Research On The Removal And Gasification Of Microplastics In Wastewater To Produce Hydrogen Gas Technology

As an emerging pollutant,microplastics exist in different environmental media and are prone to adsorbing toxic and harmful substances and pathogenic microorganisms in the substrate,posing more serious potential hazards than large plastics.This article takes microplastics in samples as the research object and explores the effects of different digestion solutions,reaction time,and other factors on the separation and extraction efficiency of microplastics.Using polystyrene（PS）microplastics as a representative and polyaluminum chloride（PAC）as a flocculant,the effects of different flocculant dosages,stirring rates,and other factors on the removal efficiency of microplastics were studied.The optimal reaction conditions were established through response surface methodology.The reaction mechanism was discussed by means of scanning electron microscope（SEM）,floc particle size,Zeta potential,floc fractal dimension and other means,providing a reference for establishing the analytical method of microplastics and studying the removal process.Using sludge rich in microplastics for supercritical water gasification to produce hydrogen,achieving the resource utilization of microplastics.（1）The results of digestion experiment show that the digestion effect of the digestion agent is in the order of nitric acid（HNO₃）>hydrogen peroxide（H₂O₂）>Fenton reagent（Fenton）>potassium hydroxide（KOH）>sodium hydroxide（Na OH）>sulfuric acid（H₂SO₄）,but the H₂O₂digestion is more gentle and has the smallest impact on the recovery rate of micro plastic recycling.The orthogonal experimental results using filtration time as the evaluation index show that all three factors have varying degrees of influence on the sample digestion effect.The primary and secondary order of their effects is digestion time>digestion temperature>dosage.The optimal digestion conditions are:80 m L H₂O₂dosage,8 hours digestion time,and 65℃digestion temperature.（2）The coagulation experiment results show that the polymer coagulant PAC has a higher removal rate of microplastics than aluminum sulfate.The removal rate of microplastics can reach 92.1%with 40 mg/L PAC,while the removal rate of 180 mg/L aluminum sulfate is only 85.4%.The removal rates of microplastics and turbidity show a trend of first increasing and then decreasing with the increase of PAC dosage.When the PAC dosage reaches 40 mg/L,the maximum removal rate of microplastics is 92.1%,and the maximum removal rate of turbidity is 91.9%at 60 mg/L.Under acidic conditions,the change in pH value has a significant impact on the coagulation effect.When pH is 5,the removal rate of microplastics and turbidity is the lowest,and when pH is 7,it is the highest.When the stirring speed is 60rpm,the removal rate of microplastics is the highest.The optimization results of response surface methodology indicate that the dosage of coagulant and stirring speed are two significant factors affecting the coagulation effect,and there is an interaction between the two.According to the model fitting results,the optimal process conditions were obtained as PAC dosage of 49.3 mg/L,pH of 6.1,stirring speed of 61 rpm,and the predicted removal rates of microplastics and turbidity were 92.1%and 89.7%,respectively.The relative error between the predicted and verified values was less than 0.25%.（3）Analysis of the flocs revealed that the time for the floc particle size to enter a stable state was shortened when microplastics were present;Under different pH conditions of water samples,the floc particle size is larger in the presence of microplastics;The microplastic flocs have stronger adaptability and shear resistance to changes in stirring speed.Microplastics increase the Zeta potential of water samples and enhance the stability of colloids;The dosage of coagulant and pH of water sample have great influence on the potential,which indicates that there is adsorption neutralization in the process of removing microplastics by coagulation.During the coagulation process,microplastics are adsorbed by the flocs and enter the interior of the flocs,becoming the backbone of the flocs.Compared to the non microplastics water sample at the same time,the particle size of the flocs is larger,the structure is denser,the branches are fewer,and the shape is closer to the spherical shape.Therefore,the settling performance of the microplastics water sample flocs is better.（4）The study on hydrogen production by supercritical water gasification of sludge rich in microplastics found that temperature and residence time are significant factors affecting hydrogen production by supercritical water gasification.At 500℃,the hydrogen（H₂）composition and yield reach 29.4%and 10.6 mol/kg;The H₂component reaches its maximum value when the residence time is 30 minutes.When potassium carbonate（K₂CO₃）is used as a catalyst,the yield of hydrogen（H₂）is 1.5 times higher than that without the addition of a catalyst.