A methodology for optimising the removal of cyanobacteria cells from a brazilian eutrophic water

Abstract

This work is concerned with optimizing the performance of the coagulation process in terms of the removal of intact cyanobacteria cells and saxitoxins (STX). The evaluation has been carried out through bench-scale jar tests to construct coagulation diagrams for aluminium sulphate, polyaluminium chloride (PACl) and ferric chloride. The test water was taken from a eutrophic surface source, collected at the inlet to the water treatment plant that supplies Ponta Grossa City, Brazil, at a time of high algal activity corresponding to a total of 108833 cells/mL of cyanobacteria. By constructing the coagulation diagram for turbidity, the optimal dose-pH conditions were used in subsequent tests involving both coagulation and sand filtration. In these tests the benefits of adding a cationic synthetic polymer and powdered activated carbon (PAC) to the overall treatment were investigated. From the results of the tests, the optimal dosages and pH for each coagulant, polymer and PAC were obtained corresponding to the lowest concentrations of cyanobacteria cells, STX and turbidity.