Techno-economic and environmental assessment of fixed-bed nitrate removal using ZnCl2-activated almond shell biochar: process scale-up and sustainability analysis

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The present study evaluated the technical, economic, and environmental feasibility of ZnCl 2 -activated almond shell biochar (BA-Zn) for nitrate removal from a synthetic aqueous solution using fixed-bed adsorption. BA-Zn exhibited an adsorption capacity of 16.1 mg/g. However, the breakthrough occurred rapidly (0.5 min), resulting in low effective bed utilization and an overall removal efficiency of 5%. Breakthrough curves were adequately described by the Yoon–Nelson, Bohart–Adams, and Yan models (R 2 > 0.98), supporting preliminary hydraulic scale-up analysis under laboratory conditions. The techno-economic analysis indicated that the process was not economically feasible under current Colombian reagent prices, although feasibility improved under low-cost reagent scenarios with payback periods of 5–7 years. Life cycle assessment identified biochar production and chemical activation as the dominant environmental hotspots, mainly due to non-renewable energy consumption and global warming impacts. These findings indicate that although BA-Zn shows adsorption potential, substantial optimization of column design, reagent consumption, and energy efficiency is required before practical large-scale application.