Kinetics of mineralization of phenols in lake water

Abstract

The kinetics of mineralization of phenol and p-nitrophenol in lake water was determined at concentrations from 200 pg/ml to 5 μg/ml. The mineralization data were fit by nonlinear regression to equations for 14 kinetic models that describe patterns of biodegradation by nongrowing cells or by microorganisms growing on either the test chemical or other organic substrates. The kinetics of mineralization of phenol in water samples collected in July was best described by first-order models for 0.5 ng of phenol per ml; by Monod-without-growth, logistic, and logarithmic models for 1.0 and 2.0 ng/ml and 5.0 ng/ml to 1.0 μg/ml, respectively, if it is assumed that the mineralizing population uses phenol as the sole carbon source for growth; by models (for phenol at concentrations of 2.0 ng/ml to 1.0 μg/ml) that assume that the phenol-mineralizing populations do not grow or grow logarithmically or logistically on uncharacterized carbon compounds but metabolize the phenol when present at levels below and above K(m), respectively, for that compound; and by a logarithmic model at 5.0 μg/ml. Under the test conditions, usually less than 10% of the phenol C that was metabolized was incorporated into microbial cells or retained by other particulate material in the water at substrate concentrations of 10 ng/ml or less, and the percentage increased at higher substrate concentrations. The mineralization of 2.0 ng of phenol per ml in water samples collected at other times of year was best described by logistic or logarithmic models if the mineralizing bacteria were assumed to be growing on phenol, by a first-order model, or by a model assuming logarithmic growth of the phenol mineralizers on other organic compounds in the water. If the lake water was incubated for 12 h before phenol was added, mineralization was zero order. Removal of particles from lake water sampled after heavy runoff from land resulted in a change in kinetics of phenol mineralization. The patterns of mineralization of 0.5 ng to 1.0 μg of p-nitrophenol per ml were best fit by the Monod-with-growth model or the logistic model if it is assumed than p-nitrophenol was the carbon source for growth, or by models that assume logarithmic or logistic growth on uncharacterized organic matter in the water. Reasons for two models fitting the same data well are considered, as are bases for selecting between models.