Advanced nitrogen removal from mature landfill leachate via partial nitrification-Anammox biofilm reactor (PNABR) driven by high dissolved oxygen (DO): Protection mechanism of aerobic biofilm

A novel partial nitrification-Anammox biofilm reactor (PNABR) operated under high dissolved oxygen (DO) with pre-anoxic - aerobic - anoxic operational mode was developed for efficient denitrogenation from mature landfill leachate. With DO concentration gradually increasing to 4.03 +/- 0.03 mg/L, the ammonia oxidation rate (AOR) was enhanced to 25.8 mgNH(4)(+) -NAL h), while nitrite oxidation bacteria (NOB) was inhibited effectively by alternating free ammonia (FA) and oxygen starvation. DO micro-distribution revealed that estimated 1900 mu m of aerobic biofilm could protect anammox biofilm underneath from being inhibited by high DO. qPCR analysis further suggested that ammonia oxidation bacteria (AOB) abundance in whole biofilm was 6.12 x 10(9) gene copies/(g dry sludge), which was twice than found in the floc. Anammox bacteria accounted for 2.39% of total bacteria in whole biofilm, contributing 90.0% to nitrogen removal. Nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) finally reached 396.6 gN/(m(3 )d) and 96.1%, respectively.