Landfill //
Organic waste should not get preference in landfills A well operated landfill can capture 90 per cent of the available generated gas on any given day.
By Mike Ritchie SAM BATEMAN has been a champion of the waste industry for as long as I have been in the sector (over 30 years). In that time, including in his latest article in Inside Waste, he has argued strenuously for the role of landfill in an integrated waste management system. On that we agree. We would agree that landfills have a role as the final repository of residual waste for which there is no higher resource value and for hazardous or intractable wastes that need to be safely removed from the economy. So yes, landfill should be part of the circular economy for the disposal of a limited number of non-recyclable low calorific-value materials, that are hazardous. But Sam’s recent article in Inside Waste titled Is landfill part of the circular economy?, in which he argued that we should preferentially landfill organic wastes, I believe, is wrong on a number of counts. In substance, he argues that the best destination for organic waste is landfill and that this results in lower 30
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greenhouse gas emissions and a more circular economy. I have set out below Sam’s key arguments and my response. I hope I have done him, and the science of landfill and climate change, suitable justice in this short reply. Sam argues that putting available organics in landfill is a good way to sequester them and take them out of the active carbon cycle, which is the source of climate change temperature increase. He said: “50 per cent of the organic carbon is resistant to the bacteria in landfill and is stored for many 100’s of years thereby taking that carbon out of the biogenic carbon cycle”. The science behind that claim is immature and highly variable. The furthest back we have excavated a landfill is only 70 years. All of the estimates of very long-term decomposition are based on laboratory experiments and stochiometric modelling. It is true that potentially 50 per cent of lignocellulosic material, such as wood, is slow to break down in a landfill. The other 50 per cent breaks down quickly (e.g. food and garden
waste). But sequestration in the context of climate change means thousands of years or preferably forever. Under perfect conditions, long term sequestration is more likely i.e.: the emission rate of methane in desert landfills can be dramatically lower than that of other landfills. But we are not talking about perfect conditions. We are talking about the thousands of landfills in Australia from the tropical north, the central deserts and the wet south. From the big landfills with gas capture through to the unlined trench landfill with no gas capture, in western NSW. For Sam’s argument to hold we would need good science on the rates of breakdown over hundreds of years under different conditions and to be able to apply a risk weighting to account for uncertainty. Because this science is immature there are currently no approved methodologies (CER or NGER) for measuring and accounting for this possible sequestration. There may be in time, but not now. Conversely, there is pretty good science that organics can be stored in biomass and soils. There are approved
methodologies for measuring and accounting for sequestration. Even so, the regulator applies a risk weighting to account for possible losses to the environment in the long future. That is also why biochar offers so much potential to farmers. We know it sequesters a proportion of the carbon for at least 2,000 years. Sam then said: “The greenhouse emissions are offset by the carbon storage and by the renewable electricity.” As stated above there are no offset mechanisms to account for carbon storage in landfills. Second, only large landfills in Australia have renewable energy generation. That is less than 30 of Australia’s 2000 plus landfills. However, those 30 receive about 60 per cent of the volume of waste. A couple of hundred have flares to – destroy the methane – the rest have nothing. What we do know is that Australia’s landfill stock currently account for over 9 MT CO2-e of fugitive emissions from landfill. That is equivalent to about 2 million cars on the road. It is a big emitter. It is also the second largest
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