Black Soldier Fly Bioreactor

A black soldier fly bioreactor is a sealed bin that turns food waste into live animal feed. The larvae eat scraps at speed, and when they finish growing they stop feeding and climb - which is what the bin is built around. A ramp up the inside wall leads them over a lip into a bucket, so they harvest themselves and nothing is sifted or picked out. About 45,000 larvae work through 24 kg (53 lb) of manure in a fortnight, halving its dry matter and nutrients.

Eggs hatch in about four days, the larvae grow through six stages over roughly a fortnight, and becoming an adult takes two weeks more. The colony needs a moist substrate - wetter and richer in nitrogen than a compost heap wants, at a carbon to nitrogen ratio between about eighteen and fourteen to one - a container the larvae cannot leave except by the ramp, and warmth. Activity falls away as temperature drops, so where there is a cold season the bin runs in the warm months only and a compost pile or worm bin carries the rest. The adult fly is no nuisance: it eats nothing, lives on fat stored as a larva, has no sting and is not known to carry disease.

Poultry and fish take the larvae live, so the bin sits between a kitchen and a compost pile: scraps in from one, frass - the dry droppings left behind - out to the other. One rule decides what the output legally is: the feed-ingredient definition covers larvae raised only on feed-grade material, so a colony fed manure, carrion or mixed waste is doing waste reduction rather than making feed. A living population is not a pile: a colony that crashes is restarted rather than stirred, and a unit left open or badly sealed will smell and breed where it is not wanted. Routine work is feeding to what the larvae are eating rather than to a schedule, emptying the bucket, keeping the ramp clear - the only moving part and the single point of failure - and taking out frass.