Remoção de Nitratos de água de drenagem agrícola utilizando biorreatores com diferentes fontes de matéria orgânica

Abstract

Nitrogen is one of the main constituents of the atmosphere, several organisms need to survive and it circulates in nature in various oxidation states, from the ammoniacal form (NH3), the most reduced, to the nitrate form (NO3-), the more oxidized. Nitrate, when transferred in large quantities to surface waters, can cause serious problems to the environment, such as the appearance of algae, and to the health of humans and animals, such as the manifestation of cancer in the gastrointestinal system and methemoglobinemia in babies. One of the most used nutrients in agriculture is nitrogen, which can drain into water bodies when not absorbed by plants. The objective of this work was to evaluate the potential of nitrate removal in agricultural drainage water, using fixed bed bioreactors with different sources of organic matter, using corn stalk, corn cob, and an inert support of high porosity: foam of polyurethane (Mini Biobobs®), with different mixtures in each reactor. The study was divided into two phases: Phase I, without temperature control and with Hydraulic Detention Times (TDH) of 24, 16, and 8 hours; and Phase II, with the controlled temperature at 18 and 30oC and TDH of 8 h. In both phases, the affluent consisted of agricultural drainage water enriched with 20 mg L-1 of N-NO3. The best results obtained in Phase I was with 24 and 16 h TDHs, in reactors filled with biodegradable supports. In Phase II, the best results were obtained with the reactor filled with a mixture of cob and Mini Biobobs® kept at 30°C and TDH of 8h, with 73.86% ± 4.88 removal efficiency. The reactor filled only with Mini Biobobs® showed no nitrate removal, indicating the need for a source of organic matter for heterotrophic denitrifying bacteria. The pH, alkalinity, and nitrite results in the two phases showed to be within the ideal conditions for the removal to occur and the NMP confirmed the presence of denitrifying bacteria in the system. The denitrification process followed a zero-order kinetic equation, indicating that, under the conditions studied, the substrate concentration did not affect the efficiency of the process. The results indicate that corn residues are promising and viable as an alternative for use in reactors aimed at removing nitrate from agricultural drainage water.