Biodegradation of a cationic surfactant in activated sludge

The biodegradation of DTDMAC (ditallowdimethylammonium chloride, a fabric softening agent) was established in semi-batch activated sludge reactors. Three ¹⁴C-forms of DTDMAC were studied separately under the simulated organic loading rates of conventional and extended aeration activated sludge treatment. Primary biodegradation was shown by means of a specific analytical technique in combination with radiochemical procedures. Ultimate biodegradation for each carbon position in the DTDMAC molecule was established by the detection of ¹⁴CO₂. Intermediate metabolites were followed throughout the study by both radio thin-layer chromatography and radiochemical procedures. Each carbon position of the DTDMAC molecule was equally accessible to metabolism and ultimate degradation by acclimated microorganisms. Degradation occurred more rapidly under extended aeration conditions and was influenced by the strong tendency of DTDMAC to associate with the microbial population. The low levels of metabolites observed were not of a single classification or characteristic and they did not persist in the activated sludge. This study suggests that DTDMAC removal in an activated sludge plant is a result of both sorption/precipitation and biodegradation mechanisms.