Biogas Production and Nutrient Dynamics in Digestate from Co-Digestion of Food Waste and Banana Stems

Purpose: Biogas production offers a sustainable approach to converting organic waste into renewable energy while generating nutrient-rich digestate for use as fertilizer. This study investigates the biogas potential and nutrient composition of digestate derived from the anaerobic co-digestion of food waste (FW) and banana stems (BS). The research aims to optimize the co-digestion process by evaluating biogas yields and nutrient retention in digestate. Methods: Anaerobic co-digestion experiments were conducted in 1L sealed reactors at 37±1°C for 45 days, with biogas volume measured using the water displacement method. The feedstocks were characterized by their biochemical composition, with FW containing 50.72% carbohydrates and 9.81% protein, while BS had 29.03% cellulose and 8.53% lignin. Co-digestion was assessed for its effect on the carbon-to-nitrogen (C/N) ratio and methanogenesis efficiency. Results: Biogas yields were recorded as 304.91 mL/gVS for FW, 216.60 mL/gVS for BS, and 330.18 mL/gVS for a 1:1 co-digestion, showing an improvement of 25.49% and 14.58% compared to FW and BS alone, respectively. Retention times varied from 25 days (FW) to 41 days (BS). Digestate analysis indicated phosphorus levels between 16.47–19.95 mg/L, potassium between 25.0–36.0 mg/L, and sodium between 12.0–18.0 mg/L, with FW-rich reactors exhibiting the highest nutrient concentrations. Conclusion: The study highlights the dual benefits of anaerobic co-digestion in enhancing biogas production and generating nutrient-rich digestate. These findings provide valuable insights into optimizing waste valorization processes for sustainable energy production and agricultural applications.