S06 - Session P16 - Don't waste your waste: how waste of microgreens cultivations becomes a resource for coconut coir-based biochar, possibly increasing substrate and product quality along the way

Authors: Kris Kunnen *, Dries Vandamme, Bart Vandecasteele, Ann Cuypers

Within urban agriculture, microgreens (crops harvested 7-14 days after germination) gained immense popularity due to potentially higher nutritional values, specific tastes and ease of cultivation. However, current substrate-based microgreen cultivation systems mainly rely on the use of peat-based growing media. More sustainable growing media, like the industrial waste stream coconut coir (CC), are less used due to inconsistency in their physical, chemical and biological properties, reducing their performance value. The current project focusses on the production of biochar (a carbon-rich by-product of pyrolysis) from the waste of CC-based microgreens cultivation systems. Firstly, this results in a carbon-sequestering resource produced from the CC substrate waste. Secondly, the implementation of this biochar into new CC could stabilize the physicochemical properties (pH, EC, nutrient retention) of the growing medium, as well as improve plant development and quality (e.g. germination, yield). Nevertheless, the physicochemical biochar properties are highly dependent on pyrolysis parameters (e.g. temperature). Therefore, production parameters of biochar were investigated in the current study. Results from a quick phenotypical screening using Arabidopsis thaliana germination suggest that pyrolysis temperatures (400, 500, 600 and 700°C) differently affect the biochar and hence root length and fresh weight of A. thaliana seedlings. These results are further explored in experiments focussing on the effects of biochar (1) on pH, EC and nutrient leaching/retention, (2) on seedling development, and (3) in its implementation in the CC-based microgreen cultivation system.