The research, led by Behnam Abooali, Behzad Satari and Mohammad Hossein Kianmehr, tackles a deceptively simple problem with an unusually demanding constraint. Composting has long been recognized as a way to convert raw bagasse into a stable, biologically active soil amendment: microbial consortia degrade cellulose, hemicellulose and lignin, enriching the material with humic substances and plant-available nutrients. Compost applied to fields improves water retention by 18 to 35 percent, sequesters 0.5 to 1.5 tonnes of carbon per hectare per year, and suppresses soil-borne pathogens through microbiome modulation. But compost is bulky and fluffy, with a bulk density of only 100 to 200 kilograms per cubic meter, which inflates transportation costs by 40 to 70 percent and makes mechanized field spreading a logistical headache. Densification through pelletization can raise that density four- to six-fold, yet conventional pellet mills run hot, often above 100 degrees Celsius, precisely the range at which the beneficial bacteria, fungi and actinomycetes that make compost valuable are killed outright.

The team’s solution is what they call cold pelletization: densification performed without external heating, with die temperatures verified by thermocouples to remain below 60 degrees Celsius throughout compression. That threshold matters because compost microorganisms typically perish above 60 degrees, while the material’s glass transition temperature, the point at which lignin begins to flow and act as a natural binder, sits much higher at 89.7 degrees Celsius, as measured by differential scanning calorimetry. In other words, the thermal route to binding is neither necessary nor desirable for this feedstock. The researchers believe this is the first systematic optimization of cold pelletization parameters for composted bagasse with explicit preservation of microbial viability, and their maximum recorded die temperature of 54 degrees Celsius stayed comfortably within the safe zone.

Getting there required navigating a minefield of trade-offs. The compost, produced by windrow composting of bagasse blended with cattle manure and urea to a carbon-to-nitrogen ratio of 25:1, was ground in a hammer mill fitted with 1, 2.5 and 4 millimeter screens. Grinding energy proved exquisitely sensitive to both moisture and screen size. At 8 percent moisture and 1400 rpm, energy consumption climbed from 11 kilojoules per kilogram with the 4 millimeter screen to 155 kilojoules per kilogram with the 1 millimeter screen, a fourteen-fold penalty. Push moisture to 16 percent and the smallest screen, and energy demand exploded to 750 kilojoules per kilogram. The culprit is plasticity: wet composted fibers deform rather than fracture, dissipating energy as heat instead of breaking cleanly. For industrial scaling, the authors conclude, coarser screens and pre-drying to 12 percent moisture or less are strongly preferred, with diminishing returns below 8 percent where dust and fire hazards emerge.

Composting itself changes the material in ways that complicate densification. Scanning electron microscopy revealed that composted fibers bear irregular surfaces, longitudinal cracks and open fiber bundles, the fingerprints of microbial attack, in stark contrast to the smooth, uniform surface of raw bagasse. X-ray diffraction showed the crystallinity index rising from 62 percent in raw bagasse to 75 percent in compost, evidence that amorphous hemicellulose and some lignin were selectively degraded while crystalline Cellulose I remained intact. Fourier transform infrared spectroscopy confirmed hemicellulose breakdown through a diminished peak near 1734 per centimeter and documented the consumption of glucose by microorganisms. These microstructural changes explain a counterintuitive result: unlike raw biomass, where fine particles pack efficiently, the mean particle size of compost had no significant effect on pellet density, because the degraded fiber geometry dominates packing behavior regardless of grind fineness.

Using response surface methodology with a Box-Behnken design of 17 runs, the team mapped how pressure, moisture and particle size jointly shape pellet quality. Pressure mattered most for density: raising compaction from 50 to 150 megapascals lifted pellet density from 0.89 to 1.08 grams per cubic centimeter, with the optimum of 1.09 grams per cubic centimeter achieved at 150 megapascals and 16.35 percent moisture. Fracture resistance told a different story, with moisture as the dominant factor. Increasing moisture from 8 to 20 percent raised fracture resistance from 14.65 to 27.095 kilograms, and the maximum fracture force of 37 kilograms, equivalent to 363 newtons, was recorded at 150 megapascals. That figure exceeds the 150 to 250 newtons typical of commercial organic fertilizer pellets, suggesting that moisture-activated natural binders, including residual proteins, lignin and starches, compensate for the cohesion lost with degraded hemicellulose.

Particle size delivered its own surprise. While mean particle size barely influenced density, coarser grinding with the 4 millimeter screen produced broader particle size distributions whose fine fractions filled the voids between larger particles, boosting mechanical interlocking and fracture resistance. Fracture force jumped from 14.65 kilograms at 1 millimeter to 26.60 kilograms at 4 millimeters under identical pressure and moisture. The effect was non-linear, remaining flat between 1 and 2.5 millimeters before rising sharply, a signature of distribution width rather than mean size. Compaction energy followed a similar nuance: at low pressure, coarser particles demanded more energy due to friction and poor packing, but at 150 megapascals the trend reversed, as larger particles fractured and rearranged more readily under extreme force.

The resulting pellets are positioned as a soil conditioner rather than a concentrated fertilizer. Chemical analysis showed 0.74 percent nitrogen, 30.66 percent organic carbon, a mature C:N ratio of 18:1 and a mildly alkaline pH of 8.68, making the pellets well suited to the acidic soils common in sugarcane regions, where they can raise pH and improve micronutrient availability. The nitrogen content falls below the 1 percent threshold of some commercial organic fertilizer standards, so the authors recommend blending with urea or other nitrogen sources for higher fertilizer value, an approach their earlier work showed can slow nitrogen release, with 80 percent released over 98 days in soil versus 61 percent in five days in water. Densifying the compost cuts bulk volume 4.6-fold, potentially lowering transport and storage costs by 60 to 80 percent, a gain that aligns squarely with circular bioeconomy goals and responsible consumption targets.

The authors are candid about the limits of their evidence. Microbial preservation was inferred from temperature control rather than measured directly, and they call for colony-forming unit counts, qPCR or phospholipid fatty acid profiling to confirm viability after pelleting. Chemical composition was characterized before pelletization, not after, and long-term storage stability under varying humidity remains untested, as hygroscopic pellets exposed to relative humidity above 70 percent may swell and lose strength. Field trials comparing pelletized and raw compost on crop yield, carbon sequestration and greenhouse gas emissions are the logical next step. Still, the demonstration that industrial-scale density and exceptional mechanical strength can be achieved cold, without sacrificing the living biology that makes compost worth spreading, marks a genuine advance for waste management in the Global South’s sugarcane belt, turning one of agriculture’s messiest byproducts into a standardized, shippable and biologically potent product.

Subject of Research: Cold pelletization of sugarcane bagasse compost for sustainable agricultural waste densification and soil amendment production

Article Title: Bagasse compost pelletization: Sustainable densification for agricultural waste management

Article References: Abooali, B., Satari, B., & Kianmehr, M. H. (2026). Bagasse compost pelletization: Sustainable densification for agricultural waste management. Cleaner Engineering and Technology, 34, Article 101316. https://doi.org/10.1016/j.clet.2026.101316

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101316

Keywords: sugarcane bagasse, compost pelletization, cold pelletization, agricultural waste management, soil conditioner, biomass densification, response surface methodology, microbial viability, cellulose crystallinity, circular economy, renewable resources, sustainable agriculture