Dong Hee Kang

Biochar, a carbon-rich material produced through pyrolysis of biomass under limited oxygen conditions, offers a potentially sustainable and cost-competitive solution (qualitative assessment; quantitative LCA and techno-economic data are beyond the scope of this review) for the removal of heavy metals from wastewater. Its high porosity, surface area, and surface functional groups enable diverse adsorption mechanisms, including complexation, ion exchange, and precipitation. Feedstock selection and production parameters critically influence biochar’s physicochemical properties and adsorption performance. Modification techniques such as chemical functionalization, metal impregnation, and composite formation enhance removal efficiency and selectivity for specific contaminants. Applications span industrial, municipal, and agricultural wastewaters, addressing multi-contaminant challenges under variable environmental conditions. Factors affecting removal efficiency include pH, temperature, contaminant concentration, and competing ions, while regeneration methods are essential for maintaining long-term functionality and are discussed. Biochar can be reused and regenerated using bases and acids, but environmental risks related to biochar use, including potential contaminant leaching and ecological impacts, require careful management and regulatory compliance. Future research should focus on novel modification strategies, scaling production for industrial use, and optimizing integration within treatment systems to meet stringent discharge standards and promote sustainable water management.

The widespread presence of tetracycline (TC) in aquatic environments poses serious risks to ecosystems and public health due to its persistence and role in promoting antimicrobial resistance. Engineered biochar has become a promising and sustainable material for removing TC because of its adjustable physicochemical properties, low cost, and multiple interaction mechanisms. This review examines the current state of biochar-based TC removal through a structure–performance–application framework that integrates material design, mechanistic insights, and real-world applications. The analysis shows that choices of feedstock, pyrolysis conditions, and modification methods—such as chemical activation, doping with heteroatoms, and metal impregnation—shape the structural features that influence adsorption and catalytic breakdown through mechanisms like pore filling, π–π interactions, hydrogen bonding, electrostatic attraction, and metal–ligand complexation. Although engineered biochars can achieve exceptionally high adsorption capacities (occasionally exceeding 1000 mg/g) under optimized laboratory conditions, most reported values fall within a broader range depending on feedstock, modification, and experimental conditions. However, their effectiveness can vary significantly in real water systems, where factors such as pH, ionic strength, natural organic matter, and other contaminants introduce competitive and inhibitory effects. Additionally, issues related to regeneration, stability, and declining performance pose major challenges for long-term use. Our review also highlights the huge gap between laboratory research and real-world implementation, stressing the importance of standardized testing, pilot-scale trials, and integration into continuous treatment systems. By linking material structure to function and operational practicality, our work offers a comprehensive guide for designing and scaling up engineered biochar technologies to effectively remove tetracycline from complex aquatic environments.

Biochar, a carbon-rich material produced through pyrolysis of biomass under limited oxygen, offers a potentially sustainable and cost-competitive solution (qualitative assessment; quantitative LCA and techno-economic data are beyond the scope of this review) for the removal of heavy metals from wastewater. Its high porosity, surface area, and surface functional groups enable diverse adsorption mechanisms including complexation, ion exchange, and precipitation. Feedstock selection and production parameters critically influence biochar’s physicochemical properties and adsorption performance. Modification techniques such as chemical functionalization, metal impregnation, and composite formation enhance removal efficiency and selectivity for specific contaminants. Applications span industrial, municipal, and agricultural wastewaters, addressing multicontaminant challenges under variable environmental conditions. Factors affecting removal efficiency include pH, temperature, contaminant concentration, and competing ions, while regeneration methods are essential for maintaining long-term functionality and are discussed. Biochar can be reused and regenerated using bases and acids, but environmental risks related to biochar use, including potential contaminant leaching and ecological impacts, require careful management and regulatory compliance. Future research should focus on novel modification strategies, scaling production for industrial use, and optimizing integration within treatment systems to meet stringent discharge standards and promote sustainable water management.

Synthetic dyes represent some of the most enduring and toxic contaminants in industrial wastewater, attributable to their intricate molecular configurations, elevated chemical stability, and resistance to standard treatment methods. Biochar-based adsorbents have emerged as effective materials for dye removal due to their adjustable surface chemistry, porous architecture, and sustainable manufacture from biomass resources. This study offers a thorough and mechanism-focused synthesis of recent progress in the development and utilization of biochar adsorbents for the treatment of dye-contaminated wastewater. The analysis combines biomass feedstock selection, thermochemical synthesis pathways, surface modification techniques, adsorption mechanisms, and operational performance to create a cohesive framework connecting biochar design with adsorption behavior. The documented adsorption capabilities for dye removal utilizing biochar-based adsorbents vary significantly, often ranging from 10 mg g−1 to over 1000 mg g−1, contingent upon feedstock composition, thermochemical conversion conditions, and surface modification techniques. The reported adsorption capacities for different dye classes are rigorously analyzed concerning experimental conditions such as solution pH, dye concentration, adsorbent dosage, and wastewater matrix composition, which substantially affect adsorption performance and hinder direct comparisons among studies. The paper additionally assesses predominant adsorption mechanisms, including electrostatic attraction, π-π interactions, hydrogen bonding, and pore-filling processes, emphasizing the influence of biochar surface characteristics and solution chemistry on the significance of these interactions. The discourse also addresses regeneration efficiency, operational stability, and the constraints related to scaling biochar-based adsorption systems for actual wastewater treatment. The findings underscore that the optimal design of biochar adsorbents necessitates a comprehensive assessment of feedstock properties, synthesis parameters, and ambient factors influencing adsorption mechanisms. Future research must include pilot-scale validation, sustainable regeneration methodologies, and assessment under actual wastewater circumstances to enable the translation of laboratory-scale adsorption studies into effective water treatment technology.

Intensive poultry production generates large quantities of poultry litter (PL), creating challenges for nutrient management and environmental protection in poultry-intensive regions such as the Delmarva Peninsula. Pyrolysis of PL into biochar represents a promising strategy for waste valorization and sustainable soil amendment; however, its agronomic performance is strongly influenced by production conditions and application rates. This study systematically evaluated the effects of pyrolysis temperature (300 and 500 °C), bedding material composition (no bedding, 10% pine shavings, and 10% rice hulls), and application rates (2% and 5% w/w), on soil chemical properties, phytotoxicity, and radish (Raphanus sativus) growth under controlled greenhouse conditions using a sandy loam soil sampled from the Delmarva Peninsula. Poultry litter biochar (PLB) produced at 300 °C and applied at 2%, significantly enhanced leaf area, biomass accumulation, root length, and root tip development without inducing phytotoxic effects. In contrast, increasing the application rate to 5%, elevated soil electrical conductivity and caused nutrient imbalance, resulting in suppressed root architecture and reduced plant growth despite increased nutrient availability. The incorporation of bedding materials reduced sodium concentrations and improved the potassium-to-sodium ratio, thereby mitigating salinity-related stress and supporting improved plant performance. The findings indicate that low-temperature PLB, derived from bedding material and applied at ≤ 2%, serves as an agronomically safe and effective soil amendment, offering practical recommendations for enhancing biochar production and land application methods to promote sustainable nutrient recycling and soil health in poultry-dominant agricultural systems.

Pluvial flooding, driven by increasingly impervious surfaces and intense storm events, presents a growing challenge for urban areas worldwide. In Baltimore City, MD, USA, climate change, rapid urbanization, and aging stormwater infrastructure are exacerbating flooding impacts, resulting in significant socio-economic consequences. This study evaluated the effectiveness of a soil profile rehabilitation scenario using a 2D hydrodynamic modeling approach for the Tiffany Run watershed, Baltimore City. This study utilized different extreme storm events, a high-resolution (1 m) LiDAR Digital Terrain Model (DTM), building footprints, and hydrological soil data. These datasets were integrated into a fully coupled 2D hydrodynamic model, the City Catchment Analysis Tool (CityCAT), to simulate urban flood dynamics. The pre-soil rehabilitation simulation revealed a maximum water depth of 3.00 m in most areas, with hydrologic soil groups C and D, especially downstream of the study area. The post-soil rehabilitation simulation was targeted at vacant lots and public parcels, accounting for 33.20% of the total area of the watershed. This resulted in a reduced water depth of 2.50 m. Additionally, the baseline runoff coefficient of 0.49 decreased to 0.47 following the rehabilitation, and the model consistently recorded a peak runoff reduction rate of 4.10 across varying rainfall intensities. The validation using a contingency matrix demonstrated true-positive rates of 0.75, 0.50, 0.64, and 0 for the selected events, confirming the model’s capability at capturing real-world flood occurrences.