New method turns corn straw into sugar and fertilizer at a lower cost

A new process for transforming agricultural waste into fermentable sugars and fertilizer could reduce costs and increase sustainability in bioenergy production. Scientists from universities and laboratories in the United States have tested a pretreatment of corn stover using a combination of potassium hydroxide (KOH) and ammonium sulfite (AS), without the need for subsequent chemical recovery.

The method achieved yields of over 95% in sugar production and demonstrated the agronomic effectiveness of the residual liquor as a fertilizer rich in potassium, nitrogen and sulfur.

The research showed that treatment with 40% KOH and 15% AS at 80°C for two hours removed almost 79% of the lignin and more than 82% of the acetylated groups from the biomass. The treated straw showed high enzymatic digestibility, with a total sugar yield of more than 87,5% in 120 hours of hydrolysis. The process also eliminated the need for effluent treatment, since the residual liquor can be used directly in the soil.

The liquid residue contains organic and inorganic compounds, including sulfonated lignin, which facilitates enzymatic hydrolysis by reducing non-productive enzyme adsorption.

The remaining chemically modified lignin has potential for agricultural use, acting as a soil conditioner and slow releaser of nutrients. Greenhouse trials with corn have shown that the liquor effectively replaces commercial potassium and sulfur fertilizers, maintaining or increasing plant biomass.

The estimated minimum cost of selling the sugar produced was US$0,285 per pound, a value considered competitive compared to conventional processes that require chemical recovery. The economic analysis took into account the reuse of the liquor as fertilizer, reducing operating costs and environmental impacts. The residual liquor, because it contains phenols and lignin derivatives, can also be used in the polymer, food and pharmaceutical industries.

The combined use of KOH and AS creates an alkaline environment that favors the breaking of bonds between lignin and carbohydrates, in addition to promoting low-temperature sulfonation reactions. Unlike acid treatments that degrade hemicelluloses, the method preserves xylan, generating more xylose. The retention of sugars and the efficiency of enzymatic hydrolysis make the process ideal for biorefineries that aim to produce ethanol, organic acids or bioplastics.

The fermentation of the sugars obtained was validated with the genetically modified bacterium Pseudomonas putida. The yield of polyhydroxyalkanoate (PHA), a biopolymer of industrial interest, reached 0,072 grams per gram of glucose consumed — efficiency equivalent to that obtained with commercial glucose. This indicates that the sugars obtained are viable as raw material for fermentation processes on an industrial scale.

The mass balance of the operation with 100 kg of corn straw showed the production of 50,9 kg of fermentable sugars and 15,8 kg of lignin in the residual liquor. The process fully utilizes the biomass components, without generating toxic waste or requiring complex purification steps.

Based on the results obtained, the study proposes the implementation of the process in integrated biorefineries, focused on the production of biofuels and biofertilizers.

More information can be found at doi.org/10.1016/j.biortech.2025.132402