Decarbonising Island Kitchens: Assessing the Small-Scale Flexible Balloon Digester’s Clean Cooking Potential in Fiji

Access to clean cooking technologies is crucial for achieving SDG7 for remote households in small Pacific Islands like Fiji and for developed countries alike. Many small households in Fiji still rely on traditional biomass for cooking. This study explores the environmental sustainability and clean cooking potential of the Home Biogas 2.0 flexible balloon digester installed at Kamil Muslim College in Ba, Fiji. Comparative bench experiments were also performed. The bench-scale experiments produced higher biogas yields than the digester trials, with optimal outputs recorded from fresh cow dung (541 mL of cumulative biogas) and vegetable waste excluding rice (125 mL). When scaled, annual energy production from fresh cow dung reached 4644.64 MJ, equivalent to replacing 7.82 standard LPG cylinders, while vegetable waste produced 3763.76 MJ, offsetting 6.34 cylinders. Notably, biogas from cow dung exceeded the estimated annual household cooking demand of 3840 MJ for a family of four persons. The biogas produced from fresh cow dung provided an average cooking duration of 1 h 29 min, while biogas from vegetable waste lasted for 1 h 21 min. The economic analysis indicated that combining liquid digestate, used as biofertiliser, and biogas from cow dung resulted in the highest financial return, with a 67% Internal Rate of Return, a Net Present Value of $12,364.30, a Benefit Cost Ratio of 5.12, and a Discounted Payback Period of 1.28 years. This indicates the potential of Home Biogas 2.0 as a climate-smart technology that integrates renewable energy production, waste reduction, and sustainable agriculture, making it particularly suitable for rural and remote communities.