BT Technology for the Control of Methane Emissions from Permafrost and Natural Gas Hydrates

Abstract

Climate change resulting from increased greenhouse gas emissions, particularly that of carbon dioxide, methane, and nitrous oxide, is of major concern as far as future global welfare is concerned. Although carbon dioxide emissions have dominated political discussions, methane release from both natural gas hydrates and permafrost in polar, particularly arctic, regions is of major concern because of methane’s markedly greater temperature forcing potential than that of carbon dioxide. Methane emissions from thawing permafrost are a direct consequence of arctic temperature increase, while methane emissions from natural gas hydrates will result from both enhanced natural release and possible byproduct release during the future exploitation of natural gas hydrate reserves. Although some sedimentary and submarine methane release occurs as ebullition, most methane released under conditions of moderate hydrostatic pressure will initially be in the dissolved state and distributed over huge areas and in massive volumes of both fresh and marine waters. High reaction rate aerobic methane oxidation (methanotrophy) has been well known as a natural microbially mediated process for more than 100 years, but as far as methane emissions control from natural sources is concerned has, with the exception of possible remediation of coal mine atmospheres, been ignored. In addition to aerobic methane oxidation, anoxic methane oxidation by methanogenic microorganisms in the presence of either sulfate or nitrate, has also been widely reported, but without reaction rate data. As far as methane elimination from aquatic systems is concerned, it is most likely that it will be methanotrophic consortia that will be harnessed in technological processes. The most promising systems for dissolved methane elimination are membrane-attached aerobic biofilm reactors employing methanotrophic consortia as the process-mediating biota. Such systems can comprise reactors based on either tubular or flat membranes, without enclosure, but with encircling buoyancy chambers, such that they are submerged, but can be drawn through water bodies either on a framework of rigid guides or by steel ropes, such as to achieve appropriate liquid velocities over the pre-established membrane-attached methanotrophic biofilms. However, further development of such systems, particularly with respect to problems such as biofilm sloughing will be necessary before technical-scale operation.