Solid waste, granular inorganic material: Column test (NT ENVIR 002)

Abstract

  This Nordtest method is a column test and the test produces eluates, which shall be analysed chemically and physically (e.g. temperature). The eluates can also be characterized ecotoxicologically. The column test is applicable for percolation dominated systems. The results from the leaching tests are interpreted on the basis of the liquid to solid (L/S) ratios which play an important role in the assessment of leaching behaviour. For a waste disposal site or a waste utilisation application of known geometry for which the rate of percolation of e.g. precipitation is known, the L/S scale may with some caution be converted into a time scale. By means of the test, information can be obtained about the concentrations to be expected in landfill leachates and also the leached amounts up to a certain L/S ratio. The column test provides information on the leaching behaviour at low L/S ratios (up to 2). If wanted, the column test can be continued to higher L/S ratios (e.g. 10). However, information on leaching at higher L/S ratios can often be more conveniently (e.g. due to shortening of testing time) obtained from the two-stage serial batch leaching tests performed at accumulated L/S ratios of 2 and 10 (Nordtest method /7/ under preparation). To place the chosen L/S ratios into perspective, it may be calculated that for a 1 m thick layer of waste with a density of 1 ton/m3 through which water (e.g. infiltrating rainwater) is percolating at a rate of 200 mm/year, cumulative L/S ratios of 2 will be attained in 10 years. For a 10 m thick layer of waste with a similar density through which water is percolating at a rate of 200 mm/year, cumulative L/S ratios of 2 will be attained at 100 years. A waste layer thickness of 1 m may be taken to represent some utilisation applications whereas an average layer thickness of 10 m is typical of many landfills. The pH and redox conditions are largely dictated by the composition of the waste and may therefore vary considerably from one type of waste to another as well as between consecutive fractions of eluate from the same test. Depending on the composition of the waste and the buffering capacity of the resulting eluates, the pH and redox potential of these eluates may also be sensitive to ambient conditions (e.g. uptake of atmospheric CO2 and/or O2) during the performance of the test.