Study On The Effect Of Microplastics On Anaerobic Digestion Performance Of Food Waste And Antibiotic Resistance Gene Propagation And Its Control

Anaerobic digestion（AD）,as one of the mainstream technologies of biological treatment of food waste（FW）,is easily affected by exogenous pollutants due to its poor stability.Currently,few studies have focused on the interaction effects of the AD processes with emerging pollutants such as microplastics（MPs）and antibiotic resistance genes（ARGs）.It is widely believed that MPs have adverse effects on environmental processes involved by microorganisms,and the particle size of plastics is a key factor in determining the degree of impact.In addition,there has been no relevant research on whether the presence of MPs will affect the environmental behavior and transmission process of ARGs in FW.To address the above problems,this study explored the effects of MPs with different sizes on AD performance and ARGs behavior during AD of FW,as well as revealed the mechanisms from the perspective of microbial community structure,function and cytotoxicity.At the same time,the influence and mechanism of biochar weakening MPs exposure on AD performance and ARGs transmission were also discussed.The main research conclusions are as follows:（1）The effects of MPs on the AD performance of FW and its mechanism were explored.The results showed that,20 particles/g-TS polystyrene MPs with the particle size from 1 mm to 1μm decreased the cumulative methane production by 1.46～18.11%compared with control group.200 particles/g-TS MPs showed a more significant inhibition effect（9.14～33.08%）,indicating that the inhibition intensity depended on particle size and dosage.Kinetic models analysis displayed that MPs decreased methanogenic potential of AD and prolonged the lag periods.Physicochemical analysis indicated that MPs with small particle size inhibited organic matter hydrolysis and volatile fatty acids（VFAs）metabolism,which was consistent with the decreased abundance of acetylation-related Proteiniphilum.In addition,small-sized MPs could induce more reactive oxygen species,causing cytotoxicity,resulting in cell membrane damage and inhibiting the activities of key enzymes(α-glucosidase,protease,acetic kinase and F₄₂₀),thus restraining methane production.The analysis of Acetyl-Co A synthase and Methyl-Coenzyme M reductase functional gene illustrated that smalled-sized MPs had negative effects on the abundance of methanogenic archaea such as Methanothrix and Methanosarcina,thus adversely affecting the acetoclastic methanogenesis pathways.（2）The impact and its mechanism of MPs on ARGs behavior during AD of FW were studied.The results indicated that MPs exposure significantly increased the target ARGs abundance,and the total relative abundance was 1.38 to 2.46 times that of the control group,as well as the effect of particle size was greater at low concentrations.MPs exposure led to an increase in the abundance of mobile genetic elements（MGEs）and induced bacteria to produce reactive oxygen species,which enhancing cell membrane permeability and promoting the horizontal transfer of ARGs.In addition,the enrichment of potential host bacteria caused by MPs exposure was the main driving factor affecting the spread of ARGs.The functional prediction analysis of bacterial community based on PICRUSt illustrated that MPs exposure increased the abundance of bacterial homologous recombination,quorum sensing,flagella assembly,bacterial chemotaxis,ABC transporters and two-component regulatory system,which enhancing the horizontal transfer of ARGs between bacteria.（3）The influence of biochar reducing MPs exposure on AD performance of FW and ARGs transmission was carried out.The results suggested that the addition of biochar could effectively alleviate the inhibition of MPs exposure on cumulative methane production during AD.The combined addition of corn straw biochar（MBC）,rice shell biochar（RBC）and bamboo biochar（BBC）compared with the separate MPs group,increased the cumulative methane yield by 6.62%,4.22%and 5.02%,respectively,and shortened the lag period by 7.69～8.10%.In contrast,the enhancement effect of MPs+MBC group was better.Due to its more pore structure and redox functional groups,biochar could accelerate the degradation and transformation of organic matter as well as the consumption of VFAs,enrich the interbacterial and methanogenic archaea,enhance the abundance of functional genes related to electron transfer,promote direct interspecific electron transfer,and increase methane metabolism.At the same time,biochar could also facilitate quorum sensing and signal transduction,slow down the inhibition of MPs on acetogenesis and methanogenesis,reduce oxidative stress and cell membrane damage caused by MPs exposure,thus promoting the recovery of AD performance.In addition,biochar could effectively reduce ARGs propagation caused by MPs exposure,in which MPs+MBC group could reduce resistance genes by 14.93%compared with the separate MPs group.Its action mechanism was that biochar addition decreased the abundance of ARGs potential hosts and MGEs,relieved the damage pressure on cell membrane caused by MPs exposure,inhibited SOS response,declined the effect of MPs on cell membrane permeability,weakened the energy production,restrainted the horizontal transfer potential of ARGs.In conclusion,this study clarified that the influences and mechanisms of MPs on the AD performance of FW and the ARGs spread.At the same time,it was found that biochar could enhance the AD performance and reduce the transmission risk of antibiotic resistance caused by MPs exposure.The results provide a theoretical reference for a comprehensive understanding of the potential risks of the coexistence of MPs and ARGs during AD,as well as the improvement of FW recycling efficiency and the prevention and control of ARGs risk.