The fouling effects of microalgal cells on crossflow membrane filtration

• Microalgal cells clog the membrane pores at the beginning of the filtration process.
• Microalgal cells caused both reversible and irreversible (irrecoverable) fouling for all membranes.
• Compared to UF membranes, the MF membrane had more filtration resistances.
• The crossflow velocity as well as the membrane pore size and the membrane material caused the filtration resistance to some degree.

The main drawback of membrane processes is biological membrane fouling which, in turn, leads to the membrane having an increased amount of transmembrane pressure and energy consumption. The fouling of microfiltration (MF) and ultrafiltration (UF) membranes caused by microalgal cells was investigated in this study. An MF membrane with a pore size of 0.20 µm (made of PVDF) and UF membranes with a molecular weight cutoff (MWCO) of 150, 50, and 30 kDa (made of PES, PESH and RC, respectively) were employed for the filtration experiments. An attenuated total reflection-Fourier infrared (ATR-FTIR) spectroscopy, a scanning electron microscope (SEM), and contact angle device were utilised in order to characterise the membranes fouled by microalgal cells. The results demonstrated that the MF membrane exhibited a faster decrease in flux when the normalised flux was reduced to as low as 0.15. An increase in the crossflow velocity (CFV), on the other hand, can dramatically decrease microalgal cells depositing on the surface of a membrane, thereby leading to higher flux. Moreover, microalgal cells caused both reversible and irreversible fouling for all membranes. In addition, the analysis of the different filtration resistances encountered in membrane filtration involving concentration polarisation, cake layer formation, and the clogging of pores was studied. The experimental results obtained in this study show that the cake resistance (Rc) had the highest resistance for the UF membranes and that the concentration polarisation (Rcp) was dominant in all crossflow velocities for MF membranes.