Valorization of food wastes with a sequential two-step process for microbial ß-carotene production: A zero waste approach.

Here, two consecutive ß-carotene fermentation processes were carried out with Rhodotorula glutinis yeast in the growth media obtained from orange and grape wastes. Firstly, waste biomasses were subjected to hot water extraction. Effects of waste type, drying pretreatment, particle size and solid/liquid ratio on the total concentration and yield of sugars recovered were tested. The highest sugar concentration was obtained by the hot water extraction of fresh grape pomace as 61.2 g total reducing sugars (TRS)/L at a solid/liquid ratio of 100 g/L. In the first fermentation process, effect of solid/liquid ratio (initial TRS concentration) on ß-carotene production pattern of R. glutinis was investigated in the media obtained directly by hot water extraction of the wastes. Microorganism and ß-carotene concentrations increased with increasing solid/liquid ratio (range 10-100 g/L), and the microbial growth data fit the Monod model well for all cases. Maximum ß-carotene concentration in the growth medium obtained from hot water extraction of 100 g/L of grape pomace was determined as 5988.6 mg/L. In the second fermentation process, ß-carotene was produced in the acid hydrolysate of extraction residues. 10.1 g/L and 6.7 g/L of TRS was obtained after acid hydrolysis of orange and grape residues, respectively, and the highest ß-carotene concentration of 370.0 mg/L was found in the medium of hydrolyzed orange peel extraction residue. Total ß-carotene production increased to 1777.1 and 3279.6 mg/L (26% and 4.9% of increase) after the second fermentation step. 85.3% and 80.2% of reduction in orange and grape waste weights were observed at the end of the process, which was an indicator of efficient waste biomass disposal. Two sequential ß-carotene fermentation steps offered significant advantages in terms of both efficiency and a zero waste approach.

Novel application of isolated Micrococcus luteus and Bacillus pumilus for Li+ ion biosorption: a comparative study.

In this study, Li+ biosorption profiles of Micrococcus luteus and Bacillus pumilus bacterial strains were investigated. Comparative surface characterization of the biomasses revealed that B. pumilus had a significantly greater surface negativity than the other, which had a direct positive effect on the ability to attract the Li+ ions. Biosorption experiments showed that B. pumilus cell had more efficient performance at all pH and initial Li+ concentration values in the ranges of 3.0-10.0 and 2.5-20.0 mg/L, respectively. The maximum adsorption capacities obtained at initial Li+ concentration of 20.0 mg/L and pH 9.0 were 1.160 mg Li+/g (167.1 µmol/g) and 2.280 mg Li+/g (328.5 µmol/g) for M. luteus and B. pumilus, respectively. For all the cases studied, the biosorption equilibrium was reached very quickly, suggesting that physical interaction dominated this process. Experimental data were found to be compatible with both Langmuir and Freundlich models under the studied experimental conditions. This study highlights the idea that B. pumilus bacterial strain will be a new and preferred biosorbent for Li+ ions by providing a low cost, rapid and quite efficient process.

A comparative investigation of lithium(I) biosorption properties of Aspergillus versicolor and Kluyveromyces marxianus.

In the current batch study, lithium(I) ion sorption behaviors of Aspergillus versicolor fungus and newly isolated Kluyveromyces marxianus yeast were investigated comparatively. Surface and structural characterization studies of the biosorbents carried out with Fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM), surface area and zeta potential analyses showed that isolated K. marxianus yeast from salty wastes has more preferable properties (i.e. higher porosity, surface area and negativity) for cation sorption. Biosorption studies also supported this estimation; higher lithium(I) sorption capacities were obtained with K. marxianus cells at all experimental conditions studied. Rapid sorption profiles of the sorbents demonstrated that physical interaction is the main mechanism in this system. The effects of pH and initial lithium(I) concentration on the lithium(I) sorption capacities of biosorbents were examined. The maximum adsorption capacities of 347.9 and 409.2 µmol lithium(I)/g biosorbent were obtained at an initial lithium(I) concentration of 20 mg/L at pH 9.0 using A. versicolor and K. marxianus, respectively. The equilibrium data fitted both Langmuir and Freundlich models in the concentration ranges studied. This study revealed that K. marxianus yeast can be used for effective, rapid and low cost capture process of lithium(I) ions from aqueous solutions.