Abstract Food wastes are typically disposed of in landfills for convenience and economic reasons. However, landfilling food wastes increases the organic content of leachate and the risk of soil contamination. A sound alternative for managing food wastes is anaerobic digestion, which reduces organic pollution and produces biogas for energy recovery. In this study, anaerobic digestion of a common food waste, brown grease, was investigated using a pilot-scale, high-rate, completely-mixed digester (5.8 m3). The digestibility, biogas production and the impact of blending of liquid waste streams from a nearby pulp and paper mill were assessed. The 343-day evaluation was divided into 5 intensive evaluation stages. The organic removal efficiency was found to be 58 ± 9% in terms of COD and 55 ± 8% in terms of VS at a hydraulic retention time (HRT) of 11.6 ± 3.8 days. The removal was comparable to those found in organic solid digesters (45–60%), but at a much shorter HRT. Methane yield was estimated to be 0.40–0.77 m3-CH4@STP kg-VSremoved−1, higher than the typical range of other food wastes (0.11–0.42 m3-CH4@STP kg-VSremoved−1), with a mean methane content of 75% and <200 ppm of hydrogen sulfide in the biogas. The blending of selected liquid wastes from a paper mill at 10 vol% of brown grease slurry did not cause significant reduction in digester performance. Using a pseudo-first-order rate law, the observed degradation constant was estimated to be 0.10–0.19 d−1 compared to 0.03–0.40 d−1 for other organic solids. These results demonstrate that brown grease is a readily digestible substrate that has excellent potential for energy recovery through anaerobic digestion.