WRAP (Waste and Resource Action Programme) have been working on waste genertated by schools.
Primary Schools (with non-production kitchens) generate (averaged out)
Garden waste 0.05kg per pupil per week = 2.19kg per year
raw fruit and veg 0.11 kg per pupil per week = 4.55 per pupil per year
cooked food 0.07 per pupil per week = 2.66kg per year
Secondary schools with production kitchens
garden waste 0.01 kg per puil per week = 0.23kg per year
raw fruit and veg 0.06 per pupil per week = 2.24 per year
cooked food 0.11 per pupil per week = 4.50 per year
So it should be a realtively simple excersise to multiply up the number of pupils to find out what your school is generating roughly.
but there are other considerations - read on! .........
Because composting is a natural – dynamic process it is extremely difficult to be cut and dried about answering this question. As a comparison think about cars and mileage. How many miles a car does to the gallon is dependent on a number of factors – type of fuel, how well the tyres are inflated, how fast you are driving and so on.So speed of composting has key considerations
• Air – are there sufficient structural materials to allow a good airflow through the mix of materials? If not the process will slow down and cool down, it will go anaerobic, start to smell bad, and will be difficult to get back on track. Adding structural materials such as dry woodchip is vital. In the early stages of setting up a composter always put plenty of woodchip in for at least the first month. You can ease off a bit then when the microbes have built up.
• Water – a shortage of water is not usually an issue as there is plenty of water contained in the fresh fruit and vegetable peelings, skins and cores etc – however whole pieces of fruit and vegetable will not release their moisture readily. Smaller pieces break down faster.
• Warmth – the Jora, Scotspin, Ridan and Hot box all have insulation and additionally the cubic capacity of the Hot Box helps keep the centre warm – but even so in the very coldest weather composting may slow down a bit as a result. Having the compost at a temperature between 50 and 60 degrees C ensures a more rapid breakdown. (If you get too hot it actually kills off many of the organisms but it is rare to get the compost going that hot)
• Microbial colonies – cooking food kills off all the bugs, fresh food has bacteria and fungi but it is always a good idea to add a bucket or two of active compost from another heap to help build up the microbial content.
• The materials you are adding –
fresh fruit and vegetable is wet, dense full of nitrogen, organic vegetables (also have more micoorganisms – non organic can have fungicides etc on which inhibit the composting process) – but fresh fruit and veg is devoid of structure and air.
Cooked food is heavy and dense, devoid of structure, micro-organisms can be very wet and sloppy and difficult to open up with woodchip etc (this is where a tumbling or turning mechanism helps)
• Maceration and dewatering – chopping or macerating materials does increase the available surface area for the bugs to work on and can speed up the decomposition process. Although schools are unlikely to really get into this area it does help to chop up materials a bit even if it’s in a bucket with a spade. Many of the commercial macerators are a bit like kitchen liquidisers and need water adding to work properly, then off course the excess water has to dealt with.
Stages of composting
Given that the conditions are right as explored above, composting proceeds through four stages
1. Getting warm – bacterial colonies can double every hour if the conditions, as described above are in place. One bacterium over 24 hours gives rise to over 8 million! Fungi and other microorganisms also proliferate and this explosion of life creates heat.
2. Hot composting – so as long as there is adequate mass and/or insulation the heat generated will not dissipate but will continue to build. Turning the materials helps the air to penetrate throughout the mass, helping it break up and compost more rapidly. After four or five days with turning a mass of material added on day one will not carry on reheating and the temperature will drop off*.
3. Stage 3 is the mirror of stage one it’s warm but cooling off – no amount of turning will induce it to reheat
4. The last stage is the maturation phase – this is a longer slower time when the worms come to the fore and work through the materials and the fungi break down the carbon, particularly cellulose.
{Carbon breakdown is a longer slower process, for example leafmould (just autumn leaves piled up in a heap) generally takes 2 to 3 years to transform from leaves into a substance resembling peat, depending on type of leaf. You can accelerate leafmould by chopping up and adding mixing in nitrogen in the form of fresh grass cuttings, urine etc.}
*Now of course we are continuing to add materials on a daily basis and so if we only have one Jora or Scotspin we have to empty it when some of the materials have only just been added but there is such a mass of more broken down material that it is very unlikely that an unwanted rodent will be interested in it, especially when safely inside a Hot Box.
The Ridan which is a continuous throughput design simplifies this because as you add fresh materials you are harvesting from the other end. This material can be sieved to recover the biggest wood chips and whole bits of fruit and veg, which can go back trough for another go.
To get the best value out of this expensive composting equipment I recommend emptying the materials when most will have been through the hot phase and putting them into a secure maturation unit such as the Scotty’s Hot Box.
OK so how much can I put in!!!
Working this stuff out is not easy! There are so many variables and, besides getting the data back from most schools is tricky. Added to that is the fact that a) they (hopefully) get better at it as time goes on and b) it depends how broken down the material is before it is moved into a maturation bin.
Case studies
Ilfracombe
With about 70 80 kilos a week had two Jora 270’s and 3 Scotty hot boxes – see below for actual data collected by the school.
Our records of waste for the Joras began 5/10/07. We have two Jora 270's, which have an insulated lining. They were easy to construct, and we put them on a higher frame so that we could get a wheelbarrow underneath for easier emptying.
We began with waste from the school playground bins, but found that sorting the noncompostable products took too long, so from May we concentrated on cooked food waste from the kitchen servery, raw kitchen waste and raw pupil cookery class waste.
The food has to be chopped finely in a bucket with spade, and mixed in a 3 to 1 ratio with woodchips, although we prefer sawdust.
From11/11/08 we began a trial of a new composter from a local farmer called Richard Gedge.
Joras
Oct 07 85.5Kg
Nov 07 113Kg
Dec 07 50Kg
Jan 08 68.5Kg
Feb 08 90.75Kg
Mar 08 153Kg
Apr 08 22Kg
May 08 69Kg
June 08 240Kg
July 08 115Kg
Sept 08 213Kg
Oct 08 216Kg
Nov 08 75 Kg
Dec 08 66Kg
New Composter (prototype Ridan)
11/11 onwards 173Kg
Dec 08 90Kg
Both Joras and new composter are difficult to turn when even half full, and until the products have significantly broken down. The Jora has food in for up to 6 weeks, the new composter has significantly decomposed food after 2 weeks.
The contents of both are put into a Scotty's hotboxes compost bin for maturation, with layers of cardboard and green, for annual decomposition. In Summer 2008 we had 20 wheelbarrow's worth of compost from 2 hotboxes (10 from each). A third hotbox (a rat proof composter made from recycled materials) was started in Nov 08.
Case study 2 My Jora 400
In the first two weeks of getting a Jora 400 I added about 80 kilos of food waste (mostly peelings and unsold vegetables from our shop that were well past their prime – But also household stuff and two dead chickens! (the chickens died mysteriously and quickly disappeared in the Jora)
To this was added nearly 40 kilos of shreddings from Proper Job – pretty woody stuff. – this filled up one side of the Jora (still allowing space to tumble.)
Temperature after 2 weeks was 65 degrees C
In the second two weeks I added around 100 KG food waste to only 20 kg of chippings – temperature was about 55 degrees C after 2 weeks
I tried to empty the first half but the plate fell out and the whole lot was tipped onto the ground! (they’ve changed the design now)
Ridan
The Ridan is being trialled at Ilfracombe, Dartington, Okehampton and Dawlish Ratcliffe schools as well as Riverford field kitchen. How much can be comfortably processed is still being fully evaluated. Dan from Ridan tells me that the Ridan will comfortably process 150 litres per week at this rate you are getting a material coming out which is pleasant to handle. But as the Rida is a continuous throughput system you can wind the materials at whatever speed you choose. Riverford did try putting 120 litres a day through (roughly one third cooked food – one third fresh peelings and one third dry woodchip). This did tend to choke the chamber up a bit so that was clearly to very maximum loading with a good deal of effort required to turn the wheel that drives the internal mechanism. Also the material coming out definitely needs further processing and maturation.
Yeah, great, really helpful; still as clear as mud!
I know, what I have been thinking is that the
• smallest schools would have a Jora 270 and a maturation bin e.g Hot Box
• the next size up would be either 2 x JK 270 and 2x maturation – or Scotspin (or JK 400) and 2x Hot box
• slightly bigger might be another maturation bin on top of that
• then 2 x Scotspins (or JK 400s) and 2 – 3 hot boxes
• then Ridan and 2x Hot Boxes
• then potentially a larger Ridan and 2 – 3 x Hot boxes or even 2 Ridans !!
• finally we are into Rockets and Big Hanna territory
Conclusion
We really need more feedback from schools re the amounts they have been putting through the existing systems. The trouble is there is quite a delay in
a) putting the systems out there
b) them getting to use the system efficiently
c) getting the data from the schools!
