Hydrodynamic behavior of a combined anaerobic-aerobic system employed in the treatment of vinasse

Abstract

The understanding of reactor hydrodynamics is essential for improving the performance of a reactor and biogas production. This study sought to evaluate the hydrodynamic behavior of a combined anaerobic-aerobic system at a laboratory scale for treating vinasse. The experiment was conducted in a system using two UASB reactors connected in series, followed by an Aerated Submerged Biological Filter (ASBF). The flow rates applied to the system and the corresponded theoretical HRTs in the UASB1, UASB2 and ASBF were respectively: 15.6 L d-1 and 1.2 d, 1.2 d and 1.0 d (Phase I - first year); 8.5 L d-1 and 2.1 d; 2.1 d and 1.8 d (Phase II - first year), 14.6 L d-1 and 1.1 d, 1.1 d and 1.0 d (Phase III - second year); 29.5 L d-1 and 0.6 d, 0.6 d and 0.5 d (Phase IV - second year). The hydrodynamic studies were carried out using pulse type stimulus-response tests, employing LiCl as a tracer. The coefficients of determination for the dispersion models (R2) indicate a close approximation of a continuous stirred tank reactor in series (multi-CSTR) model, with an average of 2.5, 2.3 and 1.2 (first year), and 1.1, 1.4 and 0.9 (second year) multi-CSTR for UASB1, UASB2 and ASBF, respectively. Results of the hydrodynamic tests carried out in UASB1, UASB2 and ASBF indicated strong tendency for flow in the complete mixture hydraulic regime, detecting a wide dispersion in the units, in addition to the presence of short circuits and dead zones.