Study of critical flux in ultrafiltration of seawater: New measurement and sub- and super-critical flux operations

Abstract

The concept “critical flux” allows for a relatively new operation optimization of ultrafiltration (UF) in fouling control strategies. The present studies mostly pay attention to colloids, organic solution and surface fresh water, which are of a less complex chemistry than that of seawater. In this work, “critical flux” was applied into the field of seawater desalination to investigate the utility of this concept for dealing with UF membrane fouling. Firstly, the nature flux mode, a new measurement for the critical flux, was proposed for UF in treating seawater and compared favorably with other measurements such as constant flux mode and constant pressure mode. Secondly, the definition (strong form J cs and weak form J cw) of critical flux for UF of seawater was evaluated to make sure whether or not the perfect operating condition (without UF fouling) is in existence. Thirdly, the effects of sub- and super-critical flux operations using different operating modes on the extent of membrane fouling were investigated by measuring hydraulic resistance. Moreover, a brief analysis of the economic feasibility of sub-/super-critical flux operations was covered. The results showed that the highest E p was yielded when operating in constant pressure mode with higher TMP under super-critical flux conditions, while the lowest E p in constant/nature flux mode with higher permeate flux under sub-critical flux conditions. When operating in constant/nature flux modes, lower E p was achieved under sub-critical flux conditions than under super-critical flux conditions.