The model binary/ternary mixtures for actual EPS solution extracted from the activated sludge in MBR using dead-end membrane filtration cell

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.

Graphene Oxide Membranes for Isotopic Water Mixture Filtration: Preparation, Physicochemical Characterization, and Performance Assessment

There is an increasing demand for nuclear reactors, driven by the global need for low CO₂ producing energy sources. The use of light (H₂O) or heavy water (D₂O) in a nuclear reactor environment produces radioactive tritiated heavy (HTO, DTO) water as an inevitable contaminant. Considering the need for tritiated water removal and also the high commercial value of purified water isotopes, technologies that can efficiently separate isotopic mixtures of water in nuclear reactors are highly desirable. This study presents an experimental approach for producing graphene oxide (GO) membranes and assessing their performance in the filtration of isotopic water mixtures. Specifically, using D₂O/H₂O mixtures as model systems, we investigate the effect of physicochemical properties of GO, as well as membrane preparation conditions on membrane filtration efficiency. We find that membranes assembled using larger GO platelets of lower oxidation level generally exhibit higher deuterated water (HDO, D₂O) rejection and filtrate flux. Moreover, membrane preparation conditions have a strong impact on the interlayer space between stacked GO nanoplatelets in the membrane, hence as a direct effect on filtration performance. Our experimental results also show a strong, nonmonotonic dependence of separation performance on operating temperature, as well as the existence of local temperature optima. Our work provides guidelines for simple and scalable preparation of GO membranes with very good mechanical stability, capable of achieving efficient separation of isotopic water.

Free-standing graphene oxide membrane with tunable channels for efficient water pollution control

In this study, a graphene oxide (GO) membrane with tunable interlayer spacing was fabricated by a facile method combining the inter-layer modification with external treatment. Congo red (CR), a negatively charged dye with π-orbital-rich groups, was adsorbed on nonoxide regions (G regions) of GO nano-sheets; thus, the interlayers were cross-linked by Ca²⁺ ions through chelating reaction. GO@CR nano-sheets π-π stacking interactions were changed by thermal reduction of the GO/Ca/CR membrane using a hot-pressing method. A broader effective inter-layer spacing control of the GO membrane in wet condition was achieved (from 7.7 ± 0.2 Å to 11.7 ± 0.25 Å). With the decrease of effective inter-layer spacing, the rejection of dyes and heavy metal ions gradually increased (i.e., methylene blue (99.5%), Cu²⁺ (98.6%), Ni²⁺ (97.2%), Pb²⁺ (97.2%) and Cd²⁺ (99.1%) at 7.7 Å) and a sufficient permeation flux was also achieved (17.1 L/m²·h·bar). Meanwhile, the diffusion mechanism of water molecules inside the interlayer gallery of GO laminates was explored by climbing image nudged elastic band (cNEB) method. The hydrogen bonding between water molecules and hydroxyl groups constrained the diffusion of water molecules; consequently, partially reduced hybrid GO membrane can show a better permeability for water and superior rejection for heavy metal ions.