Dimensionally controlled graphene-based surfaces for photothermal membrane crystallization.

Membrane-based photothermal crystallization - a pioneering technology for mining valuable minerals from seawater and brines - exploits self-heating nanostructured interfaces to boost water evaporation, so achieving a controlled supersaturation environment that promotes the nucleation and growth of salts. This work explores, for the first time, the use of two-dimensional graphene thin films (2D-G) and three dimensional vertically orientated graphene sheet arrays (3D-G) as potential photothermal membranes applied to the dehydration of sodium chloride, potassium chloride and magnesium sulfate hypersaline solutions, followed by salt crystallization. A systematic study sheds light on the role of vertical alignment of graphene sheets on the interfacial, light absorption and photothermal characteristics of the membrane, impacting on the water evaporation rate and on the crystal size distribution of the investigated salts. Overall, 3D-G facilitates the crystallization of the salts because of superior light-to-heat conversion leading to a 3-fold improvement of the evaporation rate with respect to 2D-G. The exploitation of sunlight graphene-based interfaces is demonstrated as a potential sustainable solution to aqueous wastes valorization via recovery in solid phase of dissolved salts using renewable solar energy.

Fouling and performance of outer selective hollow fiber membrane in osmotic membrane bioreactor: Cross flow and air scouring effects.

This study assessed impacts of cross-flow velocity (CFV) and air scouring on the performance and membrane fouling mitigation of a side-stream module containing outer-selective hollow fiber thin film composite forward osmosis membrane in osmosis membrane bioreactor (OMBR) system for urban wastewater treatment. CFV of draw solution was optimized, followed by the impact assessment of three CFVs on feed solution (FS) stream and periodic injection of air scouring into the side-stream module. Overall, the OMBR system exhibited high and stable performance with initial water flux of approximately 15 LMH, high removal efficiencies of bulk organic matter and nutrients. While FS's CFVs insignificantly affected the performance and membrane fouling, regular air scouring showed substantial impact with better performance and high efficiency in mitigating membrane fouling. These results indicated that periodic air scouring can be applied into the side-stream membrane module for efficient fouling mitigation without interruption the operation of the OMBR system.