Ammonia and phosphorus removal from using cash crop waste-derived agricultural runoff biochars

摘要

Adsorption of biochars(BC)produced from cash crop residuals is an economical and practical technology for removing nutrients from agricultural runoff.In this study,B C made of orange tree trunks and tea tree twigs from the Laoguanhe Basin were produced and modified by aluminum chloride(Al-modified)and ferric sulfate solutions(Fe-modified)under various pyrolysis temperatures(200℃-600℃)and residence times(2-5 h).All produced and modified B C were further analyzed for their abilities to adsorb ammonia and phosphorus with initial concentrations of 10-40 mg/L and 4-12 mg/L,respectively.Fe-modified Tea Tree B C 2h/400℃showed the highest phosphorus adsorption capacity of 0.56 mg/g.Al-modified Orange Tree B C 3h/500℃showed the best performance for ammonia removal with an adsorption capacity of 1.72 mg/g.FTIR characterization showed that P=O bonds were formed after the adsoiption of phosphorus by modified BC,N-H bonds were formed after ammonia adsorption.X P S analysis revealed that the key process of ammonia adsorption was the ion exchange between K+and N H 44.Phosphorus adsorption was related to oxidation and interaction between PO43-and Fe3+.According to X R D results,ammonia was found in the form of potassium amide,while phosphorus was found in the form of iron hydrogen phosphates.The sorption isotherms showed that the Freundlich equation fits better for phosphorus adsorption,while the Langmuir equation fits better for ammonia adsorption.The simulated runoff infiltration experiment showed that 97.3%of ammonia was removed by Al-modified Orange tree B C 3h/500℃,and 92.9%of phosphorus was removed by Fe-modified Tea tree B C 2h/400℃.