Avaliação da influência da pluviometria, da temperatura e das características do lodo na estabilidade de reatores anaeróbios e seu potencial de aproveitamento energético

Abstract

Anaerobic reactors are sewage treatment technologies capable of producing biogas, a by-product that can be recovered for energy generation. A bottleneck for energy production from biogas in sewage treatment plants (STPs) consists of understanding the variation in the profile of this by-product biogas production in different seasonal periods, while optimizing the reactor operational conditions. To this, the present work evaluated the data from 18 months of operation of two full-scale STPs using anaerobic reactors in relation to the variation of pluviometry and temperature and the typical hydrograph. From this analysis, it was shown a decrease between 10 and 20% in the production of biogas after an increase of about 12 to 14% in the sewage flow due to the occurrence of rains above 5 mm, along with a dilution and decrease in the concentration of the affluent organic matter. However, the results showed how the reactors were able to recover the biogas production within 3 days. In addition, it was found that, in the monitored range (18-25 ° C), temperature was not a significant parameter for biogas production. Finally, the results indicated that the typical hydrograph of STPs caused significant variations between the peak hours. Specifically, the increase in the affluent organic load during these periods was correlated to the reactor hydraulic dynamics, i.e. a positive correlation to biogas production and effluent upflow. Methane content in biogas showed an opposite trend than biogas production, probably due to an increase in dissolved methane in the effluent during the peak inlet flow. The second part of this thesis had the objective of monitoring the sludge blanket characteristics in a demonstration scale UASB reactor. The results showed how, generally, the anaerobic reactor showed stable performance after sludge disposal and through a long period of operation without disposal (~ 120 days). After disposals maintain the minimum mass required for the reactor, it was observed that the volume and biochemical characteristics of the sludge along the reactor did not affect the effluent treatment and biogas production. Additionally, sludge stability, estimated from biochemical methane potential tests, showed only a small tendency of decrease over time after sludge disposal. Nonetheless, even after a long monitoring period, the sludge still showed high stability and high methanogenic activity. In this way, the thesis results demonstrated how environmental and operational parameters, together with sludge blanket biochemical characteristics, are essential to understand the variations in biogas production, which allows estimating and optimizing the energy recovery.