Study On The Anaerobic Degradation Of High Concentration Polycyclic Aromatic Hydrocarbons In Seawater Sediments

Polycyclic aromatic hydrocarbons(PAHs)are persistent organic pollutants with strong toxicity,complex structure,and natural stability.Bioremediation is a promising removal strategy for PAH contamination,and its positive environmental impacts are associated with cost savings and absence of secondary pollution.PAH anaerobic biodegradation is commonly inhibited by the lack of a high-efficiency bioremediation system,insufficient knowledge on degradation mechanism,and limited metabolic pathways for this process.The comparative effectiveness of solvents and reed straw on PAH anaerobic degradation is seldom studied.Original sediment samples were collected from the coastal area in Zhoushan Island and incubated with 3.0 g/L petroleum.A highly efficient PAH biodegradation system was established using acclimated marine sediment as inoculum.This study focused on the mechanism of PAH anaerobic degradation at high concentration by adding different consortiums of carbon source in seawater sediments.The digestion of sediments without carbon source was regarded as control group(B.0).Variations in PAHs and microbial communities were investigated after the carbon source was added into marine sediments with high PAH contamination,and the reaction process was analyzed by GC/MC and high-throughput sequencing.The anaerobic degradation rate of several representative PAHs at high concentration was measured,and the characteristics and metabolic mechanism of the anaerobic degradation of several PAHs were analyzed.The main research contents and conclusions are as follows:(1)The physical-chemical indices of acclimated sediment samples were detected.The concentration of electron acceptors(nitrate and sulfate)was 0-4.7 mg/kg under the pH of 7.4-7.6.The total content of 16 USEPA priority PAHs was 22.41-34.78 mg/kg as determined by GC/MC.(2)This study focused on the use of different consortiums of acetone and dichloromethane as organic solvents of BaP.After 45 days of cultivation,200 mg/L BaP was reduced by 69.53%,95.67%,59.83%,and 64.9%in BC,B,BL,and BCL,respectively.Analysis of microbial communities suggested that the abundance of Romboutsia,Fusibacter,and Dethiosulfatibacter was significantly increased by adding acetone or dichloromethane,and Thioalbus,Sedimenticola,and Desulfuromonas may contribute to BaP anaerobic degradation.(3)The enzymes involved in BaP metabolism were hydroxylase(K00517,K03384),hydrogenase(K14128),dioxygenase(K00446,K14583,K07104,K11945,and K14579),dehydrogenase(K13953,K13954,K11947,K00001,K00121,and K04072),methylase(K00568),hydratase(K14585),and dehydratase(K13920).The metabolic intermediates of BaP were 4,5-dihydro-BaP,7,8-dihydro-BaP,phenanthrene,anthracene,benz[a]-anthracene-7,12-dione,pyrene,9-phenanthrenol,4,5-dihydro-pyrene,1,2,3,4-tetrahydro-phenanthrene,9,10-dihydro-anthracene,9,10-anthracenedione,3-methylsalicylic acid,?-(1-naphthyl)acrylic acid,benzeneacetic acid,1,2,4-benzenetricarboxylic acid,and naphthalene as determined by GC/MS.(4)A new degradation pathway of benz[a]anthracene has been discovered for the first time through GC/MS under BC control.The detected organic compound benz[a]anthracene-7,12-dione was obtained from the initial oxidation of benz[a]anthracene by using enzymes such as hydroxylase(K00517),methylase(K00568),dioxygenase(K11945 and K14579),dehydratase(K13920),dehydrogenase(K00121 and K04072),and hydratase(K14585).Hydrogenase(K14128),dioxygenase(K00446,K07104,and K11945)participated in the transformation of benz[a]anthracene-7,12-dione into 2-naphthoic acid.(5)This study focused on the use of glucose or reed straw acidolysis solution as the cometabolic substrates of benzo[a]pyrene,benzo[b]fluoranthene,pyrene,and phenanthrene.After 100 days of cultivation,the degradation efficiencies of benzo[a]pyrene,benzo[b]fluoranthene,pyrene,and phenanthrene were 1.71-1.84,0.21-0.22,3.88-4.09,and 4.02-4.16 mg/L·day-1,respectively.Analysis of microbial communities suggested that the abundance of sulfate-reducing bacteria such as Desulfuromonas,Desulforhopalus,Desulfovibrio,Desulfobulbus,Desulfobacter,and Dethiosulfatibacter and Halodesulfovibrio was significantly increased by adding glucose or reed straw acidolysis solution.This finding indicated that some sulfate-reducing bacteria are involved in PAH anaerobic degradation.