PERFORMANCE EVALUATION AND O&M COMPARISON FOLLOWING FIVE YEARS OF OPERATION OF THREE ANAEROBIC DIGESTER PROJECTS

A previous presentation (Witzgall, et. al., 1998) compared design features and construction costs of new anaerobic digesters at the Los Angeles Hyperion Treatment Plant, the Greater Vancouver Regional District's (GVRD) Annacis Island Wastewater Treatment Plant and the Sacramento Regional Wastewater Treatment Plant (SRWTP). This paper focuses on the comparative performance and operation and maintenance experience of new fixed cover and egg-shaped digesters at these three large primary/secondary wastewater plants following approximately five years of operational experience with the new and upgraded digestion systems. The following information is presented in this paper:Description of facilities.Digester operations (feedstock characterization, feed rate, solids loading rate, method of feed and withdrawal).Digester performance (volatile solids reduction, gas production, and quality, and product pathogen content)General condition of digesters (grit build-up, scum or foam on surface, corrosion/struvite issues).Comparisons and conclusions.Basic design data and process flow diagrams for the three anaerobic digester facilities are discussed. Each of the three plants has different anaerobic digester process features and operational strategies but all three process primary and waste biological sludges. The Hyperion plant has operated a 2-stage mesophilic operation in recent years, but is currently operating an innovative thermophilic Class A digestion process in egg-shaped digesters. The SRWTP has been operating in a mesophilic mode using a blending/storage digester at the end of the process. The GVRD Annacis Island WWTP is operating a unique staged thermophilic process to produce Class A biosolids.