Evaluation of biochar amendments to retain organic compounds in soil

Abstract The use of biochar is frequently recommended as a low-cost mitigation strategy. Biochar can be easily and inexpensively produced from various agricultural residues. In this study, we produced and evaluated the impact of biochar derived from rosemary, bamboo, St. John’s wort, olive tree wood, cypress, and palm trees on the mobility and retention of emerging contaminants. The initial stage of this work involved the evaluation of the potential retention capacity of various biochars produced in a low-cost metallic kiln using local biomass residues. Methylene blue was used as a proxy for organic contaminants to establish adsorption isotherms and quantify the biochars’ specific surface area and adsorption capacities. Adsorption isotherms at 20°C were fitted to different models to assess their specific surface areas. The results showed that biochars derived from rosemary, giant reed, and St. John’s wort exhibited significant adsorption capacities. Average adsorption capacities for cypress and olive tree were observed, while traditional olive and palm trees showed low adsorption capacities. In the second stage, we evaluated the dynamic retention properties of biochar using soil monolith experiments. We analyse methylene blue (MB) elution curves with and without biochar addition. The presence of biochar in the soil monoliths significantly improved the retention of MB, demonstrating its effectiveness as an adsorbent filter. Specifically, biochar-amended soil monoliths exhibited an increase in MB retention compared to unamended controls. The breakthrough curves showed a delay in the elution of MB of 2,33 pore volumes in biochar-amended monolith increase in sorption capacity. Furthermore, the total recovered MB in the effluent was reduced by 66 % in biochar-treated samples. These quantitative findings underscore the robust potential of biochar for improving water quality by mitigating pollutant transport through the soil. The results suggest that the application of biochar could serve as an effective strategy to reduce agricultural runoff contamination in vulnerable watersheds.