A Simulation Model of Combined Biogas, Bioethanol and Protein Fodder Co-Production in Organic Farming

In order to evaluate new strategies for the production of renewable energy within sustainable organic agriculture, a process-simulation model for a 100 ha organic farm was developed. Data used for the model was obtained from laboratory trials, literature data, consultancy with experts, and results from the BioConcens project (http://www.bioconcens.elr.dk).

Different design approaches were evaluated in order to establish the most suitable configuration. Rye grains, clover grass silage, maize silage, whey and cattle manure were selected as raw materials for co-production of fuels, feed and fertilizer at the organic farm, based on the fact that crops grown in organic agriculture act as key carbon sources whereas manure and whey were applied primarily as the nutrient and water supply for the fermentations within the process (anaerobic digestion and simultaneous saccharification and fermentation, respectively).

Results from batch and lab-scale fermentation trials provided basic input for the model. To cover the direct energy requirements on the farm, it was calculated that it requires approximately 16.2 ha of rye and 14 milking cows or 5.7 ha of clover grass, 2.5 ha of maize and 13 cows to supply a 100 ha organic farm with ethanol or biogas, respectively.

This calculation was based on the assumption that the electrical efficiency of CHP (combined heat and power) unit was 38%. A variety of different scenarios can be simulated to mirror the farmer's needs.