Optimization of Medium Constituents for the Production of Citric Acid from Waste Glycerol Using the Central Composite Rotatable Design of Experiments.

Citric acid is currently produced by submerged fermentation of sucrose with the aid of Aspergillus niger mold. Its strains are characterized by a high yield of citric acid biosynthesis and no toxic by-products. Currently, new substrates are sought for production of citric acid by submerged fermentation. Waste materials such as glycerol or pomace could be used as carbon sources in the biosynthesis of citric acid. Due to the complexity of the metabolic state in fungus, there is an obvious need to optimize the important medium constituents to enhance the accumulation of desired product. Potential optimization approach is a statistical method, such as the central composite rotatable design (CCRD). The aim of this study was to increase the yield of citric acid biosynthesis by Aspergillus niger PD-66 in media with waste glycerol as the carbon source. A mathematical method was used to optimize the culture medium composition for the biosynthesis of citric acid. In order to maximize the efficiency of the biosynthesis of citric acid the central composite, rotatable design was used. Waste glycerol and ammonium nitrate were identified as significant variables which highly influenced the final concentration of citric acid (Y1), volumetric rate of citric acid biosynthesis (Y2), and yield of citric acid biosynthesis (Y3). These variables were subsequently optimized using a central composite rotatable design. Optimal values of input variables were determined using the method of the utility function. The highest utility value of 0.88 was obtained by the following optimal set of conditions: waste glycerol-114.14 g∙L-1and NH4NO3-2.85 g∙L-1.

Criteria of quality assessment of regional airport services - A very last picture before the COVID-19 pandemic.

Omnipresent globalisation causes integration of societies, economies and cultures, and air transport significantly facilitates it. Before the COVID-19 pandemic, air transport was one of the most dynamically developing types of transportation. The quality of airport services was measured, as it supports the development of air transport and airports in particular. As today the future of the air transport industry is not clear, it is essential to have the last picture of service quality assessment criteria before the airports' lockdown to sustain their development after reassumption. The study covered the operation of a regional international airport in Europe before the lockdown due to the COVID-19 pandemic. A diagnostic survey was used in the study, and the data were collected through a questionnaire of 40 questions. The study covered 263 passengers who had used the services of the examined airport at least once before the lockdown. The collected data were statistically analysed. The main findings are that the passengers consider components of the quality of airport services in groups and not individually. In some groups of factors, the level of satisfaction varies depending on the frequency of airport use. The results are in accordance with the findings of other authors researching different airports. They should be considered when managing the airport and identifying the causes of low-quality services to improve them and eliminate or at least reduce passenger dissatisfaction, especially in the face of resumption of airport operations after the COVID-19 pandemic.

Effect of pH and temperature on vinasse decolorization by lactic acid bacteria in batch processes.

The waste-free policy is part of the process of sugar production from beets in which the resulting molasses are used for ethanol production. However, during this process another byproduct, namely vinasse, is created. Therefore, there is a problem with the utilization of wastewater, which cannot be disposed to the environment without being treated. Melanoidins, caramels, and hexoses alkaline degradation products contained in the vinasse give it a dark brown color. The aim of the study was to investigate the effect of the pH and the temperature on the decolorization of vinasse by lactic acid bacteria (Lactobacillus plantarum, L. casei, and Pediococcus parvulus). Experiments were performed in batch mode in a BioStatB bioreactor for 72 hrs. The medium consisted of 25% v/v sugar beet molasses vinasse, 77.34 gdm-3 of glucose, and 2.24 gdm-3 of yeast extract. The maximum decolorization was 25.14% and was achieved at noncontrolled pH 6.5 and at 30°C. PRACTITIONER POINTS: Lactobacillus plantarum, L. casei and Pediococcus parvulus showed potential for decolorization of sugar beet molasses vinasse. Controlled pH has a negative effect on sugar beet molasses vinasse decolorization. Toxic substances, i.e. acrylamide, 4-methylimidazole , 5-hydroxymethylfurfural and furfural after decolorization was not detected. Bacteria showed high degradation potential of 2-acetyl-4-(1,2,3,4)-tetrahydroxy-butylimidazole.

Effect of medium pH on chemical selectivity of oxalic acid biosynthesis by Aspergillus niger W78C in submerged batch cultures with sucrose as a carbon source.

The pH of the medium is the key environmental parameter of chemical selectivity of oxalic acid biosynthesis by Aspergillus niger. The activity of the enzyme oxaloacetate hydrolase, which is responsible for decomposition of oxaloacetate to oxalate and acetate inside the cell of the fungus, is highest at pH 6. In the present study, the influence of pH in the range of 3-7 on oxalic acid secretion by A. niger W78C from sucrose was investigated. The highest oxalic acid concentration, 64.3 g dm-3, was reached in the medium with pH 6. The chemical selectivity of the process was 58.6% because of the presence of citric and gluconic acids in the cultivation broth in the amount of 15.3 and 30.2 g dm-3, respectively. Both an increase and a decrease of medium pH caused a decrease of oxalic acid concentration. The obtained results confirm that pH 6 of the carbohydrate medium is appropriate for oxalic acid synthesis by A. niger, but the chemical selectivity of the process described in this paper was high in comparison to values reported previously in the literature.