Study On The Selective Adsorption Of Modified Biochar To Ammonia Nitrogen In Anaerobic Digestion

Ammonia inhibition is common in anaerobic digestion with rich in organic nitrogen substrates.Biochar has strong adsorbability due to its high porosity,large specific surface area and abundant surface functional groups.Biochar adsorption can effectively relieve ammonia inhibition in the digestive system.In order to quickly remove the ammonia inhibition in anaerobic digestion and further study the adsorption mechanism of ammonia nitrogen by biochar,biochar was prepared using corn stalks and rice husks as raw materials at different temperatures?350,450 and 550 ^oC?in this paper.The structure and physicochemical properties of biochar were analyzed by elemental analysis,infrared spectroscopy and specific surface area,and the effects of different physicochemical properties of biochar on the adsorption characteristics of ammonia nitrogen were studied by batch adsorption experiments.Due to the limited adsorption performance and no selectivity of the original biochar,the biochar was modified with acid,alkali and iron salt to understand the selective effect of the modified biochar on ammonia nitrogen and explore its adsorption mechanism.Modified biochar was added to anaerobic digestion to investigate the effect of modified biochar on gas production characteristics and ammonia nitrogen accumulation.The main results of this paper are as follows:With the increase of pyrolysis temperature,the carbon,ash content of corn straw biochar?CS?and rice husk biochar?RH?gradually increased,and the specific surface area and total pore volume gradually increased.The surface of biochar modified by different solutions became smooth and flat,and the number of acid oxygen-containing functional groups increased.And the adsorption capacity of modified biochar was significantly improved.The maximum adsorption capacity was increased by 2.88 times.Due to the differences of the raw materials themselves,the specific surface area and total pore volume of modified corn straw biochar decreased,while that of modified rice husk biochar increased,and its specific surface area increased by 2.5?52 times compared with unmodified.The adsorption mechanism of original biochar and modified biochar to ammonia nitrogen included chemisorption and physical adsorption,and chemisorption played a leading role.The adsorption capacity of CS was significantly correlated with its surface functional groups.The most significant correlation with the adsorption amount of RH was the specific surface area of biochar,secondly the surface functional groups,and finally the ash content.The selective adsorption of ammonia nitrogen by modified biochar was mainly affected by the pore size,electrostatic attraction and surface complexation.The modified biochar was added to the anaerobic digestion of chicken manure.The results showed that in the initial stage of fermentation,the modified biochar could effectively absorb ammonia nitrogen.And the concentration of ammonia nitrogen in the H-CS was 15%lower than that in the control group.With the addition of modified biochar,the rate of gas production in the anaerobic digestion of chicken manure increased and the peak of gas production was advanced,and the effective gas production period was shortened to 18 days,which was 2 days shorter than that of unmodified biochar,and the conversion efficiency of substrate by microorganisms was improved.But in the process of anaerobic digestion,the maximum cumulative ammonia concentration was 1246.91 mg·L^-1 without significant ammonia inhibition,which required further study under the conditions of different ammonia nitrogen concentrations.This study provides theoretical guidance for the study of selective adsorption mechanism of ammonia nitrogen by biochar in complex substrates,for the rapid elimination of ammonia nitrogen inhibition in anaerobic digestion,and for the stable operation of biogas fermentation system.