Comprehensive Exploration of the Growth and Lipid Synthesis Phases of T. oleaginosus Cultures Implementing Design of Experiments and Response Surface Methodology.

Trichosporon oleaginosus is an unconventional oleaginous yeast distinguished by its remarkable capacity to accumulate lipids in excess of 70% of its dry weight, particularly when cultivated in nitrogen-restricted conditions with ample carbon sources. A pivotal question that arises pertains to the nutrient dynamics in the culture medium, which give rise to both the excessive lipid content and corresponding lipid concentration. While previous research has predominantly focused on evaluating the impact of the initial carbon-to-nitrogen (C/N) ratio on lipid production, the precise critical thresholds of glucose and ammonium sulfate ((NH4)2SO4) at which growth and intracellular lipid production are either stimulated or impeded remain inadequately defined. This study employs an experimental design and response surface methodology to investigate the complex mechanism of lipid accumulation and its interaction with cellular growth. Application of the aforementioned methodologies resulted in the production of 10.6 g/L of microbial oil in batch cultures under conditions that correspond to a C/N ratio of 76. However, the primary objective is to generate knowledge to facilitate the development of efficient fed-batch cultivation strategies that optimize lipid production exclusively employing inorganic nitrogen sources by finely adjusting carbon and nitrogen levels. The intricate interaction between these levels is comprehensively addressed in the present study, while it is additionally revealed that as glucose levels rise within a non-inhibitory range, lipid-free biomass production decreases while lipid accumulation simultaneously increases. These findings set the stage for further exploration and the potential development of two-stage cultivation approaches, aiming to fully decouple growth and lipid production. This advancement holds the promise of bringing microbial oil production closer to commercial viability.

Chromium recovery from tannery sludge and its ash, based on hydrometallurgical methods.

The recovery of chromium from tannery sludge and from its respective ash constitutes an alternative process of tannery sludge treatment in order to ensure safe disposal. Chromium recovery was investigated based on simple hydrometallurgical processes, that is, leaching using aqueous solutions of acids. Leaching was applied either directly to air-dried sludge or to its respective ash, which results from thermal treatment of the air-dried sludge under anoxic conditions. The major parameters that influence the effectiveness of the leaching process were investigated to optimize chromium leaching. Specifically, contact time, pH value, temperature, liquid per solid ratio, and leaching agent (H2SO4 or HCl) were tested. Leached chromium, obtained directly from the initial tannery waste after 100 min leaching with H2SO4 at pH 1 and at 60°C, was used for the trivalent chromium precipitation by adding magnesia, calcium hydroxide, and sodium hydroxide as precipitation agents. The results revealed satisfactory leaching of trivalent chromium directly from the air-dried sludge. The chromium content in the solid precipitated using sodium hydroxide was about 59 wt %. In contrast, chromium was difficult to leach from the respective ash.

Stabilization of Cr-rich tannery waste in fly ash matrices.

In the present work, the stabilization/solidification of a Cr-rich ash obtained from the anoxic incineration of tannery hazardous wastes was studied. Chromium in the starting waste was exclusively in amorphous form and in trivalent state. The waste was embedded in fly ash-based cementitious material matrices. Calcium and sodium hydroxides, as well as sodium silicate, were used as activators. The proposed process combines mechanical activation with hydrothermal curing. Successful immobilization of chromium was achieved, as attested by standard leaching tests. Backscattered electron images revealed the existence of the C-S-H gel, and elemental mapping by energy dispersive X-ray spectroscopy showed a good interdispersion of chromate and aluminosilicate species, verifying that chromium was well distributed in the final amorphous cementitious matrix. X-ray diffraction confirmed the absence of Cr-rich crystalline phases of calcium aluminosilicates, where chromium can enter in hexavalent state. The stiffness of the stabilized samples was reduced with increasing the amount of added Cr-rich ash, as attested by measurements of the dynamic Young's modulus.