Advanced treatment of biologically treated heavy oil wastewater for reuse as boiler feed-water by combining ultrafiltration and nanofiltration

This work developed a new treatment system, which could effectively purify biologically treated heavy oil produced wastewater to the acceptable levels in the reused boiler at the Liaohe Oilfield, China. The ultrafiltration was used as pretreatment for the nanofiltration process. The filtration experiments of the selected wastewater were performed by modifying transmembrane pressure of the membranes. Results showed that the water quality of final permeate was improved after filtration with the ultrafiltration–nanofiltration membranes to successfully meet the admissible limit set by China’s Environmental Protection Agency. After coupling ultrafiltration with nanofiltration process, a stable permeate flux was observed, which was kept above 25 L/m2 h during 40 min of continuous treatment. It was also found that a flux recovery of 0.96 was obtained for the fouled ultrafiltration membrane after chemical cleaning with the mixture of NaOH and sodium dodecylsulphate (both at 0.2 wt.%).