Previous publications about biochar in anaerobic digestion show encouraging results with regard to increased biogas yields. This work investigates such effects in a solid-state fermentation of bio-waste. Unlike in previous trials, the influence of biochar is tested with a setup that simulates an industrial-scale biogas plant. Both the biogas and the methane yield increased around 5% with a biochar addition of 5%-based on organic dry matter biochar to bio-waste. An addition of 10% increased the yield by around 3%. While scaling effects prohibit a simple transfer of the results to industrial-scale plants, and although the certainty of the results is reduced by the heterogeneity of the bio-waste, further research in this direction seems promising.

While several EU member states have working compost markets, only about one third of the bio-waste, around 35 Mio tons is used to produce compost, and to some degree, biogas. The major part is still incinerated or landfilled together with other waste. This paper proposes the improvement of existing and the creation of new compost markets based on the integration of biochar and the implementation of obligatory recycling targets with flexible implementation approaches. Based on a literature review, the production of compost with biochar reduces some of the nitrogen and carbon losses and accelerates the composting process. This indicates economical benefits for the compost producer and the farmer, as well as reduced greenhouse gas emissions. An obligation to recycle organic waste, may it be on a national or on EU level, together with the implementation of appropriate collection systems, could provide the economic and societal base to mobilize the currently unused bio-waste. Should this scenario be realized, the annual amount of biochar-compost out of bio-waste could be used to serve around 3.7% of all arable land in the EU. This would demand no large-scale application, but instead specific uses for specific soil-crop constellations.Resources 2015, 4 458

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