Biological versus chemical coagulants – a potential solution for the developing world
M. Pritchard a* , T. Craven a , T. Mkandawire b , A.S. Edmondson a and
J.G. O’Neill c a Leeds Metropolitan University, School of the Built Environment, Leeds, LS2 8AJ, United
Kingdom b University of Malawi, The Polytechnic, Department of Civil Engineering, Private Bag 303,
Chichiri, Blantyre 3, Malawi c Centre for Research in Environment and Health, 6 Abbotsway, York, YO31 9LD, United
Kingdom
* Corresponding author email: m.pritchard@leedsmet.ac.uk
ABSTRACT
Conventional removal of turbidity from water is via a coagulation process. The two chemicals commonly used are aluminium sulphate (Al
2
(SO
4
)
3
) and ferric sulphate (Fe
2
(SO
4
)
3, termed alum and ferric. The limited availability and relative expense of these chemicals has led to other more widely available coagulants being sought for developing countries. Moringa oleifera, Jatropha curcas, Guar gum , Strychnos potatorum, Hibiscus sabdariffa and Cassia angustifolia are just a few of the most common natural plants/plant extracts used for coagulation. In particular, the seeds from the M.
oleifera tree contain a unique water coagulant, a protein as distinct from an inorganic ion, which acts as a natural cationic polyelectrolyte. There is however limited published data to derive a direct comparison between the effectiveness of biological coagulants against chemical coagulants.
A research project was therefore commissioned to investigate the performance of M. oleifera compared with that of alum and ferric. A series of jar tests was undertaken using raw water and control water. Control water consisted of deionised water spiked with E. coli (10 4 per 100 ml) and turbidity (160 NTU) artificially created by kaolin. Results showed M. oleifera to remove 82% turbidity and 88% E. coli, whereas alum removed greater than 99% turbidity and
E. coli . Tests on turbid river water of 60 NTU for M. oleifera showed a reduction of turbidity of 80% and E. coli of 93%. The equivalent reductions for alum were 93% and 98% respectively. Low turbidity water was treated with M. oleifera and ferric. Results showed a

92% and 94% reduction in E. coli for M. oleifera and ferric respectively. Although not as effective as alum or ferric, M. oleifera showed sufficient removal to encourage its use for treatment of turbid waters in developing countries.
Keywords: Alum, Coagulants, Ferric , Moringa oleifera , Water treatment .
1. Introduction
Many impurities in water and wastewater are present as colloidal solids, which do not readily settle. Finely dispersed suspended and colloidal particles that produce turbidity and colour of the water cannot be removed sufficiently by ordinary sedimentation. Colloidal particles generally carry a negative electrical charge. Their diameter ranges from 10 -4 to 10 -6 mm.
These particles are surrounded by an electrical double layer (diffuse layer and stern layer) preventing contact between each other (Bache, 2007). Adding a coagulant (generally positively charged) and mixing the water causes compression of the double layer and thus the neutralisation of the electrostatic surface potential of the particles. The resulting destabilised particles stick together upon contact forming solids known as ‘flocs’. Rapid mixing for a few seconds is important after adding a coagulant to ensure a uniform dispersion of the coagulant and also to increase the opportunity for particle-to-particle contact. Subsequent gentle and prolonged mixing (15 min) aids in the formation of flocs. These flocs then are large enough to settle by gravity and may be removed by filtration.
Inorganic coagulants and/or polymers are typically used during the water treatment process to remove suspended solids, bacteria and viruses in the water treatment. There are currently two main chemicals used to aid coagulation in the developed countries; these are aluminium sulphate (Al
2
(SO
4
)
3
) and ferric sulphate (Fe
2
(SO
4
)
3
), termed alum and ferric respectively. Due

to the limited availability and relative expense of these chemicals for the developing world, there is an urgent need to find alterative water purification solutions (coagulation aids) for rural villages.
Natural plant extracts have been used for water purification for many centuries, e.g. M. oleifera,
J. curcas, Guar gum , S. potatorum, H. sabdariffa and C. angustifolia . In particular, M. oleifera has been ranked as one of the best plant extracts for water purification (Pritchard et al ., 2009) and since the 1970s it has received various levels of interest from a number of researchers (namely:
Jahn and Hamid , 1979; Folkard, 1986; Sutherland, 1990/94; Jeyanthi, 2004).
It has been found that the active component of M. oleifera causing coagulation is a soluble protein that acts as a natural cationic polyelectrolyte during treatment and causes coagulation in turbid water (Barth, 1982; Jahn 1989). This was confirmed by Tausher (1994) when the protein was isolated and characterised using a phosphate buffer. The flocculent capacity of M. oleifera was explained by the patch charge mechanism due to low molecular weight and high charge density of isolated proteins.
There is however limited published data to derive a direct comparison between the effectiveness of a biological coagulant (such as M. oleifera ) against that of chemical coagulants (such as alum and ferric). A research project was therefore undertaken to investigate the performance of M. oleifera to that of alum and ferric in terms of coliform and turbidity removal.
2. Methodology
2.1 Stock solutions
To ensure consistency and replication throughout the testing programme stock solutions were created for dosing and artificially creating the required parameters under investigation. Even though these conditions do not replicate environmental influences, it is accepted as a

recognised procedure for empirical testing programmes and has been frequently used by other researchers, such as Suleyman et al . (1996); Duan and Gregory (1998); UNEP (1997);
Folkard et al . (1999). It also allows unequivocal direct comparisons to be made without the influence of external variables. Standard sedimentation jar test equipment was used in this testing programme to determine the amount of coagulation which occurred under the different test conditions. The experimental trials were undertaken under controlled conditions in the
Microbiology Laboratory at Leeds Metropolitan University, UK.
2.1.1 Coagulant
Good quality M.
o leifera seeds (not rotten) were shelled by hand and reduced to a fine powder using a laboratory blender. The powder was then sieved though a sieve of 1 mm aperture size.
The powder (4 g) was first partially wetted to create a paste, which was then further diluted to
200 ml. The solution was stirred for 8 min, after which it was allowed to stand for 30 min so that any remaining solids could settle. The supernatant fluid was then drawn off for dosing.
Concentrated alum solution (Al
2
(SO
4
)
3
), of which 6.3% was Al 3+ , was added to double distilled water (2 g per 100 ml) and thoroughly mixed. This diluted solution could then be used to accurately dose water samples with alum. For example to achieve a 30 mg/l dose 28 ml of this solution would need to be added to a 1000 ml water sample.
Concentrated ferric solution Fe
2
(SO
4
)
3,
of which 13.5% was Fe, was added to double distilled water (1 g per 100 ml) and thoroughly mixed. Similarly to alum, to achieve a 10 mg/l dose 7.4 ml of this solution would need to be added to a 1000 ml water sample.
2.1.2 Escherichia coli
A fresh strain of E. coli was directly isolated from an open water source, the River Aire in
Leeds, UK. A water sample was collected in accordance with WHO (1997 p. 186) from the

river and analysed for bacterial content. The sample contained E. coli (confirmed by API-20E test), which was isolated and cultured for use in this expermental trial. Single colonies of E. coli were inoculated into 10 ml nutrient broth and incubated overnight. Following incubation the culture was centrifuged at 3000 rpm for 5 min. The supernatant was aseptically removed and the E. coli pellet resuspened in 10 ml double distilled water. The centrifugation process was repeated to ensure that all nutrient broth was removed from the E. coli pellet, which was again resuspended in 10 ml of double distilled water to give a washed stock suspension of E. coli . Previous testing carried out by Pritchard et al., (2008) in Malawi indicated that up to
30,000 faecal coliforms were present in rural villages’ water supplies. In order to represent conditions found, the target E. coli dose for samples tested was set to be between 1x10 4 and
3x10 4 E. coli per 100 ml. Spread plate counts indicated that typically 1 ml of 10 -3 dilution of the washed stock E. coli suspension would produce the target E. coli count when dosed into
1000 ml of sample water.
2.1.3 Turbidity
Kaolin was used to artificially create different levels of turbidity in water samples. The kaolin used was sourced from BDH Ltd, UK (reference: 24926.295). A 120 g of kaolin powder was mixed together with 400 ml of deionised water in a laboratory blender. This was transferred to a 1000 ml beaker and diluted by the addition of a further 600 ml of deionised water. The suspension was then slowly stirred and the pH corrected to 7.5 using sodium hydroxide. It was then left to stand for 24 h after which the upper 500 ml was decanted and further diluted with deionised water to 1000 ml. The pH was again corrected to 7.5 and the kaolin stock suspension was stored at 4 o C.
2.2 Synthetic sample water
Artificial turbidity of 140-175 NTU was created with kaolin to form a control sample. This sample was then used to compare M.
o leifera and alum in terms of ability to reduce E. coli

counts. As the jar testing equipment was able to test up to six 1000 ml samples, one sample was left untreated to provide a control sample with two M.
o leifera and two alum dosed samples, e.g. 50-75 mg/l M.
o leifera and 30-50 mg/l alum. The correct amounts of kaolin stock suspension and 1x10 -3 E. coli suspension were first mixed in a 50 ml vortex tube to disperse the bacteria within the material responsible for creating turbidity. This mixture was then dispensed evenly between the five 1000 ml samples of deionised water. The 1000 ml samples were then stirred at 200 rpm for 1 min to ensure adequate dispersal. The turbidity, pH and temperature of each sample were taken prior to the tests. The required doses of either stock ( M.
o leifera or alum solution) were added into each jar test sample by a pipette. A rapid stirring period of 30 s at 200 rpm was then followed by a slow stirring period of 15 min at 20 rpm to allow coagulation to occur. Flocs which had formed were then allowed to settle for 30 min before the turbidity of the settled samples was measured.
An alternative method of dosing was also trialled. This involved the use of a muslin cloth pouch filled with the sieved M.
o leifera powder at different doses. These pouches were then attached to the stirring blades on the jar testing equipment. The same mixing procedure was undertaken as above, however an additional 10 min of stirring at 20 rpm was employed to allow the pouches to become fully saturated.
The control and best performing samples dosed with M.
o leifera and alum were taken forward for bacterial analysis. Sub-samples were taken from jars after settling and diluted in sterile
0.1% peptone water to 10 -1 , 10 -2 and 10 -3 . The samples were then filtered through 0.45μm
Whatman filters onto Petri dishes containing Membrane Lactose Glucuronide Agar (MLGA).
2.3 Natural sample water
To ensure validity of the results obtained from the synthetic water sample, two different naturally sourced water samples were also collected and tested. One of the samples was taken

from a river and the other from a reservoir. The river samples were taken from Meanwood
Valley (Leeds, UK) and had low colour and varying turbidity. The reservoir sample was taken from Albert Water Treatment Works (Halifax, UK), which collected moorland run-off, and was low in turbidity but high colour. In these tests it was necessary to measure the colour absorption (abs/m) and/or turbidity of raw water samples both before and after settling. This was done using a CECIL 1020 spectrophotometer set at 254 nm (UV-C light) and a hand held turbidimeter (Hannah Instrument: 93102; range 0-1000 NTU; accuracy ±2%). The coagulation elements of these tests were carried out in the same way as described in Section
2.2; however no kaolin or E. coli was artificially introduced.
2.4 Naturally coloured water plus kaolin and E. coli from stock solutions
In order to mimic a water source with both high colour and high turbidity content a further test was conducted using highly coloured reservoir water (Ewden Water Treatment Works) as the sample water, but in this instance both kaolin and E. coli were added to provide a coloured turbid water with a turbidity of 150 NTU and an initial E. coli count in the range 1x10 4 to
3x10 4 per 100ml.
2.5 Secondary treatment by filtration
In order to further reduce E. coli counts in the synthetic water samples a filtration stage was introduced. This was achieved by pouring coagulated settled water samples through either a muslin cloth or through a laboratory scale sand filter using fine/medium grained quartz sand.
3. Results and Discussion

3.1 Synthetic sample water
Table 1 details a comparative performance of M.
o leifera to an equivalent dose of alum in the synthetic water sample. The M.
o leifera dose was seen to reduce turbidity by over 80% compared with over 99% for that of alum. Under these conditions the alum outperformed M.
o leifera in terms of turbidity removal. The reduction in E. coli was slightly more comparable as E. coli reduction was 88% for M.
o leifera with alum removing over 99%.
A subsequent test using the muslin pouch dosing method, which is more likely to be a practical dosing method in developing countries showed more comparable results (Table 2).
In this instance, the turbidity reduction was approximately 85%, but E. coli reduction was lower at 74%. This was still a good level of reduction, but further tests using this method would be required to optimise the performance. It is important to note however that the pouch dosing method may not be as consistent as the M.
o leifera stock solution method as the small amount of powder used to dose each sample may vary in its quality. Also, if the pouch is tight the powder in the centre may not be wetted as much as if the pouch was loose. Many small variables are introduced as a result of using the pouch for coagulation.
3.2 Naturally sourced water
Two main types of naturally sourced water were tested (Tables 3-6), i.e. river and reservoir.
The reservoir water from Albert Water Treatment Works, which was of high colour, was treated initially with M.
o leifera only (Table 3). Far higher doses were required than in the synthetic water, to successfully produce coagulation in the naturally highly coloured waters.
A 750 mg/l dose showed an optimum reduction of only 53% in absorption, but yielded a faecal coliforms (FC) reduction of 73.6%.
A further test was conducted using river water from Meanwood Valley. This water had an initial absorption of 11.1 abs/m. A comparison was made with ferric, which is typically used

to coagulate water of high colour in this region of the UK (Table 4). Results showed a 40% reduction in absorption for M.
o leifera, in comparison with a 70% reduction for ferric. The chemical coagulant far outperformed the natural coagulant again and its dose was also far lower (20 mg/l for ferric compared with 500 mg/l for M.
o leifera ). However, when bacterial analysis was undertaken the results were more comparable. Reductions in FC were 77% for
M.
o leifera and 96% for ferric, and for E. coli reductions were 92% for M.
o leifera and 94% for ferric. These results indicate that M.
o leifera reduces the E. coli content by a relatively high amount considering the reduction in absorption was largely inferior to that of ferric.
River water from Meanwood Valley was also retested just after a period of rainfall. The water showed a natural turbidity of 60 NTU. A test was undertaken to compare M.
o leifera with alum, which is generally used to treat water of high turbidity in this region (Table 5).
Similarly to the coloured reservoir water, a higher M.
o leifera dose (250 mg/l) was required to produce an optimum reduction in turbidity of 80%, whereas the alum dose (50 mg/l) remained adequate to treat (93% reduction in turbidity) the water. Corresponding FC reductions of 94% and 99% were obtained from M.
o leifera and alum respectively. Reduction in E. coli was similar: 93% for M.
o leifera and 98% for alum. Although outperformed in terms of turbidity reduction the M.
o leifera still reduced bacterial content of the water sample significantly.
3.3 Naturally coloured water plus kaolin and E. coli from stock solutions
To create a scenario where highly coloured and turbid water may be present, highly coloured water from Ewden Water Treatment Works had kaolin stock suspension added to increase its turbidity. The result was a raw water sample with high colour of 20 abs/m and turbidity of
150 NTU (Table 6). During preparation of this water it had to be stored for a period of time, therefore instead of testing the natural bacterial content of the water, E. coli from the stock suspension was added to the kaolin suspension as in previous tests in order to provide a highly contaminated test sample. Results showed that optimum doses for coagulation were
1000, 50 and 10 mg/l for M.
o leifera , alum and ferric respectively. Compared with previous

tests the M.
o leifera performed better in terms of turbidity reduction by reducing turbidity by
97%, which compared well with 99% for alum and 98% for ferric. In terms of colour reduction, absorption was reduced by 73% for M.
o leifera , 88% for alum and 81% for ferric.
For this type of water overall the alum was best at reducing the properties tested and both alum and ferric outperformed M.
o leifera in absorption reduction. Comparing E. coli reduction, M.
o leifera reduced E. coli by 66%, alum 89%, and ferric 86% which again showed the chemical coagulants to be superior to that of the biological coagulant. However, it is also shown that significant E. coli reduction is possible using M.
o leifera as a coagulant, which is encouraging for its potential use as a coagulant in countries where chemical coagulants may be unobtainable.
3.3 Secondary stage treatment by filtration
The two methods of filtration used yielded different results (Tables 7 & 8). The use of muslin cloth as a filter is largely ineffective as the turbidity of the settled samples was not reduced after filtration, as shown in Table 7. Reduction in E. coli after filtration was only 71% for M.
o leifera compared with 98% for alum, which did not improve on previous non-filtered tests.
Results for the sand filter (Table 8) do however show an improvement in reduction of turbidity and E. coli . Over multiple sand filtration tests for M.
o leifera, the turbidity reduction was increased from 78-83% to 83-97% after filtration. At optimum conditions turbidity was reduced to within the WHO (2006) guideline value of 5 NTU. Sand filtration also led to an E. coli reduction of 88% to 93% which is a significant improvement over the results seen in
Tables 1, 2, 6 and 7.
4. Conclusions


Both of the chemical coagulants (alum and ferric) outperformed the biological coagulant ( M.
o leifera ) in all of the various conditions tested during this research programme.

M.
o leifera required higher dose levels to achieve optimum performance in comparison to alum and ferric. Also, M.
o leifera required higher dose levels in naturally sourced water compared with synthetic water.

M.
o leifera performed far better in naturally sourced water than synthetic polluted water.

Overall , M.
o leifera showed significant improvements in water quality, and has the potential, especially with sand filtration, to be used for rural water purification system in the developing world where the costs of importing chemical coagulants is far too expensive.
5. Recommendations

Further research work is required to optimise the performance of M.
o leifera .

Natural water should be considered to that of synthetic water for further testing programmes using M.
o leifera .
Acknowledgements
We would like to thank Leeds Metropolitan University and the Malawi Polytechnic
University for their support throughout this research programme.
References
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Table 1 Reduction in E. coli using kaolin and deionised water (initial turbidity 150NTU )
Coagulant
Moringa
Dose mg/l
50
Reduction in turbidity E. coli reduction
% %
81.9 88.0
Alum 50 99.6 99.8
Table 2 Reduction in E. coli using kaolin and deionised water (initial turbidity 140NTU)
Coagulant Dose Reduction in turbidity E. coli reduction
Moringa mg/l
50
%
84.6
%
74.0
Table 3 Reduction in FC using coloured reservoir water (initial absorption 73.3 abs/m)
Coagulant Dose
Reduction in absorption FC reduction
Moringa mg/l
750
%
53.2
%
73.6
Table 4 Reduction in FC and E. coli using river water (initial absorption 11.1 abs/m)
Coagulant Dose Reduction in absorption FC reduction E. coli reduction
Moringa
Ferric mg/l
500
20
%
41.4
68.5
%
76.8
95.61
%
91.8
94.2
Table 5 Reduction in FC and E. coli using river water (initial turbidity 60 NTU)
Coagulant
Moringa
Alum
Dose mg/l
250
50
Reduction in ST
%
80.0
92.8
FC reduction
%
93.9
98.9
Table 6 Reduction in E. coli using reservoir water with kaolin
(initial turbidity 150 NTU, absorption 20 abs/m)
E. coli reduction
%
92.6
97.7
Coagulant Dose mg/l
Reduction in ST Reduction in absorption E. coli reduction
% % %
Moringa
Alum
Ferric
1000
50
10
97.4
99.4
98.0
72.5
88.0
80.8
65.8
88.9
86.4
Table 7 Reduction in E. coli using kaolin and deionised water filtered through muslin
(initial turbidity 175 NTU )
Coagulant Dose Reduction in ST Reduction in FT E. coli reduction
Moringa mg/l
50
%
82.4
%
83.1
%
70.7
Alum 30 97.9 a 99.7

Table 8 Reduction in E. coli using kaolin and deionised water filtered through sand
(initial turbidity 150-170 NTU )
Coagulant Dose Reduction in ST Reduction in FT E. coli reduction mg/l
Moringa 25-50
%
78-83
%
83-97
%
88-93
Alum 30-50
FC – Faecal coliform
99-100 a 90-97
FT – Filtered turbidity
ST – Settled turbidity
a – Filtration not carried out as the ST was <5NTU, i.e. within the WHO (2006) guideline value