Abstract:

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.

Key words: environment, pollution, optimal design, citric acid, GLDA, heavy metals, removal rate, orthogonal experiment

摘要：

采用柠檬酸（CA）和谷氨酸N，N-二乙酸（GLDA）处理污泥重金属，研究了试剂浓度、pH和反应时间对重金属去除效果的影响，并以重金属去除率为表征，通过正交试验获得CA和GLDA处理重金属的最佳条件。结果表明，增加试剂用量、降低体系pH均有利于重金属的去除，但延长反应时间对重金属的去除效果影响不明显。CA和GLDA处理污泥重金属的最佳条件分别为：CA 0.3 mol·L^-1、pH 4、反应时间2 h和GLDA 0.05 mol·L^-1、pH 4、反应时间3 h。最佳反应条件下，对于CA和GLDA，重金属Cd、Cu、Pb和Ni的去除率可分别达80.25%、77.75%、64.66%和75.16%，及78.57%、78.48%、64.84%和76.71%。CA和GLDA对重金属的去除效果大小顺序均为：Cd>Cu> Ni>Pb，但GLDA的处理效果优于CA。污泥经CA和GLDA处理后，污泥固相酸溶态重金属含量下降幅度最大，平均达81%，残渣态重金属含量下降52.1%，而污泥液相中重金属含量则增加了17.54倍，说明重金属从污泥固相向液相转移。SEM镜检发现，污泥由处理前表面分散的絮状结构，变成更为明显的团块结构和片层结构，污泥的吸附能力下降，且体积缩小。研究结果表明，CA和GLDA处理污泥能有效降低污泥重金属含量并提高污泥固相重金属的化学稳定性，有利于污泥脱水及脱水后的进一步处理及其资源化。

关键词: 环境, 污染, 优化设计, 柠檬酸, 谷氨酸N, N-二乙酸, 重金属, 去除率, 正交试验