Yang Lei

Human urine represents a nutrient-rich reservoir that, if recycled, could significantly offset global fertilizer demands. Yet, its potential remains largely underexploited because rapid urea hydrolysis at the source drives N and P losses via uncontrolled precipitation, while causing pipe clogging and malodor formation. Here, we report a wollastonite (CaSiO₃)-integrated electrochemical alkalization and oxidation (EAO) system that enables concurrent urea stabilization and phosphorus recovery. Anodic proton-driven dissolution of CaSiO₃ releases Ca²⁺, which combines with cathodically generated alkalinity to promote phosphate precipitation, whereas anodic oxidation suppresses urease-mediated urea hydrolysis. We show that the driving force lies in the microenvironment near the electrode, which has distinct pH, Ca²⁺ and active‑chlorine gradients. Treating two‑fold diluted urine at 12 A m⁻² yields the most energy‑efficient scenario (20.11 kWh kg⁻¹ P, 2.99 kWh m⁻³ urine), achieving 96.0% phosphate recovery and robust urea stabilization in real urine. We expect the EAO system to create a scalable electrochemical route to close nutrient loops in decentralized sanitation, supporting sustainable fertilizer production and urine management.

Nitrate (NO₃^-) persistence in water poses severe ecological and health risks. Electrochemical reduction of nitrate to ammonia (ENRA) offers a promising route for simultaneous nitrate remediation and ammonia (NH₃) production. Nevertheless, its real-world application is hindered by cathode fouling, energy inefficiency, and poor performance in complex water matrices. Nitrate-selective anion exchange resins (NAERs) effectively separate and enrich nitrate from complex water, which may mitigate inorganic scaling and boost energy efficiency of ENRA, yet require chemical regeneration with substantial reagent consumption. To address these issues, we developed a hybrid innovative extraction-electrocatalysis-recovery-system (EERS) that integrates ENRA with NAERs. In simulated wastewater, EERS maintained a stable nitrate desorption efficiency of 76.5 ± 1.3% over three cycles, markedly outperforming chemical regeneration, which declined from 73.5 to 56.2%. In real nitrate-polluted groundwater, EERS achieved ∼9.5-fold nitrate enrichment and a NO₃^- removal efficiency of 86-100% over three cycles. Moreover, EERS yielded >900 mg L^-1 ammonia over each cycle. Notably, the integrated system minimizes reagent consumption by enabling continuous desorbent regeneration and electrochemical conversion, substantially reducing chemical demand and on-site storage requirements. Lastly, we confirmed the structural integrity of the resin and the Cu₂O@CF electrode, validating EERS's robustness in complex aqueous environments. These results demonstrate a scalable and sustainable platform for decentralized nitrate remediation with ammonia production in real water systems.

Lime-based precipitation, though widely adopted for wastewater phosphorus (P) removal, suffers from surface passivation. The passivation layer inhibits Ca²⁺ release, forcing excessive dosing while yielding low-quality sludge and effluent with elevated hardness and pH. Limestone, despite its economic and environmental benefits, exhibits limited efficacy under fluctuating alkalinity. Here, we develop a limestone-integrated electrochemical system that spatially decouples the dissolution and precipitation reactions. By strategically positioning limestone at the acidic anode, we ensure sustained Ca²⁺ release without passivation, while cathodic alkalinity enables efficient P recovery (85.7%). The system produces high-purity products (15.2 wt% P) at low energy consumption (14.8 kWh kg P^-1) and delivers superior effluent quality. Beyond its robustness and capacity flexibility over long-term operation, the electrochemical strategy reduces overall costs by 73.2% and carbon emissions by 29.1%, positioning it as a cost-effective and sustainable alternative to traditional lime-based wastewater treatment with remarkable passivation resistance and resource recovery efficiency.

The increasing global population has boosted fertilizer demand for food production, food waste generation, and water pollution. Here, we report an electrochemical strategy to upcycle shell waste for nutrient reclamation from wastewater to tackle these challenges in one shot, in which shell waste is decomposed by anodic-produced H⁺, supplying cations (i.e., Ca²⁺ and Mg²⁺). Meanwhile, cathode-derived alkaline promotes the crystallization of nutrients (i.e., PO₄^3- and NH₄⁺) from the wastewater. We first validated this concept's promising P reclamation (84.2-99.2%) toward three common real wastewaters with P levels ranging from 7 to 1577 mg/L, indicating its potential for diverse applications. We further designed a scalable prototype for eggshells upcycling and P-fertilizer production from urine in a household setting, showing encouraging performance P recovery (>85.7% at 1.0 kW h/m³), reduced CO₂ emissions by 76.5%, and promising economic viability. Our work outlines a sustainable map for managing food waste, harvesting nutrients from wastewater, and eliminating water pollution.

Acid mine drainage (AMD) contains toxic yet valuable heavy metals. Conventional chemical neutralization using hydrated lime is highly efficient in mitigating heavy metal pollution, yet it generates hazardous solid wastes and is inefficient in recovering critical metal resources. Here, we report the design and demonstration of an electrochemically activated limestone (EAL) system for AMD treatment and valuable metal extraction. The EAL system extracted 82.3-100.0% of different metals (Cu, Cd, Zn) with high purity (~81.3 wt% valuable metals) through electro-reduction and local high pH-mediated precipitation when treating simulated AMD with varied conditions and actual AMD at energy consumption of 0.006-0.180 kW·h g⁻¹ metal. In addition, the effluent after the EAL treatment contains high alkalinity and Ca²⁺, which is proven to have CO₂ sequestration potential. Overall, the EAL treatment reduces total costs by 17.9% and CO₂ emissions by 60.1% compared to conventional lime dosing treatment, demonstrating its economic viability and ecological superiority for the practical remediation of AMD and extraction of valuable metals.