Avaliação de sistema de lodo ativado integrado com contator biológico rotativo como pós tratamento de reator UASB sobre a remoção de carbono e nitrogênio

Abstract

The activated sludge (AS) system is born from a secular concept applied to wastewater treatment and is widely spread around the world. Although its high efficiency, several AS based alternative systems are explored in order to optimize, for instance, organic material removal, enhance nitrification and nitrogen removal, sludge settleability and reduce area requirements. Thus, combined suspended and attached growth (hybrid systems) in aerated systems presents itself as a relevant alternative in the global picture. In warm regions, such as Brazil, the combination of AS and hybrid AS systems as UASB reactors post treatment is largely applied, as the association allows savings in aeration, reduction of sludge production and no need of a sludge digestion unit. That said, the purpose of this work was to analyze the performance of a full-scale domestic wastewater treatment plant (WWTP) configurated with a AS system integrated with RBC as a post treatment for UASB reactors, in view of its design conception. For this, data from physical-chemical analyzes and quantitative and qualitative microscopic observation of the microfauna carried out during the years of 2017 to 2020 were evaluated. The results show that the WWTP started to operate in a hydraulic overload state before it reached project horizon (2024 year) and also it does not reach the project estimated efficiencies for BOD, COD and NH4+, which were 94%, 90% and 50%, respectively, plus, it was verified a failure of the nitrification process in the aeration tanks. The BOD removal during the period of evaluation was 83% (median), while COD and NH4+ removal were 81% and 38%, in that order. Overload in secondary clarifiers and failure in the nitrification process were also observed. In addition, it was found that the anoxic chambers (CA) and the aeration tanks (AT) worked with hydraulic retention times (HRT) below of what project has determined: observed CA HRT ranged from 27 to 44% of project CA HRT, and observed AT HRT ranged from 54 to 56% of project AT HRT. The short HRT applied in AS units may be related with poor flocs formation and low density of protozoans and metazoans. The calculation of the hydraulic loading rate (HLR) points to an overload in terms of clarification in 49% of the measurements made, while the overload percentual of solids loading rate (SLR) was 14%. From the analyze made, it is known that the current operation sludge recirculation ratio differs from the ratio adopted in the project, thus other parameters such as HRT, HLR, SLR are likely to affect negatively effluent quality, mostly in terms of nitrogen and TSS.