The investigation summarized in the report was undertaken to evaluate the performance of powdered activated carbon (PAC) technology used in conjunction with wet air regeneration (WAR) at municipal wastewater treatment plants. Excessive ash concentrations accumulated in the mixed liquor suspended solids (MLSS) at all facilities that relied on the WAR unit blowdown for ash control. A variety of ash control methods have been implemented and are documented. The nitric acid test for PAC was shown to substantially overestimate PAC concentrations. PAC losses across WAR or the desirability and economics of recovering the volatile suspended solids (VSS) exiting the WAR reactor could not be quantified. Other areas covered in the report include adsorptive capacity of the recycled material, tertiary filter performance, metals accumulation, oxygen transfer, operation and maintenance concerns and economic considerations. The report includes Appendices submitted by the system manufacturer that dispute many of the report conclusions and provide alternative explanations for some of the data obtained.