Desempenho de sistema combinado anaeróbio-aeróbio-anóxico sob diferentes condições operacionais na remoção de nutrientes e micropoluentes

Abstract

The problems caused by the disposal of chemicals such as organic micropollutants (OMPs), including pharmaceuticals, hormones and personal hygiene products, present in different environmental elements (sewage, surface water, soil and drinking water) are being widely evaluated. The objective of this work was to evaluate the performance of a combined treatment system, fed with synthetic sewage with the addition of OMPs of the type paracetamol, ibuprofen and ethinylestradiol. The combined system was composed of anaerobic, aerobic and anoxic fixed bed reactors, with upward flow and continuous flow, with a rectangular base and useful volume of 19.4 L, 19.3 L and 19.2 L, respectively. The support medium used to immobilize the biomass consisted of corrugated Polyvinyl Chloride (PVC) rings in the anaerobic and aerobic reactors and of ceramic block residues in the anoxic reactor. The system was operated in two stages and 5 different conditions, being: Stage 1 – HRT (8 h in each reactor) and constant aeration (5 L min-1), variation in the concentration of OMPs added to the synthetic sanitary sewer; Step 2 – Constant HRT (8 h in each reactor), intermittent aeration and variation of the recirculation rate (condition 3 – 0%, condition 4 – 100% and condition 5 – 200%). For the evaluation of the system, the following physical-chemical parameters were determined: liquid temperature, pH, total alkalinity, alkalinity to bicarbonate, volatile acids, dissolved oxygen, chemical oxygen demand, total organic carbon, total Kjeldahl nitrogen, ammoniacal nitrogen, nitrite, nitrate and total phosphorus; and paracetamol, ibuprofen, ethinylestradiol only in Step 1. In Step 1, mean removal efficiencies for paracetamol of 97.0%, ibuprofen of 96.9% and ethinylestradiol of 36.1% were obtained. System instability was observed in terms of biogas production with the presence of OMPs, with a decrease from 2.7 L d-1 to 0.3 L d-1. However, 35 days after the start of the addition of the OMPs, the biogas production was higher than 2 L d- 1, even after increasing the concentration from condition 1 to 2. In step 1, mean efficiencies of total phosphorus removal were obtained of 31,5% condition 1 and 53.1% condition 2. In Step 2 with variation in the rate of recirculation in conditions 3 (0%), 4 (100%) and 5 (200%), mean COD removal efficiencies were obtained, in raw samples, greater than 94% in all conditions, while for total nitrogen they were 26.1% in condition 3, 67.7% in condition 4 and 78.6% in condition 5. In step 2, mean efficiencies of total phosphorus removal were obtained of 17.2% condition 3, 4.0% condition 4 and 10.8% condition 5. It was possible to conclude that condition 5 presented the best removal efficiency for carbonaceous and nitrogenous matter and with the lowest concentrations of P nitrite (0.595 mgN-NO2 L-1) and nitrate (6.6 mgNO3- L-1). It is worth mentioning that the increase in the rate of recirculation caused an increase in the concentration of dissolved oxygen in the anaerobic reactor, which may cause imbalance in the anaerobic process and decrease in the production of biogas.