Ultrafiltration Testing on Tertiary Effluent from the North City Water Reclamation Plant (NCWRP): Results and Lessons Learned

Ultrafiltration (UF) membranes have already gained worldwide acceptance in the treatment of drinking water for their removal of chlorine resistant pathogens such as cryptosporidium. Tertiary treatment with UF has been established, although with a lower level of knowledge and number of installations. The City of San Diego has incorporated Ultrafiltration (UF) membranes into their 1.0 MGD Advance Water Purification Demonstration Project where municipal tertiary effluent from the North City Water Reclamation Plant is treated by UF followed by Reverse Osmosis (RO), UV and an Advanced Oxidation process. Should this Demonstration Project move forward into a full-scale plant the treated water would then be sent to a reservoir via a 22 mile pipeline, and further treated at a local Drinking Water Treatment Plant before distribution to City water customers.This paper will discuss the performance of hollow fiber membrane modules in treating tertiary effluent over a one year plus period. Parameters critical to defining the performance of a hollow fiber membrane system will be discussed such as Trans-Membrane Pressure (TMP), Flux and temperature corrected Permeability. Membrane Integrity will also be discussed with analysis of feed and filtrate turbidity along with the Direct Integrity Test (DIT) results of the daily Pressure Decay Test (PDT). Details of CIP cleanings will be presented including cleaning chemicals, dosage rates and the results of each CIP clean. Lastly, the influence of pretreatment on UF performance at the North City Plant will be presented. As the demand for potable water grows in urban areas Indirect Potable Reuse (IPR) is an attractive option for providing an additional purified sustainable water source to local water supplies. Understanding the operation and design options available of a UF system in this application will assist Utilities in their choice of unit operations for planning an advanced water purification facility.