Submerged Membrane Bioreactor Mixed Liquor Properties and Process Performance at a Wide Range of Mean Cell Residence Times Treating Municipal Wastewater
The effects of mean cell residence time (MCRT) on the effluent water quality and mixed liquor properties of a pilot-scale submerged membrane bioreactor (SMBR) and a bench-scale complete-mixed activated-sludge (CMAS) reactor both treating municipal wastewater were investigated. The SMBR produced effluent turbidity values < 0.2 NTU and the effluent soluble COD values were consistently lower than for the CMAS reactor due to retention by the membrane. Compared to the CMAS mixed liquor, the SMBR mixed liquor had higher mixed liquor soluble COD values, higher amounts of soluble microbial products (SMP) and higher colloidal material content due to membrane retention. The use of a membrane in the SMBR also created an almost perfect surface trapping environment that resulted in higher levels of filamentous microorganisms than for the CMAS mixed liquor due to the presence of nocardioform organisms. The extracellular polymeric substance (EPS) levels of the SMBR mixed liquor were lower than for the CMAS mixed liquor possibly because there is no need for mixed liquor to settle or to generate EPS. The filterability of the two mixed liquors was similar possibly due to the offsetting effects of EPS and colloidal material that is believed to affect filterability. Cationic polymer addition improved filterability of both mixed liquors but polymer overdose was observed for CMAS mixed liquor at higher doses.
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Document Type: Research Article
Publication date: 2005-01-01
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