A fluidized bed anaerobic biofilm reactor model. Applications to treatment of complex effluents

FUENTES MORA, MAUREN; SCENNA, NICOLÁS; AGUIRRE, PÍO; MUSSATI, MIGUEL

Santiago de Chile, Chile

Simposio; 12th Internacional Biotechnology Symposium and Exhibition (Biotechnology 2004); 2004

CONICYT, Chile

In general, only a few minutes are required by an industrial or pilot-scale reactor containing particles to recover the hydrodynamic steady-state after a disturbance on the flow rate is applied. This time period is one order of magnitude lower compared to the biological processes involved in fluidized beds. Indeed, the mean hydraulic residence time of the system and the bacterial duplication time can take hours or days in the case of anaerobic digestion. Changes in the porosity of fluidized bed bioreactors due to biofilm development or biofilm detachment are less significant compared to changes in the height of the bed. The biofilm accumulation, which is the net result of cellular growth and death and erosion processes, modifies the characteristics of bed fluidization due to an increase or decrease of the bed density. At the same time, different characteristics of bed fluidization can affect biofilm erosion rate. The main purpose of this work is to describe and model a three-phase fluidized bed methanogenic biofilm reactor. The three phases are: (a) the solid phase consisting of the bioparticles (inert support material plus attached biomass); (b) the liquid phase consisting of the substrate, enzymes, ions and suspended biomass; and (c) the gas phase, which is a mixture of the gaseous products from fermentation. A non-dispersive one-dimensional dynamic model with convective variation of the properties (such as phase hold-ups, superficial phase velocities, biofilm thickness and biological and chemical species concentrations) along the axial direction is proposed. Two different control volumes are considered to derive the mathematical model and, consequently, two bioreactor models are derived. First, it is assumed that the biochemical transformations only occur in the fluidized bed zone and, secondly, it is hypothesized that degradation of suspended biomass also happens in the non-fluidized bed zone, i.e. in the free-inert zone. The model results obtained by these two hypotheses are evaluated. The anaerobic degradation of complex substrates is modeled as a general study case including the hydrolysis of particulate material. The biofilm process model is coupled to the system hydrodynamics through the specific detachment rate of biofilm; which is assumed as a first-order function of the energy dissipation parameter. Dead (non-active) biomass is considered as particulate material subject to hydrolysis. The developed model was calibrated and experimentally validated based on a synthetic effluent. This model allows evaluating the reactor performance using different types of inert support particles, and simulating and optimizing the treatment of effluents from different sources after model calibration. *Abstract aceptado, pero no hubo participación por carecer de solvencia económica.