Effect of cyanobacterial peptides and proteins on coagulation of kaolinite

Coagulation of peptides and proteins produced by the cyanobacterium Microcystis aeruginosa and their influence on the coagulation of hydrophobic kaolinite particles were investigated. For this purpose, the dose of ferric sulphate used as the coagulant was optimized and jar tests with kaolinite, peptides/proteins and both kaolinite and peptides/proteins were carried out under different pH conditions. At pH 4–5.5, the peptides/proteins were efficiently coagulated and peptides/proteins were also found to contribute to the coagulation of kaolinite particles at this pH. Charge neutralization and adsorption were found to be the dominant coagulation mechanisms. The coagulation efficiency and the character of the prevailing coagulation mechanism were strongly dependent on the charge characteristics of the peptides/proteins, kaolinite and hydrolysis products of iron, thus on the pH value. At a pH of about 6, the coagulation process deteriorated due to the formation of soluble Fe-peptide/protein complexes.