The effect of ferric chloride flocculation on cyanobacterial cells

Taste, odour and cyanobacterial toxins are not generally removed during conventional water treatment and can sometimes be increased during the treatment process due to cell lysis. Some reasons for this have been documented in the literature, but there appears to be contradictory evidence regarding the effect of flocculation. In an earlier study, aluminium sulphate did not appear to cause lysis of cells of cultured Microcystis aeruginosa or Anabaena circinalis, nor increase the amount of microcystin-LR or geosmin in the water. In this study the effect of ferric chloride an cultured cells of M. aeruginosa and A. circinalis was evaluated at concentrations that would occur in a water treatment plant. The results showed that ferric chloride did not appear to cause cell lysis of cultured M. aeruginosa and A. circinalis. However, ferric chloride seemed to stimulate growth of both M. aeruginosa and A. circinalis in the experiments with South Para Reservoir Water. (C) 1998 Elsevier Science Ltd. All rights reserved.