Removal Of Sludge-based Microplastics By Hyperthermophilic Composting And Its Microbial-chemical Mechanism

Microplastics(MPs)refer to plastic granules less than 5mm in size,a new type of contaminant.The sewage treatment plant is considered to be the main receptor of terrestrial microplastic contaminants.Most of the microplastics are eventually retained in the sewage sludge through the sewage treatment stage.The application of sewege sludge is one of the most common sludge treatment methods in the world,and it has been popularized and applied in many countries.However,previous researches have shown that sewage sludge still contains high concentrations of microplastics,and the use of sewege sludge may cause environmental hazards.Moreover,conventional thermophilic composting(cTC)is not efficient at removing sludge-based MPs.Therefore,it is extremely urgent to develop a new way to efficient disposal of MPs in sewage sludge.In this study,the hyperthermophilic composting(h TC)technology was proposed and demonstrated in full-scale for in situ biodegradation of sludge-based MPs,and provided a new idea for solving the problem of microplastic pollution in sewage sludge.It has important practical significance for controlling the diffusion of microplastic pollution and its harm to the ecological environment.The main conclusions of the paper are as follows:1?Analysing the quantity,type,ditribution and morphology of microplastics in sewage sludge.The microplastics in sewage sludge contain various shapes(fibrous,rod,film,etc.),colors(white,yellow,black,etc.)and types(polyethylene,polystyrene,polypropylene,etc.).Untreated sewage sludge contains a large amount of microplastics about7.41×10~4 n/kg.After 45 d of hTC treatment,the microplastic number has decreased by 43.7%,and the removal efficiency was more than 10 times than c TC.2?The underlying mechanisms of MPs removal were investigated in lab-scalepolystyrene-microplastics(PS-MPs)biodegradation experiments.After 56 d of culture in a liquid carbon-free basal medium,the hyperthermophilic bacteria resulted to the weight lost of the PS-MPs by about 7.30%,which was 6.60 times higher than that of the control group.Further analysis on the molecular weight and physicochemical properties of PS-MPs residuals and water-soluble degradation products indicated that hyperthermophilic bacteria in h TC could accelerate the biodegradation of PS-MPs through excellent bio-oxidation performance.High-throughput sequencing suggested that Thermus,Bacillus and Geobacillus were the dominant bacteria responsible for the highly efficient biodegradation in h TC.3?Two hyperthermophilic strains FAFU003 and FAFU011 that can degrade PS-MPs were isolated from h TC samples.The results of 16S rRNA gene identification indicated that the FAFU003 strain was Geobacillus sp.and was named Geobacillus sp.FAFU003;the FAFU011strain was Geobacillus stearothermophilus and named Geobacillus stearothermophilusFAFU011.Thedegradationeffectsof hyperthermophile FAFU003 and hyperthermophile FAFU011 on PS-MPs was explored.After 56 d of culture in a liquid carbon-free basal medium,the 2 bacteria resulted to the weight lost of the PS-MPs by about 4.22%and 3.96%.Further analysis on the molecular weight and physicochemical properties of PS-MPs residuals and water-soluble degradation products indicated that 2 bacteria in hTC could accelerate the biodegradation of PS-MPs through excellent bio-oxidation performance,confirming that FAFU003 and FAFU011 have the ability to degrade PS-MPs.