*JOHN GRANZIEN **LLOYDKING
*
Leading Hand Water and Sewage Operator /
Plumber
** Water and Sewage Operator
SUMMARY
The
Esk Shire Council has recently installed a Vetiver Grass Wetlands System to
treat sewerage effluent at Toogoolawah in South East Queensland. The sewerage
treatment plant is situated on a 22-hectare site on the northern edge of town.
The
aim of this scheme was to improve water quality before the effluent discharges
to the natural wetlands. The biggest problem with the quality of the effluent
is its high nutrient loading. With the recent changes to license conditions
imposed by the Environmental Protection Agency, the existing treatment plant no
longer complies with the license and an upgrade of the plant was required.
Instead
of traditional upgrades, a new and innovative nutrient-removal technology
recently developed in Queensland by the Department of Natural Resources and Mines,
is being implemented at Toogoolawah.
The
Vetiver Grass wetlands have been constructed in rows following the contours to
allow good contact between the grass and the effluent. The Vetiver Grass takes
up the water and in particular the grass will remove the nutrients from the
water that passes through it,
As
Vetiver Grass system is very effective in removing nutrient loads, it is
expected that once the wetlands is properly established there should be no
release of sewerage effluent from the treatment plant except in times of heavy
rainfall.
COUNCIL OF THE SHIRE OF ESK
This scheme will provide a large-scale
prototype of possible sewerage treatment schemes that can be used throughout
western Queensland and other locations where there is plenty of land and where
the local government doesn�t want to pay for installing and operating high cost
solutions.
INTRODUCTION
The
Esk Shire.
The
Esk Shire is situated on the north western edge of Brisbane and covers an area of 3 946 square kilometres. However the
population of the shire is only about 14,800 people and this is scattered over
most of the shire. The shire is 125 kilometres long (running north/south) and
70 kilometres wide.
TOOGOOLAWAH
The
town of Toogoolawah is situated right in the centre of the shire. The town has
a population of approximately 1,000 persons and provides the local people with
a quiet rural lifestyle about an hour and a half drive from Brisbane.
THE
PROJECT
Toogoolawah
Sewerage Plant
The
sewerage scheme for Toogoolawah was built in 1970 and the treatment plant was
constructed as a primary sedimentation (Imhoff Tank) followed by three sewerage
ponds. The effluent from the ponds was designed to flow down into a swamp area
before it entered into the local creek. The plant construction was based on a
very simple design but it is effective. With the recent changes to license
conditions imposed by the Environmental Protection Agency (EPA) the plant no
longer complies with the license and so an upgrade of the plant was required.
The
main problem with the existing sewerage effluent was that while passing through
the three ponds the nutrients were providing an environment for the production
of high concentrations of algae thus high pH levels. Various
options were considered such as a nutrient removal plant, a sand filter or a
rock filter. These are expensive options and would require expensive ongoing
operational costs. Utilities Engineer Mr. Ralph consulted Mr. Paul Ttuong from
Veticon Consulting and it was decided to introduce a wetland system. They then
considered a Vetiver Grass wetlands system that would take up most of the
water, as well as remove nutrients and heavy metals etc. from the sewerage effluent.
VETIVER
SYSTEM
Introduction
Application
of the Vetiver System (VS) for waste water treatment is a new and innovative
nutrient removal technology recently developed in Queensland by the Department
of Natural Resources and Mines, NRM, (Truong and Hart, 2001). It is a green and
environmentally friendly wastewater treatment technology as well as a natural
recycling method. Its end-product has several uses including animal fodder and
material for organic farming.
Vetiver
Grass
VS
is based on the use of vetiver grass (Vetiveria zizanioides L.), which was
first recognised early in the 1990s for having a �super absorbent�
characteristics suitable for the treatment of wastewater and leachate generated
from landfill in Queensland (Truong and Stone, 1996). Research conducted by NRM
showed that Monto vetiver grass has a fast and very high capacity for
absorption of nutrients, particularly nitrogen and phosphorus in wastewater. In
addition it has a very high water use rate and tolerant to elevated levels of agrochemicals
and heavy metals in the effluent. As a result of these findings, presently VS
has been used successfully for these purposes in Australia, China, Thailand,
Vietnam and Senegal (Truong and Hart, 2001; Truong, 2000).
Australian
Research Results
A
demonstration site was set up at the Beelarong Community Farm at Morningside,
Brisbane to obtain quantitative data on the effect of VS in improving its
quality under field conditions and also in reducing the volume of effluent. In
this DNR and EPA funded project, VS was used to treat the discharge from a
septic system. Vetiver grass was selected after the failure of other plants
including a variety of fast growing tropical grasses and trees, and crops such
as sugar cane and banana to absorb the effluent discharge from the septic tank.
After five-month growth, vetiver was more than 2m tall and a stand of about 100
vetiver plants in an area less than 50m2 have completely dried up the effluent
discharge. Other applications are used or being trialled at Armidale, Lithgow
and Beenleigh.
Results
of MEDLI Model Simulation
For
the Toogoolawah sewage treatment plant Before any work commenced, effluent being discharged had the
following characteristic
Daily
output 350 kl
Nitrogen
concentration at 21mg/L
Phosphorus
level of 9 mg/L
The
MEDLI model simulation predicted that less than 3ha of land is needed to treat
the entire effluent output to comply with EPA licensing conditions.
However
if the effluent is pre-treated in the ponds to reduce N and P concentrations by
approximately 10% before releasing into the vetiver plots, the land area needed
would be less than 1.5ha
TREATMENT
PROCESS CHOSEN FOR TOOGOOLAWAH
Introduction
A
three-phase treatment program was adopted:
Phase
1:
Alum sludge and backwash waste water entered into sewage reticulation system.
Phase
2:
Preliminary treatment in the ponds.
Phase
3:
Main treatment by vetiver wetlands.
Phase
1. It was decided to put the backwash
waste water and sludge from two clarifiers at the water treatment plant into the
sewerage reticulation system This method has been trialled elsewhere in the
state with success. The alum reduces the amount of phosphorous in the waste
water. It has proven successful here also.
Phase
2:
Preliminary treatment of effluent in the ponds
The effluent in the three ponds is first
treated hydroponically by the vetiver pontoons, which are able to reduce N and
particularly P loading of the effluent before releasing it to the wetlands.
Floating
pontoon design: The 21 floating pontoons were designed so vetiver plants
sitting on the pontoons and the roots suspending in the effluent. The size of
each pontoon is 2.4m x 2.4m with about 300 individual plants placed on each
pontoon. The number of pontoons required will depend on the level of nutrient
load. The number of pontoons can be increased later to ensure an effective
treatment process was achieved. Maintenance program will include replacement of
dead plants, regular harvest to encourage new growth .
In
addition, vetiver is being planted at the high water level around the ponds to
further reduce the nutrient loading and also to stabilise the pond banks.
Phase 3: Main treatment Vetiver
Grass Wetlands
After
being treated hydroponically in the 3-pond system, effluent is released by
trickle irrigation to the main vetiver grass wetlands areas.
The
vetiver wetlands design: Vetiver grass were planted in rows on approximate
contour lines to spread the flood-irrigated effluent, trapping sediment,
slowing down flow velocity during storms and increasing infiltration. The
interval between rows is at about 12 metres. Temporary earth mounds were placed
behind these rows to enable the effluent to be held back so that all the young
plants receive water. Following full establishment, when the gaps between plants
are closed and the rows will take over the work of the mounds so that the earth
mounds can be removed.
Two
separate areas have been planted and each area is fed by its own pipeline
supplying effluent from the treatment ponds. This means that both areas can be
both operated at the same time, or one of them can be taken off line and dried
out so that maintenance work can be undertaken on the grass in that area. In
between the main rows of vetiver grass, extra rows were planted to increase the amount of grass in the
area.
Figure
1: A general outline of the
treatment area.
Vetiver
planting density:
Planting
density of contour rows was approximately 10plants/linear metre.
Appropriate
layout design of these rows will ensure all effluent will remain in the
wetlands area during normal sunny days and during high rainfall period all
excess flow is directed toward the natural swamp at the lower end of the
treatment area.
A maintenance program will include
replacement of dead plants, regular harvest to encourage new growth. As vetiver
grass will be highly enriched with nutrient (as high as 2.4% N), the harvested
hay can be used as mulch or composting material, it is also highly palatable so
it can be used for fodder as well.
MONITORING
PROGRAM
In
conjunction with the treatment program, monitoring of both surface and
sub-surface flows is also being carried out to ensure adequate treatment and to
provide data for the site management such as quantity and frequency of
irrigation schedule during summer and winter; and wet and dry periods.
Groundwater monitoring wells are being installed at strategic points and will
be sampled on regular basis. Service water monitoring is undertaken at the
inlet to the plant, at the outlet of the Imhoff tank and lagoons, at the natural
wetlands below the Vetiver Grass wetlands and finally at the discharge into the
local creek.
IMPLEMENTATION
The wetlands were constructed over a six
month period. The work consisted of the following stages; Site Clearing, Ground
Preparation, Survey, Grass Planting,
Floating Pontoons, Operations of the wetlands and Nursery.
Site
Clearing
The
site chosen for the wetlands is on a 16.5 ha block of land to the east of the
Toogoolawah Sewerage Treatment Plant. About 8 ha of the site is being used for the
wetlands. The site was firstly cleared of all trees and bushes. Care was taken
to remove all large root systems.
Ground
Preparation
The
site was broken up into two areas with a road down the middle. An access road
was constructed around the northern side. About 60% of the areas to be planted
were prepared. Firstly the ground was sprayed with a herbicide to kill the
grass. The ground was then ploughed using a rotary hoe and then sprayed again
using Roundup.
Survey
and pipeline construction
Using
a laser level contour rows were pegged out across the slope for each area.
These rows were about 12 metres apart with a fall of 200 mm between each row.
Trenches were then dug along each row with the spoil used to form a mound on
the down hill side of the trench. The area is fed by a 150 dia pvc pipeline from the lagoon
outflow and controlled by 2 valves.
Grass
Planting
Two
types of fertilizer was placed in each row. This included DAP and Muriate of
Potash at a rate of 300 mg per hectare for both. The grass was delivered in
clumps with about fifty plants in each clump. The grass was planted along the
rows about 100 mm apart between each plant. Watering of the plants started
immediately after each day of planting. In some cases channels were dug to each
row to ensure that water got to every plant. The mounds downstream of each row
helped to get the water to every plant.
Once
the main rows were planted then further rows about 3 metres apart were also
planted. The main problem with watering was not to flood the plants for too
long. The best results were obtained when the grass was given a good watering
and then was given time to dry out. Planting started in early February and was
substantially completed by the end of March. In total about 25,000 Vetiver
Grass plants have been placed in the wetlands so far.
Floating
Pontoons
As
already described 21 floating pontoons have been placed on the treatment plant
lagoons to improve the water quality in the lagoons. Vigorous growth has been
seen in the Vetiver Grass plants that were placed onto the pontoons. The plants
are first placed in pots and then allowed to start to grow before they are
placed onto the pontoons. These
plants remove nutrients from the lagoons and so will improve water quality. To
aid in this removal of nutrients Vetiver grass was also planted around the edge
of the lagoons. About 6,000 plants have been used in the pontoons and the same
amount was planted around the lagoons.
Operations
of Wetlands
During
the planting stage the effluent was flooded onto the wetlands to enable the
grass to grow. In most of the areas the growth was good although nothing like
the growth of the grass on the floating pontoons. However when the grass was
flooded for too long a period of time say for more than two days length then the
grass didn�t grow or growth was reduced. The grass needed time in the early
stages to dry out. The normal operation of the wetlands did not commence until
early May and so the real vigorous growth cannot be expected until the next
summer.
Nursery
Because
there was not enough staff to undertake the planting quickly a small shaded
nursery was constructed on site to keep the plants alive during planting and to
produce potted plants for the floating pontoons. Whenever the operator of the
sewerage treatment plant turns on the effluent reticulation for washing the
sides of the Imhoff tank the plants in the nursery are watered automatically.
This nursery has proven to be very worthwhile and has been a great help in
enabling the project to succeed.
RESULTS OF SCHEME SO FAR
Vetiver
Grass Pontoons
Results
of a preliminary trial conducted on site with the first 3 pontoons, show that
vetiver established and flourished (up to 1.5m in 3 months) under hydroponic
conditions of all three ponds. These pontoons have been removed and the grass
harvested to produce about 5 new stems of grass from each original plant placed
on the pontoons. The pontoons have now become the source of Vetiver grass for
the project.
Growth
In The Wetlands
The
growth of the Vetiver grass has been varied for the first three months. Where
the grass was able to dry out between watering, the growth was good. In places
where the water lay around the grass the growth was poor. Some of the grass
was
planted late and so growth is not expected unto spring.
Water
Quality
There
is already evidence that the water quality is improving in respect to nutrient
loads.
Overall
an 88 per cent reduction in the nitrogen level, an 81 per cent reduction in the
phosphate level and approx 78 per cent reduction in faecal coliforms cfu\100ml
have been achieved so far