Coagulation-Membrane Filtration of Chlorella vulgaris at Different Growth Phases

Coagulation and membrane filtration separation of Chlorella vulgaris, a species with excellent potential for CO 2 capture and lipid production, was studied at different growth stages of algal cells using chitosan as the coagulant and a surface-modified hydrophilic polytetrafluoroethylene (PTFE) membrane as the filter medium. Three samples were collected and tested: sample A in a logarithmic growth phase, sample B in a late stage of the growth phase, and sample C in a stationary phase. Sample A revealed efficient autocoagulation capability and samples B and C had poor settleability. The coagulation efficiency of algal suspension was increased with increasing chitosan dosage, reaching 99.7% removal rate at 200 mg L -1 chitosan for sample A, 99.5% removal rate at 50 mg L -1 chitosan for sample B, and 99.0% removal rate at 100 mg L -1 chitosan for sample C. Sample A, coagulated with 50 mg L -1 chitosan, had a membrane filtration flux of 10-14 m 3/m 2-min after a 5-min test. Samples B and C had poor filterability with membrane flux of less than 1.0 m 3/m 2-min after a 5-min test. Chitosan coagulation could incrementally enhance the filterability of samples B and C. Conversely, the solid contents in filtered cake from original samples A, B, and C were 26.8, 31.9, and 33.7%, respectively. That is, a long cultivation time led to a dry filtered cake after membrane filtration. Adding chitosan slightly decreased the solids content of the filtered cake from sample A, largely reduced the solids content from sample B, and first increased and then decreased the solids content of the filtered cake of sample C. Low water-solid binding energy corresponded to a dry cake after membrane filtration. Selection of the appropriate harvesting time and the required chitosan dose relies on the cost of membrane operation, coagulation operation, and subsequent drying steps. Supplemental materials are available for this article. Go to the publisher's online edition of Drying Technology to view the free supplemental file. ? 2012 Copyright Taylor and Francis Group, LLC.