IWWG Task Group on
Landfill Gas Emission and Mitigation


TG Leader: Julia Gebert / Marion Huber-Humer


Background and Scope

The CLEAR Task Group aims to coordinate interdisciplinary research on the quantification and mitigation of landfill gas emissions to the atmosphere. The Task Group emerged from a recognized need among participants at an IWWG-Workshop held in the context of the Second Intercontinental Landfill Research Symposium (ICLRS), in Asheville, North Carolina in October 2002, for a mechanism with which to coordinate international research on landfill gas emissions and oxidation.

The CLEAR Task Group now includes approx. 40 academic and industrial researchers and scientists from Europe, the United States, Canada, Australia, Malyasia and is led by Marion Huber-Humer from the Institute of Waste Management of BOKU University in Vienna, Austria (e-mail: marion.huber-humer@boku.ac.at) and Julia Gebert from the Hamburg Port Authority, Germany.

Aims and Objectives

The main focus of CLEAR is on the utilization of natural biological processes to reduce emissions of methane and non-methane organic compounds (NMOCs).  A second focus is on improved methodologies to measure and model landfill gas emissions and oxidation Moreover, CLEAR manages a large database, currently being updated, of information and scientific results on methane emissions and oxidation.

The Task Group provides a forum for members to discuss and exchange ideas, generate hypotheses, and jointly consider and relate results and findings from diverse projects. By fostering international and interdisciplinary communication and pooling data, research advances can be accelerated, and future research requirements identified and synthesized more effectively. From the synergy fostered by CLEAR, more innovative and comprehensive approaches and strategies to measure, characterize, and mitigate landfill gas emissions will emerge.

 As research efforts are coordinated and new results are generated, the Group serves as a clearinghouse and point of contact for those seeking information about measuring, modeling, and mitigating landfill gas emissions. Landfill operators, legislators, industry groups, and citizen groups are encouraged to access information through contact with CLEAR. Furthermore, collaborations from within the Group are published in international journals, so that ready access to information is available to the research community. Some of the research topics addressed by CLEAR members include:

  • landfill gas generation and emissions
  • control and mitigation strategies for LFG-emissions
  • prediction and modeling on a regional, national and global basis
  • contribution of landfill methane to the greenhouse effect and climate change
  • microbial methane oxidation
  • biodegradation of NMOCs in landfill cover soils

The current objectives of CLEAR are:

  • Standardization of methods used to measure biotic methane oxidation capacity
  • Fine-tuning isotope methods to measure methane oxidation
  • Quantification and field validation of LFG-emissions and effects of diverse mitigation technologies
  • Development and improvement of engineering systems to enhance methane oxidation in landfill cover soils
  • Modelling of methane oxidation in landfill cover materials
  • Biodegradation of NMOCs in landfill settings, including both aerobic cover soils and deeper anaerobic zones

For the latest Action Plan of the CLEAR TG, click here.

Activities and mode of operation

CLEAR encourages and implements frequent scientific exchange through an email discussion platform (CH4ox@yahoogroups.com). To date, more than 75 persons have subscribed to this list. Group activities are coordinated by the task group leader and communication between members is conducted mainly via email and through Internet web page.

Annual workshops/meetings are convened to maintain personal contact among members, introduce new members to the Task Group, and to provide a forum for presentations and interactive group discussions.  Since 2003 there have been more than ten meetings and workshops, generally during the Sardinia or Intercontinental Landfill Research Symposium (ICLRS) events.

The task-group operates in close contact with other IWWG task groups, particularly the “Sustainable Landfilling” group.


Member expertise encompasses a broad range of disciplines, including microbiology, soil science, chemistry, geochemistry, civil and environmental engineering, and waste management. Collectively, CLEAR members have many years of experience in the measurement and modelling of landfill gases at local, regional, and global scales.


Contact person:

Prof. Dr. rer. nat. Julia Gebert

TU Delft / Faculty of CITG Stevinweg 1

2628 CN Delft, NL

Tel: +31 152 782 798

E-mail: J.Gebert(at)tudelft(dot)nl

Next Task Group Meetings:

to be announced


During Sardinia 2017 the CLEAR Task Group hosted a workshop session on “Guiding documents for methane oxidation systems". About 37 people joined the workshop session and contributed with questions, statements and their personal experiences. For the workshop report, click here.

Moreover, CLEAR held its annual administrative member meeting, the minutes of the meeting can be found on the member area.


CLEAR - IWWG Task Group on Landfill Emission Abatement Research - Sardinia 2015 report

by Marion Huber-Humer and Julia Gebert

During Sardinia 2015 the CLEAR (Consortium for Landfill Emissions Abatement Research) Task Group hosted a workshop session on “Longterm efficiency of methane oxidation systems - Can natural analogies be used for long-term evaluation” (session G12) and organized an administrative member meeting afterwards. The main purpose of this workshop session was to highlight and discuss the issue if methane oxidation processes in natural systems (like wetlands) can be compared to “anthropogenic habitats” (like landfills), and if experiences from such habitats can be used as analogy to deduce long-term methane production and emission behaviour and develop emission limit values for engineered technical methane oxidation systems. Thus, overriding questions were, how to gain acceptance for the technology by authorities in the future, and how to propose acceptable emission limits and suitable monitoring strategies. 27 people joined the workshop session and contributed with questions, statements and their personal experiences.
Following a welcome note and introduction by the workshop chairs Marion Huber-Humer (BOKU University of Vienna, Austria) and Julia Gebert (Hamburg Port Authority), both gave short key-note presentations to stimulate discussion. Marion Huber-Humer presented some considerations on the topic “What can we learn from natural methane oxidation systems?”, underlining the differences between natural methane oxidation systems (like wetlands) and engineered ones on landfills. As the main difference in impact factors the methane load, which can be orders of magnitude higher on landfills than compared to natural systems, was identified. Moreover, for the construction of biocovers, biofilters and biowindows also artificial, waste–based and also “tailor-made” substrates can be applied (besides natural mineral soil material) with strongly varying properties and high heterogeneity.  However, by the selection of suitable construction materials the oxidation capacity of engineered systems can be also clearly enhanced compared to natural systems.
Julia Gebert continued with a key-note presentation on “Which monitoring approaches and controlling levels are acceptable for remaining methane emissions from engineered oxidation systems”. She addressed the question “Why we need to limit methane emissions”, pointing out, that we require them to (1) check and optimise extraction and methane utilization on landfills, (2) for safety issues on site and (3) for climate protection issues. Safety concerns must be addressed due to regulations and optimum collection and utilization of methane is more or less within the operator‘s interest. Moreover, she compared the current greenhouse gas emission situation from landfills with other industrial sectors and also with waste incineration. Arguments and statement were presented to kick off discussion on the relevance and how strictly greenhouse gas emissions from landfills shall be regulated compared to other waste treatment alternatives.
To provide further considerations for technical discussion, Heijo Scharff presented his experiences on the EU situation regarding the implementation of emission limit values for landfill gas versus “best available techniques (BAT)” advisements. He also addressed the cost effectiveness of required measures and available technologies and provided a site-specific example for a municipal solid waste landfill including the costs and emission reduction effectiveness of different post closure gas treatment techniques. From his point of view, future developments within the EU regulation on landfill gas emissions are against specific limit values, since methane emission measurement methods that
are affordable, sufficiently accurate and sufficiently reliable to stand up in a court case are currently not available, and thus the tendency will go towards the acceptance of BAT, which will be described in technical guidance documents.
Finally, Peter Kjeldsen (Technical University Denmark) presented ideas on “Approaches to propose limit values”, based on current discussions about technical guidelines for monitoring methane oxidation systems and criteria for the termination of the monitoring. He presented considerations on four general principles to set up such limit values: based on (1) what is “detectable” due to state of the art measurement methods (technical limit value); (2) typical methane emissions from natural wetlands (which is according to his literature research about  1.3 g CH4/(m2∙day)); (3) what is achievable in passive oxidation soil covers (similar to BAT); (4) optimization of expenses to mitigate societies greenhouse gas emissions (which is strongly site specific and may vary from case to case).
After the impulse presentations workshop participants took part in a joint discussion and contributed with their experiences and impressions regarding the approaches in their own country to accept methane oxidation systems as “state of the art” to mitigate landfill gas emissions.   A bit controversially discussed was the issue, if we will need definitive threshold or limit values to gain acceptance at local authorities for the implementation of methane oxidation systems. Just 7 out of the 27 workshop participants were convinced – considering their current country-specific situation – that implementation of such systems will be accepted by authorities only based on best practice (BAT considerations) without having proper target or limit values available. However, in Germany on a dredged material landfill full-scale methane oxidation systems were permitted without the need of setting specific limit value. However, an extensive monitoring program was required by the competent authority as part of the permit (see also the paper by Gebert et al. in the SARDINIA conference proceedings).
People agreed on that there are already many international, different (specific) practical experiences and a lot of existent knowledge, as well as first (national) technical guidelines available, like in Austria, Germany, France, etc.  However, a harmonized “BAT-document”, e.g on an EU –level, for engineered methane oxidation systems is not available so far, and CLEAR could act as a driver to set up such a document.
More information on the CLEAR Task Group can be found on the webpage www.tuhh.de/iue/iwwg/task-groups/clear.html.

Sessions on Methane Emissions and Oxidation on landfills during ICLRS 2014:

Monday 20th October: "Session 2C - Biocover performance assessment"
Session Chairs: Peter Kjeldsen and Stuart Denver
Tuesday 21st October: "Session 4C - Landfill methane emission measurements and modeling: Part 1"
Session Chair: Charlotte Scheutz
Tuesday 21st October: "Session 6C: Current Concerns in Methane Oxidation"
Session Chair: Alex Cabral
More information can be found at http://www.iclrs2014.com/

CLEAR - IWWG Task Group on Landfill Emission Abatement Research - Sardinia 2013 report

by Marion Huber-Humer and Julia Gebert

During Sardinia 2013 the CLEAR (Consortium for Landfill Emissions Abatement Research) Task Group hosted a workshop session on “Methane oxidation – guidelines for practical implementation” (session G13) and organized an administrative member meeting. The main purpose of the workshop was to provide a panel for interactive discussion, to exchange ideas, and to jointly consider the need and request for an internationally harmonized “state-of-the-art guiding document” for the construction, operation, maintenance and monitoring of biological methane oxidation systems. Current activities and developments as well as key-issues from already existing national guidelines were presented briefly and jointly discussed afterwards. About 32 people joined the workshop session and contributed with questions, statements and their personal experiences.

Following a welcome note and introduction by the workshop chair Marion Huber-Humer (BOKU University of Vienna, Austria), information on the “Austrian guideline on biocovers for old landfill sites” was provided. Austria has already established this technical guideline in 2009 under the umbrella of the ÖVA (download of guideline at http://www.altlastenmanagement.at/; written in German). Recommendations and criteria for material selection, biocover construction, operation and monitoring in practice have been summarised and developed in this guideline focusing on the remediation of old landfill sites. However, this document can be also applied to recently closed landfills and sites constituted of mechanically and biologically pre-treated waste with low gas emission potential. A decision-tree is included in this guideline intended to assist in finding a proper solution for a specific landfill site.

Julia Gebert (University of Hamburg, Germany) gave a key-note presentation on the development of two “New German Guidelines on Methane Oxidation” within the framework of the MiMethox research-project. Guideline I focuses on methods for the “Quantification of methane fluxes on landfills”; Guideline II on the “Design and dimensioning of landfill biocovers”. She pointed out that next to guidance on available methods the documents shall provide (1) assistance for the decision if and under which conditions methane oxidation is an appropriate measure to mitigate residual emissions, and (2) references for the setup of methane oxidation systems. The documents should be understood as experience-based recommendations and will be available most probably at the beginning of 2014.

Stuart Dever (Kimbriki Environmental Enterprises Pty Ltd and University of New South Wales, Australia) continued with an impulse presentation on the “Implementation of Biocovers and Biofilters for landfill Methane Oxidation in Australia”. In Australia, several field scale trials of passive landfill gas biofiltration were undertaken during the past years and the results were used to prepare a handbook for the design, construction, operation, monitoring and maintenance of such systems, which was published in 2010 (University of New South Wales, 2010; published by the NSW EPA). Stuart Dever stated that in Australia biocovers and biofilters are now recognized by the New South Wales EPA and EPA Victoria as legitimate methods for reducing landfill methane emissions, and are now generally considered appropriate for managing landfill methane emissions at low gas generation landfill sites as well as for supplementing an active landfill gas management system at larger landfill sites. However, so far there is no recognition of biocovers or biofilters as a means of treating landfill methane emissions under the Australian Government’s National Greenhouse and Energy Reporting (NGER) system. Currently the University of New South Wales is involved in a project developing a methodology for using passive biofilters to generate carbon credits under the Australian Government’s Carbon Farming Initiative. If successful, the outcome could be a financial driver that may encourage the installation of biofilters at old and small landfill sites.

After the impulse presentation all workshop participants took part in a joint brainstorming on examples from different countries worldwide that have already set up guidelines and/or criteria with respect to evaluation and construction of methane oxidation systems or countries that are working on such documents. However, beyond the presented activities in Austria, Germany and Australia the participants only knew of respective current activities in the UK and France.

A controversial discussion followed on the terminology of such documents. Some people stated that the term “guideline” sounds too strict and incorrect, since the community is not so far as to provide general technical recommendations for the construction, operation and monitoring of biofilters or biocovers, particularly since we have to face very different country and site specific conditions and situations. Other participants advanced the view that the community can at least provide harmonised state of the art recommendations. However, people agreed on that there are already many international, different (specific) practical experiences and a lot of knowledge available, and that this should be summarized and harmonized in something like a “technical state of the art paper” or “compendium of knowledge”. We do not have to reinvent the whole wheel in each new case study, because some fundamental processes and factors are always and everywhere the same. And these processes and mechanisms should be clearly stated and considered. CLEAR could act as a driver to set up such a compendium.

Some participants pointed out that guiding documents are really necessary and would be of great assistance to convince local authorities to implement these new concepts and local pilot projects to gain more experiences and information for further steps. E.g., some representatives from an Italian authority confirmed that previously it was hardly possible to implement new concepts like biofilter systems because regional expertise and experiences were missing. Thus, even a rough guiding document would be very helpful in the near future.

Then a more detailed discussion focused on potential technical contents of such a general guiding document. Some people stated that the functionality of a biocover or biofilter system still should be described and it should be clearly stated which system would work well for a specific situation (regarding expected gas fluxes, other impacting local factors etc.), or for a specific kind of application, and which benefits and drawbacks are connected. For example, large biocovers and small biowindows are completely different, they do not have the same impacting factors and are operating on different scales; thus the monitoring and evaluation procedure must be quite different as well. A general “decision support tool” should be developed based on such considerations.

Thus the finally focused conclusion was that currently the community is too far away from one internationally harmonized guideline due to the very different country and site specific situations, but a review of former and current project activities and a summary in a „state of the art paper“ (journal paper or handbook) would be really helpful and could push forward the implementation of biocover and biofilter systems worldwide.