This suggests that the condensable VOCs are condensing at the surface of the mist drops inside the scrubber. This condensation is believed to be responsible for the high VOC removal efficiencies. Only methanol and acetone were detected in samples taken from these facilities. However, the process gas entering and exiting the misting scrubber contained significant quantities of methanol, acetone, MEK, and high boiling point terpenes. These compounds are biological by-products of biosolids and wood chip degradation.
Methanol is produced by oxidation of wood chips at high temperatures.
Bench-scale tests have shown the increased methanol emissions likely are due to the addition of lime to the BP biosolids before composting. The three stage misting scrubber has a low HAP removal efficiency due to the highly volatile nature of the HAP compounds found in composting emissions. Overall, odor and sulfur emissions were reduced by more than 50 percent. However, the method of adding lime affects odor emissions in the receiving and transfer sources. Therefore, prelimed biosolids will emit less odor and sulfur during receiving and transfer operations.