Valorization of reactivated carbon and recovered nutrients from gas adsorption filters for sustainable fertilization.

In response to growing environmental concerns from industrial and agricultural pollution, sustainable waste management strategies are increasingly important. This study presents a dual evaluation of spent activated carbon (AC) and nutrients recovered from gas adsorption filters, focusing on both fertilizer applications and the valorization of reactivated carbon. Adsorbent materials, such as AC impregnated with magnesium oxides, effectively capture harmful exhaust gases, but their disposal poses environmental challenges. Here, the chemical composition of spent AC was analyzed, and its potential as a soil amendment was assessed. Various nutrient recovery methods, including acidic, alkaline, and water-based extractions, were evaluated for their efficiency in retrieving nutrients from the spent adsorbent. The recovered solutions were chemically characterized based on Fe, K, and Mg concentrations. Results showed that alkaline extraction using 3% KOH yielded the highest in the recovered solution (Fe 7.45%, K 1.89%, Mg 1.22%), highlighting potential for producing nutrient-rich liquid fertilizers. Water-based extraction preserved the AC pore structure most effectively, achieving the highest BET surface area (118.18 m²/g), while acidic HCl treatment was associated with reduced surface area and pore volume, suggesting restricted pore accessibility and possible structural deterioration. Reducing adsorption performance. Germination assays revealed that water-washed filtrates promoted the greatest barley root elongation, whereas KOH filtrates exhibited inhibitory effects, reflecting differences in ionic composition. Economically, water-based regeneration was the most cost-effective (< 10% of virgin AC), while KOH treatment provided the dual benefit of reactivating AC for reuse and producing nutrient-rich solutions. Overall, the findings demonstrate that reused activated carbon coupled with recovered nutrients can enhance sustainable agriculture and support circular waste management systems.