Enriquecimento de micro-organismos metanotróficos e avaliação do potencial de oxidação anaeróbia de metano a partir de lodo de reator UASB

Abstract

Methane is a major greenhouse gas related and thus global warming. In anaerobic systems is produced within the system to form the biogas, which is captured by the three-phase separator. However, it can also be detached to the final effluent, contributing to the greenhouse effect, representing environmental and economic losses. It is known that methane oxidizers micro-organisms are contained in these systems. Nevertheless, few studies about the cultivation and selection of this group and oxidative capacity, and methanotrophic activity that can occur from UASB sludge were performed. Thus, this study aimed to cultivate microorganisms methanotrophic from sludge from UASB reactor treating domestic wastewater in sequencing batch reactor (SBR) with autotrophic medium supplemented with nitrite and nitrate. The average efficiencies of removal of nitrite and nitrate were 72% (median = 57%) and 50% (median = 47%), respectively, from the concentrations of 25mg.L-1 and 100mg.L-1 along 417 days of cultivation, probably due to the heterotrophic denitrifying activity that occurred in the initial period of operation of the RBS. The composition and structure of the microbial community analyzed by next generation sequencing (NGS) and DGGE showed that the selected community in the reactor was different from that originally present in the inoculum. The dominant phyla in the inoculum were Synergistestes, Firmicutes and Euryarchaeota, whereas biomass enriched Proteobacteria and Chloroflexi predominated. Growing conditions selected the methanotrophic genres Methylocaldum and Methylosinus, respectively, with relative abundances of 8.9% and 2.3% after 241 days of cultivation. The methanotrophic activity was also assessed in cultured biomass, with median values corresponding to 17,3mLCH4.gVST-1.day-1 and 15.4 mLCH4.gVST-1.day-1 (191 and 241 days), and then declined for 12mLCH4.gVST-1.day-1 (at the end of cultivation, after 400 days). These values were higher than the methanotrophic activity observed in the sludge from UASB reactor, which corresponded to 6 mLCH4.gVST-1.day-1. From the results obtained, it suggests that the methanotrophic activity is responsible for consuming 29% of the methane inside the UASB reactor, demonstrating the importance of methanotrophic microorganisms to methane balance these systems and the possibility of using these microorganisms in the pos-treatment to reduce environmental impacts as methane dissolved in effluents from the anaerobic reactors.