High-level nitrogen removal by simultaneous partial nitritation, anammox and nitrite/nitrate-dependent anaerobic methane oxidation.

While the anaerobic ammonium oxidation (anammox) process has been applied for nitrogen removal from high-strength wastewater, nitrate accumulation in effluent still represents a major concern. Here, a novel process, named the one-stage PNAM, that integrates the Partial Nitritation (PN), Anammox and Methane-dependent nitrite/nitrate reduction reactions in a single membrane biofilm reactor (MBfR) is developed. With feeding of 1030 mg NH4+-N/L at a hydraulic retention time of 16 h, the proposed one-stage PNAM process achieved an average total nitrogen removal efficiency of 98% and a nitrogen removal rate of 1.5 kg N/m3/d (1.4-1.8 g N/m2/d) by using methane as the sole carbon-based electron donor. The N2O emission was determined to be 0.34% ± 0.01%. Microbial community characterization revealed that ammonia-oxidizing bacteria (AOB), anammox bacteria, nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) bacteria and archaea co-developed in the biofilm. Batch tests showed that AOB, anammox bacteria and n-DAMO microorganisms were indeed jointly responsible for the nitrogen removal. This one-stage PNAM process can potentially be applied to treating high-strength wastewater, such as anaerobic sludge digestion liquor or landfill leachate.