Análise do ciclo de vida e da viabilidade econômica de diferentes cenários de manejo de digestatos de efluentes da suinocultura

Abstract

Given the scenario of insufficient domestic production of mineral fertilizers, biofertilizers stabilized through anaerobic digestion emerge as a strategic alternative for fertilizing Brazilian soils, as well as for reducing dependence on imported inputs. However, this potential remains limited due to challenges associated with the logistics and viability of treatment, transport, and distribution. In this context, an analysis is conducted regarding the economic and environmental aspects of different arrangements of biogas plants integrated with technologies for the valorization of swine effluent digestate, including fertigation, drying, chemical precipitation, nitrogen removal, and ammonia recovery via air stripping. The objective is to identify technologies capable of adding value to the anaerobic reactor by-products, minimizing costs and environmental impacts. Thus, the impacts are evaluated using life cycle assessment, while the economic evaluation is determined based on indicators such as net present value (NPV), internal rate of return (IRR), payback period, and return on investment (ROI). The results demonstrate that the analyzed digestate management model constitutes a central element for the environmental and economic viability of biomethane plants, with nitrogen being the main determining factor for both environmental performance and economic viability. From an environmental perspective, scenarios based on advanced nutrient recovery significantly reduced the main impact categories. Struvite precipitation resulted in reductions of 6.69 kg CO₂ eq in global warming and 0.003 kg P eq in phosphorus losses, while ammonia recovery via air stripping presented more substantial reductions, reaching 17.18 kg CO₂ eq in global warming and 496.4 kg 1,4-DCB eq in terrestrial ecotoxicity. From an economic perspective, the internalization of logistics costs made the baseline scenario of direct fertigation unfeasible, which presented an average NPV of –3.22 million USD, an average IRR of –1%, and a 99.9% probability of no payback, with digestate transport costs accounting for approximately 86.4% of the annual costs. In contrast, the scenario based on the production of organomineral fertilizer presented the best economic performance, with an average NPV of 3.09 million USD and an average IRR of 53%, whereas the environmentally superior scenarios presented lower economic attractiveness. Therefore, a structural trade-off between environmental performance and economic competitiveness is evident.