Effects of two-step cleaning sequences on foulant extraction from multibore ultrafiltration membranes in a pilot-scale membrane filtration system for surface water treatment

Abstract

The cleaning efficiencies of fouled multibore ultrafiltration membrane (UF_MB) operated from a pilot-scale UF process for surface water treatment were systemically investigated according to the sequences of two different cleaning solutions. The experimental results decisively confirmed that HPI DOM and HPO DOM/multivalent ions complexation significantly resulted in the fouling formations on UF_MB due to their neutral charge characteristic. The basic cleaning agent effectively extracted the organic foulants attached on UF_MB, indicating that the type of cleaning agent was a critical factor influencing on the cleaning efficiency of fouled UF_MB. However, the cleaning sequence 1 (CS-1: 0.1 M NaOH >0.1 M HCl; the total DOC = 725.77 mgC∙m^-2; the total TN = 146.35 mgN∙m^-2, total inorganic contents = 132.62 mg m^-2) much more effectively extracted the foulants on the UF_MB surfaces than the cleaning sequence 2 (CS-2: 0.1 M HCl >0.1 M NaOH; the total DOC = 604.49 mgC∙m^-2; the total of TN = 121.79 mgN∙m^-2, total inorganic contents = 73.43 mg m^-2). The morphological results also clearly showed that the cleaned UF_MB surface using CS-1 were effectively recovered, as compared with those using CP-2. Overall, this study implied that the hydroxide ions from the basic cleaning agent promoted the infiltration of the acidic cleaning agent into the densely formed fouling layers on the UF_MB surfaces and demonstrated that the cleaning sequences strategy could significantly govern the restoration of UF_MB performance during the pilot-scale surface water treatment system operation.

Keywords: Membrane autopsy; Membrane fouling; Multibore membrane; Pilot-scale membrane filtration system; Ultrafiltration.