Avaliação e comparação de diferentes estratégias para o enriquecimento de bactérias ANAMMOX

Abstract

Nitrogen removal is an important aspect of wastewater treatment often accomplished by microbial processes such as nitrification and denitrification. The anaerobic ammonia oxidation (ANAMMOX) to N2 with nitrite as electron acceptor is a microbial process discovered recently, which shows great potential for nitrogen removal from wastewaters. Since the microorganisms able to perform the ANAMMOX reaction are difficult to cultivate in pure culture (one single specie has not been isolated yet), the way to study this population is through the application of enrichment and cultivation techniques. The present work has tested and compared different approaches for the enrichment of ANAMMOX biomass. Municipal activated sludge and anaerobic sludge from an UASB reactor, both used in domestic sewage treatment, were used as inocula. The three approaches used were: (i) enrichment in batch reactors containing autothrophic basal medium with ammonium and nitrite (reactors F4 and F5); (ii) enrichment in sequencing batch reactors (F1 and F2), and (iii) batch reactors with basal medium supplemented with chloramphenicol (reactors F3 and F6). One control reactor with only autothrophic basal medium (without inoculum) was also prepared. Reactors were incubated at 37°C in a shaker-incubator, and nitrite and ammonium consumptions were monitored during the incubation time which ranged from 231 to 455 days. In all reactors denitrification process was observed during the incubation time (as indicated by intense nitrite consumption), and this was not coupled to the approach used, as well as inoculum type and concentration. The duration of denitrification activity time varied for each reactor. In F3 and F6 sometimes this activity decreased, but it was not completely eliminated. In F1 and F2 reactors denitrification occurred but only in the initial stages of incubation, indicating that culture medium exchanges were important to eliminate this activity. Nevertheless, ANAMMOX activity was not observed in these reactors. Denitrifying activity might have been the favoured process by the stagnant condition of batch culture reactor, which allowed that heterotrophic biomass survived during the whole process. This is probably because heterotrophic biomass is able to live on cell lysis products and from biodegradable substrate in the influent even in the absence of oxygen, since these organisms can use nitrate and nitrite as electron acceptor. In summary, in the six reactors tested a simultaneous consumption of ammonium and nitrite, indicating anaerobic ammonium oxidation activity, was not observed. Therefore, ANAMMOX organisms were not enriched under the conditions used in this work.