Participatory science and composting – CAPOW

CAPOW – Curious About Processing Organic Waste – is a Taranaki-based citizen science project and one of the Participatory Science Platform (PSP) projects supported by the New Zealand Government. Two primary schools in Taranaki worked with a local scientist to trial the best way to process organic waste on their school sites.

The CAPOW group was made up of year 3–6 students from Stratford Primary School and Matapu School. They asked this question: What is the best practicable way to manage all organic waste at our schools?

Organic waste is unwanted material that originates from either a plant or animal and is biodegradable. Most organic waste found in schools comes from lunch boxes, paper, cardboard and general ground maintenance such as grass clippings.

CAPOW stands for Curious About Processing Organic Waste, and the project has been lots of fun. It’s been good not just finding out answers to things, but also thinking of what questions we want answered and also learning about how we can scientifically get those answers. We worked with a real-life scientist.

Student (age 10)

Learning to be scientists

The students wanted to manage organic waste by composting it. As a side investigation, they wondered whether compost makes a difference when growing vegetables and which compost product would be most effective. In order to do this, they learned about fair testing and scientific processes.

With the hands-on guidance from their CAPOW scientist, John Copplestone from Industrial Chemistry Services, the students investigated the decomposition cycle – how organic wastes break down – and the role of microorganisms and invertebrates. They learned about carbon, nitrogen and soil testing, and they looked at different soils under the microscope.

Different systems to process organic waste

The CAPOW students set up trial plots using the compost from different composting systems.

The eight plots were:

• control plot using existing soil
• bokashi
• cold compost
• tumbler compost
• worm wee and vermicast
• coffee grounds
• banana skin tea
• purchased compost.

Bokashi

Bokashi is a composting method using microorganisms. It uses an anaerobic process, meaning it requires no oxygen. Bokashi will compost most foods including meat and dairy, which other composting systems are unable to do. The common microorganisms used in bokashi are yeasts (Saccharomyces spp.), phototrophic purple non-sulfur bacteria (Rhodopseudomonas spp.) and bacteria that produce lactic acids (Lactobacillus spp.). These microorganisms are also found in the processes of making yogurt and silage. Commercial bokashi has a selection of the key microorganisms inoculated into bran that is sprinkled on top of the material to be composted.

Composting

Composting of grass clippings, leaves and kitchen scraps (no meat or bones) still requires microorganisms, but they utilise those naturally found in the soil or the compost materials. The microorganisms use an aerobic process (with oxygen) and require moisture.

To build a hot compost pile, layer piles of ‘brown’ and ‘green’ materials on the soil surface to a height and width of about 2 m. The brown part is made up of leaves, wood chips, small branches or woody weeds, and the ‘green’ part is made of grass clippings, vegetable and fruit waste, animal manure and fresh garden waste. A ratio of one part brown (carbon) and two parts green (nitrogen) material is a good mix for compost. The pile will heat up as microorganisms break down the materials. Hot compost piles need to be kept moist and should be turned once or twice a week until the pile has composted down into nutrient-rich humus.

Cold compost is one you can keep adding to and generally does not heat up to the same extent that a layered hot compost will. It takes longer for the material to break down.

Tumbler compost is a cold compost system that is turned regularly to promote aerobic conditions.

I had no clue about the environment, composting or microorganisms. Now I am so knowledgeable about compost.

Student (age 10)

Worm composting

Composting with worms is referred to as vermicomposting. The red or tiger worm (Eisenia fedida) is a common composting variety. They can eat their body weight per day to produce a nutrient-rich humus that can go back onto land or gardens. Worms will digest cardboard and most kitchen waste except bones, meat and onions. Worm farms do require care. They need to be kept moist as worms breathe through their skin. The worms can cope with changes in weather conditions, but they will work most effectively if they are in a reasonably controlled temperature. The worms do not like sunlight. Worm farms need to be turned so the vermicast does not get too compacted – this creates an easy environment for the worms to move through.

One of the things we have learned is that the soil is living and it’s so important we look after it so it can grow our food.

Student (age 9)

Coffee grounds and banana skin tea

Coffee grounds are a valuable source of nitrogen and trace minerals. They can either be sprinkled onto the soil or steeped in water overnight to use as a liquid fertiliser. Banana skins contain beneficial minerals. Soak the skins in water for 48 hours and use as liquid fertiliser.

Project results

The results of the experiment clearly showed that compost added to the soil makes a huge difference to plant growth. Of the eight trial plots, cold and tumbler composting methods were most effective in growing healthy plants.

The project also enabled students to explore sustainability in terms of the schools’ on-site waste management. Instead of paying to remove the organic waste, the compost will be used to grow trees, vegetables and fruit in their school environments.

Student action

Students have set up bokashi systems in three classrooms, worm farms in two classrooms and collection buckets in the other classrooms. The management of the waste system requires students to be responsible for emptying the collection buckets when required. The classroom compost is placed into compost bins by the school gardens.

The CAPOW expo allowed the children to share their knowledge. They felt empowered and confident. I am so proud of the students’ hard work and determination.

Stratford Primary school teacher Marlene Lewis

The CAPOW schools have a vision that every student will understand how and why we compost our food scraps. In 2017, they held a CAPOW expo as a way of communicating their findings to the wider community.