Study On The CO₂ Capture Performance Of Sludge Biochar Prepared By Conditioning Dehydration-pyrolysi

Sludge,a by-product of sewage treatment,is a solid-liquid flocculent material.Each year,China produces approximately 60 million tonnes of sludge,which contains many heavy metals and toxic and harmful substances,and if not properly disposed of will not only bring obstacles to sustainable environmental development but also threaten human health.The current disposal methods for sludge are landfill,incineration,and agricultural use,but landfill takes up a lot of land,incineration produces toxic and harmful gases,and the high content of heavy metals in sludge prevents its agricultural use.Therefore,the resourceful use of sludge is a better approach.Sludge contains a large amount of carbon and active ingredients and is a good material for the preparation of biochar.This biochar material is not only easy to prepare,it is versatile and cost effective.At the same time,the greenhouse effect is an environmental issue that needs to be addressed urgently.Since the industrial revolution,the burning of fossil fuels such as coal and oil and human activities have produced many greenhouse gases that have led to increasing global temperatures,the largest contributor of which is CO₂.CCUS technology can contribute up to 14%of the carbon reduction and is considered the most promising technology for carbon reduction.Capture technology is crucial as a part of this.The main existing carbon capture technologies are absorption,adsorption and membrane separation.The use of solid adsorbents is currently a hot topic of research and is the technology more likely to be commercially available in the future,in terms of cost and the corrosiveness of the equipment.Carbon based adsorbents are a common type of solid adsorbent,as they have a porous structure and contain many functional groups and active sites that facilitate CO₂adsorption.The preparation of sludge as biochar material for CO₂ capture is therefore of great theoretical and industrial importance.To improve the CO₂ capture capacity of biochar,chemical reagents are often used to modify the biochar,but this can increase the cost and result in secondary pollution.In sludge treatment,cracking agents and flocculants are added to reduce the water content of the sludge in order to reduce the cost of transport.Combining sludge dewatering cracking agents and flocculants with biochar preparation not only poses no additional risk but may also increase the CO₂ capture capacity of the sludge biochar.In this paper,two common sludge dewatering flocculants,cationic polyacrylamide（CPAM）and polymeric aluminium chloride（PAC）,were firstly used to condition the sludge as raw material,and the conditioned sludge was prepared as biochar（B-CPAM,B-PAC）,and the original sludge biochar（B-SS）was used as the control group to conduct a comparative study on the trapping performance of biochar,and to screen the most favourable biochar for trapping The flocculant that is most conducive to CO₂ capture by biochar was selected.The sludge dewatering cracking agent potassium permalate（K₂Fe O₄）,flocculant cationic polypropylene amide（CPAM）and chitosan（CTS）were used to prepare biochar after conditioning the sludge,and the sludge cake moisture content,sludge pyrolysis gas calorific value,agent dosage,preparation temperature and capture temperature were used as the main parameters to compare and analyse the effect of cracking agent and cracking agent+flocculant on the overall conditioning-pyrolysis process.-The effect of the pyrolysis process on the CO₂ capture by sludge biochar was compared.The mechanism of CO₂ capture by biochar was elucidated by the surface area,surface structure,surface functional groups and surface elements of biochar.The results of the study are as follows.1)Compared to B-SS（28.36 mg/g）,B-PAC（31.86 mg/g）and B-CPAM（48.54 mg/g）have increased CO₂ capacity,with B-CPAM having the highest CO₂ capacity.The microporous volume and surface area of biochar play an extremely important role in the process of CO₂ capture by biochar.The highest microporous volume（0.019639 cm³/g）and microporous surface area（37.9357 m²/g）of B-CPAM is one of the main reasons why its capture capacity is significantly higher than that of B-SS and B-PAC.The surface elements and functional groups of biochar also play a positive role in CO₂ capture.Oxygen-containing functional groups can react with hydrogen bonds on the surface of biochar,and amino groups can condense with CO₂,thus improving the CO₂ capture performance of biochar.Compared to RSB,the CO₂ capture capacity of biochar（K₂Fe O₄-B）increased from 75.69mg/g to 81.68 mg/g with the addition of K₂Fe O₄,94.81 mg/g with the addition of K₂Fe O₄+CPAM,and 86.56 mg/g with the addition of K₂Fe O₄+CTS.The addition of cracking agent and flocculant decreased the surface area of the biochar,resulting in a decrease in its physical adsorption capacity,but increased the amino functional groups,pyrrole nitrogen and carbon content that facilitate CO₂ capture.The increase in chemisorption capacity greatly improved the CO₂ capture capacity of the biochar,indicating that chemisorption plays a more important role than physical adsorption in CO₂ capture by sludge biochar.10 cycles of CO₂ capture showed that the K₂Fe O₄-CPAM-B cycle performed better than the K₂Fe O₄-CTS-B cycle,and the economic analysis showed that it had a lower cost.The study provides a reference for the selection of conditioning agents for wastewater treatment plants and offers a new solution for sludge disposal.