This investigation focused on the KwaZulu-Natal province, where a number of under-utilised and under-performing anaerobic digesters were identified. The aim of the study was to assess the potential for treatment of high-strength or toxic organic agro-industrial effluents in the available capacity. The anaerobic digestion of a textile size effluent was investigated. Inhibitory components and concentrations of the solution were identified. The size solution was degraded anaerobically but could cause overloading of a digester at high concentrations. The performance efficiency of the anaerobic digesters at the Umbilo Sewage Purification Works was evaluated. The digesters were operating efficiently and had available hydraulic and organic capacities. This investigation confirmed the potential for the treatment of high-strength organic effluents in the available anaerobic digester capacity.