Few would argue against taking better care of the environment, becoming more efficient in our use of natural resources, avoiding wasteful consumerism, and recycling where it makes sense to do so.
Well, out walking recently I was keeping pace with an Auckland Council food scraps collection truck, which stopped at every fourth or fifth property, the driver climbed out and emptied the small bespoke, plastic, lidded food scraps bin, then accelerated away to then stop at the next bin. One would hope that most of the remaining 75-80% of the dwellings are composting at home – the optimal low environmental impact solution.
Anyway, scraps collected are brought to a central station, transferred to larger trucks and transported hundreds of kilometres to a central North Island location where they are processed to produce liquid fertiliser and biogas. Similar operations are in place in Hamilton, New Plymouth and Tauranga.
The Auckland Council website [1] states that the Government’s aim is to process eventually 75,000 tonnes of food scraps annually from across New Zealand, with the system operational across the whole country by 2030. The justification given by the Council is that food scraps in landfill result in methane (CH4) and carbon dioxide (CO2) being released into the atmosphere, and that methane causes 25 times (common sources, e.g. Reference 2, say 30 times) as much global warming per tonne as carbon dioxide.
While no one disputes the release of these gases from landfill, current science indicates that the greenhouse effect from methane is in fact very small. Van Wijngaarden and Happer [2] state,”… the rate of increase of CO2 molecules, about 2.3 ppm/year (ppm = part per million), is about 300 times larger than the rate of increase of CH4 molecules, which has been around 0.0076 ppm/year since the year 2008. So, the contribution of methane to the annual increase in forcing is one tenth (30/300) that of carbon dioxide. The net forcing increase from CH4 and CO2 increases is about 0.05 W per m2 per year. Other things being equal, this will cause a temperature increase of about 0.011°C per year. Proposals to place harsh restrictions on methane emissions because of warming fears are not justified by facts”.
Carbon dioxide is critical for plant life and, from just this perspective, would ideally be at a higher level than at present, Nonetheless, anthropogenic carbon dioxide has contributed to global warming, although there is still debate in the scientific community over the temperature sensitivity of the atmosphere to further increases in carbon dioxide above the present level of around 420 ppm. Coe et al. [3], for example, state from their fairly recent modelling, that, for a further doubling of atmospheric carbon dioxide, climate sensitivity is calculated to be 0.50⁰C, including positive feedback effects from water vapour. This is well below the IPCC pessimistic scenario of up to 3⁰C temperature increase by the year 2100 [4], although this also includes factors other than carbon dioxide.
Even if we accept the proposed justification for the food scraps scheme on the basis of the greenhouse gases that have been sequestered through the recovery process, there remains the question of whether the designers of the scheme looked at its lifetime energy economics or environmental impact. It would seem certain that the fuel energy used between stops by each collection truck, weighing several tons, plus the fuel energy consumed in the subsequent trip to the depot and then the down-country large transport lorry would well exceed that which is recoverable from the food scraps load.
Overall, the energy consumed and the carbon dioxide emissions from the collection and transport process plus maintenance events, and the embedded fossil fuel energy costs and atmospheric emissions that went into building the collection trucks, manufacturing the plastic bins, and the central scraps-to-biogas-and-fertiliser plant, must significantly exceed the lifetime energy recovered carbon dioxide emissions avoided through this scheme. Even when the collection trucks are electric, the embedded fossil fuel and petrochemicals expenditure involved in their manufacture, and in their end-of-life disposal and that of the processing plant, must still make the energy and environmental balance sheet for this project look highly unfavourable.
If a comprehensive environmental impact analysis was done for this project, then it should be made available to the public, as ratepayers are covering the cost of this “service” at a time when rates increases have been running unacceptably far ahead of inflation and many households struggle to meet their rates bill.
The food scraps recycling scheme, understandable from a purely technical angle, was likely introduced through a mix of good environmental intentions and a hefty dose of green ideology, but it is hard to see the justification for it. Would it not have been better for City Councils to supply home composting bins and encourage people to grow some vegetables?
Of course, home composting lacks appeal or practicality for many people, but any scheme aimed at better protecting our atmospheric environment and at recycling nutrients, for which the ratepayer has to stump up, must be shown to deliver a net benefit to the community before it is implemented. I very much suspect this one does not but ask that the Auckland Council demonstrate otherwise if it can. Otherwise, this is just greenwashing.
John Raine is an Emeritus Professor of Engineering and has worked in Deputy Vice Chancellor and Pro Vice Chancellor roles in three New Zealand Universities. He was formerly involved in alternative fuels energy research.
References:
1. Auckland Council Website advice on the Food Scraps Collection Scheme
2. W. A. van Wijngaarden and W. Happer, “Methane and Climate”, CO2 Coalition, January 2025.
3. David Coe, Walter Fabinski, Gerhard Wiegleb, “The Impact of CO2, H2O and other ‘Greenhouse Gases’ on Equilibrium Earth Temperatures.” International Journal of Atmospheric Sciences, Volume 5 No.2, 23 August 2021, pp29-40. http://www.sciencepublishinggroup.com/j/ijaos
4. Sophie Boehm and Claire Schumer, “10 Big Findings from the 2023 IPCC Report on Climate Change”, World Resources Institute, March 20, 2023 https://www.wri.org/insights/2023-ipcc-ar6-synthesis-report-climate-change-findings
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