The Cassava Blind Spot: Why Peels, Pulp and Starch Wastewater Need Decentralized BSF Bioconversion, Not Another Open Pile Behind the Mill

Cassava is one of the world's quietest industrial crops. It feeds hundreds of millions of people, anchors rural economies from Nigeria to Thailand, and supplies the starch behind noodles, tapioca pearls, paper, adhesives and bioethanol. It also produces some of the most awkward organic waste in the agri-food sector: wet, fermentable, odorous, and generated in huge volumes over a short harvest-to-processing window. For waste management professionals, municipalities and corporate sustainability teams looking at agricultural supply chains, cassava is a textbook case of where centralized waste infrastructure does not reach and where decentralized Black Soldier Fly (BSF) bioconversion fits.

This article looks at what cassava processing leaves behind, how it is handled today, where the weak points are, and why on-site BSF bioconversion is a stronger answer for most mills than the usual alternatives.

The scale of the crop, and of what it leaves behind

World cassava output was roughly 330 million tonnes in 2024, according to IndexBox market data, down about 1 percent from a peak of around 334 million tonnes in 2023. Nigeria (about 62 million tonnes), the Democratic Republic of the Congo (about 45 million) and Thailand (about 32 million) together account for roughly 42 percent of the total. Treat country figures as indicative, since market-data aggregators are less authoritative than FAO's own statistics, but the order of magnitude is not in doubt.

Every tonne of root that enters a mill leaves residues behind. FAO's Feedipedia reports that peels make up about 5 to 15 percent of root weight and that pomace (the fibrous pulp left after starch extraction) can reach up to 17 percent of the tuber; a plant processing 100 tonnes of tubers a day generates around 47 tonnes of fresh by-products. Add the process wastewater, and a mid-sized starch factory is effectively a continuous organic waste generator that happens to also make starch.

Why these residues are hard to handle

Cassava by-products are difficult for three reasons that matter to anyone managing them.

First, they are wet and they ferment fast. Fresh pomace is 75 to 85 percent water. At a Thai starch mill described by the Institution of Chemical Engineers (IChemE), leftover pulp begins to ferment as soon as it is stored, producing strong odor and heavily polluted leachate. Piles behind a mill are both a nuisance problem and a methane emissions source, because pulp breaking down without oxygen releases methane just as landfilled food waste does.

Second, they are poor animal feed on their own. Peels and pomace are low in protein (Feedipedia lists peels at under 6 percent crude protein on a dry matter basis and pomace at 1 to 4 percent), and feeding limits apply: in pig trials, pomace inclusion at 10 percent reduced weanling performance, and in broilers inclusion above roughly 8 percent hurt results. The traditional "sell it to a feed mill" outlet therefore has a ceiling.

Third, cyanide complicates everything. Cassava contains cyanogenic glycosides, mainly linamarin. Bitter varieties can carry 200 to 300 mg/kg of hydrogen cyanide in dry matter, and peels concentrate it. A 2025 study in Environmental Monitoring and Assessment on cassava mill waste in Nigeria found effluent cyanide of 3.64 to 4.85 ppm against a permitted standard of 0.07 ppm, and BOD5 of roughly 2,500 to 3,600 mg/L against an industrial limit of 50 mg/L. Waste that is simultaneously high in oxygen demand, odor and toxicity is exactly what neighbors and regulators object to.

How the industry copes today, and where it falls short

The most sophisticated response is the one IChemE profiled in Thailand: a thermophilic anaerobic digestion (AD) system at the Chok Chai Starch plant that treats up to 370 tonnes of wet pulp a day carrying about 68,700 kg of chemical oxygen demand (COD), produces over 30,000 Nm3 of biogas daily at around 60 percent methane, and supports up to 3.4 MW of grid-connected electricity. This is a genuine engineering achievement, and we do not dismiss it. Where a mill is large, well-capitalized and close to a grid connection, biomethanisation is a credible route.

But it is the exception. Most cassava processing worldwide happens in small and medium mills, often seasonal, often far from industrial infrastructure. For them, a digester of that class is out of reach, and the realistic options are the open pile, the lagoon, the landfill, or uncontrolled burning. Even for large mills, AD leaves a digestate management problem and does little for the protein gap: it recovers energy, not nutrition.

The BSF alternative: convert at the mill, not after it

BSF (Hermetia illucens) larvae, or BSFL, eat wet, fermentable organic material and turn it into two products: larval biomass, a protein- and fat-rich insect protein ingredient for sustainable animal feed, and frass, an organic fertilizer. That is waste valorization in the plain sense: a cost line becomes two revenue lines.

The evidence base for cassava specifically is encouraging, though early-stage. A study from Institut Teknologi Bandung on BSF larvae reared on dried, ground cassava peel (mixed with water to 60 percent of total weight) tested five feeding rates between 12.5 and 200 mg per larva per day. The best waste reduction index, 2.79, came at 100 mg per larva per day, which also gave the shortest development time (about 20 days to pupation). The authors identified that rate as optimal. Two caveats are worth stating plainly: the study did not report larval protein or fat content, and peel alone is a nutrient-poor substrate (about 4 to 6.5 percent crude protein), so commercial operations typically blend streams to balance the diet. We also stress that cyanide behavior in BSF systems needs site-level validation; pretreatment such as fermentation, which the Nigerian data suggests lowers peel cyanide, and blending with other substrates are sensible design levers.

Why decentralization matters here more than almost anywhere else:

Speed. Pulp spoils within hours to days. On-site treatment catches the waste while it is still a feedstock rather than a liability.

Emissions. Keeping pulp out of open piles and lagoons avoids the anaerobic methane release and removes haulage. Under GHG protocols, that moves directly into a mill's and its customers' Scope 3 inventories, which matters for food and packaged-goods buyers working toward SBTi targets and net zero.

Land and logistics. A modular BSF unit has a small footprint compared with a lagoon system and does not depend on trucking wet waste to a distant facility.

Circularity. Frass fertilizer returns nutrients to the cassava fields that produced the waste, supporting soil health and regenerative agriculture, while larval protein offsets fishmeal and soy in feed. That is a closed loop in the circular economy sense, and a supplier story that corporate buyers can use in ESG reporting.

Fit for small mills. Because capacity is added in modules, a seasonal mill can start small and scale, which no 370-tonne-a-day digester allows.

A fair comparison

Large-scale anaerobic digestion wins on energy yield at the biggest, best-connected mills. Lagoons are cheap to build but are the worst performers on methane and odor. Selling pulp to feed mills works only up to inclusion ceilings that are low for most species. BSF bioconversion will not generate megawatts, and it needs careful substrate management, but it is the only option on this list that works at small scale, produces a protein ingredient, returns nutrients to soil, and cuts emissions at the point of generation.

What mill operators and buyers can do now

Operators should start with a waste audit: tonnes of peel, pulp and wastewater solids per week, seasonality, and the current disposal route and its cost. Buyers of cassava starch and derivatives can ask their suppliers for waste-handling disclosures, since methane from by-products sits within Scope 3 and will increasingly be asked about. And project developers should note that carbon credit methodologies for decentralized organic waste bioconversion are still maturing, so early documentation of baseline practice and measured outcomes is an investment.

The bottom line

Cassava will keep growing in importance as a food security crop and an industrial feedstock. The question is whether its residues remain an open pile behind each mill or become a managed resource stream. A handful of large mills can justify industrial digesters; the long tail of mills cannot. Decentralized BSF bioconversion gives that long tail a way to treat waste where it arises, document the result, and sell two products instead of paying to dispose of one problem. That is the B-BOX model.

Sources: IndexBox, Cassava: World Market Overview 2024 (production figures); FAO Feedipedia, Cassava peels and pomace (by-product shares, protein, cyanide, feeding limits); IChemE, "Thailand's world first in waste" (Chok Chai Starch thermophilic digestion figures); Environmental Monitoring and Assessment (2025), cassava mill effluent and peel analysis, doi 10.1007/s10661-025-13951-5; Institut Teknologi Bandung, "Growth of black soldier larvae fed on cassava peel."