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On the left-hand side of the butterfly diagram is the biological cycle, which is for materials that can biodegrade and safely return to the earth. This cycle mainly concerns products that are consumed, such as food. However some other biodegradable materials, such as cotton or wood, may eventually make their way from the technical cycle into the biological cycle once they have degraded to a point where they can no longer be used to make new products.
The biological cyclebiological cycleThe processes - such as composting and anaerobic digestion - that together help to regenerate natural capital. The only materials suitable for these processes are those that can be safely returned to the biosphere. describes the processes that return nutrients to the soil and help regenerate nature. This page will explain some of the concepts described in the biological cycle of the butterfly diagram.
Regeneration
At the heart of the biological cycle is the concept of regeneration. It is the third principle of the circular economycircular economyA systems solution framework that tackles global challenges like climate change, biodiversity loss, waste, and pollution. It is based on three principles, driven by design: eliminate waste and pollution, circulate products and materials (at their highest value), and regenerate nature.. Instead of continuously degrading nature, as we do in the linear economylinear economyAn economy in which finite resources are extracted to make products that are used - generally not to their full potential - and then thrown away ('take-make-waste')., in the circular economy we build natural capital. We employ farming practices that allow nature to rebuild soils and increase biodiversity. Our wider food system returns biological materials to the earth rather than wasting them. No longer should our focus be simply on doing less harm to the environment, but on how we can actively improve it.
Farming
We can manage farms, and other sources of biological resources such as forests and fisheries, in ways that create positive outcomes for nature. These outcomes include, but are not limited to, healthy and stable soils, improved local biodiversity, improved air and water quality, and storing more carbon in the soil. They can be achieved through a variety of practices and can together help regenerate degraded ecosystems and build biodiversity and resilience on farms and in surrounding landscapes.
To achieve these ends farmers may draw on several different schools of thought, such as regenerative agriculture, restorative aquaculture, agroecology, agroforestry, and conservation agriculture, to help them apply the most appropriate set of practices to drive regenerative outcomes on their farms.
Once food is harvested and consumed, the nutrients in organic waste streams can be collected, and returned to the soil via processes like compostingcompostingMicrobial breakdown of organic matter in the presence of oxygen. and anaerobic digestionanaerobic digestionMicrobial breakdown of organic matter in the absence of oxygen.. If nutrients are not returned, soil becomes depleted, meaning farmers are forced to rely increasingly on chemical fertilisers to keep farmland productive.
Composting and anaerobic digestion
Composting is the microbial breakdown of organic matter in the presence of oxygen. It can be used to turn food by-products and other biodegradable materials into compost, which can be used as a soil enhancer, returning valuable materials to farmland in place of artificial fertilisers. The process is biological and involves naturally occurring microorganisms, such as bacteria and fungi.
Anaerobic digestion is another way of recovering the materials embedded in organic waste. As with composting, the process involves microorganisms, but in this case in the absence of oxygen. Anaerobic digestion produces biogas and a solid residual or ‘digestate’. This digestate can be applied directly to the land or composted and used as a soil amendment.
Biogas, made primarily of methane and carbon dioxide, can be produced from both composting and anaerobic digestion and used as a source of energy similar to natural gas. This type of energy recovery is part of a circular economy since it is a byproduct of the process of returning organic material to the soil.
Cascades
These loops of the biological cycle make use of products and materials already in the economy. This could mean, for example, using food by-products to make other materials, such as textiles made from orange peel, or designing new food products using ingredients usually considered waste, like ketchup made from banana peel. It could also mean using the material for applications such as animal feed. When products or materials can no longer be used, they move to the outer loops of the biological cycle where they are returned to the soil.
Extraction of biochemical feedstock
Taking both post-harvest and post-consumer biological materials as feedstock, this step involves the use of biorefineries to produce low volume but high value chemical products. On top of this, biorefineries can produce a range of other valuable products from organic materials through a series of steps. These processes could consecutively produce, for example, high value biochemicals and nutraceuticals followed by bulk biochemicals.
