Study On The Effect Of Hydrothermal Pretreatment On Anaerobic Digestion Of Sludge And Corn Straw

Sludge,as the main solid product of wastewater treatment plants,is characterized by high organic matter storages,nitrogen and phosphorus nutrients enrichments.Anaerobic digestion is crucial to achieving"energy self-sufficiency"and"carbon neutrality"in wastewater treatment plants,as it solves environmental problems and produces biogas to alleviate energy shortages.However,the traditional sludge anaerobic digestion process is limited by the complexity of organic matter,low carbon content,and slow hydrolysis rate,which results in low energy recovery.To improve the anaerobic digestion performance,this study aims to optimize the hydrothermal pretreatment process parameters for sludge,as well as for sludge and corn straw.This study analyzes the influencing factors and mechanisms of the hydrothermal and anaerobic digestion processes,and conducts energy assessment and carbon emission accounting of the process.The main research findings are presented as follows:（1）The effect of hydrothermal pretreatment process parameters on the physicochemical properties of sludge,sludge and straw products was investigated.The results showed that hydrothermal treatment promoted the dissolution of protein,polysaccharides,COD,ammonia nitrogen,VFAs and phosphorus.During the hydrothermal process of sludge,organic phosphorus in the solid phase was hydrolyzed and converted to apatite inorganic phosphate,and fulvic acid-like and humic acid-like organics were degraded,leading to enhanced biochemical properties.During the hydrothermal process of sludge and straw,the organic phosphorus in the solid phase was hydrolyzed to non-apatite inorganic phosphate,while the content of tryptophan-like proteins and soluble microbial byproduct-like substances increased,and the content of humic acid-like organics decreased.（2）The results of anaerobic digestion gas production from sludge,sludge and straw mixture after hydrothermal pretreatment showed that methane production from sludge was 1.68 times higher than the control（R1）.The methane production from sludge and straw was 1.71 times higher than the control（R3）and 0.14 times higher than that of sludge alone.Elemental analysis revealed that the C/N ratio of sludge was 7.26,whereas the C/N ratio of sludge and straw was 26.09,and the carbon content achieved the expected effect by adding straw.Microbial community analysis indicated that methanogenic bacteria dominated the archaeal community.Moreover,the relative abundance of 10 bacterial phyla in the sludge and straw bacterial communities was greater than 1%as compared to that in the sludge.The addition of straw improved the community’s abundance,diversity,and homogeneity.（3）The energy assessment results indicated that the optimal temperature,time and solid loading of the sludge were 200℃,2.0 h and 10.0%,respectively,with a net energy output of 0.90 k J/g VS.For sludge and straw,the optimal conditions were 180℃,1.5 h and 7.5%,respectively,with a net energy output of 1.77 k J/g VS.The addition of straw resulted in a 20℃ temperature reduction and a 0.5 h time reduction,which greatly reduced energy consumption during the hydrothermal process.In terms of carbon emissions,the net carbon emissions for sludge and sludge-straw treatment processes in the control group were-12.89 kg CO₂eq/t and-13.84 kg CO₂eq/t,respectively.For sludge and sludge-straw in the hydrothermal group,the net carbon emissions were-2.51kg CO₂eq/t and-1.16 kg CO₂eq/t,respectively.Both processes achieved negative carbon emissions.