Acacia mearnsii de Wild Tannin-Based Flocculant in Surface Water Treatment

Abstract

Drinking water and wastewater treatment usually requires a coagulation/flocculation stage. Some disadvantages are presented by usual agents, above all linked to environmental, economical, and health aspects. Effectiveness of a new wood-derived flocculant agent has been studied, it consists of Acacia mearnsii modified tannin extract. Results have been very satisfactory; low flocculant dosage (up to 10 mg· L^{− 1}) may remove almost all suspended matter in surface water. Flocculant works better in acid pH (4–5), but an accurate dose minimizes the influence of this factor. Temperature does not affect effectiveness, but high initial turbidity may raise process efficiency. Duration of coagulation and flocculation stages seems to affect both positively to turbidity removal and in a non-interaction way. Dosage is much more important than both coagulation or flocculation stages. Treated water does not present either organic matter significantly increasing or a high residual tannin concentration. Microorganisms as total coliforms, fecal coliforms, and fecal streptococcus have been reduced up to 80%, 90%, and 99%, respectively.

Keywords:

• Coagulation–flocculation
• natural flocculants
• surface water
• tannins
• turbidity removal

This investigation has been supported by the Programa de Iniciación a la Investigación, Universidad de Extremadura, oriented modality, BANCO SANTANDER, S.A. subprogram, to COMISIÓN INTERMINISTERIAL DE CIENCIA Y TECNOLOGÍA (CICYT) CTQ 2007-60255/PPQ project as well as to JUNTA DE EXTREMADURA under PRI-07A031 project.