Concentrating Algal Cultures in a Semi-Continuous Process Using Temperature-Sensitive Semi-Interpenetrating Network Hydrogels

In this study, a semi-interpenetrating network hydrogel consisting of polyvinyl alcohol (PVA) intercalated into poly N-isopropylacrylamide (pNIPAAm-PVA semi-IPN) and a pNIPAAm-polyethylene glycol copolymer hydrogel (pNIPAAm-PEG), were tested for the applicability in dewatering dilute algal slurries. These absorbents can preferentially uptake the aqueous medium without removal of cells which results in an increase in cell concentration of the residual suspension. In addition, since these stimulus-sensitive gels collapse and release the absorbent medium at relatively low temperature (>32°C), the hydrogels can be reused. In comparison with the more conventional pNIPAAm gel, the pNIPAAm-PVA and pNIPAAm-PEG gels show better swelling and deswelling kinetics. Also, compression-stress measurements and rheological studies also show that the pNIPAAm-PVA gels have greater flexibility and mechanical strength than pNIPAAm gel, suggesting that they would be less susceptible to breakage during the dewatering process. Results from semi-continuous hydrogel-based algae harvesting process implementation will be presented along with detailed techno-economic analyses.