22Feb / 2018
The ACUMEN project offers an excellent template for local authority landfill operators both in the UK and beyond on how to create revenues and reduce environmental impacts from their closed landfill portfolios.
When the EU’s environmental programme came calling back in 2011, GGS were only too happy to get involved. Together with the Environment Agency, Norfolk County Council, Biogas Technology and the Warsaw University of Technology, the ACUMEN project team was born.
ACUMEN aimed to investigate new ways to reduce the climate change impact of landfill gas emissions from closed and historic landfills, particularly those owned by local authorities. A significant part of the project involved using innovative monitoring techniques to better characterise gas generation and emission rates from older and smaller landfills. While we employed a wide range of monitoring techniques throughout the project’s three years, three particular techniques stood out as great examples of GGS’ innovative approach to using monitoring to inform better decision making.
To begin with, GGS employed a combination of continuous monitoring techniques to understand both gas generation and behaviour in landfills which had not been actively managed for many years. In addition to monitoring in -waste gas compositions over a prolonged period, GGS carried out a significant number of Purge & Recovery Tests at several of the project’s demonstration sites. The GGS PRT® technique is more conventionally used to assess ground gas flux rates for brownfield sites, but during ACUMEN we explored ways of using repeated PRT tests to qualitatively assess the localised rate of gas generation in different parts of the demonstration landfills.
When considering the risks from offsite gas migrations, we were able to use a related analytical technique, Concentration-Duration Analysis, to better understand how much of a risk offsite gas migration might be to nearby receptors. The project was a great testbed for exploring and demonstrating the many benefits continuous monitoring has for understanding how hazardous gases are generated and behave in older landfills.
As ACUMEN was a climate change focussed project, a key interest was in better understanding and properly quantifying the rate of greenhouse gas emissions from the surfaces of older landfills. This is an area which is difficult to study given the large number of such sites, and the variety of emissions encountered (which are affected by age, waste type, surface material and many other factors). So much so that emissions from older landfills are often poorly recorded or not captured at all in national greenhouse gas inventories.
GGS were keen to use ACUMEN as an opportunity to improve this situation. By adapting traditional surface emissions monitoring methods (such as walkover surveys and flux box tests) with innovative data analysis and presentation techniques, we were able to develop the quantified-surface emission survey (Q-SES) method which tackles the problem by breaking the site area into a large number of grid squares and assigning an individual gas flux value to each grid. This allows you to simply calculate an overall emission flux for the entire site or survey area. This technique also demonstrated the significant spatial and seasonal variability which affects landfill surface emissions. A real highlight of the project was the opportunity to directly compare the Q-SES techniques with other more expensive techniques. The results showed that the Q-SES method produced comparable results to other more expensive techniques such as LiDAR scanning and gas tracing methods.
A final monitoring highlight of the ACUMEN project was our efforts to accurately characterise the effectiveness of a natural methane oxidation ‘biofilter’. The biofilter relies on natural bacteria to break down the methane in the landfill gas to less harmful carbon dioxide and water. A traditional concern with biofilters as a means of landfill gas treatment has been that it’s much less easy to verify whether the biofilter is working effectively relative to say a landfill gas flare. By combining surface emissions surveys with gas depth profiling, we were able to much better understand how effectively methane is broken down within the biofilter.
An interesting finding was how we discovered how ‘methane hotspots’, areas where bio-oxidation of the landfill gas was not completely effective, pop up periodically on the biofilter surface before self-healing and moving to other parts of the biofilter. This gave rise to a concern than untreated methane emissions were continuing from the biofilter surface. However, we were able to develop an innovative ‘flux sheet’ monitoring approach which allowed us to cover the entire biofilter surface and quantify the emissions from the entire biofilter. Happily, this approach demonstrated that the despite the occasional methane hot spots, the biofilter was overall destroying the vast majority of the methane in the landfill gas, thereby significantly reducing it’s impact on climate change.
While the monitoring we carried out was just one element of the broader ACUMEN project, it was really important to show that the new landfill gas management techniques the project was demonstrating were genuinely successful in reducing the greenhouse gas impact of the closed landfills. The project offers an excellent template for local authority landfill operators both in the UK and beyond on how to create revenues and reduce environmental impacts from their closed landfill portfolios. So much so, the project was recognised as part of the EU Green Week 2016 as one the EU Life+ programme’s ‘Best of the Best’ projects. This is a real testament to the team effort over the project’s three year programme.
The project also serves as an excellent example of how a holistic and innovative approach to monitoring can yield real benefits in understanding hazardous ground gas issues. GGS continues to build on the learning from the ACUMEN project to develop monitoring solutions which help our clients solve complex environmental challenges, both in the landfill sector and beyond.
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Read more about the ACUMEN study here.