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Possible utilization of the water hyacinth in nutrition and industry

Leonardo Lareo and Ricardo Bressani
Division of Agricultural and Food Sciences, Institute of Nutrition of Central America and Panama, Guatemala City, Guatemala

The water hyacinth (Eichhornia crassipes [Mart] Solms-Laubach) is a large, free-floating, tropical aquatic plant with attractive lavender flowers and shiny, bright green leaves on long petioles. It reproduces principally by vegetative means; daughter plants are produced by stolons that grow laterally below the water surface from the central rhizome, and the interconnected plants form enormous mats of vegetation. Propagation by seeds may contribute to the spread of water hyacinths and can be a potent source of reinfestation.

Water hyacinth populations increase rapidly. Holm et al. (1) reported that in one experiment, two parent plants produced 30 offspring after 23 days, and 1,200 at the end of four months. Some authors report weight gains of 4.8 per cent per day (see ref. 2). Penfound and Earle 13) reported that the number of water hyacinth plants doubled every 11.2 to 15 days in a field observation. Standard densities of 300 to 442 tons per hectare have been found. In the tropics, Lareo found a duplication of population each seven days and an annual productivity of between 930 and 2,900 tons per hectare (4).

Water hyacinths grow most rapidly in water temperatures from 28 to 30 C and at a pH from 4.0 to 8.0. They cease to grow when water temperature is above 40 or below 10 C, and the pH range for growth is between 4.0 and 10.0.

With these characteristics, the water hyacinth has become a major ecological and economic problem in this century in the tropics and subtropics; yet, in these same regions, production of nutrients for human and animal consumption has become an even more serious problem than that caused by hyacinths obstructing river transporation by blocking waterways in some areas: Guyana, the Nile, the Congo, Florida, some places in Colombia, Brazil, etc. It also blocks irrigation canals.

The first step adopted for the solution of this problem was control by known methods. Many years ago various kinds of herbicides such as 24-D, Dalapon, Diquat, and others were used in some places. The ecological problems created by these herbicides were obvious. The water could not be used for irrigation or human consumption for long periods of time, and the fauna in the eco-system were seriously affected (5, 6).

Biological control of the hyacinth was studied with several kinds of animal viruses, bacteria, and fungi (7), as well as with manatees (8), insects (9), herbivorous fish such as grass carp and tilapia,, ducks, geese (10, 11), turtles, snails (12), and other animals. However, the results were disappointing, perhaps because of defense mechanisms in the plants. For example, the larger plants form 2.5 or more leaves for each one destroyed by pathogen attack (13). The last form of control attempted was mechanical destruction. This was costly in time, money, and energy, and several of the procedures used damaged the ecology, affecting all animal life in the ponds infested by the hyacinth.

However, negative features are only one aspect of the water hyacinth; there is another side to it. On many occasions it has been demonstrated that this weed is an excellent water depollutant for domestic water wastes. In studies where the ability of the water hyacinth to remove lead, cadmium, and mercury was tested, the plant removed approximately 65 per cent of lead, 50 per cent of cadmium, and 65 per cent of mercury from water polluted with 10 ppm of lead and 1 ppm of mercury and cadmium (14). One hectare of water hyacinth plants is potentially capable of removing 160 kg of phenol per 72 hectares from water polluted with this chemical ( 15). Combinations of microorganisms with water hyacinths must be seriously considered in developing filtration systems for removing toxic trace chemicals, such as heavy metals and carcinogenic materials (16).

The results of several studies show that plants such as the water hyacinth use appreciable amounts of the inorganic forms of nitrogen and phosphorus found in domestic sewage. In so doing, they effect a significant reduction in the concentration of materials that are major contributors to the inorganic nutrient enrichment of natural waters (17).

Because inorganic nitrogen and phosphorus are accumulated to a large extent in the roots (roots represent 20 per cent of the wet weight of the plants), this quality signifies a second possible use for the water hyacinth as "compost," or organic fertilizer. Water hyacinth compost (total plant), however, presents a problem because the fibre is not degraded. Water hyacinth root compost has nevertheless been used with good results as a propagation medium for house plants (18, 19). Some papers report high levels of growth hormones such as gibberellins in the roots. These findings suggest the possibility of using the roots as organic fertilizer (20, 21).

The fibrous component might be useful as a base for a biogas-producing system. Methane-producing bacteria require such nutrients as nitrogen, potassium, and phosphorus. Many studies have shown that the water hyacinth provides these elements in the quantity and proportion adequate for good growth of bacteria and for satisfactory gas production. Work at NASA has demonstrated that each kilogram of water hyacinth ((dry weight) yields about 370 litres of biogas, with an average methane content of 69 per cent (22). Another possibility for the use of water hyacinths is as a source of pulp and paper. The findings in this respect are not in agreement, since a study at the University of Florida did not find the water hyacinth promising as an immediate source of pulp, while a Philippine study showed the opposite results (23, 24).

As an animal feed, it has been used fresh. In experiments with pigs in southwest Colombia, fresh water hyacinth was substituted for 20 per cent of commercial feed without toxicologial problems or effects on rate of growth (Lareo, unpublished data, 1979). At present in Guatemala, an attempt is being made to introduce the leaf and/or aerial part with flowers as a source of pigments in the diets of laying hens and broilers, because we have found high levels and a good distribution of pigments in the plant (Lareo, unpublished data,1981).

Silage composed of water hyacinth can be used for ruminant diets with excellent results for acceptability, dry matter, and protein digestibility. This type of feed has been evaluated with cattle and sheep (25). We think that a suitable animal for this type of feed is the goat because it is a sturdy, productive animal common in a large number of developing countries.

These uses as feed are feasible, because we have recently found that the levels of antiphysiological factors present in the plant are either very low or non-existent. We found tannins in amounts of only about 1 per cent of the dry matter from the whole plant and 2 per cent in the leaves. The plant as a whole does not have trypsin inhibitors. The tests for saponins and alkaloids were negative, and the level of oxalates was only 0.8 per cent (Lareo, unpublished data, 1981).

The uses described above are, at present, the principal ones for the water hyacinth, but on the basis of the proximal composition of the plant, others may prove feasible.

Water hyacinths have a water content of over 90 per cent. The dry matter contains between 10 and 26 per cent of crude protein, but the leaves contain higher levels (about 38 per cent). The mineral content depends directly on the water where the hyacinth grows, but the mean value ranges from 17.0 to 26 per cent. The fibre level averages about 20 per cent. Biological evaluation of a flour made from the whole plant or any of its parts fed to rats gave good results. For leaf flour, for example, a net protein ratio (NPR) value of 3.7 was found (this is 85 per cent of that in the casein control); for petioles, the NPR was 1.7, but we expected this because of the high fibre content in this part of the plant. For the total plant, the result was poor, but this can be explained on the basis of its high fibre content, and principally because of the high mineral levels in the roots (Lareo, unpublished data, 1981).

The protein quality of water hyacinth leaves grown on human waste is presented in table 1, in comparison with the FAO reference pattern. This table shows that water hyacinth may be a good source of high-quality protein and other nutrients like vitamins; however, technology for its optimum utilization must still be developed. There are many possibilities; the most important, perhaps, is that of leaf protein concentrate (LPC) production for use in countries with high rates of undernutrition and malnutrition (27, 28). It is interesting to compare the geographic area where water hyacinths grow with the hunger map of the world {see figs. 1 and 2).

TABLE 1. Comparison between the 1973 FAO Protein Reference Pattern and the Protein of Water Hyacinth Leaves Grown in Human Wastes (g/100 g Protein)

Amino Acid FAO
Water Hyacinth
Leaves Grown in
Human Waste
Lysine 5.4 5.7
Methionine +    
cystine 3.5 2.7
Threonine 4.0 4.3
Isoleucine 4.0 4.7
Leucine 7.0 8.3
Valine 5.0 5.6
Phenylalanine +    
tyrosine 6.1 8.8
Tryptophan 0.96 1.0
Histidine - 2.2
Arginine - 5.2

* Source:ref.26.

FIG. 1. Probable Current Distribution of the Water Hyacinth (adapted from ref. 29, p. 462)

FIG. 2. Hunger Map of the World (adapted from ref. 30, p. 17)

FIG. 3. Balance of Matter and Final Products Derived from a Square Meter of Water Hyacinth

Another possibility is the use of the fibrous parts of the plant (stolons and petioles) as a source of cellulose for the production of single-cell protein (SCP).

The authors studied two novel uses for this plant. The first was the production of pressed, dried material with some resin or agglutinant for making a light type of "woody" table. This requires only a simple technology, and, if it could be made waterproof, a cheap material would be obtained for internal divisions in the houses of rural areas of developing countries.

The second novel use is perhaps more important. Considering the high transpiration levels of the plant, we believe that the transpired water (vapour) could be collected, condensed, and re-used. Some initial experiments showed that basically "distilled" water can be obtained from the plants despite the highly polluted water they sometimes grow in. We are currently trying to develop an appropriate technology for a small field evaluation of this.

Research is needed in the following areas for better ways to utilize this enormous source of biomass:

- For decontamination: Research is needed into the design and management of systems to get maximum nutrient recovery throughout the year. Additional research and screening should be conducted with the numerous chemicals found in industrial waste to establish chemical Concentration levels that the water hyacinth and other aquatic plants can tolerate and remove.

- For Compost: Research is needed to determine nutrient imbalances and to find the best crops to use for this purpose, as well as to develop appropriate technology. Research on new products such as LPC and SCP derived from water hyacinths is in the first basic stages, to be followed by development of preparation and propagation technology. Obviously, these are not all the research needs in this field, but they are some basic ideas for the use of a biomass that at present is a problem but, nationally used, may prove to be a most important natural resource.

A diagram suggesting some of the possible uses of this plant in a closed aquatic eco-system is presented in figure 3.


This work was supported by funds from the United Nations University. The authors are grateful to Dr. J. Edgar Braham and Dr. Oscar Pineda for their helpful suggestions and critical reviews of the manuscript. We extend special thanks to Dr. Guillermo Arroyave for his support and continued interest in this project.


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