Respirometric Study of Microbial Degradation of Phenol

Abstract

Microbial oxidation of phenol is a recognized, cost-effective method of treating relatively low concentration (<500 ppm) phenol-containing waste streams. However, little information exists on naturally occurring bacteria or their ability to degrade phenol at relatively high concentrations. The present study characterized the physiological response of a self-sustaining bacterial population harvested from a fixed-film biological reactor used for the degradation of concentrated phenolic (>l,000 ppm) paint-stripping solutions containing cadmium and chromium. Microbial activity was monitored by the biological oxygen uptake rate, phenol concentration, ATP concentration, and dry solid weights. The effects of temperature, pH, phenol concentration, (NH₄)₂HPO₄ concentrations, Cr (K₂Cr₂O₇), and Cd (CdSO₄) metals on the respiration rate were determined, and the ability to degrade various phenolic compounds was evaluated. The bacteria were aerobic, gram-negative rods, predominantly pseudomonads. A temperature of 20°C and pH near-neutrality produced optimal respiration rates. The highest level of ATP activity was observed for a phenol concentration of 2,000 ppm, and above or below this phenol concentration the ATP levels were lower. Little or no effect on respiration rate was observed for Cr concentrations up to 120 ppm; but above this level it decreased, and at 320 ppm Cr it ceased. Cadmium, at all concentrations tested, exhibited an effect on the respiration rate.