The inhibition kinetics of FA coupling MLSS to nitrification

A lab-scale two-stage UASB-A/O combined process for treating the real municipal waste leachate and a pilot-scale SBR for treating the municipal wastewater were used to investigate the inhibition kinetics of FA(free ammonia, FA) and MLSS(Mixed liquor suspended solids,MLSS) to nitrification rate. Under the premise of achieving short-cut nitrification-denitrification stably (running 130 days) in UASB-A/O and favorable nitrogen and phosphorus removal efficiency in SBR, a number of nitrification batch test was carried out in different concentrations of FA and under different MLSS gradient with sludge which was from A/O reactor and SBR reactor. A nitrification inhibition kinetics model was established based on a large number of experiments data and the FA nitrification inhibition kinetic constants under different MLSS were deduced by function match. The relation curves of FA concentration and specific rate of nitrification match the Andrews inhibition kinetics model well at constant temperature and MLSS conditions. The both maximum specific nitrification rate (r_max) and half-saturation constant (K_FA) were maximum at MLSS=2000mg/L, but they vary greatly at different MLSS conditions. That the r_max and K_FA of A/O were 33.966 mgNH₄⁺-N/g MLSS·h and 3.297 mg/L under MLSS=2000mg/L, respectively, was higher than the values of SBR. Both the inhibition constant (K_I) were increased with the increase of MLSS, however, the A/O sludge´s increased significantly (form 4.980mg/L to 39.276mg/L) which means the inhibition was weaker when MLSS was high especially for the adapted sludge.