-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 benchscale 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.

This work used Fenton's reagent as a coagulating agent in the treatment of water samples with high true colour caused by humic substances (HS) extracted from peat. In addition, the effects of the apparent molecular size of HS on coagulation, fl occulation and fl otation were studied. To that end, four distinct water samples having the same true colour were prepared using HS with different molecular sizes, which were obtained by ultrafi ltration fractioning. Through optimisation of coagulant dosage and coagulation pH, as well as posterior construction of coagulation diagrams for each water sample, it was verifi ed that the sample prepared with the smallest apparent molecular size of HS was the most diffi cult to treat, requiring higher coagulant (Fenton's reagent) dosages than samples prepared with larger HS molecular sizes. Furthermore, fi ltration experiments after dissolved air fl otation (DAF) were carried out in an attempt to simulate conventional treatment. The most representative results in fi ltered water were: apparent colour ≤ 3 HU; turbidity < 0.5 NTU; and residual iron concentration < 0.005 mg/L. The absorbance and total organic carbon values of fi ltered water samples were also very low, suggesting that the formation of disinfection by-products with chlorine would likely be insignifi cant.

Nesta pesquisa, foi realizado o estudo da recuperação do coagulante (cloreto de polialumínio) presente no lodo da estação de tratamento de água (ETA) Pitangui operada pela Companhia de Saneamento do Paraná (SANEPAR) em Ponta Grossa/PR, sendo este reutilizado no tratamento terciário (coagulação, floculação, decantação e filtração) do efluente da estação de tratamento de esgoto (ETE) Verde da SANE-PAR, a qual emprega reator anaeróbio de fluxo ascendente em manto de lodo (RALF) seguido de lagoa de polimento, tratando o esgoto sanitário do município. A solução de coagulante recuperado (por via ácida) apresentou concentração de 130 mgAl/L. Obteve-se como resultados mais significativos concentração de fósforo de 0,6 mg/L, concentração de sólidos sedimentáveis < 0,1 mg/L e demanda química de oxigênio (DQO) abaixo do limite de detecção do método para o efluente decantado após passar pelo tratamento físico-químico.

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