Application of improved rapid mixing for enhanced removal of dissolved organic matter and DBPFP (disinfection by-product formation potential) control

Abstract

Dispersion of metal coagulant should be completed in a fraction of a second before the metal hydroxide precipitate has formed. For this reason, so-called pump diffusion flash mixing (PDFM) has been proposed, and PDFM is one reasonable method to quickly disperse the hydrolyzing metal salts. In this study, we attempt to understand the difference of removal characteristics of natural organic matter (NOM) between PDFM and conventional rapid mixing (CRM) in a water treatment system, and to enhance the removal of NOM through the improved mixing process. Dissolved organic carbon (DOC) and turbidity removal by PDFM was higher than those by CRM, while specific-ultraviolet absorbance (SUVA) of treated water by PDFM was higher than that by CRM. NOM was more effectively removed by PDFM compared to CRM due to quick and uniform dispersion of coagulants. Though the hydrophilic fraction found as major faction in bulk NOM from Han River water is enriched in haloacetic acid precursor sites as compared to hydrophobic fraction, the hydrophilic fraction was more effectively removed by PDFM rather than CRM. Therefore, PDFM is effective and innovative process in reduction of DOC and DBPFPs as well as turbidity, and requires lower coagulant dosage compared to CRM.