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An astonishing amount of food is wasted each year in the UK; to be exact, almost 12 million tonnes goes into landfill. But the damage doesn’t stop there; once in the landfill, decomposing materials generate methane, which only further contributes to the global warming problem.
However, when food is diverted from landfill and recycled, valuable products can be created. One way to divert food waste from landfill is to compost it.
Composting is most successful when only certain items are included. Some of these are egg shells, coffee grounds and tea bags, grass cutting and pruning waste and vegetable and fruit scraps. Items like meat, fish, dairy products, cat and dog excrement and diseased plants should never be added to a compost pile.
Recent years has seen a significant rise in local authority food waste collection services, and the process to manage the collected waste is burdensome.
Large Scale Composting: A Managed Process
Composting can take place in a bin placed on a residential property (known as in-vessel composting or IVC), or inside a composting facility after collection from domestic properties. In either situation, composting is a process by which all conditions must be controlled and managed though for large scale composting proper management is far more critical.
How Domestic Food Waste is Composted
Raw and biodegradable food waste is broken down by fungi, bacteria and actinomycetes. These grow over the compost material and breaks down waste, which produces heat and accelerates micro-organism activity.
Once all the sugar and starch in the material has been exhausted, the temperature of the pile decreases until it is ideal for the growth of fungi, who are responsible for breaking down any woody materials like twigs.
Before Composting Begins
Most food waste in the UK is sourced from collections by the local authority, whether it is mixed with garden waste or not. Before it is sent through for composting, this material must be screened to ensure it doesn’t contain any contaminants like metal, plastic or similar items.
The Start of the Composting Process
Once any contaminants have been removed, the material is then shredded to uniform size before being transferred to the first of two ‘barriers’ which can be in bay or tunnel form. It is in this first barrier that composting begins. The compost simply sits in the first barrier, and as it does so, existing micro-organisms begin breaking down the material. As they do this, nutrients are released and the temperature rises to between 60 and 70°C, which is high enough to kill any pathogens or seeds.
Following the time it spends in the first barrier, the waste is transferred to a second barrier where it will remain for 7 days to 3 weeks. This ensures that the compost reaches required temperatures to meet regulations. Careful monitoring and control of temperature, moisture and oxygen level occurs at this stage as well as the initial stage in order to ensure that the material is completely sanitised.
Once the process of sanitisation has completed, the compost must go through what is known as a ‘maturing’ stage. This simply means that the compost is either left in an enclosed area or in front of an open window or door for between 10 and 14 weeks. Doing this ensures that the compost is stable enough to qualify for the next step, which is screening.
Once stabilisation of the compost has been confirmed, it can then be screened for certain grades of products to be sold for use in landscaping, by gardeners, in agriculture and on brownfield sites. Compost that is ready for use as a product has a crumbly consistency and smells slightly earthy.
Composting at Home
The ideal residential compost heap is one metre square by one metre high and is enclosed in some kind of brick or timber structure so that it doesn’t get rained on. Because regular turning of the compost will be required, a space should be left at the front for this purpose.
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