Effect Of Conductive Carbon Materials On The Degradation Of Benzoic Acid Or Phenol Under Anaerobic Conditions

Benzoic acid and phenol are the most widely used organic chemical raw materials in the industry at present.Their contents in industrial wastewater are high,and they are difficult to be degraded by microorganisms for their biological toxicities under natural conditions,thus bringing great threats to human health and the environment.The anaerobic degradation of benzoic acid and phenol involve the biochemical processes of a variety of microorganisms,it's susceptible to external factors such as temperature,pH,H2,etc.,It is necessary to study the effect of these environmental factors on their degradation and employ other pathways such as direct interspecies electron transfer(DIET)to strengthen their biodegradation processes.Furthermore,benzoic acid is an important intermediate in the process of anaerobic degradation of some complex aromatic compounds,and is also an intermediate product of anaerobic degradation of phenol.Theref'ore,the exploration of anaerobic degradation of phenol and benzoic acid will help further understand the migration and transformation of aromatic compounds in the environment and have a certain good guiding significance for anaerobic degradation of other complex aromatic compounds such as polycyclic aromatic hydrocarbons(PAHs).The main contents and results of this article are as follows:1.The effect of different concentrations of granular activated carbon(GAC)and multi-walled carbon nanotubes(MwCNTs)on the degradation of benzoic acid on proper anaerobic conditions is explored in the batch mode.It is found that there is an intermediate product of acetic acid generation,and finally it is converted to methane.Compared with the control group,anaerobic degradation of benzoic acid is enhanced after the addition of the conductive carbon-based material.According to the theory of direct interspecies electron transfer(DIET),the conductive carbon-based material acts as an electron conduit,directly transferring electrons generated during the anaerobic degradation process of benzoic acid to the methanogenic bacteria,thus accelerating the consumption of intermediate product-acetic acid,thereby accelerating the anaerobic degradation process of benzoate.When GAC concentration is 5 g/L and the MwCNTs concentration is 1 g/L,the positive effect is best,and the degradation rate of benzoic acid increases by 45.09%and 15.24%(Cycle2),respectively.In addition,the inhibitory effect of headspace H2 partial pressure on its degradation is also explored.It is found that when the partial pressure is greater than 80%,the degradation of benzoic acid is completely inhibited,and as the H2 partial pressure of the headspace increased,the inhibitory effect is stronger.2.The effect of anaerobic degradation of benzoic acid is compared at the optimal concentration of three different materials,which the GAC is 5 g/L,MwCNTS is 1 g/L,and the Graphite is 100 mg/L.It is found that all carbon-based materials have a positive effect on the anaerobic degradation of benzoic acid,in which the degradation rate of 5 g/L GAC experimental group benzoic acid is fastest,followed by MwCNTs and Graphite experimental groups.Compared to the control group,the anaerobic degradation rate increases by 75%,35%,and 11%,respectively.The analysis of microbial flora shows that Proteobacteria,Betaproteobacteria and Gammaproteobacteria predominate(56.25%)in the control group.There are a wide range of microorganisms and a fairly large proportion.In the experimental group,the?,?-Proteobacteria still dominate,but the Gammaproteobacteria are dominant,andthey are replaced by Spirochaetes,Bacteroidia,and others.According to DIET theory,these microorganisms contribute to the production of hydrogen by the hydrolysis of benzoic acid,such as Synergistia.Secondly,the analysis of the archaea related to methanogenesis shows that hydrogenotrophic methanogens in the experimental group increase while acetoclastic methanogens decrease.Obviously,hydrogenotrophic methanogens must play more roles in the DIET than acetoclastic methanogens.3.The influence of the three different conductive carbon-based materials on the degradation of phenol is further explored.It is found that compared with the control group,the experimental groups of MwCNTs and Graphite promote anaerobic degradation of phenol,and the MwCNTs group has more obvious positive effect than the Graphite group.The anaerobic degradation rate increases by 59.20%and 44.40%,respectively.In addition,it is found that the degradation rate of phenol is fastest at 200 mg/L when 1 g/L MwCNTs is added in the batch mode,and its degradation rate is 33.51 mg L-1·d-1,and increases by 147%compared with the control group,while the degradation rate of Graphite experimental group is 27.38 mg L-1 ·d-1,and increases by 102%.