Single cell protein production from food waste using purple non-sulfur bacteria shows economically viable protein products have higher environmental impacts

Abstract

Landfilling of food waste in the United States is a source of unutilized resources and environmental risks. As cities look to divert food waste from landfills, microorganisms may hold the answer. Purple non-sulfur bacteria are a group of microorganisms that can treat and extract resources from food waste to produce a protein supplement for animal feed. This study includes a life cycle assessment to compare four food waste management scenarios: purple non-sulfur bacteria production offsetting soybean meal production, purple non-sulfur bacteria production offsetting fishmeal and carotenoid production, anaerobic digestion, and landfilling (status quo). Purple non-sulfur bacteria offsetting soybean meal production resulted in significantly reduced environmental impacts compared to landfilling. Specifically, the eutrophication impact, land use, and water use for the soybean meal offset scenario were 141 kg N equivalents/day, 96 ha, and 120,000 L/day lower than landfilling, respectively. However, the low value of soybean meal limits the economic viability of this scenario. When high-value fishmeal and carotenoids were the offset products, there was an increase in value of $0.023/kg FW treated over landfill disposal of food waste. Offset fishmeal and carotenoids are not without environmental tradeoffs, most significantly with respect to eutrophication and global warming. This study then demonstrated that determining maximal growth rates to a PNSB photobioreactor, growing PNSB microorganisms on sunlight, and identifying the degree to which PNSB carotenoids can replace carotenoids in fish food were plausible lines of research to improve environmental and/or economic viability of the process. The life cycle assessment developed here can inform decision making for food waste management and guide research to improve purple non-sulfur bacteria production.