High-temperature Composting Degradation Of Sludge Microplastics And Microbial Metabolism Coupling Mechanism

Microplastics are defined as plastic particles with a particle size of less than 5mm.Due to its small particle size,large specific surface area and good dispersion and hydrophobicity,it is easy to absorb organic chemical pollutants,heavy metals and other pathogenic bacteria and other microorganisms,so that it is easy to be enriched in marine organisms and increase the food chain.The bio-enrichment effect of the above causes dangerous toxic reactions after predation by animals,and indirectly threatens marine life and human health.As a new type of pollutant,microplastics have also been found in sewage many times in recent years.Some research results indicate that sewage treatment plants have been widely regarded as important transportation centers for microplastics entering the natural environment.Sludge adsorption is the main fate of microplastics in sewage,and sludge land or agricultural use is considered an important source of microplastics pollution in the soil natural environment.And the study also found that most of the microplastics in the sludge are non-degradable microplastics.These microplastics are difficult to remove by composting.However,with the country’s various restrictions on traditional plastic products,degradable plastic products have sprung up in people’s lives,and gradually began to replace the role of traditional plastic products in people’s lives.It is believed that degradable plastic products will become the mainstream in the near future.However,the corresponding use of such degradable plastic products will also produce microplastics in the ocean,land and sludge over time.There are few current studies on degradable microplastics in sludge.In this paper,it is necessary to conduct a basic study on the removal of microplastics in sludge that may be caused by degradable plastic products.This study explored the degradability of polylactic acid microplastics under different composting conditions,as well as the effects of microplastics on compost physical and chemical factors,specific organic components,compost humic acid,electron transfer capacity,and microorganisms.This provides a new direction for the future research on the pollution of degradable microplastics in sewage sludge and the composting conditions of sludge containing microplastics.The prevention and control of the risk of degradable microplastics pollution and the control of environmental hazards are quite significant.Important guiding significance.The main conclusions of the paper are as follows:(1)The degradation effect of the degradable microplastic polylactic acid in the composting process and the difference of the degradation degree of the polylactic acid microplastic under different composting conditions were analyzed.After the 33-day composting period,scanning electron microscopy found that the surface of microplastics in high-temperature composting was rougher than that of ordinary composting,and there were a lot of cracks and wrinkles,and there were also relatively large cavities.Then through Fourier transform infrared spectroscopy,it was found that after the entire composting process,the reduction of the main functional group content of the polylactic acid microplastics in the high-temperature compost was more than that in the ordinary compost.The results show that the composting process can degrade the degradable microplastic polylactic acid,and high-temperature composting has a more obvious degradation effect on microplastics than ordinary composting.(2)Analyzed the influence of microplastics on the physical and chemical factors,specific organic components,humus structure and electron transfer ability in the composting system.The research on the above-mentioned composting indicators was carried out by means of ultraviolet spectroscopy,fluorescence spectroscopy and electrochemical workstation.The results show that polylactic acid microplastics will reduce the moisture content of the pile and the nitrate nitrogen content,but will increase the ammonium nitrogen content.In addition,polylactic acid microplastics will increase the content of carboxyl groups,polysaccharides and reducing sugars,but will lead to a decrease in the content of amino acids and polyphenols.At the same time,the addition of microplastics promotes the humification of humic acid,the degree of condensation of organic matter,the aromatization of humic acid and the formation of quinone groups in humic acid.But it will inhibit the increase of the molecular weight of humic acid.Finally,the addition of polylactic acid microplastics will reduce the overall level of humic acid EAC.(3)Analyze the changes of microenvironmental factors during the existence of microplastics and their influence on microorganisms.Through heat map correlation analysis and redundancy analysis,important factors affecting microorganisms are determined.Then through the structural equation model,the possible influence of microplastics on microorganisms is carried out.The results show that the addition of microplastics will directly or indirectly affect the structure and diversity of microorganisms.And the addition of microplastics will affect the impact of these important factors on microorganisms,but it will not change the way these important factors affect microorganisms.