Influência da variação de oxigenação e TDH no sistema combinado AOA/AOA² na remoção de matéria orgânica e nutrientes em efluente sintético

Abstract

Several configurations are being studied in order to achieve the simultaneous removal of nutrients practically and economically; among them is the anaerobic–aerobic–anoxic (AOA) configuration. The objective of this work was to evaluate the AOA system in the removal of carbonaceous, nitrogenous, and phosphorous matter, regarding the influence of the aeration flow in the improvement of the nitrification, the relation of the increase of the hydraulic detention time (TDH) in the anoxic reactor for the process of denitrification and identification of microbial communities in the system. The system consisted of an anaerobic reactor (22.1 L), an aerobic reactor (21.4 L), a decanter (12 L), and two anoxic reactors (19.8 L), with an upward flow and continuous flow. The system operation was carried out in four stages, 1) monitoring the system until reaching the state of apparent dynamic equilibrium (EEDA); 2) using a dissolved oxygen concentration of 2.5 mgO2.L-¹ in the aerobic reactor (continuous aeration); 3) concentration of dissolved oxygen in the aerobic reactor of 5 mgO2.L-¹ (continuous aeration); and 4) the inclusion of anoxic reactor 2, extending the hydraulic detention time in an anoxic environment from 8h to 16h. The anaerobic, aerobic, and anoxic reactors were operated with TDH for 8h, the decanter with TDH for 4.4h, and glucose solution (5 g.L-¹) was added as an external carbon source at the decanter outlet in the four stages of operation. To monitor and evaluate the performance of the system, the following physicochemical parameters were determined: liquid temperature, hydrogen potential, total alkalinity, volatile acids, dissolved oxygen, potential water redox, chemical oxygen demand (COD), Kjeldahl total nitrogen (KTN), ammonia nitrogen, nitrite, nitrate and total phosphorus (TP). At the end of the system operation, sludge samples were collected from all the reactors, which were sent to the laboratory of the company GoGenetic for analysis of metagenomic sequencing of the 16S ribosomal RNA gene to identify microbial diversity. The system in Stage 2 of operation achieved average removals of gross COD, filtered COD, TP, TN, of 83%, 80%, 22%, and 26%, respectively. In Step 4, it obtained average removals of gross COD, filtered COD, PT, NT, of 93%, 91%, 21%, and 61%, respectively. It was concluded that the concentration of dissolved oxygen and, consequently, the aeration flow in the aerobic reactor has a direct influence on the removal of nitrogen, showing an increase in the efficiency of TN removal in Step 4 (DO at 5 mgO2L-1 and the addition of the ANO2 reactor). HDT in a prolonged anoxic environment also favored the removal of TN, the removal efficiency with just the anoxic reactor 1 was 46% in Step 3, and with the inclusion of the anoxic reactor 2, it reached an efficiency of TN removal of 61%. Genetic sequencing showed the microbial diversity of the system, and variations were observed in the microbial composition of each reactor due to the oxygenation condition. The main phyla identified in the AOA system were Firmicutes, Bacteroidota, Chloroflexi, Proteobacteria, Caldisericota, Actinobacteriota, Verrucomicrobiota, and Synergistota.