|M.Sc Student||Eppel Galina|
|Subject||Characterization of Dissolved Organic Matter in Effluents of|
Membrane Bioreactors as a Function of their
Configuration, Membrane Type and
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Michal Green|
|Professor Carlos Dosoretz|
The primary objective of this research was to examine the effluent quality, in particular the dissolved organic matter, in MBR effluents employing submerged membranes, as a function of operating conditions, system configuration and membrane separation capability, compared with that achieved by an activated sludge process.
During the research period three systems were continuously operated, fed with primary treated municipal sewage. These systems include two submerged MBRs (employing different membranes: microfiltration - MF-MBR and ultrafiltration - UF-MBR) and a sequential batch reactor (SBR).
The UF-MBR produced a larger specific filtrate volume than the MF-MBR; moreover, the permeate flux was one order of magnitude greater, 3.3 (m3 permeate produced per m2 membrane per day) compared to 0.3. Compared with the SBR, the MBR exhibited a specific flow rate 20-30% higher.
Organic matter removal, in terms of COD was ~90% for all three systems, with the highest efficiency for the UF-MBR and the lowest efficiency for the SBR.
From the soluble organic matter fractionation by hydrophobic affinity (XAD-4 and XAD-8) there appear to be no obvious trends in the effluents of the three reactors. The largest fraction obtained in all cases was that of acidic hydrophobic, which varies between 43% in the SBR, through 47% in the MF-MBR to 51% for the UF-MBR. The hydrophilic fraction is found to be the smallest and most consistent, constituting approximately 16-17% of the organic matter, while the transphilic fraction amounted to 24-30%. The neutral fractions were mostly smaller than the acidic fractions. The different fractions of organic matter obtained according to hydrophobic affinity may be separated into two groups, according to molecular weight. The hydrophobic fraction is a major component of high molecular weight compounds, with a peak of 1000 Da. Conversely, the hydrophilic fraction was found to be a major component of lower molecular weight compounds of up to 200 Da.
To conclude, organic matter removal and dissolved COD/TOC ratio in the effluent decreased with intensification of the treatment technology as a result of longer contact periods (possible only in a MBR), showing that the level of stabilization of the refractory organic matter is higher for the more intensive process. Within the conventional range of sludge ages in the MBR systems (SRT≤30 days), the dissolved organic matter and its quality exhibit a similarity between the activated sludge and MBR processes, despite the difference in technology and operating conditions.