Anaerobic Biodegradation Capabilities of Freshwater Lake Sediments: Influence of Temperature and Sulfate Concentration on the Degradation of 2,4-Dichlorophenol
Freshwater lake sediment samples from the region around Athens, Georgia, were taken anaerobically after determination of the temperature, pH, and Eh. The slurries were homogenized and incubated in anaerobic crimp tubes (20 ml samples with 16 g wet weight in 20 mM phosphate buffer pH 7.0 containing 20 ppm of added 2,4-dichlorophenol) at 18 different temperatures in the range between 5°C and 72°C. To one set of samples 0.25% (w/v) sulfate was added. Three times autoclaved mud samples were used as controls, and all samples were done in duplicate. Chlorophenol concentrations were determined using HPLC after extraction of 0.2 ml samples with 50% acetonitrile. Methane formation was measured by gas chromatography. In the tested mud samples, 2,4-dichlorophenol was transformed to 4-chlorophenol which, after additional lag periods of several weeks, was then further degraded. Adaptation periods decreased between 5°C and 30°C and the dechlorination rates showed maxima at 30°C., 35°C., and 43°C with a pronounced minimum at 40°C., suggesting that at least two groups of dechlorinating organisms were present. No degradation occurred above 53°C., although there was biological activity up to 60°C., indicated by high methane production. Between 15°C and 30°C., the dechlorination rates and the methane formation rates increased exponentially (linear part of the Arrhenius plot) and the dechlorination rate peaks coincided with methane formation peaks.