Single-Reactor Nitritation-Denitritation for High Strength Digested Biosolid Thickening Lagoon Supernatant Treatment

Abstract

Nitrogen is an essential element for living organisms, accounting for 80% of chemical elements in the atmosphere. Nitrogen is also one of the most concerned elements in the environment. The significant sources of nitrogen that released into the Canadian environment is municipal wastewater, as well as the non-point sources. The supernatant of biosolid digestate thickening lagoon contains 25-30% of the total amount of nitrogen but only 1% of the flow in the influent in WWTPs. To meet the stringent discharge standards for nitrogen in water, highly effective and energy saving nitrogen removal technologies should be investigated. The conventional nitrogen removal method, nitrification-denitrification, has been widely used in mainstream treatment. Compared to that, nitritation-denitritation can save 25% aeration cost, and 40% external carbon demand. The ammonia-rich lagoon supernatant with limited alkalinity is ideal for the single reactor nitritation-denitritation operation. In this work, an integrated fixed film activated sludge (IFAS) system was operated in sequencing batch mode at 21 oC. This thesis evaluates the feasibility and stability of single reactor nitritation-denitritation for treating ammonia rich lagoon supernatant, investigates the distribution of microbial community and predominant microbes that contribute to nitritation and denitritation. With a hydraulic retention time (HRT) of 2 days, the nitritation-denitritation reactor achieved a stable inorganic nitrogen removal rate at 98%. The dominant nitrifying and primary denitrifying genera were Nitrosomonas and Thauera, respectively. The relative abundance of both genera increased in suspension and biofilm after long-term operation. The suspended biomass exhibited higher activity than biofilm and suspended biomass were also proved to contribute more on both nitritation and denitritation process than biofilm.