Enriquecimento e caracterização de bactérias Anammox para a remoção de nitrogênio amoniacal de efluentes

Abstract

Nitrogen removal is essential in the treatment of wastewater and is typically performed by microbiological processes such as nitrification and denitrification. The anoxic ammonium oxidation (ANAMMOX) with nitrite leading to N2 is a reaction mediated by microorganisms (anammox bacteria), discovered for more than ten years ago in a denitrifying bioreactor, which presents the potential for nitrogen removal from wastewater. The aim of this study was to enrich and produce anammox biomass using as inoculum sludge from the municipal WWTP Arrudas - COPASA activated sludge system, which treats domestic sewage from the city of Belo Horizonte. The enrichment and cultivation were done in a Sequencing Batch Reactor (SBR) of 1.2 L, fed with autotrophic mineral medium under anaerobic conditions, temperature of 34°C, and hydraulic retention time of 24 hours. This procedure was performed in two different experiments. In experiment I, anammox activity started to be detected after 90 days of cultivation, by the simultaneous consuption of stoichiometric amounts of NO2 -e NH4+ in the system. Fluorescence in situ hybridization (FISH) analysis revealed that anammox bacteria accounted for 53% of total bacteria after 6 months of enrichment, and that nitrifying bacteria were not present in the reactor. The average ammonia and nitrite removal efficiency was 90%. The phylogenetic identification performed by cloning, sequencing and comparative analysis of 16S rDNA revealed that most of clones were closely related to Candidatus Brocadia sinica (with sequence similarity of more than 99%). However, one clone was related to Candidatus Brocadia sp. 40 (with 98% of identity), and might represented a novel species for which we propose the name Candidatus Brocadia brasiliensis. In experiment II, a larger volume of inoculum was used and anammox activity was detected after 50 days of cultivation. FISH analysis showed that the biomass developed in the SBR was composed by anammox cells (likely Ca. Brocadia and Ca. Kuenenia), Nitrosomonas and Nitrospira, suggesting that coexistence and competition between these populations occurred. FISH results also revealed that anammox bacteria accounted for 23 to 45% of total bacteria in this enrichment. The average ammonia and nitrite removal efficiency was 60%. Thus, it can be concluded that anammox enrichment was possible from activated sludge under controlled conditions within two to three months. The comparison results of both experiments suggested that the volume of inoculum and the composition of the feed (nitrogen compounds concentrations) probably played an important role in the selection of the microbial community developed in the RBS for each of the experiments.