CONTROLLING GASEOUS NITROGEN OXIDE EMISSIONS AND NITROGEN REMOVAL PERFORMANCE IN HOLLOW FIBER MEMBRANE-AERATED BIOFILM REACTORS

摘要

A hollow fiber membrane-aerated biofilm reactor (HFMBR) was operated at elevated temperature (30°C) and low bulk liquid dissolved oxygen (DO, <0.3 mg/l) to achieve nitritation from a synthetic, high-strength, nitrogenous wastewater. Rapid startup was achieved despite high ammonia concentrations and stable nitritation was obtained for ～70 days, at which time nitrite oxidation was observed. Of the three corrective actions used to deter proliferation of nitriteoxidizing bacteria (NOBs), decreased oxygenation via reduction of the lumen pressure appeared to be the most effective. Microbial population analysis via fluorescence in-situ hybridization (FISH) revealed biofilm aggregates throughout the reactor dominated by Betaproteobacterial ammonia-oxidizing bacteria (AOBs) hybridizing with probe Nso1225. Nitrospira genus NOBs hybridizing with probe Ntspa662 were present only at the most downstream sampling location in the reactor, where the biofilm developed latest in time when nitrite concentrations were high. Biomass sloughing and a pump failure resulted in conditions favorable for continued NOB proliferation. Nitrogen balancing revealed up to 10% of the ammonia oxidized was recovered as gaseous nitrogen oxide emissions in the outlet gas (N_2O, NO, NO_2). Two short-term corrective action experiments (increased oxygenation, elevated pH) were insufficient to mitigate these emissions, demonstrating an emerging challenge for implementing low DO nitritation systems for nutrient removal.