Introduction

The Vetiver System (VS), which is based on the application of vetiver grass (Vetiveria zizanioides L, also known as Chrysopogon zizanioides) was first developed by the World Bank for soil and water conservation in India in the 1980s. In addition to its very important application in agricultural lands, R&D conducted in the last 20 years have demonstrated that vetiver grass is also very effective for mine site rehabilitation and wastewater treatment. These are due firstly to its high tolerance levels to adverse conditions, highly tolerant to heavy metal toxicities and other pollutants and secondly to its ability to tolerate and absorbed large quantity of nutrients in the soil or water. In addition research on structural and shear strength of vetiver roots has shown that VS can be applied with confidence in steep slope stabilisation. As a result VS is now increasingly used worldwide for environmental protection purposes, as an innovative, effective, green and low cost alternative to the conventional chemical or physical solutions.

VS has been successfully used for mine waste rehabilitation, phytoremediation tailings dams, steep slopes stabilisation associated with bunds and other water management structures in Australia, Chile, China, Indonesia, South Africa, Thailand and Venezuela.

VS has also proved highly effective in both sewage effluent and industrial wastewater treatment in several countries.

Vetiver grass special characteristics suitable for environmental protection purposes

Vetiver is a fast growing, perennial grass native to the South and South-East Asian regions. It has stiff and erect stems and will grow to approximately 1-2m in height forming dense hedges when planted close together. These hedges can stand up to relatively deep-water flow, reducing flow velocities and trapping sediment. Vetiver grass has a deep, penetrating, massive, finely structured root system, reaching 3-4m depth in the soil in its first year of growth.

Vetiver grass is both a xerophyte and a hydrophyte and, once established, is not affected by droughts or floods.

The unique characteristics of Vetiver can be summarized as:

• Adaptability to a wide range of soil and climatic conditions,
• Can be established in adverse conditions: sodic, acidic, alkaline and saline soils,
• Mature plants are tolerant to extreme heat (50oC) and frost (-14oC).
• High level of tolerance to heavy metal toxicities and other pollutants
• High level of tolerance and absorption of large quantity of nutrients in the soil or water.
• Tolerant to drought due to deep and extensive root system,
• Vetiver can withstand burning, slashing and moderate tractor traffic,
• Resistant to infestation from most pests, diseases and nematodes.
• Under nutrient rich and available soil moisture vetiver grasss can produce up to 130t/ha of dry biomass
• Vetiver grass is extremely long-lived, have been observed to persist for over 50 years.

Tolerance to High Acidity, Aluminium and Manganese Toxicity:

Researches showed that with N and P fertilisers, vetiver growth was not affected even under extremely acidic conditions (pH = 3.8) and at a very high level of soil Aluminium Saturation Percentage (68%). Field-testing confirmed that vetiver grew satisfactorily at soil pH=3.0 and aluminium level between 83-87%, which is extremely high as growth of most plant is affected at level less than 30%.In addition vetiver growth was not affected when the extractable manganese in the soil reached 578 mgKg-1, soil pH as low as 3.3 and plant manganese content was as high as 890 mgKg-1.

As a result of its high tolerance level to Al and Mn toxicity, vetiver has been used successfully for erosion control in Acid Sulfate Soils with actual soil pH around 3.5 and oxidised pH is as low as 2.8.

Tolerance to High Soil Salinity and Sodicity:

With the salinity threshold level at ECse = 8 dSm-1 vetiver grass compares favourably with some of the most salt tolerant crop and pasture species grown in Australia such as Bermuda Grass (Cynodon dactylon) with threshold at 6.9 dSm-1; Rhodes Grass (Chloris guyana) at 7.0 dSm-1; Wheat Grass (Thynopyron elongatum) at 7.5 dSm-1 and barley (Hordeum vulgare) at 7.7 dSm-1

With adequate supply of N and P vetiver grew satisfactorily on Na bentonite tailings with Exchangeable Sodium Percentage of 48% and a coalmine overburden with an exchangeable sodium level of 33%. Moreover the sodicity of this overburden was further exacerbated by the very high level of magnesium (2400 mgKg-1) compared to calcium (1200 mgKg-1).

Tolerance to Heavy Metals:

Table 1 shows that vetiver is highly tolerant to As, Cd, Cr, Cu, Hg, Ni, Pb, Se and Zn.

Table 1: Threshold levels of heavy metals to vetiver growth as compared with other species

Distribution of Heavy Metals in Vetiver Plant:

The distribution of heavy metals in vetiver plant can be divided into three groups:

• Very little of the As, Cd, Cr and Hg absorbed were translocated to the shoots (1% to 5%)
• A moderate proportion of Cu, Pb, Ni and Se were translocated (16% to 33%) to the top and
• Zn was almost evenly distributed between shoot and root (40%).

Applications of Vetiver sytem in mine rehabilitation

With the above extraordinary morphological and physiological characteristics, vetiver grass has been used successfully for steep slope stabilisation and phytoremediation of mine tailings around the world.

Australian mines

• Infrastructure and mine waste: Coal, gold, zinc, lead, bentonite and bauxite mines
• Mine tailings: Coal, gold, bentonite tailings and bauxite redmud

South Africa

• Infrastructure and mine waste: Gold, Platinum and diamond mines
• Mine tailings: Gold and Platinum tailings

China

• Infrastructure and mine waste: Zinc, lead and bauxite mines
• Mine tailings: Zinc, lead tailings and bauxite redmud

Thailand

• Mine tailings: Lead tailings

Chile

• Mine tailings: Copper tailings

Venezuela

• Infrastructure and mine waste: Bauxite mine
• Mine tailings: Bauxite redmud

Future work in Chile and South America

The author is now cooperating with Fundacion Chile to introduce the Vetiver Technology to Chile and in the longer term to use the technology developed in Chile for use in other South American countries such as Brazil which has a very significant mining industry.

Applications of Vetiver system in waste water treatment

Australia

• Sewage effluent: Domestic and municipal effluent
• Industrial effluent: Landfill leachate, food processing factories and abattoir

China

• Sewage effluent: Municipal effluent
• Industrial effluent: Lead and Zinc Mine acid drain, Landfill leachate, food processing factories

Thailand

• Sewage effluent: Domestic and municipal effluent
• Industrial effluent: Industrial processing factories

Vietnam

• Industrial effluent: Industrial and food processing factories

Conclusions

Due to its high tolerance to adverse conditions and heavy metal pollutants, vetiver can establish in otherwise intractable materials under extremely hostile conditions, and as a pioneer plant it has the ability to ameliorate sites to the point that other species can then colonise voluntarily.

One of the major advantages of VS is its low cost as compared to conventional (engineering) methods for site stabilization and control of stormwater flows. Based on Australian experience, the saving over conventional engineered structures can be as high as 70% in some applications.

Once properly established, VS is virtually maintenance free, and its efficiency improves with age, unlike other conventional technology. It is long-lived (>50 years), and has no potential to become an environmental weed.

Vetiver System provides a soft, green and environmental friendly solution to the industry.