Effect of Biochar Structure on Adsorption Characteristics of Ammonia Nitrogen

Abstract

Ammonia inhibition is a common phenomenon in biogas engineering which is rich in organic nitrogen substrate. Ammonia nitrogen in anaerobic digestate slurry can be fixed by biochar adsorption. Biochar is prepared from corn stalks and rice husks as raw materials at different temperatures (350℃, 450℃, and 550℃). The purpose is to explore the correlation between the physical and chemical structure of biochar and the adsorption characteristics of ammonia nitrogen. The structure and physicochemical properties of biochar were analyzed by elemental analysis, FTIR, BET, etc., and batch adsorption experiments were conducted to investigate the effect of biochar with different physicochemical properties on adsorption characteristics of ammonia nitrogen. The results indicated that the carbon and ash content in biochar increases with an increase in pyrolysis temperature; the NH4+-N adsorption of the corn stalk biochar prepared at 450℃ (CS450) and the rice husk biochar prepared at 550℃ (RH550) follows the quasi-secondary-and quasi-first-order kinetic models. The Freundlich adsorption model can better describe the isothermal adsorption process of ammonia nitrogen in CS450 and RH550 biochar. The adsorption capacity of corn straw carbon correlated strongly with its surface functional groups. The most significant correlation with the adsorption capacity of rice husk carbon is the specific surface area of biochar, followed by surface functional groups, and finally ash content. Among them, RH550 had the best adsorption performance, and the maximum adsorption capacity was 12.16 mg·g-1.