Batch Test for Assessing the Mineralization of ¹⁴C-Radiolabeled Compounds under Realistic Anaerobic Conditions

A test system is described for assessing the mineralization of 14 C-radiolabeled compounds to carbon dioxide (CO 2 ) and methane (CH 4 ) under anaerobic conditions. Environmentally realistic concentrations of test chemicals were incubated with anaerobic digester sludge in sealed vessels at 35 °C. The headspace of these vessels was continuously purged with nitrogen, which was passed through a series of potassium hydroxide (KOH) scrubbers to trap 14 CO 2 . This effluent gas was mixed with oxygen and passed through a combustion tube containing cupric oxide at 800 °C to convert 14 CH 4 to 14 CO 2, which was subsequently trapped in a second series of KOH traps. Trapping efficiency was 97.1 ± 5% for 14 CO 2 and 108 ± 13% for 14 CH 4 . The system was used to evaluate the mineralization of several organic chemicals including glucose, palmitic acid, hexadecanol, and two surfactants, alkyl ethoxylate sulfate (AES) and alkyl sulfate (AS), in anaerobic digester sludge. Total yields of 14 CH 4 and 14 CO 2 from these compounds exceeded 80%, and the total mass balances generally exceeded 95%. Mineralization of hexadecanol was described by a simple first-order production equation, while that of the other compounds was best described by a three-half-order model. This system provided excellent recovery of radioactive gases and consequently excellent mass balances. Given the reproduction of in situ condition and the realistic ratio of test material to biomass, the test system also generated relevant kinetic data. It, therefore, has application for demonstrating the significance of biodegradation as a removal mechanism during anaerobic digestion as well as determining the completeness of anaerobic biodegradation.