Trace element exposure in the environment from MSW landfill leachate sediments measured by a sequential extraction technique.

Dredged leachate sediments from eight MSW landfills were dried and homogenized, and metals sequentially extracted. The concentrations of cadmium (Cd), copper (Cu), chromium (Cr), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn) were found to be similar to those reported for sewage sludge, and generally below the EU limits for use of sludge on agricultural land. Sequential extraction of the samples showed that the largest fractions of the heavy metals were associated with Fe- or Mn-oxides. Cr and Cu were the only metals investigated that were associated with the organic matter in the sediments to any significant extent (2-10% of Cr and 10-28% of Cu). Since the largest fractions of the metals studied were bound to Fe-oxides, and thus had a low mobility, these metals will generally have a low bioavailability under aerobic conditions when present in leachate sediments. This is most likely also valid for particulate matter suspended in MSW landfill leachate and released to the environment, since this is the source of the sediments.

Size charge fractionation of metals in municipal solid waste landfill leachate.

Municipal solid waste landfill leachates from 9 Norwegian sites were size charge fractionated in the field, to obtain three fractions: particulate and colloidal matter >0.45microm, free anions/non-labile complexes <0.45microm and free cations/labile complexes <0.45microm. The fractionation showed that Cd and Zn, and especially Cu and Pb, were present to a large degree (63-98%) as particulate and colloidal matter >0.45microm. Cr, Co and Ni were on the contrary present mostly as non-labile complexes (69-79%) <0.45microm. The major cations Ca, Mg, K, and Mn were present mainly as free cations/labile complexes <0.45microm, while As and Mo were present to a large degree (70-90%) as free anions/non-labile complexes <0.45microm. Aluminium was present mainly as particulate and colloidal matter >0.45microm. The particulate and colloidal matter >0.45microm was mainly inorganic; indicating that the metals present in this fraction were bound as inorganic compounds. The fractionation gives important information on the mobility and potential bioavailability of the metals investigated, in contrast to the total metal concentrations usually reported. To study possible changes in respective metal species in leachate in aerated sedimentation tanks, freshly sampled leachate was stored for 48h, and subsequently fractionated. This showed that the free heavy metals are partly immobilized during storage of leachate with oxygen available. The largest effects were found for Cd and Zn. The proportion of As and Cr present as particulate matter or colloids >0.45microm also increased.

Effect of an uncontrolled fire and the subsequent fire fight on the chemical composition of landfill leachate.

Landfill leachates sampled during and after an accidental landfill fire were analysed and the levels of selected metals and chemical compounds compared to those occurring in the leachate under normal conditions. The fire at the landfill site was put out by excavation and cooling by use of water. The investigation during the fire and fire fight revealed a moderate increase in the level of nitrogen and also in pH and conductivity. Heavy metals and COD in the leachate showed considerably increased levels. In general, the determined variables appeared to normalise within one week after the fire was extinguished. It can be concluded that landfill fires extinguished by excavation may lead to elevated leachate levels of especially COD and heavy metals, but that this is only a short-term effect.

Mass-balance estimation of heavy metals and selected anions at a landfill receiving MSWI bottom ash and mixed construction wastes.

An estimation of the heavy metal and anion mass-balance was made for municipal solid waste incinerator bottom ash deposited at a construction and industrial waste landfill. The mass-balance was found by comparing the content of metals and anions in the landfill leachate to the metal and anion content in the deposited bottom ash. The discharge of heavy metals ranged from 0.001% for Pb to 0.55% for Cr, which is approximately at the same level as in regular municipal solid waste (MSW) landfills. Landfilled organic material and silicates from construction waste might have contributed to the retention of metals. Chloride, and to a lesser extent sulphate, appeared to be readily released from the landfill. It was estimated that a mass corresponding to 80% of the Cl- and 18% of the SO(4)2- in the bottom ash was discharged annually. Low retention, especially of chloride, may lead to a rapid decline in the discharge of this ion in the future when the landfilling of bottom ash is discontinued.

Estimation of the mass-balance of selected metals in four sanitary landfills in Western Norway, with emphasis on the heavy metal content of the deposited waste and the leachate.

A worst-case simulation of the mass-balance for metals in the waste deposited during 1 year and the levels of cadmium (Cd), lead (Pb), mercury (Hg), chromium (Cr) and iron (Fe) in the leachate was calculated for four sanitary landfills in Western Norway. Estimates of the levels of metal content in mixed municipal solid waste (MSW) were found by using recent literature values calculated in a mass-balance study at a Norwegian waste incinerator plant. Leachate from the landfills were sampled and analyzed monthly during 1 year, and from these measurements the total annual discharge of the selected metals through the leachate was determined. The levels of the measured heavy metals in the leachate were low. For Cd less than 0.06%, for Pb less than 0.01% and for Hg less than 0.02% of the estimated year's deposited mass of metals were leached from the landfills during the year of investigation. The high retention of these metals are most likely due to sulfide precipitation, but also due to the immobile condition of the metals in their original deposited solid state (plastics, ceramics, etc.). The percentage of Cr leached was relatively higher, but less than 1.0% per year. The mass balance of Fe suggests that this element is more mobile under the prevailing conditions. The percentage of Fe leached varied and was estimated to be between 1.9% and 18%. The present study clearly supports the theory that MSW only to a small extent will lead to discharge of metals if deposited at well-constructed sanitary landfills with top layers.