195 effect of settling time on turbidity removal using moringa oleifera ...

Ozean Journal <strong>of</strong> Applied Sciences 4(3), 2011 


ISSN 1943-2429 

© 2009 Ozean Publication 

EFFECT OF SETTLING TIME ON TURBIDITY REMOVAL 

USING MORINGA OLEIFERA SEED POWDER 

* NWAIWU N.E. and ** LINGMU B. 

* Department <strong>of</strong> Civil and Water Resources Engineering, University Of Maiduguri, Maiduguri, Nigeria. 

c/o dr j. nyanganji Department <strong>of</strong> Geography, University Of Maiduguri, 

Maiduguri, Nigeria. 

*E-mail address for correspondence: nknwaiwu@yahoo.co.uk 

_____________________________________________________________________________________________ 

Abstract: This paper studies the <strong>effect</strong> <strong>of</strong> <strong>settling</strong> <strong>time</strong> on turbidity removal for low and medium turbidity pond 

(surface) water. Physico-chemical tests were carried out on two samples (low and medium turbidity water) before 

and after the water was treated with the same dosage <strong>of</strong> Moringa oleifera seed powder for <strong>settling</strong> periods <strong>of</strong> 

30minutes, 1hour, 2hours, 6hours and 24hours. The <strong>settling</strong> <strong>time</strong> <strong>of</strong> 24 hours in being advocated for Moringa 

oleifera seed powder for treating low and medium turbidity water because better coagulation and hence higher 

turbidity removal was achieved with the extended <strong>settling</strong> periods. 

Keywords: Moringa oleifera seed powder, coagulation, turbidity, total suspended solids, <strong>settling</strong> <strong>time</strong>. 

_____________________________________________________________________________________________ 

INTRODUCTION 

Turbidity in water is caused by suspended matter, such as clay, silt, finely divided organic and inorganic matter, 

soluble coloured organic compounds, planktons and other micro and macroscopic organisms (America Public 

Health Association/ America Water Works Association, 1989). Turbidity can provide food and shelter for 

pathogens and if not removed, can promote regrowth <strong>of</strong> pathogens in the distribution system. This can lead to water 

borne disease outbreaks (EPA, 1999). Increased turbidity levels adversely affects aquatic ecosystems by reducing 

photosynthesis and, therefore primary productivity at all levels <strong>of</strong> the food chain (TAG, 2002). The consumption <strong>of</strong> 

high turbid water may constitute a health risk (WHO, 1996). The removal <strong>of</strong> turbidity in water would be extremely 

beneficial as it would alleviate the majority <strong>of</strong> problems associated with turbidity. For many developing countries 

coagulation, flocculation and sedimentation (which are the processes involved in removing turbidity from water) are 

expensive processes because <strong>of</strong> the high costs involved and the difficulty in assessing the chemical coagulants 

including alum. However, there have been studies on the use <strong>of</strong> indigenous natural coagulants. The use <strong>of</strong> locally 

grown and natural coagulants may result in a more sustainable and economically viable alternative (Yung, 2003). 

Many plants have been used to clarify water. These include Moringa oleifera, Moringa stenopetala, Vicia faba 

(Jahn, 1986, 1988), Canavalia ensiformis, Bombax constatum(Faby and Eleli, 1993;Nacoulima et al, 2000 ).Crushed 

<strong>195</strong>


Moringa oleifera, seed have been found to be viable replacement coagulant for chemicals such as aluminum 

sulphate (alum) in a full scale plant treatment trial at the Thyolo treatment works in southern Malawi (Sutherland et 

al,1994). Yao et al (2005) studied the flocculating activities <strong>of</strong> the fresh stems <strong>of</strong> mucilage <strong>of</strong> Gombo (Hibiscus 

esculentus) and achieved the lowering <strong>of</strong> turbidity. 

Generally, various <strong>settling</strong> <strong>time</strong>s for Moringa oleifera water treatment have been used or proposed. Muyibi and 

Evison (1995) on s<strong>of</strong>tening hard water with Moringa oleifera seed powder used a <strong>settling</strong> <strong>time</strong> <strong>of</strong> one hour. At a 

Moringa oleifera dosage <strong>of</strong> 1800mg/l the calcium hardness had reduced to almost zero. Doerr (2005), on showing 

steps for household water treatment, recommended a <strong>settling</strong> <strong>time</strong> <strong>of</strong> one to two hours for all the particles and 

contaminants to settle to the bottom <strong>of</strong> the storage container. Lilliehook (2005) while studying the use <strong>of</strong> sand 

filteration on river water flocculated with Moringa oleifera, employed a <strong>settling</strong> period <strong>of</strong> 30 minutes to 120 minutes 

for low, medium and high turbidity water. In the experiment, it was observed that purification increased with 

increased <strong>settling</strong> <strong>time</strong>s as there was a drastic reduction in the residual turbidity between 30-45 minutes for the 50 

NTU water. The World Agr<strong>of</strong>orestry Centre (2004) suggests a duration or <strong>settling</strong> <strong>time</strong> <strong>of</strong> one hour for a clean 

supernatant to result using Moringa oleifera. On the other hand, the CDC pretreatment fact sheet 

(safewater@cdc.gov) prescribed a <strong>settling</strong> period <strong>of</strong> 24 hours before decanting <strong>of</strong>f the clear water to another 

container. Hsu et al (2006) prescribed that Moringa Oleifera seed powder mixed with water should be kept for hours 

(number not specified) in order to obtained clean water. 

This paper studies the <strong>effect</strong> <strong>of</strong> <strong>settling</strong> <strong>time</strong> on turbidity removal for low and medium turbidity pond (surface) 

water. 

The Study Area 

The study area is in the rural outskirts <strong>of</strong> Maiduguri, the capital <strong>of</strong> Borno State, North East Nigeria. Borno State is 

situated in a semi and region <strong>of</strong> the Sahel savannah. Three seasons have been identified with the area: the cold dry 

(harmattan) season (October to March), hot dry season (April – June) and the rainy season (July to September). 

Temperatures are usually extreme all the year round with hot season temperatures ranging between 39 o C and 40 o C 

under the shade. The annual rainfall is 692mm (Nwaka, 1991).Water is a scarce resource within the semi and 

region. The rainfall period is very brief making water storage imperative. At the household level, rain water in 

stored in various vessels which include drums, plastic containers, clay pots, bucket and calabashes (Nwaiwu and 

Oku<strong>of</strong>u, 2005). At the community level, rain water is stored in ponds which are some<strong>time</strong>s called river by some 

locale <strong>of</strong> the region. The ponds are large holes deliberately dug into the ground by the people for the purpose <strong>of</strong> rain 

water storage or borrow pits left after a road construction. Rain water is depended upon by 22.5% <strong>of</strong> the people but 

there is no modern storage facility available to the local people. During the rainy season these rivers/ponds supply 

11.65% <strong>of</strong> the populace while in the dry season, these river/ponds supply the water needs <strong>of</strong> 8.31% <strong>of</strong> the 

inhabitants (Nwaiwu and Oku<strong>of</strong>u, 2006). It is then necessary that an inexpensive but efficient method <strong>of</strong> treating the 

water sourced from these ponds be made available to the natives since this facility is an important source <strong>of</strong> water. 

METHODOLOGY 

Sample collection 

The pond water sample was collected from an existing burrow pit located at Jimtillo, a rural outskirt <strong>of</strong> Maiduguri, 

the Borno State capital in North East, Nigeria. The water was collected in the middle <strong>of</strong> the pond by immersing a 

plastic container completely until it was full. The cap was inserted while the container was under water. The water 

was subjected to treatment using Moringa oleifera seed powder. 

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Laboratory Analyses 

Physico-chemical tests were carried out on two samples(low and medium turbidity water) before and after the water 

was treated with the same dosage <strong>of</strong> Moringa oleifera seed powder. 

Moringa oleifera suspension Preparation 

Moringa oleifera seed pods were obtained from Gombe State, North East, Nigeria. The seed coats were removed 

to get the kernels. The kernels were dried and ground to powder. One gram <strong>of</strong> the seed powder was mixed with 

clean water in a plastic bottle to form a paste. The content <strong>of</strong> the bottle was shaken for one minute to activate the 

coagulant and then filtered through a sieve into the pond water to be treated. The water was stirred for five minutes 

and left to settle. The water was left to settle for 30 minutes, 1hour, 2 hours, 6 hours and 24 hours. After each 

<strong>settling</strong> period, the supernatant was taken for physico-chemical analyses. The parameters tested for include pH, total 

dissolved solids (tds), temperature, turbidity suspended solids (tss), salinity, electrical conductivity and colour. 

The physico-chemical tests were carried out in accordance with the procedure in Environmental Chemistry 

Laboratory Manual (2000). 

RESULTS AND DISCUSSION 

Physical properties <strong>of</strong> raw water 

The physical properties <strong>of</strong> the water samples used are presented in Table 1. these include physical, chemical and 

bacteriological properties <strong>of</strong> the samples. The two water samples used fall into two categories namely: low 

turbidity water (


In Figure 2, the variation <strong>of</strong> the concentrations <strong>of</strong> the various parameters during the 24 hours <strong>settling</strong> period is 

shown. It can also be seen that the addition <strong>of</strong> the Moringa oleifera seed powder did not alter the pH, temperature, 

salinity, electrical conductivity as well as the total dissolved solids concentration in the water. This is confirmed by 

the respective coefficients <strong>of</strong> variation which are 2.3%, 1.35%, 1.4%, 1.1% and 1.9% for the parameter values 

during the 24hour period. However, the residual concentration <strong>of</strong> turbidity, total suspended solids and colour during 

the 24 hours <strong>settling</strong> period revealed respective coefficient <strong>of</strong> variation is 43.12%, 46.5% and 37.9%. These high 

values <strong>of</strong> coefficients <strong>of</strong> variation, clearly demonstrates that turbidity, total suspended solids and colour are 

significantly affected by the presence <strong>of</strong> Moringa oleifera seed powder in water over a detention period. High 

removal efficiencies were observed for the three named parameters with respect to <strong>settling</strong> <strong>time</strong>. 

The range <strong>of</strong> turbidity removal efficiencies <strong>of</strong> 12% to 82.5% are shown in Table 2 for the medium turbidity water. 

The addition <strong>of</strong> the Moringa oleifera seed powder significantly affected the turbidity removal efficiencies. After 30 

minute into the 24 hour <strong>settling</strong> period, the turbidity removal efficiency was 12%. This reduced to 5.7% after one 

hour. After 2 hours, an increased removal efficiency <strong>of</strong> 8.96 was obtained. A six hour <strong>settling</strong> period gave a 

removal efficiency <strong>of</strong> 12.1% with a residual value <strong>of</strong> 86.30NTU which is almost the same as the turbidity residual 

within the first 30 minutes into he detention period. On increasing the <strong>settling</strong> <strong>time</strong> to 24 hours, a residual turbidity 

value <strong>of</strong> 17.2NTU with a removal efficiency <strong>of</strong> 82.5% resulted. The foregoing shows that there is the need to extend 

the <strong>settling</strong> period <strong>of</strong> water being treated using the Moringa oleifera. seed powder to a 24 hour <strong>settling</strong> period in 

order to obtain better results than would have been using shorter detention periods. This observation applied also to 

the low turbid water where the turbidity removal efficiency increased from 80% (30minutes <strong>settling</strong> <strong>time</strong>) to 96.3% 

(24 hour <strong>settling</strong> period). The removal efficiencies for colour for the low turbid and medium turbid waters increased 

from 74.59% (after 30 minutes <strong>settling</strong> period) to 88.89% (after 24 hour <strong>settling</strong> period) and 12.4% (after 30 minutes 

<strong>settling</strong> period) to 95.2% (after 24 hour <strong>settling</strong> period) respectively. The removal efficiency <strong>of</strong> the total suspended 

solids increased from 4.92% (after 30 minutes <strong>settling</strong> period) to 26.5% (after 24 hour <strong>settling</strong> period) for the how 

turbidity water. There was no recorded reduction in concentration <strong>of</strong> the TSS for the medium turbidity water, 

instead increments in concentration from a raw value <strong>of</strong> 40.33mg/l to 320. 24mg/l after one hour <strong>settling</strong> <strong>time</strong> 

resulted. This reduced to 76.28mg/l after 24 hours <strong>settling</strong> period. The results show that using the same Moringa 

oleifera seed powder dosage, the low turbidity water has a higher 24 hour removal efficiency (96.3%) the medium 

turbidity water (82.5%). Lower turbidity removal was observed as initial turbidity <strong>of</strong> water samples increased with 

the coagulant dose remaining constant for both samples. This result varies from the findings <strong>of</strong> Katayon et al (2004) 

and Muyibi and Evison (1996) which indicated that Moringa oleifera seed extract may not be an efficient coagulant 

for low turbid water. This variation in results may be due to the fact that seeds from different sources (geographic 

locations) exhibit varying coagulation performance (Narasiah et al, 2002) as a result <strong>of</strong> different protein contents 

and development <strong>of</strong> the seeds. Additionally the fact that the water samples were treated with the same Moringa 

oleifera seed powder dosage which was the optimum for low turbid water may have had an impact on the 

performance <strong>of</strong> the coagulant on the medium turbid water. Consequently the medium turbid water did not show 

initial appreciable turbidity reduction. Katayon et al (2004) that showed that increased turbidity should have an 

increased Moringa oleifera dosage. 

The Moringa oleifera seeds did not affect the pH value <strong>of</strong> the water samples, these remained within the WHO 

approved value <strong>of</strong> 6.5-8.5 (WHO, 1996) for both the low and medium turbid water (Figures 1 and 2). This result 

agrees with the findings <strong>of</strong> Ndabigengesere and Narasiah (1998) and Katayon et al (2004). The treatment with the 

Moringa oleifera seed powder resulted in a slight reduction <strong>of</strong> the pH values for both water samples. Practically, 

this means that no chemical is needed to bring the pH <strong>of</strong> the treated water within the above mentioned range. 

According to Katayon et al (2004) the slight decrease in pH may be due to hydrogen ions <strong>of</strong> the weak acidity <strong>of</strong> 

Moringa oleifera stock solution which balanced the hydroxide ions in the raw water. 

Regression Analysis 

After the addition <strong>of</strong> Moringa oleifera seed powder, the concentrations <strong>of</strong> constituent parameter were monitored for 

after 0.5, 1, 2, 6 and 24 hours. The total suspended solids was one <strong>of</strong> the parameters measured, the measurement <strong>of</strong> 

which is <strong>time</strong> consuming. Attempts have been made to correlate turbidity for predicting total suspended solids 

(Gippel , 1995;Saddle and Campbell, 1985; Holliday, Rasmussen and Miller, 2003 and Truhlar,1978). These 

predictions may be limited in statistical certainty, predictive power and logistical coordination. 

198


Despite the foregoing, there is no universal relationship between turbidity and total suspended solids. (Truhlar, 

1978; Rasmussen, 1995). Provision <strong>of</strong> a relationship between turbidity and total suspended solids will assist in easy 

monitoring <strong>of</strong> the water quality parameter during water treatment using Moringa oleifera seed powder for low and 

medium turbid water(LT for low turbid water and MT for medium turbid water). Presently R 2 (coefficient <strong>of</strong> 

determination) is used to chose the best model for turbidity- total suspended solid relationship. 

The observed trends in the relationship between total suspended solids and turbidity were in turn evaluated 

statistically using a linear, logarithmic, polynomial, power and exponential regression. The equations obtained for 

low turbid water and medium turbid water are shown in Table 3. The adjusted R 2 is given by the following 

relationship (Kleinbaum and Kupper, 1978). 

Adjusted R 2 = R 2 k/ n − k − 1 1 − R 2 (1) 

where n is the number <strong>of</strong> observation and k is the number <strong>of</strong> independent variables. The adjusted R 2 is adjusted for 

the degrees <strong>of</strong> freedom in the estimating equation to avoid the upward bias in the unadjusted R 2 when the sample 

size is small relative to the number <strong>of</strong> explanatory variable in the model (Murphy, 1973). 

The overall F is estimated from the following equation (Kleinbaum and Kupper, 1978), 

F = 

me an square regression 

mean square residual 

= R 2 / 1 − R 2 

n−k−1 

k 

(2) 

The overall F value shows that the general null hypothesis “Ho: all k independent variables considered together do 

not explain a significant amount <strong>of</strong> the variation in the dependent variable” should be rejected. This is because the 

overall F statistic is greater than the critical F value and therefore all the independent variables together explain a 

significant amount <strong>of</strong> variation in the dependent variable. 

The resulting R 2 (coefficient <strong>of</strong> determination) value for equation LT1 to LT5 generally ranged between 0.672 and 

0.956 for the low turbidity water while the medium turbidity water with equations MT1 to MT5 had R 2 values 

ranging between 0.542 and 0.905. The critical F statistic for equations LT1, LT2, LT4 and LT5 as wells equations 

MT1, MT2, MT4 and MT5 at 95% and 90% confidence intervals are F 2 , 2, 95 = 19.0 and F 2, 2, 90 = 9.0 respectively. 

Equations LT3 and MT3 have critical F-values <strong>of</strong> F 1,3,95 = 10.1 and F 1, 3,90 = 5.54 for 5% and 10% levels <strong>of</strong> 

significance. The overall F statistic for equations LT1, LT3 and LT5 are statistically significant at 10% level. 

Equations LT1 and LT5 exceed F 2, 2, 90 = 9.0 while equation LT3 exceeds F 1,3,90 = 5.54. These values are valid for 

the low turbidity water. At 5% level <strong>of</strong> significance only equation LT3 has a significant overall F-value as it 

exceeds F 1, 3, 95 = 10.1. The overall F-statistic for equations MT4 and MT5 are statistically significant at 10% level 

<strong>of</strong> significance as they exceed F 2 , 2,90 = 9.00 while equation MT3 is significant at 90% at its overall F-value exceed 

F 1 , 3, 90 = 5.54 respectively. 

A comparison <strong>of</strong> the values <strong>of</strong> the regression properties <strong>of</strong> equations LT1, LT3 and LT5 as well as MT3, MT4 and 

MT5 are shown in Table 4. For the low turbidity water, equation LT1 yielded the lowest R 2 and adjusted R 2 but the 

highest value <strong>of</strong> residual variance and residual standard deviation, while equation LT3 had the highest value <strong>of</strong> R 2 

and adjusted R 2 but the least residual variance and residual standard deviation. 

The Root Means Square Error (RMSE, Eq 3) was also used to determine the overall prediction accuracy <strong>of</strong> the 

models, and the bias (d, Eq 4) was used to evaluate the model’s over or under-prediction. 

RMSE = 

1 

n 

n 2 

i=1 d i (3) 

199


d = 1 n 

n 

i=1 d i 

(4) 

where di is the difference between the predicted and measured values and n is the number <strong>of</strong> measured values <strong>of</strong> 

total suspended solids. The lowest value <strong>of</strong> RMSE was obtained with equation LT3 (0.834). However, equation 

LT3 yielded a bias <strong>of</strong> 9 x 10 -4 . Thus considering the values <strong>of</strong> R 2 , adjusted R 2 , overall F statistic, residual variance, 

residual standard deviation as well as the RMSE and bias d, equation LT3 can be taken to give the best overall 

prediction <strong>of</strong> total suspended solids in low turbidity water during treatment using Moringa oleifera seed powder. 

The values <strong>of</strong> total suspended solids prediction from equation LT3 were compared with the corresponding measured 

values and presented in Fig 3. Alternatively, use can be made <strong>of</strong> Eq LT5 for predicting the total suspend solids in 

low turbidity water using Moringa oleifera seed powder at it yielded the next highest R 2 value and the next lowest 

value <strong>of</strong> RMSE. 

Considering the medium turbidity water, equation MT4 yielded the lowest value <strong>of</strong> R 2 and the lowest value <strong>of</strong> 

adjusted R 2 , but the highest residual variance and residual standard deviation while Eq MT3 had the highest value <strong>of</strong> 

R 2 and adjusted R 2 but the lowest residual variance and residual standard deviation. The lowest values <strong>of</strong> RMSE 

were obtained with Eq MT3 and Eq MT5 as shown in Table 4. Equation MT3 yielded the lowest value <strong>of</strong> bias, 

although the highest overall F-statistic was exhibited by Eq MT5 (F = 13.43). Considering the R 2 , adjusted R 2 , 

residual variance, residual standard deviation, F-statistic, bias and RMSE Eq 3 can be taken to give the best overall 

prediction <strong>of</strong> total suspended solids for medium turbid water which is undergoing treatment using the Moringa 

oleifera seed powder. An alternative equation which can be used is Eq MT5. 

The results <strong>of</strong> this study indicate that the polynomial equations (LT3 and MT3) give the best overall prediction <strong>of</strong> 

total suspended solids(TSS) in low-med turbid water undergoing treatment using the Moringa oleifera seed powder. 

This means that the relationship between the TSS and turbidity in water undergoing treatment using the Moringa 

oleifera seed powder is a polynomial relationship to the 2 nd order. An alternative relationship between these two 

parameter (total suspended solids and turbidity) is an exponential (LT5 and MT5). The values <strong>of</strong> predicted TSS 

values from Eq MT3 were compared with the corresponding measured values and presented in Fig 4. 

CONCLUSION AND RECOMMENDATION 

Moringa oleifera seed powder is a widely acclaimed coagulant which does not alter the pH <strong>of</strong> the finished water and 

proper Moringa oleifera seed dosage will produce better results. Cost <strong>of</strong> treatment <strong>of</strong> water in developing countries 

will greatly be reduced if the Moringa oleifera seed powder is employed in water treatment because its use will 

reduce the cost on other coagulants currently being employed in water purification. The <strong>settling</strong> <strong>time</strong> <strong>of</strong> 24 hours in 

being advocated for Moringa oleifera seed powder because better coagulation and turbidity removal was achieved 

with the extended <strong>time</strong>s 

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Yung K. (2003) Biosand Filtration: Application in the Developing World CE401 project prepared for University <strong>of</strong> 

Waterloo. Civil Engineering Department. 

202


Table 1: Physico chemical properties <strong>of</strong> raw water samples 

A. Low turbidity water 

Parameters 

Quantity 

Temperature(ºC ) 22.4 

pH 7.72 

Total dissolved solids (mg/l) 68.4 

Turbidity (NTU) 32.8 

Electrical conductivity (mS/m) 98.2 

Salinity (mg/l) 48.4 

Colour(TCU) 52.83 

Total Suspended Solids(mg/l) 51.94 

B 

Medium turbidity water 

Parameters 

Temperature (ºC ) 23.7 

pH 8.1 

Total dissolved solids (mg/l) 113 

Turbidity (NTU) 98.2 

Electrical conductivity (mS/m) 167.5 

Salinity (mg/l) 83.5 

Colour (TCU) 89.34 

Total Suspended Solids (mg/l) 40.33 

203


Table 2: Turbidity, Total Suspended Solids, and Colour removal efficiencies (%) 

with respect to <strong>time</strong> 


Parameters 

Removal efficiencies (%) with respect to <strong>time</strong> 

30 minutes 60 minutes 2 hours 6 hours 24 hours 

Turbidity(NTU) 80 84.1 86.3 87.5 96.3 

Total Suspended 4.92 12.46 16.4 22.9 26.5 

Solids(mg/l) 

Colour(TCU) 74.59 81.7 85.94 86.37 88.89 

B 


Parameters 

Removal efficiencies (%) with respect to <strong>time</strong> 

30 minutes 60 minutes 2 hours 6 hours 24 hours 

Turbidity(NTU) 12 5.7 8.96 12.1 82.5 

Total Suspended -ve -ve -ve -ve -ve 

Solids(mg/l) 

Colour(TCU) 12.4 5.5 13.69 16.8 75.2 

204


Table 3: Regression Analyses for relationship between Total suspended solids 

(mg/l) and Turbidity (NTU) 


Equation Number 

Remarks 

Equation 

LT1 TSS=2.1514T +34.254 R 2 = 0.84, Adjusted 

R 2 = 0.79, F =15.75 

LT2 TSS=5.598ln (T) +35.991 R 2 = 0.672, Adjusted 

R 2 = 0.51, F =6.15 

LT3 TSS = 0.4478(T) 2 -1.294 + 38.93 R 2 = 0.9559, Adjusted 

R 2 = 0.912, F =21.68 

LT4 TSS = 36.37T 0.1311 R 2 = 0.697, Adjusted 

R 2 = 0.596, F =6.885 

LT5 TSS = 34.955e 0.0499T R 2 = 0.855, Adjusted R 2 

= 0.807, F =17.68 

B. Medium turbidity water 

Equation Number 

Remarks 

Equation 

MT1 TSS=2.060 T +33.76 R 2 = 0.5775, Adjusted 

R 2 = 0.438, F =4.1 

MT2 TSS=87.173ln (T) -175.36 R 2 = 0.5415, Adjusted 

R 2 = 0.39, F =3.54 

MT3 TSS = 0.2653(T) 2 -26.183 + 448.22 R 2 = 0.9049, Adjusted 

R 2 = 0.8098, F =9.52 

MT4 TSS = 12.845 0.6211 R 2 = 0.7888, Adjusted 

R 2 = 0.719, F =11.2 

MT5 TSS = 57.88e 0.0145T R 2 = 0.8174, Adjusted R 2 

= 0.757, F =13.43 

205


Table 4: Comparison <strong>of</strong> Regression Analyses for relationship between Total suspended solids 

(mg/l) and Turbidity (NTU) 

A 

Low turbidity water 

Regression EquationLT1 EquationLT2 EquationLT3 EquationLT4 

EquationLT5 

Parameters 

R 2 0.84 0.672 0.96 0.697 

0.885 

Adjusted R 2 0.79 0.51 0.912 0.596 

0.807 

F 15.75 6.15 21.68 6.89 

17.68 

Residual variance 3.151 6.459 0.8696 6.0577 

2.2879 

Residual mean 0.00012 -0.000282 0.0009 0.0569 

0.0342 

Residual standard deviation 1.775 2.541 0.9325 2.461 

1.6394 

Bias1. 2*10 -4 -2.2*10 -4 9*10 -4 0.057 

0.0222 

RMSE 1.589 2.273 0.834 2.202 

1.467 

B 


Regression EquationMT1 EquationMT2 EquationMT3 EquationMT4 

EquationMT5 

Parameters 

R 2 0.5775 0.5415 0.9049 0.7888 

0.8174 

Adjusted R 2 0.438 0.39 0.8099 0.719 

0.757 

F 4.10 3.54 9.52 11.2 

13.43 

Residual variance 3192.67 3464.79 718.323 3339.32 

2925.54 

Residual mean 0.0032 0.00033 0.2437 5.9334 

4.495 

Residual standard deviation 56.50 58.86 26.802 57.787 

54.088 

Bias 3.2*10 -3 3.29*10 -4 0.244 5.393 

4.48 

RMSE 50.54 52.65 23.97 51.97 

48.59 

206

parameters 

parameters 


140 

120 

100 

80 

60 

40 

20 

ph 

tds 

temp 

tur 

tss 

salinity 

ec 

colour 

0 

0 5 10 15 20 25<strong>time</strong>(hr) 

30 

Figure 1 Residual values (low turbidity water ) with <strong>time</strong> 

350 

300 

250 

200 

150 

100 

50 

ph 

tds 

temp 

tur 

tss 

salinity 

ec 

colour 

0 

0 5 10 15 20 25 <strong>time</strong> (hr) 30 

Figure 2 Residual values (medium turbidity water ) with <strong>time</strong> 

207

predicted values 

predicted values 


51 

49 

47 

45 

43 

41 

39 

37 

35 

35 37 39 41 43 45 47 49 observed values 51 

Figure 3 Predicted versus observed values for total suspended solids (low turbidity water) 

350 

300 

250 

200 

150 

100 

50 

0 

0 50 100 150 200 250 observed 300 values350 

Figure 4 Predicted versus observed values for total suspended solids (medium turbidity 

water) 

208

195 effect of settling time on turbidity removal using moringa oleifera ...

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