Armor-Structured Interconnected-Porous Membranes for Corrosion-Resistant and Highly Permeable Waste Ammonium Resource Recycling.

Ammonium recovery from wastewater by gas-permeable membranes is promising but suffers from the tradeoff between membrane stability and permeability under harsh operating conditions. Chemical-resistant membranes display modest permeability due to the poor solubility and processibility; chemically active membranes are easier to be endowed with better permeability however hinder by instability. To resolve such a problem, we cleverly design a novel membrane configuration via one-step solution-electrospinning, with the chemical-active component (low-strength fluorine polymer) as the inner skeleton to construct interconnected porous structures and the chemical-resistant component (high-strength fluorine polymer) as the outer armor to serve as a protective layer. Due to the significantly enhanced mass transfer coefficient, the interconnected-porous armor-structured membrane exhibited much higher permeability for NH4+-N recovery, which was 1.4 and 5 times that of the traditional PTFE membrane and PP membrane, respectively. Through long-term intermittent and consecutive experiments, the reusability and durability of the armor-structured nanofibrous membrane were verified. When treating actual hoggery wastewater with complicated water quality, the armor-structured nanofibrous membrane also displayed robust stable performance with excellent antiwettability. The mechanisms of membrane formation, corrosion resistance, and mass transfer were discussed in detail.

In Situ Three-Dimensional Welded Nanofibrous Membranes for Robust Membrane Distillation of Concentrated Seawater.

Membrane distillation (MD) is a promising technology for treating the concentrated seawater discharged from the desalination process. Interconnected porous membranes, fabricated by additive manufacturing, have received significant attention for MD technology because of their excellent permeability. However, their poor hydrophobic durability induced by the deformation of pores constrains their water desalination performance. Herein, an in situ three-dimensional (3D) welding approach involving emulsion electrospinning is reported for fabricating robust nanofibrous membranes. The reported method is simple and effective for welding nanofibers at their intersections, and the reinforced membrane pores are uniform in the 3D space. The results show that the in situ 3D welded nanofibrous membrane, with a stability of 170 h and water recovery of 76.9%, exhibits better desalination performance than the nonwelded (superhydrophobic) nanofibrous membrane and the postwelded (superhydrophobic) nanofibrous membrane. Furthermore, the stability mechanism of the in situ 3D welded nanofibrous membrane and the two different wetting mechanisms of the nonwelded and postwelded nanofibrous membranes were investigated in the current work. More significantly, the in situ 3D welded nanofibrous membrane can further concentrate the actual concentrated seawater (121°E, 37°N) to crystallization, demonstrating its potential applications for the desalination of challenging concentrated seawater.

Low-Tortuosity Water Microchannels Boosting Energy Utilization for High Water Flux Solar Distillation.

Solar distillation through photothermal evaporators has approached solar light energy (E1) limit under no solar concentration but still suffers from modest vapor and clean water production. Herein, a nature-inspired low-tortuosity three-dimensional (3D) evaporator is demonstrated to significantly improve water production. The solar evaporator, prepared from polypyrrole-modified maize straw (PMS), had upright vascular structures enabling high water lifting and horizontal microgaps facilitating broad water distribution to the out-surface. Consequently, this novel PMS evaporator dramatically enhanced the utilization of the solar heat energy stored in the environment (E2) for promoting evaporation. The maximum vapor generation rate of a single PMS respectively increases 2.5 and 6 times compared with the conventional 3D evaporators and the planar evaporators of an identical occupied area. Consequently, a scaled-up PMS array achieved a state-of-the-art vapor generation rate of 3.0 L m-2 h-1 (LMH) under a simulated condition and a record-high clean water production of 2.2 LMH for actual seawater desalination under natural conditions (1 sun intensity). This breakthrough reveals great potentials for cost-effective freshwater production as well as the rational design of high-performance photothermal evaporators for solar distillation.

Quasi-critical condition to balance the scaling and membrane lifespan tradeoff in hypersaline water concentration.

Mineral scaling is an inconvenient obstacle for membrane distillation in hypersaline wastewater concentration applications, compromising membrane lifespan to maintain high water recovery. Although various measures are devoted to alleviating mineral scaling, the uncertainty and complexity of scale characteristics make it difficult to accurately identify and effectively prevent. Herein, we systematically elucidate a practically applicable principle to balance the trade-off between mineral scaling and membrane lifespan. Through experimental demonstration and mechanism analysis, we find a consistent concentration phenomenon of hypersaline concentration in different situations. Based on the characteristics of the binding force between the primary scale crystal and the membrane, the quasi-critical concentration condition is sought to prevent the accumulation and intrusion of mineral scale. The quasi-critical condition achieves the maximum water flux on the premise of guaranteeing the membrane tolerance, and the membrane performance can be restored by undamaged physical cleaning. This report opens up an informative horizon for circumventing the inexplicable scaling explorations and develops a universal evaluation strategy to provide technical support for membrane desalination.

Overlooked flocs in electrocoagulation-based ultrafiltration systems: A new understanding of the structural interfacial properties.

An integrated ferrate-induced electrocoagulation-ultrafiltration (FECUF) process is proposed to cope with the growing demand for water treatment. Although flocs formed during the electrocoagulation (EC) process are useful for contaminant reduction and mitigation of membrane fouling, few studies have been focused on their structures and properties. Herein, we investigated the formation and structural transformations of flocs and their responses to organic matter, as well as the relationships between their interfacial properties and membrane fouling mitigation. It was found that ferrate contributed to the fast formation of flocs during the ferrate-induced electrocoagulation (FEC) process, which accelerated the FECUF process. Physicochemical analyses indicated that the flocs formed in the FEC process were mainly composed of Fe(III)-(hydr)oxides with abundant hydroxyl groups and poor crystallinity, which allowed complexation with NOM. Therefore, the mobilities of the NOM and the soluble coagulant ions were reduced. The responses of flocs to NOM suggested that the period of 0-20 min resulted in the most efficient NOM removal. In addition, two patterns revealed the relationships between the interfacial properties of the small colloidal particles (SCPs) and the membrane filtration performance: i) the decline in the initial flux was closely related to the composition (gel-type substances or metal-(hydr)oxides) of the SCPs and ii) the steady-state flux was influenced by the energy barrier between the SCPs. However, when the SCPs had the same composition, the interfacial properties influenced both the initial flux and the steady-state flux. This study provides an alternative FECUF process for intensive upgrades of centralized water treatment systems.

Synergy of feed-side aeration and super slippery interface in membrane distillation for enhanced water flux and scaling mitigation.

Membrane distillation (MD) is an acknowledged promising technology for desalinating hypersaline brine, and as such can be a suitable candidate to further concentrate the seawater discharged from reverse osmosis process. Mineral scaling represents a major constraint against the application of MD for further desalination of concentrated seawater, especially when considering CaSO4 (gypsum) and NaCl. Up until now, it has been difficult to rely solely on membrane modification to mitigate CaSO4 scaling. Permeate-side aeration can lessen CaSO4 scaling, but does not permit to increase the water flux. Herein, we proposed the synergy of feed-side aeration and super slippery interface to perform concentrated seawater desalination via direct contact membrane distillation. The results of this study show that this synergistic effect could significantly increase the water flux, which was approximately 1.5 times higher in comparison to the membrane without aeration. Moreover, the synergistic effect effectively alleviates the complex scaling of concentrated seawater, achieving 90 wt% water recovery rate. Based on the observed results, we elucidated the mechanisms governing the enhanced water flux and scaling mitigation driven by the synergistic effect. In addition, we studied the optimal working condition for this system, unveiling that low-intensity large bubbles are more suitable as they lead to a better equilibrium between the economics and functionality of the process.