Toxicological Assessment of Crops Grown in Soils Amended with Municipal Solid Waste Ash

This study assessed heavy metals (As, Cd, Cr, Cu, Pb, Ni, Fe and Zn) in sites and food crops (beans and groundnuts) harvested from farmland amended with municipal solid waste (MSW) ash. Farmlands with no amendments and crops grown on such soils served as control. Soils and crops samples were collected at full maturity to determine soil levels (mgkg-1), translocation in crops and accumulation index of metals. The crops were separated into roots, leaves and grains before analysis and heavy metals were determined using VGB 210 Atomic Absorption Spectrometer. Mean concentrations (mgkg-1) of studied metals were 0.053±0.03, 0.053±0.01, 648.55±1.07, 168.699±1.05, 36.514±4.66, 339.53±0.12, 232.331±0.69 and 363.482±0.00 in test soils and 0.010±0.10, 0.050±0.01, 83.333±1.00, 38.618±1.03, 2.913±0.00, 163.248±0.22, 41.579±3.01and 82.798±0.28 in control soils for As, Cd, Cr, Cu, Ni, Pb, Fe and Zn respectively. Observed levels for test soils were significant (p≤0.05) in comparison to those of the control and were highest for Cr, Cu, Ni, Fe and Zn. Metals concentrations in the tissues of beans and groundnut grown on both sites were found to be decreasing in the order roots > leaves > grains. Levels of As, Cr, Cu, Ni and Fe fell below the WHO standard while Cd, Pb and Zn exceeded those set limits. Translocation factors for beans and groundnut cultivated on test site indicated effective translocation of arsenic from soils to the roots. Observed pattern has health implication for raised fodder for animal husbandry in such areas. Similarly, the geo-accumulation index of both test and control sites revealed they were polluted with Zn, Cr, Ni, Cu, Ni, Cu and Fe.

Characterization of ash melting behaviour at high temperatures under conditions simulating combustible solid waste gasification

To achieve high-temperature gasification-melting of combustible solid waste, ash melting behaviour under conditions simulating high-temperature gasification were studied. Raw ash (RA) and gasified ash (GA) were prepared respectively by waste ashing and fluidized bed gasification. Results of microstructure and composition of the two-ash indicated that GA showed a more porous structure and higher content of alkali and alkali earth metals among metallic elements. Higher temperature promoted GA melting and could reach a complete flowing state at about 1250°C. The order of melting rate of GA under different atmospheres was reducing condition > inert condition > oxidizing condition, which might be related to different existing forms of iron during melting and different flux content with atmosphere. Compared to RA, GA showed lower melting activity at the same condition due to the existence of an unconverted carbon and hollow structure. The melting temperature for sufficient melting and separation of GA should be at least 1250°C in this work.