Pilot-Scale Testing of a High Recovery NF/RO Integrated Treatment System for Indirect Potable Reuse

Abstract

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.

Water Treatment and Desalination

“…Most reverse osmosis systems use cross flow mechanism to decrease membrane cleaning periods. As the fluid flows through the reverse osmosis membranes, the downstream, remove the reject away from in concentrated reject water (brine) [33][34][35][36].…”

“…Charged nanofiltration membrane rejects ions with negative charge, such as phosphate or sulfate. Non-charged nanofiltration membrane rejects dissolved matter and uncharged in accordance of the shape and size of the molecule, while for positively charged ions, the rejection is affected by the membrane charge and according to the membrane fouling mechanism [17,32,34].…”

Nanofiltration – Theory and Application

“…Subsequent pilot testing with two loose and low fouling NF membranes demonstrated that significant cost savings could be attained however, the major disadvantages were found to be poor rejection of nitrate, and greater number of organic contaminant detections in NF permeates compared with the RO membrane [69,133]. Due to potential advantages of using loose NF for wastewater reclamation, the Los Angeles County Sanitation District of Southern California recently conducted pilot testing of a dual NF/RO treatment process for indirect potable reuse applications using surface spreading for groundwater recharge [135]. Due to potential advantages of using loose NF for wastewater reclamation, the Los Angeles County Sanitation District of Southern California recently conducted pilot testing of a dual NF/RO treatment process for indirect potable reuse applications using surface spreading for groundwater recharge [135].…”

Membrane Processes

“…In San Diego, CA, where 85% of the water is imported, Steirer (2011) (Mansell et al, 2011). The pilot was run at 85% recovery for the primary NF system and 54% recovery for the secondary RO system, and showed that high recovery NF/RO is a viable alternative, achieving greater than 90% overall recovery.…”