Study On The Degradation Behavior Of PHA Synthesized By Mixed Bacteria Under Aerobic Composting Of Sludge

Among the biodegradable polymer materials,polyhydroxyalkanoates(PHA)is a biodegradable biopolyester synthesized by microorganisms and is considered to be one of the most promising new materials to replace traditional plastics.As an ideal substitute material,PHA has little research on its degradation behavior and the changes in physical and chemical properties during the degradation process,especially the research on the degradation behavior of PHA with different monomer ratios.In addition,among the existing studies on the degradation behavior of PHA,there are many studies on the degradation of PHA in natural environments such as soil and water.There are few studies on the degradation of PHA under the control of engineering techniques,such as aerobic composting,and the effect of PHA on the composting system during the degradation process remains to be studied.In view of the above problems,this study is based on the analysis of the physical and chemical properties of PHA composed of different monomer ratios synthesized by mixed bacteria under different substrate types,and compared and analyzed the degradation behavior of PHA films with different monomer ratios under the conditions of sludge aerobic composting.Provide a basis for the selection of substrate types in the PHA synthesis process.It also compares and analyzes the degradation behavior of commercially available polylactic acid(PLA)films under the conditions of aerobic composting of sludge,providing a reference for the degradation behavior research of commercially available degradable plastics,and providing a basis for the evaluation of the degradation performance of biodegradable plastics.The influence of PHA on the composting system during the aerobic composting process is also studied,which has theoretical and practical significance for solving the problem of plastic waste pollution.In this study,three substrates of acetic acid(The content of acetic acid in VFAs is 100%,based on SCOD),propionic acid(62%of propionic acid in VFAs),and butyric acid(64%butyric acid content in VFAs)were selected in the PHA accumulation and synthesis stage to synthesize three PHA membranes composed of different HB and HV monomer ratios.The performance analysis of the prepared three kinds of PHA films found that the physical and chemical properties of PHA,such as relative molecular weight,thermal stability and thermal performance,are affected by the monomer composition.With the increase of HV content,the number average molecular weight of the prepared different PHA films decreases,the polydispersity index value increases,the heat resistance and thermal stability increase,the melting point,crystallinity and the glass transition temperature decrease.Through quality changes,membrane surface morphology changes,molecular weight changes,molecular structure changes and thermal performance changes,the degradation behavior of the three PHA membranes under aerobic sludge composting conditions was investigated.The results showed that the three kinds of PHA membranes all showed good biodegradability under composting conditions.On the7th day of composting,the degradation of the three kinds of PHA membranes of acetic acid,propionic acid and butyric acid were 27.7%,63.5%and 39.8%,respectively.The increase in HV monomer content increases the degradation rate;In addition,the degradation rate of the polylactic acid(PLA)film for comparison is significantly lower than that of the three PHA films,and the degradation rate at the end of composting is only 9.74%,indicating the degradation performance of PHA better than PLA.After degradation,the molecular weights of the three PHA films all decreased,from 1.61×10~5,1.44×10~5,and 1.64×10~5 to 1.38×10~5,1.32×10~5,and1.52×10~5,respectively.It shows that after degradation,the bonds of high molecular polymers are broken and degraded into low-molecular-weight oligomers and monomers;during the degradation process,different areas on the surface of the PHA film have different degrees of degradation,and the amorphous areas are preferentially degraded;there is no change in the molecular structure before and after degradation.But the thermal stability is reduced.After degradation,the crystallinity of the PHA film synthesized from the acetic acid substrate decreases,and the crystallinity of the propionic acid and butyric acid PHA films increases.Through 16Sr RNA gene high-throughput sequencing analysis,it was found that the microbial community structure composition in the three PHA membrane compost samples was similar,but the proportion of various microorganisms was different.In the effect of PHA degradation on the composting system,it was found that the addition of PHA increased the composting temperature.The peak values of the blank group and the treatment group with PHA addition of 5%,10%and 15%in the high temperature period were 51.8℃,53.05℃,53.55℃,54.95℃.It also prolongs the high temperature period and increases the degradation rate of organic matter.Both the blank group and the PHA-added treatment group can successfully complete the three-stage temperature change process of composting,which means that the degradation of PHA does not adversely affect the composting microorganisms.Compared with the blank group,the addition of PHA reduced the amount of ammonia volatilization during the composting process,and the degree of reduction was positively correlated with the amount of PHA added.The results of three-dimensional fluorescence spectroscopy showed that the addition of PHA promoted the maturity of compost.