Sustainable valorization of fish head wastes into nitrogen-based nutrients: a comparative life cycle assessment.

The production of nitrogen-based nutrients is a major contributor to climate change, with industrial ammonia synthesis releasing over 500 million tonnes of CO₂-equivalents annually—more than 1.2% of global anthropogenic greenhouse gas (GHG) emissions. This is largely due to the fossil fuel–intensive Haber–Bosch process, which remains the dominant pathway for reactive nitrogen production in global food and feed systems. However, emerging alternatives such as marine biological by-products offer a fundamentally different nitrogen sourcing pathway. In this study, we conducted a comparative life cycle assessment (LCA) of greenhouse gas emissions for peptones derived from marine fish head waste (cutlassfish, salmon, tuna) and conventional land-based sources (soybean, skimmed milk). Marine-derived peptones exhibited substantially lower greenhouse gas emissions (GWP100) —9, 4.5, and 2.6 kg CO₂-eq, respectively—compared to 22 kg for soybean and 64 kg for skimmed milk. When weighted by global production volumes, the average greenhouse gas emissions (GWP100) were 5.8 kg CO₂-eq for marine-based peptones and 49.6 kg CO₂-eq for land-based peptones—an 88% reduction. Scenario-based analysis showed that marine systems, due to their centralized and energy-intensive nature, achieved up to 90.7% additional reductions in greenhouse gas emissions under renewable electricity substitution. To ensure methodological robustness, we applied the A–B comparison framework—which reduces attributional bias when comparing systems with differing co-product structures—and found that marine-based peptones consistently outperformed land-based alternatives across all simulation runs. These findings highlight the potential of fish-processing waste valorization as a low-impact nitrogen source and underscore its strategic role in developing climate-resilient biotechnologies and sustainable protein supply chains.