Interaction Between Anaerobic Microbial Aggregates With Biogas Microbubbles And Polystyrene Nanoparticles

As a biological treatment method for wastewater that can remove pollutants and generate energy,anaerobic digestion technology is considered to be a sustainable wastewater method due to its low energy consumption,low operating costs,and methane generation to recover energy.However,so far,there are still many scientific issues that need to be explored in depth in terms of how to improve the mass transfer efficiency of the reactors,maintain the stability of the system,and reduce the risk of the effluent environment.Among them,there are two important limiting factors.(1)The mechanism of interaction between the anaerobic microbial aggregates and the biogas microbubbles is not clear,which has important theoretical significance for optimizing the design of the reactors;(2)The interaction of the new type of pollutants repressed by nanoplastics and anaerobic microbial aggregates has not been fully revealed.There is important practical guidance to maintain the stability of the reactor and reduce the risk of effluent.Therefore,this study focuses on the above two bottlenecks,using impinging-jet technology and bubble probe atomic force microscopy(AFM)technology to analyze the interaction of anaerobic granular sludge and biogas microbubbles,and expecting the mechanism of interaction between aggregates and polystyrene nanoparticles(PS-NPs)from the level of microbial communities,cells,and genes etc.to provide some theoretical guidance for the optimization and stable operation of anaerobic reactors.(1)The interaction between anaerobic granular sludge and biogas microbubbles was analyzed.The impinging-jet experiment results showed that the normalized adhesion flux ofCH4 and CO2 microbubbles on the anaerobic granular sludge decreased with the increase of Reynolds number in the range of 40-140.The adhesion flux are directly proportional with the contact angle of granular sludge,and the number of hydrophobic functional groups.Anaerobic granular sludge from protein wastewater has a more hydrophobic surface.At the same Reynolds number,the adhesion flux of CH4 and CO2 microbubbles on anaerobic granular sludge from protein wastewater is greater than that of anaerobic granular sludge from brewery wastewater.The bubble probe AFM technique was used to analyze the adhesion force between the anaerobic granular sludge and biogas microbubbles.The results showed that the adhesion force of CH4 and CO2 microbubbles to anaerobic granular sludge from protein wastewater was significantly greater than that of anaerobic granular sludge from brewery wastewater(p<0.01)(2)The effect of different charge PS-NPs on the performance of anaerobic granular sludge is explained.The results indicated that the amino-modified PS-NPs with positive charge(PS-NH2)had stronger inhibitory effect on gas production of anaerobic granular sludge than that of sulfonic acid-modified PS-NPs with negative charge(PS-SO3H).However,this inhibitory effect would be recovered in the second cycle of action.Two differently charged PS-NPs could change the protein secondary structure of EPS and penetrated the EPS layer into the anaerobic granular sludge.The 16S rRNA sequencing results showed that the relative abundance of various methanogens decreased in the first cycle,but significantly increased in the second cycle.Methane-producing functional genes(mcrA and ACAS genes)also showed similar changes.(3)The interaction mechanism of PS-NPs and anaerobic flocculent sludge was explored,based on the response of Methanosarcina acetivorans C2A to PS-NPs.In order to improve the contrast of PS-NPs in complex environmental samples,palladium-doped PS-NPs(Pd-PS)were synthesized.Compared with the blank group,Pd-PS could reduce the methane production of anaerobic flocculent sludge.After the addition of Pd-PS,the content of protein and polysaccharides in EPS of anaerobic flocculent sludge were reduced,but Pd-PS mainly interacted with protein in EPS.Because Pd-PS reduced the relative abundance of methanogens,Methanosarcina acetivorans C2Awas selected to further explore the interaction between Pd-PS and anaerobic flocculent sludge.The results showed that Pd-PS reduced the methanogenic capacity of the M.acetivorans C2A5 although it did not significantly inhibit the growth of M.acetivorans C2A.Functional genes analysis results showed that Pd-PS mainly inhibited the metabolic pathway of methanol to methane in M acerivorans C2A,so as to achieve the purpose of inhibiting its methane production.(4)The effect of PS-NPs on the horizontal transfer of antibiotic resistance genes in anaerobic microbial aggregates was studied.Six kinds of antibiotic resistance genes,such as qnrA,sull,and cmlA,were identified from the biofilm on the microplastics surface of the domestic wastewater treatment plant.Using Escherichia coli J53 as the receptor,the conjugation transfer of the sulfonamide resistance gene sull,which was closely related to mobile genetic elements,was studied.The results showed that the sull on the biofilm was transferred to E.coli J53,and the frequency of horizontal transfer was significantly higher than the horizontal transfer frequency of sludge samples in wastewater treatment plant(p<0.05).Comparative genomics results showed that E.coli J53 obtained integron information due to the horizontal transfer of sull,but did not change its metabolic function.The study also found that PS-NPs could increase the permeability of anaerobic flocculent sludge by destroying the cell membrane of bacteria,thereby promoting the horizontal transfer of sull in anaerobic flocculent sludge to environmental microorganisms.