Evaluation Of Passivation And Microbial Toxicity Of Heavy Metals In Municipal Sludge

With the rapid economic development and the acceleration of urbanization,the number of urban sewage treatment plants has gradually increased,and the output of urban sludge is also increasing.Municipal Sludge contains nutrients such as organics,nitrogen and phosphorus that are necessary for plant growth,enabling it to be used as a resource.However,sludge also contains a large amount of heavy metals that are harmful to the environment and is used directly.Therefore,how to reduce the harm of sludge heavy metals to the environment becomes key point to make treatment and disposal and resource utilization of the sludge.In this study,the treatment methods for the sludge from Hefei municipal wastewater treatment plant were studied,The effects of dolomite,ferrous sulfate and dolomite-ferrous sulfate complex as improvers on the morphology and the availability of heavy metals in sludge were studied,and the passivation mechanisms of several passivating agents were preliminarily investigated.Pot experiments were conducted to investigate the effects of passivated sludge on biomass and the accumulation of heavy metals in shoots and roots of vegetables.The long-term stability of passivation agent passivation was evaluated.Finally,this article developed a method for determining the microbial toxicity of sludge using a portable glucose meter and determined the heavy metal toxicity of various passivated sludges.The main findings are as follows:1.Taking the sludge from a sewage treatment plant in Hefei as the research object,The passivation effect of heavy metals in sludge was evaluated by adding heavy metals such as dolomite,ferrous sulfate,and dolomite-ferrous sulfate complex to passivate the heavy metals in the sludge.The results showed that the addition of dolomite could raise the pH value of sludge,however,ferrous sulfate could reduce the sludge pH.When the dolomite-ferrous sulfate complex were added,the change of sludge pH was not significant.Dolomite has a better passivation effect on Cu and Cd in sludge,however,ferrous sulfate has a significant passivation effect on As in sludge.Dolomite-ferrous sulfate complex had the significant passivation effect on heavy metals of Cu,Zn,Cd and As in the sludge.Dolomite-ferrous sulfate complex could significantly reduce the available state content of heavy metals in the sludge,5%dolomite and 5%ferrous sulfate complex treatment gave the best result,Compared with the control,the available contents of Cu,Zn and As decreased 59.58%,42.26%,40.93%and 55.68%,respectively.SEM-EDS and Visual MINTEQ simulation results showed that the carbonate ions in the dolomite can react with the heavy metal to form a precipitate.2.Through two consecutive pot experiments,the effects of passivated sludge on biomass and the accumulation of heavy metals in shoots and roots of Chinese cabbage were studied,and the long-term stability of passivation agent passivation effect was evaluated.The results showed that In the first pot experiment,10%dolomite was added to the sludge,the biomass of the cabbage increased,and the dolomite-ferrous sulfate complex did not significantly affect the biomass of the cabbage.Compared with the control group,dolomite-ferrous sulfate complex were added to the sludge.The contents of heavy metals in shoots and roots of the cabbage were decreased,and the maximum reduction rates of Cu,Zn,Cd,and As in shoots were 53.56%,34.51%,57.29,and77.04%,respectively.In the second-season pot experiment,the biomass of all treatments significantly increased,and the accumulation of heavy metals in the shoots and roots of vegetables increased significantly.Comparing the accumulation of heavy metals in the two locust vegetables can be found that,with the passage of time,the passivation agent has a reduced passivation effect on heavy metals in the sludge.From this,it can be seen that the long-term stability of the deactivating effect of passivating agents such as dolomite and ferrous sulfate is weak.3.A method for determining the toxicity of heavy metals using a portable glucose meter was developed to evaluate the microbial toxicity of single heavy metals and binary heavy metals.Optimization of the test results show that the toxicity of heavy metals by E.coli is more sensitive to the cultivation of the 30?temperature and E.coli bacteria concentration(OD₆₀₀)was 2.3,toxicity evaluation effect is better,the toxicity evaluation effect was better.The evaluation results of single heavy metal toxicity showed that the IC₅₀0 of Cu²⁺,Zn²⁺,Cd²⁺,Pb²⁺,Hg²⁺and As³⁺were 10.3,12.9,24.3,160.3,2.8 and 6.9 mg·L^-1,respectively.The order of toxicity for E.coli was Hg²⁺>As³⁺>Cu²⁺>Zn²⁺>Cd²⁺>Pb²⁺.Based on the IC₅₀0 size,Hg²⁺is the most toxic to E.coli.In the joint toxicity evaluation of binary heavy metals,Cu²⁺+Zn²⁺,Cu²⁺+Cd²⁺and Cu²⁺+Hg²⁺show a synergistic effect.Cu²⁺+As³⁺and Cd²⁺+Zn²⁺show antagonism.4.Heavy metal toxicity evaluation was conducted using the heavy metal toxicity assessment method to evaluate the heavy metal toxicity of simulated sludge?single heavy metal pollution?,actual sludge and passivated sludge.The results showed that the simulated toxicity of single heavy metal?Cu,Zn?contaminated sludge was relatively weak to E.coli.The inhibition rates of sludge from electroplating plants,steel plants,residential communities,and industrial parks were 57.4%,35.6%,17.7%,and 48.3%,respectively.The order of toxicity was electroplating plant sludge>industrial park sludge>steel plant sludge>living area sludge.Electroplating plant sludge showed the highest microbial toxicity,and the results were the same as predicted.It also proved that this heavy metal toxicity evaluation method can be used to determine the microbial toxicity of sludge heavy metals.Compared with the control group,the inhibitory effect of the passivated sludge on the growth of E.coli was reduced.To a certain extent,with the increase of the amount of passivating agent,the inhibitory effect of the passivated sludge on the growth of E.coli was smaller.