Study On Sludge Electro-dewatering Technology Based On Engineering Numerical Simulation

With the acceleration of China's urbanization process and the continuous development of industrialization,annual sludge output has increased greatly year by year in recent years.Properly addressing the problem of sludge disposal has become a hot topic in the sewage and sludge treatment industry,and it is also one of the most important tasks in solving environmental protection issues.And sludge deep dewatering is one of the important steps before the final sludge treatment and disposal.Sludge electro-dewatering(SED)can achieve deep dewatering without adding extra chemicals,which has received widespread attention in recent years.However,the current research on SED technology mainly focused on the study of operating parameters influence on dewatering effect and parameter conditions optimization,and the dynamic process of SED and the mechanism of parameter influence are unclear.In addition,the sludge properties variation process and it's influence on SED,and the influence of sludge dewatered by electro-osmosis on it's further deep dewatering by air drying are lack of coverage.Based on the above issues,the main research contents of this article include:1)Based on modeling simulation,the effect of piecewise voltage on the effect of SED and the impact mechanism of ohmic heat temperature in SED process were studied.The in-situ linear voltammetry(LSV)was used to characterize sludge resistance dynamic change during SED process.The results show that,under the same water content,applying higher electric field strength on sludge got higher resistance.Based on the conductivity vs.moisture content curve obtained from the experiment,a transient model of SED was established to simulate the current and filtrate dynamics variation in SED process.Experimental phenomenon consistent with the simulation results,which indicated that electrical conductivity is the key factor affecting the degree of SED.The experimental results of piecewise voltage showed that the combination of"high-low-high"voltage was beneficial to reduce SED energy consumption.The model simulation and experimental methods were used to study the dynamic change of sludge cake temperature during SED and the effect of temperature on SED performance.The impact of different temperature conditions on sludge particle size,surface morphology,EPS structural morphology,organic components,and electrical conductivity were investigated.The results showed that the temperature simulation results are consistent with the experimental phenomena,and there was a temperature threshold between 40 ^oC and 50 ^oC to improve the SED performance.When the temperature of the sludge cake exceeds 50 ^oC,some organic compounds in the EPS may be denatured or decomposed,and its composition was observed to be changed by 3D-EEM fluorescence spectrum.This change would lead to the dissolution of some microbial aggregates in the sludge floc,smaller floc particle size,and increased sludge electrical conductivity.Transmission electron microscopy results showed that some of the microbial aggregates in the EPS dissolve and even some microbial cells are broken when applied 35 V in SED process.When the voltage is switched from 35 V to 15 V with 50 ^oC as a switching point,SED energy consumption could be reduced to 108.23 k Wh per ton sludge.2)The effects of sludge aging on improving sludge electro-dewatering(SED)performance were studied.The typical Shanghai municipal sewage sludge was selected as the research object,with the sludge properties variation during aging process investigated.Sludge electro-dewatering performances were explored by constant voltage method(25 V)on various samples.The organic matter in the extracellular polymeric substances(EPS)was gradually consumed and decomposed during sludge aging process.Under identical electro-dewatering conditions,dewaterability and time-space yield of aged sludge achieved 50.67 wt.%water content and 223.46 kg m^-2 h^-1 respectively.Such results indicate the beneficial effects of sludge aging process in terms of SED performances,which needs further exploration into fundamental mechanisms.3)Analysis of soluble ions migration and distribution in SED process.The effects of electro-dewatering technology applied to high-salt industrial sludge dewatering performance were investigated,in terms of ions migrations and distributions by model simulation and layered tests.The simulation results of Na⁺and K⁺migrations were consistent with layered experiments during electrodewatering,where Na+ions migrated faster than K⁺ions.More than 84%Na⁺and about 45%K⁺ions were removed by electromigration,which would be useful in subsequent sludge utilization.The mass specific energy consumption was reduced from 350.08 to 295.88 k Wh per ton sludge by means of piecewise voltage electro-dewatering method.This study provided insights into the soluble ions migration and distribution mechanism in electro-dewatering process,and a method to improve commercial application performance of high-salt industrial sludge electrodewatering.4)Exploration of sludge electro-dewatering combined with low-temperature air-drying technology.The sludge was dehydrated by electro-dewatering with different electric field strengths and then air-dried.The changes in EPS composition and content,surface micromorphology and particle size distribution were investigated after SED,and recorded the mass of sludge cake during air-drying.The experimental results showed that the osmosis channel was formed during SED process,and when the applied electric field intensity reached a certain intensity,the EPS content in sludge decreased and the composition changed.The mass of sludge air-drying curve indicated that applying larger electric field intensity in SED process contribute to shorten the time required for the removal of unit mass of water in subsequent air-drying process.The sludge was dewatered by 35 V electro-dewatering for 15 minutes,and then dried by low-temperature air-drying can reduce the water content to 20 wt.%within100 minutes.Utilizing the changes in properties and structure of the sludge cake after the front-end electro-dewatering,and then performing low-temperature air-drying were beneficial to improve the space-time yield of the overall sludge treatment.