This research examined the influence of organic loading rate (OLR) and biosolids type on the performance of fermentative H2-producing membrane bioreactors (HPMBRs) with respect to H2 production and membrane fouling. Five OLRs ranging from 4.0 to 30 g COD L-1 d-1 were examined in a lab-scale HPMBR. The system performance with both suspended and granulated biosolids was also investigated.
The H2 yield from the suspended biosolids HPMBR was not significantly influenced by OLR at OLRs ≤ 13 g COD L-1 d-1, appeared to be maximized at an OLR of 22 g COD L-1 d-1, and then decreased as the OLR was increased further. An optimum OLR that maximizes H2 yield may be near the OLR that causes reactor overload with respect to substrate utilization.
Under the same operating conditions, the H2 yield from a suspended HPMBR was significantly higher than that from a granulated HPMBR. A higher H2 consumption rate and a higher concentration of bound extracellular polymeric substances from the granulated HPMBR may contribute 5–48% and 25–67% of the H2 production difference between the two systems, respectively.
The experimental results accompanied with microscopic examination of fouled membrane surfaces indicated that biosolids deposition and colloidal adhesion were the two dominant membrane fouling mechanisms in the HPMBRs. Membrane fouling was characterized by two distinct stages: an initial stage with a relatively higher fouling rate and a second stage with a lower fouling rate. Membrane fouling rates and resistances were influenced by the properties of biosolids and colloids in the mixed liquor. The fouling rates increased with increased biomass concentration, but decreased as colloids became more negatively charged. The irreversible and irremovable fouling resistance increased with increased concentration of colloids, while the removable fouling resistance had no relationship with biomass concentration. Biosolids granulation may benefit membrane performance due to a lower colloidal concentration produced.
The single cake filtration model was proper to simulate membrane performance in the initial fouling stage. Both cake filtration and combined cake-standard models provided good fits for the second fouling stage, whereas future study is required to improve model predictability for membrane fouling in this stage.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/29868 |
| Date | 31 August 2011 |
| Creators | Shen, Li Hong |
| Contributors | Bagley, David, Liss, Steven N. |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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