AIS/CESIO environmental surfactant monitoring programme. SDIA sewage treatment pilot study on linear alkylbenzene sulphonate (LAS)

The outcome of a 7-day pilot monitoring study on the anionic surfactant, LAS, at the Yorkshire Water Serviceʹs Owlwood activated sludge sewage treatment works (STW) is described. The average concentration of LAS found in daily flow related composites of raw sewage was 15.1 mg l−1 (range 11.8–18.2 mg l−1). The calculated per capita use of the surfactant at Owlwood of 4.5 g/d/person agrees closely with the predicted use of LAS in Western Europe (ca 4.0 g/d/p). Distinct diurnal variations in the raw sewage LAS concentrations were observed (3.7–31.8 mg l−1) and were apparent to a lesser degree in the treated effluent. The removal of the organic load (measured as BOD) and LAS at the works were both very high, 98 and 99.9% respectively. Hence, very low concentrations of LAS were discharged to the associated Sheffield Beck in the treated effluent (average daily composite of 10.4 μg l−1). Unexpectedly, the river upstream of the discharge was found to contribute a higher load of LAS to the river downstream than the Owlwood effluent. The average daily composite LAS concentration in the river below the mixing zone of the STW was 27 μg l−1 (range 9.4–47 μg l−1). The concentrations of LAS found on sediments in the immediate vicinity of the STW were very small (< 1 μg g−1). The implications of the study findings for the Standing Committee of Analysts (SCA) methodology used for the analysis of LAS and the design of further monitoring exercises on surfactants are discussed.