Bioaugmentation of sidestream nitrifying-denitrifying phosphorus-accumulating granules in a low-SRT activated sludge...

Sidestream granular activated sludge grown on anaerobic digester dewatering centrate was bioaugmented and selectively retained to enable high nitrification performance of a 2.5-day aerobic SRT non-nitrifying flocculent activated sludge system at 12 °C. Sidestream-grown granules performed enhanced biological phosphorus removal (EBPR) and short-cut nitrogen removal via nitrite. After bioaugmentation, EBPR continued in the mainstream but ammonia oxidation was eventually to nitrate. Low effluent NH₃-N concentrations from 0.6 to 1.7 mg/L were achieved with nitrification solely by granules, thus enabling denitrification and nitrogen removal. Molecular microbial analyses of flocs and granules also suggested that nitrifying organisms persisted on granules with minimal nitrifier loss to flocs. Mainstream granule mass at the end of bioaugmentation testing was 1.7 times the amount of sidestream granules added, indicating mainstream granular growth. Nitrite and nitrate availability during the unaerated feeding period encouraged significant growth of ordinary heterotrophs in mainstream granules, but nevertheless mainstream nitrification capacity was sustained.