Revisiting the passive biocover system at Klintholm landfill, six years after construction.

A biocover system was established at Klintholm landfill in Denmark in 2009 to mitigate methane emissions, and the system exhibited high mitigation efficiency during the first year after implementation. The biocover system was revisited in 2016/2017, and a series of field and laboratory tests were carried out to evaluate functionality about six years after establishment. Three field campaigns were executed in three different barometric pressure conditions, namely increasing, stable and decreasing. Local surface flux measurements and gas concentration profiles in the methane oxidation layer showed that barometric pressure changes had a significant effect on gas emission and methane oxidation. Elevated concentrations of oxygen were observed in the gas distribution layer, and field data showed that significant methane oxidation took place in this location. This finding was verified in laboratory-based methane oxidation incubation tests. Temperatures higher than ambient temperature were observed throughout the methane oxidation layer, with average temperatures ranging between 13 and 27 °C, even in the coldest month of the year. Field measurements showed that total methane emissions from the whole landfill cell were at the same level or lower than measurements performed in 2009/2010 after implementation of the biocover system, and laboratory tests showed methane oxidation potential approximately equal to former tests. In spite of an inhomogeneous distribution of landfill gas load to the methane oxidation layer, the performance of the biocover system had not declined over the 6-7 years since its establishment, even though no maintenance had been carried out in the intervening years.

Methane emissions from Icelandic landfills - A comparison between measured and modelled emissions.

This study compares methane (CH4) emissions from five Icelandic landfills, quantified using tracer gas dispersion to modelled emission rates using the IPCC FOD model. The average CH4 emission rates measured from the investigated landfills were 475.4 kg CH4 h-1 (Álfsnes landfill), 32.5 kg CH4 h-1 (Fíflholt), 40.8 kg CH4 h-1 (Gufunes), 9.8 kg CH4 h-1 (Kirkjuferjuhjáleiga) and 78.4 kg CH4 h-1 (Stekkjarvík). At three of the landfills (Álfsnes, Fíflholt and Kirkjuferjuhjáleiga), the modelled emission was higher than the measured emission by factors ranging from 1.1 to 4.8, neglecting any CH4 oxidation in the cover soils. Even though CH4 oxidation might play a role at some of the investigated landfills, and thus reduce the gap between modelled and measured emissions, it is likely that the model overestimated CH4 generation due to uncertainties in input model parameters. Assuming that the measured emissions at the five landfills are representative of all the waste disposed in Iceland from 2007 to 2016, the measured emission should be extrapolated to 817 kg CH4 h-1, which is relatively close to the modelled national emission of 936 kg CH4 h-1 in 2017. This study showed that the application of the IPCC FOD model at national level is appropriate for estimating landfill CH4 emissions in Iceland. CH4 emissions from landfills in Iceland can be reduced by expanding or implementing gas collection or biocover systems for optimised microbial oxidation.

Validation and error assessment of the mobile tracer gas dispersion method for measurement of fugitive emissions from area sources.

A controlled release test was carried out to assess the accuracy of the tracer gas dispersion method, which is used to measure whole-site landfill methane (CH4) emissions as well as fugitive emissions from other area sources. Two teams performed measurements using analytical instruments installed in two vehicles, to measure downwind concentrations of target (CH4) and tracer gases at distances of 1.2-3.5 km from the release locations. The controlled target gas release rates were either 5.3 or 10.9 kg CH4 h-1, and target and tracer gases were released at distances between 12 m and 140 m from each other. Five measurement campaigns were performed, where the plume was traversed between 2 and 31 times. The measured target gas emissions agreed well with the controlled releases, with rate differences no greater than 1.1 kg CH4 h-1 for Team A and 1.0 kg CH4 h-1 for Team B when quantifying a controlled release of 10.9 kg CH4 h-1. This corresponds to a maximum error of ±10%. A larger error of up to 18% was seen in the campaign with a lower target gas release rate (5.3 kg CH4 h-1). Using a cross plume integration method to calculate tracer gas to target gas ratios provided the most accurate results (lowest error), whereas larger errors (up to 49%) were observed when using other calculation methods. By establishment of an error budget and comparison with the measured error based on the release test, it could be concluded that following best practice when performing measurements, the overall error of a tracer gas dispersion measurement is very likely to be less than 20%.

Quantification of multiple methane emission sources at landfills using a double tracer technique.

A double tracer technique was used successfully to quantify whole-site methane (CH(4)) emissions from Fakse Landfill. Emissions from different sections of the landfill were quantified by using two different tracers. A scaled-down version of the tracer technique measuring close-by to localized sources having limited areal extent was also used to quantify emissions from on-site sources at the landfill facility, including a composting area and a sewage sludge storage pit. Three field campaigns were performed. At all three field campaigns an overall leak search showed that the CH(4) emissions from the old landfill section were localized to the leachate collection wells and slope areas. The average CH(4) emissions from the old landfill section were quantified to be 32.6 ± 7.4 kg CH(4)h(-1), whereas the source at the new section was quantified to be 10.3 ± 5.3 kg CH(4)h(-1). The CH(4) emission from the compost area was 0.5 ± 0.25 kg CH(4)h(-1), whereas the carbon dioxide (CO(2)) and nitrous oxide (N(2)O) flux was quantified to be in the order of 332 ± 166 kg CO(2)h(-1) and 0.06 ± 0.03 kg N(2)Oh(-1), respectively. The sludge pit located west of the compost material was quantified to have an emission of 2.4 ± 0.63 kg h(-1) CH(4), and 0.03 ± 0.01 kg h(-1) N(2)O.