Heterogeneous Modeling of an Anaerobic Sequencing Batch Biofilm Reactor (ASBBR)

Article excerpt

Abstract: The objective of this study was to estimate the first-order intrinsic kinetic constant ([k.sub.1]) and the liquid-phase mass transfer coefficient ([k.sub.c]) in a bench-scale anaerobic sequencing batch biofilm reactor (ASBBR) fed with glucose. A dynamic heterogeneous mathematical model, considering two phases (liquid and solid), was developed through mass balances in the liquid and solid phases. The model was adjusted to experimental data obtained from the ASBBR applied for the treatment of glucose-based synthetic wastewater with approximately 500 mg [L.sup.-1] of glucose, operating in 8 h batch cycles, at 30 [degrees]C and 300 rpm. The values of the parameters obtained were 0.8911 [min.sup.-1] for [k.sub.1] and 0.7644 cm [min.sup.-1] for [k.sub.c]. The model was validated utilizing the estimated parameters with data obtained from the ASBBR operating in 3 h batch cycles, with a good representation of the experimental behavior. The solid-phase mass transfer flux was found to be the limiting step of the overall glucose conversion rate.

Key words: mathematical model, glucose, simulation, ASBBR (anaerobic sequencing batch biofilm reactor), wastewater treatment.

Resume : Cette etude visait a estimer la constante cinetique intrinseque de premier ordre ([k.sub.1]) et le coefficient de transfert de masse du liquide ([k.sub.c]) dans un reacteur anaerobie sequentiel discontinu a biofilm (ASBBR), alimente par du glucose et a l'echelle du laboratoire. Un modele mathematique heterogene dynamique tenant compte de deux phases (liquide et solide) a ete developpe par les bilans massiques des phases liquides et solides. Le modele a ete ajuste aux donnees experimentales obtenues du reacteur servant au traitement d'eaux usees synthetiques a base de glucose et contenant environ 500 mg [L.sup.-1] de glucose, fonctionnant en cycles discontinus de huit heures a 30 [degrees]C et a 300 tr/min. Les valeurs des parametres obtenues etaient de 0,8911 [min.sup.-1] pour [k.sub.1] et de 0,7644 cm [min.sup.-1] pour [k.sub.c]. Le modele a ete valide en utilisant les parametres estime s avec les donnees obtenues du reacteur fonctionnant en cycles discontinus de trois heures et presentant une bonne correlation avec le comportement experimental. Le flux de transfert de masse du solide s'est avere etre l'etape limitatrice du taux de conversion global du glucose.

Mots-cles : modele mathematique, glucose, simulation, ASBBR, reacteur anaerobie sequentiel discontinu a biofilm, traitement des eaux usees.

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Introduction

Anaerobic technology for wastewater treatment has improved considerably with the development of new configurations of reactors containing immobilized biomass on support materials. Anaerobic sequencing batch biofilm reactors (ASBBR) represent a new reactor design for wastewater treatment. The immobilization of biomass on inert bed allows for more stable operations by improving the retention of microorganisms, enabling the reactor to retain a higher concentration of biomass.

The typical operating cycle of an anaerobic sequencing batch reactor (ASBR), originally proposed by Dague et al. (1992) with granulated biomass, comprises four steps: feed, reaction, settling, and removal of liquid. The use of immobilized microorganisms minimizes or suppresses the settling step, thus reducing the overall cycle time (Zaiat et al. 2001).

The ASBBR configuration, which was first proposed by Hirl and Irvine (1996), consisted of an upflow packed column reactor with liquid circulation driven by a positive displacement pump. Ratusznei et al. (2000) proposed the mechanically stirred ASBBR configuration with the biomass bed placed in a perforated basket to prevent contact between the biomass and the impeller. This design has been widely studied on a laboratory scale by Ratusznei et al. (2001, 2003), Cubas et al. (2007), and Miqueleto et al. (2005), and on a pilot scale by Sarti et al. …