Abstract
It is shown that bacteria Bradyrhizobium japonicum 273 were capable of degrading phenol at moderate concentrations either in a free cell culture or by immobilized cells on granulated activated carbon particles. The amount of degraded phenol was greater in an immobilized cell preparation than in a free culture. The application of a constant electric field during cultivation led to enhanced phenol biodegradation in a free culture and in immobilized cells on granulated activated carbon. The highest phenol removal efficiency was observed for an anode potential of 1.0 V/S.H.E. The effect was better pronounced in a free culture. The enzyme activities of free cells for phenol oxidation and benzene ring cleavage were very sensitive to the anode potential in the first two steps of the metabolic pathway of phenol biodegradation catalyzed by phenol hydroxylase—catechol-1,2-dioxygenase and catechol-2,3-dioxygenase. It was observed that at an anode potential of 0.8 V/S.H.E., the meta-pathway of cleavage of the benzene ring catalyzed by catechol-2,3-dioxygenase became competitive with the ortho-pathway, catalyzed by catechol-1,2-dioxygenase. The obtained results showed that the positive effect of constant electric field on phenol biodegradation was rather due to electric stimulation of enzyme activity than electrochemical anode oxidation.
Highlights
Phenol and its derivatives are widely distributed as a source and product of various human activities They are considered as some of the most dangerous organic pollutants released in the environment
The obtained experimental results showed that the constant electric field enhanced the biodegradation activity of the strain, for the higherelectric anode potentials, The obtained experimental resultsparticularly showed that thetwo constant field enhanced reaching up to four times higher phenol concentrations thethe broth
The electric field caused some biodetermined biodegraded of phenol, to the conclusion practically chemical effects, possibly amounts some steric changes led in the enzyme active that sites,there was affecting no electrochemical anode oxidation of phenol
Summary
Phenol and its derivatives are widely distributed as a source and product of various human activities (plastics, pesticides, etc.) They are considered as some of the most dangerous organic pollutants released in the environment. Various methods have been proposed to decrease its concentration in waste streams to harmless levels. These methods are based mostly on adsorption and ion exchange [4,5,6] or microbial processes [7,8]. Various microbial species have been tested and reported for phenol biodegradation: bacterial strains from the genus Pseudomonas [7,9,10,11], Arthrobacter [12], Bacillus [13], etc. Microbial degradation of phenol usually starts by oxygenation, in which the aromatic ring is initially mono-hydroxylated at an ortho- position to the pre-existing hydroxyl group to form catechol. The active enzyme in this reaction is phenol hydroxylase for different microbial strains
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