RESUMO
Use of agricultural and livestock by-products for anaerobic digestion (AD), in total or partial substitution of the maize silage was evaluated from an environmental and economical point of view. The evaluation process included three methodological interdependent and consequential steps: the chemical stage at laboratory and plant level, the environmental and economic steps developing the Life Cycle Assessment and Life Cycle Costing jointly. The laboratory test showed that the two mixtures prepared with by-products, in partial (MIX A) and total (MIX B) substitution of maize silage, did not show differences in bio-methane production compared to a reference mixture with the 33% of maize silage. All mixtures tested at full-scale plant, showed the same performances, resulting in a similar energy production. Environmentally, MIX B increased greenhouse gas credits derived from the avoided production of mineral fertiliser for the energetic crops, resulting also in better economic performances. The break-even transport distances follow the positive environmental pattern result, in contrast to what was found for the break-even transport distances from the economic point of view.
