Greenhouse Gas Emissions and Nutrient Recovery from Fish Waste During Composting and Burial

Fish-processing residues represent a significant environmental challenge due to their high moisture and nitrogen contents, which favor greenhouse gas (GHG) emissions during degradation. This study evaluated how different waste management strategies affect GHG emissions from fish waste, including conventional composting (Bulk), composting amended with biochar (BulkBioch), burial with soil (S), and burial with soil plus sawdust (BulkS). Daily emissions of CH4, N2O, and CO2 were monitored, and cumulative emissions were modeled using generalized additive models. Composting treatments (Bulk and BulkBioch) released higher CO2, suggesting greater microbial degradation, while burial treatments developed earlier anaerobic conditions with reduced decomposition efficiency. Bulk showed the highest cumulative CH4 and CO2 emissions, whereas N2O fluxes were greater in burial methods, reaching 2.18 g N2O kg−1 TS in S. Biochar addition was associated with 15% and 10% lower CH4 and N2O emissions, respectively, and earlier stabilization of CH4 emissions. In global warming potential, BulkBioch presented the lowest climate impact (305 g CO2-eq kg−1 fish), followed by Bulk (338 g CO2-eq kg−1), whereas BulkS reached up to 599 g CO2-eq kg−1. The use of bulking agents in burial resulted in lower CH4 buildup and greater nutrient retention. Overall, combining bulking agents and biochar may represent a promising strategy to mitigate GHG emissions while supporting nutrient conservation.