Modification of PVDF ultrafiltration membrane for high concentration of nannochloropsis as a raw material for bioethanol: Computations and experiments

Nannochloropsis sp., which is abundant in the ocean and has a high carbohydrate content, has great potential if used as a raw material for bioethanol. However, the low concentration of microalgae in the culture medium (0.5-2 µg/L) and the small size of the microalgae Nannochloropsis sp. (2-8 µm) become problems in the harvesting process. This study aims to increase the concentration of Nannochloropsis sp. during the harvesting process using a LiCl-modified polyvinylidene fluoride (PVDF) membrane. In addition, a computational approach was used to select the best solvent for PVDF and explain the conformational changes of PVDF. The results showed that N-Methyl-2-pyrrolidone is the best solvent for PVDF polymer (the lowest solvation energy is -86.25 Kjmol⁻¹, and the highest binding energy is 1.8 Kjmol⁻¹). The membrane, with the addition of 2% LiCl, had the best performance, increased the microalgae concentration ten times (from 596.4 to 5098 ppm), flux (150 Lm⁻²h⁻¹bar⁻¹), and rejection (100%). Adding LiCl to the dope solution increased the water flux (from 516 to 614 Lm⁻²h⁻¹bar⁻¹), changed the PVDF conformation from alpha to beta, and decreased the hydrophobicity of the membrane (from 94.89 to 81.68 °). Layer pore fouling is the fouling that plays a role in reducing microalgae flux during microalgae filtration by Nannochloropsis sp. Meanwhile, the type of washing recommended to overcome layer pore fouling is rinsing by increasing the speed of the filtration flow and immersion in chemical compounds.