Industrial Reverse Osmosis Membranes Research Articles

Efficient anisotropic desalination by layer-stacked black phosphorus carbide (α-PC) membrane

The crisis of global water scarcity is one of the most serious challenges that scientists and policymakers currently face. Breakthroughs in two-dimensional structures have provided a viable solution for the design and fabrication of filters in reverse osmosis (RO) desalination technologies. In this study, through molecular dynamics simulations, we show that the newly synthesized layer-stacked phosphorus carbide (α-PC) membrane can act as an auspicious performance filter for water desalination. The water permeability can reach ~30 L/cm2/day/MPa with wide interlayer distance (8 Å–12 Å) while blocking the salts, higher by two orders of magnitudes than the industrial RO membranes. Free energy analysis implies that the high ionic rejection (>98%) results from the large energy barriers (>8 kJ/mol) experienced by the ions entering α-PC nano-channels, while a considerably smaller barrier (<3 kJ/mol) is found for water transport. More interestingly, in striking contrast to previous desalination filters, the water translocation inside adjacent α-PC layers is determinant to the crystallographic directions of the buckled α-PC, resulting in highly anisotropic water permeability. Overall, our results provide a prospective candidate membrane for seawater desalination with inherently anisotropic filtering, which sheds light on the future design of the efficient filter.

Microbial biofilm communities on Reverse Osmosis membranes in whey water processing before and after cleaning

The need for recovering valuable compounds and water from side streams has increased the use of Reverse Osmosis (RO) membrane filtration in the food industry. RO membranes, however, are highly susceptible to biofilm formation, which may decrease performance and increase industrial costs. In order to identify and characterize the biofilm forming communities, industrial RO membranes from whey water recovery lines in a dairy industry were investigated before and after Cleaning-In-Place (CIP) treatments. Phase contrast and Confocal Laser Scanning Microscopy (CLSM) were used to visualize the biofilms. The Heterotrophic Plate Count (HPC) and yeast population were enumerated, and 16S, 26S, and ITS rRNA sequencing was employed to identify the dominant isolates. A dense biofilm of the filamentous yeast species Saprochaete clavata and Magnusiomyces spicifer was observed together with budding yeasts and Gram-negative bacteria. The filamentous yeasts had long hyphae, which spatially dominated the biofilm on the retentate and permeate surface and they were not inactivated by the standard CIP treatment. Since neither plate counts nor DNA-based methods reflect the wide membrane coverage of the filamentous yeasts, their role in biofouling may easily be underestimated. We suggest that filamentous yeasts are included in further research on fouling of water treatment membranes in the dairy industry when investigating the effect of different CIP treatments or new RO membrane properties.

Tannic acid treatment to deter microbial biofouling in flow cell system and on RO membrane in drip flow reactor

Membrane biofouling is a major obstacle, which considerably affects membrane performance and shortens membrane life span. In the present study, the biofouling prevention potential of the tannic acid (TA) was tested on single and mixed species culture under flow conditions in flow cell and on reverse osmosis (RO) membrane in drip flow reactor (DFR). Confocal laser scanning microscopy was used to acquire three dimensional (3D) images of biofilm samples and biofilm biovolume (μm3 ) was calculated via IMARIS software. The continuous dosing of TA at 20 mg/L to a flow cell led to a 98.2% (P < 0.05) biofilm reduction by PAO1 and 84.6% (P < 0.05) by a multispecies culture isolated from an industrial RO membrane. Furthermore, the continuous addition of TA to DFR led to 96.6% (P < 0.05) biofilm reduction by PAO1 and 98.9% (P < 0.05) by multispecies species, which further indicated the anti-biofouling effect of TA on RO membrane. These results suggest that TA can be a potential agent for the control of RO biofouling.

Nitric oxide treatment for the control of reverse osmosis membrane biofouling.

Biofouling remains a key challenge for membrane-based water treatment systems. This study investigated the dispersal potential of the nitric oxide (NO) donor compound, PROLI NONOate, on single- and mixed-species biofilms formed by bacteria isolated from industrial membrane bioreactor and reverse osmosis (RO) membranes. The potential of PROLI NONOate to control RO membrane biofouling was also examined. Confocal microscopy revealed that PROLI NONOate exposure induced biofilm dispersal in all but two of the bacteria tested and successfully dispersed mixed-species biofilms. The addition of 40 μM PROLI NONOate at 24-h intervals to a laboratory-scale RO system led to a 92% reduction in the rate of biofouling (pressure rise over a given period) by a bacterial community cultured from an industrial RO membrane. Confocal microscopy and extracellular polymeric substances (EPS) extraction revealed that PROLI NONOate treatment led to a 48% reduction in polysaccharides, a 66% reduction in proteins, and a 29% reduction in microbial cells compared to the untreated control. A reduction in biofilm surface coverage (59% compared to 98%, treated compared to control) and average thickness (20 μm compared to 26 μm, treated compared to control) was also observed. The addition of PROLI NONOate led to a 22% increase in the time required for the RO module to reach its maximum transmembrane pressure (TMP), further indicating that NO treatment delayed fouling. Pyrosequencing analysis revealed that the NO treatment did not significantly alter the microbial community composition of the membrane biofilm. These results present strong evidence for the application of PROLI NONOate for prevention of RO biofouling.