Pau Case Study: From a Wastewater Treatment Plant to a Biofactory

A wastewater treatment facility in Pau, France, will soon be modified to become a so-called “Biofactory” able to produce different resources or energy through a series of state-of-the art and innovative technologies. SUEZ will lead the consortium responsible for the design and construction of the biofactory, with commissioning planned for the beginning of 2023, and they will then operate the plant after its completion. First, the sludge treatment line will include classic and mature anaerobic digestion producing biogas, which will then be purified to biomethane before grid injection. Two innovative technologies will then be used to optimize both sludge volume reduction and energy management: (1) a hydrothermal carbonization reactor will allow for sludge volume reduction with minimal energy consumption and for additional biogas production thanks to filtrate methanisation; (2) a catalytic methanation reactor will convert the CO2 coming from the biogas purification to CH4, thanks to hydrogen coming from an electrolysis plant fed with renewable electricity produced on site; this methanation process will also supply heat for the digestion process. Additional resources will also be produced by the biofactory, with the recovery of nitrogen through the production of ammonium sulphate to be used as fertilizer. The expected performance of the Pau plant, in terms of energy, resource preservation, avoided and CO2 emissions, is a tangible indicator of the multiple benefits given by this biofactory approach.