Nitrifying, Denitrifying and Heterotrophic Biomass Present in Moving Bed-Reactor

Abstract

This study was carried out to evaluate the main bacterial communities related to the removal of nitrogen in a moving bed-reactor treating landfill leachate, relating the physico-chemical parameters with the existence of these organisms in the mixed liquor (non-attached microorganisms) and Support Material (SM). The system was operated in two phases: Phase I (without effluent recirculation) and II (with recirculation, at a flow rate of 3 times the inlet flow). To monitor the system, physico-chemical analyzes were determined in the influent and effluent: pH, alkalinity, temperature, nitrogen species, Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD). To determine the concentration of nitrifying bacteria (Ammonia Oxidizing Bacteria-AOB and Nitrite Oxidizing Bacteria-NOB) and denitrifiers, the most probable number was estimated per 100 mL (MPN.100 mL^-1). The concentration of heterotrophic bacteria was estimated by determination of colony forming unit per mL (CFU.mL^-1). The reactor showed a high percentage of NH₄⁺-N removal in both phases of operation, reaching 80% removal efficiency in Phase I and 83% in II. At pH close to 5.4 NOB activity was practically ceased, with nitrite accumulation in the system. Although the oxygen concentration in the mixed liquor was above 2.0 mg.L^-1 the concentration of denitrifying bacteria was not affected. The concentration of heterotrophic bacteria was above 10⁹ CFU.mL^-1, but COD removal in the system was low due to low BOD/COD ratio in the mixed liquor. Analyzing the physico-chemical results and correlating them with the microbiological, it is verified that the MPN.100 mL^-1 of the nitrifying organisms were strongly affected by the effluent conditions, being necessary for an effective nitrification process the control of these parameters, mainly pH.