A study of the physical and chemical damage on reverse osmosis membranes detected by autopsies
Water treatment by reverse osmosis technology has as main aim to reject the maximum percentage of ions from raw water, giving as much treated water flow as possible. When there is a loss in these two parameters performance, it is essential to find the source of the failure, in order to use the necessary tools for its recovery. At this point, membrane autopsies are a very valuable source of information in order to understand the mechanisms that may have produced membrane capabilities loss.
Genesys Membrane Products (GMP) laboratory has developed during last decade more than 600 autopsies of membranes from all over the world. Therefore all the data obtained from these autopsies are a very valuable source of information about membrane failures. These membranes studies have shown that in almost the 75% of the cases, fouling is the main cause of membrane failures and this is one of the reasons because there is a broad research developed in fouling mechanisms understanding. The data obtained from these autopsies, have demonstrated also that the worst and main impact of fouling on membranes performance is the damage of polyamide layer and on rejection capabilities (1). During the performance of reverse osmosis membranes in plants, there are many different processes that can damage the membrane surface: increases in differential pressure, backpressure phenomena, abrasion processes from fouling, massive or micro damages from scaling, oxidation processes or even degradation with time or cleanings. These damages, are commonly related to an increase in flow rate permeate and in a salt rejection decrease.
A well knowledge of membrane damage is very important considering that in more than the 30% of the membranes autopsied in GMP this phenomenon was found severe. These phenomena study is important also because, in many cases, damage is hidden by fouling and autopsies are the only way to detect a first step damage that could be prevented in plant if appropriated remedies are applied. GMP autopsies results demonstrate that almost the 80% of the studied membranes show slight signals of damage on the membrane surface, which were probably not detected in plant considering only performance failures.
In this study, statistical analysis from autopsies data will be used to check membrane damages, considering plants performance, membrane position, kind of fouling, feed water type, etc.
From the results obtained during the autopsies carried out on GMP laboratory and some preliminary tests carried out with some new techniques, the author intends to do also a review of the different analytical tools available for membrane damages detection and to check their advantages and disadvantages.