DESIGN AND STARTUP OF AN INNOVATIVE LARGE SCALE AUTOTHERMAL THERMOPHILIC AEROBIC DIGESTION FACILITY SUNRISE, FLORIDA

摘要

Introduced to North America in the 1980抯, the autothermal thermophilic aerobicrndigestion (ATAD) process has evolved from a biosolids handing component that wasrnused for small systems only, to the large facility at the Sawgrass. The SawgrassrnPOTW is sized for over 250,000 people and is located in the City of Sunrise, Florida.rnIn 1995, the City of Sunrise undertook to expand the Sawgrass facility. In theirrnplanning they collected the untreated biosolids from their Park City and Springtreernplants for central treatment at Sawgrass. The pre-existing aerobic digester atrnSawgrass was heavily loaded and experienced operational difficulties; although itrnoperated efficiently. The biosolids product was land applied as a Class B biosolidsrnproduct. To meet their projected solids handling needs, the City selected the ATADrnprocess as part of a new solids handling system. This would compliment the existingrnaerobic process and achieve a Class A product, for wider application than landrnspreading alone. The ATAD however, is only part of a larger system. Initially the Cityrnreviewed design submissions for proprietary ATAD processes. Again to meet theirrnsite-specific needs, the City instead selected a custom ATAD that would be part of arnholistic system design undertaken by one engineering team. Due to its size thernSawgrass ATAD incorporates sophisticated controls and yet retains simplicity ofrnoperation. The system includes two dissolved air flotation thickeners, the ATADrnprocess consisting of two trains of three reactors each with provision for a third train,rntruck loading and unloading facilities, unthickened biosolids storage, belt filter pressrndewatering, air scrubbing and a supervisory control and data acquisition system.rnProgrammable logic control, operator accessible portable computer stations, motorrncontrol center and adjustable speed drives are included. The ATAD is fully automatedrnto maintains setpoint reactor temperatures, undertake transfers automatically, alternaterntrains, provide heat exchanger cooling, and control foam. Operator initiated levelrnchanges allow optimization of digestion and energy consumption. The process willrntreat greater flows, achieve a better product on a smaller footprint and reduce energyrnconsumption per unit mass applied compared to the pre-existing conventional aerobicrndigester.