Removal of Pb from sewage sludge by electrokinetics: effect of pH and washing solution type.

In this study, the effect of pH and washing solution on the removal of lead from sewage sludge by electrokinetics was investigated. The six experimental runs were carried out at two different pH values--3 and 4--using acetic acid, nitric acid and phosphoric acid. In addition, the sequential chemical extraction scheme according to the BCR's (Community Bureau of Reference) guidelines was applied to the sludge samples to evaluate the effect of acidic solutions on Pb fractionation during electrokinetic processes. Using nitric acid as the washing solution resulted in the highest removal efficiency of Pb (39%) amongst all the experiments. Acetic acid also provided similar removal percentages (37% and 38%) at different pre-acidification conditions. On the other hand, the removal efficiencies were 36% and 27% with pre-acidification using phosphoric acid at pH 3 and 4, respectively, resulting in the lowest efficiencies. The results obtained by BCR analysis showed that the metal present near the anode partitioned in to more mobile forms while the metal near the cathode partitioned in to less mobile forms, such as precipitated or adsorbed forms, as the electrokinetic process proceeded. The inter-fractional transformations of Pb formed only when using acetic acid. The similar percentages obtained by using different washing solutions indicated that the type of acid used as washing solution was less effective than the values of pH for removal of Pb from sewage sludge during the electrokinetic process.

Effect of EDTA as washing solution on removing of heavy metals from sewage sludge by electrokinetic.

This paper presents the effect of ethylene diamine tetraacetic acid (EDTA) as a washing solution on the electrokinetic process for removal of Cr, Pb and Zn from sewage sludge. The sequential chemical extraction scheme according to the guidelines of BCR (Community Bureau of Reference) was applied to the sludge samples to evaluate the effect of EDTA on metal fractionation during electrokinetic processes. The highest removals of the heavy metals were 34% for Cr, 27% for Pb and 20% for Zn with 0.1N EDTA. The removal priority of the metals by electrokinetic process was found to be Cr>Pb>Zn. According to the results of BCR analysis, addition of EDTA did not create the inter-transformation of Cr, Pb and Zn although the metal concentration decreased.

Evaluation for agricultural usage with speciation of heavy metals in a municipal sewage sludge.

This study was carried out to evaluate the agricultural usage of an anaerobically digested sludge in the contents and fractions of heavy metals. Therefore, a sequential extraction scheme according to the BCR's (Community Bureau of Reference) guidelines and total acid digestion were applied to sewage sludge samples. The results of total heavy metal concentrations in sewage sludge showed that the highest total concentrations were Fe, Zn and Mn. When Turkish, Europe and US EPA directives were compared with each other by depending on the use of sludge for agricultural purposes, all the heavy metals determined for this sludge were below the maximum permitted levels, except for Cd. This sludge should not be applied to land due to its high Cd content. The results of heavy metal fractions indicated that some metals (Cd, Mn, Pb, and Fe) distributed mainly in the residual fraction. All fractions of Zn showed no variation. Cu and Cr were most abundant in the oxidizable phase while Ni was in exchangeable phase. Although total content of Ni in the sludge is lower than the maximum levels allowed by all the directives, it tends to be easily moved and dispersed in the environment. Due to its high mobility, the examined sewage sludge may cause phyto-toxicity after its agricultural application.