Hydraulic Shear Stress Calculation in a Sequencing Batch Biofilm Reactor with Granular Biomass

Abstract

This paper reports the results of an experimental study specifically aimed at developing a simple methodology for calculating hydrodynamic shear forces in a sequencing batch biofilm reactor (SBBR) system with granular biomass. Using such a methodology, the hydrodynamic shear forces are simply calculated by measuring bed porosity and pressure losses. In addition, by applying this methodology an explanation for the biomass evolution from biofilm to granules under aerobic conditions has been provided and the following mechanism has been proposed: (i) formation of a thin biofilm that fully covers the carrier; (ii) increase of biofilm thickness; (iii) break-up of the attached biofilm with release of biofilm particles; (iv) rearrangement of biofilm particles in smooth granules. The hydrodynamic shear forces trend during the start-up period provides an explanatory key for the generation process of granular biomass. In fact, during the first two steps, the SBBR is characterized by rather weak shear forces values (lower than 1 dyn/cm2). Under these weak shear forces, the biofilm grows by increasing its thickness through a porous structure and weak adhesion strengths. Such a continuous increase of biofilm thickness produces an increase of the shear forces with negative effect on biomass stability, causing the detachment of biofilm particles. In turn, such detachment causes a further sharp increase of shear forces (more than 10 times) that promotes the rearrangement of the detached biofilm particles in smooth granules. A correlation between biomass density and hydrodynamic shear forces was observed. In particular, the biomass density linearly increases with the increase of shear stress.

Hydrodynamics of upflow anaerobic sludge blanket reactors

“…9,27 Generally, mixing in a continuously flow reactor with three phases (gas-liquid-solid), such as the UASB, will mainly depend on the superficial liquid velocity, superficial gas velocity, phase physical properties, phase hold-up, and reactor geometry. 24,28,29 In the present work, both superficial gas and liquid velocities vary simultaneously (Table 1), and their effects overlap with each other. Therefore, the flow patterns should be different for different reactors and operating conditions.…”

“…It is convenient to modify this model to adapt a new anaerobic wastewater treatment system. This hydrodynamic model might be also useful in simulating other bioreactors, such as fluidized bed reactor, 31 sequencing batch biofilm reactor 28 and packed-bed reactor. 32 Furthermore, through a combination of the hydrodynamics model with the biochemical kinetics and mass transfer models, a comprehensive model could be established to simulate the overall behaviors of anaerobic reactors, including reactor performance, sludge bed expansion and contraction, biogas accumulation and entrapment, biogas abrupt occasional release, granulation and degranulation process, granular sludge flotation, etc.…”

Diffusivity of oxygen in aerobic granules

“…The aerobic granule system yields a very high biomass concentration (up to 15 g/L) (Di Iaconi et al, 2005) and has a capacity to degrade high-strength wastewater (to 15 kg COD/ m 3 d) (Moy et al, 2002), representing a compact and highly efficient wastewater treatment alternative over the conventional activated sludge system. Granulation in aerobic systems has been extensively studied (Beun et al, 2002;Mulder et al, 2001;Tay et al, 2002a,b).…”

Hydrodynamic behavior of a combined anaerobic-aerobic system employed in the treatment of vinasse

“…For the FBAS no difference was observed, since the flow regime in this unit tends to be of complete mixing, due to aeration. According to Arceivala (1981), Levenspiel (2000) and Di Iaconi et al (2005), the biogas production rate, the liquid velocity, the geometry of the reactor, the depth of the sludge blanket, among other factors can influence the mixing pattern and consequently its hydrodynamic behaviour in the UASB reactor. Therefore, different reactor designs and operating conditions can result in different flow patterns (Ren et al, 2009).…”