Pilot-scale cross-flow microfiltration of Chlorella minutissima: A theoretical assessment of the operational parameters on energy consumption

Microalgae biomass is seen as a sustainable and socially more responsible feedstock for the production of biofuels and other fine chemical products. Dewatering algae using membrane filtration is a leading technology, however the associated costs are typically not determined. This work investigates the filtration of Chlorella minutissima using a pilot-scale cross-flow microfiltration unit. A filtration model was developed and validated based on permeate flux as a function of biomass concentration (0.6-19.0 dry cell weight/L) and transmembrane pressure (ΔP, 1.80-2.10 bar). Processing times for harvesting C. minutissima were determined by iteration of the model and costs were related to energy consumption. For the experimental conditions of 1.95 bar, 1.0 g DCW/L initial biomass concentration, 0.70 kWh, 25 °C and 3.8 m2 membrane area, harvesting costs were determined as 2.86 kWh/kg biomass. Subsequent investigation of the influence of the operating parameters and scale-up effects demonstrated that significant cost reduction to 1.27 kWh/kg biomass was possible at 1.95 bar, 2.0 g DCW/L initial biomass concentration, 0.46 kWh, 20 °C and 7.6 m2 membrane area. Further, biomass concentration was demonstrated to be one of the major drivers to reduce the cost of harvesting microalgae. Membrane filtration was demonstrated to be a feasible harvesting process allowing biomass concentrations up to 150 g DCW/L without using chemicals which complicate the downstream processing stages.