RAPID REMOVAL OF LINEAR ALKYLBENZENESULFONATES (LAS) BY ATTACHED BIOFILM IN AN URBAN SHALLOW STREAM

Field observations of linear alkylbenzenesulfonates (LAS) were conduct ed in the Nogawa river, a polluted shallow stream located in Tokyo, fr om 1987 to 1990. LAS concentrations decreased from similar to 1 mg 1(- 1) in the upper stream receiving untreated domestic wastewater to less than 0.05 mg 1(-1) at 6 km downstream. Within the upper portion of a 1.8 km concrete open channel (travelling time of water: 1-3 h), more t han 80% of LAS were removed. The half-lives for LAS of similar to 1 h were considerably shorter than those obtained from biodegradation expe riments using only the river water (several tens of hours). Biodegrada tion experiments using biofilm collected from the stream bed indicated that LAS are much more rapidly degraded under the existence of biofil m. Measurement of LAS in the biofilm indicated negligible LAS accumula tion in the stream bed. The field observations and laboratory experime nts indicated that biodegradation by the stream bed biofilm is the pre dominant removal mechanism of LAS in the urban shallow stream.