Maximizing Water and Energy From New Anaerobic Wastewater Treatment Technology

Municipal wastewater treatment processes in the United States typically rely on aerobic secondary treatment, an energy-intensive process, for removal of dissolved organic contaminants. Aerobic treatment consumes 0.4-0.65 kilowatt-hours per cubic meter (kWh/m3) or 1,500-2,500 kilowatt-hours per million gallons (kWh/MG) and produces large quantities of surplus biosolids that must be hauled away and disposed. 

A new, anaerobic secondary wastewater treatment process, the staged anaerobic fluidized bed membrane bioreactor (SAF-MBR), was installed at Silicon Valley Clean Water, a full-scale wastewater treatment facility in Redwood City, California, that serves about 220,000 people and businesses in several cities. The SAF-MBR was tested at its design flow of about 90.2 cubic meters per day (24,000 gallons/day) and is achieving US secondary effluent standards in a treatment volume and footprint that are more compact than typical aerobic systems. Because of energy efficiency and increased energy production, the SAF-MBR can be net-energy positive. A full-scale wastewater treatment plant employing an SAF-MBR for secondary treatment could produce a renewable energy surplus of 0.35 kilowatt-hours per meters cubed (1,320 kWh/MG) while cutting secondary biosolids production by about 90 percent. This anaerobic system thus would enable wastewater treatment plants to transform from large power consumers into renewable energy power plants. 

SAF-MBR effluent contains sulfides and ammonia, which will interfere with disinfection using chlorine or ultraviolet light. To overcome these challenges, a treatment process consisting of sulfide oxidation by hydrogen peroxide, pathogen inactivation by UV irradiation, and chloramination was investigated. This process is capable of meeting disinfection and chlorine residual requirements established by California water reuse regulations. 

Potable water reuse treatment processes were tested on SAF-MBR effluent. These processes achieved potable reuse requirements, while reducing fouling of reverse osmosis membranes and reducing the toxicity of disinfection byproducts in the final water compared to conventional aerobic systems. Further scale-up could unlock large energy and water quality benefits.