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Addressing climate change with banana peel and carrot tops.

When it comes to strategies for addressing climate change, people don’t tend to think of discarded food.  However, food scraps that go out with the general rubbish, rot in landfill to produce methane, a greenhouse gas with 72 times more global warming potential than carbon dioxide.  Unfortunately, this is what happens to most of the food waste in Australia, with a cost to the environment and a landfill gate fee of around $60 per tonne. 

Instead of being a liability, food waste can be transformed into an environmentally and economically valuable product through composting.  Composting the millions of tonnes of food waste produced in Australia each year abates an equivalent amount by weight of greenhouse gas emissions (C02 equivalent) and retails at more than $50 per cubic metre. 

But wait there’s more.   When that compost is applied to land used for growing food, it stores carbon in the soil as well as restores nutrients and beneficial bacteria to the soil, improves soil structure and reduces the need for water and synthetic fertiliser.  It has been calculated that if every US city collected and composted food waste for use in organic farming, the effect on soil carbon storage would offset one fifth of US carbon emissions.

Given all this, why, in Australia, are we still sending most our food waste to landfill?  Adelaide is a notable exception, with most municipalities allowing residents to put their food scraps into their green waste bin for removal and subsequent composting and use in farms and vineyards. Two years ago the market value of the compost produced in this way in South Australia was $35 million and the figure is rising. However, even in municipalities where kerbside collection of food scraps is offered, collecting separated food waste from apartments presents a particular challenge, especially in high-density locations where there is no space for extra bins.  Existing apartments have not been designed with separate food waste collection in mind.  Even Green Star developments that harvest rainwater, produce their own electricity and treat their own sewerage, seldom include provision for separate storage of food scraps.

An alternative to kerbside collection of food scraps and subsequent off-site composting is to compost on-site.  A CRC-funded project is examining the feasibility of on-site composting in apartment buildings, office blocks, commercial kitchens and café precincts.  Contrary to popular belief, this does not involve odour, vermin or back-breaking labour. The research project is specifically looking at a new breed of modular worm farm and the recently-developed technology of high speed in-vessel composters.  Through providing ideal conditions for the composting microbes, namely, heat and aeration, these in-vessel composters can transform food waste into a compost product in as little as 24 hours.  The resulting compost, just a fraction of the volume of the original food waste, can be either used on-site or transported to local food-growers.

One part of the multidisciplinary research project involves examining residents’ engagement with the different composting processes.  It is clear already that while some people like to just “chuck and forget” their food scraps, others draw immense satisfaction from reducing their waste to landfill while at the same time producing a valuable product on-site.  The worm farms introduce a new dimension with the shared caring for worms a bonding experience for some apartment dwellers.  More details are at