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What can we do with old food?

I’m talking here about what “we” as a society can do with our old food rather than what “we” can do as individuals as the latter is very well covered by our Love Food Hate Waste campaign website.

| 11 Nov 09

 In Scotland we generate a lot of food and other organic waste from a variety of sources including households, large and small businesses, public sector organisations, social enterprises, churches, schools, on the street, on the transport network and basically anywhere people eat. The food waste generated by all this eating has to go somewhere and currently a vast amount of it still ends up in landfill, which is pretty much the worst option for it. If you can think of somewhere less useful than landfill to put a valuable resource like organic waste then I’d like to hear it.

Banana Peel

Will food waste trip us up on the way to a Zero Waste Scotland?

Current efforts are primarily focussed on the task of reducing the amount of organic waste we send to landfill which we can continue to achieve if everyone takes full responsibility for the waste they produce and, for example, composts or implements waste reduction measures. The next phase would be to move towards the ultimate goal: eliminating organic waste entirely, but is this realistic? It’s certainly a massive, huge, enormous task. Even taking a single example such as the food waste produced in staff canteens throughout Scotland we can see the kind of difficulties we face. Can a canteen in a workplace with several hundred or more people realistically compost their food waste, especially when it includes cooked food and meat? Well yes, actually, provided they have outside space to fit an anaerobic digester and the willingness to embrace the technology. More likely though is that the business or organisation could employ a recycling service to collect their organic waste to be composted or “digested” off-site.

What might bring the issue to a head is that there is talk (as mentioned in the soon to close consultation on a Zero Waste Scotland) of a landfill ban on organic waste in Scotland. If this happens then we will quite simply no longer have the option of putting food waste in black bin bags. We will have to embrace alternative methods and this is where we could start to see real innovation in the uses that old food can be put to.

There are two main ways in which we, as a society, can use old food and other organic “waste”:

Compost it – Simply place the organic material in an appropriate receptacle and allow nature to take its course. Can be done at home or on a larger scale. Composting can also be sped up (and made more consistent) by using “in-vessel” processes whereby the materials are given a little helping hand (see this great example of how in-vessel composting can work).

Digest it - Using either small or large scall anaerobic digesters (AD) we can produce methane plus a liquid and solid digestate all of which have a range of applications. Anaerobic digestion is a bit like what happens inside our own bodies when we eat. Bacteria work without oxygen to break food down into nutrients and byproducts. See more about how AD works here.

It starts to gets interesting when we see how the end product can be used. For example with commercial composting we now have an approved certification process for the compost (called PAS 100) which allows it to be sold for agricultural purposes and therefore it ends up back on the land to grow crops. This reduces the need for petro-chemical fertilisers and other soil conditioners. The compost can also be sold to individuals for use in home gardens and tends to be cheaper and is certainly more environmentally friendly than the peat based compost from your local garden centre (although peat free alternatives are available).


The applications available from the AD process are more varied:


  • Biomethane fuel - East Midlands airport has recently announced plans to trial biomethane fuel in the airport buses to reduce their CO2 impact. Of course it would be nicer to see planes using biomethane fuel rather than just the buses ferrying people back and forth but it’s a good start. Biogas can also power cars and trucks.
  • Power – Using the methane produced during the AD process it is possible to create energy, or even to pump the gas for direct use within industry in a similar way to natural gas (which many people may not realise contains mostly methane).
  • Heat – Methane can theoretically be pumped into homes for heating, just like natural gas. In answer to the very natural question: no it doesn’t actually smell. It can also be used to heat factories and in some cases the food waste from a business can be used to heat the same business, saving costs and helping the environment.
  • Compost - With a little gentle treatment (and time) the solid digestates can be turned into regular compost to improve the condition of soil.
  • Fertilizer – the liquid digestate can be used as a nutrient and nitrogen feed for the soil in place of chemical fertilizers.

A note of caution with all this: methane is effectively a hydrocarbon based fuel, just like fossil fuels. Combustion of methane in transport and power plants therefore releases CO2. The difference between methane produced from food/organic waste and oil is firstly that methane has a better fuel to energy ratio and secondly that, if it is sourced from waste, it is arguably better to burn it, use the energy and accept a proportion of CO2 release into the atmosphere than have the methane itself released into the atmosphere (it is 20 times more effective as a greenhouse gas). It is also renewable in the sense that it doesn’t take millenia to produce (unlike oil). It is important however to make sure that we aren’t replacing one form of CO2 producing activity (burning fossil fuels) with another (burning methane).

From a purely sustainable perspective compost, where available, has to be the better option. By breaking down organic waste using the oxygen in the air to produce a carbon filled compost substance we effectively trap the carbon in the waste and use it in the soil. Some CO2 is released during composting but this has been described as “part of the natural carbon cycle” so isn’t adding to the CO2 we, as humans, put into the atmosphere because, left to their own devices, plants grow in open soil, then die, then decay and so on. It is effectively non-athropogenic CO2, unlike that generated by burning fossil fuels.

However, we live in the real world. People need to get around and heat their homes. So AD offers a workable solution, based on existing infrastructure and known technologies. AD plants are costly at first but have low long term maintenance costs and provide skilled jobs for workers in the plants.

Hopefully the above offers a basic introduction into the various techniques for dealing with our old food. It is likely that we will hear more and more about AD and commercial composting over the coming months and years so when you do, you’ll know a bit about it now. Overall it is vital to get the right balance between what is sustainable and what is necessary for us to maintain our economy but more important than everything is that we don’t just throw our old food into landfill.

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