Estudo do tratamento de efluente de indústria sucroalcooleira empregando reator anaeróbio de leito fixo em escala piloto

Abstract

In the ethanol production process, significant volumes of vinasse are generated, a wastewater characterized by high concentration of organic matter, acid pH and significant concentrations of potassium and sulfate. The vinasse is applied in the soil for the fertigation, aiming the reuse of water and nutrients. However, this procedure may have negative impacts, such as the soil acidification and groundwater contamination, if the vinasse is applied in excess. In this way, the anaerobic digestion is an alternative for the treatment of this effluent, because it is able to reduce the concentration of organic matter and recover energy in the form of biogas, keeping the nutrients levels of the vinasse. In this context, the objective of this study was to evaluate the feasibility of applying Anaerobic Packed-Bed Reactor (APBR) in the treatment of vinasse. The pilot scale APBR reactor (useful volume of 194.5 L) was operated with vinasse during 90 days with organic load volumetric of 5.0 kgCOD.m-3.d-1, flow rate of 8.1 L.h-1 and hydraulic detention time of 24 h. The average efficiency of total COD removal was 72.1% until the 23rd day of operation, the moment in which there was a simultaneous pH and affluent temperature reduction, contributing to the decrease in process performance. During the reactor operation, it was observed that there was no nutrient removal (nitrogen and phosphorus), keeping the fertilizing power of the vinasse. Anaerobic biodegradability assays were carried out to evaluate the kinetics of organic matter degradation, sulfate reduction and methane production using different concentrations of organic matter (1.0, 2.5 and 5.0 gCOD.L-1 and the APBR’s inoculum. The results showed that the biomass was able to degrade organic matter, reduce sulfate and produce methane in the evaluated conditions, being that, at the concentration of 5.0 gCOD.L-1 were observed the highest velocities. Experimental data analysis of cumulative methane production and COD removal was performed using the Anaerobic Digestion Model Number 1 (ADM1). The parameters optimized in the model provided the concentration of biomass, composed predominantly of acetoclastic methanogenic archaea and propionic acid consuming bacteria. In general, the model was able to represent the trend of organic matter removal and cumulative methane production throughout the assay. Finally, the modeling was performed in order to simulate the behavior of the reactor effluent COD using two sets of parameters optimized in ADM1 and the monitoring data of the APBR reactor. It was concluded, from the results of this model, that the hydraulic detention time employed in the reactor operation was insufficient to achieve the desired removals. In spite of this, the reactor provided an environment favorable to the development of methanogenic anaerobic microorganisms and the anaerobic digestion process again proved to be a viable alternative for the treatment of vinasse.