AWWA ACE63177

The impact of hydraulic retention time (HRT) for flocculation was examined with respect to its impact on fouling of immersed ultrafiltration membranes. Surface water from Lake Ontario, Canada was coagulated using polyaluminum chloride (PACl), aluminum sulphate (alum) and ferric chloride. Each source of coagulated water was sent to multiple flocculation tanks with different hydraulic retention times varying from 0-25 minutes. The impact of hydraulic retention time on fouling rate, TOC removal and metals residuals was evaluated. Longer HRT values significantly lowered the fouling rates for alum and ferric chloride, however little impact was found for PACl. No impact of HRT on TOC removals was found, however metals residuals were significantly affected by HRT in some cases. Includes 4 references, tables, figures.