Abstract
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.
Highlights
For industries that use huge amounts of water, such as the sugar-ethanol sector, it is essential to treat and reuse the liquid effluents
The variation curves of lithium chloride concentrations over time in wastewater from the UASB1, UASB2 and Aerated Submerged Biological Filter (ASBF) reactors, and hydrodynamic tests carried out in the first and second experimental year are presented in Figures 2, 3 and 4
The output of Li+ was observed during the entire collection period from the UASB1, UASB2 and ASBF, and the concentrations declined over time
Summary
For industries that use huge amounts of water, such as the sugar-ethanol sector, it is essential to treat and reuse the liquid effluents. The inappropriate provision can lead to contamination of soils and groundwater. In association with this fact, it turns out that the discharge standards applied to agro-industries are often strict and below the levels that can be achieved with conventional biological treatment technologies. When used individually for treatment of agro-industrial wastewaters, the effluents normally contain nutrients (N and P) above the limit allowed by legislation. The combined use of anaerobic and aerobic processes presents great potential for wastewater treatment. The combination of these processes enables the construction of models that are more compact, with lower power consumption by aerators due to the reduced dissolved oxygen demand and lower production of biomass (sludge). The hydrodynamics and the degree of mixing that occur in a biological reactor can strongly influence the degree of contact between the substrate and the bacteria, controlling mass transfer, the biological kinetics and the performance potential of the reactors (Liu et al, 2007; Liu; Tian; Chen, 2010; Mansouri et al, 2012)
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