Just testing out some photos for my profile. Also, I have recently finished the abstract of my preliminary proposal for my PhD which I have copied below for those of you wondering what my research is all about. Somedays I actually believe I can make a difference in the world.

The influence of shear on EPS production and floc structure development in membrane bioreactors

Shear is used to control fouling in membrane bioreactors and is therefore a key process parameter. However, shear also affects the physical and physiological properties of MBR biomass. This research aims to characterize shear-induced changes in the microbial production of floc-associated and soluble EPS as well the development of floc structure (floc size, morphology and degree of dispersion) in low and high shear environments. These physical and physiological biomass characteristics are then used to explain the mechanisms leading the observed membrane fouling behavior of biomass in membrane bioreactor systems. A fundamental understanding of the relationship between the biological consequences of shear and their subsequent affect on membrane fouling provides an opportunity for process optimization.

This research is based on four primary hypotheses. (1) Biomass grown under high shear conditions is expected to decrease the production of floc-associated EPS in response to the shear-induced hydrolysis of this EPS. The decrease in floc-associated EPS production is expected to generate a corresponding decrease in soluble EPS production. (2) EPS composition is expected to play a role in maintaining the structure of flocs in a high shear environment. The decrease in EPS production with increased shear is expected to be coupled with a shift in EPS composition towards EPS with properties that are more efficient at maintaining the structural integrity of flocs in a high shear environment (ie. stickier EPS). (3) Biomass grown in a high shear environment is expected to have a smaller floc size and a more compact floc structure as well as a greater degree of dispersed growth. (4) The concentration of soluble EPS is expected to control the overall degree of membrane fouling in MBRs. Therefore, reduced EPS production will decrease membrane fouling potential. However, the particulate fraction of biomass grown under high shear conditions is expected have a higher the cake resistance because of its smaller floc size and increase level of dispersed growth.

The effect of shear is studied in two different types of MBR systems. The first part of the study used a MBR system with well characterized hydrodynamic conditions. This MBR system uses a polyethylene plastic membrane material having a pore size of about 20 mm. The rigid membrane material is manufactured into the walls of a baffled, cylindrical reactor and flow is passed through the membrane by gravity. The hydrodynamics inside this reactor geometry are well characterized and the level of shear is controlled by changing the speed of the mixing impellor. Using this MBR system, we have demonstrated that biomass grown in high shear conditions adapts to this environment by reducing both floc-associated and soluble EPS production which also corresponds to decreased membrane fouling potential as measured using constant pressure, dead-end filtration flux decline experiments. Increased shear was also found to reduce the growth of filamentous organisms in the high shear MBR and their associated cake fouling.

Future research on the effects of shear will use two MBRs having polymeric, flat-sheet, microfiltration membranes operated at differing aeration intensities. The hydrodynamics of shear generated by aeration are not well characterized. Therefore, the level of shear in these reactors will be related to the shear conditions in the baffled, cylindrical MBRs by comparing the disintegration kinetics of an ideal aggregated clay-floc suspension. Critical flux measurements will be used to compare differences in membrane fouling potential between the two reactors. The critical flux for the MBR operated at higher aeration intensity will be determined at both the high rate of aeration (operational critical flux) and low level of aeration (standard critical flux) to separate the effects of greater fouling control (ie. high shear) from lower EPS production. The effect of shear on EPS composition and stickiness will be examined in greater detail using atomic force microscopy measurements. Finally, the cake layer resistance of the particulate fraction will be determined using constant pressure, dead-end filtration experiments and related to the measured floc structure in each reactor.

The results of this work will provide a fundamental contribution toward elucidating the link between MBR process parameters, in this case the level of shear, and the resulting membrane fouling properties of MBR sludge. Ultimately, an understanding of this complex inter-relationship will help facilitate the evolution of MBR operational philosophy toward strategies that both minimize the production of biological foulants in addition to reducing the deposition of foulants on the membrane surface.