Advance nitrogen removal from anaerobic sludge digestion liquor using partial nitrification and denitrification coupled with simultaneous partial nitrification, anammox, and denitrification process

A novel two-stage continuous-flow partial nitrification and denitrification coupled with simultaneous partial nitrification, anammox, and denitrification (PND-SNAD) process was developed to treat anaerobic sludge digestion liquor. During the stable phase, the total nitrogen and chemical oxygen demand (COD) removal efficiencies were 93 +/- 3 % and 59 +/- 7 %, respectively. Free ammonia suppression (26.2 +/- 12.7 mg/L) and low dissolved oxygen (DO, 0.12 +/- 0.07 mg/L) were key factors in the operation of the PND process, while the SNAD process was restricted successfully by limited oxygen (DO < 0.1 mg/L) and short solids retention time (9.7 d). The PND process was an important pretreatment process that could remove biodegradable dissolved COD by denitrification and supply ammonium-oxidizing bacteria (AOB) to the SNAD process. Nitrosomonas and Ca. Brocadia were the dominant AOB and anammox bacteria, respectively. Overall, this research presents a distinctive SNAD combined process for anaerobic sludge digestion liquor treatment.