Bioconversion of Waste Biomass to Ethanol and Fungal Products

Bioconversion harnesses microbial metabolism to transform agricultural and food-industry residues into ethanol and high-value fungal biomass. The process typically involves pretreatment of lignocellulosic or starchy waste to release fermentable sugars, followed by enzymatic hydrolysis and microbial fermentation. Saccharomyces cerevisiae and filamentous fungi such as Neurospora intermedia, Aspergillus oryzae and Rhizopus spp. serve as workhorses for simultaneous ethanol production and biomass accumulation. Integrated biorefinery concepts now couple first-generation ethanol production with downstream fungal cultivation on stillage or hydrolysates to yield protein-rich biomass suitable for animal feed, aquafeed or even novel food ingredients. Advances in process design, including solid-state and submerged fermentations, along with optimisation of pH, temperature and nutrient ratios, have increased conversion efficiencies. Such approaches address waste management challenges, reduce greenhouse-gas emissions and contribute to circular-economy goals by valorising side streams from pistachio dehulling, spent grains, stale bread and other organic wastes.

Research from Nature Portfolio

Investigations into pistachio dehulling waste have demonstrated that hot-water extracts of this by-product can sustain Neurospora intermedia growth under optimised conditions (72 h, pH 5.5, 30 °C), yielding up to 6.7 g/L dried fungal biomass with protein contents around 20–27 %. Conversion efficiencies reached 0.37–0.49 g biomass per gram of chemical oxygen demand, highlighting potential for high-COD, low-sugar substrates. Studies have further shown that varying inoculation methods, culture adaptation and COD/N ratios can enhance both biomass yield and protein concentration, positioning this route as a promising component of a fully integrated biorefinery platform with applications in nutrition, feed and biomaterials.

Bioconversion of Waste Biomass to Ethanol and Fungal Products publication trend

The graph below shows the total number of articles in bioconversion of waste biomass to ethanol and fungal products across all publications each year (not limited to Nature Index journals).

Technical terms

Bioconversion: Biological transformation of organic waste into fuels or biomaterials via microbial action.

Filamentous fungi: Multicellular fungi characterised by thread-like hyphae, exploited for fermentation and enzyme secretion.

Solid-state fermentation: Cultivation method where microorganisms grow on moist solid substrates without free-flowing water.

Chemical oxygen demand (COD): Quantitative measure of organic pollutants in a liquid sample, indicating potential substrate load.

Pretreatment: Physical or chemical processing step that breaks down complex biomass to improve enzyme accessibility and sugar release.

References

1. Production of protein-rich fungal biomass from pistachio dehulling waste using edible Neurospora intermedia. Scientific Reports (2025).
2. From stale bread and brewers spent grain to a new food source using edible filamentous fungi. Bioengineered (2020).
3. Valorization of Bread Waste to a Fiber- and Protein-Rich Fungal Biomass. Fermentation (2021).