What is phytoremediation?
Phytoremediation is the use of living plants for in-situ (in place) remediation and clean-up of contaminated soil, sludge, sediments, or ground water. Phytoremediation may occur through contaminant degradation or containment, and in some cases, the plants are harvested and contaminants in the plant material are simply removed from the site. Growing trees on a contaminated site as a remediation method is an aesthetically pleasing, passive technique that can be used to clean-up sites with shallow or low to moderate levels of contamination. Phytoremediation can be used in place of, or in conjunction with, mechanical cleanup methods and works well for remediation of petroleum hydrocarbons, TNT or munitions waste, metals and other chemical compounds as well.
How does phytoremediation work?
Phytoremediation - is a general term for several ways in which plants are used to clean up, or remediate, pollutants in soil and water. Plants and soil micro-organisms in the soil can break down or degrade certain organic pollutants. Sometimes, the contaminants, especially heavy metals, are taken up or stabilized within the plant itself and the plant acts as a filter or trap.
Some of the methods that are being tested are described in this fact sheet.
Phytoextraction - also called phytoaccumulation, refers to the uptake and translocation of metal and chemical contaminants in the soil by plant roots in the above ground portions of the plants. Certain plants, called hyperaccumulators, absorb unusually large amounts of metals in comparison to other plants.
Rhizofiltration - is the adsorption of soil and groundwater contaminants onto, or into, plant roots. Rhizofiltration is similar to phytoextraction, but the plants are used primarily to address contaminated groundwater rather than soil.
Phytostabilization - is the use of certain plant species to immobilize contaminants in the soil and groundwater through absorption and accumulation by roots, or precipitation of the contaminants within the root zone of the plants (rhizosphere). This process reduces the mobility of the contaminants and prevents migration into the groundwater or air and reduces the bioavailability and thus entry into the food chain.
Phytovolatilization - is the uptake and transpiration of a contaminant by a plant, with release of the contaminant, or a modified form of the contaminant, into the atmosphere.
In summary, phytoremediation is a new and exciting approach to cleaning up groundwater pollution and soil contaminants using different species of plants as the primary component. This method is low-cost, environmentally friendly and effective for a wide range of chemicals such as pesticides, solvents, crude oil, polyaromatic hydrocarbons, and metals as well.
Dynamax has a wide range of devices suitable for phytoremediation site verification and monitoring. Packaged and custom systems are available for most applications. We also offer engineering, installation and training, programming, and on-site support.
Depending on the type of remediation, the recommended monitoring instruments are:
PHYTOREMEDIATION
BIOREMEDIATION
ALL REMEDIATION TYPES
IN DEPTH RESEARCH
PHYTOREMEDIATION MONITORING METHODS CHECKLIST
Here is a summary of recommendations for equipment to proceed with phytoremediation projects as proposed by Dynamax. This equipment proposal is produced in order to satisfy the main components of interest in most phytoremediation projects - 1) groundwater surface fluctuations and water balances, 2) plant growth and stress factors and 3) soil microbial activity measurement.
Plant cover can account for up to 95% of the water leaving the soil and is the most important factor in measuring evapotranspiration. In order to accurately know how much water the plants are using, you will need a Flow32 for Flow4 sap flow system. The Flow32 and Flow4 systems tell you in "Real-Time" (in grams or kilograms per hour) the transpiration rate of the plants. With this information you will know whether or not the plants are using water fast enough to prevent the contaminant plume from migrating off the site and be able to determine the phytoextraction rates. Later, when the plants are larger (>5 inches), the Flow32 can be expanded with a FlowTDP sap velocity system to continue the sap flow portion of the study.
INDEX BY CANOPY OR STEM AREA
In this approach, the plant water use is indexed to the leaf area or to the stem or trunk cross-sectional area. This allows you to extrapolate per plant water use to a land area basis, or to the total number of plants present over the site. Dynamax offers a wide range of leaf area measurement systems, both portable and lab based, for this purpose.
CROP INDEX BY WEATHER ETo
The plant sap flow should be indexed to the ETo calculations from the DynaMet weather station to make projections of annual plant water use. Sap flow data is taken periodically in blocks of 7 to 14 days throughout the season and is indexed to the ETo calculations from the DynaMet weather station. Based on continuous weather data, one may develop the crop index method of accurately forecasting water consumption, and therefore the extraction rates. With this approach, it is not necessary for the researcher to be at the site all the time but could take measurements once every two or four weeks per season.
SOIL WATER TRACKING
In addition to the sap flow system, an expansion kit or a separate datalogger with ML2 Theta soil moisture probes (buried at different depths) may be used to do a soil moisture profile and track the soil water level movement. Another Phytoremediation method includes pumping contaminated water to irrigate plants and to encourage the establishment of new plants. Clearly the soil moisture measurement is a key item for scheduling this application of water to prevent runoff and to maintain appropriate moisture for the plant itself. Other sensors can also be attached to this datalogger.
STRESS MONITORING
Plant water stress is an issue in some applications. The sap flow transpiration stress is an ideal method to collect whole plant transpiration and compare stressed periods to well watered plants. Examples of stress calculations are detailed in the presentation at the Unified Wine and Grape Symposium (van Bavel, 2005).
GROWTH FORECASTING
DEX Electronic Dendrometers can monitor the plant growth rates or stress levels over periods of 1-2 months continuously. This sensor can measure stem or fruit diameter changes as small as 0.050 mm. The data represents diurnal changes and gives a very accurate measure of the growth rate over a longer projection. Declining diameter indicates a stress level of the plant. The researcher knows "when" plant stress occurs and "how much" stress is present.
The LCi or LCpro+ portable photosynthesis systems can also be used to get a better measure of the photosynthetic rate of the plants. The system also measures leaf level stomatal conductance and transpiration rates as well.
SOIL RESPIRATION - MICROBIAL REMEDIATION
Measuring the amount of oxygen and carbon dioxide in the soil is a direct indicator of the biotic activity present. The SRS1000 gas analyzer with soil respiration chambers can be used to measure soil respiration rates. The equipment can be periodically moved around to other locations to get sample data over the whole test area. This data will give a very good idea of how much microbial activity is present in the soil and how this may change over time.
Dynamax also supplies the OXG sensors for measuring dissolved oxygen in water and soil and these can be attached to a datalogger to make continuous measurements. Sensors for pH, temperature, water depth, conductivity, REDOX potential, and more are also available.
So as you see, Dynamax has a variety of equipment for use in phytoremediation and bioremediation projects. Our approach trends from whole plant measurements and water balances down to measurements of microbial activity and detailed soil characteristics. Each application has a recommended set of measurements which are important, from the essential transpiration measurements all the way to details of plant characterization. Dynamax is pleased to offer our analysis tools for this expanding and exciting new way of cleaning up the environment.
Dynamax has produced a poster summarizing our approach to monitoring phytoremediation and transpiration. To download a PDF version of the poster, click here.