Electrocoagulation/flocculation of cyanobacteria from surface waters

Cyanobacterial blooming episodes in surface waters used for drinking purposes are increasing due to eutrophication of water ecosystems. Water treatments should be optimised to remove phytoplankton cells as well as their associated toxins. The performance of a multicell electrocoagulation reactor operating under a continuous flow and coupled with flocculation for cyanobacteria removal was examined. Electrocoagulation of a suspension of the unicellular cyanobacteria Microcystis aeruginosa and its related toxin microcystin-LR, as a model of toxic cyanobacterium and cyanotoxin, respectively, showed that cell removal occurred through charge neutralisation with the Al hydroxides generated in the system, whereas the toxin did not undergo electrolytical processes. Cell inactivation was a function of the charge loading and the cell population. Inactivation of a 10(5) cells/mL suspension was 34% for a charge loading of 50 C/L whereas only 3% was achieved by increasing cyanobacteria concentration by one-order of magnitude. Flocculation of the electrocoagulated suspensions with anionic polyelectrolytes revealed a bridging mechanism, whereas an electrostatic patch aggregation was involved with cationic flocculants. Electrocoagulation/flocculation of a cyanobacterial blooming surface water (about 10(6) cells/mL) showed quite good concordance of cell inactivation values (9.7-10.7%) with those detected previously with Microcystis aeruginosa (5.4%). However, the performance of the flocculants was slightly worse as determined from the residual turbidity values (17% vs. 7% in pure cultures of M. aeruginosa) due to the different compositions of the extracellular organic matter. (c) 2019 Elsevier Ltd. All rights reserved.