Fouling characterization during initial stage of cross-flow ultrafiltration

Abstract

Ultrafiltration (UF) membrane is an attractive pretreatment technology used in desalination water system. However, the unavoidable membrane fouling over time is the key problem in the development of this technology. Fouling evaluation in the initial stage may provide relevant information about the fouling tendencies. In this work, the extent of fouling was investigated through a new method allows evaluating the fouling in cross-flow UF in the initial filtration stage. An empirical adjustment of flux decline data based on a bi-exponential equation with 4 coefficients is proposed for determining the Rcfi and RV − CF parameters. The first parameter Rcfi is defined as the initial cross-flow resistance. The second parameter RV − CF is defined as increasing resistance per specific volume of permeate in cross-flow. The measurement of the fouling parameters is evaluated in a laboratory facility with the following established conditions: (1) operation in cross-flow mode and (2) a flow measurement period limited to roughly 1 h. The procedure is intended to detect two different flow decline zones with different fouling processes at the initial stage of cross-flow filtration. The method applicability was tested with two cellulosic membranes of 10 kDa and 20 kDa and solutions of 4 kDa and 35 kDa polyethylene glycol (PEG) and alginate at different concentrations. In the case of the Rcfi parameter, the results show measurable values with high colloidal concentration of PEG. The RV − CF results shows a sensitive increase with foulant concentration, in different degree, depending on the type of solution and membrane used.