Modeling Toxicity in Methane Fermentation Systems

Abstract

Wastewater treatment using anaerobic methane fermentation offers several significant advantages over aerobic methods, but is considered unreliable when treating wastewaters containing toxicants. Three models describing toxicity phenomena are given to help engineers develop more rational design and operational strategies. The first model describes the recovery pattern of methane fermentation systems from slug addition of toxicants as a function of toxicant type and concentration, and time. This model allows for prediction of periods of zero gas production and threshold toxicant concentrations. The second two models incorporate the effect of toxicity on the fundamental Monod-type expressions. Unsteady-state behavior is effectively described by both models and the importance of providing proper biological solids retention time is emphasized. The primary effect of toxicant addition is to alter process kinetics by temporarily or permanently increasing bacterial washout time. Therefore, to minimize the severity of both transient and chronic toxicity, a sufficiently large solids retention time is required.