Effect of individual or combined physical and chemical factors on the anaerobic biodegradation of linear alkylbenzene sulphonate

Abstract

The effect of six important factors on the anaerobic biodegradation of linear alkylbenzene sulphonate (LAS) was evaluated using a response surface methodology. The factors were: (i) co-substrate concentration (CC), (ii) contact time between LAS and microorganisms, (iii) temperature, (iv) hardness, (v) pH, and (vi) LAS source. The results showed that individually or combined, CC with chemical oxygen demand (COD) ≤50 mg L−1 was the factor that mostly favoured LAS biodegradation; whereas at COD >50 mg L−1, adsorption to sludge and solubilisation in the aqueous medium were favoured. Two-factor interactions promoted the highest percentages of biodegradation (45–52%), adsorption (43–45%), and solubilisation (18–25%). The three-factor interactions resulted in small percentage increases of up to 11%, 5%, and 13% for biodegradation, adsorption, and solubilisation, respectively, compared to those of two-factor interactions. The interactions of four, five, and six factors resulted in a non-significant effect on LAS biodegradation, adsorption, and solubilisation, with percentages close to those quantified for the two- and three-factor interactions. Concentrations of up to 30 mg LAS L−1 did not significantly affect the COD removal efficiency (74–88%) from the medium. These values are commonly obtained in full-scale anaerobic systems used to treat domestic sewage.