Life cycle assessment of bio-based materials : environmental impacts of the value chain from cyanobacteria to PHB
Creators: name: Frehner, Alena
name: Itten, René
Publisher: name: ZHAW Zurich University of Applied Sciences
Year: 2023
Subjects: Life cycle assessment
LCA
Biopolymer
PHB
Cyanobacteria
Bioplastic
572: Biochemie

description: Considering the severe impacts of synthetic polymers on the environment, the development of biopolymers is becoming increasingly important. While biopolymers such as Bio-PA or Bio-PET address the issue of fossil resource depletion, they are not automatically biodegradable and can cause significant environmental impact in their respective value chains. One alternative to fossil polymers while also being biodegradable is Polyhydroxybutyrate (PHB) and cyanobacteria are one of various bacterial strains capable of producing PHB. The aim of the project was to conduct a life cycle assessment (LCA) of PHB-producing cyanobacteria, cultivated on a thin-layer photobioreactor (PBR) pilot plant, and to extrapolate the data to an industrial-scale production scenario. The LCA further aimed to compare the cyanobacteria cultivation in different media, namely a standard mineral medium and two media based on wastewater, to identify environmental benefits between the different substrates. The two wastewater media included water from an aquaculture system and a pre-processed liquid digestate.
Primary data was collected on a pilot-scale thin-layer PBR, located at the Institute of Natural Resources Sciences of the ZHAW in Switzerland. Processes included in the LCA reach from construction of the thin-layer PBR and its operation to the centrifugation of the cyanobacteria biomass. In order to analyse the environmental impacts of the described PBR system, a comprehensive set of indicators was applied, including recommended midpoints for PEF and greenhouse gas (GHG) emissions. The environmental impacts were analysed per cultivation medium, compared to one another as well as compared to the conventional fossil-based plastic production. Results show that due to higher yields, cyanobacteria cultivation in the mineral medium records lower environmental impacts compared to the wastewater media. Main contributors to the environmental impacts of the pilot plant production were found to be the CO2 supply to the cultures and electricity consumption, across all three cultivation media. Extrapolation of the data from the pilot plant to an industrial-scale production scenario, with increased yield and decreased CO2 input, shows a reduction potential of > 80 % across all environmental impacts analysed, leaving electricity consumption as the distinct primary environmental hotspot. In terms of climate change, the industrial-scale scenario shows a reduction of GHG emissions from 35 kg CO2-eq to 4 kg CO2-eq per kg of cyanobacteria for the mineral medium. Regarding the aquaculture water and liquid digestate, GHG emissions per kg of cyanobacteria were reduced from 90 kg CO2-eq to 8.7 kg CO2-eq and 8.5 kg of CO2-eq, respectively. The study shows that while the technology is yet in its beginning stages and potential for environmental improvement is significant, further development of these production processes could indeed make this technology relevant for biopolymer production in the future.