Technologies for phosphorus recycling from water environment

Technologies for phosphorus recycling from water environment

Today, phosphorus is mostly obtained from mined rock phosphate and existing rock phosphate reserves could be exhausted in next 50 – 100 years (Cordell et al., 2009). Phosphate minerals are the main hosts of phosphorus during its environmental transformations. Whether in phosphate ores, rocks or soils, they act as the primary source of phosphorus. They can also form in situ in the environment, as transient pools of phosphorus during both bio- and geochemical processes. Their abundance, availability and reactivity are therefore key to the entire phosphorus cycle on Earth (Valsami-Jones, 2004). Phosphorus is eleventh in order of abundance in the earth’s crust, but the concentration in many rocks is very small. Its sources are found throughout the world and over 30 countries are currently producing phosphates for domestic use and/or for international trade. The main commercial deposits being exploited at present are in Morocco, West Africa, China and in the United States (Jasinski, 2008).
At present in Western Europe, of the total P use some 79 % goes to make fertilizers, about 11 % for feed grade additives for animal feeds and 7 % for detergents (Johnston and Stéen, 2000). Phosphate rocks are after crushing (beneficiation) treated with sulphuric acid to make single superphosphate or phosphoric acid, or with nitric acid to give nitrophosphates, or with phosphoric acid to give triple superphosphate (TSP). Monoammonium phosphate (MAP) or diammonium phosphate (DAP) are obtained by adding ammonia. TSP, MAP and DAP are the principal phosphorous fertilizers traded today (Valsami-Jones, 2004). Fertilizer production is therefore tightly connected with phosphorus use and since phosphorus is essential for all living processes, there is concern that the exploitation of this non-renewable resource to meet current demands is not sustainable. Climbing price of the phosphate rock from 44 $/mt in 2006 over 71 $/mt in 2007, 346 $/mt in 2008 to 125 $/mt in 2009 (World Bank, 2009) and expected scarcity problems are driving forces to find alternatives. Although farmers use animal manure and plough straw to fertilize fields in order to recycle phosphorus, however, the amount of phosphorus recycled in this way is still very low and it takes recently about 10 % (Cordell et al., 2009). Alternative sources of phosphorus can be found in environment (e.g. seawater), natural materials (e.g. biomass, yeasts) or anthropogenic materials (e.g. wood ash) (Valsami-Jones, 2004).
Another source of phosphorus can be considered water environment where excessive input of phosphorus causes serious problems mainly joined with cultural eutrophication (extraordinary plant growth resulting from nutrient enrichment by human activity) (Smith and Schindler, 2009). A variety of natural and anthropogenic sources (e.g. wastewaters, runoff from impervious surfaces, runoff from pervious surfaces – forestry, cultivated land and pasture) contribute phosphorus to streams and rivers via a number of different pathways and at different times of the year (Withers and Jarvie, 2008). However, the major sources of phosphorus to rivers are mainly sewage/industrial effluents (point sources) and agricultural runoff (diffuse sources) (Jarvie et al., 2006). Non-point source pollution from agricultural land can be particularly detrimental to water quality because discharges are untreated, often contain high nutrient and organic matter loads, and losses occur sporadically during intense rainfall events from sources that are difficult to identify, quantify and control. Surface waters are highly sensitive to P loss from agriculture because critical concentrations for eutrophication control (10 - 20 μg P•l-1) are an order of magnitude lower than soil P concentrations required for crop growth (200 - 300 μg P•l-1) (Heathwaite and Dils, 2000).
Driving forces for phosphorus recovery and recycling are closely associated with prospecting proper alternative source of phosphorus instead of phosphate rock and with the protection of environment, mainly eutrophication prevention. Several extensive reviews have been written (e.g. Morse et al., 1997; de Bashan, and de Bashan, 2004) and focuses on the technological solutions of phosphorus removal from the wastewater treatment point of view. Utilization of phosphorus is always done via transformation to solid fraction. This fraction can be an insoluble salt precipitate, a microbial mass in an activated sludge, or a plant biomass.


Precipitation of phosphorus by metal salts
Three types of metal precipitant are generally used for chemical phosphorus removal namely iron (II), iron (III) and aluminium. Calcium and magnesium salts are used very occasionally (Thistleton et al., 2001). The following parameters highly influence process performance and achievable levels of residual phosphorus in the effluent: the raw water quality (pH, suspended solids, dissolved organics), type and dose of the precipitant, location of dose application, chemical speciation, mixing conditions, process configuration, etc. Key variable is the location of the dose application (Parsons and Berry, 2004). Primary precipitation is where the chemical is dosed before primary sedimentation and phosphorus removed in primary sludge. Secondary (or simultaneous) precipitation is where the chemical is dosed directly to the aeration tank of an activated sludge process and phosphate removed in secondary sludge. Tertiary treatment is where dosing follows secondary treatment and although a high-quality effluent can be produced, this approach is not generally favored because of high chemical costs and the creation of an additional, chemical, tertiary sludge (Morse et al., 1997).

Enhanced biological phosphorus removal
Enhanced biological phosphorus removal (EBPR) promotes the removal of phosphorus from wastewater without the need for chemical precipitants. The group of microorganisms that are largely responsible for phosphorus removal are known as the polyphosphate accumulating organisms. These organisms are able to store phosphate as intracellular polyphosphate, leading to phosphorus removal from the bulk liquid phase via polyphosphate accumulating organism cell removal in the waste activated sludge. Unlike most other microorganisms, polyphosphate accumulating organisms can take up carbon sources such as volatile fatty acids under anaerobic conditions, and store them intracellularly as carbon polymers, namely poly-b-hydroxyalkanoates. Aerobically or anoxically, polyphosphate accumulating organisms are able to use their stored poly-b-hydroxyalkanoates as the energy source for biomass growth, glycogen replenishment, phosphorus uptake and polyphosphate storage. Net P removal from the wastewater is achieved through the removal of waste activated sludge containing a high polyphosphate content (Oehmen et al., 2007).

It is commonly considered that crystallization processes can recover P either as calcium phosphates that are similar to phosphate rocks, or as magnesium ammonium phosphate that is a slow release fertilizer (Song et al., 2007)

Struvite is a white crystalline substance consisting of magnesium, ammonium and phosphorus in equal molar concentrations (MgNH4PO4•6H2O). Struvite forms according to the general reaction shown below:

Mg2+ + NH4+ + PO43- + 6 H2O → MgNH4PO4• 6 H2O

Struvite precipitation can be separated into two stages: nucleation and growth. Nucleation occurs when constituent ions combine to form crystal embryos. Crystal growth continues until equilibrium is reached. In systems continuously replenished with struvite constituents; e.g. wastewater treatment plants, crystal growth may continue indefinitely. Crucial parameter of struvite processing is proper ratio between the magnesium, ammonium and phosphate and alkaline pH (Münch and Barr, 2001) Other important parameters are degree of supersaturation, temperature and the presence of other ions in solution such as calcium and can occur when the concentrations of magnesium, ammonium and phosphate ions exceed the solubility product (often denoted as Ksp) for struvite (Doyle and Parsons, 2002). Struvite is a premium grade slow releasing fertilizer because it is sparingly soluble in water (Münch and Barr, 2001)

Calcium phosphate
Calcium phosphate is the effective composition of phosphate rocks, and then can be readily accepted by the phosphate industry if it is recovered in a suitable physical form (Driver et al., 1999). There is a lack of understanding of seeded crystallization of calcium phosphate from wastewater. The wastewater solution is usually supersaturated with respect to calcium phosphates, but no precipitation reaction occurs. It is believed that the effects of some inhibitors account for this phenomenon. Among the inhibitors carbonate is the most common one (Song et al., 2002). Principally seeded crystallization has the merit of utilizing the seed as a substrate for the heterogeneous nucleation and crystal growth. The crystallization of calcium phosphate is complicated, because it concerns with the formation of several possible precursors and their transformation (Song et al., 2006). Computer software PHREEQC is often used to study the precipitation of calcium phosphate from a chemically defined precipitation system.
There is several problems that have to be solved for the full-scale application: excessive production of fine particles, encrustation or fouling of the reactor wall and of the different parts present inside of the reactor (Mangin and Klein, 2004).

Crystallization of hydroxyapatite is described by following reaction:

3 PO43- + 5 Ca2+ + OH- → Ca5(PO4)3OH

The advantages of this approach include: (a) no precipitants is required; (b) an increase of the sludge volume can be avoided; (c) the product can be dewatered easily; (d) the dehydrated product could be potentially reused as phosphorus fertilizer because its phosphorus content is comparable to phosphate rock (Song et al., 2002). The hydroxyapatite crystallization is affected by the nature of seed crystal, phosphate concentration, calcium ion concentration, pH, bicarbonate alkalinity, and reaction temperature (Jang and Kang, 2002).

Crystallization technologies
Technologies can be divided into mainstream and split-stream processes. In both variations phosphate precipitates using chemicals, e.g. calcium hydroxides, iron or aluminium salts.
The DHV Crystalactor process is based on the crystallization of calcium phosphate on a seeding grain, typically sand, within a fluidized reactor. Process conditions are adjusted to promote calcium phosphate crystallization by adding either caustic soda or milk of lime. The high rate of crystallization allows a short retention time and therefore a small reactor. Pellets are periodically removed and replaced by smaller diameter seed grains. This allows continuous operation and ensures good fluidisation. Plants can be fully automated. Full commercialization has been achieved, with a number of operational plants e.g. in the Netherlands.
The Kurita Fixed Bed Crystallization is based on similar chemistry to DHV Crystalactor. It is designed to remove phosphate from the secondary effluent by use of phosphate rock seeding grains without production of sludge. Calcium phosphate is produced (Joko, 1984). Calcium concentration and pH are the controlling factors for precipitation, and more important than the concentration of carbon based ions in the water, although these do not have effect (Brett, 1997).
The CSIR Fluidized Bed Crystallization Column uses a number of different seeding materials to produce granular hydroxyapatite or struvite (magnesium ammonium phosphate), with the objective to re-use these products as fertilizer (Momberg and Oellerman, 1992).
Unitika Phosnix recovers phosphates as struvite. Filtrate from sludge treatment process is continuously fed to the nucleation zone. Magnesium hydroxide is added at magnesium to phosphorus ratio of 1:1, nad pH is adjusted to a value between 8.2 – 8.8 with addition of sodium hydroxide. Fine struvite crystals are grown in the fluidized bed by mixing with air (Ueno, 2004).
CAFR Process (chemical ammonia precipitation with recycling) represents a follow-up development of the struvite one-way precipitation. Ammonia is stripped by means of steam from the precipitated struvite by alkalization (MgO) at temperatures of about 70 °C, so that magnesium phosphate can be used again for struvite precipitation (Janus and van der Roest, 1997).
PRISA Process starts with acidification of the raw sludge from EBPR with phosphate dissolution in reactor. Then the raw sludge is separated from the supernatant which contains the major part of the phosphate which had been biologically bound as well as a smaller part of the dissolved phosphate from the hydrolysis of biomass. More than 40 % of the phosphorus load from the raw wastewater is concentrated in this split-stream. This split-stream is mixed with centrate and by adding magnesium oxide struvite precipitates in the precipitation reactor (Montag et al., 2009).
P-RoC is the process of recovery by crystallization of calcium phosphate straight from the wastewater phase by the application of waste materials from the construction industry as seed material, i.e. calcium silica hydrate. It occurs in one single step without the addition of chemicals except for the reactive substrate (Berg et al., 2005).
In the Sydney Water Board process, gypsum provides a source of calcium ions and magnesia is used as a contact bed for amorphous precipitation of calcium phosphate (Morse et al., 1997). There is numerous other technologies e.g. PHOSPAQ, Ostara’s PEARL nutrient recovery process, NuReSys (Moerman et al., 2009).

Magnetic water treatment
Application of magnetic separation methods to wastewater treatment are based on the attachment of pollutants onto a magnetic carrier material (e.g., magnetite) and a subsequent separation of the magnetite-pollutant by a magnetic separation unit. First works have been concentrated on the phosphorus precipitation in a system including the using of the aluminium sulfate and montmorillonite and FeCl3 in addition to magnetite powder (Karapinar et al., 2004). Shaikh and Dixit (1992) investigated the magnetic removal of orthophosphate and hexametaphosphate by precipitation with aluminum sulfate and calcium nitrate, respectively. Steel slag with magnetic separation was used to remove phosphate from aqueous solutions was investigated by (Xiong et al., 2008).
Within the frame of phosphate crystallization investigations, several materials such as calcite, sand, and a variety of Ca phosphate crystals etc. have been used as seeding material to initiate and to enhance phosphate precipitation and recycling. However, magnetic removal and recycling of phosphorus require the use of such a seed, which exhibits magnetic susceptibility (Karapinar et al., 2004).

Magnetic water treatment systems, such as the Smit-Nymegen process are essentially a tertiary treatment, where lime is used to precipitate calcium phosphate, attached to magnetite and separated using an induced magnetic field. Following isolation, the magnetite is uncoupled from the phosphate in a separator unit by shear forces and a drum separator. The separated suspension of calcium phosphate or carbonate in water is then further processed depending on final product use (van Velsen et al., 1991).
Three characteristics of magnetite are used in the Sirofloc process are its density, its magnetic properties and its controllable surface charge. Under acidic conditions the particles carry a positive charge thus attracting negatively charged materials. When the pH level is raised the particles become negatively charged and attached materials are repelled. The reversible surface charge is used to remove color, iron compounds, aluminium compounds and turbidity from raw water and then to shed these unwanted contaminants as a concentrated effluent, allowing the magnetite to be continually reused (Dixon, 1991).

Solid phase adsorbents are frequently utilized in the removal of phosphorus in a variety of applications as diverse as wastewater treatment, maintenance of potable water supplies and constructed wetlands. Some of the most commonly used adsorbents are:
- naturally occurring minerals from soils (e.g. Fe-oxides/oxyhydroxides, allophone)
- naturally occurring (poly-mineralic) soils or sands
- derived from mineral deposits (e.g. wollastonite) or other natural materials (e.g. shale, serpentinite, maerl)
- synthetic analogues of natural minerals produced on an experimental or industrial scale (e.g. polymeric hydrogels, hydrotalcites)
- expanded clay aggregates
- waste materials from industrial processes that adsorb phosphate or that may also be further modified to enhance their uptake capacity (e.g. electric arc furnace, steel slag, blast furnace slag, red mud)
The effectiveness of each class of adsorbent as measured by its adsorption capacity, and relative costs, cover a wide range in the most instances and there are considerable overlaps between the different classes. In addition, there are substantial differences in the sensitivity of adsorbents to changes in pH and redox conditions (Douglas et al., 2004).

Activated sludge
Sludge containing phosphorus from conventional treatment and phosphorus removal processes can be recycled to agriculture directly, but there are processes that attempt to enhance sludge value, including phosphorus availability (Morse et al., 1997).
Wider spectrum of sludge application as fertilizer is often limited to the strong legislation about heavy metal content in the biomass. However, there are thermo-chemical methods, e.g. (ASHDEC or Mephrec), which are using temperature higher than 1000 °C and heavy metals are either vaporized or converted into liquid phase. P-fertilizers from sewage sludge and meat and bone meal ash in the EU27 could substitute up to 25 % of the necessary rock phosphate imports (Hermann 2009; Scheidig et al., 2009).

There are numerous methods about sludge utilization as fertilizer. The Simon-N-Viro process is a pasteurization treatment in which an exothermic chemical reaction is generated between primary or excess activated sewage sludge and cement kiln dust and lime, producing N-Viro soil conditioner. The Swiss Combi process uses a drum drier to convert a dewatered sludge into granules that may be used as a fertilizer or a low grade fuel. Favorable results have been reported in agricultural tests, including a phosphorus concentration of 3.5%. No information is available on the recycling potential for the phosphate industry (Morse et al., 1997).
The Krepro Process allows a separation of the sewage sludge into four fractions: iron phosphate, highly calorific organic sludge, precipitation chemicals and a carbon rich centrate. In the first step the sludge is passed into a hydrolysis reactor at a pH = 1.5, temperature of 150 °C and pressure of 4 bars. About 75 % of the phosphate is dissolved based on the used precipitant. It is mixed with the centrate from the dewatered sludge and upon the addition of ferric precipitant and a stepwise increase of pH, iron phosphate (FePO4) is precipitated and separated from the liquid phase by means of the centrifuge (Lundin et al., 2004).
The Kemicond Process is the modification of the Krepro Process. The Kemicond Process for sludge conditioning consists of a chemical treatment by sulfuric acid and hydrogen peroxide followed by a two stage dewatering unit.
The Seaborne process serves to treat organic substances, among others sewage sludge. The entire process consists of several individual modules that are linked with each other in terms of the mass flows. The supply of acid to the digested sludge results in the dissolution of heavy metals, phosphorus and the organic substance. Heavy metals are precipitated as sulfides and separated from the phosphorus containing liquid flow by the addition of H2S containing digester gas. Following an increase in the pH value by the addition of disodium carbonate, nitrogen and phosphorus are precipitated in the form of struvite from the heavy metal-depleted phase.
The Aqua Reci Process is the wet oxidation process for sewage sludge, which is run in the supercritical range of water (p > 221 bar, T > 374 °C). The sludge is considerably depleted in organic compounds. From the remaining inorganic sludge, phosphorus may be separated by the addition of base in the terms of calcium phosphate.
The BioCon process consist in a modular concept for sewage sludge treatment, comprising the three modules of drying, incineration, and the phosphorus recovery via ion exchange. In a mixing reactor (pH ~ 1), sulfuric acid and water are mixed with pulverized ashes. This leads to the partial dissolution of phosphorus compounds and heavy metals. Subsequently, the remaining mineral constituents as iron chloride, potassium hydrogen sulfate and phosphoric acid as well as heavy metals can be separated by several ion exchangers that are connected in series.
The Sephos (sequential precipitation of phosphorus) process treats sludge ash with sulfuric acid (pH < 1.5) and the residual solids (mainly sand) are separated. In the filtrate, pH value is stepwise increased with caustic soda to pH 3.5 to separate phosphorus and heavy metals. The phosphorus is precipitated as aluminium phosphate, which can be used as raw material in the electrochemical phosphate industry. It is also feasible to produce calcium phosphate by elution with base (pH 12 – 14) and separate insoluble residuals (heavy metals). The dissolved phosphorus can then be precipitated as calcium phosphate by the addition of calcium ions, potentially also via crystallization.
ASH DEC Process uses thermal treatment in the rotary furnace (~ 1050 °C) in order to remove organic substances from the sludge. Due to the supply of the 35 – 40 alkali and/or alkali earth chloride solutions as KCl and MgCl2 in molar surplus compared to the heavy metal concentrations, heavy metals are released as gaseous chlorides which are scavenged by wet deposition during gas treatment and have to be disposed as hazardous waste. The generated products are low contaminated organic-free magnesium and potassium phosphates (Adam et al., 2009).

There were tested many bacteria which proved high phosphorus uptake. Non-toxic cyanobacterium Phormidium bohneri was investigated to remove dissolved inorganic nutrients from fish farm effluents. Average efficiencies of ammonia nitrogen removal from rainbow trout (Oncorhynchus mykiss) effluent was 82 % and 85 % for soluble orthophosphate, over a one month period. From these results, the potential use of Phormidium bohneri as an alternative for the tertiary treatment of fish farm effluents is analyzed (Dumas et al., 1997). A photobioreactor containing cells of the purple non-sulphur bacterium Rhodobacter cupsulatus immobilized on cellulose beads removed organic carbon, ammonium ion, and phosphate ion from a diluted growth medium over a period of 19-22 d with a residence time of 20.6 or 10.3 h at 35 (± 1) °C and continuous light of 60 μE•m-2•s-1 (Sawayama et al., 1998).

The application is severely limited by the difficulties of harvesting the enormous microalgal population developed in the water after treatment. Therefore, the idea of entrapping microalgae for easy removal by sedimentation with spherical gels gained some momentum. For example, Chlorella vulgaris, immobilized in two natural polysaccharide gels (carrageenan and alginate), was used to treat primary domestic wastewater. Although algal cells in the carrageenan and alginate beads grew far slower than the suspended cells, the immobilized cells were more metabolically active. Over 95 % of ammonium and 99 % of phosphates were removed from the wastewater in 3 days (de Bashan, 2004).
Combination of more than one microorganism is better than a single organism and is gaining acceptance in agriculture and forestry, and is starting to appear in nutrient removal studies of wastewater. A microalga (Chlorella vulgaris) and a macrophyte (Lemna minuscula) could be applied in tandem for biological treatment of recalcitrant anaerobic industrial effluent, wastewater that otherwise prevented growth of any macrophyte. First, the Chlorella vulgaris reduced ammonium ions (71.6 %), phosphorus (28 %), and COD (61 %). Consequently, Lemna minuscula was able to grow in the treated wastewater, precipitate the microalgal cells by shading the culture, and reduced organic matter and color. However, Lemna minuscula did not significantly improve further nutrient removal (Valderrama et al., 2002).

Constructed wetlands are a low-cost, low-tech process to control environmental pollution. Basically, it is a container (as small as a bucket or as big as a very large pond) planted with mainly aquatic, but sometimes with terrestrial plants. Inflow wastewater current slowly flows either horizontally or vertically from one end to the other end and, in the process, the outflow is cleaner. Other major construction parameters are the type of substrate in which the plants grow or the container material. Both usually have some cleaning capacity by themselves. The roots of plants, especially aquatic macrophytes, both emergent and submerged, work as a giant biological filter that removes organic matter of all kinds. At the same time, microorganisms residing in the submerged roots in the wastewater are degrading other pollutants that are later absorbed by the plants.
Afterwards, the treated wastewater is commonly discarded to natural water bodies or used for irrigation of inedible plants without any further treatment. Periodically, in some constructed wetlands, the plants need replacement. Usually wetlands are not designed to remove nutrients, such as phosphorus. They do so indirectly because the ions are nutrients for the plants (de Bashan, 2004).
The removal capacity of phosphorus by a wetland can be substantial. Assessment of the contribution of duckweed Lemna gibba, a macrophyte, and its associated microorganisms (algae and bacteria forming an attached biofilm) to remove nutrients showed that the biological floating mat complex (plants and microbes) is responsible for removing up to 75 % of the nutrients in the wastewater (Korner and Vermaat, 1998).
Upgrading of the wetlands concept and increasing its economical value by directing the cleaning process and discarded effluent according to requirements and not by random, as is done in ordinary wetlands is a new notion. This might provide a better solution for operating wetlands in cold climates in winter and for treatment of recalcitrant water, which are difficult in common artificial wetland systems. Such an idea has been called an ‘‘engineered wetland.’’

Submerged macrophytes
Submerged macrophytes can reduce the concentration of different P species in the overlying water, mainly by uptaking the P from overlying water, inactivating the alkaline phosphatase activity in the sediment and overlying water, reducing sediment resuspension and controlling the release of internal P loading. Five submerged macrophytes, Ceratophyllum demersum, Elodea canadensis, Potamogeton crispus, Myriophyllum spicatum and Vallisneria spiralis were selected and their relative growth rate and the capacity of removing phosphorus in greenhouse were evaluated by hydrotropic experiments of two seasons (spring and autumn). Total phosphorus removal rates of C. demersum (91.75 % and 92.44 %) during the spring and autumn were the highest (Gao et al., 2009).
Several species of floating, floating-leaved, and submerged macrophytes were introduced in experimental enclosures in eutrophic shallow lakes. These macrophytes were intercropped in small patches and formed mosaic communities of spatial and temporal combinations (spatial and seasonal mosaic patterns) in the lakes. Macrophytes can improve water transparency quickly and the mosaic community of macrophytes system can stabilize this clear water state over a long time in turbid eutrophic shallow lakes. The constructed mosaic community of macrophytes created heterogeneous habitats that are favorable for different macrophytes and for the growth and succession of other organisms, as well as for removing water pollutants. When the eutrophic water flowed through the mosaic community of macrophytes system at a retention time of 7 days, the removal efficiency rates of the mosaic community of macrophytes system for algae biomass, NH4+–N, TN, TP and PO43−–P were 58 %, 66 %, 60 %, 72 % and 80 %, respectively (Wang et al., 2009).

Other technologies
There is numerous other technologies, which are recycling phosphorus from water environment, e.g. periphyton and phytoplankton technologies, electrocoagulation, filtration or ion-exchange technologies. However those technologies are focused mainly on the phosphorus removal from the aquatic environment and not on phosphorus recycling.

Human beings are recently addicted to the phosphate rocks for fertilizer production due to global demand for the crops. The range of organic and inorganic sources can be alternated as phosphorus fertilizers. It can be phosphorus recovered from food production, consumption chain and/or virgin sources. Another option is phosphorus removal and recycling from water environment, where its overabundance and higher concentrations cause detrimental problems. There are several promising applications, e.g. crystallization or phosphorus recycling from activated sludge with direct reuse effect as a fertilizer. Other technologies are focused mainly on phosphorus removal and recovery isn’t usually reasonable or economically viable.

The research has been undertaken by support of Project of the Ministry of Education, Youth and Sports of the Czech Republic: No: 1M0571 Research Centre for Bioindication and Revitalization of the programme “Research Centers PP2-DP01” (1M).

This manuscript has been previously published at the conference International Symposium on the Earth and Technology CINEST 2010 in Fukuoka, Japan. Authors are Marek HOLBA1,2, Nuria VALDES MEDIAVILLA1,3 and Blahoslav MARŠÁLEK1

1 Institute of Botany, Academy of Science of the Czech Republic, v.v.i., Lidická 25/27, 657 20 Brno,
2 ASIO Ltd., POB 56, Tuřanka 1, 627 00 Brno-Slatina, Czech Republic
3 Autonomous University of Madrid, Spain