Comprehensive Approach for Assessing the Kinetics of Primary and Ultimate Biodegradation of Chemicals in Activated Sludge:  Application to Linear Alkylbenzene Sulfonate

An approach has been devised for determining the kinetics of primary and ultimate biodegradation of chemicals under realistic conditions in activated sludge. A radiolabeled test chemical is dosed at an environmentally relevant concentration into biotic and abiotic activated sludge. Periodi cally, samples are removed, acidified, and analyzed by LSC to determine 14 CO 2 evolution. In addition, samples are flash-frozen, lyophilized, and extracted to recover the parent and metabolites, which are analyzed by Rad-TLC. The extracted residue is then sequentially extracted with cold TCA, ethanol/ether, hot TCA, and 10 N NaOH and combusted to determine incorporation into constituents of biomass. Loss of parent, 14 CO 2 evolution, and incorporation into biomass are fitted to a variety of decay or production functions using nonlinear regression to identify the best models and estimate rates. Linear alkylbenzene sulfonate ( 14 C-ring C 12 LAS) was tested as model compounds in two sludges. Within 8 h, 41−44% was evolved as 14 CO 2, 1−2% remained as parent, 24−33% was incorporated into biomass, and 10−15% was present as intermediates, primarily sulfophenylcarboxylates. Primary and complete biodegradation were best described by a first-order model. First-order rate constants for LAS were 0.96−1.10 h - 1 for primary loss and 0.50−0.53 h - 1 for complete degradation. This approach provides an accurate and comprehensive kinetic picture of biodegradation under realistic conditions as well as information on the mechanism of biodegradation.