Invertebrate-Free Composting

Summary

Home composting of food scraps usually brings into existence large numbers of invertebrate animals, such as earthworms, flies, beetles, springtails, and mites. These animals are born without their consent into short lives that soon end with potentially painful deaths. In this piece, I propose a possible method of composting that aims to avoid bringing invertebrates into existence. It uses only simple, cheap materials that you can buy on Amazon.com. I'm still experimenting with this method, and I haven't yet verified that compost prepared this way is free of all kinds of invertebrate animals. In particular, I'm especially worried that nematodes might still breed liberally within the composting system I propose. Until this method is verified to actually be invertebrate-free, it may be safest to instead compost anaerobically in completely sealed containers.

Update after one year

As of Aug. 2018, I've been putting my food scraps into plastic containers with pin holes poked in the lids for about a year. Out of roughly ~30 such containers, I've only been able to see invertebrates with my bare eyes (not using a microscope) in about 3 of the containers. Those 3 containers all contained fruit-fly larvae. If I recall correctly, the containers all included cantaloupe seeds and skins, so it's plausible that the fly larvae all came from that source. Maybe eggs were laid on the cantaloupe skin before it was put into the containers. It's also possible that fruit flies snuck into the containers while I was putting food scraps into them, but I haven't seen that happen, and I'm careful to open and close the containers as quickly as possible when adding new food scraps. The fruit-fly larvae in the containers seemed to already be dead when I noticed them, so maybe they suffocated. If so, that suggests that the air holes don't provide very much oxygen, although another explanation could be that I sometimes stack the containers on top of one another to save floor space in my room, and such stacking covers most of the air holes.

Having ~3 out of ~30 containers breeding fly larvae isn't a terrible rate of failure, but it is nontrivial, and this suggests that when doing bug-free composting, it may be risky to use a single large container into which you add a wide variety of food scraps, since some food scrap or other may contain fly eggs, which could contaminate the whole container.

Update from 2024

Since roughly 2019, I've stopped trying aerobic invertebrate-free composting. I've gone back to putting food scraps into sealed plastic containers. In my case, I eat a lot of dry-roasted peanuts, which come in big plastic containers with screw-on lids. Those containers are strong and seal tightly, making them good to put food scraps into. Rather than throwing out full food-scrap containers right away, I store the containers in my house until the coldest part of the year (roughly January) and put them in the trash at that point. The idea is that bugs and rodents in landfills are presumably least numerous during the coldest months, and I hope the food scraps will mostly get buried by other stuff at the landfill before spring when bugs and other animals return.

Introduction

Most methods of home composting that I've seen recommended bring into existence some invertebrate animals. For example, compost piles and barrels may be infested by flies and other insects. If you bury food scraps to prevent flies, then earthworms and other soil fauna will feed on the food scraps instead. Ideally there should be a way to compost food scraps without letting any bugs get in to the system, which is what I propose in this article.

Plastic containers

One obvious way to prevent bugs from accessing food scraps is to keep the food scraps in sealed containers. I discuss that approach in this section of another article. The particular plastic containers that I buy are these on Amazon because they're pretty cheap. The following video shows one of these sealed plastic containers in action.

The main downside with completely sealing food scraps is that, after initial oxygen in the container is used up, decomposition will occur anaerobically. This is unfortunate for a few reasons:

1. Anaerobic decomposition is slow. You might have incompletely degraded food scraps in containers for several years.
2. Anaerobic decomposition produces foul odors, although unless the containers are opened, you probably won't smell them much.
3. Anaerobic decomposition releases methane, a potent greenhouse gas. While the net impact of climate change on aggregate wild-animal suffering is unclear to me, many people oppose climate change, and I suspect it's best to err on the side of reducing greenhouse-gas emissions when possible.
4. Because anaerobic decomposition is unlikely to complete before you throw out the food scraps, the containers might burst open at the landfill and allow bugs to feed on the contents there. More completely decomposed food scraps would have less remaining food to be eaten by invertebrates at the landfill.

So it would be nice to find a way to introduce air to these plastic containers without also allowing invertebrates to enter. I discuss ideas for doing this in the next section.

Aerobic composting has several benefits, as mentioned above. However, one downside is that, as far as I can tell, aerobic composting allows biological organisms to extract more total energy from food scraps than anaerobic decomposition does. This means that aerobic composting probably supports more total life and more total metabolic activity. If you think bacteria and other non-animal decomposer organisms are capable of at least trivial degrees of suffering, then more total life means more total suffering.

Allowing air in

Poking holes

The simplest method of letting air into sealed plastic containers may be to poke holes in the containers. However, if the holes are too big, then fruit flies will likely enter. So you need to make sure the holes are extremely small. I make tiny holes by poking a pin into the lid of the plastic containers a few times, as is shown in this video.

These holes look to me too small for fruit flies to enter, but I haven't yet had a chance to put this presumption to the test. By summer 2018, my house will unfortunately contain a sizable fruit-fly population, and at that point I'll be able to see whether these hole-poked containers get infested.

Speaker cloth

Another approach to letting air into your composting containers is to remove the plastic lid and instead cover the containers with material that has extremely tiny holes. This kind of speaker cloth is one option. You can seal the material over the container with a rubber band, as is shown in this video.

By eye I've seen that the holes in the following materials are too big and would let fruit flies through: window screens, mosquito nets, and cheese cloth.

A larger-scale compost container

Composting in plastic containers is super simple, but you're likely to accumulate a large number of containers over time. It might be easier to instead put food scraps into a single larger plastic container. You could allow air into this container using the same methods as mentioned above: poking tiny holes or using speaker cloth. In this case, rubber bands are unlikely to fit around the container, so if you're using speaker cloth, you may need to keep flies from getting in under the speaker cloth in some other way.

Obviously you'd also want to avoid contaminating the contents of the bin with dirt from outside or other non-sterilized materials that might contain bugs. You should perhaps thoroughly wash out the bin before using it to remove any tiny bugs that may already be present. Sealing the bin from fly access prevents nematodes and other bugs from migrating to the bin via phoresy on flies (Steel et al. 2013).

Even if you use several smaller containers rather than one large container, it seems best to use short and wide containers to maximize surface area exposed to the air, rather than the tall and narrow containers shown in the previous videos.

Pre-freezing food waste

Even if no bugs can fly or crawl into your food-scrap containers, there remains a risk that bug eggs or larvae may already be on the food waste itself. This is a more serious risk if you're composting in a single large container because then a rogue fruit-fly-infested food scrap could contaminate your whole composting operation rather than just one small container among many.

One idea for reducing this risk, inspired by this page, is to freeze food waste before adding it to your compost bin. I don't know exactly how long to freeze for, but freezing longer is safer.

If you don't have enough room in your kitchen freezer, you can get a separate, small freezer for as little as ~$100 on Amazon.

Aeration

If you want the composting to be fully aerobic, you'll probably need to turn the compost periodically. This is easier to do if you have a single large composting bin. Unfortunately, if there's a risk that tiny animals are present in the compost (see next section), then mixing the bin contents may crush some of those creatures.

Besides stirring, you can try ventilating in other ways. University of Illinois Extension (n.d.):

Other folks attempt to improve aeration in holding units by adding one or more ventilating stacks or by poking holes into the pile. Ventilating stacks need to be placed into the center of the bin prior to making a pile. Stacks can be made out of perforated pipe, a cylinder of wire mesh or even a bunch of twigs loosely tied together. PVC pipes should be at least one inch in diameter with holes drilled randomly along the length. They can be inserted vertically or horizontally.

A big open question: Do tiny animals remain?

My biggest current source of uncertainty about the proposed invertebrate-free composting method is whether microscopic animals such as nematodes might remain in the compost, even if the container has no visible invertebrates. I hope to eventually explore this issue more, and until it's resolved, I can't give an unqualified recommendation to the methods I've proposed.

We might hope that pre-freezing your food waste would reduce the risk of residual invertebrates, but small invertebrates can be hardy. Steel et al. (2013) explain (pp. 108 and 117):

Nematodes are omnipresent in composts (on average 26 ind./g dry weight compost[...]) and are active in virtually all stages of the composting process, except during the heat peak where they can be virtually absent [...].

We [...] demonstrated that survival of nematodes during compost heat peaks is possible, even for temperature peaks up to 60°C. This is much higher than expected based solely on simple laboratory experiments aimed at identifying temperature limits of nematodes. Both our field and lab experiment indicate that Aphelenchoides sp. and Panagrolaimus sp. are able to survive higher temperatures in a compost environment, as they were present before and immediately after the (induced) heat peak. Because many juveniles could be recovered directly after the induced heat peak, these nematodes may rely on resistant dauer stages or eggs for survival. [...] The precise mechanism responsible for nematode survival in compost, however, remains to be described.

If nematodes can survive such harsh hot temperatures, it's plausible some could survive freezing as well? So I'm not confident about the ability of pre-freezing food scraps to prevent nematodes. Maybe pre-freezing for very long periods (months?) would be more likely to work, but this requires a lot of freezer space to store all those food scraps waiting to be composted.

Maybe extreme amounts of pre-heating of food scraps would kill nematodes, such as microwaving the food scraps at high temperature? Beyer et al. (1999) explain regarding mushroom compost: "One component of composting is steam pasteurization that eliminates most insects and nematodes from the substrate. Steam pasteurization takes place in a room where the substrate is layed out in beds or trays at a depth of 10 to 18 inches. Pasteurization requires 2 to 4 hr when the compost and air temperature is held to at least 140°F. The substrate containers are also steam pasteurized during this process." This seems like a pretty intense process, and I wonder if it's possible to achieve the same degree of invertebrate removal in a lower-tech and less energy-intensive way. My guess is that you wouldn't need to heat nearly as long if you're only heating a few food scraps that have a large surface-area-to-volume ratio?? Unfortunately, such pre-heating would be extremely painful for whatever bugs were present in the food scraps, and if this method didn't work, or if you accidentally introduced microscopic invertebrates to the compost bin in some other way that rendered your pre-heating efforts irrelevant, then these painful deaths by pre-heating would be a big moral cost for no benefit. I suppose you could significantly reduce this moral cost by first freezing the compost for a long time, to kill most of the invertebrates in a less painful way than heating, and then heat the frozen food scraps to kill any remaining invertebrates—though obviously this two-step process would take even more time and energy.

I wonder if the anaerobic, acidic conditions created by Bokashi fermentation could kill nematodes? Would it be difficult to ensure that every last nematode in your food scraps was killed in this way? Would dying of anoxia or acid be less painful than dying of intense heat?

Another issue is that, in principle, invertebrates as small as mites and springtails may be able to enter the air holes in your compost containers. Hopefully there wouldn't be many such animals crawling around in your house, though at least dust mites are likely abundant in your living spaces. I don't know if dust mites colonize compost.

Disposal of finished compost

Finished compost might still contain some invertebrate-edible organic matter, and putting it in your garden or elsewhere outdoors might feed some bugs. The nutrient-rich compost might also increase plant growth and thereby create more bug-edible organic matter that will increase the number of invertebrate births and deaths. To avoid these problems, it seems best to instead dispose of the finished compost in the trash. (Or maybe you could bury it deep in the ground outside? Is it possible to bury compost deep enough that earthworms and other soil fauna won't reach it? If you do dig in the soil, it's probably better to use a digging fork than a shovel to break the ground because shovels have more blade surface area, making them more likely to cut worms in half.)

If you're less hard-core about preventing as many invertebrates from being born as possible, you could use the compost in the normal ways that compost is used. At least you didn't create loads of invertebrates along the way toward getting that compost.

If you already buy compost as a garden soil amendment, then replacing that with your own invertebrate-free compost end product seems good because then you avoid creating demand for compost created by other people. As far as I'm aware, basically all small-scale and large-scale composting operations sadly bring lots of invertebrates into existence.

If you dispose of your finished compost in the trash, you can seal the composting container with a plastic bag so that it won't leak/spill before putting it in a garbage can. Alternatively, you could pour the finished compost into a separate bag for throwing out and then reuse the original composting container for another round of composting. It's probably good to wash the composting container between composting rounds in case the previous composting round accidentally had invertebrates that could get transferred to the next composting round.

My remaining todos

I've only begun to try out invertebrate-free composting and don't yet have experience with how well it works. Some things I'd like to explore more in the future:

1. Do holes in plastic containers poked with a pin allow fruit flies or other bugs to enter?
2. Can bugs get in a container covered in speaker cloth, perhaps under the rubber-band seal?
3. I'd like to find a single, large plastic container to compost in. Ideally it would be wide and short so that it would have ample surface area and thus more air access.
4. Get a powerful microscope with which to look for microscopic animals like nematodes, to make sure they're not present in the compost.
5. Find a nematologist or other expert to ask about my concern about nematodes surviving freezing and populating the compost bins.
6. Can I send compost samples to a lab for invertebrate testing?

Another idea: Hot-container composting?

Wikipedia ("Hot container composting") describes composting in an insulated container in order to retain heat and speed up the decomposition process. Because the compost is relatively sealed and reaches high temperatures, I would guess it contains few invertebrates (even nematodes?) if the process is done properly. As mentioned before, one concern with heating is that it may be a particularly painful way to kill whatever animals may already be present in the input food waste. Hypothetically I suppose you could freeze food waste for a while in an effort to kill whatever invertebrates it contains and then do hot-container composting. Freezing seems intuitively much less bad than heating to death, and freezing is one of the (less recommended) euthanasia methods for insects.

TODO: Eventually maybe I'll try hot-container composting to see how easy or difficult it is. If possible, I could look to see if the compost contains any invertebrates when it's hot.