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

Crosslinking and fluorination reinforced PTFE nanofibrous membrane with excellent amphiphobic performance for low-scaling membrane distillations

Membrane distillation (MD) has emerged as a promising technology for desalination and concentration of hypersaline brine. However, the efficient preparation of a structurally stable and salinity-resistant membrane remains a significant challenge. In this study, an amphiphobic polytetrafluoroethylene nanofibrous membrane (PTFE NFM) with exceptional resistance to scaling has been developed, using an energy-efficient method. This innovative approach avoids the high-temperature sintering treatment, only involving electrospinning with PTFE/PVA emulsion and subsequent low-temperature crosslinking and fluorination. The impact of the PVA and PTFE contents, as well as the crosslinking and subsequent fluorination on the morphology and MD performance of the NFM, were systematically investigated. The optimized PTFE NFM displayed robust amphiphobicity, boasting a water contact angle of 155.2º and an oil contact angle of 132.7º. Moreover, the PTFE NFM exhibited stable steam flux of 52.1 L·m-2·h-1 and 26.7 L·m-2·h-1 when fed with 3.5 wt % and 25.0 wt % NaCl solutions, respectively, and an excellent salt rejection performance (99.99 %, ΔT = 60 °C) in a continuous operation for 24 h, showing exceptional anti-scaling performance. It also exhibited stable anti-wetting and anti-fouling properties against surfactants (sodium dodecyl sulfate) and hydrophobic contaminants (diesel oil). These results underscore the significant potential of the PTFE nanofibrous membrane for practical applications in desalination, especially in hypersaline or polluted aqueous environments.

Bubble Turbulent Gas-Permeable Membrane for Ammonia Recovery from Swine Wastewater: Mass Transfer Enhancement and Antifouling Mechanisms

Recovering ammonium from swine wastewater employing a gas-permeable membrane (GM) has potential but suffers from the limitations of unattractive mass transfer and poor-tolerance antifouling properties. Turbulence is an effective approach to enhancing the release of volatile ammonia from wastewater while relying on interfacial disturbance to interfere with contaminant adhesion. Herein, we design an innovative gas-permeable membrane coupled with bubble turbulence (BT-GM) that enhances mass transfer while mitigating membrane fouling. Bubbles act as turbulence carriers to accelerate the release and migration of ammonia from the liquid phase, increasing the ammonia concentration gradient at the membrane-liquid interface. In comparison, the ammonium mass transfer rate of the BT-GM process applied to real swine wastewater is 38% higher than that of conventional GM (12 h). Through a computational fluid dynamics simulation, the turbulence kinetic energy of BT-GM system is 3 orders of magnitude higher than that of GM, and the effective mass transfer area is nearly 3 times that of GM. Seven batches of tests confirmed that the BT-GM system exhibits remarkable antifouling ability, broadens its adaptability to complex water quality, and practically promotes the development of sustainable resource recycling.

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.

Fouling-free membrane stripping for ammonia recovery from real biogas slurry

Hydrophobic gas permeable membranes (GPMs) exhibit great potential in stripping or recovering ammonia from wastewater, but they also suffer from severe fouling issues due to the complex water matrix, since the related process is often operated under highly alkaline conditions (pH > 11). In this study, we proposed a novel membrane stripping process by integrating a cation exchange membrane (CEM) in alkali-driven Donnan dialysis prior to GPM for efficient and robust ammonia recovery from real biogas slurry. During the conventional stripping for diluted biogas slurry, the ammonia removal across GPM finally decreased by 15% over 6 consecutive batches, likely due to the obvious deposition of inorganic species and penetration of organic compounds (rejection of 90% only). In contrast, a constant ammonia removal of 80% and organic matter rejection of more than 99%, as well as negligible fouling of both membranes, were found for the proposed novel stripping process operated over 120 h. Our results demonstrated that additional divalent cations clearly aggravated the fouling of GPM in conventional stripping, where only weak competition across CEM was found in the CEM-GPM hybrid mode. Then, for raw biogas slurry, the new stripping achieved a stable ammonia removal up to 65%, and no fouling occurrence was found, superior to that in the control (declined removal from 87% to 55%). The antifouling mechanism by integrating CEM prior to GPM involves size exclusion and charge repulsion towards varying foulants. This work highlighted that the novel membrane stripping process of hybrid CEM-GPM significantly mitigated membrane fouling and can be regarded as a potential alternative for ammonia recovery from high-strength complex streams.