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This, of course, is a terrible waste. Not only does organic waste in landfill take up a lot of space and produce the potent greenhouse gas, methane, it’s a waste of a precious resource for improving soil health and for growing nutrient-dense food.
Michelle Cox, an organic and permaculture educator who leads composting and healthy soil workshops for the Dunedin City Council, describes compost as "gold".
"Somebody the other day said it’s so expensive to buy vegetables now, and other people say it’s so expensive to get rid of our green waste, and you go - connect the two and create a solution," she said.
Healthy microbes draw minerals and water from the soil for the plant and in return receive sugars from photosynthesis. Land and plants have always had that relationship, she said.
Plants grown in healthy, living soil full of beneficial microbes not only resist disease and pests but are generally thought to be more nutrient-dense, although reliable research on this is hard to find.
Studies show that organically grown food in healthy soils has less residual pesticide and a report in Scientific American about 10 years ago showed that vegetables grown in today’s depleted soils had lower nutrient levels than vegetables grown in 1975.
The US Rodale Institute is conducting a 20-year trial to compare the nutrient levels of vegetables grown by various organic and conventional methods.
"My educated hunch is that plants grown as close as possible to optimal, natural conditions (with the full complement of beneficial soil organisms of course) will give us and the planet the best health outcomes," Ms Cox said.
Tests showed pesticides and herbicides disappeared quickly from a healthy soil because of the bio-remediation available through the soil microbes.
"There’s a lot of work now on bio-remediation, particularly with fungi - how to clean up oil spills and sites contaminated with heavy metals and so on. It’s an interesting one because if the soil is functioning and healthy, that’s a very real possibility that the soil life can deal with these things," she said.
"Finished compost should be dark and crumbly in texture and there may or may not be worms or slaters or slugs or millipedes. It should have an earthy smell and you shouldn’t be able to recognise any of those chunky broccoli stems - they should all be broken down. There may be the odd banana sticker which is really annoying, and you might have eggshells or avocado stones. They take a long time and can just go in again or into the garden if you don’t mind," she said.
There are other systems of recycling food waste such as worm farms which provide "worm wee" and vermicast which are full of beneficial microbes, or the Zing Bokashi system, available from the DCC.
Kitchen waste is put in a two-layer, sealed bucket and sprinkled with Zing, a woody waste product inoculated with beneficial microbes which ferment it.
Unlike a regular compost heap which can’t take meat, fish, dairy, fats and oils, or too much bread or pasta, the bokashi system can handle meat scraps and even chicken bones. The system doesn’t smell and the leachate is a powerful liquid manure. The pre-digested food scraps can be buried in the garden or compost heap. However, this is no help to those without gardens, although as it doesn’t smell it is useful storage for those who want to store food scraps to give to someone with a garden.
Leigh McKenzie, waste minimisation officer at the DCC, said there were a couple of alternatives for those who want to recycle their kitchen waste but couldn’t do it themselves.
Isaac Davies and Pete Ryan run Doubt Not Compost (@doubt-not-compost), a non-profit, volunteer organisation that collects compostable material from inner-city businesses such as cafes, restaurants and even hairdressers. They make compost to grow trees for the One Billion Trees programme. The service is "contribute-what-you-want" in order to promote this change of waste management and enable "conscious composting", they say.
They calculate about 44 tonnes of compostable material are generated in Dunedin households and 50 tonnes in the commercial sector each week.
Since they started in August 2018, they have saved more than 300,000 litres of waste from landfill and the number of places wanting waste collected increases weekly.
Doubt Not Compost can be contacted on email@example.com
Sharewaste (sharewaste.org.nz) connects people who want to get rid of kitchen scraps and green waste with people who can compost it in their gardens.
The council has funding to help other groups wanting to set up a composting system, though the composting site would have to meet Otago Regional Council standards so leachate didn’t run into waterways, Ms McKenzie said.
The Green Island landfill is nearly full and waste minimisation options have been discussed for a long time. Another proposal on organic waste is to go before the council in the 2021 long-term plan.
The council would decide if it would go ahead and how the waste would be treated, either in windrows, a large-scale version similar to home composting, or in a closed vessel or digester. The system had to be able to handle inappropriate material that people might put out, she said.