This research was conducted in a laboratory-scale setup to study (1) the biodegradation of laundry and dishwashing detergents under aerobic and anaerobic conditions and to quantify the degradation at steady state in terms of kinetic parameters degradation at steady state in terms of kinetic parameters and (2) the inhibition caused by the laundry and dishwashing detergents on growth-substrate utilization by unacclimated ethanol-enriched aerobic and anaerobic microbial cultures. The test reactors were monitored for chemical oxygen demand (COD), total organic carbon (TOC), and surfactant removal at different solid retention times (SRTs). Very high COD and surfactant removal were obtained within the tested range under aerobic conditions. The removal efficiency progressively deteriorated with decreasing SRT. However, even at an SRT as low as 3 days, COD removal was above 85%. The detergents had a severely detrimental effect on anaerobic microorganisms. Biogas production stopped completely after the first 10 days of the experiment. The detergents caused competitive inhibition to aerobic microorganisms at doses above 200 mg=L and to anaerobic microorganisms at doses above 25 mg=L. © 2017 American Society of Civil Engineers. © ASCE.