Mauren Fuentes

ANAEROBIC BIOFILM REACTOR MODELING FOCUSED ON HYDRODYNAMICS

This work deals with an experimental and theoretical investigation of anaerobic biofilm reactors for treating wastewaters. Bioreactors are modeled as dynamic (gas-solid–liquid) three-phase systems. The anaerobic digestion model proposed by Angelidaki et al. (1999) was selected to describe the substrate degradation scheme and was applied to a biofilm system. The experimental setup consists of two mesophilic (36°±1°C) lab-scale anaerobic fluidized bed reactors (AFBRs) with sand as inert support for biofilm development. The experimental protocol is based on step-type disturbances applied on the inlet substrate concentration (glucose and acetate-based feeding) and on the feed flow rate considering the criterion of maximum efficiency. The predicted and measured responses of biological and hydrodynamic variables are investigated. Experimental data were used to estimate empirical values of biofilm detachment coefficients. Under the evaluated operating conditions, the proposed model for biofilm detachment rate, assumed as a first-order function of the energy dissipation parameter, is appropriate to represent the interaction between biofilm systems and fluidization characteristics in non-highly disturbed flow conditions. Model validation was carried out using the experimental data reported by Mussati et al. (2006). The results do not differ from those above. This seems to indicate that the proposed AFBR model is able to reproduce the main biological and hydrodynamic successes in the bioreactor.

Modeling and optimization of biological sequential batch reactors

Abstract This work deals with modeling and operation optimization of biological sequential batch reactors (SBR). The SBR is a fill-and-draw biological sludge system for wastewater treatment. In this system, wastewater is added to a single batch reactor, treated to remove undesirable components, and then, discharged. In this paper, a global model of a gas-solid-liquid SBR is presented to investigate and optimize operational strategies. The model can address the differences between aerated and anaerobic systems by assigning adequate parameter values related to the aeration and reaction systems. Fluctuating operation conditions during cycles such as disturbances in the organic loading rate, stirring rate and cycle time, result in strong numerical discontinuities that can be included in the simulation schedules. An existing set of experimental data is used to show a model application based on an anaerobic SBR. A good agreement was obtained between experimental and predicted values. Optimization results are based on minimizing the reaction time/total cycle time ratio subjected to path pH constraints and interior- and end-point constraints related to the pollutant removal efficiency and settling conditions. A decrease of 22% in the total cycle time, i.e. an increase in the organic loading rate from 787 to 985 mg dm−3 d−1 is reached without modifying the quality of effluent.

Heterogeneous Anaerobic Biofilm Reactor Models Application to UASB, EGSB and AFB Reactors

Abstract In a previous work, a methodology developed for modeling anaerobic fluidized bed (AFB) reactors was presented. The aim of this work is to extend this methodology for modeling upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors, and compare and discuss model hypotheses and simulation results. A set of experimental data obtained by Kato et al. (2003), during the start-up of a bioreactor operating as UASB and EGSB reactor configurations, is used for model validation. A good agreement was obtained among experimental and predicted values. A simulation-based sensitivity analysis of model parameters such as the specific rate of granule rupture and the axial dispersion coefficient is performed. A decrease in the granule diameter is predicted for values of the specific rate of granule rupture higher than 1×10-7 m s2 kg-1. At low values of the axial dispersion coefficient, a decrease in the bioreactor efficiency is predicted. Simulation results are more sensitive when the bioreactor operates with a UASB configuration.

Optimization of bio-hydrogen production and C-N removal in combined anaerobic-aerobic systems

Abstract This work deals with optimization of a hybrid system for simultaneous bio-hydrogen production and C-N removal by a combined anaerobic-aerobic treatment method. The global model couples kinetics, hydrodynamics and bioparticle subsystem for each reactor model. An existing set of experimental data is used for model validation. Fluctuating operation conditions such as disturbances in the organic loading rate, feed and recycle flow rates result in strong numerical discontinuities that are included in the simulation schedules. Optimization results are based on maximized a pondered function involving the hydrogen production rate and C-N removal efficiency subjected to (pH, DO and nitrite) path constraints and interior- and end-point constraints related to the (COD and nitrogen) pollutant concentration, and manipulating feed, recycle and cations flow rates using piecewise constant functions. gOPT tool of gPROMS was used to perform the dynamic optimization.

Optimization of hybrid anaerobic-aerobic SBR-based systems

Abstract This work deals with optimization of biological hybrid systems based on both anaerobic and aerobic sequential batch reactors (SBRs). The global model can address the differences between aerated and anaerobic systems by assigning adequate parameter values related to the presence of oxygen in the medium, aeration and sedimentation times, and selecting the kinetics model to represent the digestion stage. An existing set of experimental data is used for model validation. Fluctuating operation conditions during cycles such as disturbances in the organic loading rate, feed and recycle flow rates and changes in the hydrodynamic regime result in strong numerical discontinuities that are included in the simulation schedules. Optimization results are based on minimizing the reaction time/total cycle time ratio subjected to (pH, DO and nitrite) path constraints and interior- and end-point constraints related to the (COD and nitrogen) pollutant removal efficiency and settling conditions. A decrease of 29% in the total cycle time, i.e. an increase in the organic loading rate from 443 to 611 mg dm -3 d -1 is reached without modifying the quality of effluent. gOPT tool of gPROMS was used to perform the dynamic optimization.

A three-phase fluidized bed anaerobic biofilm reactor model for treating complex substrates

Abstract The main purpose of this paper is to present a model of a three-phase solid-liquid-gas system to investigate the hydrodynamic and biological behavior and performance of fluidized bed anaerobic biofilm reactors (FBABRs). A general one-dimensional axial dispersive dynamic model is proposed for computing the variation of the properties such as hold-ups and superficial velocities of all phases, biofilm thickness and biological and chemical specie concentrations. Biochemical transformations are assumed occurring only in the fluidized bed zone but not in the free-support material zone. The biofilm process model is coupled to the hydrodynamic model of the system through the biofilm detachment rate, which is assumed as a first-order function of the energy dissipation parameter. Non-active biomass is considered as particulate material subject to hydrolysis. A scheme of carbohydrate degradation, kinetic parameters accepted in the literature and design characteristics of a hypothetical FBABR are taken into account to show the model predictions. The performance of the FBABR is analyzed for different flow patterns through different dispersion coefficients for the phases.