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The concept of the
‘hydroponic wetland’ was developed from studies undertaken
over the past twenty years and represents a new and innovative
approach to the sustainable management, re-use and tertiary
treatment of wastewater, including treated domestic effluent and
saline production water.
Briefly, wastewater
is used for the large scale hydroponic production of plants.
Using a ‘pot-in-pot’ system the plants are grown in 400 mm (27L)
pots sunk into trenches, filled with crushed rock, containing
the wastewater (note that additional nutrients can be added to
the wastewater, if required, to provide a suitable nutrient
solution to support plant growth).
Wastewater is provided to each trench through slotted,
agricultural drainage pipe laid along the floor of the trench.
It rises upwards through the crushed rock and nutrients
contained in it are removed from it by the plants growing in the
pots. The wastewater enters the trenches under gravity at a
pre-determined rate and surplus effluent is discharged through
an overflow drain consisting of slotted, agricultural drainage
laid along the length of the trench immediately below the upper
surface of the crushed rock. Since the trenches are maintained
full of wastewater any rain entering through the top surface of
the crushed rock is immediately discharged through the overflow
pipe, ensuring that the rainwater is prevented from mixing with
the effluent in the trench and is preferentially discharged to
the wider environment during heavy rain events. When plants are
harvested from the trenches the nutrients that they have
assimilated are also harvested and removed from site.
The adoption of a
‘pot-in-pot’ approach to hydroponic cropping allows flexibility
in the options that can be implemented in the wetland.
Native tree and shrub species that experience a natural
environment not dissimilar to that provided by the wetland
include a variety of riparian and rainforest species and the
book ‘Trees and Shrubs’ published in 1991 by the
Queensland Forest Service allows species likely to do well
in the wetland environment to be identified. With saline
production water chloride excreting mangroves, for example the
river mangrove or grey mangrove, can be grown as a hedgerow crop
in the trenches to remove chloride from the water and harvested
for cattle forage.
One wetland is
presently operating at Thunderbird Park near Mt Tambourine in
southeast Queensland and a second is being constructed to
provide tertiary treatment of the 0.65ML/day of secondary
effluent produced by the Kyogle STP in northern NSW.
At Kyogle the wetland has been designed to ensure that water
overflowing from the system, and discharged to the Richmond
River, reaches the NSW EPA’s provisional standard for
discharge to sensitive waters.
Charles-Edwards, D.A. (1982) In: Physiological Determinants
of Crop Growth, Academic Press, Sydney.
Charles-Edwards, D.,A. and O’Keeffe, M.S. (2003) In: An
Australian Environmental Handbook, Sci-Plan, Brisbane
Sci-Plan (1997) Effluent Re-use R&D Program: Carole Park WPCW
– Final Report. Ipswich City Council.
Sci-Plan (2007) Draft Operational Management Plan, Kyogle
Hydroponic Wetland, Kyogle Council.
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