Study On The Mechanism Of Enhanced Anaerobic Degradation And Methanogenesis Of Phenol By Biochar Addition

Phenol is widely found in petrochemical,textile,and other industrial wastewater.Its carcinogenic,teratogenic and mutagenic properties have attracted wide attention.The effective removal of phenol and other phenolic pollutants is of great significance to reduce the harm of such wastewater to the environment and human health.Anaerobic biological treatment,as a low energy consumption,sustainable technology,has drawed attentions in recent years.The toxicity of phenol inevitably induces a long lag time of methanogenesis for anerobic phenol digestion.Moreover,the methanogenesis of phenol requires the function of syntrophic microbial consortium,but this approach often have little efficiency.It is of great significance for the stable and efficient treatment of phenol-containing wastewater to explore how to reduce the inhibition of phenol and increase the anaerobic methanogenic efficiency of phenol.The feasibility of biochar for anaerobic degradation of phenol anaerobic phenol degradation was investigated in this study.Firstly,the preparation conditions of biochar were optimized,and then the effect of biochar on the kinetics of methanogenesis was investigated.Finally,based on the analysis of adsorption process and electrochemical characteristics of biochar,the mechanism for biochar enhancing the anaerobic degradation of phenol was proposed.The major contents and results are as follows:?1?The typical bio-wastes such as sawdust and cow manure were selected to investigate the effects of raw materials and preparation temperature?300,500,700??on physical and chemical properties of biochars.The results showed that compared with cow manure biochar,sawdust biochar had higher abundance of oxygen-containing functional groups.In addition,the sawdust biochar prepared at 500?showed the greatest electron exchange capacity?6.57?mol e^-/g?,and had favourable electron-mediated properties.?2?Based on batch experiments,the results showed that the efficiency of phenol degradation was improved after the sawdust and cow manure biochar were added compared with the control group?15 g/L?.The lag time of phenol methanogenesis was shortened from 15.0 days to 1.1-3.2 days,and the maximum methane production rate increased by 2.5-3.5 times.Among all the groups,the sawdust biochar prepared at 500?has the best effect on promoting methane production rate.However,the methane production rate was further increased to 12-16.7 ml/d.It indicated biochar could continuously promote methanogenesis efficiency besides the effects of acclimation.?3?GAC were selected to compare with biochar to distinguish the effects of material properties on methanogenesis of phenol.The results of batch experiments showed that,compared with the control group?15.8-36.1d,1.2-1.4 ml/d?,both biochar and GAC?15g/L?could significantly shorten the lag time of methanogenesis?9.1-10.5d?and increase the methane production rate?1.4-5.9 ml/d?.In addition,the effects of maximum adsorption capacity?biochar,54.3 mg/L,GAC,101.53 mg/g?)on the kinetics of methanogenesis of phenol were investigated at different phenol concentrations?500,800,1200,1500,1700 mg/L?.Under the condition that the phenol loads were lower than the adsorption capacity of adsorbent,the lag time was nearly maintained at 10d.But the lag time increased linearly when the phenol loads was higher than the adsorption capacity.It indicated that the adsorption capacity was crucial to shorten lag time during anaerobic phenol digestion,but the methane production rate was only related to the concentration.It is worth noting that,compared with GAC,the promotion effects of biochar was better with the increase of phenol loads(k_biochar>k_GAC).This suggests that the promotion of methane production by biochar and GAC were based on differences in material properties.?4?Microbial community analysis results showed that genus abundance of Geobacter?7.76%to 15.55%?,Syntrophorhabdus?1.1%to 5.25%?in bacteria and Methaonsaeta?49.18%to 74.11%?in archaea increased significantly compared with the control group when biochar was added,indicating that biochar selectively enriched functional microorganisms and the interspecies hydrogen transfer during the syntrophic methanogenesis of phenol was likely partially replaced by direct interspecies electron transfer?DIET?.Thus,the methane production rate of phenol was promoted.?5?The electrochemical properties of biochar/GAC polymers were characterized by in-situ cyclic voltammetry.The results showed that there is obvious redox peaks on biochar surface by in-situ analysis,indicating that biochar may plays a redox-mediated role.The above results indicated that biochar could be used as adsorbent and redox-mediator to enhance anaerobic degradation of phenol.But GAC provided a good conductive environment for microorganisms.In summary,biochar can be used as an adsorbent and redox-mediator to enhance the syntrophic oxidation degradation and methanogenesis of phenol.