Concentration of phycocyanin and coffee extracts in aqueous solutions with osmotically-assisted membrane distillation

Osmotic membrane distillation (OMD) is a dewatering process that exploits combined temperature and osmotic pressure gradients to drive water vapor fluxes under mild operation conditions. In this study, the feasibility of OMD is evaluated for the concentration of phycocyanin and coffee extract solutions, with the goal to safeguard the quality of the extracts. Different feed solution temperatures were studied, namely, 35 °C, 45 °C, 55 °C, while keeping a concentration of 4 M CaCl2 in the extraction solution. The target concentration factor was set to 4, equivalent to a water recovery rate of 75 %. The results suggest that a temperature equal to or below 45 °C should be chosen for the concentration of phycocyanin to prevent degradation and to minimize fouling, while higher temperatures may be used for the recovery of the coffee extract. The combined gradients provided water fluxes around or above 4 L m−2h−1 with both extracts under relatively mild conditions, even at high concentration factors. Qualitative membrane fouling inspection was corroborated by estimating the fraction of productivity lost due to fouling, which was larger for higher feed temperatures and for the phycocyanin extracts, and had values between roughly 20 and 70 %. Results also suggest that the quality of the extracts was maintained, based on the measured purity and content of the target compounds in the concentrated solutions. Specifically, no trace of extraneous compounds was found, and no salt passage was observed from the extraction solution to the feed solution, suggesting that OMD has the potential to concentrate sensitive components.