January 14, 2011

Duckweed Performance in Cold Climates

Duckweed grows approximately 6+ months in Cache Valley Utah. This presents an issue when using duckweed for removing nutrients from the wastewater. I've observed duckweed as early as March and as late as the end of November; however, I've only noticed full duckweed coverage from about the first of May to November 19th (World Toilet Day). Fortunately, Wellsville currently has the capacity to store water (i.e. save for treatment in the warm season) during the winter, which they do. Also, their discharge permit allows for 432 kg-P/yr (72kg during the warm season and 360kg cold season). Wellsville discharges into the Little Bear River. This excellent report by JUB Engineering provides a summary of the treatment plant where we propose using duckweed nutrient removal. I've met a few engineers from JUB and would highly recommend them.



Figure: Duckweed (L. minor and Wolffia) at Wellsville Sewage Lagoons 22 March 2010--duckweed appeared immediately along shore as ice melted.


video
Video: Water Cress growing green in Cold Cache Valley Climate (2.5min)

video
Video: Water Cress growing green in Cold Cache Valley Climate (25sec)

The figures below show temperature trends for Cache Valley, including the cold temperatures in January when that the water cress survives. These charts were retrieved online from a database/network ran by Jeff Horsburgh of the Utah Water Research Laboratory (UWRL). Jeff continuously monitors environmental data along the Little Bear River and makes it available to the public online. This is a fantastic research tool made possible by data logging equipment from Campbell Scientific, Inc. (a local Cache Valley company).

Figure: Temperature Trend two weeks preceding video on 15 Jan 2011--Cache Valley Winter

Figure: Temperature Trend before video on 15 Jan 2011 Cache Valley Winter



Most research with duckweed is conducted in climates with a 9+month growing season. Laboratory tests are usually performed at 25'C. A difficult to find article, but frequently referenced, by Culley, D.D. Jr., et al., has this to say about winter and duckweed:

"Several species rarely flower and form no turions. During the winter season the fronds are greatly reduced but remain at the surface. Occasionaly, turion-like fronds will form, but the plants continue to slowly reproduce vegatatively. These plants are probably the best plants to utilize in a culture system as restocking is virtually assured. Lemna gibba, L. valdiviana, L. minor, L. trisulca and L. minuscula are five such plants that frequently show some growth in the cool season. In some cases, L. gibba (Culley 1978) also shows rapid growth under summer conditions, making it a candidate for continuous culture. Lemna minor, S. intermedia and S. biperforata also do not form turions and rarely flower. L. minor may be a candidate for continuous culture, but the latter two are more suited for culture under warm condition. L. trisulca is a delicate, submerged form and thus will be more difficult to culture and harvest.

"At present, mixed cultures appear preferable to monoculture to insure the best yield on a yearly basis. Maintaing mixed cultures can present management problems, due to competition for space, variation in growth rates, and harvesting techniques that favor removal of certain species. For example, Wolffia species are easily suspended in the water column when harvesting in a manner that disturbs the water. Over time, the larger and more buoyant species are removed, leaving an increasing biomass of Wolffia for expansion. L. gibba, a very buoyant plant, will rise above the more flattened fronds of, for example, Spirodela polyrrhiza. Unless the plants are carefully harvested to prevent crowding the culture will gradually be dominated by L. gibba."
-Culley

Full-scale operations:

Mr. Dudley D. Culley has researched full-scale duckweed systems; however, the majority of research and duckweed work is still limited to lab and small pilot-scale studies. I am aware of only a few full-scale operations with duckweed plants; and of those, I believe only one is still operable. Duckweed grows on many wastewater lagoons, but it's rare to find one periodically harvesting the duckweed for nutrient (or BOD, TSS, etc.) treatment and even rarer to find a system with a cold climate like Cache Valley, UT. Here is a small list of the full-scale operations I'm aware of:
Most Successful: Agriquatics Mirzapur System (Bangladesh): article, website, video
Closest to Utah: Boulder City, NV wastewater treatment Lemna Corporation project supervised by Don Donahue--11 acre facultative lagoon with duckweed for BOD reduction; abandoned after 10 years. Produced high amounts of duckweed biomass but due to inadequate solids handling became too burdensome too continue. Don mentioned in personal correspondence that the duckweed stopped growing around 10'C.
Problems: Biloxi, Miss. (terminated) and Paragould, Ark. (never successful due to algae/fungus issues) as discussed here.

January 13, 2011

Investigating Duckweed for Phytoremediation and as a Toxicity Indicator of Chemicals

Click Here to View Paper

Title: Investigating Duckweed for Phytoremediation and as a
Toxicity Indicator of Chemicals
Created: May 2010
Author: Jon Farrell
Project: USU Environmental Toxicology 6270

Abstract:
Duckweed is an aquatic plant that can hyperaccumulate various nutrients and toxic metals, and can metabolize several organic chemicals. Duckweed is uniquely suited for phytoremediation of polluted surface water and for toxicity testing. Polyaromatic hydrocarbons (PAHs) are particularly toxic to duckweed and other plants due to metabolites, formed by UV photo-degradation of the parent compound, which ultimately lead to lower photosynthetic rates. On the other hand, plants like duckweed are useful from an environmental standpoint because they contribute to 45% of PAH degradation. This report reviews several studies that investigated the ability of plants like duckweed to uptake specific chemicals of concern. It also investigated the toxic effect certain chemicals like PAHs, As, Se, Cd, Cu, and chlorophenols had on duckweed—which in some instances like Cd, showed how toxic chemicals bioaccumulate through the food chain to humans. These toxic chemicals caused phytotoxicity via CYP-450 oxidation, free radicals, DNA damage, and cell membrane damage.

Background:
Duckweed has been researched extensively for more than 40 years (Clatworthy et al., 1960; Culley et al., 1981) as an ecological way of remediating polluted water and as a toxicity indicator. Researchers have investigated its ability to remove metals, inorganic nutrients, and more recently, organic chemicals including pharmaceuticals. Regarding phytoremediation, it has been noted that the best plants, including duckweed, hyperaccumulate the chemical(s) of concern, grow quickly, and harvest easily. Duckweed hyperaccumulates several toxic metals including Cd, Cu, and Se (Lone et al., 2008); has a high relative growth rate (RGR) of 0.06 up to 0.31 (Chaipraprat et al., 2005); and is a native species throughout the United States and the world (see Fig. 1), and simplifies harvesting due to the fact that it floats on water. These same characteristics make it ideally suited for toxicity testing because it uptakes many chemicals, grows on water including wastewater, and is adaptable to many environments. Both the American Public Health Association (APHA) and Environment Canada have official testing methods for duckweed toxicity testing.


Retrieved from USDA Plants Database
Figure 1: Distribution of Lemna minor (a.k.a. duckweed)

The majority of research concentrates on using duckweed for phytoremediation. A handful of studies have concentrated on using duckweed merely as toxicity indicators of aquatic environments (Tront et al., 2007; Saygideger et al., 2004) and a few of these studies have used duckweed to identify sentinel species. Sentinel species identify hazards to human health, similar to a canary in a coal mine. In a study done in Louisiana, Cd-enriched duckweed was fed to crayfish and the effect of bioaccumulation was seen as acetylcholinesterase activity diminished (Devi et al., 1996). The crayfish were labeled as sentinel species since they are only one step in the food chain away from humans. Duckweed not only shows promise for remediating polluted water, it also has proved itself in identifying harmful chemicals—some of which may end up on a dinner plate. In a very recent report from the President’s Cancer Panel, it was pointed out that 41% of Americans will be diagnosed with cancer and 21% will die from it. The United States was criticized of having a “reactionary rather than precautionary” regulatory approach. And the report pointed out that “only a few hundred of the more than 80,000 chemicals in use in the United States have been tested for safety” (USDHHS). While duckweed does not always uptake the same chemicals as humans nor experience the same toxic effects, at times it does behave similarly and also provides a relatively quick indication of hazards from certain chemicals like pharmaceuticals (Brain, 2004) and Polyaromatic Hydrocarbons (Kummerova et al., 2007).

While duckweed has been employed in full-scale remediation projects (Alaerts et al., 1996; Donahue, 2009), the majority of research has been conducted in laboratory settings and shows the effect of specific chemicals on the plant rather than entire ecological system (Bonairdi, Linton et al., 1998). Some compelling full-scale projects might include studies in North Carolina investigating duckweed as a means of cleaning up swine wastewater, specifically to remove nitrogen and phosphorus that would otherwise cause eutrophication and river impairment downstream from where lagoons discharge into rivers (Chaipraprat et al., 2005). In additional to removing inorganic nutrients, duckweed has also been shown to remove uranium and arsenic from mine drainage in Saxon, Germany (Makandawire 1 & 2) and hard to remove selenium (Ornes et al., 1991). There are several physiological characteristics that make duckweed suitable to remediation and toxicity testing.

Plant Physiology:
Duckweed is the common name for the Lemnaceae family of plants, with species like Lemna minor, Lemna Gibba, and Spirodela Polyrhizza. Duckweed is one of the smallest macrophytes, a monocot, angiosperm, and C-3 plant—which allows it to grow in colder climates with only 5-7 month growing seasons. Since water freezes in the winter and duckweed grows on water, it does best in warmer climates. Duckweed can produce seeds called turions, but typically reproduces asexually by growing more daughter fronds which eventually separate into their own colonies of 2-4 fronds.

Phytoremediation began as an interest to understand how nutrient metals were physiologically taken up by plants. These early studies looked into what factors made nutrients available to the plant from the soil. Phytoremediation as it’s known today, is concerned with using plants to remove harmful chemicals from the environment. Phytoremediation typically involves large fast growing plants rooted in soil that hyperaccumulate chemicals of concern. These plants include willows and poplars (Yifru et al., 2006); however, duckweed and other floating plants are uniquely able to remediate large water bodies without soil. Abiotic factors like pH and redox potential are the main drivers of metal availability in plants, but uptake mechanism are not solely limited to pH and ORP. Plant uptake of solutes and water depend on mechanisms such as osmotic potential, vapor potential, enzymes, microbes, and the physical nature of the chemical and the plant.

Osmotic potential is important to understanding plant-chemical relationships. Osmotic potential is the pressure gradient between the soil and plant, and is governed by the equation:

Where T=Total osmotic potential (approx. -2 to -1 Mpa); S=Solute potential (directly proportional to concentration and ionization of salts); P=Turdor potential (positive pressure as plant cells fill with water); M=Matrix potential (affinity of soils for water); and Z=pressure due to gravity (negligible)

Soil and healthy plants have a negative pressure. Depending on which pressure is greater drives where the water will go. Soil pressure is driven primarily by S + M while plant pressure is driven by S + P. If the osmotic pressure is greater in the substrate (i.e. soil or water) due to concentrated salts then the plant will not be successful at taking up chemicals.

Vapor pressure is essential to plant physiology and phytoremediation because it decreases P. as water transpires from the plant, thus drawing more water into the plant through the roots. Vapor pressure also governs whether certain chemicals, like trichloroethylene will volatilize through plant leaves (Orchard et al., 2000).

pH and redox potential effect the protonation of chemical compounds which in turn determines whether it is in a bioavailable form (Tront et al., 2007). pH and redox can be influenced by microbes near plant surfaces that hydrolyze chemicals (Makandawire). Enzymes enable certain chemicals (i.e. PO4-P) to be actively transported into and utilized by the plant functional groups.

The physical characteristics of chemicals and plants determine the type of chemicals taken up by plants and kinetic rate at which they’re taken up. Physical characteristics of the chemical include the octanol/water coefficient (Kow), molecular charge, and size. Typically, plants uptake organic chemicals with moderate to low hydrophobic Kow’s ranging from 0.5-3.5 into their tissue (i.e. lipid compounds); while on the other hand, aqueous chemicals (i.e. Kow<0.0) are easily transferred through plants via the xylem (Kim et al., 2004) or in some cases not taken up at all if the pKa is too low (Boutonnet). The uptake of hydrophobic to hydrophilic compounds by the plant via different mechanisms is shown via the root’s anatomy.

The plant’s roots can be visualized as circular layers of cells, beginning from the outermost layer: epidermis, cortex, endodermis, pericycle, and xylem. Different transport mechanisms exist to transfer chemicals through the different layers. According to Taiz, “Mineral nutrients absorbed by the root are carried to the shoot by the transpiration stream moving through the xylem” (Taiz et al., 1998) via the apoplast. Hydrophobic compounds don’t move through the apoplast; rather, they move through a network of interconnected lipid-cells known as the symplast (Taiz et al., 1998). According to Kim, non-aqueous chemicals (i.e. Kow>0) require symplastic movement through inner cells, aqueous chemicals require apoplastic movement through cell walls, and inorganic nutrients require “specific carrier- and channel-proteins” (Kim et al, 2004). Once a chemical is taken up by a plant it can be stored, metabolized (i.e. assimiliated), mineralized, or volatilized.

Physiological characteristics of plants (i.e. floating vs. rooted) make specific species more adept at removing specific chemicals. Individual laboratory tests frequently concentrate on one specie’s ability to uptake one type of chemical. In reality, ecological systems can contain multiple chemicals of concern. Some studies have looked into using multiple types of plants, each one with a particular ability to remove a specific chemical (Ornes et al. 1991). Other studies have observed competition between species that promote or inhibit multiple species (Clatworthy et al., 1960; Edwards et al., 1992, Wang et al., 2002).

Materials and Methods/Indicators of Phytotoxicity:
The majority of these studies investigating the use of duckweed and other plants for chemical uptake and toxicity were performed in the laboratory. One advantage of lab studies is that they “generate information about the fate of organic chemicals prior to field-scale tests because laboratory tests are less expensive, easier to control, and better enable investigators to elucidate fate mechanisms” (Kim et al., 2004). Each study regarding duckweed has a slightly different focus, ranging from finding uptake rates to discovering mechanisms of action. Due to a variety of focuses, each study also performed different tests (i.e. substrate solutions) and analyzed the results differently (i.e. chemical concentration vs. EC50). To begin with, a decision must be made as to what solution should be used to grow the plants, and whether or not the plants will be grown in large-several liter reactors, small shake flasks, or petri dishes. Standard methods exist for carrying out toxicity tests, but even these vary depending on what chemicals are being tested. For example, one test might require chelating agents in the nutrient solutions that in turn might make certain chemicals unavailable to the plant (Saygidegar). Nutrient solutions range from Hoagland, to Huntner, to industrial flue gas water (Sundberg et al., 2006), to wastewater.

The physical environment is often measured for light intensity, temperature, pH, ORP, and DO (Nzengung et al., 2004). These variables were used by Nzengung to demonstrate that uptake of perchlorate increased in aerobic conditions and enriched nitrate conditions; however, rhizodegradation decreased-and rhizodegradation is often preferred over plant uptake since it destroys perchlorate. In another study, pH measurements and comparison between pKa and percent protonated species revealed that chemical uptake utilized both abiotic (i.e. pH) and biotic (enzymatic transformation) mechanisms (Tront et al., 2007).

Enzymatic activity within plants were measured frequently to indicate toxicity. Activation of antioxidative enzymes were associated with free radical formation and subsequent physiological damage (Wang et al., 2004). Whereas, deactivation of acetylcholinesterase enzymes were associated with phytotoxicity due to Cd hyperaccumulation (Devi et al., 1996).

Mass balances showed the fate and motility of chemicals. The majority of studies reported the Bio Concentration Factor (BCF) which is the ratio of the amount of chemical in the plant tissue compared to the amount in the substrate solution. High BCF (typ. >1000) represent hyperaccumulation (Odjegba et al., 2004). A number of studies used C14 labeled chemicals to show the ratio of chemical in roots, to shoots, to the unaccounted chemical volatilized or degraded (Botcher).

Various extraction solutions provided similar data as C14 labeled compounds and were used to identify the chemicals connected to the roots and those in the shoots (Vadas et al., 2007), identified by the Root Concentration Factor (RCF). Similarly, extraction can be used to determine the amount of chemical adsorbed vs. absorbed/assimilated in plants. Comparable to BCF, the Transpiration Stream Concentration Factor (TSCF) shows the ratio of chemical in the transpiration stream to that in the external solute (Gomez-Hermosillo et al., 2006).

A study by Utah State University (USU) recognized the importance of carefully measuring and controlling the air to determine the fraction of chemical that was volatilized by plants. Trichloroethylene can be volatilized by fruit trees and poplar trees. USU created growth chambers specifically designed to keep track of CO2in/out, O2in/out, and also utilized CO2 traps to keep track of the fraction of mineralized chemicals (Orchard et al., 2000).

Phytotoxic effects were determined based on mass and size decrease and compared to chemical concentrations to determine toxic doses. Mass and size phytotoxic effects of chemicals were measured by relative growth rates (RGR) and Leaf Area Ratio (LAR). The toxic doses were usually reported as EC50 and LD50.

Phytotoxic effects to plants were measured indirectly in relation to photosynthesis. A decline in a plants ability to photosynthesize correlated with chlorophyll pigment reduction, which in turn was an indicator of more phytotoxic damage downstream. Several studies used non-destructive chlorophyll fluorometers to measure photosynthesis rates as they related to PAH toxicity (Slaski et al., 2002; Kummerova et al., 2007; Kapustka et al., 2004).

Chemical concentrations in solution and plant tissue required a variety of instruments ranging from Nuclear Magnetic Resonance (NMR), Inductively Couple Plasma (ICP), Atomic Absorption Spectrophotometry (AAS), Gas Chromatography (GC), and High Pressure Liquid Chromatography (HPLC).

Mechanisms of Action:
The materials and methods were often used to predict the mechanism of action (MOA) driving chemical uptake or phytotoxicity. The effect of PAHs on plants was frequently studied and the MOA driving toxicity was explained on various levels. For example, some studies simply stated that PAHs affected the chlorophyll, others stated that the damage was done in the thylakoid membrane where electron transport reactions occur (Marwood et al., 2003), and others reported MOA on the protein level (i.e. CYP-450 oxidation) (Kummerova et al., 2007). Reports show that PAH occurs naturally and anthropogenically as a parent compound (Marwood et al., 2003), but becomes more toxic after the metabolites are formed (El-Alawi et al., 2002) which can be an order of magnitude more toxic (Kummerova et al., 2007). PAH could be absorbed in solution or from the air, the principal toxic by-product is “UV-mediated photo-modification and subsequent disruption of photosynthesis [on aquatic plants]” (Kapustka et al., 2004). “Plants [uptake], translocate, transform, and accumulate PAHs,” and are responsible for eliminated up to 45% of the PAHs from the environment (Kummerova et al., 2007).

The MOA induced by Cu and Cd toxicity created free radicals that led to peroxidation of membrane lipids, which then led to loss of membrane integrity. “Plasma membrane permeability [could] result in leakage of potassium ions and other solutes and, finally, cause cell death” (Wang et al., 2004).

Uranium can enter inside of cells via mechanisms like: i) biomethylisation, which uptakes Ur via Methylobacterium spp. that symbiotically feed off of toxic plant by-products like CH4 (Taiz et al.); ii) assimilation, and iii) compartamentalization with specific enzymes (Makandawire et al., 2004, 2005).

Certain enzymes are only activated due to phytotoxicity and not physical cell damage. These enzymes include peroxidases (i.e. duckweed SpEx), superoxide dismutase, guaiacol peroxidase, and ascorbate peroxidase (Jansen et al., 2004; Wang et al., 2004). These enzymes were activated—toxicity indicator—after exposure with 2,4,6-trichlorophenol (TCP) and Copper. Chlorophenols were also enzymatically turned into glucoconjugates and incorporated into vacuoles and cell walls (Day et al., 2004).

Several MOAs were identified in a study observing the effect of duckweed exposure to pharmaceuticals. The studies quantified toxicity with plant necrosis, chlorophyll pigment, and carotenoid. The studies showed that fluoroquinolone-, sulfonamide-, and tetracycline-type compounds had the most toxic effect on duckweed. Fluoroquinolone toxicity caused bleaching of new fronds due to “inhibiting the activity of DNA gyrases.” The MOA of sulfamethoxazole is that they’re “folate antoagonists [which block] the conversion of p-aminobenzoid acid to the coenzyme dihydrofolic acid.” And the chlortetracycline inhibited protein synthesis (Brain et al., 2004, 2006).

Chemicals Studied:
Duckweed is suitable for phytoremediation of polluted surface water. It has demonstrated an ability to hyperaccumulate N, P, Cu, Cd, and Zn. Additionally, it accumulates more toxic metals such as As, Ag, Al, Cr, Fe, Hg, Ni, Pb, Ur (Objegba, Wang et al., 2004; Mkandawire et al., 2005, Olguin et al., 2005).

Organic chemicals taken up by duckweed and other plants include: N-nitrosodimethylamine (NDMA), perchlorate, trichloroethylene (TCE), di-chlorophenol (4-Cl-2-FP), triphenyltin, naphthalene, creosote, 2,4,6-trichlorophenol (TCP), chlorobenzene, and phenanthrene, plus various pharmaceuticals which have been found in the environment.

Engineering Significance & Applications:
The plants in the studies for this review were used to measure chemical uptake and toxicity in the following applications: Treatment of wastewater, mine drainage water, flue gas water, and aquatic pollution in wetlands, rivers, and lakes. Referring back to the canary in the coal mine analogy, plants like duckweed have the potential to point out the hazards associated with certain chemicals (some of which might be harmful to human health), while also removing these chemicals from impaired waters.


References:
Alaerts, G. J., Mahbubar, M. R., Kelderman, P. (1996). Peformance analysis of a full-scale duckweed-covered sewage lagoon. Water Research. 30(4), 843-852.

Boniardi, N., R. Rota, et al. (1999). Effect of dissolved metals on the organic load removal efficiency of Lemna gibba. Water Research 33, 530-538.

Bottcher, T. and R. Schroll (2007). The fate of isoproturon in a freshwater microcosm with Lemna minor as a model organism. Chemosphere. 66(4), 684-689.

Boutonnet, J. C., P. Bingham, et al. (1999). Environmental risk assessment of trifluoroacetic acid. Human and Ecological Risk Assessment. 5(1), 59-124.

Brain, A. R., Johnson, D. J., Richards, S. M., Hanson, M. L., Sanderson, H., Lam, M. W., Young, C., Mabury, S. A., Sibley, P. K., Solomon, K. R. (2004). Microcosm evaluation of the effects of an eight pharmaceutical mixture to the aquatic macrophytes Lemna gibba and Myriophyllum sibiricum. Aquatic Toxicology. 70, 23-40.

Brain, R. A., Sanderson, H., Sibley, P. K., Solomon, K. R. (2006). Probabilistic ecological hazard assessment, Evaluating pharmaceutical effects on aquatic higher plants as an example.
Ecotoxicology and Environmental Safety. 64, 128-135.

Chaiprapat S., Cheng, J. J., Classen, J. J., Liehr, S. K. (2005). Role of internal nutrient storage in duckweed growth for swine wastewater treatment. Trnasaction of the ASAE. 48(6), 2247-2258.

Clatworthy, J. N., Harper, J. L. (1960). The comparative biology of closely related species living in the same area. Comparative Biology. 307-324.

Culley Jr., D. D., Rejmankova, E., Kvet, J., Frye, J. B. (1981) Production, chemical, quality, and use of duckweed (Lemnaceae) in aquaculture, waste management, and animal feeds. Journal of World Mariculture Society. 12(2), 27-49.

Day, J. A. and F. M. Saunders (2004). Glycosidation of chlorophenols by Lemna minor. Environmental Toxicology and Chemistry. 23(3), 613-620.

Devi, M., D. A. Thomas, et al. (1996). Accumulation and physiological and biochemical effects of cadmium in a simple aquatic food chain. Ecotoxicology and Environmental Safety. 33(1), 38-43.

Donahue, D. (2009) Personal Correspondence.

Edwards, P., Hassan, M. S., Chao, C. H., Pacharaprakiti, C. (1992). Cultivation of duckweeds in setage-loaded earthen ponds. Bioresource Technology. 40, 109-117.

El-Alawi, Y. S., X. D. Huang, et al. (2002). Quantitative structure-activity relationship for the photoinduced toxicity of polycyclic aromatic hydrocarbons to the luminescent bacteria Vibrio fischeri. Environmental Toxicology and Chemistry. 2110), 2225-2232.

Gomez-Hermosillo, C., Pardue J. H., et al. (2006). Wetland plant uptake of desorption-resistant organic compounds from sediments. Environmental Science & Technology 40, 3229-3236.

Jansen, M. A. K., L. M. Hill, et al. (2004). A novel stress-acclimation response in Spirodela punctata (Lemnaceae), 2,4,6-trichlorophenol triggers an increase in the level of an extracellular peroxidase, capable of the oxidative dechlorination of this xenobiotic pollutant. Plant Cell and Environment. 27(5), 603-613.

Kapustka, L. A. (2004). Establishing Eco-SSLs for PAHs, Lessons revealed from a review of literature on exposure and effects to terrestrial receptors. Human and Ecological Risk Assessment. 10(2), 185-205.

Kim, J., M. C. Drew, et al. (2004). Uptake and phytotoxicity of TNT in onion plant. Journal of Environmental Science and Health Part a-Toxic/Hazardous Substances & Environmental Engineering. 39(3), 803-819.

Kummerova, M., S. Zezulka, et al. (2007). Photoinduced toxicity of fluoranthene on primary processes of photosynthesis in lichens. Lichenologist. 39, 91-100.

Linton, S., Goulder, R. (1998). The duckweed Lemna minor compared with the alga Selenastrum capricornutum for bioassay of pond-water richness. Aquatic Botany. 60, 7-36.

Lone, M. I., He Z., Stoffella, P. J., Yang, X. (2008). Phytoremediation of heavy metal polluted soils and water: progresses and perspectives. University of Science B. 9, 210-220.

Marwood, C. A., K. T. J. Bestari, et al. (2003). Creosote toxicity to photosynthesis and plant growth in aquatic microcosms. Environmental Toxicology and Chemistry. 22(5), 1075-1085.

Mkandawire, M. and E. G. Dudel (2005). Accumulation of arsenic in Lemna gibba L. (duckweed) in tailing waters of two abandoned uranium mining sites in Saxony, Germany. Science of the Total Environment. 336(1-3), 81-89.

Mkandawire, M., B. Tauert, et al. (2004). Capacity of Lemna gibba L. (Duckweed) for uranium and arsenic phytoremediation in mine tailing waters. International Journal of Phytoremediation. 6(4), 347-362.

Nzengung, V. A., H. Penning, et al. (2004). Mechanistic changes during phytoremediation of perchlorate under different root-zone conditions. International Journal of Phytoremediation. 6(1), 63-83.

Odjegba, V. J. and I. O. Fasid (2004). Accumulation of trace elements by Pistia stratiotes, implications for phytoremediation. Ecotoxicology. 13(7), 637-646.
Olguin, E. J., G. Sanchez-Galvan, et al. (2005). Surface adsorption, intracellular accumulation and compartmentalization of Pb(II) in batch-operated lagoons with Salvinia minima as affected by environmental conditions, EDTA and nutrients. Journal of Industrial Microbiology & Biotechnology. 32(11-12), 577-586.

Orchard, B. J., W. J. Doucette, et al. (2000). A novel laboratory system for determining fate of volatile organic compounds in planted systems. Environmental Toxicology and Chemistry. 19(4), 888-894.

Ornes, W. H., K. S. Sajwan, et al. (1991). Bioaccumulation of Selenium by Floating Aquatic Plants. Water Air and Soil Pollution. 57-8, 53-57.

Prasad, M. N. V. and H. M. D. Freitas (2003). Metal hyperaccumulation in plants - Biodiversity prospecting for phytoremediation technology. Electronic Journal of Biotechnology. 6(3), 285-321.

Reinhold, D. M. and E. M. Saunders (2006). Phytoremediation of fluorinated agrochemicals by duckweed. Transactions of the Asabe. 49(6), 2077-2083.

Saygideger, S. and M. Dogan (2004). Lead and cadmium accumulation and toxicity in the presence of EDTA in Lemna minor L. and Ceratophyllum demersum L. Bulletin of Environmental Contamination and Toxicology. 73(1), 182-189.

Slaski, J. J., D. J. Archambault, et al. (2002). Physiological tests to measure impacts of gaseous polycyclic aromatic hydrocarbons (PAHs) on cultivated plants. Communications in Soil Science and Plant Analysis. 33(15-18), 3227-3239.

Sundberg, S. E., S. M. Hassan, et al. (2006). Enrichment of elements in detritus from a constructed wetland and consequent toxicity to Hyalella azteca. Ecotoxicology and Environmental Safety. 64(3), 264-272.

Taiz, E., Zeiger, E. (1998). Plant Physiology. 2nd ed. 147-152; 173-193.

Tront, J. M. and F. M. Saunders (2006). Role of plant activity and contaminant speciation in aquatic plant assimilation of 2,4,5-trichlorophenol. Chemosphere. 64(3), 400-407.

Tront, J. M. and F. M. Saunders (2007). Sequestration of a fluorinated analog of 2,4-dichlorophenol and metabolic products by L-minor as evidenced by F-19 NMR. Environmental Pollution. 145(3), 708-714.

Vadas, T. M., X. Zhang, et al. (2007). Fate of DTPA, EDTA, and EDDS in hydroponic media and effects on plant mineral nutrition. Journal of Plant Nutrition. 30(7-9), 1229-1246.

Wang, H., X. Q. Shan, et al. (2004). Responses of antioxidative enzymes to accumulation of copper in a copper hyperaccumulator of Commoelina communis. Archives of Environmental Contamination and Toxicology. 47(2), 185-192.

Wang, Q., Y. Cui, et al. (2002). Phytoremediation of polluted waters potentials and prospects of wetland plants. Acta Biotechnologica. 22(1-2), 199-208.

Yifru, D. D. and V. A. Nzengung (2006). Uptake of N-nitrosodimethylamine (NDMA) from water by phreatophytes in the absence and presence of perchlorate as a co-contaminant. Environmental Science & Technology. 40(23), 7374-7380.

Literature Review re: duckweed for phytoremediation and toxicity indicator

Click Here to View Lit. Review Worksheet

COMMON THEMES in PHYTOREMEDIATION re: MECHANISMS OF ACTION

Wang, H., X. Q. Shan, et al. (2004). "Responses of antioxidative enzymes to accumulation of copper in a copper hyperaccumulator of Commoelina communis." Archives of Environmental Contamination and Toxicology 47(2): 185-192.

McFarlane, C., C. Nolt, et al. (1987). "The Uptake, Distribution and Metabolism of Four Organic Chemicals by Soybean Plants and Barley Roots." Environmental Toxicology and Chemistry 6: 847-856.

Topp, E., I. Scheunert, et al. (1986). "Factors Affecting the Uptake of C-14-Labeled Organic-Chemicals by Plants from Soil." Ecotoxicology and Environmental Safety 11(2): 219-228.

Sundberg, S. E., S. M. Hassan, et al. (2006). "Enrichment of elements in detritus from a constructed wetland and consequent toxicity to Hyalella azteca." Ecotoxicology and Environmental Safety 64(3): 264-272.

Odjegba, V. J. and I. O. Fasid (2004). "Accumulation of trace elements by Pistia stratiotes: implications for phytoremediation." Ecotoxicology 13(7): 637-646.

Yifru, D. D. and V. A. Nzengung (2006). "Uptake of N-nitrosodimethylamine (NDMA) from water by phreatophytes in the absence and presence of perchlorate as a co-contaminant." Environmental Science & Technology 40(23): 7374-7380.

Vadas, T. M., X. Zhang, et al. (2007). "Fate of DTPA, EDTA, and EDDS in hydroponic media and effects on plant mineral nutrition." Journal of Plant Nutrition 30(7-9): 1229-1246.

Flocco, C. G., A. Lobalbo, et al. (2002). "Some physiological, microbial, and toxicological aspects of the removal of phenanthrene by hydroponic cultures of alfalfa (Medicago sativa L.)." International Journal of Phytoremediation 4(3): 169-186.

Kim, J., M. C. Drew, et al. (2004). "Uptake and phytotoxicity of TNT in onion plant." Journal of Environmental Science and Health Part a-Toxic/Hazardous Substances & Environmental Engineering 39(3): 803-819.

Nzengung, V. A., H. Penning, et al. (2004). "Mechanistic changes during phytoremediation of perchlorate under different root-zone conditions." International Journal of Phytoremediation 6(1): 63-83.

Orchard, B. J., W. J. Doucette, et al. (2000). "A novel laboratory system for determining fate of volatile organic compounds in planted systems." Environmental Toxicology and Chemistry 19(4): 888-894.

LEMNA

Blackman, G. E., G. Sen, et al. (1959). "The Uptake of Growth Substances I. Factors Controlling the Uptake of Phenoxyacetic acids by Lemna Minor." Journal of Experimental Botany 10(28): 35-54.

Wang, Q., Y. Cui, et al. (2002). "Phytoremediation of polluted waters potentials and prospects of wetland plants." Acta Biotechnologica 22(1-2): 199-208.

Tront, J. M. and F. M. Saunders (2007). "Sequestration of a fluorinated analog of 2,4-dichlorophenol and metabolic products by L-minor as evidenced by F-19 NMR." Environmental Pollution 145(3): 708-714.

Tront, J. M. and F. M. Saunders (2006). "Role of plant activity and contaminant speciation in aquatic plant assimilation of 2,4,5-trichlorophenol." Chemosphere 64(3): 400-407.

Song, Z. H. and G. L. Huang (2005). "Toxic effect of triphenyltin on Lemna polyrhiza." Applied Organometallic Chemistry 19(7): 807-810.

Slaski, J. J., D. J. Archambault, et al. (2002). "Physiological tests to measure impacts of gaseous polycyclic aromatic hydrocarbons (PAHs) on cultivated plants." Communications in Soil Science and Plant Analysis 33(15-18): 3227-3239.

Saygideger, S. and M. Dogan (2004). "Lead and cadmium accumulation and toxicity in the presence of EDTA in Lemna minor L. and Ceratophyllum demersum L." Bulletin of Environmental Contamination and Toxicology 73(1): 182-189.

Reinhold, D. M. and E. M. Saunders (2006). "Phytoremediation of fluorinated agrochemicals by duckweed." Transactions of the Asabe 49(6): 2077-2083.

Prasad, M. N. V. and H. M. D. Freitas (2003). "Metal hyperaccumulation in plants - Biodiversity prospecting for phytoremediation technology." Electronic Journal of Biotechnology 6(3): 285-321.

Ornes, W. H., K. S. Sajwan, et al. (1991). "Bioaccumulation of Selenium by Floating Aquatic Plants." Water Air and Soil Pollution 57-8: 53-57.

Olguin, E. J., G. Sanchez-Galvan, et al. (2005). "Surface adsorption, intracellular accumulation and compartmentalization of Pb(II) in batch-operated lagoons with Salvinia minima as affected by environmental conditions, EDTA and nutrients." Journal of Industrial Microbiology & Biotechnology 32(11-12): 577-586.

Mkandawire, M., B. Tauert, et al. (2004). "Capacity of Lemna gibba L. (Duckweed) for uranium and arsenic phytoremediation in mine tailing waters." International Journal of Phytoremediation 6(4): 347-362.

Mkandawire, M. and E. G. Dudel (2005). "Accumulation of arsenic in Lemna gibba L. (duckweed) in tailing waters of two abandoned uranium mining sites in Saxony, Germany." Science of the Total Environment 336(1-3): 81-89.

Marwood, C. A., K. T. J. Bestari, et al. (2003). "Creosote toxicity to photosynthesis and plant growth in aquatic microcosms." Environmental Toxicology and Chemistry 22(5): 1075-1085.

Kummerova, M., S. Zezulka, et al. (2007). "Photoinduced toxicity of fluoranthene on primary processes of photosynthesis in lichens." Lichenologist 39: 91-100.

Kara, Y. (2004). "Bioaccumulation of copper from contaminated wastewater by using Lemna minor." Bulletin of Environmental Contamination and Toxicology 72(3): 467-471.

Kapustka, L. A. (2004). "Establishing Eco-SSLs for PAHs: Lessons revealed from a review of literature on exposure and effects to terrestrial receptors." Human and Ecological Risk Assessment 10(2): 185-205.

Jansen, M. A. K., L. M. Hill, et al. (2004). "A novel stress-acclimation response in Spirodela punctata (Lemnaceae): 2,4,6-trichlorophenol triggers an increase in the level of an extracellular peroxidase, capable of the oxidative dechlorination of this xenobiotic pollutant." Plant Cell and Environment 27(5): 603-613.

Gallardo-Williams, M. T., V. A. Whalen, et al. (2002). "Accumulation and retention of lead by cattail (Typha domingensis), hydrilla (Hydrilla verticillata), and duckweed (Lemna obscura)." Journal of Environmental Science and Health Part a-Toxic/Hazardous Substances & Environmental Engineering 37(8): 1399-1408.

Fayiga, A. O., L. Q. Ma, et al. (2004). "Effects of heavy metals on growth and arsenic accumulation in the arsenic hyperaccumulator Pteris vittata L." Environmental Pollution 132(2): 289-296.

El-Alawi, Y. S., X. D. Huang, et al. (2002). "Quantitative structure-activity relationship for the photoinduced toxicity of polycyclic aromatic hydrocarbons to the luminescent bacteria Vibrio fischeri." Environmental Toxicology and Chemistry 2110): 2225-2232.

Duxbury, C. L., D. G. Dixon, et al. (1997). "Effects of simulated solar radiation on the bioaccumulation of polycyclic aromatic hydrocarbons by the duckweed Lemna gibba." Environmental Toxicology and Chemistry 16(8): 1739-1748.

Drost, W., M. Matzke, et al. (2007). "Heavy metal toxicity to Lemna minor: studies on the time dependence of growth inhibition and the recovery after exposure." Chemosphere 67(1): 36-43.

Devi, M., D. A. Thomas, et al. (1996). "Accumulation and physiological and biochemical effects of cadmium in a simple aquatic food chain." Ecotoxicology and Environmental Safety 33(1): 38-43.

Debusk, T. A., R. B. Laughlin, et al. (1996). "Retention and compartmentalization of lead and cadmium in wetland microcosms." Water Research 30(11): 2707-2716.

Day, J. A. and F. M. Saunders (2004). "Glycosidation of chlorophenols by Lemna minor." Environmental Toxicology and Chemistry 23(3): 613-620.

Cecal, A., K. Popa, et al. (2002). "Bioaccumulation in hydrophytae plants of some microelements from alkaline sludge resulting in uranium ores processing." Revista De Chimie 53(4): 290-293.

Boutonnet, J. C., P. Bingham, et al. (1999). "Environmental risk assessment of trifluoroacetic acid." Human and Ecological Risk Assessment 5(1): 59-124.

Bottcher, T. and R. Schroll (2007). "The fate of isoproturon in a freshwater microcosm with Lemna minor as a model organism." Chemosphere 66(4): 684-689.

Boniardi, N., R. Rota, et al. (1999). "Effect of dissolved metals on the organic load removal efficiency of Lemna gibba." Water Research 33(2): 530-538.

Barber, J. L., G. O. Thomas, et al. (2004). "Current issues and uncertainties in the measurement and modelling of air-vegetation exchange and within-plant processing of POPs." Environmental Pollution 128(1-2): 99-138.

TYPES OF CHEMICALS TAKEN UP BY DUCKWEED

"Microcosm evaluation of the effects of an eight pharmaceutical mixture to the aquatic macrophytes Lemna gibba and Myriophyllum sibiricum"
Aquatic Toxicology, Volume 70, Issue 1, 18 October 2004, Pages 23-40
Richard A. Brain, David J. Johnson, Sean M. Richards, Mark L. Hanson, Hans Sanderson, Monica W. Lam, Cora Young, Scott A. Mabury, Paul K. Sibley, Keith R Solomon

"Probabilistic ecological hazard assessment: Evaluating pharmaceutical effects on aquatic higher plants as an example"
Ecotoxicology and Environmental Safety, Volume 64, Issue 2, June 2006, Pages 128-135
Richard A. Brain, Hans Sanderson, Paul K. Sibley, Keith R. Solomon

"Aquatic microcosm assessment of the effects of tylosin on Lemna gibba and Myriophyllum spicatum"
Environmental Pollution, Volume 133, Issue 3, February 2005, Pages 389-401
Richard A. Brain, Ketut (Jim) Bestari, Hans Sanderson, Mark L. Hanson, Christian J. Wilson, David J. Johnson, Paul K. Sibley, Keith R. Solomon

"Toxicity classification and evaluation of four pharmaceuticals classes: antibiotics, antineoplastics, cardiovascular, and sex hormones"
Toxicology, Volume 203, Issues 1-3, 15 October 2004, Pages 27-40
Hans Sanderson, Richard A. Brain, David J. Johnson, Christian J. Wilson, Keith R. Solomon

"Effects of a mixture of tetracyclines to Lemna gibba and Myriophyllum sibiricum evaluated in aquatic microcosms"
Environmental Pollution, Volume 138, Issue 3, December 2005, Pages 425-442
Richard A. Brain, Christian J. Wilson, David J. Johnson, Hans Sanderson, Ketut (Jim) Bestari, Mark L. Hanson, Paul K. Sibley, Keith R. Solomon

HOW DUCKWEED UPTAKES CHEMICALS (i.e. physio-chemico Phosphate system uptake of Aresenic (AS))

"Arsenic accumulation in duckweed (Spirodela polyrhiza L.): A good option for phytoremediation"
Chemosphere, Volume 69, Issue 3, September 2007, Pages 493-499
M. Azizur Rahman, Hiroshi Hasegawa, Kazumasa Ueda, Teruya Maki, Chikako Okumura, M. Mahfuzur Rahman

"The influence of Lemna gibba L. on the degradation of organic material in duckweed-covered domestic wastewater"
Water Research, Volume 32, Issue 10, October 1998, Pages 3092-3098
S. Körner, G. B. Lyatuu, J. E. Vermaat

"Toxicity of hexazinone and diquat to green algae, diatoms, cyanobacteria and duckweed"
Aquatic Toxicology, Volume 39, Issue 2, September 1997, Pages 111-134
Hans G. Peterson, Céline Boutin, Kathryn E. Freemark, Pamela A. Martin

"Ecophysiological tolerance of duckweeds exposed to copper"
Aquatic Toxicology, Volume 91, Issue 1, 18 January 2009, Pages 1-9
Myriam Kanoun-Boulé, Joaquim A.F. Vicente, Cristina Nabais, M.N.V. Prasad, Helena Freitas

Preliminary Literature Review

Title: Literature Review for Duckweed Systems: P-removal, Growth, and Harvest
Created: 29 April 2010
Author: Jon Farrell

Background:

Nutrient removal from wastewater prevents eutrophication from occurring downstream where the wastewater is discharged into water bodies such as rivers and reservoirs. One nutrient removal system that has been researched extensively over the past 40 years (Culley) utilizes duckweed plants (Lemnaceae) which uptake nutrients like N, P, K, Ca, and Mg into its biomass as it grows. Duckweed systems rely on three basic principles: nutrient uptake, harvesting, and solids management.

Duckweed plants typically contain more phosphorus in its tissue than other floating plants, which makes them suitable for phosphorus removal (Alaerts, Reddy). Duckweed systems usually treat sewage lagoons that receive weak municipal wastewater containing 1-4mg-P/L; however, duckweed is also used to treat swine lagoon waste containing 62.5-135mg-P/L (Chaiprapat).

Harvesting is an essential component of duckweed nutrient removal systems because it physically removes the phosphorus from the system via the biomass. Without harvesting, the plant tissue would die, settle to the bottom of the lagoon, decompose and then release the phosphorus and other nutrients back into the water column. This harvested biomass can be used as compost (Donahue), fodder rich in protein (Culley), or to generate fuel like methane (Clark).

Duckweed:

Duckweed grows naturally in almost every region with a growing season of at least five months. Most studies involving duckweed take place in climates with 9-10 month growing seasons; however, several also take place in regions with only 5-7 month growing seasons (Culley). Duckweed is a monocot, it floats on water, and has one of the fastest growth rates of any of the macrophytes. Duckweed is the common name for the Lemnaceae family of plants, with species like Lemna minor, Lemna Gibba, Spirodela Polyrhizza, and Wolffia (genus name). Duckweed studies range from full-scale operations with ponds covering 200m2 (Edwards) to 11 acres (Donahue); to pilot scale operations with only a few m2 (Reddy, Zimmo), to lab scale tests in jars with only 0.004 m2 surface area (Chaiprapat).

Phosphorus Removal:

Many studies have pointed out a direct correlation between %P in the plant tissue and the available P in the water column (Alaerts, Culley). As the PO4-P (bioavailable P) concentration in the water column decreases so does the %P in the tissue. While 1%-P is very common in oven dried duckweed, values have been reported from 0.3 up to 2.6%-P. Percent dry matter ranges from 5.4-8% with 69-86% being the organic (volatile) fraction. The N:P ratio is typically 5:1 (Alaerts, Edwards). Knowing the %P and %N in the duckweed tissue helps to construct a mass balance identifying the fate of phosphorus in the system.

Up to 100% phosphorus removal has been reported in bench scale tests (Chaiprapat); however, 60-75% phosphorus removal (Alaerts, Zimmo, and Kadlec) is more common. These same reports have identified duckweed biomass as contributing 13-47% of the total phosphorus removal, and one account attributes all of it to duckweed. The phosphorus concentration in the effluent coming from duckweed systems almost always falls below 1mg-TP/L and frequently less than 0.53mg-P/L down to 0.05mg-P/L (Willet, Edwards, Alaerts). Edwards observed that duckweed growth decreases when phosphorus levels fall below 0.3mg/L.

Duckweed Growth:

Most studies recommended starting and maintaining duckweed systems with enough duckweed to fully cover the surface area. Full coverage provides some of the highest growth rates (Reddy), but perhaps more importantly, it prevents algae proliferation that out competes the duckweed (Edwards, Al-Nozaily, Lemna Corp.) and leads to decreased productivity. Starting densities should be kept in the linear range between 10-120 g(dry)/m2 for Lemna minor (Reddy). Reddy and Edwards recommended starting with 10-11.9 g(dry)/m2; Culley, Chaiprapat, and Zimmo recommended 30-40 g(dry)/m2; while Willet, Lemna Corp., and Alaerts recommended 80-132 g(dry)/m2. Starting densities with fresh duckweed ranged from 500 to approx. 1500 g/m2. Typical seasonal yields ranged from 3-9.5 tons(dry)/ac·yr. Maximum yields between 17-25 tons(dry)/ac·yr have also been reported (Alaerts, Edwards). The relative growth rate (RGR, gnew/gold·day) of duckweed ranges from 0.06-0.121 for many systems (Chaiprapat, Culley, Willet) up to 0.24-0.31 for lab experiments. Al-Nozaily observed that light intensity was the single most important variable controlling RGR, and recommended providing 200-300 umol/m2·sec (ppf) for highest growth rates indoors.

Several factors limiting growth rates have been observed. Growth rate decreases as biomass accumulates to the point that fronds start overlapping each other (Al-Nozaily, Chaiprapat, Culley, Reddy). Growth rate decreases with nutrient depletion (Chaiprapat, Culley, Edwards). Duckweed prefers ammonium (NH4) to ammonia (NH3), and growth decreases when NH3>NH4 or when pH exceeds 9.25 (Al-Nozaily, Culley). Phosphorus precipitation also occurs at pH near 9.3, which also leads to nutrient deficiencies and lower growth rates. Several studies indicated that wind or movement decreased growth (Edwards, Willet). Biomass started depleting at temperatures below 17°C, and completely disappeared below 5°C (Donahue, Zimmo). Growth rate also decreased due to competition between species. Edwards noticed that Wolffia out-competed the Lemna species and yielded less biomass due to its smaller plant size. Aphids living atop duckweed mats in some instances were associated with decreased growth as well (Zimmo, Edwards).

Harvesting:

The frequency of harvesting and the amount of biomass removed per harvest varies from study to study. However, consistent observations include: 1) Maintain 100% coverage to reduce algae growth; 2) Harvest at least once every 20 days—the more frequent the better for nutrient removal; and 3) Harvest frequency and amount often depends on the available manpower and equipment available to harvest.
Continuous harvesting prevents overcrowding, biomass death, and release of nutrients back into the water column. Culley reported that up 50% of the N & P in the biomass gets released if more than 20 days go by between harvests. Alaerts harvested approx. 4.5mg(dry)/m2·day, Willet harvested 50% after the biomass had doubled the starting density, while Edwards harvested every 2-15 days depending on whether it was the dry(warm) or wet(cool) season, respectively.

Harvest rates depend not only on duckweed growth, but also on the ability to physically harvest the system. Donahue, superintendent of a Lemna Corp. duckweed covered lagoon in Boulder City, NV, reported harvesting the entire lagoon every week. This required harvesting 11acres/wk. at a rate of 37g/m2·week. This yielded approx. 71 tons (dry)-duckweed per year. Two people worked 10 hr. shifts M-Th and used mechanical harvesters with 4 ft. wide conveyors to remove the fresh duckweed that was then loaded into trucks and composted at the local landfill. Donahue reported that the duckweed system was used for approx. 10 years before being shut down because they could not keep up with the quantity of duckweed produced. Hence, careful solids management programs are necessary to guarantee sustainable and long-lasting duckweed systems.

Experimental Setup:

Background:

This study looked into the practicality of using a duckweed system to remove phosphorus from the Wellsville (UT) Municipal Sewage Lagoons. These lagoons were constructed in the 1960’s and cover 56 acres. Currently, this is a 0.5 MGD system that is expected to increase flow during the next 10 years to the point that the Utah Dept. of Environmental Quality (UDEQ) is concerned that it will not be able to meet its allowable 432kg-P/yr. discharge permit. A duckweed system for phosphorus removal seems promising in Wellsville for two principal reasons: 1) native duckweed plants (a mixed culture of Lemna minor and Wolffia) already cover the entire surface of the lagoons for at least 6 months (May through October); and 2) Wellsville has weak wastewater with approx. 4mg-P/L which results in a loading of approx. 12.2g-P/m2·yr. which is in the recommended <20g-P/m2·yr. range (Kadlec).

Material and Methods:

Phosphorus removal and duckweed growth:

A mixed culture of L. minor and Wolffia was seeded into approx. a 113 L acrylic reactor (3 ft. L x 2 ft. W x 8 in D) and divided into 3 sections simulating 3 lagoons; an identical reactor was placed next to it without duckweed as a control. The experiment took place for one year in a 25°C constant temperature room. High-pressure sodium lamps (HPSLs) were suspended 48 in. above the plants and provided 300 umol/m2/sec (ppf) 16 hrs/day. Raw wastewater from Wellsville influent was continuously fed with peristaltic pumps at a rate of approx. 1.77 Lpd. An average 66% of the influent flow evaporated per day, and so dilution tap water was continuously fed at 0.64 Lpd to provide enough effluent. The effluent was captured in 15 L buckets. Duckweed was re-seeded a few times at starting densities ranging from 15-90 g(dry)/m2 . Plant harvesting occurred every 7-14 days and removed 25-75% of the coverage. Plants were oven dried at 105°C to get dry mass of duckweed.

Measurements:

Total Phosphorus measurements were made with HACH test kit method 10127. Reactive Phosphorus (PO4-P) measurements were made with ascorbic acid APHA Standard Method 4500P-E. Total Nitrogen, Ammonia, and Nitrate measurements were made with HACH test kit methods 10071, 10031, and 10020, respectively. Alkalinity, TSS, and VSS measurements followed APHA Standard Methods. pH and DO measurements were made with Corning and Hanna probes, respectively. Duckweed tissue samples were measured by the Utah State University Analytical Lab (USUAL). Phosphorus concentrations in plant tissue and sediments were also measured for PO4-P following dry ashing at 550°C with subsequent wet aqua regia digestion; these results were verified with standard grape petiole leaves with a known 0.38%P dry weight.
References:

Alaerts, G. J., M. R. Mahbubar, and P. Kelderman. 1996. Performance analysis of a full-scale duckweed-covered sewage lagoon. Wat. Res. 30(4):843-852.

Al-Nozaily, F. G. 2001. Performance and Process Analysis of Duckweed-Covered Sewage Lagoons for High Strength Sewage. Rotterdam, NL: A. A. Balkema.

Chaiprapat S., J. J. Cheng, J. J. Classen, and S. K. Liehr. 2005. Role of internal nutrient storage in duckweed growth for swine wastewater treatment. Transaction of the ASAE. 48(6):2247-2258.

Clark, P. B., and P. F. Hillman. 1996. Enhancement of anaerobic digestion using duckweed (Lemna minor) enriched with iron. J. of the Chartered Institution of Water and Environmental Management. 10(2):92-95.

Culley Jr., D. D., E. Rejmankova, J. Kvet, and J. B. Frye. 1981. Production, chemical quality, and use of duckweed (Lemnaceae) in aquaculture, waste management, and animal feeds. J. World Maric. Soc. 12(2):27-49.

Donahue, Don. Superintendent of the Boulder City (NV) Wastewater Treatment Plant. Personal correspondence. 3/18/2009.

Edwards, P., M. S. Hassan, C. H. Chao, and C. Pacharaprakiti. 1992. Cultivation of duckweeds in septage-loaded earthen ponds. Bioresource Technology. 40:109-117.

Kadlec, R. H. 2009. Treatment Wetlands. 2nd ed. Boca Raton, FL: CRC Press.

Lemna Corporation. 1996. Operation and Maintenance Manual for Boulder City, Nevada . St. Paul, MN: Lemna Corporation.

Reddy, K. R., and W. F. De Busk. 1985. Growth characteristics of aquatic macrophytes cultured in nutrient-enriched water: II. Azolla, duckweed, and salvinia. Economic Botany 39(2): 200-208.

Willet, D. 2005. Duckweed-based Wastewater Treatment Systems: Design Aspects and Integrated Reuse Options for Queensland Conditions. Brisbane, AU: DPI&F Publications.

Zimmo, O. R. 2002. Process performance assessment of algae-based and duckweed-based wastewater treatment systems. Water Sci. and Tech. 45(1):91-101.

Lab Testing vs. Field Work

What happens when you take something from its natural environment and place it in a new environment and then extrapolate the results back into the natural environment?

Be aware that there is a difference between what you find out in the laboratory and what actually takes place in the world. Be cautious about how laboratory data is extrapolated to natural environments.

The paper below was inspired by my own experience discovering that lab studies do not reflect 100% the natural environment. I quickly discovered there's more to growing duckweed than taking it from one place and moving it to another. The duckweed I use grows naturally here in Cache Valley on the Wellsville and Logan City wastewater treatment lagoons. They grow fine outdoors in their native environment, it's not until I bring them inside that their behavior changes and I have difficulty maintain a good healthy culture.

Future posts will address the issues I've come accross (e.g. light intensities, algae-duckweed competition, phytophagous fauna, fungi, crop densities, and pH). But as a teaser take a look at the photos below which show the effect fungi can have on duckweed. The duckweed was removed from very healthy populations; however, once they came indoors the conditions began to favor a certain fungi that within days/weeks destroys the duckweed crop.

Figure 1: Start of experiment with healthy duckweed from Cache Valley (Lemna minor species).
Also shown is the Omega pH controller (pH 7.7, later lowered to 6.5), pH probe, temp. probe, 100 L reactors with nutrient solution based on hydroponic solution explained here, high-pressue soldium lamps (HPLS) 4 ft. above supplying approx. 175ppf (16/8hrs on/off), constant temp. @ 25'C.

Figure 2: Chlorosis/necrosis setting-in causing yellowing and bleaching of some duckweed fronds. Note: similar blight patches were seen in actual duckweed covers outdoors on the wastewater lagoons in Wellsville; however, it appears there is enough duckweed to overcome the blight. An interesting article titled "Dynamics of fungal infection in duckweeds (Lemnaceae)" by Rejmankova E. (1986) talks about this phenomena and is referenced on this informative website.

Figure 3: More blight and bleaching of fronds short time after.

Figure 4: Majority of duckweed is chlorotic within a short period of time.

Figure 5: The result is a mat of chlorotic/necrotic (i.e. dead) duckweed which is submerged just below the surface of water. Perhaps the submersion actually suffocates the plants.

Figure 6: The culprit. Microrganisms are thriving all over the tissues of the unhealthy duckweed plants. These observations support an intersting article discussing why invertabrates consume decaying macrophytes rather than living ones.

Figure 7: The stringy organisms appear to be fungi which mats the duckweed together and leads to its death.



video
Video: "Duckweed Feast" showing duckweed tissue in varying states of decomposition due to bacteria colonies, rotifers, vorticella, and fungi.

Title: Recognizing the effect of extrapolating lab data into natural environments
Created: 30 April 2009
Author: Jon Farrell

January 11, 2011

Duckweed Research: getting started

Duckweed has been the topic of my research for nearly 3 years now. Lab work, field work, literature review...my notebooks and data keep increasing and yet I still haven't written my proposal to initiate my official research. I have presented at a few conferences and even made a couple posters; yet, I have not yet written a paper from beginning to end discussing my objectives, methods, results, and recommendations. So it's about time.



Despite collecting oodles of information and drafting several outlines, the task of actually sitting down and writing my thesis is overwhelming. As I've pondered about how to accomplish this task I've been inspired by three sources: Mark Twain, the scriptures, and my wife. Mark Twain is credited with saying:

"The secret of getting ahead is getting started. The secret of getting started is breaking your complex overwhelming tasks into small manageable tasks, and then starting on the first one."
Mark Twain

While Alma, from The Book of Mormon, said:

"Now ye may suppose that this is foolishness in me; but behold I say unto you, that by small and simple things are great things brought to pass; and small means in many instances doth confound the wise."
Alma 37:6

And finally, my wife is credited with saying...well, a lot. She is an inspiring writer/researcher/blogger.

So that's my method for getting this proposal/thesis written--breaking the writing task into smaller pieces via blogs. By blogging about my research, it will not only provide a template for writing and brainstorming, but will also provide a place to document stuff that will never make it into my final thesis.

Here are most of the presentations and posters associated with this research project:

Water Environment Association of Utah (WEAU)--Fall 2008 Conference Poster
"Laboratory Experiment for the Evaluation of Duckweed as a Cost-Effective Technology for Management of Nutrients and Emerging Contaminants in Municipal Wastewater Systems"

WEAU--April 2009 Conference Presentation
"Ecological Engineering That Uses Duckweed to Remove Phosphorus and Nitrogen from Wastewater"

Slides prepared for Wellsville City proposing duckweed treatment and showing Boulder City, NV, project details--Summer 2009 Slides (never presented, information only)
"Presentation for Wellsville City showing Boulder City NV equipment and results"

WEAU--Fall 2009 Poster co-produced with Maureen Kesaano
"Understanding Duckweed Systems from Harvest to Disposal"

Spring Runoff Conference (Utah State University)--April 2009 Presentation--First Place
"Using Duckweed to Remove Phosphorus and Improve Water Quality"

WEAU--Fall 2010 Conference Presentation
"A Theoretical duckweed System for Removing Phosphorus from Logan City Wastewater and How it Compares with an Algae System"

USU Environmental Engineering Seminar--Spring 2011 Presentation
"A duckweed system for removing phosphorus from Wellsville City wastewater"

1st International Conference of Duckweed Research and Applications--October 2011
"Understanding a duckweed system in a temperate climate from harvest to disposal"

1st International Conference of Duckweed Research and Applications--October 2011 (co-presenter with Dr. Louis Landesman from Virginia State University)
"Modeling the growth of duckweed populations"

WEAU--Fall 2011 Conference Presentation
"What duckweed does for lagoons"

Thesis Defense--April 17, 2012
"Duckweed uptake of phosphorus and pharmaceuticals from wastewater in Wellsville City (UT)"