Study On Phosphorus Removal Performance And Soil Improvement Of Alkali Activated Magnesium-loaded Orange Peel Biochar

In recent years,the loss of phosphorus resources and eutrophication of water bodies are more prominent resource and environmental problems.At present,the prevention and control of eutrophication of water bodies in China is urgent.Under this trend,the recovery of phosphorus in wastewater has an extremely important role in alleviating eutrophication of water bodies and slowing down the consumption of phosphorus resources.As an adsorbent,biochar is environmentally friendly,inexpensive,and easy to process.It has been a hot topic of research in recent years to use it for the recycling of phosphorus in waste water.As a kind of industrial and agricultural waste,orange peel has unique natural pores and is cheap and easy to obtain;KOH can activate biochar and increase its specific surface area;metal magnesium has a strong affinity for phosphorus.Based on the above conditions,this study used KOH and MgCl₂ modified orange peel to prepare KOH activated magnesium carrying orange peel biochar?KMg-BC?,explored the influence of the preparation conditions on its phosphorus removal performance,and optimized the preparation parameters;and then studied KMg-BC Influencing factors in the process of phosphate adsorption,combined with a series of characterization and adsorption models to analyze the mechanism of phosphorus removal;finally explore the improvement effect of the material?KMg-BC/P?on soil after phosphorus removal and the impact on soybean growth,and assess its potential as a soil amendment.?1?KMg-BC has better phosphorus removal performance under the conditions of the mass percentage of KOH in the KOH solution is 2.5 wt%,KOH and MgCl₂ mass ratio of 1:1,immersion time of 2 h,and firing temperature of 600°C.KOH and MgCl₂successfully changed the surface morphology and material composition of biochar,so that KMg-BC has good phosphorus removal performance.?2?KMg-BC has a better phosphorus removal effect when the dosage is 4 g·L^-1;When the initial pH of the solution is 3?9,the phosphorus removal effect of KMg-BC is better,and the lower pH can promote the phosphorus removal effect of KMg-BC;coexisting ions CO₃^2-and HCO₃^-will reduce the phosphorus removal efficiency of KMg-BC at high concentration,but in reality it has little effect,so KMg-BC has a higher adsorption selectivity for phosphate;and KMg-BC shows good phosphorus removal performance in actual wastewater tests,and it has the potential for practical application.?3?The adsorption process of phosphate by KMg-BC conforms to quasi-second-order kinetics and Sips adsorption isotherm model.The adsorption of phosphorus by KMg-BC is the chemical adsorption of monolayer adsorption and multiphase surface and multilayer adsorption,the theoretical maximum adsorption capacity obtained by Sips model fitting is 226.28 mg·g^-1;adsorption isotherm and adsorption thermodynamics data analysis shows that the KMg-BC's phosphorus removal reaction is an exothermic reaction,and temperature rise is not conducive to phosphorus removal.?4?The KMg-BC dephosphorization process is affected by physical adsorption,electrostatic attraction,surface complexation,and precipitation reactions,but it mainly provides Mg²⁺and phosphate to produce Mg HPO₄ and Mg?H₂PO₄?₂ precipitation on biochar through the loaded MgO,MgCl₂ and Mg?OH?₂ to achieve the purpose of phosphorus removal.?5?KMg-BC/P has the effect of improving the soil,it will increase the soil pH,conductivity,organic matter content,cation exchange capacity,available phosphorus content,total phosphorus content,phosphorus release and water holding capacity;and it will increase Ca₂-P,Ca₈-P,Al-P,Fe-P,LOP,MLOP,MROP content;but it has little effect on the content of O-P and Ca₁₀-P in the soil,and it will reduce the content of HROP.In addition,after KMg-BC/P is added to the soil,the soil alkaline phosphatase activity will gradually increase;at the same time,it will promote the growth and reproduction of soil bacteria.The bacterial diversity is unchanged but the abundance is increased.The microbial community shifted towards the direction of bacteria.?6?Planting soybeans with KMg-BC/P modified soil can promote soybean growth,which is reflected in its ability to increase soybean germination rate,make soybean leaves greener,and increase soybean plant height,root length,number of leaves,plant fresh weight,stem thickness and number of pods.Therefore,the phosphorus-removed KMg-BC has potential as a soil amendment.