Demonstration of Advanced Primary and Secondary Wastewater Treatment Technology

The Issue

The long-used Conventional Activated Sludge (CAS) treatment paradigm is fundamentally at odds with the goals of energy efficiency and recovery because it misdirects influent solids. Up to 88 percent of influent organic material in wastewater treatment plants is in a particulate form that is not rapidly biodegradable. Much of this material passes through typical primary clarifiers into CAS treatment where it requires a long residence time to decompose, requiring large reactor footprints. Wastewater must be aerated during this decomposition, consuming substantial power to oxidize and destroy most of the chemical energy in the wastewater. Only one third of the energy is transferred to biomass with a potential recovery value. This biomass has a high initial moisture content and is just 30-50 percent digestible, limiting its potential for resource recovery. These limitations result in a 20-50 percent maximum recovery of the chemical energy in wastewater treated with CAS. Although CAS can reliably achieve today’s U.S. Secondary Effluent standards, it does so at a high cost in terms of energy, footprint, and complexity. Its chief byproduct, biosolids, are of limited resource value, contain controversial “contaminants of concern,” and require additional management costs for volume reduction, pathogen destruction, and transport.