Study On The Conversion Of Eggshells Into Layered Double Hydroxide And Their Adsorption Properties Of Short Chain Fatty Acids

At present,biological methods are widely used in environmental pollution prevention and control.The use of biological methods for the denitrification and dephosphorization of wastewater requires an electron donor and usually requires an external carbon source.However,the commonly used liquid organic carbon source needs to be replenished frequently,which is likely to cause secondary pollution of the water body,and thus is not conducive to long-term treatment of sewage.The study found that solid-state slow-release carbon sources are more conducive to the stable operation of water treatment systems.Therefore,in this paper,the adsorption properties of matrix materials for short chain fatty acids were studied under the premise of waste resource utilization.This can provide a reference for the preparation of new solid-state slow-release carbon sources.A large number of studies have shown that short-chain fatty acids?SCFAs?produced by fermentation of excess sludge in sewage treatment plants have good sewage treatment efficiency as carbon sources.However,studies on the adsorption of short chain fatty acids to prepare novel carbon sources have not been reported.For this situation,this research used ultrasonic assisted method to synthesize magnetic layered double hydroxide with super-paramagnetic ferrite and layered double hydroxide?LDH?,and explored the adsorption performance of magnetic LDH on short chain fatty acids.Due to the effects of adsorbent dosage,adsorption time and speed on the extraction of short chain fatty acids,using uniform design and response surface methodology to optimize the extraction conditions.In order to broaden its action surface,this study also used a one-step foaming method to prepare a magnetic LDH/PU composite by combining the synthesized magnetic LDH with polyurethane?PU?.The performance of eggshell-based magnetic LDH/PU composites for extracting short chain fatty acids as bio-denitrification carbon sources was studied.Major conclusions were listed below:1.The National Medium-and Long-Term Plan for Science and Technology Development?2006-2020?clearly states that the principles of waste recycling should be followed in three important areas:environment,resources and energy.In this study,eggshells and sludge were successfully utilized.The study investigated the adsorption properties of the skeleton materials on short chain fatty acids,thus realizing the utilization of waste resources and effectively reducing the research cost.At the same time,it laid a theoretical foundation for follow-up research.2.In the single-component adsorption experiment,the amount of magnetic LDH and the adsorption time have a significant effect on the adsorption of short chain fatty acids.When the adsorbent dose was increased from 2 g·L^-1 to 14g·L^-1,the adsorption efficiency of magnetic LDH to SCFAs increased rapidly from 27%to 90%.The adsorption of SCFAs by magnetic LDH is a rapid reaction process.When adsorbed for 10 min,the adsorption efficiency has reached 85.9%.After 30 min of adsorption,the adsorption efficiency can reach92.4%,and the adsorption efficiency tends to be stable until 60 min.In addition,the adsorption kinetic data of SCFAs is more in line with the quasi-second-order kinetic equation.This further proves that the magnetic LDH prepared by ultrasonic assisted method is a new type of high-efficiency adsorption material,which can effectively adsorb SCFAs.3.Based on the single factor adsorption performance experiment,the regression equation was obtained by analyzing the experimental data of magnetic LDH adsorption SCFAs by the combination of uniform design and response surface method.The result shows that when the adsorbent dosage is 16g·L^-1,the adsorption time is 50 min and the speed is 70 r·min^-1,the theoretical maximum extraction rate of SCFAs is 95.7%.4.In order to get closer to the practical application of the project and broaden action surface,this study prepared a magnetic LDH/PU composite by combining LDH and PU.The material has the advantages of good magnetic LDH adsorption and large porosity and porous surface area of the PU foam material.The results show that the adsorption efficiency of magnetic LDH/PU composites on SCFAs is about 20%higher than magnetic LDH.The results also show that the magnetic LDH and PU composite can achieve effective extraction of SCFAs,and the foam material dispersed in the solution can be quickly recovered by using an external magnetic field.5.This study confirmed the removal performance of NO3-N by using magnetic LDH/PU-SCFAs as magnetic denitrification carbon sources after adsorption of SCFAs on magnetic LDH/PU composites.The experimental results show that the utilization efficiency of carbon source is higher when C/N is 4:1 than when C/N is 6:1,indicating that some carbon sources are used by microorganisms for self-growth at higher C/N conditions.Moreover,when C₆H₁₂O₆ and magnetic LDH/PU-SCFAs were used as the external carbon source control respectively,it was found that the magnetic LDH/PU-SCFAs had a significant sustained release effect during carbon release.Under the same conditions,the carbon source utilization ratio of LDH/PU-SCFAs was increased by 6.7%compared with C₆H₁₂O₆,indicating that magnetic LDH/PU-SCFAs can be used as a new efficient and effective slow-release carbon source in biological nitrogen removal process.6.The materials before and after adsorption were characterized by XRD,FT-IR,TG,DSC,SEM and TEM.The results show that the magnetic LDH prepared in this study has a typical hydrotalcite layer sheet structure.The magnetic LDH/PU composite material has the characteristics of large porosity and porous surface area of the PU foam,and the LDH is uniformly dispersed throughout the system.After the analysis of the material's regeneration performance.The results show that the magnetic LDH and magnetic LDH/PU composites can not only be used as an external slow-release carbon source after adsorbing SCFAs,but also can supplement SCFAs in multiple cycles to achieve full utilization of materials,improve utilization efficiency and reduce costs.This study has important theoretical and practical significance for wastewater nutrient removal,waste resource utilization and technical engineering.