Characterization of a phenol degrading mixed population by enzyme assay

The metabolic response of a mixed population to stepwise increase in phenol concentration was followed with the assay of pyrocatechase activity. The mixed population was grown in a laboratory scale activated sludge plant for 40 days. The inlet phenol concentration (750 mg l−1) was then increased stepwise to 1250, 2500 and 4500 mg l−1, corresponding to low, moderate and high level increases in phenol loading, respectively. Pre- and post-shock assessments were performed on samples collected from the aeration tank. Pyrocatechase activity increased following each step increase in phenol and the level of increase was dependent on the magnitude of the step increase. Following low level increase in loading, phenol was not detected from the aeration tank. At moderate level loading phenol was temporarily detected in the aeration tank but disappeared after 7 days. At high level loading phenol was accumulated in the aeration tank throughout. Pyrocatechase activity was dependent on the concentration of phenol in the aeration tank. From pyrocatechase activity assay it was possible to demonstrate the metabolic response of the activated sludge to changes in phenol concentration. The accumulation of phenol and decrease in pyrocatechase activity are considered as the stage when the system no longer copes with increase in phenol loading.