Biodegradation of Surfactants in Saturated Subsurface Sediments: A Field Study

Abstract

ABSTRACTThe mineralization of linear alkylbenzene sulfonate (LAS), linear alcohol ethoxylate (LAE), benzylamine, and monoalkyl and dialkyl quaternary ammonium compounds was determined as a function of depth in sediment profiles from beneath a laundromat waste‐water pond and pristine control pond. In addition, bacterial number, microbial activity, and concentrations of LAS and quaternary ammonium compounds were measured. Surfactant concentration decreased dramatically with increasing depth in the laundromat profile. Bacterial number and activity decreased with depth in both profiles; however, biomass and activity were higher in the laundromat profile. Mineralization was measured by amending samples with 14C‐labeled substrates and following the evolution of 14CO2 with time. LAS was mineralized without a lag period at all depths in the laundromat profile; its half‐life ranged from 3.2 to 16.5 days. In the control pond, it was mineralized more slowly (half‐life 5.2 to 1540 days) and only after a lag period of 2 to 40 days. LAE was also mineralized with shorter lags and more rapidly in the laundromat than in the control profile; half‐lives ranged between 2.8 to 8.6 days in the former and 3.5 to 137 days in the latter. Although monoalkyl and dialkyl quaternary ammonium compounds were not mineralized in the control profile, slow but significant mineralization of these compounds occurred in the laundromat profile. Benzylamine was rapidly degraded without a lag in both profiles. Field concentration data and the results of mineralization studies indicated that biodegradation combined with the effects of adsorption is a practical mechanism of surfactant removal in subsurface environments. In addition, adaptation resulting from exposure of microbial communities to surfactants is an important factor governing the fate of surfactants in the subsurface.