Chia-Hung Hou

Waste-derived biochar supports circular wastewater treatment by removing contaminants, recovering resources, and integrating life cycle and techno-economic assessments for sustainable scale-up. Biochar, produced from industrial and agricultural waste, has evolved from an agricultural soil amendment to an effective and sustainable material for wastewater treatment. Engineered/modified biochar produced using chemical or physical methods possesses a high surface area, porosity, stability, and a variety of surface functional groups and active sites for removing a wide spectrum of organic and inorganic contaminants, including heavy metals, nutrients, and antibiotics. However, its performance depends on feedstock characteristics and pyrolysis conditions. Slow pyrolysis optimized with artificial intelligence and machine learning technologies is increasingly adopted because of its operational simplicity, high yield, and economic feasibility. Alkali treatment enhances surface functionality, whereas acidic modification promotes the formation of oxygen-containing groups. Experimental evidence indicates that the solution pH is a critical parameter influencing heavy metal adsorption onto biochar, and nanomaterial-based biochar composites can further improve treatment efficiency and cost-effectiveness. Recent advances are shifting toward tailor-made, regenerable biochar integrated into membranes, electrodes, photocatalysts, biofilters, and nutrient-recovery systems. Despite its potential, challenges remain in long-term performance, regeneration, spent-biochar management, and full-scale comparison with activated carbon. Overall, biochar supports environmental, social, and governance principles and sustainable water management while contributing to circular economy strategies and the United Nations' sustainable development goals.

Ion exchange membranes (IEMs) separate ions of opposite charges, enabling a variety of applications, including desalination and mineral recovery via electrodialysis (ED). ED is uniquely suited for ion separation and recovery from high-salinity waters, especially for ions of low concentrations, as ions, instead of water, are transported in an electrical field. However, the application of ED is limited by the lack of selectivity of the counterions in the existing IEMs. Here, we developed a thin-film composite cation exchange membrane (TFC-CEM) consisting of an ultrathin polyamide coating, a porous polysulfone support, and a dense cation exchange polymer layer, which provides excellent separation between divalent and monovalent cations, high mechanical strength, and effective separation between cations and anions. At a constant current of 0.24 mA cm^-2, the TFC-CEM demonstrated monovalent over divalent cation selectivity of 49.32-136.79 in mixed cation solutions with a divalent to monovalent cation molar ratio of 25. The selectivity increased with increasing divalent to monovalent cation concentration ratios and correlated strongly with the difference in the hydrated size of the cations. Furthermore, the asymmetric structure of the TFC-CEM led to unique limiting current density behaviors, revealing that ion transport through the polyamide coating was rate-limiting. Finally, TFC-CEM demonstrated great potential for lithium extraction from hypersaline brines.

Precise separation of ions of the same polarity and similar valence and size remains a critical need in resource recovery from waste streams. Here, we report the rational design and scalable fabrication of a thin film nanocomposite (TFN) cation exchange membrane to achieve precise selectivity for lithium over competing cations. The precise selectivity is realized by an ultrathin polyamide (PA) layer incorporated with amine functionalized β-monoclinic lithium titanium oxide (N-LTO) nanoparticles using a scalable interfacial polymerization process that allows high N-LTO loading while minimizing interfacial defects. The TFN membrane demonstrates superior Li⁺ permeability, with Li⁺/Ca²⁺ and Li⁺/Na⁺ selectivity reaching 173.90 and 13.58, respectively. The Li⁺/Na⁺ selectivity is attributed to the Li⁺-exclusive transport pathway in the layered structure of the N-LTO, while size exclusion by the highly cross-linked N-LTO-PA also contrubutes to the Li⁺/Ca²⁺ selectivity. Molecular dynamics simulation shows that the electrical field drives Li⁺ dehydration and accelerates the migration of the dehydrated Li⁺ while Na⁺ is blocked due to its larger size than the Li⁺ cavity. The high Li⁺ selectivity and permeability enable energy-efficient, precise, and chemical-free lithium extraction using the electrodialysis process. The TFN membrane architecture also allows simple and scalable fabrication of a multi-functional polymer-inorganic nanocomposite membrane.