Characterization of Multiporous Structure and Oxygen Transfer Inside Aerobic Granules with the Percolation Model

Abstract

The characteristics of aerobic granules for wastewater treatment are greatly related to their complex internal structure. However, due to the limitation of characterizing methods, information about the granule internal morphology and structure is very sparse, and mechanism of mass transfer process is yet unclear. In this work, the internal structure of aerobic granules was explored using nitrogen adsorption method and confocal laser scanning microscopy technique. It was found that aerobic granules had multiporous structure with cross-linked gel matrix structure. With a consideration of the hydrodynamic regime and the porous structure of granules, a twodimensional percolation model was established to describe the mass transfer in granules. With the approaches, interesting and useful results regarding the pore distribution and mass transfer in aerobic granules have been obtained. The results demonstrate that the intragranule convection could enhance mass transfer, hence ensure an efficient and stable operation of aerobic-granule-based reactors. Such approaches might also be applicable to characterizing the multiporous structure and mass transfer of other microbial aggregates for wastewater treatment.

Modeling and optimization of granulation process of activated sludge in sequencing batch reactors

“…Based on individual‐based model (ibM) and a mixed‐culture biofilm model, two different models have been, respectively, developed to quantitatively describe the granulation process (Ni et al, 2010; Xavier et al, 2007). In these two models, all of granules have the same size, which is apparently inconsistent with experimental results about granule size distribution (Liu et al, 2010a). Moreover, the sedimentation process, a key selection step for sludge granulation (Qin et al, 2004), is not taken into account in these two models.…”

“…The defaulted or measured values of input parameters of this model are summarized in Table I, where M , N , and K are determined based on our previous study (Su and Yu, 2006b). Parameters of the boundary of radius and SS concentration ( R max , R min , X max , and X min ) are selected from the studies regarding aerobic granules (de Bruin et al, 2005; Liu et al, 2010a; Muda et al, 2010; Su and Yu, 2005; Zhu et al, 2011). A program is developed using MATLAB® (Mathworks, Inc., Natick, MA) for the calculation.…”

Aerobic Granules: Microbial Landscape and Architecture, Stages, and Practical Implications

“…Conceptual and mathematical models of granules assume a spherical shape with an outer layer and an inner core. Although this approach has increased our understanding of the process, models are often only validated against macroscale results with limited or no microscale observations (21,22). Despite the fact that the physical architecture of the granules is intrinsically related to mass transport, conversion processes and niches partitioning within the granules, few reports describe details on the microstructure of aerobic granules (23,24).…”

Quantitative image analysis for the characterization of microbial aggregates in biological wastewater treatment: a review

“…Although most of the literature on image analysis applications on biological WWT processes describes procedures for unstained samples, coupling it with dyes and molecular techniques, such as staining or fluorescence in situ hybridization (FISH), is expanding. This technique allows rapid quantification of several microorganisms (Hug et al 2005) and deeply characterization of microbial aggregates (Liu et al 2010). The combination of fluorescence staining techniques, confocal laser scanning microscopy (CLSM), two-photon or multiphoton laser scanning microscopy (2PLSM), intensity imaging and lifetime imaging offers a wealth of opportunities in order to collect multiple pieces of information from highly complex biological systems such as microbial aggregates and biofilms (Neu et al 2010).…”

“…The use of image analysis combined with epifluorescence techniques is usually followed by fluorescence microscopy or CLSM (Kuehn et al 1998;Schmid et al 2003). CLSM is particularly adapted to the study of 3D structures, such as aggregates of cells (Lawrence et al 1998) and aerobic granules (Liu et al 2010). According to Lopez et al (2005), selection of the most appropriate technique depends on the object being investigated.…”