Centre for Plant & Water Science - Central Queensland University

Centre for Plant & Water Science 2008 Annual Report
GREEN WASTE – IS IT A WASTE OR AN UN-TAPPED RESOURCE
SUMMARY
Recent trends in waste management emphasise that all wastes should be rigorously assessed
for their alternative uses before being discarded as a ‘waste’. In support of this concept, we
have explored various ways of utilizing shredded green waste that was produced at
Rockhampton city council.
The first trial involved testing the green wastes for weed seeds, pathogens, heavy metals and
organic contaminants. Our tests indicated that the greenwaste generated at Rockhampton
contained none of the above components at levels that would prevent them from being used
for various purposes. Our field trials to use the green waste as a source of ‘mulch’
demonstrated significant benefits to plant growth. However, this use did not become popular
due to lack of demand and high transportation costs. Mixing of green waste with coal in
power generation at Stanwell Power station proved a feasible option, but dedicated units
were required to continue with this practice. Establishment of a power generating plant that
relied on the wastes (e.g. green waste, biosolids, saw dust, paper, etc.) as the feed stock was
also investigated, but this too required huge investments in infrastructure. The current trials
therefore focussed on conversion of green waste into biogas, biochar and landscape mix.
Two major options are being explored to test further use of shredded green waste. The first
trial explored the potential of producing biogas and biochar from the green waste. Samples
of green waste have been sent for analysis by BEST Energies. Economic viability of this
option is currently being determined.
The second option consisted of mixing green waste with other wastes such as biosolids,
water treatment sludge (alum), cow paunch and limestone tailings, with the view to
producing a ‘landscape mix’. Preliminary analysis suggested that none of the above
ingredients could be used on their own to synthesize a plant growth media, due to
constraints in pH, salinity or heavy metal compositions. Thus, trials are being carried out to
mix these ingredients at different proportions, and to test their effects on plant growth.
Two landscape mixes were prepared by mixing the above ingredients at different
proportions. The effect of these mixes on plant growth is currently being tested on (a)
vegetable crops, (b) native landscaping plants (see Fig 1) and (c) turf grass.
Fig 1. The effects on plant growth of two landscape mixes prepared from green waste and
other urban wastes generated at Rockhampton Regional Council.
PROJECT STAFF Principal Investigator: Assoc Prof Nanjappa Ashwath
Co-Principal Investigator: Andrew Rank, Sunita Lata
Others:
Lindsay Best, Craig Dunglison
FUNDING Rockhampton Regional Council
INCOME $24,225
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