Sorghum has fed people and livestock for millennia. It grows on six continents, tolerates drought, and asks for little. But a new study is looking at this ancient grain through a different lens—not as food, but as fuel.
Researchers tested eleven sorghum varieties for their potential to produce bio-CNG through anaerobic digestion, and the results suggest that what variety you grow may matter as much as how you process it. Not all sorghum performs equally, and identifying the right ones could quietly shift how farm biomass fits into the clean energy picture.
A familiar crop, a new energy role
Sorghum (Sorghum bicolor) ranks among the world’s most widely cultivated cereals. It tolerates poor soils, resists drought, and grows across Africa, Asia, and the Americas at scale—traits that also make it an appealing candidate for energy production, specifically as a lignocellulosic feedstock for anaerobic digestion.
Anaerobic digestion breaks down organic material without oxygen. Microbes consume the biomass and release biogas—a mixture of methane and carbon dioxide—as a byproduct. That gas can then be compressed and purified into bio-CNG, a cleaner-burning alternative to diesel and petrol for vehicles and farm machinery.
What research had largely overlooked is that sorghum varieties are not interchangeable. Most prior studies treated the crop as a single feedstock category. This study challenged that assumption directly, and the differences found were significant enough to matter at an industrial scale.
How the experiment was designed
The researchers tested eleven sorghum varieties using 250 mL batch-scale anaerobic digestors over 60 days—long enough to capture the full arc of microbial activity and produce reliable yield estimates.
Two temperature regimes were compared: mesophilic conditions at 37 °C and thermophilic at 55 °C. Temperature is not a minor variable here. Thermophilic digestion accelerates microbial activity and consistently produced higher biogas yields across every variety tested. The team tracked biogas yield, biodigestibility, total solids, volatile solids, and chemical oxygen demand (COD) removal—indicators that together show how efficiently each variety converts biomass into usable energy and how cleanly it does so.
The standout varieties and what makes them different
Four varieties separated themselves from the rest: CSV-48, CSV-49SS (a sweet sorghum variety), yellow sorghum, and white sorghum. Each outperformed the others on biogas productivity and on removal efficiencies for total solids, volatile solids, and COD.
The researchers traced those results to two structural advantages. These varieties had a favorable lignocellulosic composition, making them more accessible to digesting microbes, and a more balanced carbon-to-nitrogen (C/N) ratio, which supports process stability and improves how thoroughly the substrate breaks down. Varieties with a poorly balanced C/N ratio can slow digestion or reduce methane output. Choosing the wrong variety is not just a missed opportunity; it is an operational liability.
From biogas to bio-CNG: The numbers
Under thermophilic conditions, bio-CNG potential ranged from 36.06 to 83.27 Nm³ per ton of fresh biomass, assuming 50% methane content. Electricity and heat generation ranged correspondingly from 146.3 to 337.9 kWh per ton of fresh biomass.
The fuel replacement figures are where this becomes tangible. Top-performing varieties could replace approximately 78.3 liters of diesel or 87.4 liters of petrol per ton of fresh biomass. For a farm processing hundreds of tonnes annually, that is a meaningful reduction in fossil fuel dependency. At an industrial scale, variety selection stops being an agronomic detail and becomes an energy-planning decision.
Cutting emissions: the climate case for sorghum bio-CNG
The emission reductions follow the fuel replacement logic. Switching to sorghum-derived bio-CNG could reduce CO₂ emissions by 90.9 to 209.8 kg CO₂-equivalent per ton of fresh biomass on a diesel basis—or 87.5 to 201.1 kg CO₂-equivalent on a petrol basis.
Bio-CNG carries a lower lifecycle carbon footprint than fossil fuels because the carbon released during combustion was recently absorbed by the growing plants, unlike fossil fuels, which release carbon stored over millions of years. For smallholder farmers in sorghum-growing regions, this also points toward something more immediate: generating fuel from crop residues rather than purchasing diesel at market prices.
What this means for industrial biogas systems
The practical implication is fairly direct. Variety-specific feedstock management should become standard practice in commercial biogas operations, since using well-characterized, high-yielding varieties reduces unpredictability in both gas output and process efficiency.
That said, the study’s results come from batch-scale digestors under controlled conditions. Continuous industrial digestors operate differently, and scaling effects could alter some yield figures—a limitation the researchers themselves flag for further investigation. Scaling trials, economic feasibility analysis, and integration with existing agricultural supply chains will ultimately determine whether these findings translate into deployable systems. If they do, a crop that has sustained human populations for 6,000 years may be about to take on a second, quieter role: powering the farms that grow it.
Kelly is an experienced writer with 15 years of experience exploring the big stories that shape our world, from tech breakthroughs and space exploration to climate, energy, and the fascinating quirks of science. She has a talent for turning complex ideas into sharp, memorable insights that stay with readers long after they’ve finished reading.
