Employing forced aeration (FA) in composting static windrows (SW) from fish waste (FW) has the potential to enhance the development of process and, organic fertiliser quality. However, due to the impact of season, the FA may lead to excessive drying of SW and, difficulty in thermophilic temperature maintenance. The aim of this study was to assess the effects of passive aeration (PA) and FA on the composting of FW in SW during the summer and winter seasons. The temperatures of the windrows remained within the thermophilic range for most of the composting period, with peak temperatures observed shortly after starting and turning the windrows (at 50 and 70 days). The aeration benefited the initial TS degradations, resulting in 86.66 and 45.99% of the TS total reduced to FA and PA piles, at 50 days during the winter. The C organic reduction was 77.77 and 76.33% in summer and winter to FA piles, respectively, but this reduction was 59.24% and 67.82% for winter and summer, respectively, in PA windrows. At 50 days, the N reduction in FA piles was already at 70.32% and 71.87% for winter and summer. The volatile solids reductions were significantly higher (p < 0.01) in FA piles during the summer. Although the FA has been shown to enhance the organic constituents' degradation during the composting of FW, its adoption was not enough to improve the compost composition. Thus, by conducting piles on a small scale, with the perforated wall, as described in this study, the FA could be dispensed.

Methane (CH₄) emissions from aquaculture can be enhanced by organic waste accumulation and oxygen-limited conditions, yet field-based emission estimates remain scarce, particularly for intensive tilapia production in above-ground tanks in Brazil. This study evaluated how aquaculture waste composition and oxygen availability affect CH₄ emissions and quantified emissions from a commercial intensive Nile tilapia production system. A controlled experiment assessed water and sediment characteristics and CH₄ emissions during decomposition of feed, feces, and fish carcasses under contrasting residue combinations and aeration conditions. Field measurements quantified diffusive and ebullitive CH₄ fluxes from production tanks and a sedimentation pond during 13 sampling campaigns conducted between February 2023 and November 2024. The non-aerated treatment receiving mixed residues showed the highest CH₄ emissions, whereas aeration reduced mean flux by approximately 98.8%. At commercial scale, emissions were concentrated in the sedimentation pond and dominated by ebullition, while emissions from aerated production tanks were negligible. Annual CH₄ emissions were estimated at 325.9 kg CH₄ ha⁻¹ yr⁻¹, corresponding to 8799 kg CO₂-eq ha⁻¹ yr⁻¹ and 0.147 kg CO₂-eq kg⁻¹ fish produced during the nursery phase. These findings identify oxygen availability and waste accumulation as key targets for CH₄ mitigation through aeration and improved residue management, providing insights into strategies to reduce the environmental impact and support the sustainability of intensive tilapia production.

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.