Electrocoagulation reduces harvesting costs for microalgae.

Centrifugation is the most commonly used method for harvesting autotrophically produced microalgae, but it is expensive due to high energy demands. With the aim of reducing these costs, we tested electrocoagulation with iron electrodes for harvesting Chlorella vulgaris. During extensive lab-scale experiments, the following factors were studied to achieve a high harvesting efficiency and a low iron content in the harvested biomass: electric charge, initial biomass concentration, pH, temperature, agitation intensity, residual salt content and electrolysis time. A harvesting efficiency greater than 95% was achieved over a broad range of conditions and the residual iron content in the biomass complied with legislative requirements for food. Using electrocoagulation as the pre-concentration step prior to centrifugation, total energy costs were reduced to 0.136 kWh/kg of dry biomass, which is less than 14% of that for centrifugation alone. Our data show that electrocoagulation is a suitable and cost-effective method for harvesting microalgae.