Preparation Of Modified Sludge Carbon Material And Its Adsorption Characteristics Of Pollutants In Wastewater

In sewage treatment,it is difficult to avoid generating a large amount of sludge.How to dispose the sludge reasonably has been concerned.Using pyrolysis technology to make sludge into biochar material was a very effective way of sludge treatment.However,the direct pyrolysis of sludge to produce biochar had simple structure,small specific surface area and obscure characteristics,making it difficult to recycle and limiting its application.In order to improve the adsorption performance of sludge carbon,using sludge as raw material,potassium ferrate（K₂Fe O₄）,citric acid（C₆H₈O₇）and urea（CH₄N₂O）three activators,different modified sludge carbon materials were prepared by pyrolysis method,and the adsorption characteristics of different modified sludge carbon materials on pollutants in wastewater were studied.The research contents are as follows:（1）K₂Fe O₄and C₆H₈O₇were selected to conduct“double pore-making”on sludge to prepare porous sludge carbon material for adsorption of dye Congo red（CR）in wastewater.The adsorption capacity of mixed modified porous sludge char(SAC_CA-PF)was obviously higher than that of single modified and unmodified porous sludge char.By means of characterization,the specific surface area of the mixed and modified SAC_CA-PFreached 136.34m²/g,3.8 times that of the unmodified direct pyrolysis sludge char（SAC_N）,which was mainly microporous.At the same time,the surface of SAC_CA-PFhad O-H,Si-O-Si,C=O and other oxygen-containing functional groups.At the optimum temperature（25℃）and p H（6）,the adsorption capacity of SAC_CA-PFwas 98.61mg/g,which was 1.6 times that of SAC_N.The results showed that the adsorption process of CR was more consistent with the second-order kinetic model and Langmuir isothermal adsorption model,and it was mainly single molecular layer chemisorption.The adsorption mechanism of SAC_CA-PFfor CR was mainly hydrogen bond and electrostatic attraction binding of amino groups in the dye,and the surface active sites of the material were increased after modification.The removal rate of adsorbent could still exceed 80%after 5 times of regeneration by Fenton oxidation process.SAC_CA-PFhad adsorption effect on different CR dye wastewater,the concentration was 300mg/L,the adsorption capacity was 128.7mg/g,and the material also had certain adsorption capacity for different dyes methylene blue（MB）and rhodamine B（RB）,the adsorption capacity was 40mg/g and 97mg/g,respectively.（2）The sludge was mixed with K₂Fe O₄and CH₄N₂O,and the graphitized nitride sludge carbon material(SAC_U-PF′)was prepared at high temperature based on the nitrogen doping,which was used to remove cadmium(Cd²⁺)from wastewater.The characterization results showed that the specific surface area of SAC_U-PF′was 61%higher than that of the unmodified SAC_N′.It contained hydroxyl and other oxygen-containing functional groups,and the pore structure of SAC_U-PF′was mostly mesoporous.The experimental results showed that the adsorption capacity of SAC_U-PF′to Cd²⁺was 9.69mg/g,5.5 times that of SAC_N′at 25℃and p H 6,after CH₄N₂O and K₂Fe O₄modification.The adsorption process of Cd²⁺by SAC_U-PF′was closer to that of second-order kinetic model and Langmuir isothermal adsorption model,and the electrostatic attraction played a major role.The adsorption of Cd²⁺was carried out by electrostatic attraction,ion exchange,physical adsorption and the complexation between metal ions and the oxygen-containing functional groups of SAC_U-PF′.Three kinds of analytical sorbents（HNO₃,Na OH,EDTA）were selected in this study,and all of them could achieve the regeneration of SAC_U-PF′.The regeneration effect of Na OH was better than the other two.The practical application capacity of SAC_U-PF′was studied.The results showed that SAC_U-PF′was suitable for treating low concentration heavy metal ion wastewater,and also had certain removal capacity of different heavy metals(Pb²⁺and Mn²⁺),with adsorption capacity of4.9mg/g and 8.1mg/g,respectively.Two kinds of modified sludge carbon materials were successfully prepared by coupling activation methods such as K₂Fe O₄,C₆H₈O₇and CH₄N₂O,which improved the adsorption and removal performance of pollutants in wastewater and provided technical support for sludge resource utilization.