Materials, Methods & Technologies ISSN 1314-7269, Volume 14, 2020 Journal of International Scientific Publications www.scientific-publications.net Page 177 PHENOL BIODEGRADATION OF IMMOBILIZED BRADYRHIZOBIUM JAPONICUM CELLS. PART 2 Tsvetomila Parvanova-Mancheva, Evgenia Vasileva, Venko Beschkov Institute of Chemical Engineering, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl.103, 1113 Sofia, Bulgaria Abstract With the development of technologies and the rise of the standard of living worldwide, the generation of wastewater is steadily increasing and at the same time the requirements for their purification are being increased before they are released into the environment. Wastewater treatment methods are diverse, chemical ones which have a significant drawback, are expensive and generate secondary pollutants. These disadvantages are avoided by the use of biological methods, which are very flexible and easy to manage. This article examines the ability of cells from the Bradyrhizobium japonicum 273 strain, successfully immobilized on activated carbon, to oxidize and degrade phenol. Initial pollutant concentrations are (in g dm -3 ): 0.02, 0.04, 0.06 and 0.08, but they do not have a significant effect on the rate and amount of phenol degradation, which in 240 hours is approximately 10 g dm -3 . It is higher by 80% than for free cell degradation rate. In our opinion, the reason is that the activated carbon adsorbs the phenol and gradually releases it in cell-tolerant amounts, i.e. thus avoiding substrate inhibition. Key words: bradyrhizobium japonicum, biodegradation, phenol, immobilized cells 1. INTRODUCTION A large number of Rhizobium microorganisms are able to degrade many types of xenobiotics, phenol in particular. The ability of Rhizobia to use carbon sources as aromatic compounds has been studied before [1 – 9]. The degradation of phenol from Bradyrhizobium japonicum has not been extensively investigated, but its possibilities for oxidation of other aromatic compounds, which S. Latha and A.Mahadevan [7] have systematized in Table 1, are known. The results of our laboratory studies on the ability of Bradyrhizobium japonicum to break down phenol have been systematized and described in a two-part article. In the first part, we have covered what phenol is, how dangerous it is, how it falls and where it comes from in waste and groundwater, and what its metabolic pathway is. The experimental material presented in the first part reflects the experiments carried out with free cells and in the second one - with immobilized cells on activated carbon. The experiments were conducted with two working media – poor, i.e. mineral one and another one rich in yeast extract and glucose. We investigated the effect of different initial pollutant concentrations on the rate and amount of degraded phenol. The impact of the additional carbon source was also investigated. As a result, we prove the advantage of immobilized cells from the Bradyrhizobium japonicum strain to the free ones.