Orange County Sanitation District
What new technologies have you been evaluating/implementing and are interested in investigating?
After two years of study, the Orange County Sanitation District (OCSD) is moving toward a full-scale demonstration of the solids processing technology known as supercritical water oxidation (SCWO) as implemented in the AquaCritoxA® process (SCFI Group, Cork, Ireland). If it is successful, SCWO could provide a one-step approach that would replace multiple solids and biogas treatment processes at significantly lower cost and higher efficiency.
In SCWO, organic materials are reacted with liquid oxygen at elevated temperature and pressure (above 705oF and 3206 psia). At these conditions, oxidation of any organic substance is virtually complete, resulting in a gaseous product stream composed of pure carbon dioxide (CO2) and nitrogen (N2). In addition, large amounts of recoverable heat are released, resulting in an overall thermal efficiency of about 90%. The only solid waste stream is a dewaterable granular material (typically 3-5% of the feed solids) containing minerals such as phosphorus, iron, and silica. Recovering the excess heat as steam allows it to be used for process heating if desired, or it can be fed to a steam turbine/generator to produce electricity. As a rule of thumb, one dry ton of feed solids can generate one megawatt-hour of electricity, which is about four times the electricity produced from anaerobic digestion followed by a biogas-fueled internal combustion engine.
What are your facility drivers/needs?
OCSD has anaerobic digesters, gas compressors, and related equipment that are nearing the end of their useful lives, making this an opportune time to consider alternatives to simple like-for-like replacements. In addition, with a Class B biosolids program that manages about 700 wet tons per day, there is ample opportunity for cost savings if the biosolids amounts can be reduced or eliminated. Finally, there is always a desire to increase treatment operating efficiencies, reduce costs, and make better use of wastewater solids as a renewable resource. With single train feed capacities up to 17,000 ft3/day (at 15% solids), AquaCritox holds promise for providing notable improvements in each of these areas.
If there were one technology you would pilot or collaborate on tomorrow, what would it be?
Currently, OCSD is engaged in a detailed engineering study to determine the optimum location in its treatment plants for an AquaCritox installation, the performance expectations, and the projected capital and operating costs. Following the completion of that study in mid-2016, the agency will decide whether to proceed with the construction of a SCWO plant.
How has LIFT helped, or how would you like LIFT to help your facility?
SCWO is one of the technologies identified by LIFT’s Biosolids to Energy subgroup. OCSD would welcome the participation of other LIFT utilities as we move into demonstrating this uniquely disruptive approach to solids treatment and resource recovery.