Prospecção de bacteriófagos para o controle de bactérias heterotróficas e nitratantes no processo de desamonificação em efluentes ricos em nitrogênio

Abstract

Carbon and nitrogen are elements in organic and inorganic molecules and constitute pollutant compounds in effluents from sectors such as agribusiness, livestock, and meat-packing plants, among others. Not treated or managed correctly affects the environment and human health. Anaerobic digestion is an already consolidated technology for treating effluents with a high concentration of organic carbon; however, the generated digestate presents a low C/N ratio. A promising alternative for treating these effluents with high nitrogen concentrations is deammonification, which uses ammonia-oxidizing bacteria (AOB) and Anammox in its metabolic pathway. However, a problem faced in the deammonification process is the appearance of unwanted microorganisms, such as nitrite-oxidizing bacteria (NOB) and heterotrophic bacteria, which grow in this medium and end up affecting the nitrogen removal process and inhibit the functional bacteria responsible for the deammonification. Operational strategies based on process parameters (engineering) are limited and cannot inhibit the activity of the undesired species. Aiming to control these bacteria, this work sought to isolate bacteriophages with antimicrobial capacity against nitrite-oxidizing and heterotrophic bacteria. Samples of biological sludge from a nitrification/denitrification system and from a decanter after deammonification were used to isolate NOB and heterotrophic bacteria. To isolate heterotrophic bacteria, a sewage sample was collected and used to isolate a bacteriophage that infected a previously isolated strain. The results were positive and showed that the isolated species was Pseudomonas monteilii. The double-layer agar assay was used to confirm the presence of phages; the host spectrum and plating efficiency test were performed to gauge the infective ability of the phage. The final concentration of the purified phage stock was 1.2x1010 PFU/ml, satisfactory for the purpose at hand. Afterward, inhibition tests were performed in the liquid host culture, where the isolated phage showed a higher inhibition efficiency at a multiplicity of infection (MOI) of 1 and 0.1. As for the isolation of BON, the isolated strain was identified as belonging to the genus Nitrobacter and concentrations in the range of 100 to 300 mgNaNO2 L-1 were ideal for the growth of these bacteria. However, there was difficulty in growing these bacteria on solid medium, preventing the prospection of a specific phage. It is estimated that with the results of this study, it is possible to perform the deammonification process in effluents containing carbon concentrations without inhibiting to the system.