 WATER CLARIFICATION USING MORINGA
---------------------------------------------------------
OLEIFERA SEED COAGULANT
---------------------------------------------------------
The removal of organic and inorganic material from raw water is essential before it can be
disinfected for human consumption. In a water treatment works, this clarification stage is
normally achieved by the application of chemical coagulants which change the water from a
liquid to a semi-solid state. This is usually followed by flocculation, the process of gentle and
continuous stirring of coagulated water, which encourages the formation of ‘flocs’ through
the aggregation of the minute particles present in the water. Flocs can be easily removed by
settling or filtration. For many communities in developing countries, however, the use of
coagulation, flocculation and sedimentation is inappropriate because of the high cost and
low availability of chemical coagulants, such as aluminium sulphate and ferric salts.
This Technical Brief gives an overview of the application of an indigenous, naturally derived
coagulant, namely seed material from the multi-purpose tree Moringa oleifera Lam. (M.oleifera)
which offers an alternative solution to the use of expensive chemical coagulants.
Background
----------
How do the seeds work?
---------------------
The seed kernels contain significant
quantities of a series of low molecularweight,
water-soluble proteins which, in
solution, carry an overall positive
charge. The proteins are considered to
act similarly to synthetic, positively
charged polymer coagulants. When
added to raw water the proteins bind
to the predominantly negatively
charged particulates that make raw
waters turbid (silt, clay, bacteria etc.).
Under proper agitation these bound
particulates then grow in size to form
the flocs, which may be left to settle by
gravity or be removed by filtration.
Household water treatment
-------------------------
The traditional use of the M.oleifera
seeds for domestic household water
treatment is limited to rural areas in
Sudan. Village women, collecting their
water from the River Nile, place
powdered seeds in a small cloth bag
with a thread attached. This is then
swirled around in the turbid water to
promote coagulation and flocculation.
The flocculated solids are allowed to
settle and the treated water is removed
before boiling and subsequent
consumption.
Are the seeds toxic?
-------------------
Studies have been carried out to
determine the potential risks
associated with the use of the
seeds in water treatment. To date,
all the studies have concluded
that there is no evidence to
suggest any acute or chronic
effects on humans, particularly at
the low doses required for water
treatment.
COMMUNITY WATER TREATMENT SYSTEMS
---------------------------------
For practical reasons of solution
preparation, the use of powdered seed
kernels is only recommended for
treatment systems up to 10m3/hour.
As with all coagulants, the effectiveness
of the seeds may vary from one raw
water to another. Jar testing should be
undertaken to determine their
effectiveness on a particular water, and
to establish preliminary dosing regimes
depending on the season. The practical
application of dosing solutions is exactly
the same as for all other coagulants.
Figure 1 (above) demonstrates the
stage of application in two alternative
treatment ‘trains’.
Two further advantages of seed
treatment are that:
the effectiveness is, in general,
independent of raw water pH;
and
the treatment does not affect the
pH of the treated water.
Coagulant solution preparation
------------------------------
Seed solutions may be prepared from
either seed kernels or the solid residue
(‘presscake’) obtained following the
extraction of seed oil.
Shelled whole seed
-----------------
(1) Seed pods are allowed to mature
and dry naturally to a brown colour
on the tree.
(2) The seeds are removed from the
harvested pods, and shelled.
(3) The seed kernels are crushed and
sieved (0.8mm mesh or similar).
Traditional techniques used to
produce maize flour have been
found to be satisfactory.
(4) The finely crushed seed powder is
mixed with clean water to form a
paste, and is then diluted to the
required strength. Dosing solutions
can be prepared from 0.5 to 5 per
cent concentration (e.g. 0.5 to 5g/l).
(5) Insoluble material is filtered out
using either a fine mesh screen or
muslin cloth.
(6) The solution is ready for use.
Presscake
---------
Presscake should be ground to a fine
powder and sieved (0.8mm mesh or
similar). Solution preparation then
follows steps 4 to 6
on the left.
Note:
Solution containers
should be cleaned
between batches to
remove insoluble seed
material. Fresh solutions
should be prepared
every eight hours.
Coagulant dose requirement
--------------------------
As for all coagulants, the amount of
seed required will vary depending on
the raw water source and on the raw
water quality. One advantage of seed
use is that, in general, there is a wide
dose range over which effective
treatment may be achieved and
maintained. The dose ranges shown in
Table 1 are given as a guide only, and
jar testing should be carried out to
determine more specific dose
requirements for the raw water in
question. Dosages are given as
equivalent weight of seed powder or
presscake material required to make
up the dosing solution.
Seed requirement
----------------
The area under cultivation to produce
the annual seed requirement depends
on the size of the treatment works and
raw water quality (as noted in Table 1).
Assuming the average seed kernel
yield for a mature tree is 3kg, then at
an average seed dose of 100mg/l the
harvest from a single tree will treat
30 000 litres of water. Using the same
assumptions and a recommended tree
spacing of 3m, the harvest from 1ha of
mature trees (approx. 3000kg) would
treat 30 000m3 of water. This equates
to a small treat-ment works producing
10m3 per hour if operated eight hours a
day for a full year.
GENERAL INFORMATION
-------------------
Description
-----------
A native of northern India,
M.oleifera is now grown widely
throughout the tropics. It is
sometimes known as the
‘drumstick’ or ‘horseradish’ tree.
Ranging in height from 5 to 12m
with an open, umbrella-shaped
crown, straight trunk and corky,
whitish bark, the tree produces a
tuberous tap root. The evergreen
or deciduous foliage (depending
on climate) has leaflets 1 to 2 cm in
diameter; the flowers are white or
cream coloured. The fruits (pods)
are initially light green, slim and
tender, eventually becoming dark
green, firm and up to 120cm long,
depending on the variety. Fully
mature, dried seeds are round or
triangular, the kernel being
surrounded by a lightly wooded
shell with three papery wings.
Climate and soil conditions
---------------------------
The M. oleifera prefers hot, semiarid
regions (annual rainfall 250-
1500mm), although it has been
found to adapt well to hot, humid,
wet conditions with annual rainfall
in excess of 3000mm. Considered
to be suitable only for lowland
cultivation at altitudes less than
600m, the adaptability of the tree
was demonstrated by the
discovery of natural strands at
altitudes of 1200m in Mexico.
Although preferring well-drained
sandy or loamy soils, heavier clay
soils will be tolerated, although
water logging should be avoided.
The tree is reported to be tolerant
of light frosts and can be
established in slightly alkaline soils
of up to pH9.
Cultivation
-----------
The tree grows rapidly from seeds
or cuttings, and growth up to 4m in
height; flowering and fruiting have
been observed within 12 months of
planting out. In areas where the
climate permits, e.g. southern
India, two harvests of pods are
possible in a single year. Recent
estimates suggest that, for a
spacing of 3m, a likely annual seed
yield is 3 to 5 tonnes per hectare.
Raw water turbidity
(NTU)
Dose range
mg/l
< 50 10 - 50
50 - 150 30 - 100
>150 50 - 200
ADDITIONAL PRODUCTS AND USES OF MORINGA OLEIFERA
------------------------------------------------
Vegetable
---------
• Green pods, fresh and dried leaves
Oil
---
• Seeds contain up to 40% of oil by weight
• Used for cooking, soap manufacture, cosmetic base and in lamps
Other uses
----------
• All parts of the plant are used in a variety of traditional medicines
• Leaves are useful as animal fodder
• Presscake, obtained following oil extraction, is useful as a soil conditioner
• Grown as live fences and windbreaks
• Fuelwood source after coppicing (cutting back the main stem to
encourage side shoots).
• As an intercrop with other crops
• Wood pulp may be used for paper-making.
Additional products and uses of M. oleifera
The leaves have outstanding nutritional
qualities, among the best of all
perennial vegetables. The protein
content is 27 per cent and there are
also significant quantities of calcium,
iron and phosphorus, as well as
vitamins A, B and C. This nutritional
value is particularly important in areas
where food security can be threatened
by periods of drought. M.oleifera
leaves can be harvested (and dried)
during dry seasons when there are no
other fresh vegetables available. The
immature green pods are consumed
by Asian populations world-wide and
canned pods are exported from India.
The seeds contain up to 40 per cent
by weight of oil and the fatty acid
profile of the oil shows it to be, on
average, 73 per cent oleic acid. The
oil approaches the high quality of
olive oil. |
|
|
|
|
|
