Harvesting of microalgal biomass using MF membrane: Kinetic model, CDE model and extended DLVO theory

Abstract

In this paper, the Carman–Kozeny (C–K) model is proposed as a means of predicting flux decline for every stage of membrane cleaning, which can be strongly affected by pore blockage and by the growth of a cake layer. A combination of a kinetic model and the C–K model was utilized to determine specific parameters that can be used to estimate the decline in flux. The model was shown to be in excellent agreement with the experimental data obtained during the crossflow microfiltration of microalgal biomass over several cleaning cycles. The mean flux, given suitable transmembrane pressure (TMP), was also predicted by the model. The cleaning kinetics of the process suggested that a higher energy barrier Ec and a higher rate constant k0 were present for the final cycle of cleaning process, resulting from the extra energy required to break the bonds between the deposited cells and the membrane. This paper also focused on the electrostatic interaction between the microalgal cells and the membrane surface. The concentration polarization (CP) thickness of microalgae on a cellulose acetate (CA) membrane was calculated by the CDE model based on the balance of three transport mechanisms, namely, convection, diffusion and electrophoretic migration, with consideration being given to the negative charge of the microalgae and the membrane surface. The CP thickness was found to be strongly dependent on the membrane surface charge and the number of membrane cleaning cycles. The full interaction between the microalgae and the membrane was characterized according to a DLVO and an extended DLVO approach based on the strength of three separate interactions, namely, the van-der-Waals interaction (vdW), electrostatic (ES) repulsion and acid–base (AB) interactions. Both DLVO and XDLVO analysis provide useful methods for predicting the potential role of these interactions in the adhesion of microalgae to membranes. The XDLVO analysis determined a higher repulsion than did the DLVO analysis as a result of the high AB interaction energy in aqueous systems.