Use of process residues as fertilizer

One of the key points of biomass crops as feedstock is to reduce the energy needed for their production as well as the related GHG emissions. Both challenges can be partly met by reducing mineral fertilizer inputs. The use of process residues from biomass pre-treatment and conversion processes provides an opportunity to substitute chemical fertilizers. This task aimed at assessing the use of Torwash residues and another residual streams from biomass densification or conversion as a fertilizer to substitute non-renewable inputs.

A pot experiment with Giant Reed was established to test the use of liquid residues from wet torrefaction of biomass for fertigation. The effects of two liquids (prewash residues (PW) and Torwash residues (TW)) on the growth of giant reed and on soil properties and leached water quality were tested. Main findings showed a lower aboveground biomass in TW, probably due to the limited evapotranspiration of plants, which responded to stress by increasing the production of roots. As a conclusion, while the PW could be used for fertigation and restoring the K content in the soil, the TW seems to not be suited for fertigation and its high content of volatile fatty acids suggests a better reuse for other applications (i.e. anaerobic digestion).

Giant reed plot near Pisa ((c) SSSA).

The results of this experiment are reported in this deliverable, while recommendations as to the agronomic use and valorization of torwash residues are provided here.