Pilot Plant Demonstration of Activated Carbon Injection With Baghouse Filter for Removal of Mercury From Multiple Hearth Sewage Sludge Incinerator Exhaust

The Central Contra Costa Sanitary District (District) operates a multiple hearth sewage sludge incinerator to process biosolids from the activated sludge process. EPA is considering new emission limits or volatilized metals from sewage sludge incinerators. This pilot project tested the concept of using dry carbon injection in conjunction with bag house filtration (DCI/BF) to reduce mercury in the incinerator flue gas.DCI/BF was found to be effective for removing mercury from the flue gas. The pilot plant results show almost 80% mercury removal, although the precise mechanism is pending further investigation. The effects of DCI on other volatilized metals examined cannot be conclusively determined from this pilot test. However, the results show that baghouse process was able to effectively remove most of the metals from the gas stream, indicating that they are mostly particulate bound. Further testing is recommended to confirm the exact mechanism of the metal removal.