Researchers at São Paulo State University (UNESP) have determined that low concentrations of sodium hydroxide, commonly known as caustic soda, significantly improve biogas production from banana waste compared to higher doses. The study, published in BioEnergy Research, tested thermo-alkaline pretreatment concentrations ranging from 0.2% to 3% on banana peels and unsellable fruit collected from wholesale markets.
Banana waste contains high organic matter, but its energy potential is locked within rigid structural compounds like cellulose and lignin that hinder microbial access during anaerobic digestion. The pretreatment aims to partially break down this lignin barrier to release fermentable sugars.
Contrary to the expectation that more reagent would yield better results, the lowest concentration tested, 0.2% NaOH, achieved the greatest solubilization of carbohydrates and the highest methane production rate at 12,110 milligrams per liter, compared to 4,785 mg/L for untreated material. A slightly higher concentration of 0.4% produced the highest cumulative methane volume.
At concentrations above 0.4%, the caustic soda began to inhibit the microorganisms responsible for methane production, reducing process efficiency. Lead researcher Sandra Imaculada Maintinguer noted that high reagent use increases costs, inhibits microbial activity, and creates greater environmental impact during effluent treatment.
Microbial analysis revealed that the 0.4% pretreatment reactor hosted dominant bacterial genera Paraclostridium and Clostridium, alongside methanogenic archaea Methanothrix and Methanoregula. Tracking these microbial consortia and their metabolic pathways provides data to guide industrial optimization.
The research is part of a broader UNESP program converting agroindustrial waste, including orange and guava residues, into energy. São Paulo state, a major fruit producer, generates vast amounts of such waste, which the team aims to divert from landfills into bioreactors.
The findings suggest that minimizing chemical input lowers operational costs and simplifies downstream effluent management, improving the technology's prospects for industrial adoption. The study emphasizes that process efficiency depends on both substrate availability and the specific microbial community dynamics.
A related study currently under peer review by the same group investigates anaerobic co-digestion strategies for biohydrogen production, indicating ongoing work to diversify energy outputs from fruit waste streams.
Small doses of caustic soda increase biogas production from banana waste
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