Influência de temperaturas baixas no desempenho de reator anaeróbio híbrido para tratamento de esgoto sanitário

Abstract

The use of hybrid anaerobic reactors (HUASB) for the treatment of effluents in hot climate regions has been extensively studied in recent decades, even so, there is a lack of work on the efficiency of these reactors in cold climate regions. Temperate climate environments represent a challenge, since anaerobic digestion, carried out by archaea and bacteria, responsible for the removal of organic matter in HUASB, has its functioning altered, due to the metabolism of these microorganisms. This work aims to analyze the operation of a HUASB, on a bench scale, with low temperatures in a controlled environment. The HUASB, fed by synthetic domestic sewage, was built in glass, with dimensions of 1.00 m x 0.12 m x 0.20 m, two three-phase separators and useful volume of 22.10 L, filtering material composed of corrugated PVC rings. Using the Central Composite Rotatable Design (CCRD), 10 operating stages were established, with temperatures of 4.13, 6.00, 10.50, 15.00 and 16.86 °C and Hydraulic Retention Time (HRT) of 7.17, 8.00, 10.00, 12.00 and 12.82 h. To evaluate the performance of HUASB, the parameters of pH, temperature (t), total alkalinity (TA), volatile acids (VA), removal of raw chemical oxygen demand (CODt), turbidity, sulfate and biogas production were analyzed. The volumetric organic load (VOC) of the effluent (EFL), during the 150 days of operation, varied between 1.0 (± 0.0) and 1.9 (± 0.1) kg COD m-3d-1, due to the different HRT, with an average CODt of 525 (± 57) mg L-1. The pH, TA and VA of the EFL presented the respective averages of 7.7 (± 0.3), 162 (± 6) mg CaCO3 L-1 and 43 (± 18) mg HAc L-1. In its operation, the HR maintained, for these same parameters, the pH close to neutrality, remaining between 6.8 (± 0.1) and 7.1 (± 0.1). For TA and VA, the means obtained were 250 (± 7) mg CaCO3 L-1 and 27 (± 8) mg HAc L-1. The biogas generation fluctuated during the 10 stages, even in situations with similar physicochemical characteristics, varying between 54 (± 44) and 2115 (± 555) mL d-1, for temperatures of 10.75 (± 0.0) and 15.50 (± 0.15) °C and, the HRT, 10.00 and 8.00 h, respectively. For CODt removal, the lowest and highest efficiency were, respectively, 82 and 93%, with temperatures of 6.20 (± 0.2) and 15.98 (± 0.6) °C and, the HRT, from 12.00 and 10.00 h. These results show that the use of HUASB reactors is advantageous in the removal of organic matter, even at low temperatures, despite the low generation of biogas.