All homes and businesses across the UK produce some degree of bio-waste. It ranges from the food we get rid of at home, the large supermarkets who need to manage out of date products and farms that have to deal with animal by-products to garden waste such as grassing clippings and hedge trimmings. All of this bio-waste can be composted and used as fertilizer.
As with other refuse, successful bio-waste management depends largely on what is called the waste hierarchy. Outlined in the EU Waste Framework Directive, the hierarchy defines how we should first prevent, then reuse and recycle before finally disposing of our waste.
Prevention and Reuse:
One of the major factors in managing food waste is to prevent its creation in the first place. For homeowners that means only buying what is needed. It’s something we have not been too good at in the past, particularly in the West where supply is plentiful. Prevention also requires us to use what we have when we buy it, making best use of leftovers and freezing unused food for later. For supermarket, things are more difficult and a large amount of food goes to waste on a daily basis when it passes its sell by date. Measures to pass this food onto places like charities and food banks is gaining popularity across Europe and major outlets like Tescos are now changing their own business habits.
Recycling: The biggest part of dealing with food and garden waste in the UK is recycling. This normally involves processes such as composting and anaerobic digestion that produce valuable fertiliser and can, with the right equipment in place, even produce heat, biogas and electricity. Most councils nowadays have facilities in place that are designed for the collection and processing of food and garden waste. Agricultural industries for their part are also sending less of their animal by-products and other farming waste to landfill.
Despite these recent improvements, we still send far too much food waste to landfill rather than converting it to fertilizer or using it to create energy and biogas.
Composting is a natural process by which organic matter is broken down into a rich soil which can then be used on the garden, in parks or for agricultural purposes. The benefit is that you safely dispose of food and garden waste and return valuable nutrients to the soil rather than simply drop it into landfill. It’s a simple way to manage bio-waste of this type and usually only requires a compost bin, some worms and a little bit of time.
Find out more about bio-waste equipment.
Councils operate on a larger scale and use two main methods for composting:
- In-Vessel Composting: Food and garden waste are mixed, shredded and then placed in large, closed containers where moisture content and air flow are carefully controlled to promote fast composting.
- Windrow Composting: This takes place in the open rather than a closed container. The height of the compost heap must be no more 1.5 metres and the material needs to be turned on a regular basis. This takes longer and is usually restricted to garden waste rather than food waste because of the hazard of attracting vermin.
What Can You Compost at Home?
For your average domestic compost heap there are wide range of biodegradable materials that can go into the waste. These include the obvious things such as garden cuttings and trimmings, nettles and weeds and herbivore manure. You can also include shredded paper, coffee grounds, egg shells, hair and even the dust from a hoover bag.
There are a few things you should not put in your compost heap if you have one at home:
- Cooked and raw meat or fish (because they might carry disease and attract vermin).
- Cat litter and dog and cat faeces.
- Glossy magazines that degrade slowly and have chemicals on the paper.
- Coal ash and waste from your barbecue which may of sulphur oxides in them.
Anaerobic Digestion and Biogas Production
One of the major advances in recent years when it comes to handling bio-waste is anaerobic digestion. Food and other agricultural waste can be put in a container with little or no oxygen and some useful bacteria and broken down. In more advanced systems, this process produces methane gas which can be captured and used to generate electricity or as fuel for combined heat and power systems. This process is nowadays used on many farms to provide local power and reduce running costs. Once the anaerobic process has finished, you are left with a concentrated residue that can also be used for fertilizer.
While anaerobic digestion has long been popular with our European neighbours, it is also beginning to grow across the UK. There are now over 100 sites across the country though there is certainly room for more improvement. The future could well see all towns and cities with their own anaerobic digestion plants producing biogas, fertiliser and energy for the local community.
There are two different types of AD depending on the temperature that decomposition takes place at:
- Thermophilic Anaerobic Digestion operates at around 60°C.
- Mesophilic Anaerobic Digestion operates between 35 and 40°C.
Both are equally efficient but Mesophilic AD often requires the addition of a pasteurising unit to make sure no dangerous bacteria are produced. For this reason, it is generally unsuitable for animal feed stock processing.
Find out more about the types of bio-waste.