Fouling of spiral-wound reverse osmosis (SWRO) membrane systems is a pervasive problem. Here we demonstrate that a mobile, low cost magnetic resonance imaging (MRI) apparatus operating at the earth’s magnetic field (low magnetic field, LF) can non-invasively (i) image the inside of a SWRO membrane system with glass fiber outside casing in a pressure vessel during cross flow operation and can (ii) detect the location of foulant, in this study sodium alginate. LF-MRI images of the module were successfully acquired in less than eight minutes using a spin-echo protocol, the internal structure of the modules was clearly evident and images compared well with high resolution MRIs obtained using a large-sized, costly high magnetic field superconducting MRI system. By parameter optimisation (specifically the echo time employed) it was possible to differentiate flowing and stagnant fluid in the clean and fouled membrane systems, and to determine the presence of alginate foulant on the feed-side of the fouled SWRO membrane system. This study motivates further investigation of the sensitivity of LF-MRI and the development of bespoke low cost LF-MRI hardware for the monitoring of industrial SWRO membrane installations.

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Reverse osmosis (RO) membranes inevitably foul due to the accumulation of material on the membrane surface. Instead of trying to reduce membrane fouling by chemical modification of the membrane, a different approach was taken here based on adding a sacrificial coating of two polyelectrolytes onto the membrane. After membrane fouling, this coating was removed by flushing with a highly saline brine solution, and a new coating was regenerated in situ to provide a fresh protective layer (PL) on the membrane surface. The utility of this approach was demonstrated by conducting four consecutive dead-end filtration experiments using a model foulant (alginate, 200 ppm) in a synthetic brackish water (2,000 ppm NaCl). Brine removal and regeneration of the PL coating restored the water flux to an average of 97 ± 3% of its initial flux, compared to only 83 ± 3% for the pristine membrane. The average water flux for the PL coated membranes was 15.5 ± 0.6 L m-2 h-1 until the flux was decreased by 10% versus its initial flux, compared to 13.4 ± 0.5 L m-2 h-1 for the non-treated control. The use of a sacrificial PL coating could therefore provide a more sustainable approach for addressing RO membrane fouling.

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Biofouling studies addressing biofouling control are mostly executed in short-term studies. It is unclear whether data collected from these experiments are representative for long-term biofouling as occurring in full-scale membrane systems. This study investigated whether short-term biofouling studies accelerated by biodegradable nutrient dosage to feed water were predictive for long-term biofouling development without nutrient dosage. Since the presence of a feed spacer has an strong effect on the degree of biofouling, this study employed six geometrically different feed spacers. Membrane fouling simulators (MFSs) were operated with the same (i) membrane, (ii) feed flow and (iii) feed water, but with feed spacers varying in geometry. For the short-term experiment, biofilm formation was enhanced by nutrient dosage to the MFS feed water, whereas no nutrient dosage was applied in the long-term experiment. Pressure drop development was monitored to characterize the extent of biofouling, while the accumulated viable biomass content at the end of the experimental run was quantified by adenosine triphosphate (ATP) measurements. Impact of feed spacer geometry on biofouling was compared for the short-term and long-term biofouling study. The results of the study revealed that the feed spacers exhibited the same biofouling behavior for (i) the short-term (9-d) study with nutrient dosage and (ii) the long-term (96-d) study without nutrient dosage. For the six different feed spacers, the accumulated viable biomass content (pg ATP.cm–2) was roughly the same, but the biofouling impact in terms of pressure drop increase in time was significantly different. The biofouling impact ranking of the six feed spacers was the same for the short-term and long-term biofouling studies. Therefore, it can be concluded that short-term accelerated biofouling studies in MFSs are a representative and suitable approach for the prediction of biofouling in membrane filtration systems after long-term operation.@en

Global freshwater demand has significantly increased over the past century and continued growth is expected in the coming century. Since more than 97 percent of the water in the world is seawater, desalination technologies have the potential to solve the fresh water crisis. Currently, the most used desalination technology is reverse osmosis, where a semipermeable membrane is used to separate the salt from the water. The driving force of reverse osmosis desalination is hydraulic pressure, which has to be greater than the osmotic pressure of the seawater. Due to the high hydraulic pressure reverse osmosis has a high energy demand. Lately, hybrid desalination systems, e.g. indirect desalination with forward osmosis combined with low pressure reverse osmosis are getting more importance. Forward osmosis is also a membrane based process that uses the osmotic pressure difference as driving force. One of the main advantages of forward osmosis is the limited amount of external energy requirement compared to reverse osmosis. The major problem of membrane desalination process is fouling, the accumulation of unwanted material on the membrane surface, causing performance decline and increase of costs. Several types of fouling can occur in membrane processes, biofouling (microbial biofilm formation), scaling (mineral salt precipitation), organic fouling (deposition of organic macromolecules) and colloidal fouling (deposition of particulate matter). In practice biofouling is considered as the major problem in membrane systems. @en