| Currently,rapid industrialization and urbanization have led to the release of toxic pollutants,such as persistent organic pollutants,pesticides,and emerging organic pollutants(e.g.antimicrobial agents)into the aquatic environments and threatened the aquatic environment.As a sedimentation tank for rivers,the sediment contained various organic and inorganic substances,especially some persistent organic pollutants and heavy metals.The contaminants in sediments will transfer to the overlying water,which will affect the aquatic quality and the surrounding environment.Introducing electron donors and acceptors(such as methanol and nitrate)could enhance the removal of organic pollutants in the sediment.Moreover,Based on the principle of bioelectrochemistry,regulating the bioelectrical stimulation of the anode(electron acceptor)or cathode(electron donor)can enhance the removal of various organic pollutants in(e.g.petroleum hydrocarbons(PHs),polycyclic aromatic hydrocarbons(PAHs)).More importantly,the bioanode is environmentally friendly as a fixed electron acceptor with no byproducts.In this study,the electron donors and acceptors were introduced to the sediment to regulate sediment microbial respiration for degrading the organic pollutants in the sediment.The succession of the sediment microbial community during the remediation process and the dominant bacteria in different periods were discovered.The correlations between the characteristic organic pollutants removal and potential functional bacteria were analyzed,and the conceptual models of the exogenous electron donors and acceptors combined with bioelectrochemistry for the enhanced bioremediation of complexly contaminated sediments were summarized.With the stimulation of exogenous methanol as selective electron donor,the removal rates of petroleum hydrocarbons and polycyclic aromatic hydrocarbons in the sediment were 81.6-92.5% and 68.2-73.3% within 65 d,respectively,which increased by 4.8-18.5% compared with the control.Moreover,with the increase of methanol dosage,the degradation efficiency is slightly improved.Methanol in the overlying water was completely consumed within 6 d,and on the fourth and fifth d,the concentration of acetic acid and propionic acid increased by 33%,indicating that methanol stimulated the growth of the hydrolyzed acidified bacteria,thereby enhancing the hydrolysis and acidification of organic matter in the sediment.In the methanogenic stage,the addition of methanol leads to a decrease in the phylogenetic index.At different time periods,the sediment microbial community was significantly different.In the methane production stage(MP),the relative abundance of Methanomethylovorans could reach 25.87-58.53%,which was consistent with the phenomenon of methane production at this stage;in the medium of the operation stage(MO),the relative abundance ratio of sulfur-oxidizing bacteria Sulfuricurvum increased to 34-39.2%,which was significantly positively correlated with TPHs and PAHs degradation efficiency(r = 0.45-0.59,P <0.01);and in the final stage of remediation,the difference between the terminal point(TP)and the original sediment was found to be decreased.With the joint stimulation of methanol and bioelectricity for the complexly contaminated sediments remediation,the degradation rate of total petroleum hydrocarbons(TPHs)and polycyclic aromatic hydrocarbons(PAHs)increased by 1.45-4.38 times,and the removal rate of total organic carbon(TOC)and loss on ignition(LOI)of the sediment increased by 6-12%.After adding methanol,the TOC concentration of the overlying water was obviously increased,while the pH decreased,and the lowest pH could reach 5.5.In the next 20 days,the TOC of the overlying water returned to the state before addition,and the pH returned to about 7.5.After the combined stimulation with methanol and electrode,the phylogenetic diversity of the anodic biofilm was reduced.Methanol stimulation promoted the selective enrichment of key electroactive degrading bacteria(Geobacter and Desulfobulbus).The relative abundance and characteristic pollutants(e.g.TPHs,PAHs,and cycloalkenes)and TOC degradation efficiency(r = 0.81-0.83,P ? 0.001)were significantly positively correlated.This study provided a new strategy to improve the bioremediation of complexly contaminated sediments stimulated by co-substrate(such as methanol),and found that the electroactive degraders were obviously enriched under the joint stimulation of methanol and electrode.Air intermittent aeration(oxygen acted as external electron acceptor)combined with bioelectricity enhanced the removal of phthalate,herbicide(e.g.alachlor and butachlor)and antibacterial triclosan in the sediment.The removal efficiency of phthalate and herbicide could reach more than 85%,while the degradation rate of triclosan was only 42.5%,even though the removal rate was nearly doubled compared with the control.During the aeration of the sediment,the TOC,TN and turbidity of the overlying water increased.After 15 days,the TOC and TN decreased to the pre-aeration level.When the second aeration was performed,the water quality fluctuation was significantly less than the first time,and the water recovery time was shortened to 10 days.Compared with the unaerated experimental group,the TOC and TN concentrations of the overlying water were lower,indicating that intermittent aeration could improve the water quality of the overlying water.The sediment microbial community diversity of anodic biofilms is affected by aeration disturbance,and the diversity of anode biofilm with intermittent aeration(OAF)is higher than that of anode biofilm without intermittent aeration(AAF).RDA analysis indicated that the degradation rates of pollutants were positively correlated with the microbial communities of the aeration disturbance.Nitrospira in the sediment was significantly enriched in both the sediment and the anodic biofilm due to intermittent aeration.It was found that the TN concentration of the overlying water was significantly inversely proportional to the relative abundance of Nitrospira,Which is a good illustration of the importance in the process of nitrogen removal from water.Sulfur-reducing bacteria(SRB)such as Desulfobulbus and Desulfobacca,which were involved in the sulfur cycle,have a higher proportion in the anodic biofilm than those in the sediment,while the sulfur-oxidizing bacteria Sulfuricurvum was more abundant in the sediment than that in the bioanode.In the sediment,the metabolic cycle of sulfur could be related to the degradation of various contaminants.In this study,the synergy of electron donor/receptor and electrical stimulation enhanced the degradation of representative organic pollutants in the river sediment.The results revealed the microbial metabolic activities involved in the remediation process and found potential functional degraders which had a significant correlation with the removal efficiency of targeted pollutants.The study provides new ideas for the potential application of complexly contaminated sediment bioremediation technology introducing electron donors and acceptors. |
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