STARTUP OF A TWO-PHASE DIGESTION PROCESS: DOCUMENTING AN EMERGING TECHNOLOGY

The City of Turlock, California operates a 15 mgd facility that treats a combination of industrial and municipal wastewater. This facility converted its anaerobic solids stabilization process to a two-phase digestion process in September 2006. The city's advanced digestion process consists of a single acid-phase digester, which receives a blend of thickened primary and secondary solids. Acid-phase solids are transferred to five methane phase digesters using batch sequencing.Two-phase digestion is a technology that separates anaerobic digestion into acid-phase and methane-phase reactors. Each is uniquely designed and operated to create an environment with the most favorable growth conditions for its specific bacteria. When compared to conventional anaerobic digestion, two-phase digestion offers many benefits, including capacity optimization, increased volatile solids reduction, increased dewaterability, and increased gas production.This paper focuses on the start-up procedures that were used by the city to convert a conventional high-rate anaerobic digestion facility to two-phase digestion to maximize the potential benefits achieved through two-phase digestion. Building on experience gained from assisting in the start-up of two-phase digestion processes at both the City of San Bernardino and Inland Empires Utilities Agency in Southern California, Carollo worked with the City of Turlock to optimize their advanced digestion system. The importance of several operating parameters, including hydraulic retention time, volatile solids loading rate, and pH will be discussed. This paper will also cover the unique aspects of the two-phase digestion process at the City of Turlock, including a new system using heated acid-phase solids to pre-heat primary solids in order to reduce clogging and plugging of the piping.