Temperature Effect on Water Extractability of Cadmium, Copper, Lead and Zinc from Composted Organic Solid Wastes of South-West Nigeria

The effect of temperature changes (10 to 80 °C) on water-extractable metal (Zn, Cu, Cd and Pb) concentrations of composted wastes of Nigerian origin was investigated in batch extraction experiments. Metal concentrations were measured using a calibrated atomic absorption spectrophometer after acid digestions. Results showed that the water-extractable metal fractions (I) did not exceed 10% of total metal concentrations of the bulk composts, which corresponded to 0.30 to 6.63% for Zn, 0.09 to 7.51% for Pb, 1.83 to 9.29% for Cu and 0.67 to 9.23% for Cd. Water extractable metal fraction showed positive correlations (r = 0.137 to 0.917*; p* < 0.01) for Cu, Cd and Pb in most cases but negative for Zn (−0.067 to −0.445). Simulations revealed that a steady temperature rise from 0.1 to 1.5 °C might increase I by 0.13 to 168% for all the metals, although stability to gradual temperature rise was demonstrated in some instances. The study revealed that the degree of temperature effect on water extractability of heavy metals from the bulk composts was dependent on metal type, compost formulation and waste type.