Flocculation characteristics of anaerobic sludge driven-extracellular polymeric substance (EPS) extracted by different methods on microalgae harvesting for lipid utilization

Microalgae harvesting is the crucial step in algal biofuel production, which accounts 20-30% of the total production cost. The present study investigates the potentiality of anaerobic sludge-driven extracellular polymeric substance (EPS) as a bioflocculant. Five different methods, including physical and chemical, have been employed for EPS extraction from anaerobic sludge. Chemically extracted EPS showed better performance in microalgae harvesting as compared to physical ones. Maximum flocculation efficiency of 91.8 % was obtained using 30 mL L-1 EPS (0.40 g EPS g(-1) biomass) extracted by formaldehyde-NaOH. However, microalgal lipid content was drastically decreased using chemically extracted EPS. In contrast, EPS extracted by thermal method had no significant effect on lipid recovery. Combining the bioflocculation performance and the lipid recovery suggests that the thermally extracted EPS was the most suitable for microalgae dewatering. Kinetic analysis revealed that pseudo-second-order kinetics (R-2 = 0.979 - 0.999) and intra-particle diffusion (R-2 = 0.974 - 0.986) are the most qualified for modeling of microalgal flocculation. Cost analysis showed that the cost of microalgae harvesting using EPS extracted by the thermal method was USD 1.95 and USD 4.9 for the recovery of 1 kg biomass and that of 1 kg lipid, respectively. The study was an attempt to develop a suitable microalgae harvesting technique using bio-based flocculant derived from a renewable resource.

Automated summary

The study investigated the potential of anaerobic sludge-driven extracellular polymeric substance (EPS) as a bioflocculant for microalgae harvesting. Chemically extracted EPS showed better performance but reduced microalgal lipid content, while thermal method extracted EPS had no significant effect on lipid recovery, making it the most suitable for microalgae dewatering. Kinetic analysis revealed pseudo-second-order kinetics and intra-particle diffusion as the most suitable for modeling microalgal flocculation. Cost analysis showed that using EPS extracted by the thermal method for microalgae harvesting was cost-effective.