Inhibition effect of linear alkylbenzene sulphonates on the biodegradation mechanisms of activated sludge

The study presents a conceptual approach for the identification of the inhibition mechanisms of biodegradable inhibitors. Synthetic sewage was selected as the model degradable substrate to simulate domestic wastewaters. LAS, known to be a biodegradable but inhibitory compound, was selected as a model substrate for the determination of the inhibition mechanisms. Biodegradation of synthetic sewage and LAS were monitored through oxygen uptake rate (OUR) tests conducted to observe the dynamic response of the system when fed with synthetic sewage and synthetic sewage–LAS mixtures. The approach uses respirometry to calibrate the kinetic and stoichiometric coefficients of the proposed biochemical model. Model simulation results confirmed that presence of LAS has inhibitory effects on the biodegradation mechanisms of synthetic sewage. LAS imposed non-competitive inhibition on the hydrolysis process with an inhibition coefficient of 500 mg COD/L and effected heterotrophic growth through a competitive inhibition mechanism with an inhibition coefficient of 150 mg COD/L.