Remoção de nitrogênio de esgoto doméstico tratado por reator UASB: comparação entre biorreator com membranas híbridas (aeração - permeação) e ultrafiltração-osmose inversa-membranas contactoras

Abstract

Sewage contains several contaminants, such as organic matter and nitrogen. UASB reactors are capable of removing organic matter; however, nitrogen removal is minimal, requiring post-treatment, which can be biological or physicochemical. Among the biological processes, partial nitrification, anammox and simultaneous denitrification stand out due to their potential to remove nitrogen and organic matter in a single bioreactor. This process can be intensified by using membranes for aeration, supplying oxygen to nitrifying bacteria, and membranes for filtration, retaining slow-growing bacteria, e.g. autotrophic bacteria. As for physicochemical processes, the integration of ultrafiltration (UF), reverse osmosis (RO) and contact membranes (CM) is interesting due to their ability to produce reused water and recover nitrogen. Thus, this research aimed to compare the nitrogen removal by two integrated processes: (1) partial nitrification, anammox and denitrification in a hybrid bioreactor with membranes for filtration and aeration (MF-MABR) and (2) UF-OI-MC process. Thus, a 5.7 L bioreactor with hollow fiber ultrafiltration membranes for aeration and filtration was operated, with hydraulic retention times of 28.5 h and fed with UASB effluent from the city of Contagem/MG (total nitrogen, ammonia and COD concentrations of the effluent of 51, 46 and 75 mg.L-1 , respectively). Removal efficiencies for organic matter, ammonia and total nitrogen of 61%, 62% and 43% were obtained, respectively, meeting the current discharge standard in the state of Minas Gerais of 20 mg.L-1 . The main genera found in the biofilm formed on the aerated membrane and in the suspended biomass were Nitrospira, Denitratisoma, Candidatus Brocardia, Solibacterales and Limnobacter. In parallel, in the physicochemical route, the UASB effluent was directed to UF and the permeate generated to RO. The RO permeate presented characteristics suitable for reuse, while the concentrate was directed to MC, varying the pH (8 to 11) and temperature (25, 42.5 and 60 °C). Values above 91% removal and 86% recovery of ammonia were observed when the RO concentrate had a pH higher than 10 or temperatures of 60 °C. The most optimized condition was with pH 10 and temperature of 25 °C, removing 98% and recovering 90% of ammonia. Finally, an economic analysis of the two processes studied was performed for different scales of application. Economically, the biological route proved to be more viable X for lower flow rates (<100 L/s), while the physical-chemical route was more viable for higher flow rates (500–3000 L/s). This work is aligned with the UN SDGs (Sustainable Development Goals) number 6 (clean water and sanitation), 11 (sustainable cities and communities), 12 (responsible consumption and production), 13 (climate action), and 14 (life below water).