Toxicity of anionic surfactants to the bacterial population of a waste water treatment plant

Abstract

This study was undertaken to compare the toxicity results (EC-50 3 hours) of common anionic surfactants, LAS (Linear Alkylbenzene Sulfonate), AS (Alcohol Sulphate) and AES (Alcohol Ether Sulphate), to the activated sludge of a treatment plant basically operating on domestic sewage. For LAS, commercial products were tested, as well as its single homologues C 10 -C 14 . C 12 -LAS showed the highest toxicity of all homologues tested as a consequence of the equilibrium amongst all processes taking place simultaneously, namely adsorption, precipitation and biodegradation. In any case the EC-50 3hr values found, are almost two orders of magnitude higher (500-1000 mg/L) than with LAS concentrations usually found in untreated sewage entering treatment plants. The safety margin for aerobic sludge bacteria is therefore very high. AS and AES are even less toxic than LAS, possibly due to the same processes.