From caddy to compost

CARDIFF will build its own in-vessel composter this year - but what is in-vessel composting and why does our food and green waste need to travel all the way to Derbyshire meanwhile? I went to take a look at an in-vessel composting site to see how it all works.

Composting starts in your home with a small green bin called a kitchen caddy. Vegetable peelings and food scraps all go in a biodegradable bag inside the caddy. When full, this goes into your green wheelie bin alongside your garden waste for weekly collection.

Your food and garden waste then heads to Lamby Way, Rumney, to be stored in a shed with other people’s food and garden waste. It is picked-up daily by large articulated lorries that take it all the way to a VitalEarth composting site at Ashbourne, Derbyshire, over 150 miles away (see map below).

Kitchen caddy slideshow




Above map: Journey from Cardiff to Ashbourne composting site

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After a three-hour long drive, your food and garden waste arrives at the composting site, which is a series of several large sheds. The site is surprisingly tidy. There is a sweet silage smell and a bit of mud, but amazingly there are no nasty smells.

The lorries dump their loads into a reception shed and a tractor scoops the waste up bit-by-bit. The tractor puts it on a picking line to remove contaminants such as glass, metal and plastics. According to Site Managing Director, Steve Harper, who showed me around, Cardiff waste is usually very clean whereas waste from other councils is often full of contaminants.

The waste is then mixed, shredded and poured into composting vessels, which look like small boxes on wheels. The Ashbourne site has over 70 composting vessels meaning it processes about 64,000 tonnes of waste every year.

Audio One: The waste enters the reception shed

Above photo: Waste dumped in reception shed

The vessels are sealed to prevent bad smells getting out and fans blast air through a false floor to get the bugs working. After a day or so, the fans calm and the vessel is heated to 65 degrees for 96 hours to fulfil Defra and composting regulations. The heat kills off salmonella, E coli and any weed seeds. Halfway through the heating process, the vessels are emptied and refilled to mix the contents and ensure all corners have been heated through.

Audio Two: The waste enters the vessels

Above photo: The in-vessel composters

Above photo: The temperature gauge on an in-vessel composter

Above photo: The changeover bay at the halfway stage

After a week, the vessels are emptied into a maturation shed and left with fans pumping air underneath, for six weeks. A Solvita test checks if the bugs have finished doing their job.

When the compost is ready, a tractor will load it into a hopper, taking it through a screening process which is like a big sieve. All oversized pieces go back to stage one to go through the process again.

Audio Three: The material goes in the maturation shed for six weeks

Above photo: The material is left for six weeks in the maturation shed

Above photo: Once mature it goes into the blue hopper for screening


Above video: The screening machine

Above photo: The material on the floor is the sieved compost

Above photo: Oversized bits go back through the process

Audio Four: The compost is ready for use on your garden

Photo: The finished product ready for bagging

The kitchen caddy and green wheelie bin scheme has been available to most Cardiff households since October last year. Cardiff residents have had mixed reactions.

Sue Johnson, 52 from Ely, said: “You can only leave [the kitchen caddies] a matter of days, other than that it stinks the kitchen out. It’s just a waste of money and a waste of time.”

Her friend, Beryl Habvard, 53, also from Ely, added: “ A few years ago you just got a black bin, that was a lot easier.”

But Sharon Norman, 37, from Heath, says: “It may cost people more in taxes and things, but I think if we don’t do something for our environment then the generations of future years will have nothing. Somebody has to start somewhere.”

Audio Five: Sue Johnson and Beryl Habvard give their opinions on food caddies

Audio Six: Sharon Norman gives her opinion on using a food caddy

Cardiff Council received planning permission for an in-vessel composting site at Lamby Way in July last year, but it was delayed as the Environment Agency needed to do a flood risk assessment. Building has yet to start but it should be ready in the autumn. Compost from the Cardiff site will be used for planting in local parks and as top soil for the landfill site. The council also hope to sell the compost to local contractors.

The waste is being transported to Derbyshire at the moment for financial reasons, creating six tonnes of carbon a day, until the project is complete. There is criticism about the environmental impact of this, but a spokesman for Cardiff Council says this impact is minimal as the trucks were already travelling to South Wales – a claim challenged by opposition councillors.

Heather Webber from Cardiff Friends of the Earth, said: “It is not ideal that the waste is being transported to Derbyshire. However, it might still be better for the environment as waste is being diverted from landfill.”

Steve Harper also emphasised the environmental benefits of composting rather than sending waste to landfill. He also explains the importance of composting like this as an alternative to peat-based compost: “The term compost is too general and can be misleading. With peat-based compost, no composting process actually takes place, it is simply dug up from peat bogs - destroying natural habitats as well as releasing carbon, trapped for thousands of years. Our compost is completely peat free.”

Cardiff is one of only a few local authorities to be implementing a kitchen caddy and green-waste composting scheme. Clearly, the scheme offers a fantastic alternative to sending waste to landfill and it provides an alternative to peat-based compost, however, this is at a substantial financial cost.