M.Sc Thesis

M.Sc StudentPeleg Galia
SubjectIntegrating Suspended Carriers in a Membrane Biological
DepartmentDepartment of Civil and Environmental Engineering
Supervisors PROFESSOR EMERITUS Carlos Dosoretz
DR. Sharon Avrahami


Membrane bioreactor (MBR) technologies are an efficient advanced technology for wastewater reclamation. Due to the intrinsic nature of biological reactors there is a tendency of the growing biomass to adhere/attach onto the membrane surface thus generating biofouling.

This research evaluated the dynamics of a hybrid suspended-attached growth membrane bioreactor (HyMBR) for wastewater treatment, in which biomass immobilized on a suspended carrier coexists with suspended biomass in a single stage configuration system.

In order to characterize the influence of the suspended carrier on the membrane permeability two HyMBRs were operated for approx. 400 days each; one at 3 days solids retention time (SRT) and 50% carrier volumetric loading ratio (CLR) and the other at 16 days SRT and CLR between 20 and 60%. A control (MBR) with no carriers was performed for each set of conditions.

The findings depict an improvement in membrane permeability in the HyMBR, which probably resulted form a decrease of the suspended biomass and consequently, less cake layer formation on the membrane surface. The introduction of carriers reduced almost by half the amount of suspended solids due to the formation of attached biomass at expense of the carrier colonization. However, the increase in membrane permeability was moderate, indicating that other fouling mechanisms may have become more dominant, predominantly fouling by Extracellular Polymeric Substances (EPS). The increase of temperature-normalized permeability seems to be in part, related to the decrease of metabolic activity during the wintertime, which favored membrane performance. The performance of both MBR and HyMBR reactors, in terms of organic matter removal and nitrogen metabolism, were similar.

A comparison between the three biomass microenvironments (suspended, carrier attached and membrane attached) was conducted according to microbial communities structure (DGGE) and microbial activity (BIOLOG). Surprisingly, the suspended biomass and that attached on the carrier resulted close related microenvironments, while the microbial community on the membrane was very different. Moreover, it could be seen that the membrane provided an unattractive environment for nitrifying bacteria. In general, the α, β, γ -Proteobacteria group were detected in the sludge and carrier samples only, whereas the Bacteroidetes group were detected in all three microenvironments. The most dominant bacterium retrieved from the membrane surface was closely related to Nocardioidaceae str. Ellin101 within the Actinobacteria.

The findings obtained indicate that suspended carriers are not an efficient solution for membrane fouling in MBR, and further research with fixed carriers should be performed for evaluation of HyMBRs.