Comparative Study of the Leachability of Heavy Metals from Sewage Sludge, Sawdust and Organic Fraction of Municipal Solid Waste

Abstract

The comparative study of the leachability of sewage sludge, sawdust and organic fraction of municipal solid (OFMSW) waste was conducted at different rainfall intensities. First, the natural moisture content of the three categories of waste were obtained. Samples of the wastes were air-dried and then subjected to heavy metal tests to determine the initial and overall heavy metal content. Sewage sludge, sawdust and OFMSW were subjected to different rainfall intensities and the concentrations of cadmium (Cd), lead (Pb), chromium (Cr), arsenic (As) and copper (Cu) in the resultant leachates were determined using atomic absorption spectrophotometer. The pH ranges of 6.08 to 6.28, 7.62 to 8.38 and 7.62 to 8.27 were obtained for leachate from saw dust, sewage sludge and OFMSW respectively. The moisture content of sawdust, sewage sludge and OFMSW were 4.58%, 44.4% and 56.06% respectively. Sewage sludge had the highest heavy metal content distributed as follows: Cu (0.4 ppm), As (4.3 ppm), Cr (0.207 ppm), Cd (0.362 ppm) and Pb (2.57 ppm) with arsenic and lead being the highest. There was a good correlation between the concentrations of heavy metals in the waste media. The highest correlation was between Cd and Pb (R =-0.99996). There was no significant difference in the concentrations of the various heavy metals in the waste media at 95% confidence limit. Copper was the most leachable and sawdust was the most susceptible to copper leaching. On the other hand, cadmium, arsenic and lead exhibited the least leachability, suggesting a measure of affinity between these metals and the wastes.