Abstract

In this study, assays were carried out to evaluate the efficiency of cactus Opuntia stricta cladodes as a coagulant for removal of cyanobacteria cells. To carry out the coagulation assays, water from eutrophic reservoir Bodocongó, in Brazilian semiarid, with cyanobacteria bloom of Microcystis aeroginosa, Plankthotrix isothrix and Cylindrospermopsis raciborskii were sampled. This water was submitted to coagulation with different forms of O. stricta cladodes (crude, pulverized and solution), concentration (10; 50 and 100 mg/L) and time (5, 15, 30, 60 and 120 min). In order to assess cell removal, readings were made in aliquots of 5 mL of samples analyzed by triplicates counting on sedimentation chambers using an inverted optical microscope, according to the Utermöhl method.  Dosage of 100 mg/L from the solution form of O. strica cladodes gave the best cell and turbidity removal. Colonial species were fast removed than filaments. The most removal occurred in the first 30 min of experiments. No significant differences were observed for pH changes in the experiments. O. stricta cladodes gave satisfactory results in reducing cyanobacteria cell in water; however, complete removal was not obtained; further studies are necessary to evaluate the best concentrations and the mechanisms of cyanobacteria removal.

Key words: Eutrophication, biobased coagulants, Cactus.