Nitrogen removal from dewatering liquid of landfill sludge by partial nitrification and denitrification

Two pilot-scale two-stage anoxic/oxic membrane bioreactors were operated at different dissolved oxygen (DO) levels to evaluate nitrogen removal performances for treating landfill sludge dewatering liquid. Under either high (5.0-6.0 mg/L) or conventional DO (2.0-3.0 mg/L) conditions, partial nitrification (PN)-denitrification was both achieved, and high-concentration free ammonia (FA) ensured stable PN. The high DO system exhibited higher nitrite accumulation (98.5 %) and nitrogen removal (98.0 %), and its nitrogen removal was mainly ascribed to PN-denitrification (53.8 %). Kinetic inhibition tests and microbial sequencing results demonstrated that high DO condition improved the abundance and ability of ammonia-oxidizing bacteria (AOB) rather than nitrite-oxidizing bacteria under the FA inhibition. Pseudomonas, Thauera, and Soehngenia were characteristic genus in the high DO system, and Nitrosomonas was only AOB. Metagenomic analysis confirmed the important role of PN on nitrogen removal in high DO system. This provides valuable references for the efficient and economic treatment of ammonia-rich wastewater.