Can a fly help the circular economy?

 By Eniday Staff

A world free of rubbish. Total cleanliness. It would be beautiful. A dream. And not just free of household rubbish or waste from production, but all of it: tiny pieces, litter on streets, shopping bags strewn by inconsiderate people, sewage sludge, mattresses propped up against wheelie bins – not just bad-mannered, but illegal – and scrap from industry. Is such a neat and tidy world really possible?

The answer is, well, no. Of course, proper education can prevent a lot of rubbish building up, especially litter, as can creating less of it in the first place, for example through more sustainable packaging, so that there’s less to collect, process, reuse and destroy later. Every rubbish cycle can be improved, but sooner or later you’ll come up against the second law of thermodynamics, which states that every transformation increases the disorder in a system. An increase in disorder stops us using all of the energy inside this system, producing disordered and useless waste. Yep, more waste! Mother nature tends to put this into a new cycle, though: sometimes very brief, like the rapid decomposition of biological tissue, sometimes very long, like the massive deposits of carbonate from animal shells and skeletons on the sea bed. To be clear, the second law of thermodynamics applies to nature too. It’s just that it cheats a little, by putting the sun’s energy into every living system and using it to minimise disorder – although there’s a lot more disorder produced on the sun than gets eliminated down here on earth.

New technologies for a sustainable future 

We don’t always have the solutions to hand, but talent and technological research can point us in the right direction. That’s what the Eni group relies on, building bio-refineries that produce fuel and other valuable material from Used Cooking Oil (UCO) or the organic component in solid urban waste. ENEA does the same: it is studying how to produce advanced fuel, fertiliser and biodegradable material using the talent – and voraciousness – of insect larvae. The species in question is Hermetia illucens, a diptera insect, member of the family Stratiomyidae, commonly know as black soldier fly. The insect is native to the Americas but can now found around the world.

A specimen of adult Hermetia illucens (Enviroflight, LLC)

The adults’ thin, shiny black bodies, a couple of centimetres long, make them unappealing to the eye. But it’s not the flies that do the dirty work. It’s their larvae, which are tiny – a couple of millimetres long at most – but can eat huge quantities of decomposing organic material. During their growth, these larvae, which vary in colour from beige to light brown, can create reusable molecules from the vast range of waste material they feed on, including sewage sludge from urban waste water, waste from food production, rubbish from public green spaces and manure. It’s often difficult to find a suitable, efficient method of treatment for all these, but thanks to black soldier fly larvae they can be converted into fats, proteins and polysaccharides for energy, cosmetics, pharmaceuticals and agriculture.

Hermetia illucens larvae (ENEA)

The project, in collaboration with the Lombardy and Emilia Romagna Experimental Zootechnic Institute (IZSLER), has resulted in a sort of experimental bio-refinery, where methods can be tested for producing two simultaneous results: in one, organic material is destroyed and fuel is extracted; in the other, the larvae’s excrement is used and turned into high-quality fertiliser. According to ENEA’s researchers, this is a particularly efficient process. When placed on a substrate, black soldier fly larvae can metabolise up to 80% of it in less than two weeks. And that’s not all. Larvae even have a potent cleansing effect on the environment they inhabit. The microbiome that is their digestive system can modify the flora on the substrate, greatly reducing bacteria harmful to human health, like E. coli and Salmonella enterica. The next step in the research is studying the best mixes of substrate, combining different material, like the organic component in solid urban waste and residue from the anaerobic fermentation of biomass.

Image cover by Melissa McMasters, Flickr

READ MORE: Welcome to the Circular Garden by Paola Arpino

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Eniday Staff