The Effect Of BmimCl Or [P（CH₂OH）₄]Cl Ionic Liquids In The Process Of Anaerobic Digestion

Ionic liquids are widely used in biomedicine,catalysis chemical,synthesis and other fields as"green chemicals"that can replace volatile organic solvents.However,its low biodegradability and high stability make it a persistent threat to terrestrial and aquatic environments,and it is considered as a representative emerging persistent pollutant.In recent years,the environmental potential toxicity of ionic liquids has been a research hot spot.Nevertheless,up to now,toxicological studies on ionic liquids have mainly focused on monocultures or single organism,with little information available to complex syntrophic consortium that dominates the complex and successional biochemical processes,such as anaerobic digestion.The lack of systematic studies hindered the understanding of the ecological risks of ionic liquids.Therefore,in this study,the traditional ionic liquid 1-butyl-3-methyl-imidazolium chloride（BmimCl）and the hydrated ionic liquid tetrakis（hydroxymethyl）phosphonium chloride（[P（CH₂OH）₄]Cl）were taken as the model ionic liquid to explore the behavior and mechanism of their influence on the glucose anaerobic digestion process.Based on the above research,the effect of the structure of ionic liquid on the methane production rate was investigated to further explain the influence of ionic liquid on anaerobic digestion.In this thesis,the effects of different levels of BmimCl（0,1,5,10,15 and 20 mg/L）on glucose anaerobic digestion were investigated.The results showed that BmimCl inhibited glucose anaerobic digestion,and the inhibition degree became more significant with the increase of BmimCl concentration.The presence of BmimCl not only reduced the maximal biochemical methane potential,but also slowed the maximum methane production rate,and prolonged the lag phase of digestion.In addition,BmimCl inhibited acidogenesis,acetogenesis,hydrogenotrophic methanogenesis,and acetotrophic methanogenesis during anaerobic digestion.In the process of anaerobic digestion,extracellular polymeric substances（EPS）adsorbed and accumulated BmimCl through carboxyl,amino and hydroxyl groups,and the presence of BmimCl can destroy microbial cell membranes and even induce cell apoptosis.BmimCl changed the bacterial and archaea community structure in the anaerobic digestion reactors,reducing the relative abundance of some genera involved in acidogenesis and methanogenesis（such as Bacteroides,Clostridium＿sensu＿stricto＿1and Methanosaeta）.The effects of different levels of[P（CH₂OH）₄]Cl（0,0.1,1,2,3 and 4 mg/L）on the anaerobic digestion of glucose were investigated simultaneously.The results showed that[P（CH₂OH）₄]Cl not only reduced the carbon fluxes from glucose to methane,but also remodeled the carbon flows among acidogens,acetogens,and hydrogenotrophic and acetoclastic methanogens.Toxicological mechanism studies revealed that[P（CH₂OH）₄]Cl interacted with EPS through hydrogen bonding and electrostatic attraction,leading to loose or even damage structure of EPS,and[P（CH₂OH）₄]Cl destroyed the cell wall and membrane of anaerobic bacteria,thereby resulting in the apoptosis of anaerobic bacteria.Mi Seq sequencing data illustrated that the abundances of key acidogens and methanogens（such as Bacteroides,Clostridium＿sensu＿stricto＿1,and Methanosaeta）decreased remarkably after exposure to[P（CH₂OH）₄]Cl.Based on above studies,the effects of seven chloride-based ionic liquids(BmimCl,Hmim Cl,Omim Cl,[P（CH₂OH）₄]Cl,[P_4,4,4,4]Cl,[N_4,4,4,4]Cl,Bmpyr Cl)on the methane production rate during glucose anaerobic digestion were investigated using short-term batch texts.The results showed that different chloride-based ionic liquids have different effects on the rate of methane production.In general,imidazolium-based and pyridinium-based ionic liquids showed stronger inhibition than that of tetrabutylammonium and tetrabutylphosphonium ionic liquids.Moreover,in the three imidazolium-based ionic liquid,the inhibition of the ionic liquids was enhanced by the extension of the alkyl-chain length in ionic liquids,e.g.,BmimCl<Hmim Cl<Omim Cl.This study comprehensively investigated the carbon flow,mechanism and microbial characteristics of BmimCl and[P（CH₂OH）₄]Cl in the glucose anaerobic digestion,and deepened the understanding of BmimCl-involved and[P（CH₂OH）₄]Cl-involved anaerobic digestion.