Land application of sewage sludge: A soil columns study

A column study was conducted to assess the potential Cr, Ni, Cu, Zn, Cd and Pb movement through a reconstructed soil profile to which surface composted sewage sludge was applied. Sewage sludge was mixed into the top 100 mm of each column at the rates of 357 (H), 223 (M) and 22 Mg·ha-1 (L). Treatment H was calculated according to the critical soil concentration and treatments M and L were calculated according to the amount of metals which may be added to agricultural land on 10 yr average (M) and 1 yr (L) according to European legislation. Soil columns were leached with 5 000 ml of water. After leaching, soil columns were sampled at depth intervals of 0 to 100, 100 to 300, 300 to 500 and 500 to 840 mm. Metal balance accounted for over 97% of metals and over 86% of metals were retained in the first 100 mm of the column. The average percentage of metals leached decreased in the order Cd (0.04%) > Cu (0.02) ~ Ni (0.02) ~ Zn (0.02) > Pb (0.01) ~ Cr (0.01). The maximum metal concentration in leachates was lower than the limit value for irrigation water but metal concentrations exceeded the drinking water levels for Pb and Ni in all treatments. Thus, harmful health effects may result from the application of sewage sludge.