(725c) Impact of Organic Compounds in Produced Water on Desalination By Membrane Distillation
AIChE Annual Meeting
Friday, November 20, 2020 - 8:30am to 8:45am
Membrane Distillation (MD) is an emerging potential solution for desalination of produced water. Unlike pressure-driven membrane desalination processes, the main driving force for membrane distillation is the vapor pressure difference across the membrane, which is not significantly affected by salinity. Therefore, MD is uniquely suitable for treatment of high salinity produced water. The presence of high concentration of organic compounds in produced water may be challenging for MD technology because they can cause membrane fouling and wetting and reduce the selectivity of this process. In particular, surfactants can promote membrane wetting by adsorbing onto the membrane surface to alter its hydrophobicity. If that happens, it would be necessary to remove surfactants in a pre-treatment step to achieve high water recovery without membrane fouling to maintain high permeate flux.
In this study, raw produced water from Permian Basin, Texas was obtained and tested in a laboratory-scale membrane distillation system. Increase in permeate salinity observed when treating this produced water was attributed to membrane wetting was observed in this system. It was found that the total organic carbon (TOC) of the produced water can be reduced from 120 mg/L to 20 mg/L by biological treatment and further reduced to 2 mg/L by activated carbon adsorption. However, this reduction in TOC did not eliminate apparent membrane wetting. These preliminary results suggest that membrane wetting by this produced water is primarily due to low surface tension caused by non-adsorbable polar compounds or due to volatilization of organic or inorganic salts present in the produced water.
Several organic compounds and surfactants, including âNonyl phenol ethoxylateâ, were detected in both raw water and the permeate. Polymeric form of this surfactant âNonylphenol polyethylene glycolâ was tested in synthetic produced water and membrane wetting was observed. However, membrane wetting due to âNonylphenol polyethylene glycolâ was irreversible while the wetting caused by the actual produced water can be reversed by simple washing with DI water. Several synthetic solutions were tested for their ability to pass through the membrane and it was found that volatilization of organic and inorganic salts is the primary the observed increase in permeate conductivity. Therefore, the usual practice of using the permeate conductivity to monitor membrane wetting may not be appropriate when treating complex wastewaters.