Anaerobic co-digestion of oil refinery waste activated sludge and food waste.

The technology of anaerobic co-digestion to treat the excess biological sludge discharged from activated sludge systems in oil refineries was evaluated in bench scale experiments. Mixing food waste rich in fruits and vegetables with this sludge increased the reduction of volatile solids and biogas yield. An experimental design indicated that the best co-digestion condition was the use of waste activated sludge without previous dewatering (3.5% total solids) and food waste in an 80:20 ratio (% v/v), without the addition of inoculum. After 45 days at 35 °C, this condition resulted in volatile solid (VS) removal of 52% and biogas yield of 80.7 mL biogas/g VS, against only 19% and 38.5 mL biogas/g VS in mono-digestion of sludge alone. Anaerobic co-digestion demonstrates promising results and the potential for a simple and effective treatment method for excess biological sludge generated at refineries.