Comparison Between Acidogenic and Methanogenic Inhibition Caused by Linear Alkylbenzene-Sulfonate (LAS)

J. L. García-Morales, E. Nebot, L. I. Romero and D. Sales

Abstract
The anaerobic mixed microbiote may be inhibited through different mechanisms: inhibition by product or substrate, by the physical characteristics of the medium (pH or temperature), and by inhibitory substances, organic or inorganic. Biological activity tests have been the most widely used, of different experimental procedures known, to evaluate the toxicity of various compounds in anaerobic processes. The present study evaluates the inhibitory effect of the anionic surfactant LAS (linear alkylbenzene-sulfonate) on the main anaerobic microbiotes (acidogenic and methanogenic) involved in anaerobic digestion in a reactor treating organic wastewater in the thermophilic range, by means of specific activity tests. Inhibition functions are obtained for inhibition in both microbiotes. The EC50 (the concentration that reduces by half the activity of a population) is also calculated, giving EC50 (meth)= 6.3 ppm, and EC50 (acid)= 18.9 ppm. The results show that the methanogenic microbiote is more sensitive to LAS than the acidogenic.

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Keywords
thermophilic anaerobic digestion, activity determination, LAS