeted as an attractive alternative fermentation feedstock for the production of fuel ethanol, cellulosic ethanol is not yet an industrial reality because of problems in bioconversion technologies relating both to depolymerization and fermentation. In the production of wood pulp by the sulfite process, about 50% of the wood (hemicellulose and lignin) is dissolved to produce cellulose pulp, and the pulp mill effluent ("spent sulfite liquor" SSL) represents the only lignocellulosic hydrolysate available today in large quantities (about 90 billion liters annually worldwide). Although softwoods have been the traditional feedstock for pulping operations, hardwood pulping is becoming more popular, and the pentose sugars in hardwood SSL (principally xylose) are not fermented by the yeasts currently being used in the production of ethanol from softwood SSL. This study assessed the fermentation performance characteristics of a patented (US Pat. 5,000,000), recombinant Escherichia coli B (ATCC 11303 pLOI297) in anaerobic batch fermentations of both nutrient-supplemented soft and hardwood SSL (30-35 g/L total reducing sugars). The pH was controlled at 7.0 to maximize tolerance to acetic acid. In contrast to the high-performance characteristics exhibited in synthetic media, formulated to mimic the composition of softwood and hardwood SSL (yield approaching theoretical maximum), performance in SSL media was variable with conversion efficiencies in the range of 67-84% for hardwood SSL and 53-76% for softwood SSL. Overlimiting treatment of HSSL, using Ca(OH)2, improved overall volumetric productivity two- to sevenfold to a max of 0.42 g/L/h at an initial cell loading of 0.5 g dry wt/L. A conversion efficiency of 92% (6.1 g/L ethanol) was achieved using diluted Ca(OH)2-treated hardwood SSL. The variable behavior of this particular genetic construct is viewed as a major detractant regarding its candidacy as a biocatalyst for SSL fermentations.

The effect of carbon dioxide on xylose fermentation byPichia stipitis

Carbon dioxide was found to reduce the xylose fermentation rate of two different strains ofPichia stipitis (CBS 5773 and CBS 5776) significantly in anaerobic batch fermentations. The maximum specific fermentation rate in a carbon dioxide atmosphere was about 45% lower than the fermentation rate in nitrogen atmosphere. Further-more, the fermentation rate was found to be correlated to the growth rate. It is probable that the carbon dioxide influences the fermentation rate partly through decreasing the growth rate. It was also found that the fermentation rate of CBS 5773 was higher than for CBS 5776 and that the specific fermentation rate was lower at a higher cell density.

Ultimate anaerobic biodegradability of some agro-industrial residues

Anaerobic mesophilic batch fermentations of the agro-industrial residues sugarbeet pulp, potato pulp and brewery grain were carried out to evaluate their ultimate biodegradability and first-order decay rates. Each 5-liter batch reactor was operated for 37–85 days, at substrate-to-inoculum ratios (S/I) ranging from 0·5 to 1·3 on initial total volatile solid (TVS) mass basis. Ultimate biodegradabilities of 92–94% for sugarbeet pulp, 86–91% for potato pulp and 76–78% for brewery grain were obtained at the S/I of 0·8. There was no big difference in the ultimate biodegradability based on two independent methods: biogas production or mass loss. The substrate degradation was described by two distinct first-order decay rates (k 1 and k 2) which could be separated by a simple visual fitting. At the S/I of 0·8, most initial decay reactions accelerated within 4–7 days with an average k 1 of 0·26 day −1 for sugarbeet pulp, 0·19 day −1 for potato pulp, and 0·18 day −1 for brewery grain. The mean values for the long-term, batch, first-order decay coefficients (k 2) were 0·071 day −1 for sugarbeet pulp during days 7–37, 0·016 day −1 for potato pulp during days 15–85 and 0·063 day −1 for brewery grain during days 7–24.

Modeling Anaerobic Batch-Fermentation of Glucose to Methane

ABSTRACT THE rate equations for substrate degradation, inter-mediates appearance and disappearance, and end-product production for anaerobic batch fermentation of organic matters to produce methane were formulated based on conservation of chemical oxygen demand (COD) and the stoichiometric equations of the fermentation. The substrate COD was partitioned into cells' COD and products' COD. The amount of COD to each product was based on the relative amount of COD of the product in the stoichiometric formulas. The simulation shows that quantitative changes of substrate, intermediates and products can be predicted based on the assumption that the COD in the anaerobic fermentation is conserved. The relationships between substrate, intermediates and the products follow the relationship of the stoichiometric equations. Since the formulation of the rate equations concerns with only COD values and the substances without COD value are not included in the formulation, this will greatly reduce the complexity of the simulation processes.

In situ methane fermentation of combined agricultural residues

Agricultural activities produce large quantities of residues from which energy may be recovered. An experimental feasibility program was conducted on high solids in situ or batch anaerobic fermentation of combined agricultural residues for conversion to fuel gas. Several straws (rice, wheat, and barley) and food processing wastes in combination with several types of manures were tested. The orientation of this work was to large scale methane recovery from controlled landfilling. Individual fermenter runs were monitored for long periods and with various combinations of waste materials, nutrients, buffer, moisture, and NaOH pretreatment. It was found that total residue conversion (dry weight) to fuel gas was 21% for untreated rice straw and 16% for untreated wheat straw after 60 days in situ anaerobic fermentation at mesophilic conditions, buffered with CaCO 3 with inocula and nutrients from sewage digester effluent. Tomato pulp reached 50% conversion to fuel gas at 40 days and 75% conversion at 175 days. Rice straw pretreated with 0.1 N NaOH combined with tomato wet waste and dairy cattle manure reached 26% conversion at 175 days. Onion/garlic residues suppressed methane fermentation but permitted fermentation to organic acids. Calcium carbonate aqueous slurry was an effective method to control pH during in situ fermentation, and may be practical for single year-to-year treatment of straw and food waste, as a low capital cost methane recovery process compared to conventional higher technology/capital systems which would be operated for short times. Results are not conclusive and longer term experiments should be conducted.