Alternativas de mitigação dos gases de efeito estufa durante a biodegradação dos resíduos de pescado

Abstract

The generation of fish processing residues in aquaculture represents an environmental challenge due to their high moisture, lipid, and nitrogen contents, characteristics that favor greenhouse gas (GHG) emissions and nutrient losses when improperly managed. Composting emerges as an alternative for the treatment and valorization of these residues; however, its dynamics may intensify emissions, requiring the development of mitigation strategies such as the use of physicochemical additives. Thus, this thesis aimed to: (i) address composting as a sustainable alternative for treating fish processing residues, as well as the application of physicochemical additives to reduce GHG emissions during the process (Chapter I); (ii) evaluate the effect of different disposal methods for fish residues, comparing composting (with and without biochar) and burial (with and without wood shavings as cover) on GHG emissions and nutrient recovery (Chapter II); and (iii) investigate the influence of different doses of biochar and zeolite as GHG-mitigating additives, as well as their effects on the degradation of organic constituents and the quality of the compost produced from fish processing residues (Chapter III). Chapter I was developed based on a review of studies addressing waste generation in aquaculture, composting principles, emissions associated with this process, and the potential of additives such as biochar and zeolite to mitigate GHG emissions. These materials were found to have mitigation potential, as they can enhance microbial activity during organic matter degradation due to their physical properties, including high porosity, adsorption capacity, and cation exchange capacity. In Chapter II, a pilot-scale experiment was conducted to evaluate two treatment methods for fish residues: composting (with and without the inclusion of 10% bamboo biochar) and burial (with and without wood shavings cover). Composting without biochar addition resulted in the highest cumulative emissions of CH₄ (0.72 g CH₄ kg⁻¹ total solids of fish residue) and CO₂ (2.57 kg CO₂ kg⁻¹ total solids), whereas burial with soil only showed the highest cumulative N₂O emissions (2.18 g N₂O kg⁻¹ total solids), followed by burial with wood shavings and soil cover (2.08 g N₂O kg⁻¹ total solids). The highest concentrations of nitrogen (N), phosphorus (P), and potassium (K) were observed in composting with biochar (1.74%, 30.8 g kg⁻¹, and 4.6 g kg⁻¹, respectively), while burial treatments resulted in the lowest concentrations of these nutrients. Chapter III evaluated the effect of two doses (5% and 10%) of two additives (biochar and zeolite) aiming to mitigate GHG emissions and improve compost quality. CH₄ emissions were significantly reduced by both biochar and zeolite, with reductions exceeding 60% compared to the control (p < 0.001). Regarding N₂O, zeolite showed lower emissions (957 mg kg⁻¹ total solids) compared to biochar (1468 mg kg⁻¹) (p < 0.05), resulting in the lowest CO₂ equivalent emissions, with a 20.6% reduction. Overall, the additives intensified organic matter transformations, promoting greater reductions (p < 0.001) in carbon (C), nitrogen (N), and ether extract (EE). Zeolite demonstrated greater efficiency in reducing C at the end of the process (p < 0.001), while higher doses of both additives increased N losses. Furthermore, additive use promoted nutritional enrichment of the compost compared to the control, with higher concentrations (p < 0.001) of potassium (K), copper (Cu), and manganese (Mn). Zeolite stood out by providing higher levels (p < 0.001) of K, calcium (Ca), magnesium (Mg), zinc (Zn), and boron (B), whereas biochar favored higher concentrations of P and Ca at the 5% dose. Overall, zeolite showed more consistent performance when considering both emission mitigation and agronomic quality of the compost.