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Saturday, April 4, 2009

Eichhornia crassipes

Eichhornia crassipes, commonly known as Common Water Hyacinth, is an invasive species of plant, which is native of Amazon basin. This plant is also used like a medicinal plant.

Invasion of Lake Victoria

The plant was introduced by Belgian colonists to Rwanda to beautify their holdings and then advanced by natural means to Lake Victoria where it was first sighted in 1988. There, without any natural enemies, it has become an ecological plague, suffocating the lake, diminishing the fish reservoir, and hurting the local economies. It impedes access to Kisumu and other harbors.


Its habitat ranges from tropical desert to subtropical or warm temperate desert to rainforest zones. It tolerates annual precipitations of 8.2 dm to 27.0 dm (mean of 8 cases = 15.8 dm), annual temperatures from 21.1°C to 27.2°C (mean of 5 cases = 24.9°C), and its pH tolerance is estimated at 5.0 to 7.5. It does not tolerate water temperatures >34°C. Leaves are killed by frost and salt water, the latter trait being used to kill some of it by floating rafts of the cut weed to the sea. Water hyacinths do not grow when the average salinity is greater than 15% that of sea water. In brackish water, its leaves show epinasty and chlorosis, and eventually die.

Neochetinia eichhorniae causes "a substantial reduction in water hyacinth production" (in Louisiana); it reduces plant height, weight, root length, and makes the plant produce fewer daughter plants. Neochetinia eichhorniae was imported from Argentina to Florida in 1972.

Azotobacter chroococcum, an N-fixing bacteria, is probably concentrated around the bases of the petioles. But it doesn't fix N unless the plant is suffering extreme N-deficiency.

Fresh plants contain prickly crystals. This plant is reported to contain HCN, alkaloid, and triterpenoid, and may induce itching. Plants sprayed with 2,4-D may accumulate lethal doses of nitrates, as well as various other nocive elements in polluted environments. See further down.



Because of its extremely high rate of development, Eichhornia crassipes is an excellent source of biomass. One hectare of standing crop can thus produce more than 70,000 m3 of biogas. According to Curtis and Duke, one kg of dry matter can yield 370 liters of biogas, giving a heating value of 22,000 KJ/m3 (580 Btu/ft3) compared to pure methane (895 Btu/ft3)

Wolverton and McDonald report only 0.2 m3 methane 7 per kg, indicating requirements of 350 MT biomass/ha to attain the 70,000 m3 yield projected by the National Academy of Sciences (Washington). Ueki and Kobayashi mention more than 200 MT/ha/yr.[10] Reddy and Tucker got an experimental maximum of more than a half ton a day. Bengali farmers collect and pile up these plants to dry at the onset of the cold season; they then use the dry water hyacinths as fuel. They then use the ashes as fertilizer. In India, a ton of dried water hyacinth yield circa 50 liters ethanol and 200 kg residual fiber (7,700 Btu). Bacterial fermentation of one ton yields 26,500 cu ft gas (600 Btu) with 51.6% methane, 25.4% hydrogen, 22.1% CO2, and 1.2% oxygen. Gasification of one ton dry matter by air and steam at high temperatures (800°) gives circa 40,000 ft3 (circa 1,100 m3) natural gas (143 Btu/cu ft?) containing 16.6% H3, 4.8% methane, 21.7% CO, 4.1% CO2, and 52.8% N. The high moisture content of water hyacinth, adding so much to handling costs, tends to limit commercial ventures. A continuous, hydraulic production system could be designed, which would provide a better utilization of capital investments than in conventional agriculture, which is essentially a batch operation.

The labour involved in harvesting water hyacinth can be greatly reduced by locating collection sites and processors on impoundments that take advantage of prevailing winds. Wastewater treatment systems could also favourably be added to this operation. The harvested biomass would then be converted to ethanol, natural gas, hydrogen and / or gaseous nitrogen, and fertilizer. The byproduct of water and fertilizer can both be used to irrigate nearby cropland

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