Immobilized Microbial Remediation Of Cd-PAHs Composite Contaminated Soil

In view of the problem of heavy metal-polycyclic aromatic hydrocarbon composite pollution in soil,this study investigated the remediation effect of solid-based waste materials on Cd-PAHs composite contaminated soil based on immobilized microbial technology,supplemented by surfactants,and provided a theoretical basis for the development of immobilized enhanced remediation technology for heavy metal-PAHs composite contaminated soil and the construction of immobilized microbial remediation technology system for composite contaminated soil.The vector for immobilizing the microorganism is important.Using the composite biochar（BBm）prepared by calcination of wheat straw and boron sludge（mass ratio 1∶1）at 700°C for 2 h in a muffle furnace as the immobilization carrier,by controlling the different factors affecting the adsorption performance of BBm to Cd²⁺,and designing orthogonal experiments,setting the Cd²⁺removal rate as an evaluation index,and determining the optimal reaction conditions of BBm for Cd²⁺adsorption by analyzing the range and variance,the experimental results show that 100.00 m L of water contains Cd²⁺at 25°C and p H=8 At a concentration of 200.00 mg/L,0.5 g of BBm was added and oscillated at 200 r/min for 180 min,and the removal rate of Cd²⁺was as high as99.99%under the best reaction conditions.BBm was added to the solution containing single PAHs and phenanthrene（Phe）and pyrene（Pyr）composite PAHs,and the changes of BBm adsorption of PAHs with time were investigated under the condition of 25°C and 180 r/min under the condition of avoiding light oscillation.Experiments show that BBm has good adsorption effect in single PAHs solution,and there is competitive adsorption in Phe and Pyr.Mucormyces,Aspergillus niger,mycobacteria and complex fungicides with a compound ratio of 2∶1∶1 were selected,because Phe has a simple molecular structure and is easily biodegraded in water,and its degradation kinetic process is only studied for Pyr.Experiments have shown that the compound has the best degradation effect on Pyr.After 48 hours（30°C,180 r/min）on a shaker by immobilized microbial adsorption method,the BBm immobilized bacteriological agent was obtained by sieving under sterile conditions,and the initial concentrations of Pyr were added to the solution with the initial concentration of Pyr 5.00,20.00 and 40.00 mg/L respectively,and the degradation effect of BBm immobilized bacteriological agent and free compound bacteriological agent on Pyr was investigated.Experiments show that when the initial concentration of Pyr is high,the degradation rate of BBm immobilized bacteria to Pyr is 7.69%higher than that of free bacteria,and the degradation effect of immobilized bacteria is better than that of free bacteria,and the immobilized vector can provide a safe living environment for microorganisms.Five carrier materials,biochar,blast furnace slag,boron sludge,fly ash and BBm,were selected to make the corresponding immobilization agents,and were added to the Cd-PAHs composite contaminated soil with 1%and 5%application amounts,and samples were taken on days 0,30 and 60,respectively.Through the extraction and detection of effective Cd and Phe and Pyr,the changes of the concentration of effective Cd and Phe and Pyr in simulated soil were investigated,and the remediation effect of immobilized fungicides on Cd-PAHs composite contaminated soil was studied.On this basis,four surfactants（solid-liquid ratio 5∶1）were added to 5%rhamnolipid,saponin,Tween-80 and microemulsion,and samples were taken on days 0,30 and 60 to explore the effect of surfactants on the repair ability of immobilized bacteria.Experiments show that when the immobilized dosage is 5%and saponin surfactant is added,immobilized bacteriological agent（BBm）has the best effect on the removal of pollutants in Cd-PAHs composite contaminated soil.The passivation rate of Cd in contaminated soil can reach 35.38%,the degradation rate of Phe in contaminated soil is 98.01%,and the degradation rate of Pyr in contaminated soil is 87.10%.