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Highlights1. PES/GO membranes were prepared in combination with various pore forming agents.2. Higher flux and improved rejection were achieved with the addition of GO.3. Synthetic solutions of protein and dyes were rejected efficiently at 1 bar. 4. Membrane fouling was reduced with the addition of GO.

Wastewater from textile dyeing plants contains a complex mixture of dyes, salts, surfactants and other additives which make it challenging to treat and harmful to release directly into the water system. Current treatment technologies are composed of many steps, increasing the cost and complexity of water management. Air gap membrane distillation (AGMD) is a versatile water treatment process which has potential to reduce the complexity of textile dyeing wastewater but has not yet been investigated for this application. In this work, we used commercial polytetrafluoroethylene (PTFE) membranes in AGMD to recover pure water from simulated textile wastewater containing NaCl and either sunset yellow (SY) or rose bengal (RB) dyes and sodium dodecyle sulfate (SDS) surfactant. 100% salt and colour removal was achieved for binary feed solutions (NaCl + SY or RB) over 20 h of testing, whilst maintaining stable fluxes between 11.7 and 12.6 L m -2 h -1 (LMH) throughout. After 24 h of continuous testing of the ternary feed solution (NaCl + RB + SDS) the flux was as high as 11 LMH with permeate conductivity less than 50 µS cm -1 . However after 70 h these had reached ~3 LMH and 421.8 µS cm -1 , respectively indicating a need for cleaning or back-flushing between batches. Parallel direct contact membrane distillation (DCMD) tests achieved lower colour and total carbon removal after just 8 hours of testing with the ternary feed solution. Comparisons between our tests and those found in the literature are made and indicate that AGMD may be the most suitable configuration for this application due to reduced flux decline and potentially higher thermal efficiency.

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This work demonstrates very high removal rates (below the detection limit of 0.045 ppb) of inorganic arsenic from water using electrospun polyvinylidene difluoride (PVDF) membranes enhanced by the addition of functionalized graphene oxide in membrane distillation. This shows potential for applications in the many parts of the world suffering from arsenic-contaminated groundwater. These membranes were enhanced by the addition of reduced graphene oxide functionalized with superhydrophobic polyhedral oligomeric silsesquioxane molecules (POSS-rGO) into the spinning solutions. The flux of the best-performing rGO-enhanced membrane (containing 2 wt % POSS-rGO) was 21.5% higher than that of the pure PVDF membrane and almost double that of a commercial polytetrafluoroethylene (PTFE) membrane after 24 h of testing, with rejection values exceeding 99.9%. Furthermore, the flux of this membrane was stable over 5 days (∼28 L m –2 h –1 ) of continuous testing and was more stable than those of the PTFE and control membranes when treating a concentrated fouling solution of calcium carbonate and iron(III) sulfate heptahydrate. It also achieved higher permeate quality in these conditions. The Young’s modulus and ultimate tensile strength of the best-performing membrane increased by 38 and 271%, respectively, compared to the pure polymer membrane, while both had similar porosities of ∼91%.

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