Landfills //
Landfills are strong GHG emitters – that is what the science says By Mike Ritchie IN Net zero targets and landfill methane emissions in the June/July issue of Inside Waste, Sam Bateman argues that landfills are net carbon sinks and better than Energy from Waste (EfW) from a Greenhouse Gas (GHG) perspective. I wish landfills were net carbon sinks that we could rely on to store organics. It would solve many challenges, but it is just not true. The word ‘net’ gives the impression that they sequester more than they release. The problem is landfills are significant GHG emitters. They sequester some carbon but not enough. Don’t take my word for it, take the science from the Australian Clean Energy Regulator (CER), the National Greenhouse and Emissions Reporting Methodologies (NGERS), the Australian Department of Environment, the US EPA and NASA. They all say ‘keep organics out of landfill’ because the emissions outweigh any sequestration (carbon sink). I go through Sam’s arguments in this article but before I do let me say that Sam has been a massive champion of “best practice” landfills. He, like me, has a world of criticism for poorly run, poorly financed landfills/tips. They are contaminated sites that generate methane and should be regulated accordingly. Sam champions closing old tips and consolidating disposal into well-run bioreactor landfills with gas capture. We agree.
If that was the only choice we had, then better a well-run landfill with gas capture and electricity generation, than a local tip. But that is not our only choice. Recycling and resource recovery trump landfills every day. EfW is higher up the waste hierarchy than landfill. We need to be led by the science. In the emissions and climate change space, we have for too long been led by politics and tactics. We don’t have time for that. We never did. The IPCC says we have less than a decade to get emissions growth stabilised, with a target of zero emissions by 2050 or earlier just to stay below 1.5 degrees C. Current international commitments put us on track for a 2.4 degree warming. That will not be a benign planet to live on. We need to close almost all local tips and consolidate them into well-run bioreactors with gas capture and also reduce the total amount of waste being landfilled through better resource recovery and EfW. It is this last bit to which Sam takes most umbrage. Let’s go through the science of his claims: • L andfill remains the only waste disposal option that actually stores carbon. Demonstrably incorrect. First, soil sequestration from the use of compost and biochar are much better storage options for carbon. They are also much bigger. The CER specifically recognises the utility of soil sequestration
Putting organics in a landfill should be the last option.
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of compost with a carbon credit methodology and ACCU’s (Australian Carbon Credit Units). It further credits the diversion of organics from landfill. In other words, it recognises the harm of putting organics in landfill. Second, the science of storing carbon (sequestration) of carbon in landfill is very weak. Sam suggests the opposite by quoting his personal experience with one landfill at Wollert in Melbourne. Sorry Sam. “One swallow does not a summer make”, to quote Shakespeare. There are no CER-approved methodologies for sequestering carbon in landfill, nor agreed methods of accounting for it. In his defence, there is no doubt that some carbon is stored in landfill but how much, or over what period of time, is unknown. For carbon storage to be real, it needs to be stored for thousands of years. There is absolutely no evidence of this. Third, much of the organics eventually decomposes into methane and much of that is fugitively emitted. That makes landfills net GHG emitters, not valuable carbon sinks. • The overall methane emissions of a landfill have been managed to such a low level that the carbon storage inherent in burying organic waste in an anaerobic environment leads to a net carbon sink. Not true. Landfills represent 3 per cent, or 11 million tonnes annually, of Australia’s direct GHG emissions. That
is equivalent to almost 2.5 million cars on the road. There is just no science to show that the limited sequestration in the landfill outweighs fugitive emissions of methane. Put another way, if we increased the organics we send to landfill, GHG emissions would increase. Not decrease. The maths tells us the same thing. Here is an example for those readers mathematically inclined: Let’s imagine we landfill one tonne of green waste in a well-run landfill. Let’s also generously assume that only 50 per cent of this decomposes over 1000 years. That means 50 per cent is sequestered (carbon sink) and 50 per cent decomposes anaerobically to form methane. Let’s further assume 75 per cent of the methane is captured over the life of the landfill and burnt to CO2. This again is very generous, as even Sam does not claim 75 per cent capture rates over the whole of life of a landfill. The best science from the US EPA and leading landfill gas experts says that it is 50 per cent over the whole life of the landfill. So, 12.5 per cent (50 per cent x 25 per cent) of the carbon atoms from that one tonne of green waste are now being fugitively emitted as methane. But methane has a 28 times higher Global Warming Potential (GWP) than carbon dioxide. In other words, methane stays in the atmosphere and reradiates heat far more effectively than carbon dioxide. That 12.5 per cent of methane causes 28 times the damage that would have occurred if that green waste had not been landfilled, i.e., allowed to naturally aerobically decompose or be aerobically composted. The key point is that landfills are anaerobic environments that generate methane not carbon dioxide. Methane is a far more potent greenhouse gas. The result of landfilling our one tonne in a well-run landfill, in terms of the heating effect on the planet is 3.5 times higher (12.5 per cent x 28) than if the green waste had been composted or left to decompose in your garden, or burnt in an EfW. Methane is even more carbon forcing over short time frames. It is 80x over 20 years. Food and paper are even worse in landfill. Much more than 50 per
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