Polyhydroxybutyrate from sewage sludge: Life cycle assessment methodological choices and inventory

Polyhydroxyalkanoates (PHAs) are polyesters produced by bacteria as intracellular carbon and energy reserves. Cheap and easy processes are needed to make PHAs really competitive respect to fossil-based plastic. BPLAS DEMO project aims to produce PHAs by means of sewage sludge and mixed microbial cultures. This would permit to reduce the costs. The project includes the application of the Life Cycle Assessment (LCA) methodology to evaluate the environmental performances of the system. As first step of the environmental analysis, a review of 14 LCA studies on PHAs and PHB was performed. The review covered both methodological aspects and final results. The “Goal and Scope Definition” phase has been delineated in the light of the review outcomes. The final results of the reviewed papers show that both the choice of feedstock and the use of process residues and co-products for energy production can lower the environmental impacts of the production process. Climate change impact values generally are between 1 and 6 kg of CO2-eq. per kg of PHAs produced, whereas in most studies the energy requirement is higher than 29 MJ per kg of biopolymer.