Odor generation and control from the Autothermal Thermophilic Aerobic Digestion (ATAD) process

The final wastewater solids product from Autothermal Thermophilic Aerobic Digestion processes (ATAD) meet the pathogen and vector attraction requirements of the EPA's 503 regulations (Walker). However, the ATAD process itself generates odors, and has the potential to warrant complaints from people living downwind of a wastewater treatment facility. Odorous emissions from an ATAD process and the effectiveness of odor treatment measures were evaluated and are reported in this paper.Air, liquid, and solids samples were taken at different stages in the treatment process. Liquid and solids samples were taken from the waste activated sludge (WAS) holding tank, post drum thickening with polymer addition, the ATAD, and the final biosolids dewatered cake. In addition, air samples were taken from the exhaust of the ATAD treatment unit and the exhaust of the biofilter used to treat the ATAD gas emissions, which have already had ammonia removed in a wet scrubber. Ammonia, dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide were detected in the ATAD samples. In addition several volatile organic compounds were detected including acetone, toluene, and numerous mixed alkanes.The Odor Index Value (ODI) was calculated for each sample. Solids from the WAS holding tank, produced an ODI of 635,000, followed by the rotary drum thickener solids stage with an ODI of 224,000. The gas from the ATAD generated an ODI of 19,600,000 due to large concentrations of organic sulfides, all of which have extremely low detection thresholds, resulting in extremely high Odor Index Values. The final biosolids cake contained ammonia, and did not emit any significant quantity of organic sulfides. Therefore, the final biosolid product produced from the ATAD process had an ODI of 4050, several magnitudes lower than that for the solids samples from the ATAD.The final biosolids demonstrated greater than a 99% reduction in odors compared to the solid samples upstream of the ATAD. In addition, wet scrubbing and biofiltration of the exhaust air from the ATAD resulted in greater than 99% reduction of the ODI associated with the gases released from the ATAD.The ATAD process at this facility is a reliable and efficient way to create a class A biosolid. High concentrations of odorous compounds are generated within the ATAD, which are controlled with a wet scrubber and biofiltration. Due to the high rate of degradation of odor precursors within the ATAD, the final biosolids product appears to be very stable and minimizes odors from this facility and the resulting biosolids.