Study On Removal Of Heavy Metals From Sludge In Tibet By Pretreatment Enhanced Electrolysis

With the establishment of sewage treatment plants in various regions,a large amount of sludge is produced in sewage treatment plants.However,sludge contains a large number of toxic and harmful substances such as pathogenic bacteria,heavy metals,antibiotics,etc.,so the problem of sludge disposal needs to be solved urgently.The Tibet Autonomous Region is located in the hinterland of the Qinghai-Tibet Plateau,and the ecological environment is relatively fragile.In order to improve the sewage treatment problem in the region,the number of sewage treatment plants has increased from 1 in 2010 to 9 in 2020,which has led to the need for sludge treatment and disposal in urban areas in Tibet.get a reasonable solution.In order to solve the problem of heavy metals in sludge in Tibet,this paper firstly analyzes the ecological hazards of heavy metals in sludge in Tibet according to the risk assessment of heavy metals,and then uses electrolysis to treat and supplemented with different pretreatment agents to investigate the treatment effect.First,by sampling sludge from sewage treatment plants in Lhasa,Shigatse,Nagqu,and Qamdo,the total amount and morphological distribution of heavy metals in sludge in Tibet were analyzed,and the heavy metals in sludge in this area were evaluated in combination with heavy metal pollution evaluation methods.ecological hazards.The following conclusions are drawn through the research;it can be found that heavy metal elements such as Hg,Cd,Pb,Cu,Zn all exceed the local soil background value.According to the Nemerow index evaluation: the Cd element in the sludge of Shigatse,Nagqu,Qamdo and Lhasa has serious ecological hazards.If it is greater than 3.0,it has reached the level of heavy pollution;the geoaccumulation index shows that Hg and Cd pollution are the most serious in Lhasa and Qamdo areas,while the potential ecological risk index method evaluation results show that Hg and Cd pollution are the most serious.Based on the above evaluation methods,it is concluded that the pollution risk level from large to small is:Hg>Cd>Zn>Cu>As>Pb>Ni>Cr.Speciation analysis of heavy metals shows that Cu,Zn,Cd,and Pb are mainly present in exchange and reduced forms in this area,which indicates that the removal and transformation of these heavy metals is relatively easy.Secondly,according to the evaluation results,five heavy metal elements were selected for electrolytic removal analysis.Through different pretreatments of the sludge,and according to the changes of the current intensity during the electrolysis process,the changes of the heavy metal forms in the sludge with the electrolysis time and the changes of the total amount of heavy metals were analyzed.The initial current intensity varies from 340 m A to 2059 m A due to different pretreatment agents.The change of current intensity gradually decreases with the electrolysis time.The current intensity of the five groups of experiments is the same after electrolysis for 120 hours.Stable at around 100 m A.The removal results of the total amount of heavy metals in the sludge showed that the removal efficiency of each element was different under different pretreatment conditions.In the case of using rhamnolipid for treatment,the removal rate of Pb element reached 49.86%;in the case of using IDS to pretreat sludge,the removal effect of Zn and Cd was better,reaching 77.26% and69.42%.%;in the case of pretreatment with EDDS,the Cu element was well treated,and the removal rate reached 59.78%;while the Ni element was pretreated with GLDA,the removal rate reached 47.6%.From the change of heavy metal species distribution percentage content,the situation of no additive and using rhamnolipid as additive is relatively good.After the reaction,the exchange state and reducible state of sludge basically show a downward trend;the oxidizable state and residue state basically increase.However,when the three chelating agents,IDS,EDDS and GLDA were used for pretreatment,the percentage of exchange state content increased,which was quite different from the former two.From the total amount of morphological changes,the decrease rate of exchange state and reducible state is between 26% and 98%,while the content of oxidizable state and residue state shows an upward trend for some elements in different experimental groups.It is very beneficial to change the mobility of heavy metals in sludge.According to the above experimental results,it can be seen intuitively that the electrokinetic method is very effective in removing heavy metals from sludge.During the experiment,the changes of electric current during electrolysis and the law of heavy metal migration and transformation in sludge were clarified,and the changes in the form of heavy metals in sludge during electrolysis were also analyzed in detail,revealing the treatment mechanism of heavy metals in sludge by electrolysis in Tibet.