The objective of this study was to demonstrate the viability and potential application of a high recovery NF/RO integrated treatment system concept. Compared to typically designed and operated high-pressure membrane systems, implementation of the NF/RO Integrated System could reduce
the volume of concentrate that needs to be disposed of by approximately one half. The integrated treatment system concept includes a primary NF system and a secondary RO system that is used to treat concentrate produced by the primary NF system. Permeate produced by each system is blended
together to achieve an overall recovery greater than 90%. To demonstrate the viability and potential application of the integrated treatment system concept, pilot-scale testing was conducted at the Sanitation Districts of Los Angeles County's San Jose Creek West Water Reclamation Plant
using final effluent as feedwater. The final effluent was first treated by a UF system before being fed to the NF/RO integrated system. The system was tested for approximately 2,000 hours at recoveries of 85% for the primary NF system and 54% for the secondary RO system. The operating fluxes
during testing were 15 gfd and 10 gfd for the primary NF and secondary RO systems, respectively. The results of this study demonstrate that the high recovery NF/RO integrated treatment system is a viable alternative for indirect potable reuse applications. The system is capable of operation
at relatively low overall feed pressure requirements compared to typical high-pressure membrane systems that employ RO membranes. The system achieved a high degree of rejection for some of the constituents that are relevant for indirect potable reuse projects including TOC and select chemicals
of emerging concern such as pharmaceuticals, personal care products, and endocrine disrupting compounds. However, relatively poor rejection was achieved for other relevant constituents including nitrate, NDMA, and 1,4-dioxane. Although the integrated system achieves relatively poor rejection
for these constituents, application of this system may still be feasible if it is employed as one component of a multi-barrier treatment system. Nitrate removal and control can be achieved biologically upstream of the integrated system. And, as is typically done, a downstream UV/AOP process
can be used for removal and control of NDMA and 1,4-dioxane.
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