In-line flocculation-submersed MF/UF membrane hybrid system in tertiary wastewater treatment

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Journal Article
Separation Science and Technology, 2008, 43 (7), pp. 1839 - 1851
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Coagulation/flocculation pre-treatment of feeds can successfully mitigate the drawbacks of membrane micro- and ultra filtration processes: fouling and limited ability to remove organic pollutants. Laboratory experiments conducted with a synthetic wastewater (representing biologically treated secondary effluent) using 0.1m pore size hollow fiber membrane showed that simple in-line flocculation pre-treatment with inorganic coagulants dramatically reduced membrane fouling rates. The hybrid system also ensured over 70% organic matter removal in terms of dissolved organic carbon (DOC). In the experiments in in-line flocculation outperformed clarification pre-treatment at optimum coagulant dosages. Differences in floc characteristics and elevated suspended solids concentrations in the membrane tank may explain this finding, but the exact causes were not investigated in this study. The beneficial effects of in-line flocculation pre-treatment to MF/UF separation were also confirmed in the treatment of septic tank effluent in a membrane bioreactor (MBR). The fouling rate of the 0.4m pore size (flat-sheet) membrane was substantially reduced with 10-100mgL-1 ferric chloride coagulant doses, and total dissolved chemical oxygen demand (DCOD) removal also increased from 66% up to 93%. These findings are consistent with the results of other experimental studies and show that pre-treatment controls submersed MF/UF filtration performance.
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