Ferns as a Natural Water Filter

BY :TEGUH TRIONO

MARCH 11, 2015

Pollution has posed a serious threat to human life since the industrial revolution of the developed world, and rivers have always borne the heavy brunt of factory pollutants. Water pollution caused by chemical substances such as heavy metals and other toxic compounds can seriously affect a river’s ecology.

Heavy metals can accumulate from water to sediments through a settling process and some particles can also find their way into the biota.  It is therefore crucial to create systematic management strategies that work to both prevent and reduce the level of pollutants in lakes and rivers before they can contaminate their surrounding ecosystem.

Phytoremediation

Phytoremediation is an effective environmental clean-up strategy in which various types of plants are used to remove, render environmentally toxic pollutants harmless in contaminated soil and water.

This method, however, has garnered both support and backlash. Advocates of the method say that phytoremediation has been successful in reducing pollution levels over time without involving chemicals or other harmful techniques.

Skeptics, meanwhile, argue that the process is far too unreliable. Some instances saw the new plants or trees have an immediate effect on their surroundings upon planting.

In numerous cases, however, it has taken at least two years before the new greenery can manifest any changes in the contaminated area.

The process, they added, would also require significant resources to: plant a large crop of species that have the ability to accumulate, store or degrade contaminants; tend to and properly maintain the plants or trees; harvest the crop to separate the heavy metals from the phytomass; and finally replant or use the phytomass for compost.

Despite the pros and cons behind phytoremediation, a wide range of native and non-native plants have been used extensively to reduce water pollution.

Hyperaccumulators: ferns

Greening polluted watersheds that contain hyper accumulator plants — capable of growing in heavily contaminated areas — can also be a solution, though the method is also somewhat controversial.

As I previously explained, phytoremediation is an environmentally friendly management strategy to prevent and reduce water pollution, particularly by heavy metals in industrial areas.

There are ways to expedite the rate at which new plants accumulate pollutants: choose a fast growing plant species with a high accumulation capacity — those that thrive in soil containing high levels of heavy metals.

Among the species perfect for phytoremeidation is a fern called Pteris vittata, also known as the Chinese ladder brake, found in Asia (including Indonesia), some parts of Africa and Australia.

The species is a hyperaccumulator for arsenic (As), the first to be discovered, making it a perfect choice for the phytoremediation of water and soil contaminated with the dangerous chemical.

Scientist discovered the fern’s abilities after collecting a sample from an area surrounding a lumber factory that had been using chromated copper arsenate (CCA) to treat its output. The fern accumulates 23 grams per kilogram of arsenic in its fronds without showing symptoms of toxicity. The fern removes heavy metal pollutants from contaminated waters, converting them into biomass.

Periodical harvest of plants that have the ability to absorb pollutants is another way of speeding up the phytoremediation process.

Harvested plants containing heavy metals can be disposed of or treated to recycle the metal.

Rhizofiltration — a water filtration system using plant roots — using Chinese ladder brakes contains many of the benefits of other phytoextraction techniques; it is low cost and does not damage the environment.

A continuous flow system circulates the contaminated water through specially designed plant containment units in which older plants are harvested and replaced.

Nowadays wastewater and pollution treatment using the phytoremediation or rhizofiltration method employs floating vegetated filters rather than expanding a treatment plant or creating a new large wetland; the floating system offers a decidedly less expensive alternative.

It is an engineering system that is easy to implement and requires less maintenance. The interest is mainly ecological, economical and aesthetic, especially when this system is installed in a city’s industrial areas.

Plants native to Indonesia can work to treat polluted sites while also providing a greener landscape.

The floating vegetated filters are covered with a mat of coir fiber covered with helophytes, or marsh plants.

Beneath the vegetation is a layer of Xylit fiber, which is often used in purifying pond water and will work to draw in pollutants to the ferns.

The combination of the floating mats and Chinese brake ferns could purify larger volumes of water and sequester heavy metal pollutants.  The method provides a phytoremediation system with a natural look.

Teguh Triono is program director of the Indonesian Biodiversity Foundation (Kehati).

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