THE USE OF VETIVER GRASS WETLANDS
FOR SEWERAGE EFFLUENT   TREATMENT
IN ESK SHIRE QUEENSLAND AUSTRALIA


 

 

*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.

         

 

                     Software: Microsoft Office

     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.

 

 

Software: Microsoft Office

 

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


 

 

 

AMMONIA

TOTAL

N

TOTAL

P

15-10-2002

PREVIOUS

EFFLUENT

9.1

20

6.3

8-4-2003

LAGOON

INFLUENT

49

58

6.6

 

LAGOON

EFFLUENT

0.65

15

3.3

 

WETLAND

EFFLUENT

0.57

6.7

1.2

20-5-2003

LAGOON

INFLUENT

34

41

9.2

 

LAGOON

EFFLUENT

2.9

14

4.4

 

WETLAND

EFFLUENT

0.072

7.3

2.1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CONCLUSION

 

The information above and the results achieved so far do indicate that the Vetiver Wetland System is treating the effluent to a better standard. Also the system is very easy to implement and is a very low cost method for treating effluent and leachate in both domestic and industrial scenarios.