Enhanced biogas production using ozone – lysis reactor design and integration with anaerobic digestion of biosolids

Ozone treatment of wastewater biosolids is an effective method of cell lysis for digester feed pretreatment, to increase solids destruction and to increase biogas yield. A plug-flow reactor provides the most efficient use of ozone - the full flow of oxygen gas injected with the ozone, however, cannot be sent directly to the digester for both process and safety reasons. This study develops a system design that controls the oxygen content of the treated digester feed, while maintaining the efficiency advantages of a pipeline contactor. Flow and separation studies were conducted for model fluids and wastewater sludges. Two-phase flow maps were confirmed to indicate bubbly flow over the gas/liquid ratios of 0.1-1.0. Vertical separator design was found capable of limiting oxygen to low levels in treated sludge; oxygen monitoring would also be used for safety. Secondary benefits are anticipated, such as effective reduction of biogas sulphur content. The system described represents a significant new application of ozone for reducing waste solids and increasing energy recovery in wastewater treatment.