Superior ammonia nitrogen adsorption capacity and reusability biochar microsphere applied in live fish transportation

Ammonia nitrogen is a major stressor that negatively affects the welfare of fish during transportation, leading to considerable economic losses. However, there is a lack of effective materials to adsorb ammonia nitrogen in water during the transportation. In this study, we prepared a biochar microsphere, chitosan loaded magnesium biochar microsphere (CS-Mg-SB-M), which showed the superior ammonia–nitrogen adsorption efficiency and reusability compared to the materials prepared with either magnesium impregnation or chitosan modification alone. The removal rate of ammonia nitrogen reached 83.41 % in water containing 50 mg L −1 ammonia nitrogen. The Pseudo-second-order kinetics and Langmuir isotherm models fitted the adsorption process well, suggesting that chemical and monolayer adsorption play a dominant role in ammonia nitrogen adsorbed by CS-Mg-SB-M. The adsorption mechanism of ammonia nitrogen removal by CS-Mg-SB-M involved the synergistic effects of physical absorption (colossal surface area and pore size) and chemical absorption (including coordination bonds, hydrogen bonds, and ionic bonds) according to results of SEM, XRD, FTIR and molecular dynamic simulation. In practical applications, CS-Mg-SB-M demonstrated 33–53 % ammonia nitrogen absorption efficiency, elevating survival rates to 40–60 % alongside measurable enhancements in muscle quality (e.g., cellular structure, drip loss, whiteness, brightness, and redness) of fish after 24 h of transporting in high-density and individual packing modes. This study represents the first application of feasible material to remove ammonia nitrogen in the live fish transportation system, concurrently enhancing survival rate and muscle quality.