Study On The Modification Of Biochar And Its Adsorption Properties For Nitrogen In Biogas Slurry

In recent years,with the development of large-scale biogas engineering in China,the output of biogas slurry has been increasing.Nitrogen is an important nutrient in the biogas liquid,and the content of ammonia nitrogen was as high as 80%.If it was not recycled or treated,it would cause serious environmental pollution and waste of resources.At present,the main technical methods for the recovery of nitrogen in the biogas slurry were MAP and ammonia stripping,but there were many problems such as low removal efficiency and high technical cost,and the adsorption method has attracted more and more attention.The key of adsorption recovery technology was to choose suitable adsorbents.In recent years,biochar has been widely used as adsorptive materials in many fields because of its good adsorption properties,carbon fixation and soil improvement.It was also one of the hot topics in the study of surface modification of biochar.In order to analyze the adsorption mechanism and effect of different modified biochar on ammonia nitrogen,the preparation and screening of modified biochar,the study of the surface characteristics of biochar,the adsorption characteristics on the ammonia nitrogen and the influence factors were studied.The dynamic adsorption effect of biochar on ammonia nitrogen in biogas slurry was analyzed by adsorption column,and the optimum adsorption conditions were selected.The main contents and results were as follows:?1?Biochar were prepared from 3 kinds of agricultural waste,corn straw,corn cob and wood sawdust at 550,600 and 650?.The modification of biochar by sodium hydroxide and microwave modification?NaOH+Microwave?,ferric chloride modification?FeCl₃?,potassium hydroxide modified?KOH?and nitric acid modification?HNO₃?treatments,through the study of the adsorption effect of modified biochar to ammonia nitrogen,4 kinds of modified biochar with better adsorption effect on ammonia nitrogen were screened,which were straw carbon-550?-NaOH+Microwave?A-550-NaM?,straw carbon-550?-KOH?A-550-K?,corn cob carbon-550?-FeCl₃?B-550-Fe?,and sawdust carbon-600?-NaOH+Microwave?C-600-NaM?.?2?The surface area of modified biochar and the surface properties of functional groups were analyzed.It was found that the surface area of modified biochar was significantly increased,and the strong power supply group on the surface of modified biochar increased significantly,which made the adsorption capacity of ammonia nitrogen enhanced obviously.The adsorption process of modified biochar to ammonia nitrogen were in accordance with the second stage kinetic model and Langmuir isothermal model.The maximum saturated adsorption capacity of the Langmuir single molecular layer were 101.86,94.82,200.24 and 64 mg NH₄⁺-N/g,respectively.?3?The 3 stage dynamic adsorption device was designed.The modified biochar A-550-NaM,A-550-K and B-550-Fe were used as the dynamic adsorption matrix.The dynamic adsorption experiment of ammonia nitrogen in the biogas slurry were carried out.The optimum process conditions for the adsorption of ammonia nitrogen were as follows:the flow rate was 5L/h the modified biochar B-550-Fe and A-550-K were modified.The packing height corresponding to A-550-NaM were 30 cm,50 cm and 70 cm,respectively.The adsorption penetration time and the saturated adsorption time of ammonia nitrogen were prolonged By the series adsorption process of optimization process,and the adsorption rate of ammonia nitrogen was greatly improved.