Study On Sludge Pretreatment Based On DBD Plasma And Its Coupling Technology

The increase of the amount of excess sludge in the city has brought serious environmental pollution.In order to reduce the pollution of excess sludge,certain treatment and disposal are required.Sludge dewatering and anaerobic digestion are the two most commonly used treatment processes,but the actual application effect is not good due to the limitation of lysis.Therefore,it is necessary to carry out a certain pretreatment on the remaining sludge,the pretreatment of the sludge flocs and cell structure to enhance the treatment effect.Dielectric barrier discharge plasma is widely used in various types of sewage treatment because of its advantages of simple structure,fast reaction,and rich active substances.In recent years,some researchers have reported the lysoidal effect of plasma on bacteria,which indicates that plasma may be used in sludge treatment and disposal.Therefore,this article introduced DBD plasma into the treatment of sludge,and examined its treatment effect through SCOD,CST and other indicators.In the meanwhile,considering that the effects of UV light,O3,and heat in the discharge reactor have not been fully applied,PMS,Fenton-like and DBD plasmas are respectively combined into a coupling system to explore the sludge treatment effect of the two coupling systems.In addition,the mechanism of sludge cracking was preliminarily analyzed by OM,FT-IR and other characteristics.The research results are as follows:1.Separate DBD plasma treatment of sludge(1)When the sludge was hydrolyzed with the assistance of DBD plasma,the increase of reactor voltage and frequency could positively affect the cracking and dehydration performance of the sludge.Under the conditions of discharge voltage 1lkV,frequency 10kHz,and reaction for 12min,the sludge reached the minimum CST value of 28.3s and extended the reaction time to 24min.And the peak value of the sludge SCOD was 939.65mg/L.2.DBD/PMS coupling treatment of sludge(1)DBD/PMS coupling could improve the cracking effect of sludge,because PMS could be activated by high-energy electrons,heat,O3,UV light and other effects in the process of DBD discharge,and it also improved the strong oxidizing SO4-· and increased the utilization rate of various energy in the discharger.The addition of TBA and MeOH proved that SO4-·and·OH were simultaneously present in the sludge cracking process.In addition,the coupling technology had a significant advantage in improving the dewatering performance of sludge.When PMS(HSOs-meter)1.0 mmol/gTS was added to the reactor,under the conditions of the same voltage(11 kV)and frequency(10 kHz),the coupling system could shorten the discharge time required for sludge to reach the CST lower limit by 8min compared with the DBD discharge alone.(2)The RSM optimization test showed that there was a significant interaction between discharge voltage and PMS concentration.In addition,the data model established according to the test results predicted that the optimal conditions for the cracking sludge of the coupled system were:discharge voltage 11kV,time 21.91min,PMS concentration 1.07mmol/gTS.(3)An anaerobic fermentation test was carried out on the sludge under optimal cracking conditions,and it was found that both DBD and DBD/PMS technologies could effectively promote the anaerobic acid production of sludge.The peak acid production of the two pretreatment groups(DBD,DBD/PMS)was increased by 2.28 and 3.56 times compared with the raw mud group,respectively,and the optimization of acid production components was achieved.3.DBD/zero-valent iron/H2O2 coupling treatment of sludge(1)Fenton-like could achieve the improvement of sludge cracking and dehydration.The optimal dehydration conditions for Fenton-like were:Fe0 dosage was 360mg/gTS,H2O2 content was 24mg/gTS,initial pH=3.0,reaction time was 60min,but the best cracking conditions for sludge by Fenton-like technology was to increase the content of H2O2 to 60mg/gTS.(2)The Taguchi test results showed that there was a certain synergy in the DBD/Fenton-like coupling system,which could achieve an improved sludge cracking effect.At the same time,the physicochemical effects generated by the DBD plasma may expand the suitable pH range of the Fenton-like to a certain extent.According to the analysis,the optimal reaction conditions for the DBD/Fenton-like combined system were:Fe0 dosage 450mg/gTS,H2O2 content 60mg/gTS,discharge voltage 11kV,frequency 10kHz,initial pH=4,reaction time 18min.In addition,the CST data in the Taguchi test indicated that the coupling system was not suitable for improving the sludge dewatering effect.(3)Anaerobic fermentation was carried out on the sludge under the optimal cracking condition,and it was found that the dissolution amount of organic substances of the sludge samples increased significantly after cracking,resulting in the increase of VFAs output by 967.35mg/L(Fenton-like)and 1592.02mg/L(DBD/Fenton-like),respectively,and the peak acid production was 2d earlier.In addition,the proportion of acetic acid in each pretreatment group increased.4.Analysis of sludge cracking mechanism(1)OM microscopic examination showed that the sludge flocs were broken and dispersed after pretreatment,which led to a decrease in stability but enhanced hydrophobicity and then was beneficial for water removal.SEM electron microscopy scan showed that after the sludge was discharged and treated by coupling,the filter cake appeared loose and the porous structure,which helped the water to drain from the pore channel and improve its dehydration performance.At the same time,the formation of the structure also indicated the destruction of the sludge structure and the occurrence of lytic hydrolysis.FT-IR spectroscopy showed that the sludge cell structure and EPS were destroyed,the dry sludge groups were lost,and related organic substances flowed into the liquid phase,which could improve sludge dehydration and anaerobic fermentation performance.