Study On The Effect Of PVC Microplastics In Sludge On Hydrogen/VFAs Production By Anaerobic Fermentation

The impact of microplastics on sludge treatment process and the environmental risk of sludge disposal have attracted extensive attention of researchers.Anaerobic fermentation is an effective technology for sludge resource utilization,and it is of great significance to study the effect of microplastics on anaerobic fermentation and explore its mechanism for sludge resource utilization.The effect of microplastics in seed sludge on hydrogen production by glucose mesophilic anaerobic fermentation was studied by batch experiment.The changes of hydrogen production,substrate and EPS with different PVC microplastics were compared,and results showed that the short-term existence of PVC microplastics in seed sludge had no effect on hydrogen production from glucose(P>0.05).However,hydrogen production was inhibited with microplastics soaked in the seed sludge for a long time,and hydrogen production of Q2 group(50 mg PVC/g COD)decreased by 4.3%,while that of Q3 group(200 mg PVC/g COD)decreased by 25.9%(P<0.01).In addition,PVC microplastics had little effect on EPS in the short term,while the concentration of EPS was directly proportional to the abundance of microplastics with microplastics soaked in the seed sludge for a long time(r =0.930,P<0.05).The effects of microplastics on the acid production and substrate of anaerobic fermentation of sludge were studied by batch experiment.The effects of microplastics on the acid production process were further clarified by simulating each step of anaerobic fermentation,and results showed that the middle and high abundance microplastics had the promotion effect on acid production,while low abundance microplastics had a slight inhibition effect.In addition,microplastics can promote the dissolution of sludge,and the higher the abundance is,the stronger the dissolution is.Too low or too high abundance microplastics will inhibit glucan degradation,but medium abundance is conducive to the degradation of glucan,and the proteolysis process is generally inhibited by microplastics.In the acidification stage,middle and high microplastics can inhibit the acidification of carbohydrates,but microplastics with the same abundance can promote the acidification of amino acids.In the process of acetic acid production,the high abundance of microplastics will inhibit the process of acetic acid production.High abundance of microplastics can inhibit the process of methanogenesis and sulfate reduction.The mechanism of hydrogen and acid production was investigated by bisphenol A(BPA)test,FTIR,SEM and molecular biology.There existed a two-way process of leaching and adsorption between microplastics and BPA.BPA in the scope of this study(less than 0.27 ug/L)can promote hydrogen and acid production.EPS plastic binding SEM and micro analysis showed a surface functional group,micro plastic sludge is gradually "endocytosis" phenomenon occurred during fermentation,which is advantageously formed on the surface of microbial growth "plastic ring" environment.For the hydrogen production system,microplastics inhibited microbial diversity as a whole,and inhibited the growth of planctomycetes and Actinobacteria,and the decrease of Clostridium?sensu?stricto?1 is the main reason for the low hydrogen production with high abundance of microplastics.For the acid production system,although the microbial diversity is still inhibited,the high abundance promotes the coexistence of different microorganisms in the biofilm due to the stronger environmental effect of "plastic circle".The low and middle abundance of microplastics is favorable for the growth of Proteobacteria,and reached 29.8% with middle abundance,while high abundance inhibited its growth(only 19.3%),which was the main reason for the highest acid production.The main hydrogen producing bacteria in hydrogen production system were Enterobacter spp and Clostridium butyricum,and BPA selectively inhibited Clostridium butyricum;However,it can promote the growth of Enterobacter spp.For the acid production system,BPA can promote the growth of acetic acid producing bacteria(FIHFS),and ultimately increase the amount of acetic acid(the main component of TVFA).At the same time,microplastics can inhibit methanogens,so BPA can increase the production of VFAs.