Water Science & Technology—WST Vol 61 No 1 pp 235–242 © IWA Publishing 2010 doi:10.2166/wst.2010.479

Turbidity removal effect and surface charge shift for electrochemically treated retentate without coagulant addition

Toshiya Uchibori, Takeshi Fujino and Takashi Asaeda

An electrolytic treatment method promoting dense aggregates was developed in order to thicken retentate quickly without coagulant addition. A kaolin suspension with a turbidity of 200 NTU with a large fraction of colloidal particles was used as the retentate. Comparative testing showed that the electrolytic treatment increased aggregate size and enhanced the turbidity removal effect up to 75% on average with increasing retention time. Even though the Al ion concentration in the treated retentate was much lower than 0.1 mg/L, along with the large upward shift of surface charge, the turbidity removal effect was enhanced considerably with independently stabilized pH compared with alum as the coagulant. Comparison between the charging behaviors indicated that the electrochemical treatment generates polymeric Al hydroxide species that form adsorption layers with fewer defects, thereby inducing a stronger removal effect.

Keywords: electrolytic treatment; polymeric Al hydroxide species; retentate; surface charge; turbidity removal effect

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