Investigating the biomass-specific inhibitory effect of benzalkonium chloride on anaerobic granules: A kinetic approach

Benzalkonium Chloride (BAC), a quaternary ammonium compound commonly used in industrial disinfection processes, was studied for its biomass-specific inhibitory effect on the specific methanogenic activity (SMA) of anaerobic granules. Inhibition batch assays were conducted with varying BAC concentrations (5–40 mg/L), resulting in biomass-dependent inhibition. Considering its surface-active nature, a biomass-specific BAC load was a suitable parameter to determine IC₅₀ values, ranging from 4.3 to 6.1 mg BAC/g VS. For predicting the corresponding biomass-specific inhibition constant in ADM1, the inclusion of an additional adsorption-inhibition term was required for a better validation of results. The model yielded a biomass-specific IC₅₀ of 5.3 mg BAC/g VS. The results encourage a change in perspective on IC₅₀ for surfactants by determining a biomass-specific IC₅₀, particularly in scenarios when surfactants accumulate within anaerobic reactors. Hereby, the reliability and practical relevance of IC₅₀ is increased, driving the development of mitigation strategies.