Elimination of aromatic surfactants from municipal wastewaters: comparison of conventional activated sludge treatment and membrane biological reactor

Abstract

Behaviour of anionic surfactants of linear alkylbenzene sulphonates (LAS) type and non-ionic surfactants of nonylphenol polyethoxylate (NPnEO) type was studied in the conventional mechanical/biological sewage treatment plant (STP) as well as using a membrane biological reactor (MBR). LAS and NPnEO were determined using high performance liquid chromatography (HPLC) equipped with spectrofluorimetric detection. Liquid chromatography/tandem mass spectrometry (LC/MS/MS) was used for identification and quantification of stable metabolites, including nonylphenol (NP), nonylphenol monoethoxylate (NP1EO), nonylphenol diethoxylate (NP2EO) and nonylphenoxy carboxylic acids (NPnEC). The study showed that aromatic surfactants belong to the most prominent constituents in the examined municipal wastewaters with typical LAS and NPnEO concentrations of 2–10 mg/L and 0.1–0.5 mg/L, respectively. The removal of aromatic surfactants in conventional STP showed well-known features reported in the literature, including an efficient microbial transformation of the parent molecules and formation of stable metabolic products. The elimination efficiency of aromatic surfactants using the MBR unit was higher than that in the conventional STP, while the composition of recalcitrant nonylphenolic residues in the effluent seems to be ecotoxicologically more favourable due to the lower contributions of the lipophilic metabolites.