Life cycle assessment of single and integrated recovery modules
Life cycle assessment is a standardized framework to quantify the potential environmental impacts of products or systems throughout their life cycles. This chapter applied life cycle assessment to assess the environmental impacts of high-value bioenergy products recovered from wastewater, comparing them with the conventional commodities they could potentially substitute. Polyhydroxyalkanoate, polyhydroxybutyrate, and single cell protein were selected as examples. Seven recovery processes for these products were compared with 42 conventional processes for producing polyethylene terephthalate, polyethylene, polypropylene, polylactic acid and protein feed across various technologies and regions. The overall cradle-to-gate impact assessment results (especially global warming potential) suggest that polyhydroxyalkanoate and polyhydroxybutyrate have higher overall environmental impacts than their fossil-based counterparts (largely contributed by electricity and heat use during their production), while single cell protein is comparable to some conventional protein feeds. However, a more comprehensive inventory and a wider system boundary with the end-use and disposal stages are needed to compare the environmental impacts with a greater certainty. The challenges and opportunities to conduct life cycle assessments on integrated recovery (i.e., integrating with different forms of resource recovery, or integrating with handling other waste streams) were explored. This chapter further discusses the future outlook of using plant-wide modeling, conducting consequential and end-user perspective life cycle assessments, and evaluating emerging value-added resource recovery pathways such as those covered in previous chapters.
