Is semi-flocculation effective as pretreatment to ultrafiltration in wastewater treatment?

In this study, ferric chloride (FeCl3) flocculation was used as a pretreatment to ultrafiltration (UF) in treating synthetic wastewater containing synthetic organic matter (SOM). The effect of flocculant dose was studied in terms of organic removal and membrane flux decline. The UF with optimum dose of FeCl3 (68 mg L−1) did not experience any flux decline during the whole operation of 6 h. The preflocculation with a smaller dose of 20 mg L−1 of FeCl3 led to a severe flux decline in the UF (more than 65% in 6 h). To understand the phenomenon of the flux decline of UF, the MW ranges of SOM removed by different doses of FeCl3 and by the post treatment of UF were studied. Flocculation with at least 50 mg L−1 of FeCl3 dose was found to be necessary to avoid any significant flux decline and to obtain superior DOC removal.