New methodologies for removal of methane from the atmosphere

The goal of this project is to develop low cost ways to remove methane from the ambient air. Many methane sources, such as emissions from cattle and other farming activities, and low-grade emissions from the gas industry, cannot easily be reduced. As a result, volumes of high-methane air persist around the sources. This proof-of-concept study will improve methods of locating such volumes of high-methane air, and also design and test simple inexpensive methane removal methods, such as soil methanotrophy in greenhouses, and catalytic removal of methane around gas installations, in order to develop new ways of reducing methane emissions from otherwise intractable sources.

Methane is a potent global warmer, and is the second-most important anthropogenic greenhouse gas. Methane, which is rising rapidly at present, is emitted both by natural and anthropogenic sources, with about three-fifths of the emissions caused by human actions. These human-caused emissions include agriculture and waste (about a third of global total emissions), such as cattle breath and rice fields, landfills, and sewage systems, as well as fossil fuel sources such as gas leaks and coal mine venting. Many such sources are widely disseminated (e.g. cow breath) and thus regarded as intractable to reduction. Similarly, while larger gas and coal mine leaks can be identified and stopped, smaller disseminated leaks are harder to eliminate.

Thus developing low-cost methods for removing methane from ambient air is a very important pre-requisite for reducing the global methane burden. But such disseminated emissions of high-methane air are not easily amenable to leak reduction efforts. The purpose of this proposal is to design and prove low cost ways of taking methane out of air, in ways that can easily be applied in settings where large amounts of methane are emitted. The aim is not to remove all methane, but to reduce mixing ratios of high-methane air where it is 'habitually' present.

The first part of the work focuses on improving methods of detecting high-methane air in the ambient environment. This work will use mobile vehicle-mounted high-precision cavity-based analysers, coupled with grab sampling for high-precision isotopic analysis to identify the sources (e.g. using C-isotopes to distinguish gas leaks from nearby landfill gas emissions). The study will develop ways of quantifying volumes of high methane air in typical locations, and thus of assessing flow rates targetted for removal in ambient settings.

In cow barns, feed lots and open milk sheds, the project will design and test methane reduction by using soil methanotrophy in active greenhouses next to the source. Methane-rich air will be extracted close to the source (for example from the mouths and noses of cattle in an open milking shed), and pumped under the substrate soil/growing medium of a greenhouse nearby. Here, methanotrophic bacteria will oxidise the methane to CO2, which will then be taken up by the plants in the greenhouse. The experimental work will test the feasibility of the method (e.g. energy costs) and optimise the conditions (temperature, humidity, air flow, etc).

In industrial settings such as gas compressor sheds, or near large waste systems in enclosed spaces, removal by inexpensive chemical catalysis using MnO and CuO will be tested. These systems will be based on the reliable, low cost zero-air generators used in methane labs. The intention is not to remove all methane, but optimise economic partial-removal flow rates, optimal temperature and moisture conditions, frequency of regenerating the catalyst etc.

The final part of the work will be in synthesis studies to assess the feasibility of methane reduction. An effective reduction policy, whether supported by subsidy or imposed by a regulatory framework, must be inexpensive to be acceptable. The design challenge is to find methodologies that are simple, robust in typical applications, and low cost.

The potential impacts of this research are large. Hitherto, many sources of methane emissions, such as agricultural sources, have been considered 'intractable'. For example, Schaefer et al. (Science, 352, 80-84, 2016) pointed to an inherent clash between the need for food and the competing problem of methane emission. Feasible methods for removal of methane from air around such 'intractable' agricultural and industrial sources will thus have important positive impacts on compliance with the commitments made under the 2016 Paris Agreement on Climate Change, both for the UK and also in high-emission nations worldwide.

The immediate beneficiaries of the research will be the UK livestock industry, as well as those operating landfills, sewage systems and gas distribution networks. Public policy towards these industries will benefit if feasible and low-cost methods of cutting emissions become available: the response will likely be a mix of new regulatory frameworks and subsidy to encourage methane removal, while sustaining the economic basis and profitability of these industries.

If successful, the technologies will have strong domestic and export potential. There will be high demand, both in the UK and globally, for successful methane removal systems. Moreover, most such technologies pass through decades of optimisation and improvement (e.g. in adjusting methanotroph cultures, bio-environment and substrate; or in catalyst fine-tuning). Thus there will be continuing impact if the UK develops such skills, and potentially a sustained new industry designing and providing such methane removal systems.

More widely, the work, if successful, will provide important new pathways for the UK and other similar economies to meet their commitments under the Paris Agreement, within the UN Framework Convention on Climate Change. This will be a significant impact, as the targets are very challenging and a substantial contribution from methane reduction will be extremely helpful in reaching national and international goals.