Assessment of the Anaerobic-Oxic-Anoxic (AOA) system on the removal of pharmaceuticals and the effect of recirculation on denitrification process

The human organism does not entirely absorb pharmaceuticals, which increasingly presence has been recorded in sanitary sewage. The complex chemical structure of these compounds interferes with their removal in wastewater treatment plants, resulting in their discharge into receiving water bodies. In this study, the performance of an Anaerobic-Oxic-Anoxic (AOA) system was evaluated in the treatment of synthetic wastewater containing 17 alpha-ethinylestradiol (EE2), acetaminophen (ACE), and ibuprofen (IBU). In addition, the influence of recirculation rate was verified to improve nitrogen removal. In Phase 1, the AOA system achieved removal efficiencies higher than 87% for Chemical Oxygen Demand (COD), higher than 60% for Total Ammonia Nitrogen (TAN), 55% for EE2, 85% for IBU, and 99% for ACE when operated with 2.4 L h(-1) at HRT of 8 h, and air flowrate of 5 L min(-1). In Phase 2, with no addition of micropollutants, the system was operated with 2.4 L h(-1) at HRT of 8 h, intermittent air flowrate of 5 L min(-1) (3 h aeration; 1 h no aeration), under recirculation rates of 0%, 100%, and 200%. AOA system achieved COD removal efficiencies greater than 90% under these conditions. At 100% and 200% recirculation rates, nitrification increased from 83.6% to 85.3% and 89.4%, and denitrification from 28% to 79% and 88%, respectively. AOA system maintained high removal of organic matter and removal of pharmaceuticals greater than 50%, obtained mainly by biodegradation, in Phase I. In addition, recirculation, without adding external carbon source, improved denitrification in Phase II.