Decreasing membrane fouling during Chlorella vulgaris broth filtration via membrane development and coagulant assisted filtration

Membrane filtration has been reported as an interesting low-cost technique for microalgae harvesting, either in a separated process or in a coupled process as in a membrane photobioreactor. However, the filtration performance can still be improved if the membrane fouling problem could be properly managed. In this study, the improvement of the filterability of a Chlorella vulgaris broth is investigated via both membrane development and via coagulant dosing before filtration. For the membrane development (via the process of phase inversion), four basic membrane preparation parameters were studied, namely polymer concentration, time gap between casting and coagulation, addition of water as a non-solvent into the casting dope solution and the addition of polyvinylpyrrolidone as an additive to a polyvinylidene fluoride/N,N-dimethylformamide system. For coagulation, FeCl3 and chitosan were tested using a polycarbonate 0.1 μm membrane. Later, three new membranes were tested against two commercial membranes with and without coagulant dosing. The performance of the membrane was evaluated using the improved flux stepping filtration method and using a simple dead-end filtration for the coagulation/filtration study, respectively. Results show that the membrane properties and the filterability could be well manipulated by using the four phase inversion parameters. Both coagulants increased the filterability of the broth. When applied to the optimized membranes and the two commercial membranes, dosing 10 ppm chitosan in the C. vulgaris broth had inconclusive effects. It improved filterability for most of them but imposed negative effect for the rest, which suggests that the coagulant type and dosing of a membrane filtration system should be optimized per membrane.