Moving bed biofilm reactor (MBBR) technique is a useful technology for the treatment of mature landfill leachate. The reactor
start-up and acclimation processes illustrated that many factors, such as biomass, C/N ratio, and influent volumetric loading rates,
could affect the ammonium-nitrogen (NH4+–N) and COD removal. The factorial experiments were carried out to determine the
optimal reactor operational conditions, and the results demonstrated that when DO 2-4 mg/L, pH 7.5, and hydraulic retention
time (HRT) 16 h, the high removal efficiencies of NH4+–N and COD would be achieved at 0.2-0.25 kgNH4+–N/m3•d of influent
NH4+–N volumetric loading rate and 0.6-0.8 kgCOD/m3•d of influent COD volumetric loading rate, respectively. To achieve the
effective removal of NH4+–N or COD at optimal conditions, the effluent reflux ratio would be controlled to obtain proper influent
NH4+–N or COD volumetric loading rates; to simultaneously achieve the effective removal of NH4+–N and COD at optimal
conditions, influent volumetric loading rates and C/N ratios would be properly taken; moreover, proper amounts of extra
nutrients would be added to promote the growth and activity of microorganisms in the treatment processes. Stable short-cut
nitrification with high nitrosation rate and low nitrate-nitrogen concentration could be achieved at the conditions of low DO
concentration, moderate pH value, and low C/N ratio. Moreover, controlling different operational conditions could achieve the
accumulation of different concentrations of nitrite, and then different subsequent biological processes would be applied for the
effective removal of NH4+–N.