Nitrification bioaugmentation in mainstream flocculent activated sludge systems using sidestream aerobic granular sludge
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Increased nitrification capacity in flocculent activated sludge wastewater treatment systems may be required to meet lower effluent ammonia-nitrogen (NH3-N) concentration limits, to handle higher influent flows, and/or for conversion to nitrogen removal. A novel approach to increase nitrification capacity in flocculent activated sludge systems is through bioaugmentation with nitrifying granular sludge grown in a sidestream treatment reactor fed anaerobic digester dewatering centrate. Granules from the sidestream reactor are added to the mainstream flocculent activated sludge system to increase the nitrifying biomass concentration without increasing aeration tank volume. The granular sludge solids retention time (SRT) can be decoupled from the low SRT of the flocculent sludge by selective granule retention due to the larger size and faster settling velocity of granules. Retention and accumulation of the granule biomass results in a high volumetric nitrification capacity. The main research goal was to demonstrate viability of the granular sludge nitrification bioaugmentation process and address fundamental scientific and process application considerations pertaining to sidestream and mainstream treatment performance, nitrification kinetics, and granule biopopulations. Different types of nitrifying granules were grown on simulated centrate and evaluated for mainstream bioaugmentation potential based on granule nitrification capacity yield and physical characteristics favorable for mainstream retention. Granules performing a) nitrification only and b) nitrification, denitrification and enhanced biological phosphorus removal showed the greatest potential and were further studied in centrate treatment systems. Successful growth of both granule types was obtained with centrate feeding and consistent production of waste granular sludge for bioaugmentation. 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. Mainstream effluent NH3-N concentrations near 1 mg/L were achieved at 12 degrees Celsius. Granule removal at the end bioaugmentation immediately resulted in near-complete loss of nitrification. Molecular microbial analyses showed changes to the granule microbial community composition in mainstream treatment and low abundance of ammonia oxidizing bacteria in waste flocculent sludge. The overall results of this research demonstrate that nitrification bioaugmentation with granular activated sludge from sidestream centrate treatment can greatly intensify treatment capability of flocculent activated sludge systems by enabling nitrification and nitrogen removal in otherwise non-nitrifying flocculent activated sludge.
- Civil engineering