Combined Biosurfactants And Electrokinetic Treatment Remove Heavy Metals From Sludge

Sludge produced in the wastewater treatment process,which can cause serious harm if not be effectively treated and disposed.The sludge can be safely and effectively treat and dispose,which has become a concerned problem.Sludge contains a large amount of nutrients such as nitrogen,phosphorus,potassium and organic matter,and heavy metals seriously restrict it resource reuse.In order to solve this problem,these factors effect on heavy metals removal efficiencies by biosurfactant,and heavy metals release kinetic,and the combined biosurfactant and electrokinetic treatment remove heavy metals from sludge.At the same time,heavy metals migration behavior and fate path were analysed,and heavy metals speciations variations,ecological risk analysis,stability,leaching toxicity and nutrient variations of sludge were investigated in this study,which could provied technical support for effective dispose of heavy metal pollution in sludge.Based on the factors effect on heavy metals removal efficiencies by rhamnolipid,saponin and sophorolipid.Biosurfactant concentrations,reaction times and liquid-solid ratios were optimized.First-order-kinetic equation and pseudo-second-order kinetic fit the desorption data of Cu,Zn,Cr,Pb,Ni and Mn.The results indicated that Cu,Zn,Cr,Pb,Ni and Mn removal efficiencies increased with the increase of biosurfactant concentration,reaction time and liquid-solid ratio.Heavy metal obtianed the highest removal efficiency by used saponin.The optimal parameters heavy metal removal efficiency by used response surface methodology,which were as follows:saponin concentration was 6.0 g/L,reaction time was 30 h,and liquid-solid ratio was 35.Heavy metal desorption data more close fit pseudo-second-order kinetic,and Cu,Zn,Cr,Pb,Ni and Mn relative coefficient were 0.9990,0.9989,0.9993,0.9991,0.9986,0.9965,respectively.On the basis of Cu,Zn,Cr,Pb,Ni and Mn removal efficiencies of effect on rhamnolipid,saponin and sophorolipid,which combined and electrokinetic were used to enhance removal heavy metal from sludge.The electrode solutions variations,sludge characteristics variations,heavy metal migration behavior and fate in different electrokinetic treatments were analyzed.Results showed that under different electrokinetic treatments,the conductivity of the anolyte ranges from 600 to 1000μS/cm,and the conductivity of the catholyte ranges from 800 to 1000μS/cm.Sludge pH of the near the anode chamber is maintained 2.0 and 6.0,near the cathode chamber using nitric acid as the cathode electrode solution is maintained at about 7.0.Combined rhamnolipid and electrokinetic treatment obtained the highest removal efficiencies,and Cu,Zn,Cr,Pb,Ni and Mn removal efficiencies were 55.8±5.46%,73.8±6.23%,64.0±5.11%,51.6±5.32%,60.8±2.12%,and 56.0±3.21%,respectively.Heavy metal fate analysis showed that heavy metal contents accounted for a large proportion in the electrode solution and repaired room.Cu,Zn,Cr,Pb,Ni and Mn contents of proportions were58.63%,71.34%,63.04%,52.95%,61.74%,56.24%in the electrode solution,respectively.Cu,Zn,Cr,Pb,Ni and Mn contents of proportions were 38.02%,26.20%,32.56%,42.69%,36.34%,42.35%in repaired room,respectively.The biosurfactant and the biosurfactant combined electrokinetic treatment effect on the heavy metal speciation,ecological risks,stability,leaching toxicity and nutrients of in sludge were analyzed.Results showed that the biosurfactant combined electrokinetic treatment is beneficial to the exchangeable speciation change into ionic speciation,and oxidizable speciation change into reducible speciation,residue speciation increased,which is beneficial to heavy metal stability in the sludge.The potential hazard coefficients(E_r~i values)of Cu,Zn,Cr,Pb,Ni and Mn were 175.774,3.363,2.976,5.775,15.601,0.800,respectively,and the comprehensive ecological risk index(RI value)is 204.289,and the ecological risk grades were strong pollution for Cu,light pollution for Zn,light pollution for Cr,light pollution for Pb,light pollution for Ni,mild pollution for Mn.The ecological risk grade of is moderate pollution,and heavy metal pollution level has decreased after the combined biosurfactant and electrokinetic treatment.Heavy metal leaching rate is the lowest after the combined rhamnolipid and electrokinetic,Cu,Zn,Cr,Pb,Ni and Mn were 2.01%,1.85%,5.04%,5.21%,6.22%and 2.95%,respectively.Organic matter,total nitrogen and total phosphorus contents in sludge after by electrokinetic treatment were 240.82±3.45 g/kg,11.84±2.34 g/kg and 19.70±2.11 g/kg,respectively.It indicated that the treated sludge still has high nutrients contents and great agricultural use.