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Environmental assessment of BIOGASNET technology. Life Cycle Assessment
The LIFE BIOGASNET project aims at demonstrating a new cost-effective and environmentally friendly technology for sour biogas desulfurization based on biological processes, being able to obtain a high-quality biogas and valuable by-products. The BIOGASNET technology will allow to reduce the H2S concentration of biogas up to 90% of initial concentration. To this, two BIOGASNET prototypes were designed and constructed for to different relevant operational environments: (1) a municipal (medium size) solid waste landfill in Cádiz (Spain) and (2) a municipal (large size) solid waste treatment plant in Fili town, Athens (Greece). These two different scenarios differ in the type of biogas and the nitrogen (N) source used for the biomass sustenance, leachate ammonium (NH4+) in the case of Cádiz and ammonia (NH3) enriched composting exhaust gas in Athens. The prototypes consist of two bioreactors, an aerobic nitrifying reactor and an anoxic biotrickling filter or bioscrubber (depending on the site needs). Among the available biological techniques, anoxic bioprocess is one of the most attractive, being its main advantage the coexistence in a unique process of simultaneous biogas desulfurization and denitrification.
Environmental performance of the BIOGASNET prototypes have been assessed by means of the Life Cycle Assessment (LCA) methodology and compared with a conventional desulfurization technology, the chemical scrubbing. The assessments have been performed according to the principles described in the ISO standards (14040:2006 and 14044:2006).
The results revealed that chemical scrubbing environmental impact at low concentrations of H2S co-dominated by energy and chemicals consumption, but as higher the concentration higher the dominance of the chemicals consumption to the environmental impact, which is in accordance with the logic of this process that eliminates H2S by consuming chemicals. In the case of BIOGASNET prototypes the energy consumption is the main driver of impact regardless of the concentration of H2S. A sensitivity analysis revealed that in the case of Cádiz site the turning point (H2S concentration in which different desulfurization technologies has the same environmental performance), in which BIOGASNET technology has better environmental performance than chemical scrubbing is 206 ppmv. The Athens prototype reduce the turning point to a concentration of around 75 ppmv (this difference is due to the higher energy demand for Cádiz site related to the leachate dependence for its N-source in contrast to Athen’s site which N-source is obtained from a gaseous stream).
The environmental assessment caried out determined that BIOGASNET technology has better environmental performance than chemical scrubbing for the removal of H2S when site conditions are suitable for its operation. Therefore, its implementation in sites where the desulfurization of sour biogas is needed, it is recommended instead of the use of chemical processes but after a characterization of the site to study the availability of nitrogen and carbon waste stream sources. In addition, given the electricity consumption dominance of the BIOGASNET technology, the minimization of energy consumption, such as use of residual heat, self-produced electricity or with certified origin from renewable sources will significantly improve the environmental performance of the BIOGASNET technology.