Fouling mitigation by iron-based electroflocculation in microfiltration: Mechanisms and energy minimization.
High-energy demand presents a major obstacle in the application of advanced water-purification systems. In this work, energy minimization and fouling mitigation by iron-based electroflocculation in dead-end microfiltration were investigated. Highly pure water contaminated with Silica-CMP (chemical mechanical polishing) particles were pretreated by electroflocculation at short operation times and a constant electrical current intensity of 0.4 A, followed by different slow-mixing times and filtration without any sedimentation step. By using a new method for filtration-energy appraisal, we found that an over 90% reduction in filtration energy could be achieved. The improvement was observed at all pH values examined (pH 6-8); pH values below 7 were problematic because the permeate turned yellow as a result of residual iron. The appearance of residual iron was explained by the dependence of Fe(2+) to Fe(3+) reaction rates on pH. Scanning electron micrographs of the fouled membrane surface showed the important role played by the sweep-coagulation mechanism in mitigating fouling. When internal fouling was the dominant mechanism, the amorphous iron-hydroxide solids formed a layer that filtered out the primary particles, protecting the membrane pores from plugging. Iron-hydroxide particles also reduced the hydraulic resistance of the cake when the external fouling mechanism dominated. Significant energy reduction was observed, even without the slow-mixing step, as a result of the local flocculation conditions near the membrane surface. Additional energy savings were obtained due to the significantly higher initial-flux restoration rates (>90%) resulting from electroflocculation pretreatment.
Ben Sasson
Moshe
M
The Department of Soil and Water Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel. mosheinspain@hotmail.com
Adin
Avner
A
D057219:Biofouling / Q000517:prevention & control*; D004563:Electrochemistry / Q000379:methods*; D005374:Filtration / Q000379:methods*; D005427:Flocculation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007501:Iron / Q000494:pharmacology*; D008567:Membranes, Artificial; D008855:Microscopy, Electron, Scanning; D012822:Silicon Dioxide / Q000737:chemistry; D013816:Thermodynamics; D013997:Time Factors
D008567:Membranes, Artificial; D012822:Silicon Dioxide; D007501:Iron