The Predicament Faced by the City of Sunrise with Their ATAD System

In the late 1980's, the use of Autothermal Thermalphillic Aerobic Digestion (ATAD) became a popular process to treat biosolids generated from wastewater treatment plants throughout the United States. However, the popularity of ATAD facilities have diminished significantly, and today the mere mention of the process to utility managers bring chills to their bodies. The process while it can produce a Class A and even a Class EQ product with low detention times, it was reported to produce a wide varying range of off gas emissions that historically have been difficult to treat. The off gas emissions from ATAD facilities can include high concentrations of ammonia, hydrogen sulfide, mercaptans, dimethyl sulfide, dimethyl disulfide and other reduced sulfur compounds. While ammonia and hydrogen sulfide off gases are typically easy to treat with today's technologies, the reduced sulfur compounds in the off gas emissions are the compounds that have presented a more difficult challenge. Consequently, the popularity of ATAD facilities to produce a product that can be beneficially reused has fallen off significantly throughout the United States, which was also the case for the City of Sunrise, Florida.In 1997, to meet the growth in the region, the City of Sunrise, Florida commissioned the design of the upgrades to the Sawgrass wastewater treatment facility (WWTF), which was brought on line in the late fall of 1999. These improvements expanded the treatment capacity of the Sawgrass WWTF to 20 million gallons per day (mgd). An element of this expansion program was intended to improve the processing of the biosolids produced at this facility, as well as the odor control at this site. The primary components of the biosolids management facilities consisted of an ATAD process followed by dewatering using a belt filter press. Odor control of the off-gas emissions from the ATAD and dewatering facilities consists of a 2-stage chemical scrubber system.Within 3-months of starting up the ATAD process, the dewatering component of the biosolids management facilities was shutdown. The primary cause was the fact that the biosolids from the ATAD process emitted such high concentrations of odorous compounds that the operation staff could not operate the belt filter press. What's more, the neighbors in the upscale business office park filed numerous odor complaints with the City when the biosolids was dewatered and stored in the enclosed truck-loading portion of the building. Since that time, the City has been hauling liquid biosolids, which has significantly increased the operating budget of the City's Sawgrass WWTF.What the City of Sunrise has faced over the past 5-years with their biosolids management facility is not uncommon with a majority of the older ATAD facilities in operation throughout the United States today. Depending on the operating characteristics of these older ATAD facilities, most have either spent millions of dollars treating the ATAD off-gas emissions or have completely shut down the ATAD process entirely and implemented another biosolids treatment process.This paper provides an overview of the ATAD process as it has evolved over the past 20-years, as well as the studies that have been completed at the City of Sunrise WWTF to remedy this problem, and includes the following specific details:Case studies of ATAD facilities and the odor control technologies that are currently in use to treat the off gas emissions throughout the United States.Recent trends regarding ATAD facilities operation and design to improve the final product to be beneficially reused.Specific experience and effectiveness of the City of Sunrise ATAD and odor control technologies that are currently in operation.Results from the on-site monitoring and modeling of the off-gas emissions at the City's Sawgrass WWTF site.Evaluation of alternatives and the development of a capital plan to improve the operation of the City's Sawgrass WWTF, minimize odor complaints and reduce operating costs.