Study On The Performance And Mechanisms Of Anaerobic Sludge-Digesting Methanogenesis Enhanced By Red Mud

Anaerobic digestion of methane is one of the important ways to achieve sludge reduction and resource utilization.In anaerobic digestion,the efficiency of electron transfer between microorganisms is a key factor in determining their methanogenic properties.Although the addition of conductive materials can effectively improve the efficiency of electron transfer,most commonly used conductive materials are costly and the production process is complicated,which limits its large-scale popularization and application.Red mud is a highly alkaline by-product produced by bauxite ore refining alumina.It has good conductivity due to its rich iron oxide and therefore has the potential to promote interspecies electron transport.Based on the above considerations,this paper takes residual sludge as the research object,selects red mud as conductive material,explores the influence and mechanism of red mud addition on the anaerobic digestion of methane production,as well as clarifys the response mechanism of endogenous redox mediators?ERMs?to temperature induced by red mud.The main research contents and experimental results are as follows:?1?Red mud addition?20.0 g/L?significantly improved the methane production performance of sludge anaerobic digestion,and increased the accumulation of methane by 35.5%.Red mud effectively accelerated hydrolysis-acidification of organic compounds in the sludge,which resulted in the increase of protein,polysaccharide,and VFAs by5.1–94.5%,offering more substrate for methanogenesis process.Moreover,the addition of red mud significantly enhanced electrical conductivity of the anaerobic digestion system and effectively improved direct interspecies electron transfer?DIET?.Microbial community analysis showed that red mud addition can effectively increase the relative abundance of Syntrophorhabdaceae,Geobacter,Clostridiaceae,Ruminococcaceae,and methanogenic archaeas like Methanosaeta and Methanosarcina,enhance direct interspecies electron transfer and promote the anaerobic digestion of sludge to produce methane.?2?Multivalent cations from red mud can combine with EPS secreted by microorganisms to promote the formation of biological aggregates and create conditions for direct electron transfer?DIET?.In addition,the addition of red mud significantly promotes EPS secretion,especially the tightly bound EPS?TB-EPS?,which contains a large amount of ERMs such as c-type cytochromes?c-Cyts?and humic substances.These ERMs can also mediate the electron transfer process between syntrophic bacteria and methanogenic archaea,thereby increasing methane production.?3?The methane production potential under different temperature conditions is linear with the redox parameters such as electron exchange capacity?EEC?.The promotion effect of red mud on methane production by anaerobic digestion of sludge accelerated with the increase of temperature.Spectral analysis further indicated that change of temperature wouldaffect the types and concentrations of key groups in ERMs,thereby affecting the formation of methane.The model fiting result revealed that the contribution of ERMs to the CO₂ reduction to CH₄ increased from 35.2±1.4%to 58.6±1.5%when the temperature rose from 15? to 35?.The above research results manifest that the addition of red mud can promote electron transfer efficiency of microbial species through multiple ways,thereby improving the methane production performance of sludge anaerobic digestion.This will give a new perspective for the resource utilization of industrial waste,and also provide an important scientific basis for improving the efficiency of treatment and disposal of excess sludge.