Effect of voltage and electrode material on electroflocculation of Scenedesmus acuminatus

Microalgae are a promising new source for biomass production. One of the major challenges in regards to cost effectiveness is the biomass harvest. High energy input is required for the separation of the small algal cells from a large volume of surrounding media. Electroflocculation is reported as a promising harvesting technique to improve cost effectiveness within the downstream process. In the present study, six electrode materials were tested for electroflocculation of Scenedesmus acuminatus. Besides the commonly used aluminum and iron electrodes, magnesium, copper, zinc and brass electrodes were tested for biomass harvest and compared. The influence of four different voltages (10, 20, 30 and 40 V) was investigated and evaluated. Electroflocculation was applicable with all tested electrode materials. The highest flocculation efficiency was achieved using magnesium electrodes followed by Al, Zn, Cu, Fe and brass. Using magnesium, 90% of the suspension was clarified at 40, 30, 20, and 10 V after 9.2, 12.5, 18.5, and 43 min, respectively. All electrode materials showed the fastest flocculation at 40 V and the lowest at 10 V. The pH increased from 7.5 to values between 9.3 and 11.9 during the flocculation processes. Reuse of the supernatant showed no adverse effect on algal growth. The highest cell counts after 12 days of incubation were achieved with iron at 1.86 × 107 cells ml−1 and the lowest with copper at 1.23 × 107 cells ml−1. Besides the commonly used iron and/or aluminum electrodes, other materials like magnesium, copper, zinc and brass can be successfully used for microalgal biomass harvest. For special biomass applications like food or feed additives, metals like magnesium have other advantages besides their high flocculation efficiency such as their low toxicity at high concentrations. Higher voltages increased the maximum flocculation efficiency but also increased the required energy input.