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A comparative analysis of biogas upgrading technologies: Photosynthetic vs physical/chemical processes

Toledo-Cervantes, Alma, Estrada, José M., Lebrero, Raquel, Muñoz, Raúl
Algal research 2017 v.25 pp. 237-243
activated carbon, algae, anaerobic digestion, biofertilizers, biogas, biomass, drying, economic incentives, energy, environmental impact, greenhouse gas emissions, income, models, operating costs, photobioreactors, photosynthesis, sludge, wastewater treatment
Two biogas upgrading technologies, viz. an innovative algal-bacterial photobioreactor and a conventional activated carbon filter coupled with a water scrubber, were comparatively evaluated in terms of environmental, economic and social performance by using the IChemE Sustainability Metrics. The upgrading of 300Nm3/h of biogas generated from the anaerobic digestion of mixed sludge in a wastewater treatment plant was used as a model scenario for the comparative analysis. Despite the algal-bacterial photobioreactor entailed 1860 times higher land requirements, the two-stage physical/chemical technology exhibited ×3.8 higher energy consumptions and larger environmental impacts in terms of material and water consumption and greenhouse gas emissions (the latter by a factor of ~45). The investment cost for the algal-bacterial photobioreactor was 1.6 times higher than that of its physical/chemical counterpart due to the biomass drying unit required to produce an algae-based fertilizer. However, the operating cost of the physical/chemical technology was ~7 times higher due to the frequent replacement of the activated carbon. A further analysis of the net present value (NPV 20) revealed that photosynthetic upgrading would yield revenues from year 5 of operation mainly due to the sale of the algal bio-fertilizer produced, even without tax incentives for bio-methane.