Electrical approaches to algae dewatering include exploiting electrophoresis, electrofloc­culation, and electroflotation. An obvious consideration, because algae normally carry a negative charge, is electrophoresis. In a water solution, however, both electrophoresis and electroflocculation can occur under the same set of circumstances. If a tray of algae in its growth medium were exposed to an electric field by placing metallic electrodes on two sides of the tray and energizing them with a DC voltage, algae concentrations would occur at both electrodes (electrophoresis) and at the bottom of the tray (electroflocculation). A study fo­cused on assessment of the factors influencing electrophoresis and electroflocculation of algae in its growth medium was conducted (Pearsall et al., 2011). The reported experiments show that electrophoresis does occur but is complicated by the effects of the fluid motion. It appears that the coupling of the algal cell and the fluid can be sufficiently strong that fluid motion effects can influence or dominate behavior. Electroflocculation appears to be a robust process (Poelman et al., 1997; Alfafara et al., 2002; Azarian et al., 2007). It does, however, inherently leave electrically induced trace metal flocculants in the dewatered algae.

As mentioned in Section 5.3.5.2, fine gas bubbles formed during the electrolysis, causing the algal particles to float to the surface, where they are skimmed off. An efficient bench-scale electroflotation system for algae flocculation was reported by using the magnesium hydrox­ide formed in the electrolysis to enable precipitation and, consequently, flocculation (Contreras et al., 1981). Laboratory — and field-scale electroflotation units for algae removal from wastewater oxidation pond effluent were operated (Sandbank et al., 1974; Schwartzburd, 1978; Kumar et al., 1981). A 2 m2 pilot-scale unit was tested for clarification of high-rate oxidation pond effluent (Shelef et al., 1984). For satisfactory algae separation, electroflotation is to be followed by or be operated concurrently with alum flocculation (Sandbank et al., 1974).

A wide range of microalgae species were harvested by electroflotation with up to 5% solids in the harvested algae. Decantation after one day further increased the solids concentration to 7-8% (Sandbank, 1979). The energy needs of the electroflotation process are generally high, but for small units (<5 m2 area) electricflotation operating costs are less than those of dissolved-air flotation units (Svarovsky, l979).