Temperature-induced algae harvesting with grafted poly(N-isopropylacrylamide)

Microalgae biorefinery has a broad spectrum of applications, but the high cost of the algae harvesting process restricts the scale-up of this industry. This work developed a new method for algae harvesting by using grafted poly(N-isopropylacrylamide) (PNIPAM). PNIPAM has a temperature-induced phase change property that can be taken advantage to capture algae cells in the cultivation medium. Grafting PNIPAM onto some substrate materials (cotton fabric, polyester sheet, polyester fabric and polystyrene flexible sheet) can make the recycling and reuse of PNIPAM more convenient and cost-efficient. The findings showed that PNIPAM-300 kDa grafted on the cotton fabric achieved the highest grafting yield (2.38 mg/cm²) and the best algae harvesting efficiency (AHE) (72 %) among all the tested grafted PNIPAM. Allowing the polymer to fully dissolve before heating to initiate algae harvesting significantly enhanced the AHE. Furthermore, PNIPAM-grafted cotton fabrics can be reused more than 20 cycles before the AHE started decreasing. The grafted PNIPAM on substrate materials is a promising cost-efficient algae harvesting technique to promote the commercialization of microalgae biorefinery.