RIDANs, Rockets and Green Johannas

RIDANs, Rockets and Green Johannas

Composting for the 21st Century!

Modern composters make it possible for schools (and businesses) to compost almost all their food waste without any smells, flies or hassle. Today’s composters are sophisticated, neat and tidy. Run well they can reach 40-60º C, which kills harmful bacteria as well as fly larvae to produce clean compost for growing food.

There are a range of systems to suit every size including, for example:


RIDAN composter
RIDAN composter

… Rockets …

Rocket composter - requires electricty
Rocket composter – requires electricty

… and Green Johannas

Green Johanna - a sealed composter with an insulating jacket See http://www.greatgreensystems.com/green-johanna for details
A sealed composter with an insulating jacket

Funding may be available for cost, delivery and installation of a composter. There may also be a local organisation that can offer support in carrying out an audit and getting you going.

It’s best to start with a waste audit of how much food waste you are producing now. This gives you a baseline measurement to show how much things have improved, but it will also help you decide what size of composter will be needed. One that’s too big won’t work efficiently – they are hungry beasts and need to be fed! Carrying forward 1 or 2 achievable actions from all the information you’ve gathered, and keeping it all a manageable size means you’re more likely to succeed and keep up the momentum.

It can be a good idea to start small-scale until you establish the manpower and support to make sure you can keep up the composting, before investing in something more long-term. Starting off with non-avoidable food waste like veg peelings can be an easy first step, as can using an insulated compost bin like the Green Johanna.

Only use food waste produced on site (not donations from other people) and only use the compost you make to grow things on site. As soon as you get into the ‘import-export’ business with composting, you need to comply with strict legislation. Making and using the compost yourself means you don’t need to.

It’s important the composter doesn’t get too hot, or the helpful microbes that break down food will be killed too. If it gets too cool, it just needs more carbon rich food (sawdust) and a good stir to get it going again.

Potatoes can be problematic. Chunks of raw potato can come through unchanged and sprout in the compost bin. It might be worth keeping them out too.

Fuelling your composter – composters need carbon to get hot. Sawdust and woodchip are good sources and you may be able to get them from a school technical department, tree surgeon or sawmill. Ideally sawdust would come from untreated wood. If not, you’ll have to think about the likelihood of treatment chemicals getting into the food chain and how you can avoid it.


Visit to Charleston Academy, Inverness

Inspecting the compost maturation bins at Charleston Academy
Inspecting the compost maturation bins at Charleston Academy

Charleston Academy has a medium (200 litre) RIDAN composter, capable of taking 100kg a week of food waste, and some compost maturation bins.

Food waste from the canteen (about 25kg a week) goes into the RIDAN with and equal volume of sawdust from the technical department, and gets a minimum of 5-6 turns each time a load goes in.

The geared handle is easy to turn. The internal paddle system means waste doesn’t fall forward along the body of the RIDAN until it’s nice and dry.

The composter works at optimum efficiency when it’s three quarters full.

Leaving out wet slops like soup and custard avoids having to add excessive amounts of sawdust to balance up the compost mix. Around two weeks later, a lovely, dry mix pops out the other end.

It then goes to the compost bins to mature. It can be layered with straw or crushed cardboard at this stage and can sit in the bin for 6-12 months. It’s also possible to dig the fresh compost into soil in autumn and let it mature over winter

The compost relies on a few pupils weighing and collecting the canteen waste. Finding the right volunteers is key and leads to interest from others.



Tomatoes in compost filled raised beds
Tomatoes in compost filled raised beds

Thanks to donations of plants and seeds from Simpsons, a local garden centre, the pupils started with some so fast-growing plants such as salads and herbs so they can see rapid results. They’ve also grown slower maturing plants such as tomatoes, and have even rescued some wild strawberries which are absolutely thriving in the raised bed frames have been made by a member of the technical department.

The growing area is used by different classes and pupils and there are plans to incorporate it into Enterprise Projects next year. Teacher Richard Smith told us, “It’s a great way to get pupils to plan long term, something that can be challenging.” Composting and growing fits into many areas of the curriculum – from weighing and measuring to discussing nitrates in soil

With thanks to Charleston Academy, Inverness and ROWAN (Ross-shire Waste Aware Network) for their time and advice.