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I'm a fan of indoor, cold, worm composting (vermicomposting) to reduce my rubbish. This uses a box with many worms that eat your vegetable remains in a very efficient way, without any odor, and outputs earth and vermicompost "juice". And it is also very entertaining to have such pets!!

The benefit of this practice are:

  • reducing the amount of rubbish to be sent to landfill,
  • having rubbish less humid to avoid the use of additives to burn the rubbish in the garbage processing centers,
  • reducing the weight of rubbish and reduce the frequency and number of bin lorry,
  • transform this rubbish into a re-usable product (fertilizer), can be used indoor in city where people usually doesnt have a garden to make traditional composting.

However, it seems that vermicomposting creates massive greenhouse gas due to the intrinsic chemical process in the worm gut which produce nitrous oxyde (N2O), a greenhouse gas hundreds time more powerful than CO2. However, vermicomposting produces less mathane (CH4) greenhouse gas than hot composting; also N2O emission in vermicomposting can be reduced with several factors (temperature, humididy rate, aeration, carbon etc) (2, 3).

My question is: globally, and in the context of global warming, is it more appropriate to throw their vegetable waste to the bin or to use vermicomposting at home?

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If I understand, the overall CO2 (and weighted N2O, CH3 equivalents) net balance of of in home vermicomposting (or other composting) is at the crux of the question here.

Some rigorous and easily repeatable testing of the compost vs vermicultivation has been done, the results put vermicomposting as in improvement in general; and that CO2 and CH3 reduction performance could be improved with the sufficient inclusion of carbonaceous material, aka 'Brown' and also improves with increasing density of worms.

It seems than any net CO2 (N2H, NOx , H2S, plastic nanoparticles) discussion could include the net effects of the total emissions caused by transportation systems for large scale collection of wastes. Simply not adding to that source of emissions makes some sense in reducing net CO2 and other equivalents. Whatever that amount is, zero is less than any.

Then, in the case of the resulting fertilizer from on-site vermicomposting, there is the potential for further net reductions by not purchasing or transporting fertilizer to your garden; however small that might be. Add to that the further reduction in transportation of the vegetables costing only the breath walking from garden to kitchen. Truly, this isn't a facetious argument; the net total of all CO2 from consumer produce shipping is made up of exactly all our little bits we didn't grow or gather ourselves, and by conservative estimates most produce contributes an average of 0.1kg of CO2 equivalent per 1.0 kg of food due to transportation of that food.

source https://science.sciencemag.org/content/360/6392/987

a comprehensive meta-analysis of 1530 studies, supplemented with additional data received from 139 authors, assessed against 11 criteria designed to standardize methodology, resulting in 570 suitable studies with a median reference year of 2010. The data set covers ~38,700 commercially viable farms in 119 countries and 40 products representing ~90% of global protein and calorie consumption'.

One reference for actual numbers comparing composting to worms: http://dx.doi.org/10.1016/j.jclepro.2016.08.058

Vermicomposting as a technology for reducing nitrogen losses and greenhouse gas emissions from small-scale composting

As all food waste byproduct not incinterated will eventually undergo decomposition, whether intentional or simply buried in a landfill; any situation which worms participate in the process appears to reduce harmful emissions overall.

In both composing cases; at home or collected/municipal; the total food waste emissions might change in rate of release vs duration of decay, but not in aggregate total emissions. So, it would appear that little net difference in direct emissions is made if none, any, or all homes compost. As the ratio of vermicomposting is used to replace composting; the specific emissions should decrease as shown.

Any reduction of transportation related emissions in the pursuit of a transition from composting to vermicultivation appears to be a tangental but beneficial outcome. In some specific situation where the transition would increase the distance, total net mass, or utilize dirtier energy sources this might work against those gains.

TLDR; Vermicomposting reduces nitrogen loss 10–20% over composting, decreasing N2O 25–36% and methane emissions by 22–26% and may be less overall when including transportation related CO2 and other greenhouse emissions.

So, if forced to choose worms or composting, the worms are marginally better overall. If the total volume of food waste was handled at home; compost or vermiculture, the reduction in transportation is the same, and reduced emissions would occur to the extent that worms are preferred over compost.

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  • Thank you Haw'n Hillbilly to show that vermicomposting is clearly better than hot composting in term of greenhouse gas emission. But about the balance between the very powerful greenhouse gas that worms produces (N2O) versus the far less powerful greenhouse gas (C02) that transportation would produce if the waste are thrown to standard bin? I mean if vermicomposting would be everywhere, would it impact negatively the fight against climate changes? I know it is not an easy question, but I find it worth to be asked. Maybe there is no research yet on this issue?
    – Noil
    Apr 13, 2022 at 12:36
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    I see the fine point. Quite possibly at a 'total vermicultivation' society scale, the net N2O could signifiacntly effect the climate. Perhaps, this would be mostly by Ozone layer scavenging where this has more effect than just a CO2 equivalency. But, lacking a significantly complex metric for what the actual volume of N2O emissions might be from the median global households and the net potential total for that scenario... hmm, let me see about that; in terms of global food waste total volumes by region... 'Hold my beer' ~HH Apr 16, 2022 at 6:59
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    I've edited to clarify the lack of a relationship between percentage emissions of N2O for transportation (the standard bin) vs vermiculture. Apr 20, 2022 at 7:34
  • "As all food waste byproduct not incinterated will eventually undergo decomposition, whether intentional or simply buried in a landfill; any situation which worms participate in the process appears to reduce harmful emissions overall." Good point for the case of comparing vermicomposting VS landfill burying. What about in countries where incineration is the norm?
    – Noil
    Apr 20, 2022 at 15:10
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    Incineration has so many different emission profiles possible. Is is pure organic waste or mixed post consumer plastic and electronics? Are the wastes burned in an open pit? Are they vaporized in an anoxic reducing chamber, then charged into plasma to use paramagnetic effects to essentially refine them into Carbon Monoxide and H2 for secondary use as fuel for IC engines and steam generation? Short answer; most likely case is at this time most of the CO2 is headed airborne fast if it's incineration. Apr 21, 2022 at 23:47
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Any kind of home composting will result in less greenhouse gas emissions than sending the waste to landfill. The waste composting at home will indeed release CO2, as a result of the worms and microbes respiring, but this is exactly balanced out by CO2 removed from the atmosphere by photosynthesis when the food was growing. However, in a landfill, there is less oxygen available than in a home composting situation, so some anaerobic digestion will take place, and methane, a more potent greenhouse gas than CO2, will be released. Even in the best case, the waste would decompose in landfill and emit the same amount of CO2 as in the home composter anyway. I suppose that in some cases the methane may be captured for use as fuel, but for general landfill I would suspect that the proportion captured this way is not high enough to counter the negatives that the original poster mentions. I have seen a few projects based on collecting food waste for anaerobic digestion to methane, but these tend to be small scale operations focused on very local sources of waste, often using bikes to transport the waste, rather than long distance trasnport in trucks.

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  • Thanks Andy for your comment. it allowed me to be more precise in my question (I've just edited it). Your explanation with CO2 makes senses, however, it seems that vermicomposting and composting creates greenhouse gas that are far more powerful than CO2: Methane (CH3) especially for hot compost; and Nitrous Oxyde (N2O) for vermicomposting (from the worm's guts).
    – Noil
    Apr 5, 2022 at 12:30
  • I wasn't aware of home composting producing gases other than CO2, so I don't really have the knowledge to help much further. My gut feeling is that it should still be better to compost at home, because of the truck emissions and that some of the same processes may happen in landfill anyway (I assume that eventually worms would get to food waste in landfill).
    – andyyy
    Apr 7, 2022 at 7:58

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