Rhizofiltration is a form of

phytoremediation Phytoremediation technologies use living plants to clean up soil, air and water contaminated with hazardous contaminants. It is defined as "the use of green plants and the associated microorganisms, along with proper soil amendments and agronom ...

that involves

filtering Filter, filtering or filters may refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component tha ...

contaminated Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc. Types of contamination ...

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...

surface water Surface water is water located on top of land forming terrestrial (inland) waterbodies, and may also be referred to as ''blue water'', opposed to the seawater and waterbodies like the ocean. The vast majority of surface water is produced by prec ...

and

wastewater Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industr ...

through a mass of

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...

s to remove

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...

substances or excess

nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

Overview

Rhizofiltration is a type of

, which refers to the approach of using hydroponically cultivated plant roots to remediate contaminated water through absorption, concentration, and precipitation of

pollutant A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oi ...

s. It also filters through water and dirt. The contaminated water is either collected from a waste site and brought to the plants, or the plants are planted in the contaminated area, where the roots then take up the water and the contaminants dissolved in it. Many plant species naturally uptake

heavy metals upright=1.2, Crystals of osmium, a heavy metal nearly twice as dense as lead">lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as ...

and excess

s for a variety of reasons: sequestration,

drought resistance Drought tolerance is the ability to which a plant maintains its biomass production during arid or drought conditions. Some plants are naturally adapted to dry conditions'','' surviving with protection mechanisms such as desiccation tolerance, detox ...

, disposal by leaf

abscission Abscission () is the shedding of various parts of an organism, such as a plant dropping a leaf, fruit, flower, or seed. In zoology, abscission is the intentional shedding of a body part, such as the shedding of a claw, husk, or the autotomy of a ...

, interference with other plants, and defense against

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

s and

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

s. Some of these species are better than others and can accumulate extraordinary amounts of these contaminants. Identification of such plant species has led environmental researchers to realize the potential for using these plants for remediation of contaminated soil and

Process

This process is very similar to

phytoextraction Phytoextraction is a subprocess of phytoremediation in which plants remove dangerous elements or compounds from soil or water, most usually heavy metals, metals that have a high density and may be toxic to organisms even at relatively low concentra ...

in that it removes contaminants by trapping them into harvestable plant

biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...

. Both phytoextraction and rhizofiltration follow the same basic path to remediation. First, plants that have stable root systems are put in contact with the contamination to get acclimated to the toxins. They absorb contaminants through their root systems and store them in root biomass and/or transport them up into the stems and/or leaves. The plants continue to absorb contaminants until they are harvested. The plants are then replaced to continue the growth/harvest cycle until satisfactory levels of contaminant are achieved. Both processes are also aimed more toward concentrating and precipitating heavy metals than organic contaminants. The major difference between rhizofiltration and phytoextraction is that rhizofiltration is used for treatment in aquatic environments, while phytoextraction deals with soil remediation.

Applications

Rhizofiltration may be applicable to the treatment of surface water and groundwater, industrial and residential effluents, downwashes from power lines, storm waters,

acid mine drainage Acid mine drainage, acid and metalliferous drainage (AMD), or acid rock drainage (ARD) is the outflow of acidic water from metal mines or coal mines. Acid rock drainage occurs naturally within some environments as part of the rock weathering ...

, agricultural runoffs, diluted sludges, and

radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transfer ...

-contaminated solutions. Plants suitable for rhizofiltration applications can efficiently remove toxic metals from a solution using rapid-growth root systems. Various

terrestrial plant A terrestrial plant is a plant that grows on, in, or from land. Other types of plants are aquatic (living in water), epiphytic (living on trees) and lithophytic (living in or on rocks). The distinction between aquatic and terrestrial plants is ...

species have been found to effectively remove toxic metals such as Cu²⁺, Cd²⁺, Cr⁶⁺, Ni²⁺, Pb²⁺, and Zn²⁺ from aqueous solutions.Dushenkov, Viatcheslav, Harry Motto, Ilya Raskin, and P.b.a. Nanda Kumar. "Rhizofiltration: the Use of Plants to Remove Heavy Metals From Aqueous Streams." Environmental Science & Technology 30 (1995): 1239-1245. It was also found that low level

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...

contaminants can successfully be removed from liquid streams. A system to achieve this can consist of a “feeder layer” of soil suspended above a contaminated stream through which plants grow, extending the bulk of their roots into the water. The feeder layer allows the plants to receive fertilizer without contaminating the stream, while simultaneously removing heavy metals from the water.

Tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...

s have also been applied to remediation. Trees are the lowest cost plant type. They can grow on land of marginal quality and have long life-spans. This results in little or no maintenance costs. The most commonly used are

willow Willows, also called sallows and osiers, from the genus ''Salix'', comprise around 400 speciesMabberley, D.J. 1997. The Plant Book, Cambridge University Press #2: Cambridge. of typically deciduous trees and shrubs, found primarily on moist s ...

s and poplars, which can grow 6 - 8’ per year and have a high flood tolerance. For deep contamination, hybrid poplars with roots extending 30 feet deep have been used. Their roots penetrate microscopic scale pores in the soil matrix and can cycle 100 L of water per day per tree. These trees act almost like a pump and treat remediation system.Suthersan, Susan S. Remediation Engineering: Design Concepts. CRC P, 1997. Willows have been successfully used as “vegetation filters” for nutrient (e.g. nitrogen and phosphorus) removal from municipal wastewater and polluted groundwater.

Common Plants

There are a series of aquatic and land plants that are used for rhizofiltration with varying degrees of success among them. While many of these plants are

hyperaccumulator A hyperaccumulator is a plant capable of growing in soil or water with very high concentrations of metals, absorbing these metals through their roots, and concentrating extremely high levels of metals in their tissues. The metals are concentrated a ...

s, other plant species can be used as the contaminants do not always reach the

shoot In botany, a plant shoot consists of any plant stem together with its appendages, leaves and lateral buds, flowering stems, and flower buds. The new growth from seed germination that grows upward is a shoot where leaves will develop. In the spri ...

s (stems and their appendages: leaves, lateral buds, flowering stems and flower buds). Some of the most common plant species that have shown the ability to remove toxins from water via rhizofiltration:Henry, Jeanna R.,
An Overview of the Phytoremediation of Lead and Mercury"
National Network of Environmental Management Studies, U.S. Environmental Protection Agency, (2000). 21-22. *

Sunflower The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as ...

Indian Mustard ''Brassica juncea'', commonly brown mustard, Chinese mustard, Indian mustard, leaf mustard, Oriental mustard and vegetable mustard, is a species of mustard plant. Cultivar ''Brassica juncea'' cultivars can be divided into four major subgroup ...

Tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

* Rye *

Spinach Spinach (''Spinacia oleracea'') is a leafy green flowering plant native to central and western Asia. It is of the order Caryophyllales, family Amaranthaceae, subfamily Chenopodioideae. Its leaves are a common edible vegetable consumed either f ...

Corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. Th ...

* Parrot's Feather * Iris-leaved Rush *

Cattail ''Typha'' is a genus of about 30 species of monocotyledonous flowering plants in the family Typhaceae. These plants have a variety of common names, in British English as bulrush or reedmace, in American English as reed, cattail, or punks, in A ...

* Saltmarsh bulrush *

Scirpus Robustus ''Bolboschoenus robustus'' is a species of flowering plant in the sedge family. It is known by many common names: saltmarsh bulrush, alkali bulrush, sturdy bulrush, seacoast bulrush, stout bulrush, three-cornered sedge or leafy three-cornered se ...

Cost

Rhizofiltration is cost-effective for large volumes of water having low concentrations of contaminants that are subjected to stringent standards. It is relatively inexpensive, yet potentially more effective than comparable technologies. The removal of

s from water using

sunflower The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as ...

s was estimated to cost between $2 and $6 per thousand gallons of water treated, including waste disposal and capital costs.Cooney, C M. "Sunflowers Remove Radionuclides From Water in Ongoing Phytoremediation Field Tests." Environmental Science and Technology 30 (1996): 194.

Advantages

Rhizofiltration is a contamination treatment method that may be conducted

in situ ''In situ'' (; often not italicized in English) is a Latin phrase that translates literally to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in ...

, with plants being grown directly in the contaminated water body or

ex situ Svalbard GLOBAL SEED BANK, an ''ex situ'' conservation. ''Ex situ'' conservation literally means, "off-site conservation". It is the process of protecting an endangered species, variety or breed, of plant or animal outside its natural habitat; ...

, where plants are grown off-site and later introduced to the contaminated water body. This allows for a relatively inexpensive procedure with low capital and operational costs, depending on the type of contaminant. In some cases, contaminants have been shown to be significantly decreased in a very short amount of time. One study found that roots of sunflower reduced levels of Uranium by nearly 95% in just 24 hours. This treatment method is also aesthetically pleasing and results in a decrease of water infiltration and

leaching Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). and may refer to: * Leaching (agriculture), the loss of water-soluble plant nutrients from the soil; or applying a small amou ...

of contaminants. After harvesting, the crop may be converted to biofuel briquette, a substitute for fossil fuel.Modeling rhizofiltration: heavy-metal uptake by plant roots P. Verma*, K. V. George, H. V. Singh, S. K. Singh, A. Juwarkar and R. N. Singh National Environmental Engineering Research Institute (NEERI), Nehru Marg, Nagpur 440 020, India

Disadvantages

This contamination treatment method has its limits. Any contaminant that is below the rooting depth will not be extracted. The plants used may not be able to grow in highly contaminated areas. Most importantly, it can take years to reach regulatory levels. This results in long-term maintenance. Also, most contaminated sites are polluted with many different kinds of contaminants. There can be a combination of metals and organics, in which treatment through rhizofiltration will not suffice. Plants grown on polluted water and soils become a potential threat to human and animal health, and therefore, careful attention must be paid to the harvesting process and only non-fodder crop should be chosen for the rhizofiltration remediation method.

External links

Phytoremediation and Hyperaccumulator Plants
Comprehensive overview.

- fro
Agricultural Research magazine Modeling rhizofiltration: heavy-metal uptake by plant roots
Much data.

References

{{Reflist, 1 Bioremediation - Water treatment