Project Overview
Approved for funding through ERA’s Biological GHG Management Program in 2014, the City of Lethbridge collected data to help refine the Alberta offset protocols for landfill emissions, which previously used calculations based on studies outside the province and, therefore, may not be accurate. By its completion in 2015, the project recovered core samples from landfills for testing, obtaining reliable experimental data which could be used to verify or correct the models the province uses to measure methane emissions from landfills.
Collecting Valuable Data for Landfill Gas Emission Model Validation
Methane is an extremely potent greenhouse gas. One of the main sources of methane emissions is from decomposing organic waste at landfill sites. Models and protocols developed for the quantification of methane emissions from landfills estimate the rate and quantity of methane production via the waste decay rate constant and the maximum methane yield. Alberta’s model for estimating landfill gas emissions, the Alberta Landfill Gas Quantification (ALGQ) Model, is based on the Intergovernmental Panel on Climate Change (IPCC) First-Order Decay Model. The model requires several landfill-specific inputs as well as regional assumptions. The ALGQ model is central to the province’s protocol for the reduction or offset of landfill methane emissions through waste prevention, waste diversion, carbon sequestration, and carbon credit allocation programs. All programs are dependent on the landfill or Alberta-specific waste decay rate and methane yield of the waste-in-place. To estimate a reliable Alberta-specific landfill waste decay rate requires determining several landfill sites’ rates, of which the average may be used province-wide. Project data could potentially be used in the validation of the ALGQ model estimates or fine-tuning degradation models relevant to the greenhouse gas mitigation protocols for landfills in Alberta.
Enhanced Understanding of the City’s Landfill Waste Characteristics
Characteristics of organic waste and microbial communities are complementary to the rate and extent of landfill degradation and therefore contribute to the potential amount of GHG emissions released. Biochemical methane potential and physical waste characterization were performed by Alberta Innovates – Technology Futures (AITF), and molecular characterization of microbial communities was performed by Alberta Livestock Research Branch on 45 spent municipal solid waste (MSW) samples collected from two City of Lethbridge landfills.
Physical characterization revealed that spent MSW were highly heterogeneous, containing residual organic materials and inert materials. On a dry weight basis, the average waste composition was 49% organics, 23% visible inerts, 16% paper, and 13% wood. There were no statistically significant differences between the physical characteristics, degradation rates, and maximum methane yields for samples from both landfills. Molecular identification of microbial communities showed the presence of fungi, highly salt-tolerant bacterial species, and anaerobic bacteria.
Unfortunately, methanogenic bacteria and archaea communities were not observed in the samples, which leaves several key questions unanswered, especially the biological basis of methane production and GHG emission from the two landfill sites in the City of Lethbridge. This aspect of the work needs to be pursued in order to advance knowledge regarding the biological basis of landfill waste degradation and GHG emission.
What’s next?
The ALGQ Model requires several inputs, some of which may have to be determined experimentally. This study generated experimental landfill methane yield data relevant to the City of Lethbridge landfill and has improved on understanding of landfill waste characteristics in the region. It has therefore provided Alberta-relevant data to support or fine-tune the province’s landfill gas offset protocol. Where a reliable field-based degradation rate is available, the data may represent a basis for relating lab-based degradation rate to field-applicable rates for the verification or validation of landfill gas emission models.
The degradation rates and maximum methane yields obtained are comparable with current rates reported and, therefore, would be useful in establishing a correction factor for laboratory to field degradation rates. Data generated from this study will therefore be a valuable laboratory-based asset for landfill gas emission model validation. For a comprehensive validation of the ALGQ Model, this study will hopefully be the first of many toward a province-wide model validation initiative. For a province-wide assessment of the ALGQ model, similar tests are recommended on other landfills. A representative landfill selected in each specific provincial sub-region is required to obtain baseline field degradation rate data.