Physiological and Microbial Community Analysis During Municipal Organic Waste Leachate Treatment by a Sequential Nitrification-Denitrification Process

The decomposition of municipal organic waste (MOW) results in the generation of gasses and liquid fractions called leachates that may contain high concentrations of organic matter and ammonium (NH 4 + ). Leachates can be treated through biological processes to reduce the environmental problems they cause. Thus, in the present study, the physiology and microbial community of a sequential nitrification-denitrification process (SNDP) were analyzed during MOW leachate treatment. First, the acclimation of nitrifying (SBR with up to 600 mg NH 4 + -N/L) and denitrifying (UASB reactor with up to 166 mg NO 3 - -N/L d) sludge was carried out. The SBR was then fed with leachate (28.92 ± 13.32–76.26 ± 13.94 mg NH 4 + -N/L and 5661.69 ± 1002.36–6070.28 ± 554.04 mg COD/L), and the effluent was fed to the UASB reactor. Both processes were completed during acclimation, and efficiencies and yields higher than 92% and 0.89 were obtained, respectively. During the leachate treatment, the SBR reached an ammonium consumption efficiency (ENH 4 + -N) of 99.01 ± 1.79% and a COD consumption efficiency (ECOD) of 81.62 ± 13.15%. However, the yields and specific production rates of nitrate decreased by 41.0% and 99.8%, respectively. The UASB reactor fed with the SBR effluent (17.68 ± 0.77 mg/L nitrate , 55.20 ± 0.84 mg/L nitrite, and 55.20 ± 0.84–324.86 ± 9.94 mg COD/L) reached nitrate, nitrite, and ECOD efficiencies of 81.53 ± 1.53%, 64.49 ± 1.03%, and 97.42 ± 2.03%, respectively. During acclimation in the nitrifying SBR, the groups that predominated in the microbial community were Nitrospira , Bacteroidetes , Nitrosomonas , and Thauera (25%, 21%, 4%, and 3%, respectively). However, in the presence of leachate, nitrite accumulation and low O 2 availability decreased the values of Nitrospira and Nitrosomonas to 0.2% and 0.08%, respectively. In the UASB reactor, members of the family Pseudomonadaceae and the genera Cecembia and Thauera were predominant, regardless of the stage evaluated. The use of an SNDP allowed the removal of up to 99% of NH 4 + and 98% of COD, and thus, it may be an alternative method for MOW leachate treatment.