ESTIMATING THE REMOVAL AND BIODEGRADATION POTENTIAL OF RADIOLABELED ORGANIC-CHEMICALS IN ACTIVATED-SLUDGE

A two-step procedure is described to characterize the removal and biod egradation potential of nonvolatile C-14-labeled organic compounds in activated sludge, In the first step, trace concentrations of radiolabe led test materials are dosed in influent wastewater to continuous-flow activated sludge (GAS) systems which have been previously exposed or acclimated to unlabeled test material, Radiolabel is quantified in inf luent, effluent, and activated sludge mixed liquor to determine total C-14 removal and partitioning of radiolabel in solid and liquid compar tments, The C-14 data are used to calculate the amount of removal due to sorption and biodegradation and to estimate the apparent sorption c oefficients for C-14 activity to activated sludge solids, The C-14-lab eled CAS studies are followed by biodegradation studies in batch-activ ated sludge (BAS) systems using sludge derived from the CAS system, Th e kinetics of biodegradation (defined as mineralization to (CO2)-C-14) are measured in the BAS system to confirm the CAS biodegradation resu lts and generate mineralization rate constants for kinetic modeling, T he two-step procedure was applied to radiolabeled anionic (linear alky lbenzene sulfonate) and cationic (dodecyltrimethylammonium chloride, d istearyldimethylammonium chloride) surfactants which differed greatly in their biodegradation and sorption profiles, Laboratory removal figu res for these materials were comparable to values measured in full-sca le wastewater treatment systems, although the amount of removal due to sorption and biodegradation varied significantly for the different su rfactants. In general, the C-14 method has several advantages over sta ndard methods used in the United States and Europe which employ unlabe led materials, These advantages include the use of realistic concentra tions and test conditions for acclimating and dosing activated sludge microorganisms and the ability to generate partitioning and kinetic co nstants that can be used more broadly in environmental fate and exposu re models. (C) 1996 Academic Press, Inc.