High heavy metals content is the major drawback of sludge resource

especially for sludge derived from industrial wastewater treatment plan. Citric acid and GLDA were used to treat sludge heavy metals in the present study

and the effects of the reagent concentration

pH and reaction time of citric acid and GLDA on the availability and removal of sludge heavy metals were investigated. An orthogonal experiment was performed to obtain the optimum reaction condition of CA and GLDA treatment of the sludge heavy metals. The results indicated that the higher reagent concentrations and the lower pH led to the higher removal rate of heavy metals

but the effect of longer reaction time on heavy metal removal was not obvious. The best conditions of CA andGLDA treatment of sludge heavy metals were: CA 0.3 mol·L-1

pH 4 and reaction time 2 h

and GLDA 0.05 mol·L-1

pH 4 and reaction time 3 h. Under the optimum reaction conditions of the CA and GLDA

the removal rate of Cd

Cu

Pb and Ni can reach 80.25%

77.75%

64.66% and 75.16%

and 78.57%

78.48%

64.84% and 76.71%

respectively. Both of CA and GLDA

the removal efficiency of heavy metals was ranged as Cd>Cu> Ni>Pb

but the effect of GLDA treatment was better than that of CA. After CA and GLDA treatment

the acid-soluble contents of heavy metals in the solid phase of sludge decreased most and reached an average of 81%

the residual contents decreased an average of 52.1%

and the heavy metals in the liquid phase of sludge increased an average of 17.54 times

leading to the transfer of the heavy metals from the solid phase into liquid phase. SEM observation showed that the flocculent structure of sludge was replaced obviously by mass structure and the layered structure after treatment. And at the same time

the adsorption ability and volume were reduced. The research results showed that the CA and GLDA treatment of sludge can effectively reduce the sludge heavy metal content and improve the chemical stability of heavy metals in solid phase of sludge

which was advantageous to the sludge dehydrating and its further processing and utilization.