Effects of dynamic or secondary-layer coagulation on ultrafiltration

This research focused on testing different coagulation pre-treatment techniques to improve membrane filtration in water separations, namely ultrafiltration (UF). These three techniques were 1) conventional coagulation, 2) forming a dynamic, or secondary, coagulant-based layer on the membrane, and 3) injecting the coagulant into the feed line so that it runs inline with the raw water across the membrane. Results showed that the dynamic membrane's mode of operation achieved higher steady state flux values than UF alone and than conventional coagulation pretreatment ahead of UF, while in-line coagulation displayed the worst flux decline. UF alone was ineffective in removing solids and dissolved organic carbon (DOC), while conventional coagulation and dynamic UF modes rejected solids and DOC at similar rates. Through membrane autopsies, irreversible fouling measurements for the dynamic membrane mode were significantly lower than for the conventional coagulation mode. Thus, a coagulant-based dynamic membrane has the potential to be an effective method to improve UF efficiency in water separation applications as well as to decrease pretreatment costs associated with operation. Upon reduction of associated costs, membranes can also become competitive in advanced wastewater treatment and water reuse processes.