| Lemna minor | |
|---|---|
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Scientific classification  | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Monocots |
| Order: | Alismatales |
| Family: | Araceae |
| Genus: | Lemna |
| Species: | L. minor |
| Binomial name | |
| Lemna minor | |
Lemna minor, the common duckweed [2] [3] or lesser duckweed, is a species of aquatic freshwater plant in the subfamily Lemnoideae of the arum family Araceae. [4] L. minor is used as animal fodder, bioremediator, for wastewater nutrient recovery, and other applications.
Lemna minor is a floating freshwater aquatic plant, with one, two, three or four leaves each having a single root hanging in the water. As more leaves grow, the plants divide and become separate individuals. The root is 1–2 cm long. Leaves are oval, 1–8 mm long and 0.6–5 mm broad, light green, with three (rarely five) veins and small air spaces to assist flotation. It reproduces mainly vegetatively by division. Flowers are rarely produced and measure about 1 mm in diameter, with a cup-shaped membranous scale containing a single ovule and two stamens. The seed is 1 mm long, ribbed with 8-15 ribs. Birds are important in dispersing L. minor to new sites. The sticky root enables the plant to adhere to the plumage or feet of birds and can thereby colonize new ponds.[ citation needed ]
Lemna minor has a subcosmopolitan distribution and is native throughout most of Africa, Asia, Europe and North America. It is present wherever freshwater ponds and slow-moving streams occur, except for arctic and subarctic climates. It is not reported as native in Australasia or South America, though it is naturalised there.[ citation needed ]
For optimal growth conditions pH values between 6.5 and 8 are required. L. minor can grow at temperatures between 6 and 33 °C. Growth of colonies is rapid, and the plants form a carpet covering still pools when conditions are suitable. In temperate regions, when temperatures drop below 6 to 7 °C, small, dense, starch-filled organs called 'turions' are produced. The plants then become dormant and sink to the ground for overwintering. The following spring, they restart growing again and float back to the surface. [3] [5]
Duckweeds in general need some management effort to be cultivated. The small free floating plants are susceptible to being blown into heaps which results in open water surface allowing algal growth. For this reason, long narrow ponds running perpendicular to the prevailing wind are recommended. The equal distribution of added nutrients in the ponds can be achieved by several inlets. To maintain a dense cover of plants on the water surface and prevent a too thick layer for growth, coordinated harvesting and replenishment of nutrients are required. [6]
The fertilizer requirements for growing duckweed depend on the water source and the geographic isolate of L. minor that is used. [7] L. minor grown in ponds that are filled with rainwater, need an additional application of nitrogen, phosphorus and potassium. Total Kjeldahl Nitrogen should not drop below 20–30 mg/L if high growth rates and crude protein contents are to be maintained. Regarding phosphorus, good growth has been reported in concentrations between 6 and 154 mg/L (there is no notable sensitivity for high phosphorus concentrations on growth rates). [6] Effluents from domestic animal production have very high concentrations of ammonium and other minerals. They often need to be diluted to a balanced nutrient concentration. For the L. minor isolate 8627 cultivated in swine lagoon liquid, the best production rates were reached when grown in swine lagoon liquid diluted to 20% (Total Kjeldahl Nitrogen: 54 mg/L, Ammonium: 31 mg/L, Total Phosphorus: 16 mg/L). [8] Sewage water, which often has an adequate concentration of potassium and phosphorus, can be used to grow duckweed, but nitrogen concentrations need to be adjusted. [9]
Lemna minor has been shown to remove heavy metals like lead, copper, zinc and arsenic very efficiently from waters with non-lethal concentrations. [10] One particular study found, that more than 70% of arsenic was removed after 15 days at initial concentration of 0.5 mg/L. [11] Another one says, that viable L. minor biomass removed 85-90% of Pb(NO3)2 with an initial concentration of 5 mg/L. Higher lead concentrations though result in a decrease in relative growth rate of L. minor. [12] Because L. minor is temperature tolerant, shows rapid growth and is easy to harvest, it bears high potential for the cost-efficient use in wastewater treatments. [12] The Devils Lake wastewater treatment, located in North Dakota, USA, utilizes these beneficial properties of L. minor and other aquatic plants in the treatment of municipal and industrial wastewater. [9] After a certain growing period, the plants are harvested and used as soil amendment, compost material or protein source for livestock. [9] [13] In industrial affected regions, where heavy metals accumulate in waters, soils and sediments due to anthropogenic activities like mining and burning of fossil fuels, the harvested L. minor should not be reused, but disposed accordingly. [13] [14] [15] Because heavy metals have carcinogenic effects in humans, [16] persist long in nature and accumulate in living organisms, their removal from the environment is important. [17] Lemna minor has also been shown to remove organic micropollutants such as pharmaceuticals [18] and benzotriazoles from wastewater. [19]
Depending on the literature, different yields of L. minor are registered. Grown under ideal conditions, yields up to 73 tonnes dry matter per hectare and year were recorded. [20] Common duckweed has a high protein content varying from 20 to 40% depending on the season, the nutrient content of the water and environmental conditions. It doesn't build up very complex tissue structures and therefore has a low fiber content less than 5%. Basically all of its tissues can be used as fodder for fish and poultry and make duckweed an interesting food supplement. [13]
Experimental investigations have shown, that L. minor is able to completely replace the add-on of soy bean in the diet of ducks. It can be cultivated directly on the farm resulting in low production costs. Therefore, using common duckweed as a food supplement in broiler diets is very profitable also from an economic point of view. [21] An investigation showed, that the expensive sesame oil cakes in chicken diets could partially be replaced by cheap L. minor with increased growth performance of broiler. Nevertheless, because of a lower content of digestible proteins in L. minor (68.9% compared to 89.9% in sesame oil cake), common duckweed could only be used as a food supplement in broiler diets. [22] Also when feeding lying hen partially with dried L. minor (up to 150 g/kg fodder), hen showed the same performance like when being fed with fish meal and rice polish, while the yolk colour was positively affected by the duckweed diet. [23]
Lemna minor as fast growing, nitrogen and phosphorus accumulating aquatic plant with high nutritional value for livestock, finds another application in the nutrient recovery from livestock wastewater. [5] This application is known to be executed in farming systems in south east Asia, where manure and excremet are deposited in small eutrophic ponds. The water of those ponds then fertilizes bigger ponds on which L. minor is grown for the further use as fodder for ducks. [20]
Growing selected geographic isolates of L. minor on diluted swine lagoon liquid in North Carolina resulted in yields up to 28.5 g m−2 day−1 (104.03 t ha−1 y−1) and removal of over 85% of the total contained nitrogen and phosphorus.
Anaerobic pretreatment (e.g. through anaerobic digestion in a UASB) of the wastewater and dilution of the liquid to below 100 mg/L total Kjeldahl nitrogen and 50 mg/L total phosphorus, led to the best performance regarding growth and nutrient removal. [8] [24]
Cultivating L. minor in anaerobic pretreated wastewater is a low cost application, with the potential to improve domestic manure by producing valuable animal feed. Additionally, environmental pollution can be diminished through removal of nutrients from effluents. [25] [26] [27]
Lemna minor is very suitable for bioethanol production. Due to its low cellulose content (approximately 10%) compared to terrestrial plants, the conversion procedure of the starch to ethanol is relatively easy. [28] Grown in swine lagoon diluted water, L. minor accumulates 10.6% starch of total dry weight. Under ideal conditions in terms of phosphate, nitrate and sugar availability and optimal pH, the proportion of starch to total dry weight is slightly higher (12.5%). Suppressing the photosynthetic activity of L. minor by growing it in the dark and the addition of glucose further increases starch accumulation up to 36%. [28]
After harvesting, enzymatic hydrolysis releases up to 96.2% of starch bound glucose. [28] The ethanol yield per dry weight in the subsequent fermentation process depends on the glucose content and nutrient availability in the growth medium, but can be compared to ethanol yields from lignocellulose of energy crops like Miscanthus and Giant reed. [28] [29] But in contrast to these energy crops, L. minor biomass does not require any thermal or chemical pretreatments. [28]
Lemna japonica has been genetically engineered to produce up to seven times more oil per acre than soybeans. [30]
Lemna minor is commonly used for the ecotoxicity assessment of organic and inorganic micropollutants [31] as well as for evaluating the toxicity of wastewater and landfill leachates. [32] Information for the applied methodology are provided in the relevant OECD protocol. [33]
Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of microorganisms that may deplete the oxygen of water. Eutrophication may occur naturally or as a result of human actions. Manmade, or cultural, eutrophication occurs when sewage, industrial wastewater, fertilizer runoff, and other nutrient sources are released into the environment. Such nutrient pollution usually causes algal blooms and bacterial growth, resulting in the depletion of dissolved oxygen in water and causing substantial environmental degradation.
Aquatic plants also referred to as hydrophytes are vascular plants and non-vascular plants that have adapted to live in aquatic environments. In lakes, rivers and wetlands, aquatic vegetations provide cover for aquatic animals such as fish, amphibians and aquatic insects, create substrate for benthic invertebrates, produce oxygen via photosynthesis, and serve as food for some herbivorous wildlife. Familiar examples of aquatic plants include waterlily, lotus, duckweeds, mosquito fern, floating heart, water milfoils, mare's tail, water lettuce, water hyacinth, and algae.
Water pollution is the contamination of water bodies, with a negative impact on their uses. It is usually a result of human activities. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water pollution results when contaminants mix with these water bodies. Contaminants can come from one of four main sources. These are sewage discharges, industrial activities, agricultural activities, and urban runoff including stormwater. Water pollution may affect either surface water or groundwater. This form of pollution can lead to many problems. One is the degradation of aquatic ecosystems. Another is spreading water-borne diseases when people use polluted water for drinking or irrigation. Water pollution also reduces the ecosystem services such as drinking water provided by the water resource.
The purple sulfur bacteria (PSB) are part of a group of Pseudomonadota capable of photosynthesis, collectively referred to as purple bacteria. They are anaerobic or microaerophilic, and are often found in stratified water environments including hot springs, stagnant water bodies, as well as microbial mats in intertidal zones. Unlike plants, algae, and cyanobacteria, purple sulfur bacteria do not use water as their reducing agent, and therefore do not produce oxygen. Instead, they can use sulfur in the form of sulfide, or thiosulfate (as well, some species can use H2, Fe2+, or NO2−) as the electron donor in their photosynthetic pathways. The sulfur is oxidized to produce granules of elemental sulfur. This, in turn, may be oxidized to form sulfuric acid.
Lemna is a genus of free-floating aquatic plants referred to by the common name "duckweed". They are morphologically divergent members of the arum family Araceae. These rapidly growing plants have found uses as a model system for studies in community ecology, basic plant biology, ecotoxicology, and production of biopharmaceuticals, and as a source of animal feeds for agriculture and aquaculture. Currently, 14 species of Lemna are recognised.
A constructed wetland is an artificial wetland to treat sewage, greywater, stormwater runoff or industrial wastewater. It may also be designed for land reclamation after mining, or as a mitigation step for natural areas lost to land development. Constructed wetlands are engineered systems that use the natural functions of vegetation, soil, and organisms to provide secondary treatment to wastewater. The design of the constructed wetland has to be adjusted according to the type of wastewater to be treated. Constructed wetlands have been used in both centralized and decentralized wastewater systems. Primary treatment is recommended when there is a large amount of suspended solids or soluble organic matter.
Wastewater quality indicators are laboratory test methodologies to assess suitability of wastewater for disposal, treatment or reuse. The main parameters in sewage that are measured to assess the sewage strength or quality as well as treatment options include: solids, indicators of organic matter, nitrogen, phosphorus, indicators of fecal contamination. Tests selected vary with the intended use or discharge location. Tests can measure physical, chemical, and biological characteristics of the wastewater. Physical characteristics include temperature and solids. Chemical characteristics include pH value, dissolved oxygen concentrations, biochemical oxygen demand (BOD) and chemical oxygen demand (COD), nitrogen, phosphorus, chlorine. Biological characteristics are determined with bioassays and aquatic toxicology tests.
Aerobic granular reactors (AGR) or Aerobic granular sludge (AGS) are a community of microbial organisms, typically around 0.5-3mm in diameter, that remove carbon, nitrogen, phosphorus and other pollutants in a single sludge system. It can also be used for wastewater treatments. Aerobic granular sludge is composed of bacteria, protozoa and fungi, which allows oxygen to follow in and biologically oxidize organic pollutants. AGS is a type of wastewater treatment process for sewages and/or industrial waste treatment. AGR was first discovered by UK engineers, Edward Ardern and W.T. Lockett who were researching better ways for sewage disposal. Another scientist by the name of Dr. Gilbert Fowler, who was at the University of Manchester working on an experiment based on aeration of sewage in a bottle coated with algae. Eventually, all three scientists were able to collaborate with one another to discover AGR/AGS.
The phosphorus cycle is the biogeochemical cycle that involves the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movement of phosphorus, because phosphorus and phosphorus-based materials do not enter the gaseous phase readily, as the main source of gaseous phosphorus, phosphine, is only produced in isolated and specific conditions. Therefore, the phosphorus cycle is primarily examined studying the movement of orthophosphate (PO4)3-, the form of phosphorus that is most commonly seen in the environment, through terrestrial and aquatic ecosystems.
Scenedesmus is a genus of green algae, in the class Chlorophyceae. They are colonial and non-motile. They are one of the most common components of phytoplankton in freshwater habitats worldwide.
Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels that uses algae as its source of energy-rich oils. Also, algae fuels are an alternative to commonly known biofuel sources, such as corn and sugarcane. When made from seaweed (macroalgae) it can be known as seaweed fuel or seaweed oil.
The Trophic State Index (TSI) is a classification system designed to rate water bodies based on the amount of biological productivity they sustain. Although the term "trophic index" is commonly applied to lakes, any surface water body may be indexed.
Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage discharges. Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater. There are a high number of sewage treatment processes to choose from. These can range from decentralized systems to large centralized systems involving a network of pipes and pump stations which convey the sewage to a treatment plant. For cities that have a combined sewer, the sewers will also carry urban runoff (stormwater) to the sewage treatment plant. Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporates a tertiary treatment stage with polishing processes and nutrient removal. Secondary treatment can reduce organic matter from sewage, using aerobic or anaerobic biological processes. A so-called quarternary treatment step can also be added for the removal of organic micropollutants, such as pharmaceuticals. This has been implemented in full-scale for example in Sweden.
Most organisms involved in water purification originate from the waste, wastewater or water stream itself or arrive as resting spore of some form from the atmosphere. In a very few cases, mostly associated with constructed wetlands, specific organisms are planted to maximise the efficiency of the process.
Sewage is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from residences and from commercial, institutional and public facilities that exist in the locality. Sub-types of sewage are greywater and blackwater. Sewage also contains soaps and detergents. Food waste may be present from dishwashing, and food quantities may be increased where garbage disposal units are used. In regions where toilet paper is used rather than bidets, that paper is also added to the sewage. Sewage contains macro-pollutants and micro-pollutants, and may also incorporate some municipal solid waste and pollutants from industrial wastewater.
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Spirodela polyrhiza is a species of duckweed known by the common names common duckmeat, greater duckweed, great duckmeat, common duckweed, and duckmeat. It can be found nearly worldwide in many types of freshwater habitat.
Wolffia arrhiza, commonly known as spotless watermeal or rootless duckweed, is a species of flowering plant in the Araceae family, which includes other water-loving plants such as Arum and Pistia. It is the smallest vascular plant on Earth. Native to Europe, Africa, and parts of Asia, it has also naturalized in various other regions around the globe.
Lemnoideae is a subfamily of flowering aquatic plants, known as duckweeds, water lentils, or water lenses. They float on or just beneath the surface of still or slow-moving bodies of fresh water and wetlands. Also known as bayroot, they arose from within the arum or aroid family (Araceae), so often are classified as the subfamily Lemnoideae within the family Araceae. Other classifications, particularly those created prior to the end of the twentieth century, place them as a separate family, Lemnaceae.
Anammox is a wastewater treatment technique that removes nitrogen using anaerobic ammonium oxidation (anammox). This process is performed by anammox bacteria which are autotrophic, meaning they do not need organic carbon for their metabolism to function. Instead, the metabolism of anammox bacteria convert ammonium and nitrite into dinitrogen gas. Anammox bacteria are a wastewater treatment technique and wastewater treatment facilities are in the process of implementing anammox-based technologies to further enhance ammonia and nitrogen removal.
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