Changes in density and composition of algal assemblages in certain unit processes of two South African water purification plants

Abstract

The water purification plants at Virginia and Bothaville, South Africa, experience problems with cyanobacteria and other algae. Their algal assemblages were studied during 2010 and 2011 to determine the dominant species that may pose problems in purification. Cyanobacteria, diatoms and green algae were the dominant phytoplankton taxa and constantly succeeded each other in both plants. Blooms of cyanobacteria in the raw water were due to high temperatures and nitrogen concentrations. These organisms were mostly eliminated during sedimentation, indicating that the purification procedures were sufficient for effective removal of cyanobacteria. It was possible to relate algal assemblages, dominance and succession to prevailing environmental variables.