A novel low cost microalgal harvesting technique with coagulant recovery and recycling

In this study, a novel low cost and sustainable microalgal harvesting technique was developed using the concept of coagulant recovery concentration and recycling. Al³⁺ can be recovered from harvested Scenedesmus acuminatus biomass with 0.1 M HCl, at an acid solution-biomass ratio of 250 ml g^-1. The residual Al³⁺ content in the purified biomass was reduced to 0.11 ± 0.0006 mg g^-1, while a higher content of 59.74 ± 3.11 mg g^-1 was found in the coagulation harvested biomass. The recovered Al³⁺ solution was concentrated 25 times and then reused for the harvesting of S. acuminatus. The Al³⁺ recovery and reuse were repeated 5 times, and the harvesting efficiencies were found higher than the fresh Al³⁺ as a result of the presence of extracellular polymeric substances in the recovered coagulant solution which aided the coagulation process. According to the technical-economic analysis, the cost of chemicals decreased 50% after 5 times recycling.