INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 4, No 3, 2013
© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0
Research article ISSN 0976 – 4402
Received on September 2013 Published on November 2013 259
Effectiveness of crude extract and purified protein from Vigna unguiculata
seed in purification of charco dam water for drinking in Tanzania Nancy Jotham Marobhe
School of Environmental Science and Technology (SEST), Ardhi University (ARU)
P.O Box 35176, Dar es Salaam, Tanzania
doi:10.6088/ijes.2013040300005
ABSTRACT
Due to chronic water supply problems prevailing in most rural areas of Tanzania, households
are obliged to use man made water reservoirs (charco dams) for drinking after receiving
inadequate treatment using powdered seeds from different plant species. This study is aimed
at investigating the capacity of crude extract and purified proteins (coagulant proteins) from
Vigna unguiculata (VUP) seed to purify drinking water from Nunguru charco dam.
Coagulant proteins were purified from V. unguiculata crude seed extract (VUCE) by
modified ion exchange chromatography technique. The VUP were found to be cationic in
nature and have the molecular mass of about 6 kDa, which is very similar to the coagulant
proteins purified from Moringa oleifera and Parkinsonia aculeata seeds. The coagulation
potentials of VUP and VUCE were verified by jar experiments and the performances were
compared to those of aluminium sulphate (alum) using water samples with initial turbidity of
880 NTU. The coagulant proteins reduced most pollutants to the levels that complied with the
Tanzania Drinking Water Standards and WHO standards. Minimum residual turbidity
achieved by both VUCE and VUP was 3 NTU and 12 NTU for alum. The VUP performed
best at the dosage of 8 mg/L which was almost ten times lower than that observed for VUCE
(76 mg/L). The VUP reduced organic load in treated water by 80% while VUCE increased it
by almost 100%. Although the VUP and VUCE did not alter the pH and alkalinity of the
treated water, the VUP increased the conductivity of water substantially without affecting the
water palatability. The VUP and VUCE reduced Fe2+ in coagulated by 93 - 98% while NO3-
and PO43- were reduced by 91 – 99% and 94 - 99.6%, respectively. The VUP and alum
reduced fecal indicators by 94 and 98.6% respectively. The purification procedure of
coagulant proteins is simple and user friendly and hence it could be scaled up for large scale
production of coagulant proteins for use in water treatment processes in Tanzania. The VUCE
and VUP are recommended for production of drinking water and other domestic uses so as to
reduce the incidences of cholera and improve people’s health and hygiene.
Keywords: Cation exchanger, coagulant seed proteins, turbid water, rural areas.
1. Introduction
Drinking water sources contaminated by intestinal pathogens including inorganic and organic
pollutants are responsible for various health hazards in many poor countries (Wilson and
Andrews, 2011; Pokhrel and Viraraghavan, 2004). The removal of turbidity during water
treatment process in inevitable since suspended particles are media for transmission of harmful
organic and inorganic contaminants, taste, odor and color– producing compounds and
pathogenic organisms (Raghuwanshi et al., 2002). Safe water supply coverage in Tanzania is
still very low whereby less than 73% and 50 % of urban and rural population respectively, have
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 260
access to safe water supply. Due to chronic shortage of clean drinking water supply in most
rural areas of Tanzania, the Government of Tanzania and development partners have opted to
invest in construction of charco dams (man-made reservoirs) as one of the reliable sources of
water supply that will cater for both human and animal’s needs throughout the year (URT,
2002).
Production of clean and safe water from most raw water sources necessitates application of
coagulation-flocculation process to remove turbidity in the form of suspended and colloidal
matter. Although aluminium salts (e.g. Al2(SO4)3.18H2O) and synthetic organic polymers are
the most widely used coagulants in water treatment works, cost implications and deleterious
environmental effect of these chemicals has triggered interest in research for plant seeds that
could act as natural coagulants (Katayon et al, 2005).
Coagulation of turbid surface water sources in rural areas of Tanzania like in many other
developing countries is done at a household level using plant materials (Jahn, 1984; Al-Samawi
and Shokralla, 1996; Leite, 2007). The seed powder of Vigna unguiculata is among the natural
coagulants that are widely used for purification of water fetched from charco dams and rivers in
rural areas of Tanzania. Studies conducted by Marobhe et al. (2007a) on effectiveness of crude
extract of V. unguiculata seeds on removal of river and synthetic water turbidities under varied
operating parameters revealed that, the seeds possess high coagulating potential. Several
detailed research papers have been published on the performance of natural coagulants of
which, Moringa oleifera has been studied extensively (Okuda et al., 2001; Ghebremichael et
al., 2005; Arnoldsson et al., 2008). It has been observed that the main disadvantage of using
crude seed extracts in water treatment is the increased chemical oxygen demand (COD) in the
treated water due to organic nature of such extracts and hence it enhances deterioration of
treated water upon storage for prolonged period of time (Ndabigengesere and Narasiah, 1998;
Arnoldsson et al., 2008). Thus, the aim of this study was to investigate into the effect of crude
extract of V. unguiculata seed (VUCE) and coagulant proteins purified from the crude extract
of VUCE on various physical, chemical and microbiological quality parameters in the treated
charco dam water. To the best of my knowledge, this is the first intensive investigation that
explores on use of purified seed proteins of V. unguiculata plant for purification of charco dam
water for drinking and other domestic purposes.
2. Material and methods
2.1 Source of V. unguiculata seeds and charco dam water samples
V. unguiculata seeds used as natural coagulant in this study were obtained from Singida rural
district in central parts of Tanzania. The dry pods of V. unguiculata were collected from rural
households and transported to the Applied Environmental Microbiology laboratory at the Royal
Institute of Technology (KTH), Sweden, for purification of coagulating protein. Coagulation-
flocculation experiments to remove suspended particles including fecal indicator bacteria in
charco dam were conducted at the laboratory of microbiology and technology at Ardhi
University, Tanzania using coagulating proteins purified in Sweden. Water samples were
collected from Nunguru charco dam in Singida rural district, Tanzania during dry season.
Approximately, 10 l of water samples were collected in plastic buckets and transported to the
Environmental engineering analytical laboratory at Ardhi University for experimental analysis.
Water samples for bacteriological analysis were collected in sterile one liter glass bottles and
transported to the Singida district water laboratory for analysis.
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 261
2.2 Preparation of crude seed extracts and purification of coagulant protein
The V. unguiculata crude seed extract (VUCE) was prepared as five percent (5%, W/W)
solution from the fine seed powder in distilled water as detailed by Marobhe et al. (2007b).
The quality parameters of VUCE were analyzed according to the procedure detailed in the
Standard Methods for the examination of Water and Wastewater (APHA et al., 1998).
Coagulant proteins were purified from the VUCE using a cation exchange resin followed by
elution of bound proteins using 0.3 and 0.6 M sodium chloride (NaCl) as detailed by
Marobhe et al. (2013) for purification of Parkinsonia aculeata coagulant proteins. The eluted
proteins from the cation exchanger resin were termed V. unguiculata pure proteins or simply
VUP. Protein concentration in samples collected during the purification process was
measured using dye binding method (Bradford, 1976). Protein samples that were eluted with
0.6 M NaCl were used in all coagulation experiments to study the quality of water treated
with the proteins due higher amount of proteins eluted than that when 0.3M NaCl was used.
For comparison purposes, alum was also prepared as 5% solution (W/V), while the coagulant
protein purified from Moringa oleifera (MOCP) was provided by the Department of
Environmental Microbiology at KTH, Sweden. The Sodium Dodecyl Sulphate-
Polyacrylamide Gel Electrophoresis (SDS-PAGE) to check the purity and molecular masses
of the VUP was carried as detailed by (Hultmark et al., 1983; Ghebremichael et al. 2006).
2.3 Coagulation experiments and water quality analysis
2.3.1 Coagulation experiments
The jar tester apparatus (Model, Phipps and Bird – PB-700TM) was used in coagulation-
flocculation experiments whereby different dosages of VUCE, VUP and alum were added into
six different beakers each containing one liter of water samples. The intensity and duration of
rapid and slow mixing including settling time of coagulated water samples were set as detailed
by Marobhe and Gunno (2013).
2.3.2 Measurement of water quality and analytical methods
The quality of water sample coagulated with both natural and chemical coagulants was
examined using the methods stated in the Standard Methods for the Examination of Water
and Wastewater (APHA et al., 1998). The physical and chemical water quality parameters
that were analyzed included turbidity, pH, Total Dissolved Solids (TDS), conductivity,
salinity, alkalinity, cation concentration (Fe2+), and anion concentration (NO3-, PO4
3- and
SO42-) and organic compounds measured as COD as described earlier by Marobhe and Gunno
(2013) for P. aculeata coagulant protein. The turbidity was measured using a 2100 P
turbidimeter from Hach Company. The density of fecal coliforms (FC) and other coliform
bacteria in the raw and treated water samples were enumerated using Standard Method 9221E
Faecal Coliform Membrane Filter Procedure (APHA, et al., 1998) after 30 min of settling
time of coagulated water.
3. Results
3.1 Water quality in charco dams
Table 1 presents the typical turbidity and pH levels in selected charco dams located in
Singida rural district in central parts of Tanzania. The results revealed that, charco dams have
very high turbidities, in which, during dry and rain seasons the turbidity ranged from 1570 to
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 262
4300 NTU and 550 to 400 NTU respectively. The pH level in the charco dams during both
dry and rain season range from 6.9 and 7.5. Also, Table 2 shows the average, range and
standard deviation of raw water quality parameters of Nunguru charco dam based on three
analyses. It is evident that Nunguru dam is very turbid (730 - 900 NTU) and also, it contains
high concentration of iron (Fe2+) (23.8-31.5 mgl-1), which makes it objectionable for drinking
without treatment.
Table 1: Physical quality and capacity of selected charco dams
Reservoir/
charco dam name
Estimated
volume (m3)
Average turbidity (NTU)
Average pH
dry season rain
season
dry
season
rain
season
Nunguru 280,000 2790 550 7.1 7.5
Mipilo 89,000 4300 780 7 7.3
Ngororijanda 36,400 1570 520 7.1 7.2
Suke 570,700 1900 450 6.9 7.2
Sagara 573,600 1590 430 7 7.4
Ikungi 190,000 1980 400 7.2 7.4
Ikomesi 197,400 2680 590 6.9 7.2
Table 2: Representative water quality parameters of Nunguru charco dam
Parameter Average Range STDEV
pH 7.4 7.2- 7.5 ± 0.17
0.173205
Turbidity (NTU)
810 730-900 ± 85.4
Total Dissolved Solids (TDS) (mg/L)
)
37.8 33.5-41 ± 3.9
Electrical conductivity (µs/cm) 72.9 69.7-80 ± 72.9
Alkalinity (as CaCO3) (mg/L)
)
74 68.6-80 ± 5.72
Iron (mg/L)
)
27 23.8-31.5 ± 4
Chloride (mg/L)
120 99 -136 ± 19
Nitrate –N (mg/L)
)
33 27-43 ± 7.9
Phosphate (mg/L)
)
9 6.6-12.4 ± 3.03
Chemical Oxygen Demand 80 75-87 ± 6.24
(COD) (mg/L)
3.2 Purified coagulant seed protein for coagulation of charco dam water samples
Table 3 shows the average values of selected quality parameters of VUCE and VUP eluted by
0.6 M NaCl based on two analyses. The VUCE contains more organic matter expressed as
Chemical Oxygen Demand (COD) (8,700 mg/L) and protein content (1,280 mg/L) than in
VUP samples which contained 920 of COD and 440 mg/L of proteins. Also, the VUP
samples had the conductivity of 32,400 µs/cm which is much higher than that in the VUCE
samples (233 µs/cm).
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 263
Table 3: Physico-chemical characteristics of crude seed extract and purified coagulant
proteins
Parameter Units VUCE VUP (0.6 M NaCl
eluted) pH
6.57 6.4
Total Dissolved Solids (TDS) mg/L
118.6 16,400
Conductivity µs/cm 233 32,400
Salinity
ppt 0.1 4.8
Alkalinity (as CaCO3)
mg/L
80 20
Iron (Fe2+)
mg/L 0.66 0
Nitrate (NO3-)
mg/L 10.5 0
Phosphate (PO4-2)
mg/L 17 0
Protein content mg/L 1280 440
Chemical Oxygen Demand (COD) mg/L 8,700 920
Note. VUCE and VUP are abbreviations for V. unguiculata crude extract (VUCE) and
purified proteins (VUP) eluted by 0.6 M NaCl, respectively.
The results for SDS-PAGE of coagulant proteins at different stages of purification starting
with VUCE, unbound proteins, VUP and MOCP (as a reference) are displayed in Figure 1.
The results showed that the bound proteins of VU were eluted in pure state as indicated by
thick single bands situated in the region of about 6 kDa, which is very similar to the
molecular weight of the MOCP and that of P. aculeata coagulant protein (PAP) reported by
Marobhe and Gunno (2013).
Figure 1: SDS – PAGE of V. unguiculata proteins at various stages of coagulant protein
purification. Lane 1 shows marker protein with molecular masses of 4 – 148; Lane 2
represents purified protein of M. oleifera; Lane 3 crude seed extract; Lane 4 and 5 shows
unbound proteins and Lane 6 and 7 represents proteins eluted by 0.3 M and 0.6 M NaCl
respectively.
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 264
3.3 Effect of coagulants on the quality of treated water samples
Coagulation-flocculation experiments were run in triplicate and the results were highly
reproducible. The results of the quality of water coagulated with purified coagulant proteins
after 30 min of sedimentation are shown in Figure 2 through 6. Standard deviations from three
analyses were computed and indicated in graphs as vertical lines.
3.3.1 Turbidity and chemical oxygen demand
The effects of varying the dosages of VUCE, VUP and alum on turbidity and COD of the
treated water are presented in Figure 2a and b, respectively. The results showed that the
reduction of turbidity increased with increasing the dosage of VUCE, VUP and alum until the
optimal dosages for the maximum turbidity removal was ensued. Figure 2a shows that the
optimal dosage for VUCE was 76 mg/L which reduced turbidity from 880 NTU at zero dosage
to 3 NTU. Also, the results showed that, at the optimal coagulation dosage of the VUCE, the
COD increased from 80 in raw water to 182 mg/L in treated water which suggests that, most of
organic component in the VUCE (Table 1) flocculated and settled along with other particulate
matter in the water. Similarly, Fig. 2b shows that the minimum residual turbidity of 3 and 12
NTU were attained after coagulation with 8 and 14 mg/L of VUP and alum, which correspond
to turbidity removal efficiencies of 99.7% and 98.6% respectively. Likewise, the COD of the
treated water dropped from 80 mg/L at zero dosage of coagulants to 20 and 15 at optimal
coagulation dosages of VUP and alum, respectively.
0
50
100
150
200
250
300
350
400
450
0
100
200
300
400
500
600
700
800
900
1000
0 20 40 60 80 100
CO
D (
mg/
L)
Res
idua
l tu
rbid
ity
(NT
U)
Dosage of coagulants (mg/L)
VUCE (turbidity)
VUCE (COD)
Figure 2a: The effect of different dosages of crude seed extract (VUCE) on turbidity and COD
levels in the treated water.
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 265
Figure 2b: The effect of different dosages of purified coagulant protein (VUP) and ALUM
on turbidity and COD levels in the treated water.
3.3.2 Effect on pH and alkalinity
The pH and alkalinity levels in water treated by different dosages of VUCE, VUP and alum are
shown in Figure 3a and b. It is deduced from the results that the water treated with VUCE and
VUP demonstrates insignificant variation in pH and alkalinity levels.
The results depicted that the pH of treated water remained more or less constant between pH
7.2 and 7.4 while the values for alkalinity ranged from 50 to 55 mg/L (as CaCO3) throughout
the range of dosages tested. Unlike coagulant proteins, the pH and alkalinity of water treated
with alum dropped from 7.4 to 4.3 and 70.7 to 3 mg/L (as CaCO3) respectively (Figure 3b).
Figure 3a: The effect of variation of dosages of crude seed extracts (VUCE) on pH and
alkalinity of treated water.
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 266
Figure 3b: Effect of variation of the dosages of purified coagulant proteins (VUP) on pH and
alkalinity of treated water in comparison with alum.
3.3.3 Electrical conductivity
The conductivity data of water treated with different dosages of VUCE, VUP and alum are
presented in Figure 4a and 4b. Figure 4a shows that at optimal coagulation dosage of VUCE
(76 mg l-1), the electrical conductivity in the water increased from 75 µs cm-1 at zero dosage to
92 µs cm-1 (22% increase) after treatment. Moreover, minor variations in water electrical
conductivity were seen at dosages above those optimal for turbidity removal. The observed
conductivity values in the treated water are however; lower than those observed in the VUCE
(Ref. Table 1). The results shown in Figure 4b revealed that unlike VUCE, the electrical
conductivity of the water treated with VUP increased considerably with increase of the dosage
of VUP and alum. At the optimum dosages for turbidity removal of VUP (8 mg l-1) and alum
(14 mg l-1), the electrical conductivity increased from 74 µs cm-1 of raw water to 713 and 1270
µs cm-1 respectively. This is due to incorporation of Cl- into the water from sodium chloride
used for protein purification and SO42- from alum used in coagulation process.
0
20
40
60
80
100
120
0 20 40 60 80 100 120
Con
duct
ivit
y (µ
s/cm
)
Dosage of VUCE (mg/L)
VUCE
Raw water (untreated)
Figure 4a: Conductivity of water treated with different dosages of crude seed extract (VUCE).
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 267
0
200
400
600
800
1000
1200
1400
1600
0 2 4 6 8 10 12 14 16
Cond
uctiv
ity
(µS
/cm
)
Dosage of coagulants (mg/L)
VUP
ALUM
Figure 4b: Conductivity of water treated with different dosages of purified coagulant
proteins (VUP) and alum.
3.3.4 Iron and nutrients concentration
The change in concentration of Fe2+, NO3- and PO4
3- in water after treatment with VUCE, VUP
and alum is shown in Figure: 5a and b. It was observed that the concentration of Fe2+, NO3- and
PO43- in the treated water decreased with the increase of dosage of VUCE, VUP and alum. The
concentrations of Fe2+, NO3- and PO4
3- at zero dosage of coagulants were 21.1, 33.3 and 7.5
mg/L respectively. The concentrations of Fe2+, NO3- and PO4
3- at optimal dosage of VUCE for
turbidity removal including the removal efficiencies in parentheses were 0.39 (98.1%) 0.14
(99.6%) and 0.42 (94.4%) mg l-1. Moreover, the results in Figure 5b showed that the
concentration of Fe2+, NO3- and PO4
3- in water treated with optimum dosage of VUP for
turbidity removal were 1.4, 3 and 1.4 mg/L which correspond to the removal efficiencies of
93.4, 91 and 81.6% respectively. However, much lower concentrations of pollutants in the
treated were observed at the protein dosage slightly higher than those required for turbidity
removal. Similarly, the removal efficiencies of 46, 95.5 and 96% respectively, were observed
for Fe2+, NO3- and PO4
3- in water treated with optimal dosage of alum for turbidity removal.
0
5
10
15
20
25
30
35
40
0 20 40 60 80 100 120
Con
cent
ratio
n (m
g/L
)
Dosage of coagulants (mg/L)
VUCE (ferrous ion)
VUCE (phosphate)
VUCE (nitrate)
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 268
Figure 5a: The effect of varying the dosages of crude seed extracts (VUCE) and on
concentration of ferrous, nitrate and phosphate ions in the treated water.
Figure 5b: The effect of varying the dosages of purified coagulant protein (VUP) and alum
on concentration of ferrous, nitrate and phosphate ions in the treated water.
3.3.5 Indicators of fecal pollution (Coliforms)
The counts of total and fecal coliforms before and after water coagulation are shown in Figure
6. The untreated charco dam water had an average total coliforms density of 4x104/ml and
2.3x103/ml of fecal coliforms. Un-coagulated water removed between 24.8% and 26.4% of
total coliforms and fecal coliforms, respectively, by plain sedimentation. The removal
efficiencies of total coliforms and fecal coliforms by VUP were 95% and 94% respectively,
whereas for alum were 98.7 and 98.6% respectively. The results also revealed that, the optimal
dosages for bacterial removal were similar to those observed for turbidity removal.
Figure 6: The effect of purified coagulant protein (VUP) and alum on fecal indicator bacteria
in the water coagulated with different dosages of coagulants.
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 269
4. Discussion
There is scientific evidence that, interventions targeted at poor populations could provide
significant health benefits and contribute to poverty alleviation (Gundry et al., 2004).
Since water in charco dams is highly polluted with particulate matter and inorganic pollutants
especially iron (Table 1 and 2), purification of the water prior drinking and other domestic
uses is unavoidable. This will be possible by appraisal of existing natural and/or traditional
water coagulation methods through scientific investigations. It is anticipated that, the natural
water coagulation technology will not only benefit the rural populations but also, the urban
water utilities, which often distribute insufficiently treated water to consumers due to
inadequate resources at water treatment plants.
Purification of coagulant proteins from VUCE using ion exchanger chromatography has
verified that the VUP have very similar characteristics to coagulant proteins purified from
other types of seeds. The electrophoretic pattern of VUP was found to be very similar to that
of the reference coagulant protein from Moringa seed (MOP), which was also reported
previously by Ghebremichael et al. (2006) as well as to that observed for P. aculeata
coagulant protein (PAP) (Marobhe and Gunno, 2013). Such homologies among coagulant
proteins may form the basis for explaining the coagulation potential of other seeds that have
been traditionally used in water clarification in different rural areas of Tanzania (Marobhe et
al., 2007b). However, it is possible that VUP, PAP, MOP and other coagulant proteins might
have variations in other characteristics especially the polypeptide sequences. Past studies
done by Marobhe et al. (2007b) have revealed that VUP and PAP either as a protein
concentrate or powder (lyophilized protein) are stable and could be stored easily at different
conditions. It is apparent that a single elution step using 0.6 M NaCl is sufficient to remove
most non-coagulating proteins from VUCE to produce a sample rich in active coagulating
proteins. Since the main drawback of VUCE is the addition of organic and inorganic matter
into treated water, application of purified proteins will circumvent the problems associated
with VUCE. Due to consistency of charco dam water, the VUCE could help rural households
to produce drinking water although coagulant dosage needs to be carefully controlled so as to
reach optimum destabilization. The dosages (seed powder) applied by households in rural
areas of Tanzania to clarify water fetched from charco dams is extremely high (up to 125
times higher than the optimum dosage of VUCE that has been established in this work).
Excessive dosages of natural coagulants are associated with fast deterioration of treated water
due to regrowth of residual bacteria upon storage at room temperature (Marobhe et al., 2007a;
Wilson et al., 2011).
With respect to water purification, both the VUCE and VUP purified water from the charco
dam to the level that complied with the Tanzania Drinking Water Quality Standard (TDWS) of
30 NTU and World Health Organization (WHO) standard of 5 NTU. Maximum turbidity
removal of VUP was achieved at the dosage about ten times lower than that required for the
VUCE. Also, water coagulation using VUP reduced up to 80% COD in the treated water, while
VUCE increased the COD by almost 100%. Coagulation of turbid water using minimum
dosage of VUCE for maximum turbidity removal will prolong the storage time of the treated
water and also will help households in rural areas to save the seeds for food and other uses.
However, further studies to ascertain the cost implications and shelf life of surface water
samples treated using crude seed extracts and purified proteins are necessary.
Unlike alum, coagulation of charco dam water using VUCE and VUP did not affect the pH and
alkalinity of the treated water. The pH values of treated water were within the pH range
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 270
acceptable for drinking water which is 6.5 to 8.5 (WHO, 1996). The propensity of alum to
reduce the pH of water during coagulation process has been reported by Martyn et al. (1989).
These results suggest that, coagulant proteins possess natural buffering property that avoids the
need for application of lime or bicarbonate to raise the pH and hence, it reduces the cost for
water treatment. Although the VUP increased the conductivity of the treated water
significantly, the water retained its palatability. However, elution of proteins using low
concentration of salt solution could be advantageous. Similar to VUCE, the crude extract of M.
oleifera seed also did not have a significant effect on conductivity of treated water
(Ghebremichael at el., 2006; Ndabigengesere and Narasiah, 1998).
The removal of Fe2+, NO3- and PO4
3- in water after coagulation with VUCE and VUP was
substantial and the residual ions conformed to the TDWS set at 1 mg l-1, 10 mg/L and 30
mg/L respectively. Similarly, the removal of up to 92.1% and 89.6% of Fe2+ in wastewater
and charco dam coagulated by Moringa seed powder and PAP respectively, has been
reported by Sajidu et al. (2005) and (Marobhe and Gunno, 2013). The results also support
previous observations, which showed that a lower turbidity of treated water is an indicator of
more efficient removal of organic and inorganic contaminants associated with particulate
matter (Kavanaugh et al., 1978). The removal of PO43- and perhaps other ions could be due to
aeration and adsorption of ions onto large flocs of colloidal particles that settled along with
flocs (Özacar and Sengil, 2003). As shown in Table 2 and 3, water from charco dams is very
turbid and contains high concentration of Fe2+, which causes the water to be reddish brown in
color. The removal of Fe2+ from water is necessary not only for health reasons but also for its
effects on laundry. The water from Nunguru dam treated with VUCE and VUP were very
clear and appealing for drinking. The removal of NO3- in drinking water limits the risk of
gastric cancer (Yang et al., 1998) and methaemoglobinaemia in infants, which is otherwise
widely spread in rural areas of Tanzania.
The prevalence of many waterborne diseases, especially cholera, typhoid and bacillary
dysentery in many rural areas of Tanzania is due to consumption of untreated or partially
treated charco dam water at household levels. Water coagulation using VUP and alum
decreased considerably the counts of fecal coliforms in the clarified water. The performance
of alum in bacterial removal surpassed the VUP because of the propensity of alum to
remarkably reduce the pH of water, which is lethal for most of the bacteria. The effectiveness
of coagulants proteins on turbidity and bacterial removal may render these natural materials
suitable for simultaneous coagulation and disinfection of turbid surface waters for rural and
peri-urban populations in developing countries. However, post treatment of the water
clarified by coagulant proteins using natural materials reported by Dalsgaard et al. (1997);
Clasen and Bastable, 2003; Sarah et al., 2011) to destroy residual bacteria prior drinking is
necessary.
The natural coagulation technology is one of several environmentally friendly interventions,
which could help rural and semi-urban populations to produce clean drinking water and provide
a means of combating poverty (Sajidu et al., 2005; Gundry et al., 2004).
The cost for production of coagulant proteins will be low compared to conventional methods
for purification of proteins, which requires special equipment, reagents and trained personnel.
About 2900 mg of proteins could be purified from 7g of V. unguiculata and about 6200 mg
VUP can purify 1 m3 of turbid water. Therefore, approximately less than 1.5 USD will be
enough to treat about 1 m3 of high turbid water using VUP. Supplementing or replacing
chemical coagulants with coagulant proteins will be suitable for agro-based developing
Effectiveness of crude extract and purified protein from Vigna unguiculata seed in purification of charco dam
water for drinking in Tanzania
Nancy Jotham Marobhe
International Journal of Environmental Sciences Volume 4 No.3, 2013 271
countries such as Tanzania because large scale production of these coagulants could improve
the socio-economic conditions of people.
5. Conclusion
From the present study, it may be concluded that, water in charco dams is highly polluted and
hence proper treatment through appraisal of traditional water coagulation methods is needed.
Coagulation-flocculation and sedimentation of charco dam water samples with V. unguiculata
crude seed extracts (VUCE) and coagulant proteins purified from VUCE (VUP) removed
suspended matter and most other pollutants to the levels that complied with Tanzanian
Drinking Water Standards and WHO for drinking water.
More specifically:
1. The turbidity removal efficiencies of VUP, VUCE and alum differed very slightly.
The lowest turbidities at optimum dosages of both VUP, VUCE was 3 NTU while
the observed minimum turbidity for alum was 12 NTU, which, corresponded to the
removal efficiency of to 99.7 and 98.6% respectively. The optimal coagulation
dosage of VUP was about ten times lower than those of VUCE.
2. The VUP reduced organic load in treated water by 80% which makeit possible to
store the treated water for long periods without deterioration.
3. Unlike alum, the VUCE and VUP had no significant effect on pH and alkalinity of
the treated water. This avoids the need for additives for regulating the pH and
alkalinity of water treated natural coagulants.
4. The VUCE and VUP reduced significant amounts of Fe2+, NO3- and PO4
3- from
treated water. The aesthetic quality of charco dam water treated with coagulants
improved significantly due to the removal of substantial amounts of ferrous ions.
5. The coagulant proteins reduced up to 94% of fecal coliforms in coagulated water
after 30 min of settling time. Additional natural disinfection of coagulated water to
remove pathogens is necessary before the water is drunk.
6. The protein purification technique used here is simple and rapid and can be easily
scaled up for production of large quantities of coagulant protein for households and
water treatment plants applications. The VUCE is recommended for household
water treatment but careful control of coagulant dosage is needed to give optimum
coagulation.
Acknowledgements
I acknowledge the financial support provided by Sida-SAREC. I appreciate the assistance
extended by Mr. Mbulume. R and Mr. Ndimbo during laboratory work. My thanks also goes to
the Department of Environmental Microbiology at the Royal Institute of Technology (KTH),
Sweden for the facilities used during protein purification. I also thank Prof. Gunno Renman for
the fruitful discussions and inputs.
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