Oil-in-water separation with graphene-based nanocomposite membranes for produced water treatment

The treatment of wastewater from the oil and gas industry presents a very specific problem because the wastewater produced is comprised of a complex mixture of oil and water that can be difficult to treat. In this work, polybenzimidazole (PBI), graphene oxide (GO) and reduced GO (rGO) nanocomposite membranes were developed via the common blade coating and phase inversion technique for the treatment of produced water from the oil and gas industry. The nanocomposite membranes were dip-coated by polydopamine (PDA), which is known for its antifouling properties. For the industrially relevant produced water, stable emulsions with high salinity, sharp unimodal size distribution and average oil droplet size of less than 500 nm were prepared. The incorporation of just a few weight percent GO into the PBI matrix resulted in superior oil-removal efficiency up to 99.9%, while maintaining permeance as high as 91.3 ± 3.4 L m−2 h−1 bar−1. The presence of GO also increased the mechanical stability of the membrane. The biofouling test of the nanocomposite membrane over 180 days showed remarkable improvement compared to the pristine PBI membrane. The nanocomposite membranes described in this work demonstrated promising long-term performance for oil-in-water emulsion separation as well as antifouling and antimicrobial properties without any alkaline or acidic cleaning. The membranes were capable of de-oiling high salinity emulsions with excellent reusability, highlighting that these membranes are promising for produced water treatment under harsh industrial conditions.