CONTROL OF ATAD ODORS AT THE EAGLE RIVER WATER AND SANITATION DISTRICT

The Autothermal Thermophilic Aerobic Digestion (ATAD) process, which became popular in North America in the late 1980's, achieves high volatile solids and pathogen reductions by digesting sludge at elevated temperatures (50° to 65°C). Because most ATAD systems do not maintain truly aerobic conditions at all times, high concentrations of ammonia and reduced sulfur compounds can be formed and subsequently released from the process off-gas as well as from downstream dewatering and storage operations. While the ammonia and hydrogen sulfide emissions are easily treated in wet scrubbers, biofilters, or biological scrubbers, the malodorous, higher molecular weight sulfur compounds such as mercaptans, dimethyl sulfide, and dimethyl disulfide can be difficult to treat by such technologies. Because of the high inlet concentrations and the low odor detection thresholds of these compounds, odor control systems must often be designed to achieve high removal efficiencies in order to prevent nuisance conditions from developing.This paper presents a description of the ATAD process and a review of odor control technologies that have been or are currently being used to treat the off-gases from ATAD processes in North America. Specific experience with ATAD odors at wastewater treatment plants in Avon and Edwards, Colorado is discussed. These systems were evaluated in detail as part of plant-wide odor control studies conducted at the two facilities. Design criteria of the unique, multi-stage odor control systems are reviewed. Performance data showing the removal of odor (dilutions to threshold), ammonia, hydrogen sulfide, methyl mercaptan, dimethyl sulfide, dimethyl disulfide, carbonyl sulfide, and other compounds are presented.