Investigação da emissão de óxido nitroso em sistemas nitrificantes utilizando reatores com biomassa aderida

Abstract

In this work, the emission of nitrous oxide (N2O) and the ammoniacal nitrogen removal (NH4 + -N) were evaluated in two moving-bed biofilm reactors (MBBR) (R1 and R2), subjected to varying NH4 + -N surface loading rates under autotrophic conditions. The study was carried out in three stages, according to the applied load ranges: low (0.3 – 4 g NH4 + -N/(m².d), medium (4.1 – 8 g NH4 + -N/(m².d)) and, high (8.1 – 25 g NH4 + -N/(m².d)). To evaluate the effect of the carrier media for microbial adhesion, R1 was filled with AnoxKaldnes K1 media and the R2 with the Mutag Biochip media. A significant difference between the NH4 + -N removal performance between the reactors was only observed at high applied loads. The maximum load removed in R1 was 9.9 g NH4 + - N/(m².d), higher than that observed in R2 (7.5 g NH4 + -N/(m².d)). For R1, the N2O emission increased as the applied nitrogen load was incremented, showing a maximum emission flux of 4.6 g N2O-N/(m².d). In R2, the emission was lower and less influenced by the increase in the influent load, reaching a maximum emission flux of 1.4 g N2ON/(m².d). Free ammonia concentrations and nitrite accumulation in the bulk, as well as the form of microbial adhesion to the carriers, influenced the emission of N2O. The N2O emission factors varied between 0.03 and 1.1 % of the influent NH4 + -N, lower than the values proposed by the Intergovernmental Panel on Climate Change (IPCC) 2019, suggesting that the MBBR system proved to be an alternative to achieve high nitrification rates with low N2O emission even under high nitrogen loading rates.