Re-packing Food Waste
As food collections become the standard in kitchens across the country, it’s worth taking a look at what happens next: where does the food go, and how is it ‘recycled’?
The two main processing routes are Anaerobic Digestion (AD) and composting, where the food collected becomes ingredients in a new recipe.
In the simplest terms, AD breaks down organic materials using micro-organisms in the absence of oxygen. This process produces biogas (which can be combusted to produce heat and electricity) and liquid fertiliser. An AD plant is a large, circular tank with a domed roof, and works like a churning stomach.
During composting, food waste is combined with green waste (grass cuttings, hedge trimmings, leaves etc.). One type of composting – in vessel composting (IVC) – happens in a controlled environment like a silo or shipping container with the door closed.
Air is added, and the temperature is increased to 60-70ºC, killing all pathogens so the compost can be used as a soil improver – mainly in agriculture – or to replace topsoil.
Quality is key
As with any successful recipe, good quality ingredients are the starting point.
Most of what is put into a food waste bin can go to AD or composting: fruit and vegetables, meat, fish, plate scrapings, rice, pasta, tea bags, and coffee grinds can go into all food collections.
The main difference is the bags.
For the recycling processor, the bag is the packaging.
Corn starch or paper bags are preferred for IVC because they go straight into the compost mixture and break down quickly.
AD plants require clear plastic bags because it’s easy to see inside and check that only the right ingredients are being added into the digestion soup. The bags are emptied at the start of the AD process, so no plastic goes into the mix.
Non-food items also impact the quality of the ‘feed’. In significant volumes, paper napkins and compostable packaging can cause problems for AD plants.
Napkins, disposable plates, cups, or boxes are bulky, so a bag quickly fills up while containing a smaller amount of food. For an AD plant, this mix has lower nutritional value: bulk without calories.
The odd one or two non-food items in a bin will be fine for AD, however, if your outlet uses a lot of compostable disposables, it’s best to ensure food collections are going to a composting plant.
Easy to use?
Food waste collections are widely available. At this stage, the market is skewed with the majority of commercial collections going to AD, mostly driven by capacity and cost.
Across the UK, there are 142 AD plants which process food waste produced by businesses, households, and manufacturers – in comparison to fewer than 35 IVC sites.
Food disposal through AD is far cheaper because the process is subsidised by the gas, electricity, and fertiliser generated.
Waste companies are charged for disposing the materials they collect, and in 2016, the average cost of taking 1 tonne of food to an AD plant was £29 vs. £46 per tonne for composting (WRAP; 2016 Gate Fees).
If food waste was a country, it would be the 3rd largest greenhouse gas emitter.
One of the most significant differences between the two processes is how the produced gas is captured. All organic materials release methane as they break down – which is twenty times more potent than CO2. This explains why food waste is such a large contributor to greenhouse gases.
AD produces methane-rich biogas and digestate. The methane is captured as part of the process, while heat and electricity are generated from the biogas – a renewable energy. The digestate produced is a liquid fertiliser.
Compost is nutrient-rich and contributes to healthy soil by returning organic matter into the ground. It can also be used to replace topsoil where it has been eroded or washed away, e.g. after flooding.
The IVC process does not capture methane, and the gas is released into the atmosphere through the composting process. However, there is an argument that healthy soil stores carbon-reabsorbing greenhouse gas from the atmosphere.
AD and composting are significantly more sustainable disposal routes for food in comparison to landfill or macerating food and washing it into the sewer systems,
Whilst the government’s recently published Clean Growth Strategy includes targets to increase diversions of food from landfill, the greatest commercial, social, and environmental benefits will be delivered through implementing measures to reduce food wastage.
For the majority of food businesses, there will always be an unavoidable element of uneaten scraps at the end of each day. Rather than this being ‘waste,’ how about rethinking the food bin bag as a way of repacking raw ingredients to be sent off to become new ingredients in an AD plant or composting processor.