| A large amount of sewage sludge is produced every year in China.Thanks to its high water content and containing harmful substances,such as organic matter,heavy metal and pathogenic microorganism,it will cause serious land resource waste and secondary pollution if it is not treated.As an efficient and environmental friendly method for contaminated soil remediation,the electrokinetic can improve the removal of heavy metal and accelerate the sludge dewatering,which has a broad application prospect.In order to improve the effect of remediation,the complexing agents are always used in the experiment.However,due to the biotoxicity and high cost of complexing agents,it is difficult to popularize the method.Aiming at exploring a more reasonable and economical method,sophorolipid is applied to electrokinetic test to strengthen the restoration and drainage of sludge.The electrode arrangement,sophorolipid concentration and voltage are optimized,and the mechanism of sophorolipid is discussed.What's more,this paper contrasts sophorolipid with rhamnolipid and citric acid to verify the feasibility of the method.Main corresponding results are listed in what follows.(1)Compared with electrode arrangements at left and right,the arrangements on top and bottom has a better performance on the heavy metal removal rate and drainage effect,while the homogeneity seems to be worse.The effect of gravity drainage is only ten percent of electro-osmotic,and the migration speed is very slow.Therefore,it is suggested that the electrode can be arranged on top and bottom in ex-situ electrokinetic treatment.(2)Sophorolipid can promote the heavy metal removal and sludge drainage.The removal rates of Zn,Cu and Cd in anodic area are increased with the sophorolipid concentration increased.In view of the heavy metal concentrations in discharge liquor,the optimum concentration of sophorolipid is between 0.1%and 0.125%.In addition,high concentration of sophorolipid can cause the inhibition of electro-osmotic dewatering.(3)Voltage has an influence on the treatment effect.Increasing voltage can promote the migration of heavy metal ions.When applying 40V(initial potential gradient 2.0V/cm),The removal rate of Zn,Cu and Ni is highest,while Cd has a better removal efficiency when applying 50V(initial potential gradient 2.5V/cm).Besides,the larger voltage,the more consumption.And the accumulate displacement increases at first and then gets worse.(4)Sophorolipid can promote heavy metal removal by ion exchange,complexation,solubilization,mobilization and functional groups.While in the sludge drainage,sophorolipid plays a role in decreasing surface tension and destroying EPS.(5)Compared with rhamnolipid,the removal effect of Zn and Cd is better by applying sophorolipid.As for Cu and Ni,rhamnolipid has a good performance.And citric acid can reduce the accumulation effect of heavy metals in the middle part.In consideration of drainage,sophorolipid and citric acid seem to be better.(6)The complex solution of biosurfactant and complexing agent can promote the migration of heavy metals.For the sludge which has high content of Zn and Cd,it is recommended using sophorolipid or complex solution of sophorolipid and citric acid.While for high content of Cu and Ni,the complex solution of rhamnolipid and citric acid is more suitable.If there are some requirements on drainage in the actual sludge treatment,mixed solution with rhamnolipid and citric acid is not a good choice. |
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