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.
Highlights
The final disposal of solid waste in landfills is a widely used waste treatment technique
Ammonia Oxidizing Bacteria (AOB) ranged from 106 MPN.100 mL−1 (38th operation day-Phase I) to 108 MPN.100 mL−1 (125th day-Phase II) and Nitrite-Oxidizing Bacteria (NOB) ranged from 105 MPN.100mL-1 in the 5th day (Phase I) to 107 MPN.100 mL−1 in 38th (Phase I) and 74th (Phase II) days
From 74th day to 125th, AOB decreased in the order of 102 MPN.100 mL−1 and NOB in the order of 105 MPN.100 mL−1
Summary
The final disposal of solid waste in landfills is a widely used waste treatment technique. This technique minimizes the environmental impacts and allows the decomposition of the residues under controlled conditions until their transformation into inert and stabilized material (Renou et al, 2008). Leachate composition varies with the age of the landfill, climatic factors and characteristics of the waste (Kjeldsen et al, 2002; Bhalla et al, 2012). In contrast to organic matter, the concentration of nitrogen present in the leachate does not depend on the decomposition phase of the residues, because during the life of the landfill what changes is the way in which it presents itself (Kjeldsen et al, 2002)
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