A new reactor design for harvesting algae through electrocoagulation-flotation in a continuous mode

Abstract

The low energy requirements to grow microalgae combined with the very fast reproduction gives microalgae unique abilities to utilize them for industrial and environmental applications. However, harvesting these algae still remains energy consuming and, as a consequence, expensive. In this work a new electrocoagulation-flotation set-up with a tubular coaxial reactor, developed by Noah Water Solutions, is investigated for the autonomous harvesting of the green microalgae species Chlorella vulgaris. No pH adjustment or other pretreatments were applied in order to make the method applicable in the field. With this type of electrocoagulation-flotation reactor the algae were on average a factor 100 more concentrated, i.e. starting from the influent microalgae suspension of 0.2 g·L−1 up to 18.5 g·L−1 with iron electrodes and 35.2 g·L−1 with aluminum electrodes. Moreover, with this reactor type only low currents (0.8 A for Fe and 0.3 A for Al) had to be applied, resulting in low energy consumptions (2.0 kWh·kg−1 for Fe and 1.1 kWh·kg−1 for Al). Remaining metal concentration in the harvested algae was low, i.e. 0.6% for the Fe electrodes and 0.3% for the Al electrodes. Combining these results with the autonomous and continuous removal of the concentrated algae makes this tubular electrocoagulation-flotation reactor excellent for harvesting microalgae on industrial scale.