Evaluation of hydrodynamic behavior as a tool to optimize anaerobic reactors of attached growth

Abstract

The conditions of the non-ideal flow in reactors affect their performance; the common causes are short circuits, dead zones and internal recirculation by kinetics and/or density stream. In this study, the design of an anaerobic filter at full scale that treats cassava starch wastewater was optimized. It presented halt damming problems and low removal efficiencies. The initial hydrodynamic behavior showed the presence of dual flow (32% plug flow - PF and 37% mixed flow - MF), dead zones (20%) and absence of short circuits; additionally the modelling reactor indicated a high dispersion degree and tendency to a mixed reactor in series of two units. Based on these results, the following two modifications were implemented in the reactor design: false bottom and perforated pipe for biogas evacuation. This allowed to increase the PF fraction (44%), reduce the dead zones fraction (15%), decrease the dispersion index (DI) and increase the tendency of the reactor to MF in series of three units, which improved the real hydraulic retention time (HRT) from 9.6 to 10.2 h (HRT theoric 12 hours) and the theoric removal efficiencies from 73 to 78%.