Non-destructive assessment of household reverse osmosis water treatment membrane biofouiling
Markwardt, Stephen Donald
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Reverse osmosis (RO) membrane treatment is well known for its ability to desalinate sea and brackish waters on a massive scale in large treatment plants. Conversely, RO membranes are also used to treat freshwater from questionable sources at the point of use. Both types of systems suffer from the negative effects of membrane fouling. There are four basic types of fouling: inorganic, colloidal, organic, and biofouling. Traditional methods for assessing fouling either cannot differentiate between the fouling types or destroy the membrane in the process. Currently, many new and innovative methods to non-destructively assess the degree and type of fouling inside a membrane unit are being researched. Most of these methods require the use of expensive electrodes and equipment which is not economical for point of use systems. This research was aimed at determining economical non-destructive methods to assess biofouling in point of use RO membrane treatment systems. Experimentation was performed on three parallel household RO membrane units operated under controlled feed water conditions to promote biofouling, inorganic fouling and a combination of both. Operational and biological parameters were monitored throughout the systems' lifespan. Membrane autopsies were also done to assess the degree and type of fouling. Statistical models were performed on the operational data to determine statistically relevant parameters between the fouling types that were subsequently validated by the membrane autopsies. Several non-destructive methods to assess the presence of biofouling were determined. Permeate flow rates decreased in a significantly different way when biofouling was present compared to when it was not. Large increases in permeate conductivity were also noted in membranes suffering from biofouling while they were not observed in membranes that had been inorganically fouled. The concentration of cell clumps in the retentate also increased in membranes experiencing biofouling while they did not increase in membranes that were inorganically fouled. These methods were found to not be sensitive enough to provide early warning for the presence of biofouling. However, these methods could be used to conveniently and economically assess the types of fouling problems being experienced household RO systems.