| Microplastics are a new type of pollutant that inevitably enter the municipal sludge treatment system,and have negative effects on sludge components,enzyme activities,and microbial community diversity.Anaerobic fermentation technology is the most widely used technology in sludge treatment.At present,there are few reports that microplastics effect on anaerobic fermentation process of sludge for acid production and phosphorus release.Therefore,it is necessary to carry out research that the effects and mechanisms of microplastics on anaerobic fermentation process of sludge for VFAs production and phosphorus release,as well as the interaction mechanism of the two.Firstly,polyethylene(PE)widely presented in WAS considering the microplastics content.By using sequential batch and continuous flow methods,the article studied the effects and mechanisms of PE on VFAs production from sludge anaerobic fermentation under different fermentation conditions.Sequencing batch test results showed that PE enhanced the VFAs production from sludge anaerobic fermentation,and high content was more significant for enhancement of sludge hydrolysis and acidification.The continuous flow test results showed that the change trend of VFAs production in the anaerobic fermentation system first increased and then decreased,and was gradually lower than the blank control group.In addition,the low content of PE(75 plastic/g-TS)had little effect on EPS.Under the effect of high content of PE(200 plastic/g-TS),the Zeta potential of EPS was lower,which increased the contact between PE and cells.We also found the content of protein(PN)and polysaccharide(PS)in EPS increased,which can resist the high concentration of toxicity of PE.Through 3-D fluorescence,we discovered that zone II(type II aromatic protein substances),zone III(fulvic acid-like substances)and zone V(humic acid-like substances)of non-biodegradable organic matter increased under the action of high concentration of PE,which meant that PE promoted non-biodegradable organic matter concentration to inhibit the acid production in anaerobic fermentation.Combining the detection of enzyme activity and microbial community,the results showed that high concentration of PE(200 plastic/g-TS)inhibited the activity of protease,?-glucosidase and AK.Moreover,the microbial diversity in the fermentation system was the lowest,and the relative abundance of genera related to acid production reduced,such as Bacillus,Proteiniclasticum,Bacteroides,and Corynebacterium.In summary,high concentrations of PE has an inhibitory effect on the enzyme activity and functional flora to inhibit the VFAs production.Then,the effect and mechanism of PE on phosphorus release during anaerobic fermentation were studied.Sequencing batch test results showed that phosphorus release was consistent with the VFAs production.The reason was that short-term existence of PE promoted sludge cracking and the release of phosphorus-containing organics,which increased the concentration of phosphorus in the fermentation supernatant.The continuous flow tests result showed that the change trend of PO43-in the supernatant first increased and then decreased,and under non-constant alkaline conditions,the PO43-in the supernatant was gradually lower than the blank control group.Combined with the analysis of the morphological distribution of phosphorus by SMT method,it was found that phosphorus existed mainly NAIP in the solid phase.High concentration of PE reduced the abundance of dissimilatory metal-reducing bacteria Clostridium,so as to reduce the conversion of Fe3+compounds,meanwhile the production of VFAs reduced,which reduced the supply of organic substrates and electron donors for Fe3+reduction.Therefore,the presence of phosphorus existed mainly NAIP in the sludge and reduced the conversion of PO43-.Under non-constant alkaline conditions,the content of PO43-in the liquid phase was gradually lower than the blank control group.Because the high concentration of PE inhibited the activity of methanogens and enzymes,resulting the large accumulation of VFAs in the system and the decrease of p H.Low p H is not conducive to the growth and reproduction of microorganisms,and inhibits microbial activity.This was negative impacts on the production of VFAs and the conversion of PO43-.Finally,the influence of anaerobic fermentation process on PE was studied.The FTIR and XPS spectra of PE showed that the new absorption peaks appeared at1712cm-1 and 3300cm-1 and the bond between C-O and C=O increased.The aging index CI and O/C ratio showed that the anaerobic fermentation process could oxidize PE and make it aging,and the aging rate was faster under non-constant alkaline conditions.The analysis of SEM and water contact angle proved that anaerobic fermentation changed the surface structure and hydrophilicity and hydrophobicity of PE.The ability of aging microplastics to adsorb toxic chemicals in the sludge was enhanced,thereby inhibiting the activity of anaerobic fermentation microorganisms,resulting in lower anaerobic fermentation efficiency.The interaction mechanism between PE and anaerobic fermentation process is revealed... |
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