Small doses of caustic soda increase biogas production from banana waste
Low concentrations of caustic soda (sodium hydroxide, NaOH) are more efficient than high doses for preparing organic waste for biogas production. This finding increases methane production, reduces reagent consumption and, consequently, diminishes process costs and minimizes the risk of inhibiting the microorganisms responsible for the process.
A study conducted by researchers at the Bioenergy Research Institute (IPBEN) at São Paulo State University (UNESP) has found that small doses of caustic soda are more effective than higher concentrations in increasing biogas production from banana waste. This discovery could significantly reduce processing costs and minimize the risk of inhibiting the microorganisms responsible for the anaerobic digestion process.
Banana peels and unfit-for-sale parts are rich in organic matter but contain substances like cellulose and lignin that hinder microorganisms' access to fermentable sugars, limiting the efficiency of anaerobic digestion. To overcome this challenge, the researchers employed thermo-alkaline pretreatment, which combines heat and chemical products to break down the lignin barrier, making carbohydrates more accessible to microorganisms.
The study tested various concentrations of sodium hydroxide (NaOH) ranging from 0.2% to 3%. Contrary to expectations, the lowest concentration, 0.2%, yielded the highest results, producing 12,110 milligrams of methane per liter (mg/L), compared to 4,785 mg/L for untreated material. While a slight increase to 0.4% also increased cumulative methane production, the 0.2% concentration produced gas at the highest rate.
The researchers emphasize that using less sodium hydroxide not only reduces costs but also minimizes the risk of inhibiting microorganisms and has a smaller environmental impact. São Paulo State, being a major fruit producer, generates significant waste that can be transformed into renewable energy, closing the cycle instead of sending waste to landfills.
The research also highlights the importance of understanding the microbial consortium present in the reactor and the metabolic pathways the microorganisms follow. This knowledge can guide strategies to further enhance biogas production efficiency. The study is part of a broader program by the UNESP group to transform agroindustrial waste into energy sources and valuable products, including banana, orange, guava waste, and wastewater from fruit processing.
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