Valorization of biochars from pinewood gasification and municipal solid waste torrefaction as peat substitutes

Abstract

Gasification and torrefaction have both gained significant interest as bioenergy techniques. During biomass gasification together with fuel gas, carbon-rich solid substances are produced, whereas torrefaction process is mainly used to prepare a final product with higher calorific value and carbon content than the feedstock, through a low temperature pyrolysis. Both materials (carbon wastes from gasification and torrefied product) could be classified as alternatives to biochar obtained from slow pyrolysis of biomass. The use of biochar, typically from the slow pyrolysis of biomass, as soil amendment and, more recently, as growing media components has been widely researched. However, to our knowledge, no studies have compared the use of biochar from gasification and torrefaction as growing media component for growing media formulation. The objective of this work was to study the effect of two biochars on peat-based growing media: a pinewood gasification biochar (BG) and a biochar (BT) obtained by torrefaction of the organic fraction of municipal solid waste. Growing media mixing PT (peat) with 50%vol of BG or BT were prepared and characterized according to their chemical, thermal and hydrophysical properties. Phytotoxic experiments and growth of Lolium perenne were also performed. Results indicated that peat substitution in growing media by BG and BT at a 50%vol ratio improved their hydrophysical properties. Specifically, bulk density increased more than 50%, air space increased by 43%, the increment of the total porosity was 20%, and, finally, the water holding capacity increased by 18.3%. Significantly, a positive effect on plant biomass production (yield increment: 274%) was observed after addition of BT, whereas no significant differences were observed after addition of BG biochar. Therefore, it can be concluded that both BT and BG could be used as peat substitutes in growing media formulation.