The Research On Performance Of Excess Sludge Reduction By Discharge Plasma

In recent years,with the acceleration of urbanization,the capacity of sewage treatment plants in China is increasing,and the sludge produced is also growing linearly.The excess sludge contains a large number of viruses,pathogenic bacteria,heavy metals,etc.,which is extremely toxic and harmful.If it is not properly disposed and treated,it will cause serious secondary pollution to the environment.The traditional sludge treatment and disposal method has certain drawbacks due to its high water content of sludge,thus the problem of excess sludge cannot be solved completely.How to dehydrate and realize sludge reduction effectively is a hot spot in the current environmental field.Discharge plasma is an advanced oxidation technology,which can effectively destroy sludge flocs and cells,and release sludge intracellular substances into the liquid phase to achieve sludge dehydration.In this study,the theoretical analysis and experimental research on the technology of discharge plasma oxidation excess sludge reduction are focused on the effects of different treatment condition on the sludge reduction by discharge plasma and the changes of the sludge characteristics before and after treatment.The purpose is to reveal the cracking law and mechanism of the discharge plasma on the sludge to determine the influence of the discharge plasma on the sludge reduction performance.The experiments obtained the following main conclusions:1.Discharge plasma can crack the excess sludge cells effectively,and has a good reduction effect on the excess sludge.Increasing the discharge voltage or prolonging the discharge time is beneficial to improve the sedimentation performance and dewatering performance of the sludge.Compared to non-discharge,under optimum conditions,SV₃₀consisting of 98%to 36%,SVI reduced from 170.52 mL/g to 89.55 mL/g,the viscosity of the sludge is reduced from 35.31 mPa·s to 8.23 mPa·s,The moisture content of the sludge filter cake decreased from 81.92%to 76.03%,and the MLSS concentration decreased from5630 mg/L to 4020 mg/L,and the reduction rate reached 28.6%.In addition,sludge initial temperature,and acidity and alkalinity will affect the effect of discharge cracking of excess sludge.The optimum reaction conditions were obtained:the discharge voltage was 20 kV,the initial sludge temperature was 20?,the initial pH of the sludge was 7,and the discharge treatment time was 60 min.Different anions will affect sludge reduction.Adding Cl^-,NO₃^-,SO₄^2-will promote the sludge reduction,while CO₃^2-obviously inhibits the sludge cracking.2.The plasma discharge has a good lysis function and can effectively destroy the sludge floc structure.After the discharge plasma effectively breaks down the sludge cells,the extracellular polymer of the sludge and the organic matter contained in the sludge microbial cells enter the aqueous phase from the sludge solid phase,which is apparently represented as SCOD,TOC,NH₄-N,NO₃-N and other indicators increase;the results of three-dimensional fluorescence confirmed the appearance of intermediate products and the evolution of cracked products;the addition of the active substance capture agent during the sludge reduction process significantly inhibits the effect of the discharge plasma cracking the sludge,indicating the active substance produced by the discharge during the sludge reduction process,for example:·OH,·O₂^-,excitation ¹O₂ and O₃,H₂O₂,etc.can effectively act on the sludge cells to dissolve;the sludge particle size and SEM results further confirmed the change of sludge floc morphology and composition before and after discharge,which showed that the sludge flocs became loose from complete compaction,the size of excess sludge particles became smaller,and the specific surface area increased.The changes of functional groups in sludge were analyzed by XPS results.The moisture loss and pyrolysis behavior in the sludge were analyzed by thermogravimetric?TGA-DSC?results.