Application of nanofiltration to water management options for oil sands operations

A membrane separation process, nanofiltration (NF), has been applied successfully for treatment of oil sands waters, particularly to water softening and removal of toxic components. This study focused on the selection of appropriate membranes and the assessment of their performance for the removal of polyvalent ions (hardness) and naphthenic acids (NA) (the main acute toxicant in oil sands process-affected waters) from both imported and potential discharge waters. Experiments were carried out using a bench-scale flat sheet membrane system with several commercially available NF membranes. It was found that after membrane filtration, both water hardness and the NA concentrations were reduced significantly (>95%). A permeate flux was maintained at 15 L/m2/h or higher, with a retentate volume of about 10% of the feed volume.

Results of the research conducted in this study suggest that membrane NF is an effective process for the improvement of water management in oil sands operations, both for selective water softening and for potential discharge requirements. Proper application of membrane technologies can result in better reuse of process waters, reduction of raw water intake by replacement with NF produced water and the improved possibility of meeting discharge water quality criteria by reduction of toxicity properties in process-affected waters. Specifically, it was found that: 1. NF was effective in removing divalent ions of Ca2+, Mg2+ and SO42–, which were responsible for high water hardness, with average rejection efficiency of more than 95%. NF may provide an efficient approach for water softening of selective water streams that could be preferable to wider scale application of lime-softening technology. 2. NF was effective in the removal of TOC and in particular the naphthenic acids, with rejection efficiency of generally >95%. This should be sufficient to remove acute toxicity associated with these materials in process-affected waters. 3. Among membranes tested in this work, Desal 5 was found to be the most suitable membrane for the applications discussed for oil sands waters.