Efeitos da remoção de nitrogênio amoniacal do inóculo e digestato líquido na produção de energia e estabilidade da digestão anaeróbia de resíduos alimentares

Abstract

This thesis investigates the valorization of food waste through anaerobic digestion, focusing on process optimization for biomethane production. The collected food waste exhibited a low C/N ratio (10.1 to 14.9). Therefore, a strategy for excess N removal was adopted. Initially, the study focused on ammonia removal from the inoculum (digestate) through volatilization and chemical precipitation of struvite, aiming to balance the nutrients by improving the C/N ratio and consequently biogas production. The treatment that used pH 8.7 and a molar ratio of Mg:PO₄ ³⁻ of 1:1 achieved the highest biomethane production (466.5 mL CH₄/gSV), representing a 74% increase compared to the control, with 94% biodegradability. Ammonia removal increased the process C/N ratio by up to 27.3%, enhancing energy recovery. Finally, a new operational strategy for reactors was evaluated, involving the recirculation of liquid digestate after nitrogen removal by volatilization and struvite precipitation. The condition with pH 9.5 and a molar ratio of Mg:PO₄ ³⁻ of 1:1 resulted in the removal of 45.5% of total ammoniacal nitrogen and 65.5% of free ammoniacal nitrogen, with improvements in alkalinity and organic matter removal (COD, VS, and TS) by 97%, 95%, and 91%, respectively. This strategy allowed for a reduction in the hydraulic retention time of the reactor, accelerating the stabilization of organic matter. The energy balance for the reactor with an HRT of 30 days was positive at 7.0 kWh/t of food waste. In summary, this thesis demonstrates that anaerobic digestion of food waste can be optimized through ammonia removal and liquid digestate recirculation, promoting a more sustainable and efficient management of this waste