Abstract and SummaryControlled amounts of C‐14 labeled trisodium car‐boxymethyloxysuccinate, an experimental detergent builder, were added to a laboratory anaerobic digester system. The daily dosages were increased incrementally from 4 to 20 ppm, dosages being held at each level for 24 days. Biodegradation commenced after 6 days, and once complete acclimation occurred, removals were rapid and complete at all dosage levels, yielding CO2 and CH4 as virtually the only end‐products of decomposition. After 96 days of application, total removal was in excess of 95%. Further, this com‐pound did not interfere with the normal digestion processes or display any inhibitory effects on the bacterial population.