Biogas will play a key role in achieving the targets of the European Renewable Directive. Consisting mainly of methane and carbon dioxide, biogas from anaerobic digesters in wastewater treatment plants must be freed of impurities before use. The BiogasApp project will tackle three main issues regarding biogas upgrading: (i) the presence of siloxanes, (ii) the conversion of CO2 to methane, and (iii) the difficulties in selecting the most adequate treatment technology.
Firstly, aiming at improving the state-of-the-art technology, the removal of siloxanes by adsorption and regeneration, will be investigated. Multicomponent adsorption curves for siloxanes and other trace compounds in biogas will be obtained, thus contributing to improve current design and operation practices. Making use of the main outcomes of the SIRENA project, special emphasis is placed in developing simple water-based/thermal regeneration procedures based on the ability of certain carbon materials and zeolites to promote ringopening reactions.
The second approach regarding siloxane removal merges two recent innovations: membrane separation and biological removal. In that sense, the development of membrane biological reactors (MBR) as considered within the BiogasApp project aims to be a technological breakthrough. MBRs may help solving mass transfer limitations already identified when using biotrickling filters for the same purpose. Additional value arises from i) the addition of activated carbon which may further improve gas-liquid phase mass transfer and promote biodegradation if activated carbons able to catalyse ring-opening are used, and ii) the use of proper enrichment and up-to-date molecular techniques.
Regarding CO2, the BiogasApp project also explores novel, ground-breaking approaches. Conventional technologies are mainly based on separation techniques that aim at increasing the CH4 content through the removal of CO2. Based on the experience gathered during the development of the BEST-ENERGY project and recent research in the field, Bioelectrochemical systems (BES) will be assessed for the conversion of CO2 to CH4. The use of BES will be explored combining basic knowledge acquisition with the evaluation of process performance aspects, such as energy balance and power recovery, which directly affect the eventual technology development.
Finally, the technologies developed within the BiogasApp project will be compared with current, well-established abatement techniques such as non-regenerative adsorption for siloxanes, or pressure-swing adsorption for CO2 removal. The evaluation will consider technical, social, economic and environmental aspects. The key indicators for a suitable integrated assessment of the existing and developed technologies for biogas upgrading will be identified and a multicriteria Decision Support System (DSS) able to recommend the most adequate biogas upgrading technology(ies) for a given scenario will be set-up.