HEAPED up in the corner of the shed is an elephant-sized mound of brown,
crumbly powder. Hesitating slightly, I thrust my fingers in, scoop up a handful
and take a cautious sniff. To my surprise, it鈥檚 as pleasant-smelling as a bag of
peat from your local garden centre, the sort of thing you鈥檇 happily dust from a
freshly-picked carrot before taking a bite. Who鈥檇 suspect that just weeks ago
this stuff was flushed down the toilet?
Here at the Redlands Shire water plant, 30 kilometres south of Brisbane,
Queensland, 40 tonnes of sewage sludge arrive every day. And every day, 40
tonnes of hungry worms set to work, devouring every last lump, converting it
into top-grade soil conditioner.
These wrigglers are farmed by a small Sydney-based outfit called Vermitech.
The company has succeeded in doing what has stumped many others: it has expanded
worm composting from a backyard hobby to a profitable, large-scale business. Its
compost is already being used on fruit and vegetables shipped to supermarkets
across Australia, and new studies appear to show that 鈥渧ermicompost鈥� is endowed
with qualities that are surprising even the most ardent worm fans.
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Worm-based sewage recycling is nothing new. People have been doing it on a
small scale for years using manure worms鈥攕maller, wrigglier, cousins of
the earthworm. The idea is to mix these worms with sewage sludge鈥攖he
solids left over after raw sewage has been through the treatment plant. As the
worms chomp on the sludge and break it down in their gut, they digest the
harmful bacteria it contains and turn it into a much less objectionable mixture
that can be spread on flower beds or crops.
There鈥檚 certainly no shortage of worm food. New York City, for example,
creates almost a million tonnes of sewage sludge each year. It鈥檚 difficult to
dispose of, and environmental regulations mean it can no longer be dumped at sea
or buried in landfills. Drying the sludge into pellets or sterilising it with
quicklime is expensive, and you鈥檝e still got to get rid of the final product.
Feeding it to the worms seems like the perfect solution.
In practice it鈥檚 not that simple. Sewage sludge contains bucket-loads of
pathogens such as Salmonellaand faecal coliform bacteria that must be
destroyed before the waste can be used on food crops. One answer is to combine
worm treatment with traditional composting. You mix the sludge with plant debris
and incubate it in heaps up to 15 metres high. As bacteria digest the sludge,
they produce heat, warming the pile to 70 掳C and killing the pathogens. Once
cooled, the mix can be fed to the worms to make a clean product that鈥檚 welcome
on the fields.
Unfortunately, precomposting makes the whole process time-consuming and too
expensive to be profitable. It鈥檚 also inherently unnatural, says Mike Lotzof,
CEO of Vermitech. 鈥淲hen you go out into the forest,鈥� he says, 鈥測ou don鈥檛 see
15-metre compost heaps steaming away, you see very small amounts of material
deposited at different times.鈥� So Vermitech is trying to do things the way
nature does, but with a level of automation far beyond the shovels and
wheelbarrows of traditional vermicomposters.
Vermitech鈥檚 worm beds are roughly 1 metre across, 1 metre deep and 70 metres
long. 鈥淎 single bed is a replication of the earth,鈥� says Lotzof, 鈥淲e have a
surface and we have a subterranean area that鈥檚 been designed for the worms鈥�
biology.鈥� Each day, a thin layer of sludge is spread on top of the bed, and an
equal amount of processed product is scraped from the bottom. The worms stay in
the top third, feeding on the fresh sludge and laying eggs. It takes about 40
days for material to move through the bed, giving eggs time to hatch and mature
so that the young worms aren鈥檛 harvested out the bottom.
As the worms swallow the sludge, their powerful gizzards grind it into small
pieces, releasing nutrients and allowing soil microbes to proliferate. The worms
then digest most of those microbes, along with the dangerous pathogens, and
absorb them. Any pathogens that might survive are simply outcompeted by benign
soil microbes that flourish in the worm casts.
Wandering through the rows of worm beds, I鈥檓 surprised at how odour-free the
place is, even in the steamy Queensland air. Lotzof explains that before they
spread the sludge on the beds, they add a secret deodorant that binds any
smelly, volatile chemicals. Then they aerate the sludge so thoroughly that it
has little opportunity to turn anaerobic and smelly.
Vermitech has had to implement strict quality control
processes鈥攃onditions in the worm bed are carefully monitored and samples
are regularly shipped to an independent lab and tested for pathogens. The worm
treatment produces a 100 to 1000-fold reduction in levels of faecal coliforms,
as well as cutting numbers of Salmonella, gut viruses and parasitic worm eggs.
The end product is so good that the New South Wales and Queensland environmental
protection agencies allow its use on food crops.
As well as disposing of sewage sludge, vermicompost seems to have benefits
for farmers too. The day after my visit to Redlands, Steve Capeness, a Vermitech
horticulturalist, drives me from farm to farm on the land north of Brisbane.
It鈥檚 a low-lying region of tea tree and eucalyptus swamps, punctuated by the
sheer spires of exposed lava cores鈥攍ike fossilised teeth鈥攖he remains
of long vanished volcanoes. In the past, flood waters deposited silt across the
region, creating a rich loam that supports a large vegetable and pineapple
industry.
Decades of intense agriculture have taken their toll, however and farmers say
the soil is giving out in places. They tell me about small, loosely controlled
trials of vermicompost. The farmers using the compost aren鈥檛 seeing superplants,
but they do believe they鈥檙e getting consistently higher yields, less plant
disease and bigger profits.
Peter Stephens, a plant pathologist with the Queensland Horticultural
Institute in Stanthorpe, is conducting more rigorous studies on Vermitech鈥檚
behalf. He鈥檚 found that carrots fed as little as 2 tonnes of vermicompost per
hectare weigh more than twice as much as untreated carrots 66 days after
planting. Stephens doubts this is due to the extra nutrients vermicompost
provides. 鈥淭wo tonnes per hectare is virtually nothing,鈥� he says. 鈥淚 think it
could be due to plant hormones.鈥� Indeed, the soil microbes that flourish in the
casts extruded by worms produce a variety of hormones such as indoleacetic acid,
gibberellins and kinetins, and other compounds such as humates, which are known
to modulate plant growth.
Clive Edwards, a soil ecotoxicologist at Ohio State University in Columbus
who originally developed some of the methods now used by Vermitech, is also
investigating plant hormones. He has found that vermicompost hormone extracts
consistently produce the same level of increased growth as the vermicomposts
themselves.
Edwards believes that the plant hormones and the soil microbes which produce
them may be the crucial difference between vermicomposts and traditional,
worm-free composts. 鈥淲henever we do a trial,鈥� says Edwards, 鈥渨e always put at
least one traditional compost in there as a comparison, and every time we鈥檝e had
much, much better results with vermicompost.鈥� He suspects the high temperatures
that occur during traditional composting kill the beneficial soil microbes.
鈥淲e鈥檝e done studies on the microbial communities in the two materials,鈥� Edwards
says, 鈥渁nd there鈥檚 no comparison. We get a much more diverse microbial community
in vermicompost than we do in traditional compost.鈥�
Controlled trials also suggest that vermicomposts may suppress plant disease.
A recent study by Stephens, for example, found that the severity of the fungal
disease clubroot was significantly reduced in broccoli plants treated with one
of Vermitech鈥檚 products. Edwards has seen similar results for other diseases in
studies using vermicomposts. No one is sure of the exact mechanism, but Edwards
believes the beneficial soil microbes that flourish in worm casts may be
outcompeting the plant-pathogenic ones.
While much of the benefit from traditional composts stems from the nutrients
they provide, vermicomposts serve instead to inoculate the soil. 鈥淲hat we鈥檙e
doing is growing bacteria, lots of bacteria,鈥� says Capeness. In other words, a
little goes a long way. Farmers spread as much as 10 tonnes of traditional
composts per hectare. But vermicomposts are often used at rates as low as 1
tonne per hectare鈥攕o little that you might not even spot it as you walk
across a field.
This avoids one of the serious drawbacks associated with recycled sewage
sludge: it contains significant levels of heavy metals such as cadmium.
Environmental agencies impose strict limits on how much of these metals can be
deposited on land. Using one-tenth as much compost as normal means you take 10
times as long to hit that limit鈥攕everal centuries in some cases.
The Redlands plant processes about 15,000 tonnes of sludge per year, and
Vermitech hopes to open a larger plant in Sydney towards the beginning of 2002.
This could reduce the cost of the city鈥檚 sludge management by up to 25 per cent
per tonne compared with current methods, Lotzof claims.
Vermicomposting is also being investigated in the US. In small-scale studies,
Bruce Eastman, manager of the Orange County Environmental Protection Division in
Orlando, Florida, has attained pathogen destruction similar to Vermitech鈥檚. He鈥檚
now organising a larger study with help from the US Environmental Protection
Agency. 鈥淭hey鈥檝e indicated to me that they would be willing to accept
vermicomposting as an alternative stabilising methodology [for sludge] once
we鈥檝e come up with the standard operating procedures,鈥� Eastman says.
Meanwhile other companies, such as Sunburst Nominees at Mount Gambier, South
Australia, are developing ways to harness hungry worms to digest municipal
waste鈥攖hings like paper, cardboard and textiles. And in the long term,
vermicomposters will have to become even more sophisticated, says David Murphy,
a consultant to the vermicomposting industry based in Maryborough, Victoria. To
be successful, he says, they will have to be able to alter their product as
required, tweaking it to match different soil conditions such as pH, for
example.
Back on the farm, the Sun is sinking and I鈥檓 talking with a farmer. He鈥檚
disappointed with many of the soil products that salesmen try to foist off on
him. 鈥淎nd then,鈥� he adds, 鈥渢hey come along and try to sell you human waste.鈥� But
this time he鈥檚 not complaining. The stuff actually works.