Harvesting of mixed microalgae culture grown in actual wastewater using cross-flow ceramic membrane filtration: Filtration performances and membrane fouling mechanisms

In this study, the performance of cross-flow filtration using tubular microfiltration (MF) (0.2 mu m) and ultrafiltration (UF) (300 kDa and 50 kDa) ceramic membranes were investigated for harvesting mixed microalgae cultivated in actual domestic wastewater. The steady-state flux decline rates (J/J0) for 0.2 mu m and 300 kDa membranes were comparable (22 % and 26 % of their initial fluxes, respectively), but higher for 50 kDa was (31 %). The resistance-in series model showed that the major fouling mechanism for all three membranes was the cake resistance (Rc) which accounted for 97.8 % (0.2 mu m), 88.1 % (300 kDa) and 74.8 % (50 kDa) of the total resistance (Rt). The reversible fouling resistances (Rr) were 98.2 % (0.2 mu m), 92.4 % (300 kDa), and 84.2 % (50 kDa). Sequential filtration experiments for microalgae concentration and performance evaluation of the cleaning procedure showed that chemical cleaning restored pure water fluxes (97.7 % for 0.2 mu m, 90.4 % for 300 kDa), but only 56 % for 50 kDa, indicating severe irreversible fouling. Sequential filtration experiments also demonstrated high biomass yields for 300 kDa and 0.2 mu m, achieving concentrations of 905 mg/L and 780 mg/L, respectively, whereas the 50 kDa indicated significantly lower performance, with a yield of only 550 mg/L, due to its smaller pore size and increased membrane fouling. Based on flux measurements, particle size distribution (PSD) analysis, and cleaning efficiency, the 300 kDa membrane was more appropriate for harvesting of mixed microalgae due to its high flux recovery, lower fouling, and high biomass enrichment.