Rice Husk

The husk is the pair of floral structures — lemma and palea — that enclose the rice grain and are stripped off when rubber rolls or an impact huller shear them away. It is not a bran layer and it is not part of the seed: it is a covering that never was edible. It is largely cellulose, lignin, and silica, and its very low bulk density means the volume of husk a mill produces looks even more disproportionate than its weight.

The oldest and largest outlet is fuel. Husk has a usable calorific value and is available exactly where energy is needed — at the mill — so husk-fired furnaces drive paddy dryers and, at larger scale, husk-fuelled power generation. Burning concentrates the silica into rice husk ash, which is itself a product: a suitably burned ash is a pozzolanic material used in cement and concrete, and a source of silica for other industrial uses.

• Energy — boiler and furnace fuel at the mill, notably for paddy drying, and power generation
• Industrial — rice husk ash as a pozzolan in cement and as a silica source
• Agriculture — animal bedding, poultry litter, and a horticultural substrate
• Feed — as a bulk fibre filler only, and of very limited value

Uncontrolled burning and dumping of husk remain common where no outlet has been developed, and the piles are a nuisance and a fire risk. Where husk is used well, it is because a mill has invested in the equipment to use it — which is the practical difference between a residue and a resource.

Husk is difficult material. It is extremely light and bulky, so transporting it any distance rarely pays and it is used near the mill or not at all. It is abrasive enough to wear conveying equipment. And the dust it generates is a respiratory hazard: silica-bearing dust is a recognised occupational concern, and mills that handle husk in volume manage it accordingly. Piles of dry husk are also a fire hazard, and they smoulder rather than burn cleanly once alight.