Accelerated flushing of contaminants from MSW landfill at the field scale using a fill-and-draw method.

A fill-and-draw flushing test on a landfill cell containing MSW waste was carried out to examine the operational viability of this method for accelerating the flushing of contaminants and landfill stabilisation. During the fill cycle, 800 m3 of water containing the tracer bromide was pumped into the base of a 0.44 ha landfill cell, resulting in the estimated saturation of 9,400 m3 of waste. Abstraction took place in two phases, during which 1,100 m3 of tracer/leachate was recovered. Samples of leachate were analysed for the tracer, electrical conductivity and indigenous solutes chloride and ammonia. Tracer recovery was between 63 and 72 % for bromide. An estimated 227 kg of ammonia and 575 kg of chloride were removed. Test data was used to calibrate a 1D, dual-porosity model involving advection in a mobile zone, and diffusion into 'blocks' of a less mobile zone. The model fitted well to the early time data, whereas later data appears to have been affected by recharge. The results of this trial demonstrate the possibilities of the 'fill-and-draw' concept using the basal leachate drainage system of landfills as a potential accelerated landfill remediation technique. However, modelling results suggest low contaminant removal efficiency. Including a pause between the fill and the draw cycles improves mass removal.

Experimental study of the intrinsic permeability of municipal solid waste.

Changing patterns of municipal solid waste (MSW) management, for example sorting for recycling and mechanical-biological treatment (MBT), will change the nature of the residual material going to landfill and in particular its intrinsic permeability. This is an important parameter, not least because of its influence on gas and leachate flows and the ramifications for gas and leachate management. This paper reports the results of laboratory permeability tests on specimens of MSW recovered from boreholes drilled in a Chinese landfill, under both liquid and gas flow. The test results are used to assess the intrinsic permeability of the waste, and are compared with corresponding data from raw and MBT municipal solid wastes from developed countries in the context of differences in waste composition, porosity and particle size. For the Chinese waste, the intrinsic permeability decreased with depth, while at a given depth the permeability determined with gas flow was consistently larger than that determined with liquid flow. Intrinsic permeabilities determined in liquid flow showed no clear trend of variation with effective particle diameter d10, but reduced with drainable porosity (the drainable porosity, ne, being a more appropriate and useful measure than the total porosity, n). Conversely, intrinsic permeabilities determined in gas flow showed a clear decrease with decreasing d10, but no consistent variation with porosity. These differences are potentially significant in assessing the impacts and interactions between gas and liquid flows; some reasons for them are suggested.

Evaluating landfill aftercare strategies: A life cycle assessment approach.

This study investigates the potential impacts caused by the loss of active environmental control measures during the aftercare period of landfill management. A combined mechanistic solute flow model and life cycle assessment (LCA) approach was used to evaluate the potential impacts of leachate emissions over a 10,000year time horizon. A continuum of control loss possibilities occurring at different times and for different durations were investigated for four different basic aftercare scenarios, including a typical aftercare scenario involving a low permeability cap and three accelerated aftercare scenarios involving higher initial infiltration rates. Assuming a 'best case' where control is never lost, the largest potential impacts resulted from the typical aftercare scenario. The maximum difference between potential impacts from the 'best case' and the 'worst case', where control fails at the earliest possible point and is never reinstated, was only a fourfold increase. This highlights potential deficiencies in standard life cycle impact assessment practice, which are discussed. Nevertheless, the results show how the influence of active control loss on the potential impacts of landfilling varies considerably depending on the aftercare strategy used and highlight the importance that leachate treatment efficiencies have upon impacts.

Enhanced biodegradation at the Landgraaf bioreactor test-cell.

From 2001 to 2011, a bioreactor demonstration was performed in a 25,000m(3) (8m deep, 3500m(2) surface) test-cell. In this bioreactor, biodegradation was enhanced by premixing and homogenizing of waste, recirculation of leachate and aeration. Anaerobic biodegradation was completed within four years and was followed by two years of aeration. Ultimately a residue was obtained that had lost approximately 95% of its biogas potential. Biodegradation resulted in a significantly reduced leaching potential for dissolved organic carbon (DOC) and specific heavy metals. For other inorganic components, less progress was achieved. Increased flushing would be required for further reduction of the leaching potential. A significant reduction in chemical oxygen demand (COD) and ammonia (NH4(+)) in leachate was not demonstrated during the relative short-term aeration: COD concentrations actually increased slightly and there was no effect on NH4(+). During the project, it became clear that moisture flow through the waste followed preferential flow paths. Therefore, attention was also paid to gain better understanding of leachate flows. From a tracer test, it was concluded that part of the waste contaminants are held in immobile blocks and are to a large extent unaffected by flow occurring in the surrounding preferential flow paths.

Characterisation of the recalcitrant organic compounds in leachates formed during the anaerobic biodegradation of waste.

This study investigates the use of UV absorption and fluorescence spectroscopy to assess the early development of recalcitrant organic compounds in leachates formed during the anaerobic biodegradation of municipal solid waste. Biochemical methane potential tests were carried out on fresh waste (FW) and composted waste (CW) over a period of 150 days and leachates produced from the degradation of two wastes were analysed for humic-like (H-L) and fulvic-like (F-L) structures by UV spectroscopy and fluorescence excitation-emission-matrix analyses. During anaerobic biodegradation, the synthesis and utilization of H-L and F-L structures in the leachates over time was indicative of the generation of the recalcitrant organic compounds. The results obtained from UV absorption and fluorescence spectroscopy suggested that CW leachates resulted in a higher concentration and more condensed form of recalcitrant H-L and F-L molecules than FW leachates. These findings demonstrate how fluorescence and UV absorption spectroscopy can be used as an indicator for monitoring the evolution of recalcitrant organic compounds (H-L and F-L substances) in leachates formed at different stages of waste biodegradation.

Effect of normal variations on disease classification of Raman spectra from cervical tissue.

In this paper, we examine how variations in normal tissue can influence disease classification of Raman spectra. Raman spectra from normal areas may be affected by previous disease or proximity to areas of dysplasia. Spectra were acquired in vivo from 172 patients and classified into five tissue categories: true normal (no history of disease), previous disease normal (history of disease, current normal diagnosis), adjacent normal (disease on cervix, spectra acquired from visually normal area), low grade, and high grade. Taking into account the various "normal" states of the tissue before statistical analysis led to a disease classification accuracy of 97%. These results indicate that abnormal changes significantly affect Raman spectra, even when areas are histopathologically normal. The sensitivity of Raman spectroscopy to subtle biochemical differences must be considered in order to successfully implement it in a clinical setting for diagnosing cervical dysplasia and cancer.

Detecting temporal and spatial effects of epithelial cancers with Raman spectroscopy.

Epithelial cancers, including those of the skin and cervix, are the most common type of cancers in humans. Many recent studies have attempted to use Raman spectroscopy to diagnose these cancers. In this paper, Raman spectral markers related to the temporal and spatial effects of cervical and skin cancers are examined through four separate but related studies. Results from a clinical cervix study show that previous disease has a significant effect on the Raman signatures of the cervix, which allow for near 100% classification for discriminating previous disease versus a true normal. A Raman microspectroscopy study showed that Raman can detect changes due to adjacent regions of dysplasia or HPV that cannot be detected histologically, while a clinical skin study showed that Raman spectra may be detecting malignancy associated changes in tissues surrounding nonmelanoma skin cancers. Finally, results of an organotypic raft culture study provided support for both the skin and the in vitro cervix results. These studies add to the growing body of evidence that optical spectroscopy, in this case Raman spectral markers, can be used to detect subtle temporal and spatial effects in tissue near cancerous sites that go otherwise undetected by conventional histology.