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of Alternative Technologies for Freshwater Augumentation
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PART B. TECHNOLOGY PROFILES
2.3 Clarification Using Plants and Plant Material
Native plants have traditionally been used to improve the quality of the
water in a number of countries in Africa and Latin America. For example,
the seeds of the Moringa oleifera are commonly used in Guatemala,
and peach and bean seeds are used in Bolivia, as coagulant aids to clarify
water. Dried beans (vicia fava) and peach seeds (percica
vulgaris) also have been used in Bolivia and other countries for this
purpose. An emergent aquatic plant used for water quality treatment in
Bolivia and Peru is Schoenoplectus tatora, commonly known as totora
in those countries. This plant, which is similar to the cattail, is used
to remove phosphorus and nitrogen from effluents before they are
discharged to natural drainage systems. The plant biomass is then used for
a variety of handicraft purposes, including the weaving of baskets and the
production of the well-known reed boats of Lake Titicaca.
In addition to providing the basis for clarification, aquatic plants are
also used in aquaculture applications, the production of aquatic organisms
(both floral and faunal, but generally including fish) under controlled
conditions. Aquaculture has been practiced for centuries, primarily to
grow food, fiber, and fertilizer.
The use of aquaculture as a means of treating wastewater involves both
natural and artificial wetlands and the production of both algae and
higher plants (submersed and emersed), invertebrates, and fish, to remove
contaminants such as manganese, chromium, copper, zinc, and lead from the
water. The water hyacinth (Eichhornia crassipes) appears to be one
of the most promising aquatic plants for the treatment of wastewater and
has received the most attention in this regard. Other plants are also
being studied, among them duckweed, seaweed, and alligator weed.
An experimental technology that has been tested successfully on the
Bogotá savannah in Colombia is a form of hydroponic cultivatin of
grasses using domestic wastewater. This procedure works through three
mechanisms: physical, adsorption, and absorption. It not only removed more
than 70% of the organic content and suspended solids but produced a large
grass crop that could be used to pasture livestock. It might also be
practicable for restoring eroded lands. Because of the space requirements,
it is best suited to rural areas. Since it has been tried only under
controlled conditions, its real cost and possible disadvantages need
The seeds of many plants native to the South American continent contain
essential oils and have other properties that have been exploited by
traditional cultures for centuries. Among these is the ability of certain
seed extracts to flocculate particulates in water. To prepare the seeds
for use as a coagulant aid, the following procedure is commonly used:
- Extract the seeds from the plant or fruit.
- Dry the seeds for up to three days.
- Grind the seeds to a fine powder.
- Prepare a mixture of water and ground seed material; the volume of
water depends on the type of seed material used (in the case of Moringa
oleifera, add 10 cm3 of water for each seed; for peach
or bean seeds, add 1 l of water to each 0.3 to 0.5 g of ground seed
- Mix this solution for 5 to 10 minutes; the faster it is stirred, the
less time is required.
- Finally, after the sediments settle, decant the treated water.
Testing it for pH, color, and turbidity is recommended.
- If the test results are acceptable, the treated water can be used for
consumption and other domestic purposes.
Several aquatic plants have been used in water purification and
wastewater treatment. Among the most widely used are cattails, totora,
water hyacinth, and duckweed.
Totora and cattails grow in shallow lakes, rivers, and
impoundments. The plants are rooted in the soil or bottom sediments of the
body of water at depths of about 1 m and grow to between 2 m and 3 m above
the water surface. These plants can absorb nitrate, phosphate, heavy
metals such as manganese, and other chemical compounds. They are generally
used to provide secondary treatment of effluents, in small lagoons filled
with cattails or totora. Several physical and chemical processes
take place in these lagoons:
- Sedimentation of suspended solids.
- Biological decomposition of organic compounds.
- Nitrogen removal through absorption by the plants and fixation by the
plants and attached organisms, and denitrification by aerobic bacteria
associated with the plants that convert organic forms of nitrogen into
inorganic forms, including N2 and N2O gases that
escape into the atmosphere (at high pH, ammonium is converted into
ammonia gas, which also escapes into the atmosphere).
- Phosphorus removal by absorption and fixation in the plant biomass
and/or its adsorption onto suspended particulates which later settle to
the bottom of the lagoon (the amount of phosphorus removal is a function
of the plant density in the treatment area).
- Removal of manganese, copper, zinc, and lead.
- Reduction of pathogenic microorganisms due to the grazing by
protozoans, adsorption onto clay particles, and exposure to
environmental extremes such as pH variations within the lagoon.
Design criteria for a treatment system using cattails or totora
include the flow rate of the water to be treated; the initial nitrogen and
phosphorus concentrations; the initial concentrations of other water
quality parameters, such as heavy metal concentrations and pH; the desired
water quality of the effluent; and the potential uses of the treated
water. In Peru, a small system capable of treating 5 l/s required 900 m2
of totora lagoon, with a maximum water depth of 0.9 m. These
techniques are especially useful in rural areas where advanced technology
for water treatment is not available and where high turbidity and color
are the primary water quality problems.
The water hyacinth, a native of South America, is found naturally in
waterways, bayous, and other backwaters. It thrives in nitrogen-rich
environments, and consequently does extremely well in raw and partially
treated wastewaters. When it is used for effluent treatment, wastewater is
passed through a water-hyacinth-covered basin, where the plants remove
nutrients, suspended solids, heavy metals, and other contaminants. Batch
treatment and flow-through systems, using single and multiple lagoons, are
used. Because of its rapid growth rate and inherent resistance to insect
predation and disease, water hyacinth plants must be harvested from these
systems. While many uses of the plant material have been investigated, it
is generally recommended as a source of methane when anaerobically
digested. Its use as a fertilizer or soil conditioner (after composting),
or as an animal feed, is often not recommended owing to its propensity to
accumulate heavy metals. The plant also has a low organic content (it is
primarily water) and, when composted, leaves behind little material with
which to enrich the soil.
Design criteria for wastewater treatment using water hyacinth include
the depth of the lagoons, which should be sufficient to maximize root
growth and the absorption of nutrients and heavy metals; detention time;
the flow rate and volume of effluent to be treated; and the desired water
quality and potential uses of the treated water. Land requirements for
pond construction are approximately 1 m2/m3/day of
water to be treated. Phosphorus reductions obtained in such systems range
between 10% and 75%, and nitrogen reductions between 40% and 75% of the
influent concentration. Table 9 presents performance data from four
different wastewater treatment systems using the water hyacinth.
TABLE 9. Performance of Four Different Wastewater Effluent
Treatment Systems Using Water Hyacinth.
Source: U.S. Environmental Protection Agency,
Innovative and Alternative Technology Assessment Manual,Washington, D.C.,
1976, (Report No. EPA-430/9-78-009).
Wastewater treatment using natural and constructed wetland systems
remains largely in the developmental stage, although several full-scale
experimental demonstration systems are in operation, including one in
Puno, Peru. Wetland treatment systems generally use spray or flood
irrigation to distribute the wastewater into the wetland area.
Alternatively, the wastewater may be passed through a system of shallow
ponds, lagoons, channels, basins, or other constructed areas where emersed
aquatic vegetation has been planted and is actively growing.
Extent of Use
The use of plant materials is a traditional technology for clarifying
potable water that is still in widespread use in rural areas of Latin
America. The use of natural products has recently been rediscovered by
water-supply technologists and is being further developed along more
Treatment of wastewaters using artificial wetlands is still
experimental, but is receiving a moderate amount of use. It has been
tested and is currently being used in Guatemala and to treat water from
rivers near La Paz, Bolivia. Totora technology is also being used
in Bolivia and in Puno, Peru, on the shores of Lake Titicaca, to treat
small wastewater flows (of 5 to 6 l/s). However, higher flow rates (30 to
50 l/s) can be treated using larger aquatic plant pools. The totora
treatment systems used in Bolivia involve transplanting natural plants
into the treatment lagoons. Experimental results from Bolivia indicate
that heavy metals are absorbed by totora rooted in a gravel bed.
The use of aquatic plants appears to be effective only during the growing
season, and is subject to temperature constraints. This technology should
be very useful in developing countries with hot climates and low land
Treatment systems using water-hyacinth-based technology are also still
in the developmental stage, with a number of full-scale demonstration
systems in operation. Some small water-hyacinth systems are in use in
Mexico. This technology is useful for polishing treated effluents. It has
potential as a low-cost, low-energy-consuming alternative, or addition, to
conventional treatment systems, especially for small flows. It has been
successfully used in combination with chemical treatment and overland flow
land treatment systems. Wetland systems may also be suitable for seasonal
use in treating wastewaters from recreational facilities, some
agricultural operations, and/or other waste-producing activities where the
necessary land is available. It also has potential application as a method
for the pretreatment of surface waters for domestic supply and stormwater
Operation and Maintenance
Operation and maintenance of plant-based water clarifiers are very
simple. For plant-seed solutions a household mixer or blender is the only
equipment needed. The totora treatment systems are also simple,
requiring no machinery or specialized labor. Maintenance involves periodic
removal of non-biodegradable materials, and the harvesting and disposal of
plant material. Disposal may either be in the form of composting, methane
gas generation, or use for fiber-based handicrafts. Dredging of sediments
may be required every 3 to 5 years.
Gravity flows are generally used in wastewater treatment systems using
the water hyacinth. Energy to operate the water-hyacinth-based systems is
provided by sunlight. However, the plants must be harvested regularly.
Fifteen to 20 percent of the plants should be removed at each harvest.
While the water hyacinth system can successfully cope with a variety of
stresses, the health of the plants must be maintained for most effective
treatment. Several precautionary steps have been identified. Studies have
shown that the presence of high chlorine residuals inhibits plant growth.
Therefore, chlorination of the effluent is best done after water hyacinth
treatment. However, if local conditions dictate that pre-treatment
chlorination is necessary, care should be taken to maintain chlorine
residuals in the influent at less than l mg/l. The system should also be
monitored for the presence of weevils and other insects that damage the
plants. Diseased or damaged plants should also be removed.
In wetland treatment systems, a knowledge of the mosquito life cycle and
habitat needs helps managers avoid mosquito breeding problems. Open water
areas, which are subject to wind action and provide easy access to
predators (such as fishes), will limit mosquito production. Maintaining
good water circulation in vegetated areas also gives access to predators
and lessens mosquito production. The vegetation resulting from wetland
systems can be utilized as compost or as animal feed supplements, or
digested to produce methane. Depending on the plant species involved and
their fiber content, plant material can also be used for handicrafts and
the manufacture of specialty papers. Skill requirements for the operation
and maintenance of wetland treatment systems are low.
Level of Involvement
These forms of treatment have been practiced primarily by the private
sector in rural areas, and by universities and government institutions for
research and development purposes. The Government of Peru has contributed
financial and technical resources to the construction of two experimental
treatment facilities using totora in Puno, Perú. In
Bolivia, experiments have been performed at the University of San Andrés
Very little information is available concerning the cost of
plant-based technologies. This is especially true in the case of water
clarification using Moringa oleifera and other seeds. The main
cost appears to be the labor in acquiring the plant seeds and producing
the flocculent solution.
Cost estimates of wetland-based wastewater treatment systems are equally
scarce. The cost of the totora treatment system in Peru is
estimated at $65 000. Generalized construction, operation, and maintenance
costs for wetland systems are shown in Figure 23. The costs shown in this
figure were derived from wetland treatment systems at Vermontville and
Houghton Lake in Michigan, U.S.A.
Effectiveness of the Technology
In using ground seeds for water clarification, the size of the
particles is an important factor: generally speaking, the smaller the
particles, the more efficient the clarification process. This is
particularly important in the removal of color using peach and bean seeds
(Figure 20). The concentration of the resulting coagulant solution has
also an effect on the reduction of turbidity in the product water (Figure
21). For most plant seeds, the lower the pH of the water, the more
effective the treatment. Suspended materials coagulate better at lower pH
values. Peach seeds are an exception to this rule of thumb. Moringa
oleifera was found to be more efficient at reducing turbidity than
aluminum sulfate (alum). In general, also, the higher the initial
turbidity, the higher the removal rate.
Figure 20: Percent Color Removal as a Function of Seed
Source: Freddy Camacho Villegas,
Institute of Hydraulics and Hydrology, UMSA, La Paz.
Figure 21: Turbidity Reduction as a Function of
Source: Freddy Camacho
Villegas, Institute of Hydraulics and Hydrology, UMSA, La Paz.
Wetland treatment systems using totora are quite
efficient at removing nutrients and oxygen-demanding substances from
effluents. Table 10 shows the percentage of removal of chemical compounds
from wastewater by the system in Puno. Parasites were also removed from
the inflow waters, and total and fecal coliforms were reduced in
concentration by 80% and 99%, respectively. The experiments performed in
Bolivia on the removal of heavy metals by totora show that lead,
silver and copper can be removed from effluents in less than 2 days.
Figure 22 shows the decline in concentration of several heavy metals in a
TABLE 10. Removal of Chemicals by Totora.
|| % Removed
Source: Freddy Camacho Villegas, Institute
of Hydraulics and Hidrology, UMSA, La Paz.
Figure 22: Absorption of Heavy Metals by Totora.
Freddy Camacho Villegas, Institute of Hydraulics and Hydrology, UMSA, La
Figure 23: Generalized Construction and Operation and
Maintenance Costs for Aquaculture and Wetland Systems.
Edward J. Martin. Handbook for Appropriate Water and Wastewater Technology
for Latin America and the Caribbean, Washington, D.C., PAHO and IDB, 1988.
These technologies are useful in areas where suitable
plants are readily available. In areas where they are not, any
introduction of plants species must be undertaken with caution to minimize
the possibility of creating nuisance growth conditions. Even introducing
them into constructed enclosures should be done carefully, and with the
foreknowledge that there is a strong likelihood that they will enter
natural water systems (especially as they must be harvested from the
treatment systems and disposed of).
- Moringa oleifera trees are hardy and drought-resistant,
fast-growing, and a source of large numbers of seeds. They are nontoxic
and effective coagulants useful for removing turbidity and bacteria from
- The cost of both seed treatment and wetlands is very low, in most
cases negligible. These technologies are traditional, rudimentary, and
easy to implement, ideal for rural areas.
- Wetland systems are easy to build, simple to operate, and require
little or no maintenance. Most small-scale wetland treatment systems
require relatively small land areas.
- Wetland technologies reduce nutrient contamination of natural
- Heavy metals absorbed by the plants in wetland treatment systems are
not returned to the water.
- Water-hyacinth-based and other wetland systems produce plant biomass
that can be used as a fertilizer, animal feed supplement, or source of
- In some places plant seeds may not be readily available.
- Totora treatment systems require an initial capital
investment that may not always be easily accessible to potential users.
- The lifespan of totora as an efficient water quality
treatment technology is still undetermined.
- Temperature (climate) is a major limitation, since effective
treatment is linked to the active growth phase of the emersed (surface
and above) vegetation.
- Herbicides and other materials toxic to the plants can affect their
health and lead to a reduced level of treatment.
- Duckweed is prized as food by waterfowl and fish, and can be
seriously depleted by these species.
- Winds may blow duckweed to the windward shore unless wind screens or
deep trenches are employed.
- Plants die rapidly when the water temperature approaches the freezing
point; therefore, greenhouse structures may be necessary in cooler
- Water hyacinth is sensitive to high salinity, which restricts the
removal of potassium and phosphorus to the active growth period of the
- Metals such as arsenic, chromium, copper, mercury, lead, nickel and
zinc can accumulate in water hyacinth plants and limit their suitability
as fertilizer or feed materials.
- Water hyacinth plants may create small pools of stagnant surface
water which can serve as mosquito breeding habitat; this problem can
generally be avoided by maintaining mosquitofi-sh or similar fishes in
- The spread of water hyacinth must be closely controlled by barriers,
since the plant can spread rapidly and clog previously unaffected
- Water hyacinth treatment may prove impractical for large-scale
treatment plants because of the land area required.
- Evapotranspiration in wetland treatment systems can be 2 to 7 times
greater than evaporation alone.
- Harvesting the water hyacinth or duckweed plants is essential to
maintain high levels of system performance.
Seed treatment is not widely known in Latin America and the Caribbean,
and its acceptability cannot be conjectured.
Use of aquatic plants as a wastewater treatment medium is well accepted
in areas where it is a traditional technology. It is especially well
accepted in the Andean areas, where the plants used in the treatment
process have value for handicraft production, cattle feed, and other
Further Development of the Technology
Other native plants and plant materials should be investigated as
coagulants for use in the removal of color and turbidity, and the control
of pH. Additional studies will be needed to establish the appropriate
dosages of flocculent solutions to be used in water quality treatment.
The use of totora or other aquatic plants can help to clean
nutrient- and metal-laden water from agricultural and mining operations,
both for water reuse and to eliminate downstream contamination. Future
development should be focused on determining appropriate aquatic plant
densities required to clean certain types of wastewaters and improving the
efficiency of plant uptake after several water treatment cycles. Other
uses of the harvested plants should be investigated to make this
technology economically attractive.
Sources of Information
Freddy Camacho Villegas, Instituto de Hidráulica
e Hidrología (IHH), Universidad Mayor de San Andrés (UMSA),
Casilla Postal 699, La Paz, Bolivia. Tel. (591-2)79-5724 - 25. Fax
Erika Gehler A., Carlos Arce L., Hans Salm and Alfredo
Alvarez C., Instituto de Ciencias Químicas, UMSA, Calle 27
s/n, Cota Cota, Casilla de Correo 303, La Paz, Bolivia. Fax (591-2)79-2622
Luis A. Ochoa Marroquín, Instituto Nacional de
Sismología, Vulcanología, Meteorología e Hidrología
(INSIVUMEH), 7 Avenida 14-57, Zona 13, Guatemala, Guatemala. Tel.
(502-2)31-4967 / 31-9163. Fax (502-2)31-5005.
Juan Ocola Salazar, Instituto Nacional de Desarrollo
(INADE), Proyecto Especial Binacional Lago Titicaca (PELT), Ave. El Son
839, Puno, Perú. Tel. (51-54)35-2305 / 35-2392.
Guillermo Sarmiento, Dirección de Agua Potable y
Saneamiento Básico, Ministerio de Desarrollo Económico,
Bogotá, Colombia. Tel. (57-1)287-9743. Fax (57-1) 245-7256 /
Alvarez C., Alfredo, and Carlos Arze. 1990. Totora como
Descartamiento de Aguas en Movimiento. La Paz, UMSA, Instituto de
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