Preparation And Application Of Modified Biochar Materials In Eutrophication Control

The problems of eutrophication caused by excessive nitrogen,phosphorus and other nutritions in water should be solved urgently.The traditional physico-chemical treatment methods have the problems of complex equipment,high cost,low removal efficiency or secondary pollution.Biochar material has high research and application value because of its advantages of low cost and regeneration performance,and thus can be used to solve the problem of eutrophication.However,the unmodified biochar also has the disadvantages,such as low adsorption capacity,poor adsorption selectivity,unable to adsorb ammonia nitrogen and phosphate contaminants simultaneously.In this thesis,biochar composite materials with high adsorption capacity were prepared based on bamboo powder enriched in Jiangsu Province and Zhejiang Province.The biochar was modified by rich functional groups.The modified biochar would achieve high adsorption efficiency of ammonia nitrogen and phosphate in eutrophic sewage,because of the synergy of adsporption such as physical adsorption,complexing adsorption,static adsorption,and so on.Then,the two biochar materials were designed and assembled into a packed tower to test their dynamic adsorption and operation stabilities.1.In order to prepare a biochar material with high adsorption capacity and selectivity to ammonia nitrogen,bamboo powder was pyrolyzed at various tempature,and specific surface area and porosity of biochar were simultaneously controlled by addition of KHCO₃ as pore-forming agent via physical and chemical reactions.The amounts of functional groups on the surface of biochar were increased by dipping in H₂O₂ solution.The results showed that the increase of the specific surface area and acidity could improve the adsorption capacity of ammonia nitrogen.Then,the adsorption capacity and selectivity to NH₃-N could be further improved by combination of the adsorption effect from biochar and coordination effect from Prussian blue（PB）.The theoretical maximum adsorption capacity of biochar to NH₃-N is expanded up to 24.4 mg/g and the removal efficiency reaches over 95%within 60 min after PB modified biochar.The mechainism of the ammonia nitrogen adsorption by PB modified biochar was investigated,and the adsorption fit the Langmuir model and pseudo-second-order kinetic equation.In addition,PB modified biochar material can catalyze H₂O₂ to generate·OH,and achieve catalytic degradation of organic contamination of humic acid（HA）and adsorption of ammonia nitrogen.Moreover,the modified biochar material can be regenerated by impregnating with Na Cl solution,which shows certain recycling ability.2.To prepare biochar with high adsorption capacity for PO₄-P pollutants,the N-doped biochar was produced by adding urea during the pyrolysis process of bamboo powder.The N-doped modification could decrease the negative charge on the surface of biochar and the electrostatic repulsion between the surface of biochar and PO₄-P.Then,the biochar-Fe₃O₄ was obtained by loading Fe₃O₄ on the surface of biochar by in situ deposition.The adsorption capacity was tested by KH₂PO₄ solution as the model of PO₄-P pollutants.The results showed that the highest removal efficiency could be over 95%at pH 7,and the maximum adsorption capacity in theory is 20.3 mg/g.The adsorption mechanism was discussed and its isotherms fit Langmuir equation model and pseudo-second-order kinetic model.In addition,the Fe²⁺and Fe³⁺in biochar material can form Fenton oxidation process in the existence of H₂O₂,and oxidize humic acid and adsorb PO₄-P at the same time.3.In order to achieve the dynamic adsorption of eutrophic sewage,the biochar composite prepared in the last two chapters were used as the fillers,and a packed tower was designed and assembled.The dynamic adsorption and operation stability of the packed tower were tested through three different eutrophic sewages.Then the penetration time of ammonia nitrogen and phosphate were measured respectively.The dynamic adsorption capacity of biochar was less than the theoretical maximum adsorption capacity because of the competition between pollutants.The weight of biochar has no effect on the dynamic adsorption capacity of biochar.Adding H₂O₂ solution would decrease the competitive adsorption among N,P and organic pollutants and increase the exhaustion time.It was proved that the two biochar materials have strong removal of ammonia nitrogen and phosphate in dynamic adsorption.In summary,in this thesis,bamboo powder as raw material was used to prepare modified biochar materials through different modification methods,which improved the adsorption effect of ammonia nitrogen and phosphate.The adsorptions from biochar and Fenton reaction were combined to achieve the simultaneous removal of organic pollutants and nutrients of N and P in multicomponent sewage.The packed towers filled with two kinds of biochar verified the dynamic adsorption of N,P and organic pollutants.The biochar materials and the packed towers in this thesis show broad application prospect in the treatment in eutrophic sewage.