Investigating the effect of compression on solute transport through degrading municipal solid waste

Abstract

The effect of applied compression on the nature of liquid flow and hence the movement of contaminants within Municipal Solid Waste was examined by means of thirteen tracer tests conducted on five separate waste samples. The conservative nature of bromide, lithium and deuterium tracers was evaluated and linked to the presence of degradation in the sample. Lithium and deuterium tracers were non-conservative in the presence of degradation, whereas the bromide remained effectively conservative under all conditions. Solute diffusion times into and out of less mobile blocks of waste were compared for each test under the assumption of dominantly dual-porosity flow. Despite the fact that hydraulic conductivity changed strongly with applied stress, the block diffusion times were found to be much less sensitive to compression. A simple conceptual model, whereby flow is dominated by sub-parallel low permeability obstructions which define predominantly horizontally aligned less mobile zones, is able to explain this result. Compression tends to narrow the gap between the obstructions, but not significantly alter the horizontal length scale. Irrespective of knowledge of the true flow pattern, these results show that simple models of solute flushing from landfill which do not include depth dependent changes in solute transport parameters are justified.

Multiple-tracer tests for contaminant transport process identification in saturated municipal solid waste

“…Thus, in both tests the recovered mass of Li was considerably below 100 %. This corroborates the relative reduction in lithium observed by the closed-loop tracer test reported by Woodman et al (2014). Figure 2 shows that at the end of the tests all tracers in Test 0B were further into the tail than Test 0A, which may explain why there was a greater measured mass recovery (89.4 %).…”

“…The enrichment due to evaporation would be expected to be less than experienced by closed loop tracer tests, where the leachate and tracer is repeatedly recirculated through a storage reservoir where evaporative processes may come more into play. Woodman et al (2014) observed significant enrichment in a closed-loop test, although…”

“…Batch tests have not shown significant sorption of lithium in leachate onto MSW (Stegemann et al, 2006;Öman and Rosqvist, 1999). However, two recent papers have observed nonconservative behaviour of lithium in MSW under closed loop conditions (Woodman et al, 2013, Woodman et al, 2014 To achieve a target concentration of 30mg/L, for Test 0A, 74 g of laboratory reagent grade 99%…”

“…The fitted mass-adjustment factor, f, Woodman et al,2013;Woodman et al,, 2014 ) in closed-loop tracer experiments. Because of the good fits achieved for lithium, no problems with the mass-adjustment model are identified.…”

“…Here the method is evaluated with application to waste. Previous studies have used simultaneous application of multiple tracers in MSW (Woodman et al, 2013, Woodman et al, 2014, however the primary focus in these studies was on the effect of operating conditions rather than on process identification.…”