It may be the ecological equivalent of turning lead into
gold.
Canadian and Indian researchers are combining fly ash
from electricity generating plants, municipal sewage sludge, and ó in
some cases ó the water hyacinth plant to produce a potent soil
replacement for Indian communities. Each of these, on its own, is an
environmental menace. Together, they could hold huge benefits for worn-out
soil.
Raw materials
The background is this: coal-fired turbines generate
four-fifths of India's electricity. The 200 million tonnes of low-grade
coal that they burn each year discharge up to 100 million tonnes of fly
ash into enormous settling ponds, causing siltation, flooding, and
contamination of water sources for millions of people. (Harder grades of
coal used in North America burn more cleanly, generating only about two
percent fly ash waste by weight.) As well, every city in India produces
huge amounts of mostly untreated sewage sludge, another water
contamination risk. Finally, water hyacinth, a free floating weed
introduced from South America before 1900, now infests an estimated
200,000 hectares of Indian waterways, choking off plant, fish, and animal
growth.
Yet mixing the three materials creates a tonic, rather
than a toxic, for soils where nothing has grown for a century or more,
says Mike Powell of the University of Western Ontario. Dr Powell is one of
the lead investigators on the Land Restoration through Waste Management
project, funded by the International Development Research Centre (IDRC),
the Canadian International Development Agency (CIDA), the India-Canada
Environment Facility (ICEF), and the Indian Institute of Technology, where
his counterpart is Dr Subhasish Tripathy.
Soil replacement
With some primary treatment, sewage sludge can be mixed
with fly ash and sometimes hyacinth to yield more than just a fertilizer.
Combining the sludge's nitrogen and organic matter with the minerals found
in fly ash yields a potent soil replacement substance.
Fly ash does a lot for the soil, says Dr Powell. It
reduces bulk density, increases water holding capacity, buffers pH (soil
acidity), and adds both macro and micro nutrients. The major elements are
potassium, phosphorus, calcium, magnesium, and carbon from unbound coal.
Potential trace elements include boron, molybdenum, selenium, nickel,
copper, zinc, and many exotic elements whose functions are not fully
understood in plant physiology. The trick is getting just enough to be
beneficial, but not enough to be toxic.
Applications
So far, the data show that vegetation grown on lands
treated with this mix absorbs low levels of heavy metals. For now, the
Indian private sector is using it to grow commercial tree species for
plywood, and some sugar cane. Public-sector users have hopes to produce
non-timber forest products for local villages, such as fuel wood, animal
feed, medicinal plants, and grasses on marginal/wasteland and salt
effected soils. The researchers have also planted small plots of edible
crops to compare different ratios of ash and sludge, and to analyse the
plants for metal uptake from the reconditioned soil.
All the data to date prove that the [amount of] metal
uptake is within international guidelines, says Dr Powell. There are a
couple of exceptions in the case of lead and chromium, but even these
aren't far from the upper allowable limits. We are convinced this
technology can be used on edible crops, but caution that we are still in
the experimental phases.
Fly ash versus fertilizer
In certain badly depleted soils where climatic conditions
and long use have eroded soil and leached out nutrients, the fly ash mix
seems more effective than standard chemical fertilizers. But Dr Powell
notes that it is tricky to compare it directly with chemical fertilizer in
growing plots, because Indian planting programs hold so many variables.
In poorly operated programs where, say, eucalyptus trees
get one application of chemical fertilizer at planting and no subsequent
watering, only half of the trees may survive, growing to a spindly and
useless few centimetres in diameter after seven years. With more careful
planting and tending in good social forestry programs, harvest-ready trees
can be produced in the same length of time. The question is whether or not
this new technology produces higher yields in the same amount of time.
Biomass yields
I do not want to mislead anyone, says Dr Powell, (but) we
have preliminary data to show that we will get around two to three times
the biomass using our technology. He cautions that these are best-case
results from a private-sector plot that combined sophisticated fertilizer
and drip irrigation techniques. But if our feasibility study is any
indication, we should get from a 50 to 100 % improved growth rate. This is
only a prediction ó we'll know much more by next year.
According to Dr Powell, social forestry schemes in India
usually invest about 12,000 to 20,000 rupees (CA$420 to $700) to reforest
each hectare with chemical fertilizers. By contrast, the fly ash mix costs
about 30,000 to 60,000 rupees (CA$1,050 to $2,100) per hectare. However,
the initial reforestation is a labour-intensive process, so it provides
short-term local employment at the outset. Moreover, the trees grow bigger
and perhaps twice as many live. By the time they mature, he suggests, a
community can recoup its investment three or four times over. There's a
real financial or economic benefit to using our material.
Supporters
Current supporters of this technology include the Cuttack
Municipal Corporation, which is funding use of the fly ash mix; several
Indian states including Orissa, Uttar Pradesh, and Madhya Pradesh; and
dozens of villages rehabilitating their lands.
Dr Powell believes that once this research is further
advanced in India, it could be applied around the world in countries that
already use fly ash and sewage as soil supplements. Still, he cautions
that the mix is no panacea. High transportation costs limit its
suitability to communities near large cities like Calcutta, which have
coal-fired power plants and plenty of sewage. He adds that much research
and longer-term monitoring remains ó to determine how the mix performs
with different species of trees, plants, and agricultural crops, and to
fully assess its potential.
- Keane J. Shore is an Ottawa-based writer and
editor. (Photo: M. Powell)
- [Reference: IDRC Project Number 951400]
- ------------------------------------------------------------------------
- For more information:
- Dr Michael A. Powell, Associate Professor,
Department of Earth Sciences, Biological and Geological Building,
University of Western Ontario, London, Ontario, Canada, N6A 5B7; Tel:
(519) 661-4214; Fax: (519) 850-2334; Email: powell@julian.uwo.ca
- Dr S. Tripathy, Associate Professor
Geology/Geophysics, Indian Institute of Technology (IIT), Kharagpur, 721
302 West Bengal, India; Tel: (91) 3222-83384; Tel/Fax: (91) 3222-77194;
Fax: (91) 3222-55303 Email: trip@gg.iitkgp.ernet.in
November,2000 |
The reproduction of this
article was made possible by the kind consent of Dr.Mike Powell and
Canada's International Development Research Centre [IDRC], at whose
website idrc.ca, this and
many similar stories may be found
Testing fly- ash sludge mix |