Simultaneous partial nitrification, endogenous and autotrophic denitrification in a single-stage...

Simultaneous partial nitrification-denitrification (SPND) is a promising process for nitrogen (N) removal from kitchen digested wastewater characterized by a low C/N ratio. However, its widespread application is often restricted due to the unstable partial nitrification and unsatisfactory denitrification performance. This work developed a novel simultaneous partial nitrification, endogenous and autotrophic denitrification process using a single-stage electrolysis-integrated sequencing batch biofilm reactor (E-SBBR) with anoxic/electro-anaerobic/aerobic operating strategy. The novel process considerably enhanced the stability and N removal efficiency (NH₄⁺-N>94.5% and TN>90.8%) of the SPND process. The pre-electro-anaerobic phase achieved alkalinity and H₂ generation, and intracellular carbon storage. The increased alkalinity resulted in increased free ammonia (FA) which secured complete suppression of nitrite-oxidizing bacteria (NOB). SPND efficiency in the aerobic phase was dramatically improved using polyhydroxyalkanoates (PHAs) and H₂ as electron donors for endogenous and autotrophic denitrification. Microbial community analysis indicated the successful washout of NOB and the enrichment of ammonia-oxidizing bacteria (AOB), denitrifying glycogen accumulating organisms (DGAOs), autotrophic and heterotrophic denitrifiers in the system. This research presents a distinctive SPND process for intensified kitchen digested wastewater treatment and gives insights into the underlying mechanism.