City lab uses banana peel, cauliflower stem waste to boost biogas production

Chennai: Banana and cauliflower may be good for our health, but city-based researchers found that their waste is also good for the environment because it boosts biogas production and helps cut CO2 emissions.Researchers at CSIR – Central Leather Research Institute (CSIR-CLRI) developed a low-cost biogas technology that uses banana peel and cauliflower stem to stabilise food-waste digesters and significantly increase clean energy generation.
Researchers said the technology is based on anaerobic co-digestion, a process in which food waste is broken down by microbes in the absence of oxygen to produce biogas. Food waste alone degrades rapidly and turns acidic, which suppresses methane-producing microbes and reduces gas output. The researchers addressed this by adding banana peels and cauliflower stems, which are naturally alkaline, to act as biological buffering agents.The system was tested through 30-day laboratory-scale batch digestion experiments. Food waste collected from restaurants and a university mess hall in the city was mixed with banana peel waste or cauliflower stem waste in a 70:30 ratio. The reactors were monitored for biogas production, acidity (pH), alkalinity, accumulation of volatile fatty acids, digestion speed, and microbial activity. The study found that the added vegetable waste prevented acid build-up, maintained stable conditions for methane-producing microbes, and improved overall reactor performance."The addition of banana peel waste and cauliflower stem waste to food waste improved the pH from 5.0 to 7.0 and increased alkalinity over time from 1200 to 3200mg/L as CaCO3 equivalence (a standard measure of buffering capacity, expressed relative to calcium carbonate), acting as a slow-release buffer without the addition of an external chemical buffer," said Sri Bala Kameswari Kanchinadham, the corresponding author of the paper. As a result, biogas production increased by 30% in food waste mixed with cauliflower stems and 22% with banana peels, compared to food waste alone.Microbial analysis confirmed higher populations of methane-producing microorganisms in the co-digestion systems, explaining the improved stability and gas output. After banana peel and cauliflower stem waste were added, the reactors showed a higher abundance of methane-producing microorganisms such as Methanosarcinia and Methanomicrobia, which are crucial for converting organic acids into methane. Researchers said results of the study, based on lab experiments, do not yet capture long-term performance and operational challenges of continuous, full-scale biogas plants.Beyond energy gains, the technology also offers measurable climate benefits. When scaled to handle 1 tonne of waste a day, the system could avoid 1,391–1,854 kg of CO2 emissions a year.