Efficacy of Coagulants and Ballast Compounds in Removal of Cyanobacteria (Microcystis) from Water of the Tropical Lagoon Jacarepaguá (Rio de Janeiro, Brazil)
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Eutrophication is considered the most important water quality problem in freshwaters and coastal waters worldwide promoting frequent occurrence of blooms of potentially toxic cyanobacteria. Removal of cyanobacteria from the water column using a combination of coagulant and ballast is a promising technique for mitigation and an alternative to the use of algaecides. In laboratory, we tested experimentally the efficiency of two coagulants, polyaluminium chloride (PAC) and chitosan (made of shrimp shells), alone and combined with two ballasts: red soil (RS) and the own lagoon sediment, to remove natural populations of cyanobacteria, from an urban brackish coastal lagoon. PAC was a very effective coagulant when applied at low doses (≤8 mg Al L−1) and settled the cyanobacteria, while at high doses (≥16 mg Al L−1) large flocks aggregated in the top of test tubes. In contrast, chitosan was not able to form flocks, even in high doses (>16 mg L−1) and did not efficiently settle down cyanobacteria when combined with ballast. The RS itself removed 33–47 % of the cyanobacteria. This removal was strongly enhanced when combined with PAC in a dose-dependent matter; 8 mg Al L−1 was considered the best dose to be applied. The lagoon sediment alone did not promote any settling of cyanobacteria but removal was high when combined with PAC. Combined coagulant and ballast seems a very efficient, cheap, fast and safe curative measure to lessen the harmful cyanobacteria bloom nuisance in periods when particularly needed, such as around the 2016 Olympics in Jacarepaguá Lagoon.
KeywordsBloom control Chitosan Cyanobacteria Eutrophication Mitigation PAC
This study was sponsored by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brasil, through a Science without Borders Grant, SwB (400408/2014-7) and by Fundação de Apoio à Pesquisa do Estado do Rio de Janeiro, FAPERJ, Brasil (111.267/2014). L. De Magalhães PhD scholarship was funded by Federal Government of Brazil, Ministry of Education, through CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Ministério da Educação). V.Huszar was partially supported by CNPq (309700/2013-2). M. Mucci PhD scholarship was funded by SwB/CNPq (201328/2014-3). This study was conducted under the flag of the CAPES (Brazil)/NUFFIC (The Netherlands) project 045/12.
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