Impact of free ammonia and free nitrous acid on nitritation in membrane aerated bioreactors fed with high strength nitrogen urine dominated wastewater

Nitritation can help lower ammonia oxidation treatment costs through traditional nitrogen removal processes for wastewaters with high nitrogen (N) concentrations or low carbon to nitrogen ratios (C/N) and facilitate the anammox process. Free nitrous acid (FNA) or free ammonia (FA) can inhibit nitrite oxidizing bacteria (NOB). Only a few studies have evaluated control of nitritation at elevated TN concentrations and none for TN concentrations > 2000 mg/L, characteristic of confined animal feeding operation (CAFOs) or source separated wastewaters. This study evaluated the factors that promote nitritation in membrane aerated bioreactors (MABRs) treating urine dominated wastewaters (670–4900 mg-N/L) at DO > 3 mg/L and without solids wasting. FNA concentrations > 0.2 mg-N/L and/or FA concentrations > 3 mg-N/L partially inhibit NOB similar to inhibitory concentrations observed in studies for lower strength wastewaters. FNA > 1 mg-N/L completely inhibited NOB. Direct addition of nitrite (NO2-) or pH manipulation to increase either FNA or FA can inhibit even established NOB populations, leading to stable nitritation. For urine dominated wastewaters with TN concentrations > 1000 mg/L or reactors designed to produce an effluent with ~1:1 total ammonia nitrogen (TAN) to NO2- (pre-anammox), all operating regimes (loading or pH) inhibit NOB. These results extend the applications of MABRs to treat high TN concentration, urine dominated wastewaters. MABRs are ideal for remote locations or other applications (off grid communities, CAFOs, underdeveloped countries) that cannot support complex control systems for pH or DO control and eliminate the need for solids processing.