Study On The Adsorption Of Ammonia In The Wastewater By Sulphuric Acid Modified Biochar

Biochar can be produced from a wide range of sources,and can also be used as slow-release fertilizer.Recently,biochar has drawn much attention by helping to reduce the pressure on recycling of rural straw and other agricultural waste,to improve the efficiency of nitrogen and nitrogen recovery efficiency.This study focuses on the deficiency of ammonia adsorption on ammonia nitrogen,and tries to modify biochar materials with sulfuric acid.The effects of sulfuric acid on the adsorption of ammonia and nitrogen were studied with experiments on the kinetics,isotherm,pH impact and ion impact in the water.The surface area,distribution of pore size,surface functional groups of biochar were studied.Results reveal that the adsorption of ammonia nitrogen has been increased by 1.69 times as before,and modified biochar showed obvious transformation on its physical and chemical characteristics.Results of experiments on kinetics show that adsorption curves on ammonium nitrogen are better fitted by pseudo-second order kinetic.Maximum equilibrium adsorption capacity is 4.18 mg/g(70%sulfuric acid with 12 h reaction time)among all modified biochars with an initial concentration of 75 mg/L ammonium nitrogen.Isotherm curves of modified biochar are better fitted by Langmuir adsorption model,with a maximum adsorption capacity(q_m)of 19.12 mg/g(90%sulfuric acid with 24 h reaction time),which is obviously superior to raw biochar(11.31 mg/g).The pH value has some fluctuation during the adsorption process,while solution with higher pH is beneficial forthe adsorption of ammonia nitrogen.Material characterization of modified biochar reveals that the pore size distribution mostly gathers between 0.6 to 1.0 nm..The number of oxygenated functional groups is evidently increased.The pH at Zeta isoelectric point decreased after modification.The adsorption mechanism of ammonia on the surface of the biochar material is due to the electrostatic interaction between the negatively charged biochar and the positively charged ammonium ions.On the other side,ammonium moles are affected by the van der Waals force after diffusion into the pores of the ammonia molecules.These are two important mechanisms of the ammonia nitrogen adsorption.In the fixed bed adsorption experiment,the adsorption capacity of biochar was much higher than that of unmodified biochar(100 min till breakthrough point).The economic benefits are also calculated by producing fertilizer using recycled nitrogen.The adsorption of ammonia nitrogen was influenced by weak alkali metal cations and small molecule organic compounds,rather than strong alkali metal cation,anion and macromolecule.These phenomena are consistent with the physical and chemical properties of the modified biochar material.