engleski

Elimination of Aromatic Surfactants from Municipal Wastewaters - Comparison of Conventional Activated Sludge Treatment and Membrane Biological Reactor

Aromatic surfactants, including linear alkylbenzene sulphonates (LAS) and alkylphenol polyethoxylates (APnEO) with estimated annual worldwide production rates of about 3 x 106 and 6 x 105 tons, respectively, belong to the most popular surfactant classes. Due to their widespread use and considerable toxicities to aquatic life, LAS and APnEO should be considered potentially important environmental contaminants [1]. It was shown that both LAS and APnEO exhibit a complex metabolic behaviour, yielding a variety of relatively stable metabolic products [2]. The composition of alkylphenolic compounds in raw effluents might often be ecotoxicologically rather unfavourable due to the enhanced relative contributions of the toxic and endocrine-disrupting alkylphenolic compounds such as alkylphenols (AP) and lipophylic APnEO that are formed under hypoxic conditions in the sewer system. This paper provides a comparison of the aromatic surfactant behaviour in municipal wastewaters during conventional activated sludge and membrane biological reactor (MBR) treatments. LAS and nonylphenol polyethoxylates (NPnEO), including their stable metabolic products, were determined using an approach based on HPLC separation followed by spectrofluorimetric detection, which involved both reversed-phase (separation of homologues) and normal-phase (separation of oligomers) systems [3]. Liquid chromatography/tandem mass spectrometry (LC/MS/MS) was used for identification and quantification of nonylphenol (NP) and nonylphenoxy carboxylic acids (NPnEC). The study of the conventional activated sludge process was performed in the sewage treatment plant (STP) of Velika Gorica (Croatia). The MBR facility used in this study was a pilot-scale unit, which consisted of a primary settling tank and an aerated secondary tank equipped with an immersed hollow fiber microfiltration membrane (ZW-10, Zenon, Canada). The study showed that aromatic surfactants belong to the important constituents in Croatian municipal wastewaters with typical LAS and NPnEO concentrations of 2-5 mg/L and 0.1-0.5 mg/L, respectively. Both surfactant classes are rather complex mixtures, consisting of various homologues, isomers and/or homologues. The composition of LAS and APnEO residues, found in municipal wastewaters, indicated the presence of those commercial mixtures, which are typically used in detergent formulations. The removal of aromatic surfactants in conventional STP showed well-known features reported earlier in the literature [2], including an efficient biological transformation of the parent surfactants and formation of stable metabolic products. With respect to the overall elimination of alkylphenolic compounds, the mechanical/biological STP of Velika Gorica showed a sub-optimal performance, which often remained below the target value of 80 %. The elimination efficiency of aromatic surfactants using the MBR unit was significantly higher, exceeding 80 % for the overall removal of recalcitrant alkylphenolic compounds. Moreover, the composition of the effluents, resulting from the MBR-treatment, was ecotoxicologically more favourable due to the lower contributions of the lipophylic metabolites

alkylbenzene sulphonates (LAS); alkylphenol polyethoxylates (APnEO)

nije evidentirano