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Vermifiltration: Worms At Work

Most of us already know how effective worms are at turning kitchen waste into rich garden goodness, but there are other ways they can help around the home.

Composting worms are identified by their red colour and surface-dwelling nature.

Worm farms have become an increasingly common sight in productive backyards and urban gardens over the last few decades. And given their compact design, lack of odour and minimal labour investment, it’s easy to see why.

While worm farming (also known as vermicomposting) remains one of the best ways to convert organic waste into soil-improving compost, the system also has the potential to do some heavier lifting for us around the house. Recent studies have shown vermicomposting is also an excellent option for treating grey and black wastewaters, stabilising heavy metals in soils and even degrading persistent chemicals within our soils.

How They Work

There’s a difference between composting worms and your regular earthworms, but the way they process their ‘food’ is the same. Earthworms are a burrowing worm that prefer darkness, while composting worms are surface dwellers, love nutrient-rich environments and are usually smaller and red in colour. While both comprise a range of species that will effectively process waste, the most popular is a composting worm called Eisenia fetida, also known as the red wriggler or tiger worm.

With a high tolerance of both a wide pH and temperature range, the red wriggler is chosen for its ability to consume a diversity of food sources, from food scraps to manures and even industrial sludge. These worms can even help to decompose pesticides, herbicides and other hard-to-break-down chemicals, making them incredibly versatile and powerful recyclers.

Worms thrive in an environment that has a ratio of approximately one part nitrogen to 20 parts carbon which not only makes them more space efficient than regular compost, which requires a higher amount of carbon (a 1:30 ratio), but means worms can deal with larger amounts of food waste.

Magic Microbes

Without teeth, worms eat by grinding their food with tiny pieces of dirt and sand they also consume. Grinding of food allows for digestive enzymes and gut bacteria to break down food sources. This process helps to neutralise pH and convert food into plant-available minerals. But the real magic comes when worms poo. They excrete castings, which happens to be a perfect habitat and food source for a super high level of beneficial microbes.

These magic microbes help to convert harsh waste chemicals, such as ammonia, into plant-available nutrients. Worm castings also contain humus, which is a spongy, life-supporting substance, but the important point here is worm castings are completely chock full of beneficial microbes that work to cycle nutrients and outcompete soil pathogens. By doing this, they are a huge help in kickstarting and feeding biological cycles in the soil food web that contributes massively to healthy soil.

In this way worms can be considered ‘ecosystem engineers’, a species majorly influencing its environment. Similar to a beaver building a wetland to slow down and spread water through a landscape, worms dominate soil processes to create habitat for beneficial soil microbes that in turn create fertile top soil.


Clockwise from top left Earthworms are soil aerators and aid with water and oxygen distribution; Nutrient-loving plants will thrive in and complement vermifiltration systems; The castings worms produce have endless benefits for your garden; A bathtub should be big enough to process most homes’ greywater. Illustration By Samantha Haworth

Water Filtration

One great use for worm farms is filtering household wastewater. Studies have shown that when implemented accurately and effectively, average domestic wastewater, including sewage and greywater, can be filtered through a worm farm and be safe enough to irrigate fruit trees, perennial crops and even some vegies intended for cooking. Known as ‘vermifiltration’, wastewater can be diverted by redirecting plumbing from bathrooms, laundries and kitchens into worm farms. If you are lucky enough to live in a raised house with exposed plumbing, or on a sloped block, this can easily be achieved with gravity alone. Otherwise, greywater can be pumped into the worm farm via a storage tank.

Vermifiltration is effective because humus and worm castings act as a huge filter trap for pretty much everything in wastewater that isn’t actually water, while also helping to neutralise pH (something that septic systems don’t typically do). As the worm farm traps and slows water, worms eat the solids in the wastewater as food. From here it’s the same as a standard worm farm; beneficial microbes increase in population, outcompete pathogens and turn wastes into plant-available nutrients. Common wastewater pathogens like E. coli and salmonella are actively eaten by worms and are further outcompeted by beneficial microbes via worm castings. After water exits the system, it’s pure enough to irrigate most crops with the exception of raw leafy greens.


A vermifiltration system doesn’t have to be on a grand scale – bathtub-built worm farms are generally an ideal size for filtering household wastewater – but there are some important considerations if you intend to implement one at your place. No major alterations are needed from conventional worm farms, just ensure you have a thick layer of gravel or river stones at the base of the system. This not only helps worm tea drain out and ensures the system remains aerobic, but many important microbes including nitrifying bacteria live in this layer.

Slower water inputs will lead to higher levels of water remediation. This can be achieved by having a thick layer of mulch on top or spreading distribution through a higher number of holes. PVC or agricultural pipes work well.

Planting nutrient-loving plants directly into the system will aid the filtration process. Worms are sensitive to salts, so aim to use low impact soaps and shampoos in the house. Information on building worm farms for both wastewater and organic scraps is readily available, so be sure to research what’s best suited to your specific situation as well as any regulations your local council requires.

Creating Wetlands

You can increase filtration by diverting the drained water into a bed of reeds. This can be useful if you are concerned about nutrients leaching through your soil layer into surrounding ecosystems and groundwaters.

If you are a bit more ambitious and have the space to do so, household worm-farm filtration systems can operate as starting cogs for an aesthetically pleasing and functional wetland system. Not only does this increase filtration properties, but creating a chain of reed beds and wetland ponds offers important benefits for local wildlife, habitat/ microclimate creation and crop production. This requires more planning, but if it’s done well could completely transform a garden and perfectly complement a productive permaculture system.

Building Soils

In permaculture circles, worm castings are often touted as excellent soil improvers and fertilisers – but sometimes it’s a little unclear why. Firstly, worms are amazing at quickly producing humus. Unlike conventional compost, which can take several years to mature into humus, worms excrete humus in their castings which provides instantaneous soil- improving benefits.

As well as pests and diseases, worms have the ability to remediate heavy metal contamination in soils

The creation of humus is not the only benefit to soil quality. Through their role as expert recyclers, worms and their microbial allies produce high levels of plant- available nutrients – again at levels much higher than conventional compost. Burrowing actions of earthwormsaerate soils and spread fertility, while the large amounts of beneficial bacteria in worm castings hugely increase the biological activity of soils. Along with providing nutrients, castings contain growth hormones that both enhance seed germination and aid the development of young plants.

Deterring Nasties

Insect pests as well as a range of bacterial and fungal diseases have been observed to be reduced by applying worm castings and teas to crops. Because of its water- holding capacity, humus helps decrease plant disease by reducing water stress. It also helps build positive interactions which are occurring in the soil food web. Specifically, the castings increase the numbers of beneficial microbes available to outcompete pathogen microbes seeking to infect plants via roots and leaves.

As well as pests and diseases, worms have the ability to remediate heavy metal contamination in soils. It’s not uncommon to find a surprising amount of heavy metal contaminants in cities and built-up areas. It’s a challenging issue, and it’s worthwhile knowing all the options when it comes dealing with toxic legacies, but don’t discount worms as way to give you a helping hand with the clean- up process.

Lead is particularly common in cities due to lead-based paints used on housing while chromium is commonly found around old industrial precincts due to its usefulness in a range of manufacturing processes. Areas near mining operations, conventional livestock farming and landfills may also see high levels of heavy metals in the landscape. These contaminants, when consumed via dust, water or food can lead to health conditions over time. Because of this, anyone keen to grow food in an urban setting should be aware of any potential contaminants. You could start by checking the website, which is a global quick-reference guide that maps soil, dust, water and paint samples, and which publishes the levels of as many as eight contaminants.


Stabilising  Contaminants

Vermicompost has the ability to stabilise heavy metals in humus. While the science itself is pretty heavy, at a basic level, by binding with humus, metals may not only change to less-toxic forms (called speciation) but also become more difficult to be absorbed by living organisms. This area has been heavily studied and there have been contradictory results due to the unpredictability of natural processes, so it is always recommended to conduct soil tests before and after any remediating actions you take at home.

Earthworms themselves also have the ability to accumulate heavy metals in their tissues without any detrimental effects on their health. So by applying vermicompost to contaminated soil or vice versa, worms will accumulate metals over a period of several months. Depending on the metal, this process can see metal removal ranging from between 20 and 70 percent!

Get A Wriggle On

The more we learn about worms and their amazing ability to process all sorts of waste and turn it into a hugely valuable soil improver, the more we can appreciate their enormous potential to complement our every permaculture systems, regardless of the scale.

Whether you have a small homemade worm farm to process your organic waste from the kitchen or a complex system of wetland areas working to filter your home’s wastewater, putting worms to work means you’re not only reducing waste and producing a valuable soil improver, but you’re creating beneficial microbial life which will battle pests and diseases in your patch.


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