Nanofiltration of oil sands boiler feed water: Effect of pH on water flux and organic and dissolved solid rejection

Nanoflltration (NF) is a promising advanced treatment technique for oilfield wastewaters. In this study, we performed a crossflow NF on model boiler feed water (BFW) obtained from a thermal in-situ bitumen recovery process called steam assisted gravity drainage (SAGD) with the intent to remove dissolved organic matter and silica. Nanofiltration with a tight NF membrane was selected as the treatment technique since it provided reasonable product quality in a single-stage process and was found to be more energy efficient than reverse osmosis (RO). Two different feed pH values, 8.5 and 10.5, were investigated. Total organic carbon (TOC) and Si rejection of approximately 98% and divalent cation rejection greater than 99% was achieved at both pH values. Higher total dissolved solids (TDS) rejection, but lower flux rates were seen at pH 8.5 compared to pH 10.5. Surface characterization of the fouled membranes indicated the presence of organics (primarily carbon and oxygen) and inorganics (mainly silicon and iron) in the fouling deposits. Larger amounts of deposit were seen at pH 8.5 compared to pH 10.5. Increasing feed pH from 8.5 to 10.5 recovered the water flux more than 20% which demonstrated the critical role of pH as a pulsation technique to reduce membrane fouling. Fluorescence excitation emission matrix spectros-copy (FEEMs) on the feed and permeate showed that the organic matter that passed through the membrane was mainly hydrophilic compounds. Overall, this research indicated that NF is a viable treatment process for silica and TOC removal for SAGD BFW. (C) 2014 Elsevier B.V. All rights reserved.