Avaliação de sistema de lodo ativado híbrido empregado no póstratamento de reator UASB em região de clima quente

Abstract

One of the most widely used technologies for the biological treatment of domestic and industrial wastewater is the activated sludge process (LA), due mainly to high effluent quality and reduced area requirements. Among the existing configurations, the activated sludge system used in posttreatment of UASB reactors (UASB + LA) has been widely used in warm climate regions, since it allows for aeration economy, less sludge production and already stabilized sludge, leading to savings in its treatment. Nevertheless, this configuration changes the composition of the influent substrate, causing problems in its operation, such as the presence of sludge on the surface of the secondary decanter, due to uncontrolled denitrification in this unit (even in systems designed to remove nitrogen), low concentration of suspended volatile solids in activated sludge and inefficient denitrification. Therefore, this work’s goal is to investigate the COD and nitrogen removal performance in a full-scale treatment plant, composed of an UASB reactor followed by anoxic-aerobic reactors with a combination of suspended and attached biomass (hybrid system). For this purpose, the research was divided in three phases: (1) monitoring of the physical-chemical parameters (COD, NH4 + , NO2, NO3, VSS) of the treatment system; (2) Determining influent COD fractions and (3) characterization of the autotrophic bacteria metabolism. Phases 2 and 3 were performed with respirometry, a technique based on the oxygen consumption measurement by microorganisms, induced by the addition of substrates. The results showed that the system was operated under favorable conditions of temperature (30ºC), sludge retention time (7,1d), pH, and alkalinity for total nitrification, but the presence of biodisks and the high concentration of suspended volatile solids in the system may have influenced the diffusion of DO, which reflected in an unsatisfactory nitrification and the occurrence of simultaneous nitrification-denitrification in the aerated reactor. In addition, the UASB reactor promoted the reduction of the easily biodegradable fraction and the increase of the inert soluble fraction of the total COD, which reflected in lower COD removal efficiencies and lower rates of denitrification.