Study On The Effect Of Different Conductive Additive Dosages On The Anaerobic Digestion Characteristics And Microbial Action Mechanism

Problems that cause the low biogas production efficiency such as difficulty in optimizing and matching the raw materials ratio are offen found in the biogas projects.But the conductive additive is one of the important ways to improve the production efficiency of anaerobic digestion.Clarifying the effect of conductive additives on the anaerobic digestion characteristics is of great significance to guide the use of conductive additives and improve the theoretical basis in anaerobic digestion.In this study,cow manure and food waste were used as digestion substrates respectively.Biochar,magnetic biochar and magnet powder were added at four dosages of 0%,2.5%,5%and 7.5%,and the effects of biogas production characteristics,process characteristics,and microbial characteristics in single-anaerobic digestion were analyzed.The dynamic changes of various characteristic parameters were combined to explore the mechanism of the effect of conductive additives on anaerobic digestion,and to clarify the key role of conductive additives on the methanogenesis pathway.The main results of this study are as follows:（1）Conductive additives help to improve the biogas production and efficiency of single-anaerobic digestion,and the interaction between the types and dosage of conductive additives was the key driving factor affecting the biogas production characteristics of anaerobic digestion.The anaerobic digestion of cow manure with the addition of 2.5%biochar,7.5%magnetic biochar and 5%magnet powder had the best total biogas production,which were 274.17 ml/g VS,303.16 ml/g VS and 241.08 ml/g VS,respectively.The anaerobic digestion of food waste with adding 2.5%biochar,2.5%magnetic biochar and 5%magnet powder had the highest total biogas production,reaching 657.15 ml/g VS,665.24ml/g VS and 686.27 ml/g VS,respectively.（2）The addition of three conductive additives can affect the process characteristics of anaerobic digestion.Among them,the concentration of volatile fatty acids and carbon-nitrogen ratio are both significantly related to the biogas production of the two digestion substrates after the adding conductive additives（P<0.05）.Conductive additives can improve the hydrolysis of organic matter to volatile fatty acids,and improve the chemical oxygen demand degradation rate of digestion substrates.Among them,the highest chemical oxygen demand degradation rate of cow manure was 57.27%,and 71.06%for food waste.The addition of 5%biochar,7.5%magnetic biochar and 2.5%magnet powder in the treatments of cow manure has better effect.And the best treatments of food waste process characteristics were consistent with the best treatment of biogas production.（3）The composition of microbial community changed obviously with digestion time,and the interaction of bacteria,archaea and enzymes was most related to the changes of environmental factors of the digestion system.In the archaeal community,Methanosarcia was the dominant microorganism.And Bacteroidetes and Firmicutes were the dominant microorganism in the bacterial community.The influence order of the three additives on the methanogenic metabolic module of cow manure was:magnetic biochar>magnet powder>biochar;the influence order on the methanogenic metabolic module of food waste was:magnetic powder>magnetic biochar>biochar.The addition of conductive additives helped to increase the relative abundance of functional genes corresponding to methyl-Co M reductase,which is a key link shared by the four metabolic pathways.（4）The direct interspecies electron transfer of microorganisms was affected by the types of conductive additives and digestion time.Conductivity additives can affect the rate of change in the abundance of archaea and bacteria involved in direct electron transfer.The pil A functional gene was mainly distributed in Clostridium,Pseudomonas and Thauera.Conductive additives affect microbial functional characteristics by affecting microbial composition,and microbial functional characteristics further affect digiestion process characteristics.Process characteristics and microbial functional characteristics jointly affect biogas production.The key factor affecting biogas production is the methanogenic metabolic pathway in microbial functional characteristics,which is also affected by the electron transfer between microorganisms.（5）The biogas project using conductive additives to treat 1 t waste was simulated.And2.5%biochar（CO₂emission reduction of 5.04 kg,income increase of 45.52%）,and 7.5%magnetic biochar（CO₂emission reduction of 5.58 kg,income increase of 28.68%）were added to cow manure for better performance.Adding 2.5%biochar（CO₂emission reduction of 10.64 kg,increased income by 50.05%）,2.5%magnetic biochar（CO₂emission reduction of 10.77 kg,increased income by 46.06%）and 5%magnet powder（CO₂emission reduction of 11.11 kg,increased income by 34.15%）in food waste had better performance and were suitable for promotion.In conclusion,the biogas production effect was significantly improved when 7.5%magnetic biochar was added in cow manure anaerobic digestion and 5%magnet powder was added in food waste anaerobic digestion.However,considering both environmental protection and economic benefits,adding 2.5%biochar was more suitable for practical biogas projects.This study systematically revealed the mechanism of conductive additives on biogas production characteristics,process characteristics and microbial characteristics of anaerobic digestion,and the key step for methanogenic metabolic pathways was clarified.In addition,a solid theoretical basis for the application of conductive additives in biogas projects production.