Microfiltration of algae: Impact of algal species, backwashing mode and duration of filtration cycle

- Microfiltration characteristics of mixed algal system were investigated.
- C. vulgaris exhibit lower cake forming potential than C. reinhardtii.
- Online backwashing was found as effective as offline backwashing.
- Feasibility of membrane microfiltration for mixed algal system is established.

The objective of this study was to investigate and compare the microfiltration characteristics of mixed algal cultures containing two species of green microalgae: Chlorella vulgaris and Chlamydomonas reinhardtii. Submerged membrane filtration experiments with 300 mg L− 1 suspensions of pure algal cultures indicated that while membrane fouling potential was comparable in both cases, Chlorella vulgaris had a lower cake formation potential. Filtration experiments were carried out with 1000 mg L− 1 suspensions of mixed algal culture over several 12-h cycles with backwashing, either in the on-line or off-line mode. While on-line backwashing caused more fouling, this did not significantly affect the flux through the membrane, which was controlled by the cake formation on the membrane. The algal mixed culture was also filtered over many 3-h cycles with on-line backwashing. Lower cycle duration resulted in lower average cake resistance and hence allowed more membrane throughput, but at the cost of more frequent backwashing. Chemical washing of the membrane could remove the fouling resistance only partially. Thus, despite periodic chemical washing, the intrinsic membrane resistance increased consistently with cumulative throughput through the membrane.