Effect of metal spiking on different chemical pools and chemically extractable fractions of heavy metals in sewage sludge

Abstract

A laboratory experiment was conducted to study the effect of metal spiking and incubation on some properties and sequentially extractable chemical pools of some heavy metals (F 1, two extractions with 0.1 M Sr(NO 3) 2; F 2, one extraction with 1 M NaOAc (pH 5.0); F 3, three extractions with 5% NaOCl (pH 8.5) at 90–95 °C; F 4, three extractions with 0.2 M oxalic acid + 0.2 M ammonium oxalate + 0.1 M ascorbic acid (pH 3.0); and F 5, dissolution of sample residue in HF–HClO 4 (residual fraction,) and also 1 M CaCl 2 and 0.005 M DTPA extractable heavy metals in sewage sludge. Metal spiking and incubation decreased pH and easily oxidizable organic C content of sludge but increased electrical conductivity. Metal spiking and incubation increased F 1 fraction of all heavy metals, F 2 fraction of Ni, Pb, Cu, and Cd, F 3 fraction of Pb, Cu, and Cd, F 4 or reducible fraction of Ni, Cu, and Cd and residual fraction of Zn and Pb, but decreased F 2 fraction of Zn, F 3 of Zn and Ni, F 4 fraction of Zn and F 5 fraction of Ni, Cu, and Cd. Metal spiking and incubation increased 1 M CaCl 2 and 0.005 M DTPA extractable amounts of all heavy metals in sludge except for 0.005 M DTPA extractable Zn, which registered only very marginal decrease.