Production of Biotechnological Molecules from Agro- Industrial By-Products Using Cell Immobilization on Solid Supports

Abstract

The growing demand for sustainable energy sources and environmentally friendly waste management solutions has driven interest in the biotechnological valorization of agro-industrial by-products. This thesis explores innovative strategies for the production of biotechnologically valuable molecules specifically bioethanol and acetic acid through the use of immobilized microbial systems on solid supports. Initially, sixty (60) yeast strains were isolated from olive oil wastewater (OOWW), a challenging substrate due to its high polyphenol content and inhibitory load. Among these isolates, thirteen (13) strains were identified as belonging to the genus Saccharomyces sp. One strain Saccharomyces cerevisiae Y17 was selected for its outstanding tolerance to inhibitory compounds and high fermentative performance, achieving an ethanol concentration of 11.3 g/L from untreated OOWW after 72 hours of fermentation. Comparative analyses revealed its superior adaptability over commercial yeast strains under identical conditions. Subsequently, an integrated approach combining enzymatic hydrolysis and simultaneous saccharification and fermentation (SSF) was developed. Immobilization of S. cerevisiae cells on pozzolan rock enhanced process stability and enabled efficient ethanol production from a mixture of OOWW, sugarcane molasses (SCM), and milk whey (MW). Optimization of process parameters led to a maximum ethanol concentration of 34.56 g/L after 72 hours, significantly surpassing conventional fermentation outcomes. Strong correlations between glucose consumption and ethanol production emphasized the critical importance of substrate availability and controlled fermentation conditions. Secondly, research was conducted on the use of Bacillus strains, isolated from bovine rumen, for acetic acid production from olive mill wastewater (OMW). A total of 25 bacterial strains were isolated, among which five (5) were selected for detailed evaluation. Among these, Bacillus sp. strain 15 exhibited the highest acetic acid yield, reaching 28 g/L after 108 hours of fermentation. This study introduces Bacillus species as novel agents for acetic acid production from OMW, expanding the range of microbial candidates available for industrial bioconversion processes. Overall, this thesis demonstrates the potential of combining cell immobilization, enzymatic enhancement, and mixed-substrate strategies for the sustainable production of bioethanol and acetic acid. The findings contribute valuable insights toward the development of scalable, economical, and environmentally responsible bioprocesses based on the valorization of agro-industrial residues.