Enrichment Of Naphthalene Anaerobic Digestion Based On Biochar/Zero-valent Iron And Study Of Microbial Community Response

Nowadays,much attention has been paid to the petroleum hydrocarbon contaminants.As the main ingredient of the petroleum hydrocarbon contaminants,polycyclic aromatic hydrocarbons(PAHs)are the persistent organic pollutants with the volatile,persistent and the high toxicity.Hydrophobic and low solubility in water make much of PAHs deposit to the soil,that causes the pollution to environment.Researches have pointed out that the microbial anaerobic degradation is the main way of PAHs natural attenuation.However,the anaerobic digestion(AD)has the disadvantage of low efficiency,and the research on mechanism is relatively few.Therefore,the researches on the AD of PAHs can provide necessary theoretical foundation and data support for the evaluation of the trend of PAHs in deep soil environment and the pollution remediation under the anaerobic condition.In this study,Naphthalene(Nap),a typical PAHs,was selected as the research object.Combined with the actual environmental pollution background value,laboratory experiment was conducted to simulate the in-situ pollution conditions in the Yellow River Delta on study the combined pollution effects of Nap and NaCl to microbial community structure.Hydroxypropyl-?-cyclodextrin(HP-?-CD)was added for solution-promoting,zero-valent iron(ZVI)and biochar(BC)were added to AD system of Nap based on the change of interspecific electron transport(IET).The mechanism of ZVI/BC-Nap digestion was explored,the abundance variation of tolerant microorganisms under different salinity was analyzed,and the response mechanism of microbial community was revealed.The specific research details are as follows:1.Based on the background value of petroleum hydrocarbon pollution in the Yellow River Delta region,the response of AD to the combined pollution with Nap and NaCl was studied.The results showed that the presence of NaCl and Nap had a significant impact on the macroscopic indices of methane production and microscopic indices of microbial community in AD.Under the condition of 25‰ NaCl and 150 mg/L Nap,the maximum inhibition of methane production was observed(inhibition rate of 99.22%).The effect of NaCl concentration was greater than Nap in the combined pollution.The highest abundance of the salinity tolerant Methanofollis was obtained in the 4.38‰ saline treatment,accounting for 83%of methanogen.Hydrotrophic methanogens were enriched with NaCl addition,while the acetoclastic methanogens were enriched with Nap addition separately2.Based on the above results,The ZVI and BC were added to the AD system of Nap to explore the regulation mechanism of ZVI/BC mediated.The results showed that the AD efficiency of Nap was significantly improved with the addition of moderate dosage of ZVI/BC.The performance of AD based on BC-Nap showed that the optimal system was observed with the 300 mg/L Nap and the 5.81 g/gVS BC.The maximum methane yield was increased by 30.05%compared with the control.While,IN30-1(Nap 30 mg/L,ZVI=8.40 g/gVS)system achieved the optimal promotion effect(P_CH4=1 04.60 mL/gVS)with the ZVI and Nap added.Compared with the control(P_CH4=95.12 mL/gVS),the maximum methane production increased by 10%and K_max increased by 42.86%.16S rRNA sequencing showed that the addition of BC and ZVI significantly improved the microbial community structure.The methanogenesis was further optimized due to the increasing abundance of syntrophic VFA-oxidizing bacteria,acetogens and methanogens.The abundance of hydrotrophic methanogen was increased due to the existent ZVI and BC.Moreover,the microorganism involved in interspecific electron transfer was enriched such as Geobacter,Methanothrix,Chloroflexi,etc.,the highest abundance occurred to BN_300-0.5(Nap=300 mg/L,BC=5.81 g/gVS)and IN300-0.2(Nap=300 mg/L,ZVI=1.68 g/GVS),respectively3.UASB reactor was runned continuously with the Nap added.The HP-?-CD was added into UASB to promote the dissolution of Nap.Based on the optimal dosage of above batch tests,the BC(5.81 g/gVS)and ZVI(8.40 g/gVS)were added into reactor.It was found that the stability of UASB reactor was destroyed due to the continuous addition of Nap.However,the strengthen and control of ZVI/BC and H-?-CD increased the methane production(58.33%).Microbial community analysis and in-situ metabolic experiments showed that the abundance of syntrophic propioniate/butyrate oxidization bacteria(SPO/SBO)and hydrotrophic methanogens was increased,while syntrophic acetate oxidization bacteria(SAO)and acetoclastic methanogens was decreased with the continuous contamination of Nap.Metabolomics analysis showed that HP-?-CD increased the solubility of Nap,the proportion of intermediate products of Nap degradation increased from 0.06%to 0.09%.