Open Access Original article

Ecological and economic evaluation of biogas from intercrops

Nora Niemetz* and Karl-Heinz Kettl

Author Affiliations

Institute for Process and Particle Engineering, Graz University of Technology, Inffeldgasse 21a, Graz, 8010, Austria

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Energy, Sustainability and Society 2012, 2:18  doi:10.1186/2192-0567-2-18

Published: 4 September 2012

Abstract

Background

Biogas made from main crops (e.g., corn) is commonly used for producing electricity and heat. Nevertheless, the production of energy from monocultures is highly unsustainable and not truly renewable. Since neither monocultures nor food competition are desirable, intercrops can be used to increase the yield per hectare instead of leaving agricultural fields unplanted for soil regeneration. The extra biomass can be used for biogas production. In a case study, the economic as well as the ecological feasibility of biogas production using intercrops, cattle manure, grass and corn silage as feedstocks for fermenters was analyzed.

Methods

The set-up for the case study included different feedstock combinations as well as spatial distributions of substrate supply and heat demand for modeling and optimization. Using the process network synthesis, an optimum structure was generated representing the most economical technology constellation which included transport of substrates, heat and biogas (when applicable). The ecological evaluation was carried out by using the sustainable process index method.

Results

The application of both methodologies to different scenarios allowed a constellation to be found which is economically feasible while entailing low ecological pressure. It is demonstrated that the production of intercrops for producing biogas has so far not been regarded as a viable option by the farmers due to a variety of barriers. Sensitization is needed to emphasize that planting intercrops holds many advantages like positive effects on soil regeneration and raised nitrogen fixation, as well as increased biomass output per hectare and, last but not least, it allows the production of energy without conflicts between food and energy production.

Conclusions

Using intercrops for the production of biogas has the potential to decrease the ecological footprint decisively while still offering opportunities in the lucrative biogas market. The transfer of know how regarding this option should be taken up by agricultural training.

Keywords:
Decentralized networks; Biogas; Intercrops; Crop rotation; Process network synthesis; PNS; Sustainable process index; SPI; Ecological footprint