Making compost in the classroom with a Rotbot

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Caitlin Goodwin
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1 Making compost in the classroom with a Rotbot Teachers Notes Composting in the classroom is an excellent way to demonstrate to pupils the power of microbes to perform useful tasks, such as the breakdown of waste. Once microbes have created usable compost, it can be used to grow a seedling and demonstrate the growth and nutrition requirements of a green plant as well as a host of life processes. A Rotbot also makes an excellent subject for investigation or experiment. Overview A Rotbot is a simple but effective composting vessel which can be easily made from an empty plastic drinks bottle by students working individually or in small groups. Rotbots allow students to watch and photograph the composting process over 4 to 6 weeks, and then observe and record the growth of a plant in the compost they have created. Rotbots demonstrate the composting process in action. If the resulting compost is used to grow a seed, it also shows how compost can be used as a medium for growing plants completing the whole cycle. The composting process will work effectively in a warm classroom year round and can therefore be used instead of (but ideally complementary to) a traditional garden compost bin as a learning aid. Worms can be added to Rotbots. Students doing so will be able to compare the effectiveness of normal composting and worm composting. If worms are to be used, two Rotbots can be prepared using the same mix of materials with worms being added to the second bottle only, to allow a comparison between the two to be made.

Making a Rotbot Equipment required (per student / per group) to make one Rotbot One 2 litre plastic bottle One pair of sharp scissors A small piece of breathable fabric: mesh cloth / muslin / garden

Compostable organic Ingredients A mixture of "green" (nitrogen-rich) and "brown" (carbon-rich) ingredients are required for the composting process to work effectively.

2 Making a Rotbot Equipment required (per student / per group) to make one Rotbot One 2 litre plastic bottle One pair of sharp scissors A small piece of breathable fabric: mesh cloth / muslin / garden fleece A rubber band A sticky label and pen / a permanent marker pen One tablespoon One saucer / dish (on which a completed Rotbot can be placed) Compostable organic ingredients (see below) Compostable organic Ingredients A mixture of "green" (nitrogen-rich) and "brown" (carbon-rich) ingredients are required for the composting process to work effectively. You are aiming for a ratio of 2 parts green ingredients to 1 part brown ingredients. These should be placed in the Rotbot in alternating layers. To kick start the composting process you might also want to use an activator. Worms are optional. Browns: These are carbon-rich ingredients that also help to create air pockets in compost which aid the degradation process. Examples of browns: Straw, hay, small twigs, small pieces / strips of paper or cardboard, shredded paper, sawdust (from untreated wood), eggshells, tea-leaves. Greens: These are nitrogen-rich ingredients that typically also help to retain moisture and keep the compost moist.

3 Example greens: Grass / grass cuttings, vegetable leaves, vegetable waste and peelings - potato and apple work well; chopped up banana skins, coffee grounds, seaweed. Comfrey and nettle leaves are excellent greens, but are prickly so gloves should be worn if these are to be used. Where young children are making the Rotbot it is strongly recommended that only clean, fresh, uncooked vegetable based food materials are used, this excludes leftover foods from packed lunches or school dinners. The composting process should produce a rich earthy smell. If a sharp ammonia smell is produced, please double check the contents of your Rotbots! Tips It is good to have a mix of different coloured ingredients at the start of the process so that layers of different materials can be clearly seen inside the bottle. Always avoid adding cooked foods, meats, dairy, oily foods and grains they will smell, attract vermin and may harbour harmful bacteria as they degrade. If worms are to be added to the Rotbots, do not add citrus fruit peelings as there is an oil in the skin that worms do not like. Adding too many browns will slow down or stop the composting process. Your Rotbot will likely dry out quickly and stop working. Adding too many greens will lead to the Rotbot becoming too wet and the conditions may become anaerobic. If this happens, the compost will look slimy and will probably smell quite bad. Activators: One or two layers of compost taken from an active compost bin can be added. These will contain large quantities of the bacteria needed to kickstart the composting process. Worms: 5-10 composting worms can be placed in each Rotbot. Please ensure that only composting worms are used! Don t be tempted to dig worms from the soil in a garden as these will be of the wrong species. You need compost worms, such as Tiger Worms or Dendras which live naturally in compost bins. These can be bought online cheaply from places such as Amazon. See also:

4 Soil: If you intend to grow a seedling in your Rotbot it is essential that there is a 2cm layer of soil added to the top of the compost. Add the soil once the compost has reached a usable state (4-6 weeks old) and plant the seed into this Procedure 1. Rinse the bottles and remove sticky labels from its surface. Filling a bottle with hot water can help loosen the tough glues used to attach some labels. 2. Adult Carefully poke or drill one or more drainage holes in the bottom of the bottle(s). If using scissors to do this, please be extremely cautious. 3. Adult Cut the top off the bottle(s) using scissors. Be careful to remove any sharp pieces of plastic. Some people cover the cut edge with tape as an additional safety precaution. 4. Prepare the ingredients by tearing or cutting the organic materials (straw, twigs, leaves, grass, vegetable and fruit scraps) into small pieces. The material can be moistened by the addition of water at this stage. However, if the Rotbots are to be moved later, water can be added as at Stage 7. (Leaving the addition of the water to stage 7 is the cleaner option) If added at this stage the mixture should be moistened only slightly achieving a consistency similar to a wrung out sponge. 5. Build up the layers in the Rotbot. It is best to put a good layer of browns in the Rotbot first as these will aid with drainage and keeping air circulating freely. Then add the fresh compost activator (if using), followed by alternate layers of greens and browns. 6. Fill the bottle to within 3cm of the top of the Rotbot. 7. Add three to six tablespoons of water if the materials were not moistened at Stage 3. If the Rotbots are to be taken home it is best to leave them dry until they have been transported before wetting. 8. Stand the Rotbot in a saucer or waterproof tray (to catch excess water leaking from the drainage holes. 9. If using worms add them at this stage. 10. Cover the top of the Rotbot with breathable fabric and secure this in place with a rubber band. 11. Place the Rotbot somewhere reasonably warm but not in direct sunlight.

5 12. As the composting process takes place the material may sink in the bottle. Top up with additional material so that when the final layer of soil is added and the seed is planted, it will be near the top of the bottle. Add more water it if it starts to dry out. 13. The compost is ready when the ingredients look like dark, rich soil, this typically takes 4 to 6 weeks. 14. At this stage a layer of soil can be added to the top of the Rotbot and a seed planted into it. See growing a seed below. If not, the compost can be emptied out into a garden or plant pot. Growing a seed 1. Choose a suitable seed dwarf beans and marigolds are a good choice. Plant 2 per Rotbot. 2. Plant seeds in the layer of soil on top of the compost. 3. Place the Rotbot in a well lit place and water regularly. 4. Thin the seeds if necessary. 5. If a dwarf bean has been sown you should be able to harvest a few pods to cook and eat. Extension activities 1) Encourage your class to decorate their Rotbots with materials that would otherwise have been thrown away. Use scrap paper, yogurt pots, sweet wrappers and so on to decorate the Rotbot, make it look like a vase for flowers, add a face, or see who can insulate their Rotbot the most efficiently. Make sure that the decoration doesn t block the drainage holes at the bottom of the Rotbot, and that there is a window remaining so that the composting process can still be observed through the clear plastic bottle. 2) It is possible to set up a range of simple investigations into the variables that affect the rate of decomposition / composting using Rotbots. It is also possible to see who has made the fastest Rotbot and at the same time demonstrating composting as an exothermic (heat producing) microbial process. Variables to investigate: By creating two or more Rotbots it is possible to investigate the effect of the following on the rate of decomposition / composting: The ratio of greens to browns placed in the Rotbot. The ideal ratio for quick decomposition is 2:1 of green to brown materials. If this variable is investigated please be careful not to massively exceed a 3:1 ratio of greens to browns. Excessive quantities of brown materials will lead to a very slow rate (or cessation) of decomposition with no other negative consequences. However, excessive quantities of green materials can lead to anaerobic conditions forming in the Rotbot. In this scenario anaerobic bacteria are likely

6 to flourish, leading to the production of nasty smells (due to the production of sulphrous gasses and ammonia) and slimy residue, which are probably best avoided in the classroom. The effect of moisture by differentiating the frequency with which Rotbots are watered. Excessive over watering should be avoided to keep the Rotbot an aerobic environment (see above). The effect of adding composting worms The effect of temperature keeping Rotbots in a warm or a cool location. The effect of surface area by adding roughly chopped ingredients to one Rotbot, and finely chopped ingredients to another. The effect of adding more oxygen / air regularly add more air to one Rotbot by stirring the contents with a stick whilst leaving another Rotbot to do its thing. Rotbot racing Use a thermometer to see who has created the fastest Rotbot in your class. The bacteria that break down the organic materials present in an aerobic compost bin / Rotbot release heat as they work. The bacteria thrive in this environment, which subsequently has the effect of speeding up the rate of decomposition further, in turn increasing the temperature of the compost further. In very large compost heaps the internal temperature can reach 71oC, which is enough to denature (kill) the seeds of weeds and other plants. This means that they won t sprout when the compost is spread on the garden. This is a very useful property as gardeners do not want to use compost that is likely to introduce unwanted weeds and plants into their gardens. It is possible to measure the temperature achieved in a Rotbot simply by sticking a simple thermometer / digital probe thermometer into the middle of the Rotbot. The warmer the Rotbot, the faster it is working to create compost. It might be necessary to insulate your Rotbot, to aid heat retention, in order to get good results. Why not have a competition to see who can make the hardest working / fastest Rotbot by looking into the factors which are likely to increase the rate of decomposition, for example: The ratio of greens to browns How finely chopped the organic materials are when added to the Rotbot. Layered compostables versus mixed compostables Keeping the Rotbot somewhere warm or somewhere cold Dry Rotbot versus moist Rotbots.

7 Disposing of your Rotbots Rotbots can be used again and again after the compost has been emptied out and the plastic washed They can also be used to make squirrel proof birdfeeders, jewellery, hats, a bowling game and a multitude of other items. Look here for inspiration: If you do have to discard your Rotbot, please make sure that you place it into your plastic recycling bin. Glossary Organic: Anything that is grown or produced by a living thing (organism), such as an animal or a plant is organic. Decay: Is the process by which things break down over time into their constituent parts. Decay is also called rotting, decomposition, or degradation. Composting is a special type of decay that produces compost. Fertilise: When plants need fertilising, they need feeding. Fertilisers feed plants the nutrients that they need to live and grow. Fertiliser is plant food. Compost: Is a mixture of decaying and decayed organic substances that are broken down enough to fertilise growing plants. Compostable: Is anything that can be broken down by bacteria to make compost. Activator: Is something that starts an action, event or process. A composting activator is something that starts the composting process. Vermin: are animals that appear where they are not wanted, for example a rat or a mouse in your kitchen. Temperature: is a measure of how hot or cold something is on a scale (such as degrees Celsius). Gas: A gas is a flowing substance such as air that is not a solid or a liquid. Air is actually a mixture of lots of different gasses all mixed together. Oxygen: A type of gas that is present in air. Other gasses present in air are Nitrogen, Hydrogen and Carbon dioxide. Bacteria: Are tiny (microscopic) living things (organisms). There are many different types of bacteria, most of which do helpful jobs such as turning garden waste into compost. However, some bacteria can make us ill.

8 Composting in schools & the law It is a legal requirement that schools and other educational establishments hold permits for the composting of waste materials, and for the use of the resultant compost as a soil improver. These permits are free and simple to apply for. Additional guidance is available from the Environment Agency via the links below: Waste exemption: T23 aerobic composting and associated prior treatment : Waste exemption: U11 spreading waste to benefit non-agricultural land: Find out more Learn from a Master Composter - Mater Composters offer free information and advice on composting, including Rotbots. Free school talks are available. Composting and growing in school - Home composting - Visit the Microbe Zoo - A virtual zoo where you can learn about different types of microbes and how these tiny organisms affect our lives. Can you find the Zoo compost heap and find out what type of microbes live there? Herman the Worm - The interactive autobiography of a worm. Did you know that European migrants took worms to America with them? Dumptown - Take control of Dumptown and see what effect composting has on waste in the virtual city. This worksheet was created with the help of Master Composters at

Classroom Composting

Classroom Composting Grade Level: Elementary and Middle School Subject Correlation: Science, Writing Objectives: Students will be able to: 1. Observe and describe the cyclic nature of life. 2. Appreciate