Technological watch

Biogas plants are able to exploit organic residues from livestock farming, agriculture and the food industry to produce renewable electricity or biomethane. The Cremona area is home to numerous plants of this type and this very peculiarity is at the root of the collaboration in this field between the Cremona Campus of Politecnico di Milano and A2A. The goal is to improve the environmental sustainability of the biogas and biomethane supply chain, especially by exploiting the potential of digestate, a residue generated by biogas plants.

Developed by A2A and Polo delle Microalghe, a centre of expertise in which the Istituto Spallanzani of Rivolta d’Adda, Politecnico di Milano and the University of Milan-Bicocca collaborate, the project proposes the cultivation of microalgae for the production of biostimulants for agriculture from digestate with a view to circular economy.

Microalgae can grow by exploiting sunlight, nutrients in digestate and CO2 in waste gas streams. They can also grow using waste from the food industry, harnessing chemical energy in addition to or as an alternative to solar energy. This flexibility allows reducing the surface area required to capture solar radiation and compensating for seasonal variations.

The aim of the project was to assess the feasibility of the design idea, with tests at laboratory and then pilot scale. The results showed that strains belonging to the genera Chlorella and Scenedesmus may adapt to the project cultivation conditions and produce a biomass of sufficient purity and quality compatible with the constraints imposed by the EU Fertiliser Regulation. Pre-treatment of the digestate to separate a low-turbidity liquid phase and long-term validation are the future steps to be taken.

“Thanks to this project, an important step has been taken towards promoting a sustainable supply chain in agriculture through resource recovery,” as Prof. Elena Ficara, who supervised the work in the field, points out: “The development of biorefineries that recover both energy and higher value-added products from waste will improve the environmental and economic performance of the agro-industry.”