Single-stage Fermentation Research Articles

Direct fermentation of potato starch in wastewater to lactic acid byRhizopus oryzae

The fungal species ofRhizopus oryzae 2062 has the capacity to carry out a single stage fermentation process for lactic acid production from potato starch wastewater. Starch hydrolysis, reducing sugar accumulation, biomass formation, and lactic acid production were affected with variations in pH, temperature, and starch source and concentration. A growth condition with starch concentration approximately 20 g/L at pH 6.0 and 30°C was favourable for starch fermentation, resulting in a lactic acid yield of 78.3%–85.5% associated with 1.5–2.0 g/L fungal biomass produced in 36 h of fermentation.

Rapid-rate thermophilic, single-stage and two-phase methane fermentation of synfuel-industry wastewaters

Thermophilic (55 degrees C) anaerobic digestion of wastewaters from wet carbonization of Minnesota peat was conducted in a simple, upflow digester at an HRT of one day to provide a methane yield of 0.20 SCM/kg VS added and a BOD5 reduction of 85%. Carbonization of Maine peat conducted for a much longer duration of thermal treatment produced recalcitrant and potentially toxic end products that reduced the biodegradability of wastewaters. Methane fermentation of the Maine-peat wet-carbonization waste was inhibited at an HRT of one day in the single-stage digester. However, two-phase digestion with separate acid-phase fermentation to promote hydrolytic degradation of toxic end products followed by separate methane fermentation at an HRT of 2 days exhibited a methane yield of 0.21 SCM/kg VS added and a BOD5 reduction of 76%. Volatile fatty acids profiles along the depths digesting cultures indicated that single-stage and two-phase digestion could be accomplished at one-half the reactor residence times (one day for single-stage and three days for two-phase) used in this research.

Coimmobilized whole cells of Pseudomonas reptilivora and Micrococcus glutamicus in calcium alginate gel for the production of L-glutamic acid

A novel method of coimmobilized whole cells of Pseudomonas reptilivora and Micrococcus glutamicus, entrapped in calcium alginate beads have been used for the production of L-glutamic acid in a single stage fermentation process, using selected production medium enriched with glucose as substrate. The results obtained were compared with the L-glutamic acid production by free cells of Micrococcus glutamicus and by mixed culture of Pseudomonas reptilivora and Micrococcus glutamicus. The yield of glutamic acid obtained with mixed culture is relatively more than that the yield obtained with Micrococcus glutamicus alone. The properties of coimmobilized whole cells of Pseudomonas reptilivora and Micrococcus glutamicus in calcium alginate gel matrix have been investigated thoroughly and compared with those of free cells under most suitable conditions of fermentation.

Acidogenic fermentation of lactose

Cheese whey is the main component of waste streams from cheese manufacturing plants. Whey is a high biochemical oxygen demand (BOD) effluent that must be reduced before the streams are sent to the sewer. It is proposed in this article that the production of methane by anaerobic fermentation would be the best use of this stream, especially for small plants. Single-stage fermentation of lactose, the main component of whey, results in a very low pH and a stalled process. Two-phase fermentation will eliminate this problem. The acidogenic stage of fermentation has been studied at pH of between 4 and 6.5. The nature of the main products of the reaction have been found to be pH dependent. Below a pH of 4.5 a gas (CO(2) and H(2)) is produced along with ethanol, acetate, and butyrate. Above a pH of 4.5 no gas was produced, and the liquid products included less ethanol and butyrate and more acetate. A separate study on the conditions for gas formation showed that if the pH dropped for a short time below 4.5 gases were formed at all subsequent pH. This would indicate a change in population distribution due to the period at a low pH. By assuming that the desired products from the acidogenic stage were butyrate, acetate, and no gases, the optimum pH range was found to be between 6.0 and 6.5.

Fermentation pattern of Zymomonas mobilis at high sucrose concentrations

Zymomonas mobilis was grown in batch concentrations between 200 and 400 g/l sucrose. The fermentation pattern revealed that the efficiency of sucrose hydrolysis dropped only from 94 to 78.6% whereas the efficiency with which the hydrolyzed products were converted to ethanol decreased from 94 to 43%. The ethanol yields were relatively constant for final concentrations which lay between 80 and 132 g/l. Fermentation times increased to 72 hours at the higher sucrose concentrations. Sorbitol and fructose were identified as the major by-products. Preliminary evidence suggests that the ratio between the two by-products depends on the pH of the culture medium. Results suggest the possibility of processes producing ethanol plus fructose, ethanol plus fructose and sorbitol, or ethanol plus sorbitol in a single-stage batch fermentation.

Semi-continuous and Continuous Production of Aspergillus niger Spores in Submerged Liquid Culture

SUMMARY: Sporulation of Aspergillus niger was induced in continuous tower fermenters by restricting growth with nitrate limitation. Semi-continuous production of spores was achieved in a single-stage fermentation by alternating full-nutrient and nitrogen-deficient media to the culture. Continuous spore production was obtained in a two-stage fermentation system using the first stage for the growth of vegetative mycelium under optimum conditions and the second, larger, stage for sporulation induction in a constant nitrogen-deficient environment. Spores were produced from much simplified sporulation structures. Using a new sporulation index (Ω), which relates spore numbers produced to the quantity of substrate utilized, the average production efficiency of the two-stage continuous system was shown to be more than twice that of the semi-continuous production system. The tower fermenter was shown to be ideal for controlling organism morphology, thus providing conditions which allowed the development of continuous fungal sporulation.

Optimizing the continuous production of Candida utilis and Saccharomycopsis fibuliger on potato processing wastewater.

The yeasts Candida utilis and Saccharomycopsis fibuliger were propagated as a source of single-cell protein in a continuous, mixed, aerobic, single-stage cultivation on blancher water generated during potato processing. A series of steady-state experiments based on a two-level factorial design, half-replicate modified with an intermediate experiment, was performed to determine the effect of pH, 3.8 to 4.8; dissolved oxygen, 42 to 80% saturation; dilution rate, 0.17 to 0.31 h(-1); and temperature, 27 to 32 degrees C on the amount of carbon consumed, the rate of carbon consumption (R(c)), the amount of reducing sugar consumed, the rate of sugar consumption (R(g)), the amount of protein produced, the rate of protein production (R(p)), the yield from carbon, and the yield from reducing sugar. The results were analyzed by stepwise multiple regression and Fisher's least significant difference test. Analyses showed that high dilution rates resulted in increased R(c), R(g), and R(p) and indicated that a rate of 0.31 h(-1) was below the critical dilution rate. A temperature of 32 degrees C increased the amount of carbon consumed by 34%. A pH of 4.3 to 4.8 increased the amount of protein produced. The yield from carbon was constant, and the relatively high yield from reducing sugar indicated that other substrates were consumed. Dissolved oxygen was in excess at 42% saturation and above. Since C. utilis predominated the mixed cultures and amylase production appeared to be limited, a single-stage fermentation lacked efficiency. The experimental design allowed preliminary optimization of major environmental variables with relatively few experiments and provided a basis for future kinetic studies.

Continuous Cellulase Production

AbstractTrichoderma viride QM 9414 growth characteristics on glucose were investigated in single stage continuous stirred tank reactor operation and growth parameters μmax, Ks, QO2 identified. Multistage stirred tank fermentors in series with the first stage utilizing glucose and the subsequent stages utilizing cellulose yielded results in general agreement with theoretical predictions. Significant increase in enzyme productivity over single stage fermentation was obtained in multistage operation.