Review of the effect of Moringa oleifera seeds on reducing water turbidity and pathogens

Review of the effect of Moringa oleifera seeds on reducing water

turbidity and pathogens

Nick Kelley

SCSC 658

Dr. Jacqueline Peterson

April 25, 2013

Review of M. oleifera seeds 2

Introduction

This is a review of two research papers that studied the effects of Moringa oleifera seeds

on the reductions of water turbidity and pathogen concentrations, specifically in the context of its

use in impoverished or third-world communities. These papers are the Use of Moringa oleifera

seed extracts to reduce helminth egg numbers and turbidity in irrigation water 19; and

Bioremediation of turbid surface water using seed extract from Moringa oleifera Lam.

(Drumstick) Tree 11. A third paper was also used as a supporting supplement, providing some

comparative information regarding various water parameters and their effects on the coagulation

properties of M. oleifera 18, primarily referenced in the discussions about the former two studies.

Description of M. oleifera

Lea 11 provides an overview of the description of the M. oleifera tree, which is native to

northern India but is also widespread through Africa, Asia, and Latin America. The tree is easily

cultivated in tropical environments 4, providing a convenient resource in parts of the world where

millions of people have access only to water of very poor quality. For example, the most

common source of irrigation water used in Ghana is derived from dug-outs, streams, and

stormwater that is typically polluted with untreated wastewater 19. This is a scenario that is most

likely replicated in many other places around the world, especially along the tropical and sub-

tropical belts.

The M. oleifera tree provides two distinct benefits: exceptional coagulation and

flocculation properties, and a rich source of nutrients. As for the latter, almost every part of M.

oleifera is consumed as food, except for the trunk and roots 11. The pods of the tree are typically

the most valuable part, while the seeds and flowers can also be eaten. The leaves are apparently


high in nutrients, containing “[…] more Vitamin A than carrots, more calcium than milk, more

iron than spinach, more Vitamin C than oranges, and more potassium than bananas […]” 11 as

well as protein levels that rival eggs and milk.

In the context of water, however, M. oleifera’s most important characteristic is the

coagulating property of its seeds. In the two main studies under review in this paper, Lea 11 found

a reduction in turbidity of 80.0 – 99.5% using M. oleifera seeds, while Sengupta et al. 19 saw a

reduction of 85 – 96%.

Action of Coagulation/Flocculation

The action of coagulation caused by M. oleifera is derived from proteins found within the

seeds 11. These proteins are water-soluble organic polymers known as polyelectrolytes 13. While

it is agreed that suspended particles have a negative charge and that the polyelectrolytes have a

positive charge, the exact method of how the polyelectrolytes bind suspended matter and form

floc is still not exactly known, though several explanations have been provided. One possible

mechanism is that the positive polyelectrolytes bind to the negative particles, neutralizing their

surface charge and resulting in reduced electrostatic repulsion, allowing the particles to

flocculate. Another explanation is that the polyelectrolytes adsorb to parts of the particle surface,

resulting in differently charged particle surface areas that attract oppositely charged surface areas

of other particles and form floc 1,2,8 15.

Comparison of Coagulation Methods

The main link between the studies presented by Lea, and Sengupta et al. is that of the

coagulation effect of M. oleifera, along with consideration of its practical use in third-world or


impoverished communities. Sengupta focused his study in the country of Ghana and the

application of M. oleifera for treating water from wastewater-polluted sources typically used for

irrigation of food crops. Turbidity levels of irrigation water used in Ghana may be as high as 791

NTU (nephelometric turbidity units) during dry seasons, which is far above the 2 NTU

recommended by the US EPA 6. Lea references Jahn 10, stating that M. oleifera seeds can

increase clarity of water with initial turbidity as high as 10,000 NTU. Lea’s study focuses on

developing specific preparation and application protocols of M. oleifera seeds that can be easily

followed by members of poor rural communities. Both studies considered dosage rates of M.

oleifera (measured in mg/L or ml/L) against varying levels of water turbidity (measured in

NTU).

Preparation of M. oleifera seeds was approached slightly differently in both studies.

Sengupta took a more empirical approach; crushing the seeds into powder using a mortar, mixing

the powder in tap water to final concentrations of 3% and 5% w/v, stirring the mixture and

filtering through a sieve cloth, and utilizing the filtrate as the coagulating agent. Sengupta also

performed tests in both a lab setting and in the field in Ghana.

Conversely, Lea provides basic protocols for preparing the coagulating agent which are

more rudimentary (assumedly, since Sengupta does not list every step of his preparation process)

and applicable to the people who would actually use the seeds to treat their water. One protocol

is an adaptation of a similar procedure by Price 17 and includes extracting oil from the seeds

which can then be used in other applications, thus increasing the value of the seeds. This protocol

can result in either a dried seed cake which can be stored for later use, or fresh seed powder

which is then used immediately. Either product is used to create a paste which is then diluted and


filtered to obtain the extract solution. Lea’s tests are performed in the field under real-world

conditions, though he also references other studies for result support/validation.

Concerning the classification of turbidity levels, Sengupta et al. used three different

categories of turbidity for his laboratory tests and one category for the field tests while Lea

references four different ranges. Sengupta’s lab waters included low turbidity, or tap water

having <50 NTU; medium turbidity, or wastewater having 50 – 150 NTU; and high turbidity, or

turbid water having >150 NTU. As for his field tests, Sengupta used local irrigation water taken

from an on-farm pond in Kumasi, Ghana; the turbidity of this irrigation water ranged 42 – 183

NTU. Lea’s categories included: low at <50 NTU; medium at 50 – 150 NTU; high at 150 – 250

NTU; and extreme at >250 NTU. Coincidentally, Sengupta’s ranges were derived from Lea’s

study (Lea 11 is cited in Sengupta’s paper).

Dosage and Coagulation Results

Both studies consider optimum M. oleifera dosages with regards to turbidity levels.

Starting with Sengupta’s results, which are more empirical than Lea’s, Sengupta compared

turbidity with dosage as well as turbidity over time. He found that dosage was highly dependent

on the type of water being treated. Using two M. oleifera coagulating agent concentrations of 3%

w/v and 5% w/v, different optimum dosages were revealed for each turbidity group. The

irrigation water had optimum dosages of 100 ml/L for 3% solution and 20 ml/L for 5% solution.

Turbid water (>150 NTU) saw maximum reduction with 8 ml/L of 5%, while wastewater (50 –

150 NTU) saw maximum reduction with 4 ml/L of 5% solution.

Lea’s dosages, similar to his protocols, are more practical in the context of real-world

use. He references Doerr 3 and notes that one shelled seed is equivalent to about 200 mg and that


this is typically enough to treat 1 liter of very turbid water. With this in mind, Lea suggests the

following dosages: 1 seed/4 liters of low turbidity water (<50 NTU); 1 seed/2 liters of medium

turbidity water (50 – 150 NTU); 1 seed/liter of high turbidity water (150 – 250 NTU); and 2

seeds/liter for extreme turbidity water (>250 NTU). Both studies found that M. oleifera is not an

effective coagulant for low turbidity (<50 NTU) water 11, and in the case of Sengupta, found that

M. oleifera actually increased the turbidity of tap water. This is probably due to the fact that M.

oleifera itself has some level of turbidity 19 and that it was added to water that has extremely low

turbidity to begin with.

Despite the doses suggested by Sengupta and Lea, both studies mention using the jar test

14,15 to assess coagulation efficiency of the M. oleifera extract to determine the best clarification

dose for a specific water source, as not all water is the same. Lea includes this test as a support

protocol due to its ease of use within a primitive household.

Focusing now on Sengupta’s study and the relationship of turbidity and time, he found

that turbidity did decrease naturally with time, however, turbidity decreased faster with the

inclusion of M. oleifera agent. Irrigation water saw an 85% decrease in turbidity one hour after

treatment. Turbid water saw a 96% decrease in turbidity one hour after being treated, compared

to an 82% reduction without treatment; and wastewater saw an 85% reduction in turbidity one

hour after treatment compared to 54% without treatment. Optimal settling times were also

calculated to be 120 minutes for turbid water and 90 minutes for wastewater, after which no

significant changes in turbidity were observed.

Comparison of Pathogen Studies


Along with reductions in turbidity, Lea and Sengupta also saw reductions in certain

pathogenic elements, specifically coliform bacteria, and helminth eggs, respectively.

Sengupta looked at helminth eggs specifically because contaminated irrigation water used

in Ghana has shown concentrations of helminth eggs in the range of 5 – 10 eggs per liter of water

16,9. This range is above the World Health Organization’s (WHO) standard for wastewater used

for irrigation, which requires a concentration of ≤1 helminth egg per liter 23. Helminth parasites

of concern to human health include the roundworm (Ascaris lumbricoides), whipworm

(Trichuris trichiura), and hookworms (Ancylostoma duodenale and Necator americanus) 5,7.

Helminth eggs are also notorious for being highly resistant to environmental stresses 22 and

wastewater treatment systems in poor areas (if present) may not adequately reduce helminth egg

concentrations to safe levels. High levels of turbidity can also impede treatment for helminth

eggs, as the eggs tend to flocculate with and settle at the same velocity as suspended particles 20.

Higher efficiencies of turbidity reduction using M. oleifera may also reduce helminth egg

concentrations.

Sengupta et al. 19 found that helminth eggs were reduced by 94% when irrigation water

was treated with M. oleifera, from 14.0 eggs per liter down to 0.8. Helminth eggs were found to

reduce exponentially in treated water, with an optimum settling time of 2 – 2.5 hours. In lab

experiments, removal of helminth eggs was significantly higher in all water types treated with M.

oleifera compared to untreated water. On average, 93% of Ascaris eggs were recovered in treated

water compared to 74% in untreated water. In treated water, 92% of Trichuris eggs were

recovered compared to 68% in untreated water. Sengupta also found a positive correlation

between turbidity and number of helminth eggs in water treated with M. oleifera.


Lea states that M. oleifera can also reduce bacterial concentrations as well, namely fecal

coliforms by 90.00 – 99.99% 12 within the first one to two hours of treatment. This is due mainly

to the fact that bacteria tend to adsorb to suspended particles; the bacteria settle out of the water

along with the sedimented sludge. However, Lea does not advise M. oleifera treatment to be the

sole treatment method used for turbid waters. He notes that M. oleifera treatment does not

guarantee 100% removal of pathogens and suggests that M. oleifera be used as a pretreatment to

reduce turbidity, allowing additional treatment for pathogens to become more effective. He lists

several support protocols that may be used to treat specifically for pathogens, including: biosand

filtration; disinfection by natural pH shift (using naturally acidic solutions to lower pH to kill

pathogens); disinfection by solar pasteurization; and disinfection by chlorination (though it

results in harmful disinfection byproducts when exposed to organic matter, so use of chlorine in

conjunction with M. oreifera is not recommended).

Discussion of Turbidity Results

Both studies 11,19 evaluated M. oleifera coagulation treatment on waters of varying

turbidity levels. Unfortunately, the two studies used different metrics for the amount of M.

oleifera agent used. Sengupta used a w/v (weight per volume) suspension measured as an initial

percentage of M. oleifera powder in tap water, which was then filtered and the filtrate dosage

measured in ml/L. Lea used the more direct metric of mg/L of M. oleifera powder or cake in

water. This complicates the comparison of optimum dosages suggested by the two studies as

some kind of conversion is needed to get the dosages in the same metric. To help provide an

extra reference, Pritchard et al. 18 claims a dose of 50 mg/L as a general optimum dosage across a

turbidity range of 40 – 200 NTU, however, he does note that optimum dose increases linearly as


initial turbidity increases. This is compared to Lea’s suggested dosage of roughly 200 mg/L for

turbidity levels greater than 50 NTU (he also notes that M. oleifera is not effective at levels

below 50 NTU). One reason for this discrepancy may be the difference in conditions under

which the M. oleifera was applied; Pritchard studied M. oleifera under laboratory conditions

while Lea prepared and applied the agent in the field under real-world conditions. An additional

finding made by Pritchard is that M. oleifera coagulation is influenced by water temperature and

that the warmer the water, the more effective the coagulation. Water temperature was not

mentioned in Lea’s study, and so the water temperature may have differed between Lea’s and

Pritchard’s studies (and Sengupta’s study, as well).

Discussion of Pathogen Results

While these two studies did not focus on the same pathogens, they did demonstrate that

M. oleifera is not only an effective coagulating agent but can also be an effective disinfectant,

depending on the target pathogen. It should also be satisfying to note that both studies do not

recommend M. oleifera treatment as a sole treatment method for water. Both Sengupta and Lea

recommend additional treatment options, for example, sand filtration, if the water is going to be

used for drinking or irrigating food crops. And the fact that M. oleifera not only cleans

particulate from the water but some pathogens as well makes additional treatment and

disinfection that much easier.

Comments

It is very interesting to learn that natural plant products can achieve equivalent results in

water quality compared to anthropogenic compounds that may be costly and/or harmful to


synthesize, as well as toxic to handle. These two studies do a wonderful job of demonstrating the

effectiveness of a naturally-derived and easily-obtainable resource for effectively treating a

common water issue (turbidity) that exists across the globe, and is an issue that millions of

people struggle with every day. I think these studies 11,18,19 provide a reliable and significant body

of work regarding the use of M. oleifera in water treatment. I did come across some mentions of

similar plant compounds being used to treat water issues, however, I don’t believe the research

regarding those compounds was as extensive as M. oleifera, or their effects as well known.

Moringa oleifera has been used by many peoples around the world for hundreds of years; it’s

only just within the last couple of decades that it has really been scientifically studied. It is also

interesting to note that M. oleifera has been successfully tested full-scale as the primary

coagulant at a water treatment facility in Malawi 21, demonstrating that naturally-derived

compounds and methods have the ability to function at the same level as industrially-produced

chemicals typically used in water and wastewater treatment.

I really enjoyed Lea’s approach to studying M. oleifera. Rather than studying its effects

solely in a laboratory setting using equipment and methods that are not really not applicable or

practical outside a lab, he established a real-world connection. By taking his study beyond the

lab, he generated a protocol that is applicable outside a lab and allows the actual people who use

this plant to better treat their own water. Hopefully that is knowledge that the people using M.

oleifera can maintain within their communities and pass down to future generations. I think there

needs to be more scientific study that takes the science out of the lab and into the lives of those

affected by water quality issues, particularly those living in developing and under-developed

nations. It’s one thing to assess the effectiveness of a method in a lab using calibrated equipment

specifically designed for empirical uses, which is necessary to determine potential or theoretical


effectiveness and health effects, etc. However, transferring that method to a real-world situation

in which one does not have access to such equipment and making it practical is very important if

we, as members of developed and industrialized nations, are to continue addressing the water

quality issues and the people of less developed communities.


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Review of the effect of Moringa oleifera seeds on reducing water turbidity and pathogens

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