Nitrogen removal in RBC to landfill leachate treatment
Nitrogen removal is important for wastewater treatment, including landfill leachate treatment. The application of alternative biological routes for its removal is essential and research based  on the anammox process (Anaerobic Ammonium Oxidation) and other innovative bioprocesses has been conducted worldwide. Rotating Biological Contactors (RBCs) appear as an interesting alternative for the treatment of leachate when compared to conventional processes, since biofilm reactors have, as main advantages, a long retention time of the biomass and high resistance to organic and nitrogen shock loads. In this context, the present research aimed to evaluate the performance of this technology for nitrogen removal from landfills leachate. A bench-scale reactor with a working volume of 3.9 L was initially operated without inoculum, to observe the natural development of nitrifying biomass, which occurred within a few days of operation. The feed was carried out in the first stage of the research with synthetic wastewater, with the gradual increase of the concentration of ammoniacal nitrogen from 50 to 1000 mg N.L', and in the second stage with diluted landfill leachate in the proportion of 1:3, with an average concentration of 500 mg N.L'. Except for the adaptation period, in which a hydraulic retention time (HRT) was maintained at 36 hours, the reactor was operated with HRTs in the range of 24-10 h. Continuous and intermittent rotation were evaluated and rotation speeds between 5 and 10 rpm for continuous rotation, as well as different rotation cycles for intermittent rotation. The use of continuous rotation, regardless of speed, in the first phases of Step I, reached high DO values (7.7-1.4 mg.L-'), and high nitratation efficiencies, with values reaching 99.7 %, and it was evident that, for the specific occurrence of nitritation and posterior simultaneous development of anammox, higher concentrations of ammoniacal nitrogen would be necessary to supporting the suppression of NOB. However, the concentration of 1000 mg N.L' caused system failure, mainly explained by the inhibition by free ammonia. The use of intermittent rotation consisted of an innovative approach and resulted in micro aeration (0.15-2.1 mg.L-'). Along with the reduction of HRT for 12 hours, this approach possible to reach higher values of nitritation efficiency, with a maximum value obtained of 54.6%, which were proven by the dominance of AOB and suppression of NOB in molecular biology analyses using the FISH technique. In Step II, feeding the system with leachate was aggressive to the microbial community and affected the nitritation efficiencies observed previously, obtaining a maximum of 34.0% and OD values between 0.8 and 1.8 mg.L'. The presence of anammox bacteria in the biofilm was observed in both stages, but it was not possible to create favorable conditions for its dominance. Even so, the results indicating the potential of the system for the development of the partial nitritation-anammox process and its application for landfill leachate, provided that a gradual adaptation of the microbial community is carried out for this type of effluent.