The effect of sedimentation by chemical coagulants and the rapid sand filters on algal removal at drinking water treatment plants in Egypt

Abstract

Abstract Background The Nile River included diverse phytoplankton compositions belonging to five main phytoplankton categories. Algae have been classified and identified through comparative morphology. Results The Pyrrophyta, Charophyta, Cyanophyta, Chlorophyta, and Bacillariophyta were presented through the full period of investigation with 1, 3, 14, 23, and 28 species, respectively. Therefore, it may be important to note that diatoms were recorded as an abundant group in all investigated samples. The numbers of diatoms ranged between 1.45 × 106 and 1.18 × 107 Organism/l, this was followed by green algae that ranged from 7.0 × 105 to 1.22 × 106 Organism/l. While the lowest count of blue-green algae was ranged between 1.6 × 105 and 7.03 × 105 Organism/l. The treatment of Nile water using two chemical coagulants "aluminum sulfate (Al2(SO4)3⋅16H2O) and aluminum oxide (Al2O3)" removed algae by about 85% and 90%, respectively. As for, the Cyanophyceae species, they were removed completely in treated water using the sedimentation, filtration, and chlorination process. The sedimentation basins removed from 20 to 100% of the total algal count while the rapid sand filters removed from 65 to 100% of the total algal count during the water treatment that depends on the species of algae. Conclusions This study concluded that the removal of algae from the Nile water may be more or less easy depending on the nature of the prevailing algal group. Water treatment plants must modify alum and chlorine doses in their water treatment processes according to the count and species of the algal groups, to provide an aesthetically acceptable and biologically safe water supply.