| With the continuous development of society and the improvement of urban sewage treatment technology,the annual output of sludge is also increasing rapidly.Relevant data show that in 2018,the annual output of sludge in China will reach nearly 10 million t,three years later,the annual output of sludge in China will increase to 70 million t,and it is estimated that the annual output of sludge in China will reach 100 million t in 2025.At present,the commonly used sludge disposal technologies are mainly land use,dry incineration,sanitary landfill and so on.However,land use,dry incineration,sanitary landfill and other disposal technologies all need to reduce the sludge moisture content to a certain range.Therefore,the focus of sludge treatment and disposal is mainly on reducing the sludge moisture content.The traditional sludge dewatering method is mechanical dewatering,but it can only reduce the water content of sludge to 70%～80%.The combination of mechanical pressure and electro-osmotic dehydration can further reduce the water content of sludge to below 60%,but the problems of high energy consumption and corrosion of anode materials in the later stage of dehydration also restrict its practical application.Therefore,it is necessary to seek a more efficient and energy-saving sludge dewatering scheme.In this study,activated carbon and graphite were selected as physical conditioners of sludge,and the deep dehydration of sludge was studied in combination with pulsed electric field.In the preliminary experiment,activated carbon with different particle sizes was used to explore the influence of activated carbon particle size on sludge dewatering,and the optimal particle size parameters were determined.Activated carbon and graphite have excellent adsorbability and conductivity respectively,so activated carbon,graphite and activated carbon doped graphite are used to condition sludge,and 37.5g of conditioned sludge is taken for electro-osmotic dehydration under constant voltage of 30 V DC.By recording the curves of current,sludge cake temperature,sludge cake partial pressure and filtrate quality with time during the experiment,the mechanism of activated carbon and graphite on electro-osmotic dehydration of sludge was explored.In addition,the influence of activated carbon and graphite on the sludge cake after the experiment was analyzed by detecting the p H value,conductivity and thickness of the sludge cake after the experiment.The changes of anode and cathode surface morphology of vacuum freeze-dried sludge cake were observed by scanning electron microscope.The filtrate filtered by 0.45μm was determined by threedimensional fluorescence spectrometer and total organic carbon analyzer,and the changing rules of total organic carbon,protein and organic components in the filtrate under different working conditions were compared.Eight common heavy metal elements such as Cu,Mn,Cr,Ni,Cd,Zn,Hg and Pb in cathode filtrate were determined by inductively coupled plasma atomic emission spectrometry,and the adsorption of heavy metals by activated carbon and graphite was studied.Based on the comparative analysis of the moisture content of sludge cake under different working conditions,the optimum adding parameters of activated carbon and graphite were determined.According to the optimal dosing parameters of activated carbon and graphite,the dosing ratio and dosage of activated carbon and graphite were further optimized,and the influence of physical conditioner combined with pulsed electric field on electro-osmotic dehydration of sludge was further studied by changing waveform(sine wave/square wave)and duty ratio(20%,40%,60%,80% and 100%).The changes of current,sludge cake temperature,voltage at both ends of sludge cake,filtrate quality with time,sludge cake thickness,sludge cake p H,sludge cake conductivity after the experiment,cathode filtrate p H,cathode filtrate TOC value and cathode filtrate 3D-EEM analysis were recorded to further explore the influence of activated carbon(graphite)on sludge electroosmosis deep dehydration.The results show that activated carbon has a better effect on reducing the water content of sludge than graphite.When the dosage of activated carbon is 5% DS,the dewatering effect is the best,and the apparent water content of sludge is reduced to 41.0 wt.%.Both activated carbon and graphite can improve the conductivity of sludge,and graphite can improve the conductivity of sludge more strongly than activated carbon.Therefore,adding graphite as a physical conditioner makes the temperature in the sludge cake higher,which further destroys the extracellular floc structure of sludge and releases the organic components in extracellular polymers.The adsorption capacity of activated carbon is stronger than that of graphite,and it can intercept organic components,viscous protein,heavy metals(Cu,Mn,Cr,Ni,Cd,Zn,Hg and Pb)in sludge.According to the outflow rate of cathode filtrate,total organic carbon in filtrate and 3D-EEM analysis of filtrate,it is shown that the ability of activated carbon to improve the discharge rate of filtrate and adsorb organic substances is higher than that of graphite,while the effect of impurity of activated carbon and graphite is between them.Activated carbon combined with pulsed electric field can further reduce the moisture content and energy consumption of sludge cake,in which the dosage of activated carbon is 5%DS,the waveform is square wave and the duty cycle is 80%.Under the pulsed electric field,with the increase of duty ratio,the water content of sludge cake showed a trend of first increasing and then slowing down,which was consistent with the quality change law of cathode filtrate.With the increase of activated carbon dosage,the moisture content of sludge cake can be further reduced.After the experiment,the p H,total organic carbon and three-dimensional fluorescence spectrum of the cathode filtrate were measured.The results showed that with the increase of duty ratio(square wave/sine wave),the p H value of the cathode filtrate gradually increased,and with the increase of activated carbon dosage,the p H value of the cathode filtrate further increased.With the increase of duty ratio(square wave/sine wave),the electrochemical reaction is enhanced,which releases the organic matter in the sludge and promotes the release of water in the sludge,resulting in the gradual decrease of the total organic carbon value in the filtrate,and the addition of activated carbon can intercept the organic components,thus further reducing the total organic carbon value in the filtrate;The increase of activated carbon dosage can reduce the fluorescence intensity of tryptophan-like protein and aromatic protein in cathode filtrate.Under square wave,with the increase of duty cycle,the fluorescence intensity of tryptophan-like protein and aromatic protein in cathode filtrate gradually decreases,while under sine wave condition,it shows the opposite trend.To sum up,in the experimental study of activated carbon/graphite-assisted electro-osmosis deep dewatering of sludge,the best parameters are adding 5%DS activated carbon,square wave,duty cycle of 80% and frequency of 50 Hz.Under this working condition,the moisture content of the sludge cake is 40.3 wt.%,and its dehydration energy consumption is 0.27649 Kwh/Kg,which is 0.11933 Kwh/Kg;less than that without adding,under the condition of 100%DR;... |
PDF Full Text Request