Influence of activated sludge derived-extracellular polymeric substance (ASD-EPS) as bio-flocculation of microalgae for biofuel recovery

Microalgae have great potential as an alternative feedstock for high-valued biofuel due to rapid growth and high lipid content. However, the harvesting process, which usually accounts for about 20–30% of total production cost, is a bottleneck in microalgal biofuel technology. This study characterizes the bio-flocculants potential of activated sludge derived-extracellular polymeric substance (ASD-EPS) for microalgae harvesting. The efficiency of two physical (thermal, sonication) and one chemical (NaOH) extracted EPS was compared to a control (i.e., without flocculant). The enhancement of flocculation activity of microalgae is closely related to the carbohydrate concentration of EPS. Thermal extracted EPS contains the highest carbohydrate and protein concentration. In contrast, the chemical protocol led to the extraction of a large amount of inorganic matter, and reduction in the lipid composition of the microalgal cell membrane. Thermal extraction is the most suitable protocol with the highest biomass (microalgae) recovery of up to 87.24% and is least harmful to the lipid composition of the cell membrane. Among the tested three algae strains, Chlorellavulgaris is an ideal candidate showing high flocculation activity with ASD-EPS and large lipid production.