Estudo da biotransformação de fenol por Candida tropicalis ATCC 750 livre e imobilizada em bagaço de caju

Abstract

Biological treatments have been widely studied for being more efficient and economical than to physical and chemical treatments of waste water containing phenol. However, microbial biotransformation undergoes inhibitory effects at higher phenol concentrations which represents a bottleneck for successful bioremediation. The use of immobilized cells guarantees a greater resistance of the microorganism to factors that interfere in the processes. In this context, a phenol biotransformation by a pure culture of Candida tropicalis ATCC 750 free and immobilized in cashew-apple bagasse was studied using a discontinuous reactor, in order to develop a viable process of biotransformation. Cashew-apple bagasse was used because it is a cheap and abundant support alternative. Degradation kinetics of phenol with immobilized cells was compared with degradation kinetics using free cells. The maximum degradation rates were 16.17 mg.g-1.h-1 (99.7%) and 15.25 mg.g-1.h-1 (99.8%) for free and immobilized cells, respectively. The best conditions of degradation was obtained at 30 °C, pH 6.0, 150 rpm and 1100 mg.L-1 initial phenol concentration, for studies with free and immobilized cells. 73% of the immobilized cells can be effectively retained during storage at 4 °C for up to 30 days and can be reused for more than eight cycles of biotransformation. In addition, after a previous adaptation of the microorganism to the medium with phenol, it was possible to obtain biotransformation results for concentrations of 1400-2000 mg.L-1 phenol. The analysis of the metabolic pathway showed that the degradation process of the phenol follows the path of ortho-cleavage of the aromatic ring by the enzyme 1,2-dihydroxyigenase leading to the formation of cis, cis muconic acid. For studies with immobilized cells, a simple evaluation of the external mass transfer was performed in order to identify any type of limitation by diffusion effects, consisting of such limitations occurring, but at a low intensity. The results obtained justify the applicability of cashew-apple bagasse as a support matrix for the immobilization of C. tropicalis ATCC 750 to biotransformation of phenolic compounds from industrial waste water, and is a promising process.