Assessment of the distribution of heavy metals in the different fractions of irradiated sewage sludges

摘要

An experiment was conducted using three kinds of sewage sludge: raw, secondary treated and digested which exposed to three gamma radiation doses: 0, 3, 6 KGy. Samples analysis included total and DTPA heavy metals contents. The heavy metals forms were determined by sequential extraction procedure: 1) CaCl<,2> solution to remove soluble+exchangeable fraction 2) acetic acid solution to remove metals bound by inorganic sites 3) potassium pyropbosphate solution to remove metals bound by organic sites 4) acid oxalate solution to remove metals bound by free oxides. The tested metals were: Cd, Pb, Fe, Zr. The data indicated that Fe and Pb maintained the highest percent in the free oxide fraction and the lowest in the extractable fraction. The percentage of iron occluded by free oxides is almost similar in the different sludges. Percentage of Fe in the organically bound fraction was highest in the digested sludge comparing with the other two sludges. The percentage of Pb occluded by free oxides was as follows: secondary treated aludge>raw sludge>digested sludge. In the organic fraction, secondary treated sludge (Helwan WWTP) exhibited the highest Pb percentage comparing with the other two sludges. The digested sludge showed the highest Fe & Pb percentage, out of the total content, in the extractable fraction. Radiation did not exhibit a specific trend on metal content in the different fractions.