Browsing by Author "Davies, S."

Now showing 1 - 4 of 4
  • Thumbnail Image
    ItemOpen Access
    Compositional analysis of excavated landfill samples and the determination of residual biogas potential of the organic fraction
    (Elsevier, 2016-06-08) Garcia, J.; Davies, S.; Villa, Raffaella; Gomes, D. M.; Coulon, Frederic; Wagland, Stuart Thomas
    The objectives of this study were to assess the biogas potential of landfilled materials and to further validate the suitability of the enzymatic hydrolysis test EHT as a valuable alternative to substitute the standardised test currently in use (BMP). Both tests were applied to a range of landfill waste samples. The waste composition and volatile solids content (VS) profile together with the BMP test results showed that the biogas potential of the waste samples was directly related to their VS content, as expected. The positive correlation between the VS and the BMP test (r = 0.67) suggests that the first could be used as a primary indicator of biogas potential of waste samples. Nevertheless, it should be validated against the BMP test because, occasionally, the VS content does not equate to the biogas production. This was mainly due to the paper content of the samples which also correlates positively (r = 0.77) with the BMP biogas production. The EHT results showed a higher correlation with the BMP test (r = 0.91) than in previous studies which used a wider mixture of enzymes containing cellulase, hemicellulase and carbohydrase. This finding positions the EHT as a quick assessing method for the biodegradability of waste samples in future sample regimes.
  • Thumbnail Image
    ItemOpen Access
    Compositional and physicochemical changes in waste materials and biogas production across 7 landfill sites in UK
    (Elsevier, 2016-08-28) Frank, R. R.; Cipullo, Sabrina; Garcia, J.; Davies, S.; Wagland, Stuart Thomas; Villa, Raffaella; Trois, C.; Coulon, Frederic
    The aim of this study was to evaluate the spatial distribution of the paper and fines across seven landfill sites (LFS) and assess the relationship between waste physicochemical properties and biogas production. Physicochemical analysis of the waste samples demonstrated that there were no clear trends in the spatial distribution of total solids (TS), moisture content (MC) and waste organic strength (VS) across all LFS. There was however noticeable difference between samples from the same landfill site. The effect of landfill age on waste physicochemical properties showed no clear relationship, thus, providing evidence that waste remains dormant and non-degraded for long periods of time. Landfill age was however directly correlated with the biochemical methane potential (BMP) of waste; with the highest BMP obtained from the most recent LFS. BMP was also correlated with depth as the average methane production decreased linearly with increasing depth. There was also a high degree of correlation between the Enzymatic Hydrolysis Test (EHT) and BMP test results, which motivates its potential use as an alternative to the BMP test method. Further to this, there were also positive correlations between MC and VS, VS and biogas volume and biogas volume and CH4 content. Outcomes of this work can be used to inform waste degradation and methane enhancement strategies for improving recovery of methane from landfills.
  • Thumbnail Image
    ItemOpen Access
    Development of a low-maintenance measurement approach to continuously estimate methane emissions: a case study
    (Elsevier, 2016-12-18) Riddick, Stuart N.; Hancock, B. R.; Robinson, Andrew D.; Connors, Sarah; Davies, S.; Allen, Grant; Pitt, Joseph; Harris, Neil R. P.
    The chemical breakdown of organic matter in landfills represents a significant source of methane gas (CH4). Current estimates suggest that landfills are responsible for between 3% and 19% of global anthropogenic emissions. The net CH4 emissions resulting from biogeochemical processes and their modulation by microbes in landfills are poorly constrained by imprecise knowledge of environmental constraints. The uncertainty in absolute CH4 emissions from landfills is therefore considerable. This study investigates a new method to estimate the temporal variability of CH4 emissions using meteorological and CH4 concentration measurements downwind of a landfill site in Suffolk, UK from July to September 2014, taking advantage of the statistics that such a measurement approach offers versus shorter-term, but more complex and instantaneously accurate, flux snapshots. Methane emissions were calculated from CH4 concentrations measured 700 m from the perimeter of the landfill with observed concentrations ranging from background to 46.4 ppm. Using an atmospheric dispersion model, we estimate a mean emission flux of 709 μg m−2 s−1 over this period, with a maximum value of 6.21 mg m−2 s−1, reflecting the wide natural variability in biogeochemical and other environmental controls on net site emission. The emissions calculated suggest that meteorological conditions have an influence on the magnitude of CH4 emissions. We also investigate the factors responsible for the large variability observed in the estimated CH4 emissions, and suggest that the largest component arises from uncertainty in the spatial distribution of CH4 emissions within the landfill area. The results determined using the low-maintenance approach discussed in this paper suggest that a network of cheaper, less precise CH4 sensors could be used to measure a continuous CH4 emission time series from a landfill site, something that is not practical using far-field approaches such as tracer release methods. Even though there are limitations to the approach described here, this easy, low-maintenance, low-cost method could be used by landfill operators to estimate time-averaged CH4 emissions and their impact downwind by simultaneously monitoring plume advection and CH4 concentrations.
  • Thumbnail Image
    ItemOpen Access
    Evaluating leachate recirculation with cellulase addition to enhance waste biostabilisation and landfill gas production
    (Elsevier, 2016-07-05) Frank, R. R.; Davies, S.; Wagland, Stuart Thomas; Villa, Raffaella; Trois, C.; Coulon, Frederic
    The effect of leachate recirculation with cellulase augmentation on municipal solid waste (MSW) biostabilisation and landfill gas production was investigated using batch bioreactors to determine the optimal conditions of moisture content, temperature and nutrients. Experimentation was thereafter scaled-up in 7 L bioreactors. Three conditions were tested including (1) leachate recirculation only, (2) leachate recirculation with enzyme augmentation and (3) no leachate recirculation (control). Cumulative biogas production of the batch tests indicated that there was little difference between the leachate and control test conditions, producing on average 0.043 m3 biogas kg−1 waste. However the addition of cellulase at 15 × 106 U tonne−1 waste doubled the biogas production (0.074 m3 biogas kg−1 waste). Similar trend was observed with the bioreactors. Cellulase addition also resulted in the highest COD reduction in both the waste and the leachate samples (47% and 42% COD reduction, respectively). In both cases, the quantity of biogas produced was closer to the lower value of theoretical and data-based biogas prediction indicators (0.05–0.4 m3 biogas kg−1 waste). This was likely due to a high concentration of heavy metals present in the leachate, in particular Cr and Mn, which are known to be toxic to methanogens. The cost-benefit analysis (CBA) based on the settings of the study (cellulase concentration of 15 × 106 U tonne−1 waste) showed that leachate bioaugmentation using cellulase is economically viable, with a net benefit of approximately €12.1 million on a 5 Mt mixed waste landfill.