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The Scientific World Journal
Volume 2014, Article ID 656101, 8 pages
Research Article

About Merging Threshold and Critical Flux Concepts into a Single One: The Boundary Flux

1Department of Chemical Materials Environmental Engineering, University of Rome “La Sapienza”, Via Eudossiana 18, 00184 Rome, Italy
2Chemical Engineering Department, University of Granada, 18071 Granada, Spain

Received 30 August 2013; Accepted 1 December 2013; Published 29 January 2014

Academic Editors: F. Oktar, Z. Qu, and Z. Zhang

Copyright © 2014 Marco Stoller and Javier M. Ochando-Pulido. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


In the last decades much effort was put in understanding fouling phenomena on membranes. One successful approach to describe fouling issues on membranes is the critical flux theory. The possibility to measure a maximum value of the permeate flux for a given system without incurring in fouling issues was a breakthrough in membrane process design. However, in many cases critical fluxes were found to be very low, lower than the economic feasibility of the process. The knowledge of the critical flux value must be therefore considered as a good starting point for process design. In the last years, a new concept was introduced, the threshold flux, which defines the maximum permeate flow rate characterized by a low constant fouling rate regime. This concept, more than the critical flux, is a new practical tool for membrane process designers. In this paper a brief review on critical and threshold flux will be reported and analyzed. And since the concepts share many common aspects, merged into a new concept, called the boundary flux, the validation will occur by the analysis of previously collected data by the authors, during the treatment of olive vegetation wastewater by ultrafiltration and nanofiltration membranes.