Study On Preparation Of Humic Acid-Based Energy Storage Material From Typical Pretreatment Sludge

Anaerobic digestion is the major trends of sludge treatment and disposal under the background of carbon neutrality.Nevertheless,humic acid（HA）from the residual activated sludge needs to be removed by pretreatment since it could inhibit the efficient conversion of biomass energy.However,HA is an ideal precursor source of high-efficiency energy storage materials.Accordingly,this study recovers HA from typical pretreated sludge and prepared supercapacitor electrode materials,which not only improve biogas production during the subsequent anaerobic digestion process,but also achieve the high value-added utilization of HA as energy storage materials.The study aims to develop a more green and friendly new way for the comprehensive and full utilization of potential resources in sludge.Taking the sludge pretreated by alkali as the research target,the structural characteristics and electrochemical properties of electrode materials prepared by thermal reduction method,as well as the influence of activation conditions and temperature on material properties are emphatically discussed.The results show that the carbonized materials have excellent rate performance,and their specific capacitance is as high as 185.9 F/g（0.05 A/g）after KOH activation at 700℃with a mass ratio of 1:1.More than 97%of capacitance（1 A/g）remains even after 1000 cycles.After determining the preparation process,the properties of HA-based energy storage material（HAC）prepared from the ultrasonic or cationic pretreated sludge are studied by examining the parameters,including ultrasonic temperature,ultrasonic time,total solid concentration,cation type and dosage.It is revealed that,the materials originated from the sludge treated by 4 wt%of Fe³⁺have capacitance of 255.9 F/g（0.05 A/g）and remains96.1%（1 A/g）,while for the ultrasonic pretreated sludge derived HAC,the highest specific capacitance（282.6 F/g,0.05 A/g）and retention rate（98.2%,1 A/g）are found for HAC-U-30,when the ultrasonic specific energy（SE）keeps 54000 kJ kg^-1·TS.Obviously,both ultrasonic and cationic pretreatment can significantly improve the electrochemical performance of HACs.By characterizing the material structure,it is found that the specific surface area and total pore volume of HAC-U-30 is 52.8%～55.3%and 46.2%～66.1%higher,respectively,than the alkali and cationic pretreated sludge derived materials,and it also exhibits a more hierarchical porous system and higher degree of graphitization,which leads to a remarkable energy storage performance of HAC-U-30.With the purpose to improve the efficient conversion of biomass energy,this study proposes a new idea for high value-added utilization of sludge by recycling HA as the precursor of high efficiency energy storage materials in a green and cheaply manner.