Aerobic Granular Sludge Bioaugmentation in Low-SRT Flocculent Activated Sludge: Bench-Scale Demonstration and Pilot Testing

摘要

This research investigates bioaugmentation with aerobic granules from sidestream centrate treatment to enable nitrogen removal in non-nitrifying mainstream activated sludge treatment, where granules have a longer SRT by selective retention. Process viability was demonstrated at bench-scale with two types of granules: 1) aerobic granules performing nitrification only (NIT granules) and 2) aerobic granules performing nitrification, denitrification and enhanced biological phosphorus removal (NDN-PAO granules). Sidestream nitrogen loading rates were 0.58 and 0.54 kg TN/m~3-d for the NIT and NDN-PAO reactors, respectively. Average ammonia removal efficiency in the NIT reactor was 80% and average TN removal efficiency in the NDN-PAO reactor was 88%. In separate bioaugmentation tests using the different granule types, addition and selective retention of granules sustained nitrification and allowed nitrogen removal by denitrification in non-nitrifying flocculent activated sludge. Bench-scale mainstream effluent NH3-N concentrations near 1 mg/L were achieved at 12°C and 2.5 day aerobic SRT. Granule removal at the end bioaugmentation immediately resulted in near-complete loss of nitrification. Nitrification capacity associated with waste sidestream granular sludge was 2.4 times higher for the NDN-PAO system; therefore pilot design at a municipal WRRF was based on bioaugmentation with NDN-PAO granules. The pilot sidestream reactor achieved similar TN loading and removal rates as the bench-scale system within 90 days of startup, which was facilitated by seeding with small granules harvested from a full-scale continuous-flow anaerobic-aerobic conventional activated sludge process. Mainstream granule-floc separation and bioaugmentation performance in the pilot system are being evaluated in ongoing work.