PYRAMID: an innovation for the sustainable valorisation of anaerobic digestion digestates
Valuing digestates: the PYRAMID project and innovation from Carnot MICA
Zeolites and microalgae: a winning combination for digestate valorisation and sustainable fertilisation
In a context where anaerobic digestion is becoming increasingly important among renewable energy production solutions, the question of how to valorise digestates—the by-product of this biological process—has become a major challenge. Although these digestates are rich in nutrients, they can generate significant environmental and economic constraints: transport costs, greenhouse gas emissions, risks of nutrient leaching, and so on.
It is in this context that the PYRAMID project was launched, funded by Carnot MICA and coordinated by APESA, in partnership with RITTMO and IS2M. The goal of PYRAMID is to design an innovative biorefinery scheme combining thermochemical processes (pyrolysis) and biological processes (anaerobic digestion, microalgae cultivation, etc.) to transform digestates into valuable resources for agriculture. One of the main barriers to digestate valorisation is their high ammonium content, which creates a toxic environment for microalgae cultivation. However, these microorganisms are particularly interesting because they can capture the nutrients present in digestates to produce biomass that can be used as fertilisers, biostimulants, or soil amendments.
To overcome this barrier, the researchers used zeolite, a natural mineral capable of capturing ammonium and other refractory molecules. This pre-treatment makes digestate compatible with microalgae cultivation, thereby promoting their growth and agronomic valorisation while reducing the excessive water use usually required to lower digestate toxicity.
But that is not all: once saturated with nitrogen, zeolite becomes a natural fertiliser as effective as urea, without the environmental drawbacks associated with mineral fertilisers. Early agronomic trials confirm its potential, showing efficient nutrient release to plants and reduced losses through volatilisation.
