The goal of this study is to assess the technical feasibility of remediating siloxane contaminants in biogas via a photochemical process. Specifically, we studied in the laboratory a process that involves the use of an ultraviolet (UV) photodecomposition reactor (PhoR) to convert siloxane trace impurities, commonly found in biogas produced in water treatment plants and landfills, into silica particulates. These can then be effectively removed from the reactor effluent with the use of a downstream filter. High siloxane conversions were obtained, which demonstrates the effectiveness of the technique. The proposed technology is presently being field-tested in a California landfill.

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The goal of this research was to determine the feasibility of employing the catalytic steam reforming of biogas to increase its energy content by converting the methane it contains into a hydrogen-rich syngas mixture and using this reformate product intermixed with raw biogas in a lean-burn gas engine in order to enhance combustion stability and to reduce NOX emissions. The field-testing component of the project involved catalytically reforming a side stream of biomethane from a landfill gas collection system at a California landfill via a waste energy chemical recuperation process, in which waste heat from a gas engine was used to promote the reforming reaction of biogas. In the study, the total flow of raw biogas diverted to the engine remained constant. A fraction of that biogas was, however, separated and directed to the aforementioned catalytic reactor. The reformer exit stream was then dried, blended with the remaining biogas, and burned in an internal combustion engine to produce electricity. When operating on the blended biogas mixture, combustion stability was enhanced, and the engine ran smoothly at the full speed of 3600 rpm with a 60 Hz output frequency. On the other hand, when burning raw biogas without any reformate gas blended, the test engine ran poorly, sputtering and never reaching 3600 rpm. Also, when operating at various loads under fuel-lean (excess-air) conditions, NOX emissions were significantly reduced when compared to the engine operating on propane under the same load conditions. Similar comparative testing could not be performed on raw landfill gas alone because the engine would not operate at full speed, as noted above. The research presented here has validated the technical and economic feasibility of using reforming products during biogas combustion in a lean-burn gas engine in order to reduce NOX emissions and to enhance combustion stability. This, in our opinion, is an important contribution to the scientific/technical literature and a significant advance for the field of biogas utilization.

We present in this paper the results of the field testing at a California Landfill of a UV photodecomposition reactor (PhoR) used for the removal of siloxane impurities from landfill gas (LFG). Prior to its field testing, the PhoR technology was tested in the laboratory with simulated LFG and was shown to be capable of completely removing the trace siloxane compounds and to convert them into silica particulates. The key objective of the field test was to validate the ability of the PhoR system to treat real LFG in a practical setting. The field-scale PhoR again proved quite efficient in attaining complete siloxane removal at different concentrations in the real landfill environment. These promising findings have led us to propose a scaled-up, commercial size PhoR system, competitive to conventional adsorption systems that can be practically applied in existing landfill plants to obtain 99+% siloxanes removal rates without associated secondary emissions.