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Department of Plant Sciences

Creating value from waste

One third of all food grown goes to waste, with wastage being split between growers, packers, supermarkets and homes. What can be done to help generate some value from all this waste? That is the question that is being tackled by Alison Smith’s Lab, working in partnership with researchers from the University of Ghana, NIAB and AgriGrub on a GCRF IAA Pump-Prime funded project. Last week the Ghanaian partners were in the UK, and Joanna Wolstenholme joined them as thy toured two AD power plants and AgriGrub’s insect farm.

The international team are developing a waste valorization system, feeding food waste to insect larvae. The insect larvae will then be used for feed and food, and the larvae byproduct, known as “frass”, used as a fertiliser and biorepellant. To enrich the nutritional value of the insect larvae, the team are looking at feeding them vitamin B12 rich micro-algae, which have been grown on another waste product – digestate from an anaerobic digestion (AD) plant. Whilst the Ghanaian researchers were in the UK last week, Payam Mehrshahi and Matthew Davey from the Smith group took the opportunity to take them on a field trip to see the component parts of this value chain.

The first stop on the tour was the anaerobic digestor at G’s mushroom farm in Littleport. Site manager, Matthew Hunt, described the plant as a ‘concrete cow’ – it is fed on a regular basis, has 4 anaerobic stomachs, or digesters, and its rear end produces both solid and liquid digestate, as well as methane. However, unlike most cows, the methane is captured and burned to generate enough power for the mushroom farm and 7000 homes, with the latter being heated by the AD plant too.

This ‘concrete cow’ runs 24/7, being fed a mix of maize and food waste - £3000 of feedstock a day. When we were there the diet was maize, radishes, mushrooms and bread – the latter three all either misshapen or stale and so redirected to the animal food chain where they were then bought by the AD plant. From this feedstock, 15 tonnes of solid digestate and 100m3 of liquid digestate were produced every day – all given away for free to farmers to use as fertilizer. Or, in the case of this project, for algal enthusiasts to try and grow algae on!

The food waste theme continued at the next stop on the tour, AgriGrub’s insect farm, where we saw boxes of mouldy oranges waiting to be fed to their Black Soldier Fly larvae. The team are fine tuning their systems for growing the larvae and have experimented with all manner of waste food streams – mushrooms, celery, supermarket mixed scraps… but found that oranges are best to give a sugar boost. They have a steady supply of oranges, which means they are able to provide a nutritionally stable larvae and frass product.

Frass is the discarded skins and droppings of the larvae, which is used as a fertiliser and biorepellant. Due to the high levels of chitin (14%) it stimulates the plant immune system, leading to plants that are less attractive to aphids and other sapsuckers. The larvae themselves are currently sold live as pet food, but the team are looking to branch out into dried larvae for the bird food market. It was great to see the mountains of mouldy oranges being ‘upcycled’ into a not one but two useful products.

AgriGrub have been running trials to see if it is possible to produce more nutritionally rich and healthier larvae by feeding them with algae grown in the Algal Innovation Centre. So far the trials have proved successful – the larvae were happy to eat the algae and it proved a good food source. Now more work needs to be done on what nutritional benefits are transferred and if the fecundity of the insects improved. 

The second field trip day began at the NIAB Park Farm where we learnt about the core crop and non-mainstream crop development and energy efficiency projects being led by NIAB and the innovation farm’s director Dr Lydia Smith.  We then went onto visit another AD plant run by Pretoria Energy Ltd. At Pretoria Energy they grow all of their own energy crops to feed into the digestors meaning that they have more control and a sustained feedstock year round. The biogas is then fed into the national network for heating and power generation.

The visit was finalized by the Ghanaian researchers learning, hands-on, how to grow and extract lipids from algae and analyzing the samples on GC-MS, GC-FID and FT-IR. At the Algal Innovation Centre we looked at how the algae are scaled up from 50ml lab cultures to 200l in large scale bioreactors, using the AD waste from the biogas plants.

All involved felt it had been a very worthwhile visit, and it was great to see the team bouncing ideas around for future projects. Watch this space for more updates on the outcomes from the project!

The Ghanaian team: