Harvesting microalgae using the temperature-activated phase transition of thermoresponsive polymers

Microalga is a promising feedstock for biofuel, chemical, food, and animal feed; however, harvesting is a critical barrier for its commercial application. This communication demonstrates a new harvesting technology by utilizing the phase separation of thermoresponsive polymers and charged copolymers of N-isopropylacrylamide and allylamine. Chlorella protothecoides cells are separated from solution when the mixture of algae and polymers is heated above the lower critical solution temperature of polymers (similar to 32 degrees C), where the polymer phase separates from the aqueous media and aggregates into a solid-gel phase. It was found that copolymer concentration, allylamine content (mol%) and charge (based on initial solution pH) affect the extent of polymer phase separation and alga separation efficiency. The copolymer containing allylamine with lower than 2.6 mol% displayed nearly complete algal cell separation at polymer concentrations of 25-50 mg/mL and pH 7. The results indicated that thermoresponsive polymers provide a promising technology for alga harvesting using recyclable and reusable materials. (C) 2015 Elsevier B.V. All rights reserved.