Published: CABEQ 18 (4) (2004) 409–415
Paper type: Original Scientific Paper

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Influence of Linear Alkylbenzene Sulphonates (LAS) on Microbial Activity of Activated Sludge

M. D. Coello Oviedo, D. Sales Márquez and J. M. Quiroga Alonso

The purpose of the present work was to study the influence of the anionic surfactant sodium linear alkylbenzene sulphonate, LAS, on the microbial population present in a activated sludge unit of a wastewater treatment plant. Both, traditional control methods to measure volatile suspended solids and chemical oxygen demand, and specific techniques for the measurement of microbial activity (dehydrogenase activity and specific oxygen uptake rate), were used and the results were compared. It is shown that activity measurements are more adequate for the control of biological system, concretely, the results obtained showed that the specific oxygen uptake rate is the simplest and quickest method to carry out a routine control. Three concentrations of LAS have been assay in the experiments (25, 50 and 100 mg L–1). Inhibitions of microorganisms have been observed when the biggest mass concentration (100 mg L–1) was added, although before this a maximum inhibition of microbial activity was observed. Likewise, LAS influences the degradation capacity of, both, organic matter and itself in aerobic processes, increasing the residual COD and LAS mass fraction obtained, and diminishing LAS biodegradation rate. When comparing biodegradation rates of the individual homologues, the highest rate was observed for those with the longest alkyl chain.

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microbial activity, activated sludge, dehydrogenase activity, LAS, specific oxygen uptake rate.