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Journal of Water Supply: Research and Technology—AQUA Vol 56 No 5 pp 327–333 © IWA Publishing 2007 doi:10.2166/aqua.2007.009

Color removal by coagulation, flocculation and sedimentation from water containing humic substances with different apparent molecular sizes

Sandro X. Campos, Eduardo Ribeiro de Azevedo, Tito J. Bonagamba, Eny M. Vieira and Luiz Di Bernardo

State University of Ponta Grossa, UEPG, Ponta Grossa, PR Brazil
Institute of Physics of São Carlos, University of São Paulo, São Carlos, Brazil
Institute of Chemistry of São Carlos, University of São Paulo, São Carlos, Brazil
Department of Hydraulics and Sanitation, School of Engineering at São Carlos, University of São Paulo, Brazil, Av. Trabalhador    São-Carlense, #400, 13 566-570, São Carlos, SP Brazil Tel.: 16 3373 95 28; Fax: 16 3373 95 50. bernardo@sc.usp.br


ABSTRACT

Samples of water with true color of approximately 100 HU, prepared with humic substances of different molecular sizes (filtered through a 0.45 mm membrane with weights in the range of >100 kDa; 100 to 30 kDa; <30 kDa) were studied in order to verify the influence of the apparent molecular size on the performance of coagulation, flocculation and sedimentation of flocs formed using aluminum sulfate as coagulant. To achieve the same degree of color removal, the water samples with higher apparent molecular size fractions required lower dosages of aluminum sulfate (approximately 50% of those necessary for the water prepared with the fraction of the smallest molecules). The results of nuclear magnetic resonance (NMR) and Infrared Spectroscopy (FTIR) studies demonstrate that, under the same conditions, the higher the number of oxygen-containing functional groups, the lower the level of color removal becomes.

Keywords: apparent molecular size of humic substances; coagulation; color; flocculation; sedimentation


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