Short-cut waste activated sludge fermentation and application of fermentation liquid to improve heterotrophic aerobic nitrogen removal by Agrobacterium sp. LAD9

Conventional anaerobic waste activated sludge (WAS) fermentation has been proved efficient in WAS reduction and internal carbon sources (e.g. volatile fatty acids) production for heterotrophic aerobic nitrogen removal, but to be time-consuming (within weeks). This study revealed similar efficiency for nitrogen removal enhanced by Agrobacterium sp. LAD9 capable of heterotrophic aerobic nitrogen removal using products from short-cut WAS fermentation process improved by thermal-alkaline pretreatment within only 14 h. Bench-scale experiments demonstrated that about 30% organics could be extracted for carbon sources recovering and sludge reduction during short-cut WAS fermentation, and addition of CaO, MgCl2·6H2O and polyacrylamide sequentially into fermented WAS exhibited better sludge dewaterability and higher carbon recovery efficiency. With the similar initial biomass concentration, the activated-sludge system with addition of LAD9 and short-cut fermentation products (chemical oxygen demand to nitrogen (COD/N) = 9) excellently performed with nitrogen removal efficiency of 86.4% within 6 h, much higher than those of 74.2% with addition of LAD9 only (COD/N = 6) and 52.5% with neither LAD9 nor short-cut fermentation products (COD/N = 6). The proposed system modified with LAD9 is of great potential for on-site reduction, reuse and recycling of WAS, and more efficient than conventional nitrogen removal systems by using short-cut WAS fermentation liquid.