Pilot-scale study on the treatment of basal aquifer water using ultrafiltration, reverse osmosis and evaporation/crystallization to achieve zero-liquid discharge

• Basal aquifer water was treated using UF, RO, and evaporation-crystallization.
• The RO permeate TDS levels were below the maximum target of 1000 mg/L.
• Membrane autopsies indicated that iron was the primary foulant on the membranes.
• Softening of the RO reject was required to avoid scaling in the evaporator.
• The ZLD approach was effective to produce freshwater and minimize brine discharges.

Basal aquifer water is deep groundwater found at the bottom of geological formations, underlying bitumen-saturated sands. Some of the concerns associated with basal aquifer water at the Athabasca oil sands are the high concentrations of hardness-causing compounds, alkalinity, and total dissolved solids. The objective of this pilot-scale study was to treat basal aquifer water to a quality suitable for its reuse in the production of synthetic oil. To achieve zero-liquid discharge (ZLD) conditions, the treatment train included chemical oxidation, polymeric ultrafiltration (UF), reverse osmosis (RO), and evaporation-crystallization technologies. The results indicated that the UF unit was effective in removing solids, with UF filtrate turbidity averaging 2.0 NTU and silt density index averaging 0.9. Membrane autopsies indicated that iron was the primary foulant on the UF and RO membranes. Laboratory and pilot-scale tests on RO reject were conducted to determine the feasibility of ZLD crystallization. Due to the high amounts of calcium, magnesium, and bicarbonate in the RO reject, softening of the feed was required to avoid scaling in the evaporator. Crystals produced throughout the testing were mainly sodium chloride. The results of this study indicated that the ZLD approach was effective in both producing freshwater and minimizing brine discharges.