Ultra low-pressure filtration system for energy efficient microalgae filtration

Microalgae-based products have gained growing interest leading to an increase in large-scale cultivation. However, the high energy associated with microalgae harvesting becomes one of the bottlenecks. This study evaluated an energy-efficient microalga harvesting via ultra-low-pressure membrane (ULPM) filtration (<20 kPa) in combination with aeration. ULPM offered various benefits especially in terms of reducing the energy consumption due to it operated under low transmembrane pressure (TMP). High TMP often associated with high pumping energy hence would increase the amount of energy consumed. In addition, membrane with high TMP would severely affect by membrane compaction. Results showed that membrane compaction leads to up to 66 % clean water permeability loss when increasing the TMP from 2.5 to 19 kPa. The Chlorella vulgaris broth permeabilities decreased from 1660 and 1250 to 296 and 251 L/m2hrbar for corresponding TMPs for system with and without aeration, respectively. However, it was found that membrane fouling was more vulnerable at low TMP due to poor foulant scouring from a low crossflow velocity in which up to 56 % of permeability losses were observed. Membrane fouling is the biggest drawback of membrane system as it would reduce the membrane performance. In this study, aeration was introduced as membrane fouling control to scour-off the foulant from membrane surface and pores. In terms of energy consumption, it was observed that the specific energy consumption for the ULPM were very low of up to 4.4 × 10-3 kWh/m3. Overall, combination of low TMP with aeration offers lowest energy input.