The scope of this project was to determine if low pressure membranes such as nanofiltration (NF) and ultra-low pressure reverse osmosis (ULPRO) membranes can meet water quality requirements necessary for indirect potable reuse while meeting acceptable operational parameters such as feed pressure, permeate flux, and flux decline. A total of 12 NF and ULPRO membranes were screened in this study and one ULPRO and one NF membrane were selected for a pilot-scale assessment (19 gpm) at a water reuse facility. Results of this study suggest that ULPRO and NF membranes can achieve similar removal efficiencies for the selected trace organics, nitrogen and bulk parameters tested as commonly employed RO membranes. While providing a similar water quality, these membranes can be operated at significantly lower feed pressures. These results suggest that ULPRO and NF membranes are viable for water reuse projects where a high permeate quality is required.
This research attempted to identify characteristic coordinates responsible for significant flux decline in low pressure membrane filtration, and to explain relationships among those coordinates with a modeling approach. A Pearson's correlation matrix supported that significant flux decline over a short time frame (low delivered DOC) is highly correlated with high molecular weight (MW) components of NOM. Simulations of flux decline by model equations were close to the experimental results revealing that low pressure membrane fouling is dominantly affected by NOM characteristics and membrane properties. One source water, exhibiting the highest flux decline, showed mostly cake formation as a fouling mechanism. The results indicate that significant flux decline is caused by high MW components leading to formation of a cake layer. Principal component analysis (PCA) revealed that high MW polysaccharides are the most important NOM component affecting significant membrane fouling.
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