Joseph Tagbo Nwabanne, Christopher Chiedozie Obi

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COAGULATION-FLOCCULATION PERFORMANCE OF SNAIL SHELL BIOMASS IN ABATTOIR WASTEWATER TREATMENT

Joseph Tagbo Nwabanne, Christopher Chiedozie Obi

ABSTRACT

The work involves the treatment of abattoir wastewater (AWW) by coagulation technique using snail shell biomass as coagulant. The raw snail shell (RSS) sample and the processed snail shell coagulant (SSC) were analyzed for the determination of the predominant functional groups and surface morphology using Fourier Transform Infrared (FTIR) and Scanning Electron Microscopy (SEM) analytical techniques, respectively. Reduction in the turbidity of the effluent was used to assess the performance of the treatment process. The effects of the various factors affecting the efficiency of pollutants removal in the coagulation treatment process was studied in a one factor at a time (OFAT) process. A central composite design was used for designing the experiments, building models and determining the optimum conditions. FTIR spectroscopy revealed that the distinctive functional groups of RSS and SSC are amine, amide, hydrocarbons, and ethers. SEM analysis indicated that the processed SSC sample has a well-developed ac-tive site which is not present in the RSS sample. The coagulation-flocculation experiments showed that the removal efficiency of turbidity of the effluent increases with a decrease in solution pH and increase in coagulant dosage, settling time and temperature. A kinetic study revealed that the removal rate of total dissolved and suspended solids (TDSS) in the effluent showed conformity with the pseudo-second-order kinetic model. In the optimization study, an optimum turbidity removal of 94.39 % was obtained at initial pH of 2, coagulant dosage of 1000 mg/l, settling time of 50 minutes and operating temperature of 50oC. A second order polynomial regression equation with R2 value of 0.9985 was obtained in the modeling process. The study has proved that snail shell biomass can successfully be used as coagulant in the coagulation treatment of abattoir wastewater.

Keywords: abattoir wastewater, snail shell, coagulation, flocculation, turbidity, removal efficiency, modeling, optimization.

Received 10 May 2018Accepted 25 January 2019

Journal of Chemical Technology and Metallurgy, 54, 6, 2019, 1177-1188

Department of Chemical Engineering, Faculty of EngineeringNnamdi Azikiwe University, P.M.B. 5025, Awka, NigeriaE-mail: obichristopher27@gmail.com

INTRODUCTION

Wastewater produced by abattoirs is one of the sources that significantly contribute to the pollution of water bodies and the immediate environment. This is be-cause the wastewater is characterized with high organic load as expressed in the reported high chemical oxygen demand (COD) and biochemical oxygen demand (BOD) values [1 - 3]. Abattoir wastewater (AWW) is unpleasant in appearance and offensive in odour. When AWW are discharged on land they constitute land pollution and when discharged in water bodies, this resulted in water pollution which endangers the survival of aquatic live. Discharging untreated AWW will constitute both social

and environment challenges. Therefore, there is need for the treatment of the wastewater before discharging it to the environment.

Among the different techniques employed in the pri-mary treatment of wastewater, coagulation-flocculation technique is preferred due to its capability to successfully reduce the suspended and dissolved particles in waste-waters. Coagulation-flocculation has been defined as the process of adding substance (coagulant) to waste efflu-ent to make the suspended and dissolved particles bind together (coagulation) and subsequently aggregate into visible flocs (flocculation) that settle out of the water [4]. The application of coagulation-flocculation treatment technique in the treatment of various wastewaters has

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been reported by various authors [5 - 7]. The effective-ness of coagulation - flocculation method for treatment of abattoir wastewater using various coagulants has been reported by many researchers. The usage of ferric sulfate with and without coagulant on the coagulation treatment of AWW has been reported by [8]. Similarly, in [9] was investigated the usage of Fe2(SO4)3, Al2(SO4)3 and PAX-18 as coagulants for removal of phosphorus from AWW by coagulation process. The effectiveness of three coagulants, alum, ferric chloride and ferric sulfate on COD removal from AWW has been examined by [10]. Furthermore, the performance of the combination of coagulation and Fenton’s reagent on COD, TOC and TN removal from AWW has been studied and reported by [2].

The conventional coagulants used in coagulation process are inorganic salts such as alum, ferric sulfate, ferric chloride, ferrous sulfate, and sodium aluminate [6, 11 - 13]. When these inorganic coagulants are used the disposal of the resulting sludge becomes a challenge be-cause of the environmental concerns associated with it. It has also been reported that the presence of aluminium in water treated for human consumption has the potential to cause Alzheimer’s disease [4, 14].

Recently, researches in this field are directed towards the development of natural (biodegradable) materials that can successfully replace the chemical coagulants in coagulation treatment of wastewaters. The applica-tion of natural materials in the coagulation treatment of wastewaters has been studied by various authors [15 - 18]. Snail shell has been used as a coagulant in the treatment of quarry effluent [19], pharmaceutical efflu-ent [16, 20], fibre-cement effluent [21] and wastewater from the food industry [22].

In Nigeria snails are rampant in the environment. They are produced by animal farmers but the quantity of snails that naturally grow in the surroundings is far higher than those produced by snail farmers. In other words, snails are everywhere in Nigeria. Snails are con-sidered a cheap source of animal protein by the few who consume it. Presently in Nigeria, the only useful part of snail is the edible part. When the edible part is removed, the shells are disposed as wastes in the environment. It is common to find snail shells everywhere in an environ-ment where it is consumed. Therefore, there is need to harness the usefulness of this abundant waste material by using it as a coagulant in wastewater treatment.

The present study is aimed at investigating the ef-

fectiveness of snail shell biomass in the coagulation treatment of AWW. The modeling and optimization of the process were also studied using the Response Surface Methodology (RSM).

EXPERIMENTAL

Materials and MethodsEffluent Collection and Analysis

The sample of AWW used in these experiments was collected from an abattoir at Obosi, Anambra State, Nigeria. The effluent was preserved and analyzed for various wastewater characteristics before and after treat-ment by standard methods [23].

Processing of Snail Shell (SS) into a CoagulantThe snail shells were collected from the waste bin

of a local market where snails are sold. The shells were washed with water and sun dried for five days. It was first crushed using a pestle and mortar. The crushed sample was further air dried for three days to remove possible remaining moisture. The sample was then ground into powder using a mechanical grinding machine and sieved with a laboratory sieve of 0.05 mm size. The powdered snail shell sample was then processed into a coagulant, Snail Shell Coagulant (SSC), using the method described in [24, 25].

Coagulation-Flocculation Experiment (Jar Test)The coagulation-flocculation experiments were car-

ried out using jar test apparatus. The operating variables investigated were: pH, coagulant dosage, settling time and temperature. The pH was controlled by adding either 1 M HCl or 1M NaOH.

The AWW sample used for the experiments was well agitated in order to obtain a homogeneous mixture. It was then fractionated into beakers containing 250 ml of the wastewater solution each. The desired amount of coagulant was added to each beaker containing the wastewater. Thereafter, the beakers were agitated at 250 rpm for 2 minutes and 30 rpm for 20 minutes. The effect of pH was studied at pH range 2 - 10 at varying coagulant dosages in the range 200 mg L-1 - 2000 mg L-1 at constant settling time and temperature. Thereafter, the effect of settling time was studied in the range (5 - 60 minutes) at varying coagulant dosages, constant temperature and at optimum pH. The effect of temperature was then studied

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in the range (30 - 60oC) at varying settling time, optimum pH and optimum coagulant dosage. At the end of each jar test experiment, the sample was allowed to settle at a specified time, thereafter, a portion of it was collected at 2 cm depth beneath the surface of the water for analysis.

The coagulation efficiency of the coagulants was investigated in terms of percentage turbidity removal using equation 1.

% Removal = 0

0

100T TT−

× (1)

where To is the turbidity of the raw influent and T is the turbidity of the effluent after treatment.

Design of Experiment for the Statistical Modeling and Optimization Study

The modeling and optimization studies were per-formed using the Central Composite Design (CCD). Four important factors which are pH, coagulant dosage, settling time and temperature were used as independent variables. The percentage removal of turbidity was the response variable (Table 1). This was done to determine the best conditions for optimum removal of turbidity from abattoir wastewater and to develop a model that best describes the response. A set of 30 experiments were performed. The distance of the star-like point α used was 2. The factor ranges were selected based on the results of the ‘one factor at a time’ studies. The numerical method of the Design Expert version 10.1 by State Ease U.S.A was used.

RESULTS AND DISCUSSIONCharacterization of AWW before and after coagulation

The characteristics of the abattoir wastewater before and after coagulation process are presented in Table 2. The result showed that the values of the pollution factors measured such as COD, BOD, turbidity, and TSS before

the treatment were high but these values were reduced drastically after the coagulation treatment, affirming the effectiveness of the treatment process. The values of pH, COD, BOD5, TS, and TSS recorded for the raw sample are compared with the findings of other authors as presented in Table 3.

FTIR studies of RSS and SSCThe results of FTIR studies for the Raw Snail shell

(RSS) and the processed SSC are presented in Figs. 1 and 2, respectively. The results were analyzed based on the standard peaks as presented by [30] for the func-tional groups. It can be seen that RSS sample has more distinct peaks than SSC sample, an indication that some

Table 1. Factor levels of independent variables.

Independent -α Low Medium High +α

Factors level (-)

Level (0)

level (+)

pH 1 2 3 4 5 Coagulation dosage, mg L-1 750 1000 1250 1500 1750 Time, min 35 40 45 50 55 Temperature, OC 35 40 45 50 55

Wastewater Before After characteristics coagulation coagulation pH 6.80 6.02 COD, mg L-1 1814 145 BOD5, mg L-1 920 58 TS, mg L-1 2660 399 Turbidity, NTU 330 22 Total hardness, mg L- 1 60.31 58.6 Sulphate, mg L-1 13.85 1.84 TSS, mg L-1 1080 70 Lead, mg L-1 Nil Nil Iron, mg L-1 2.09 0.16 Potassium, mg L-1 0.10 0.08 Magnesium, mg L-1 57 54.5 DO, mg L-1 2.38 3.18

Note: TSS - Total suspened solids, TS - Total solids,COD - Chemical Oxygen Demand, BOD5 - Biochemi-cal oxygen demand (5 days) at 20oC.

Table 2. Characteristics of AWW before and after coagula-tion process.

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functional groups were eliminated in the course of the processing of the shell into a coagulant.

Fig. 1 revealed that distinctive absorption bands ap-peared at 3280 cm-1, 2926 cm-1, 1744 cm-1, 1636 cm-1, 1148 cm-1, 995 cm-1 and 780 cm-1 for the RSS sample. The band at 3280 cm-1 is associated with the amine group with N-H stretch. The presence of hydrocarbon with C-H stretch

was exhibited by the presence of the band at 2926 cm-1. The peaks at 1744 cm-1, 1636 cm-1, 1148 cm-1 depict the ester, amide, ether groups, respectively, while the peaks at 995 cm-1 and 780 cm-1 show the presence of alkene and aromatic compounds. Fig. 2 showed distinct peaks at 3280 cm-1, 2922 cm-1, 1513 cm-1, 1032 cm-1and 898 cm-1, which are characteristic of amines (N-H stretch), hydro-

Table 3. AWW characteristics from various authors for some key wastewater parameters.

Parameter

Value/Range of values

[2] [26] [27] [28] [29] Present Study

pH 6 -10 7.1 7.2 6.78 4.9 - 8.1 6.80

COD, mg L-1 1600-8000 1806 1820 2240 1250 -15900 1814

BOD5, mg L-1

TSS, mg L-1

1200-5000

100-2000

940

NS*

900

430

NS

1020

610 - 4635

300 - 2800

920

1080

* NS = Not stated, mg L-1

Fig. 2. FTIR result for SSC sample.

Fig. 1. FTIR result for RSS sample.

Sample ID:Chinedu 9 Method Name:Transmittance MethodSample Scans:16 User:AdminBackground Scans:16 Date/Time:2016-07-29T09:03:17.624+01:00Resolution:8 Range:4000 - 650System Status:Good Apodization:Happ-GenzelFile Location:C:\Program Files\Agilent\MicroLab PC\Results\Chinedu 9_2016-07-29T09-03-17.a2r

7/29/2016 9:22:28 AM page 1 of 1

Sample ID:Chinedu10 Method Name:Transmittance MethodSample Scans:16 User:AdminBackground Scans:16 Date/Time:2016-07-29T09:04:41.1+01:00Resolution:8 Range:4000 - 650System Status:Good Apodization:Happ-GenzelFile Location:C:\Program Files\Agilent\MicroLab PC\Results\Chinedu 10_2016-07-29T09-04-41.a2r

7/29/2016 9:22:44 AM page 1 of 1

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carbons (C-H stretch), amide, alkyl halide and aromatic compounds, respectively for the SSC sample. Alkene and ester functional groups were among the functional groups present in RSS sample but absent in the SSC sample.

SEM studies of RSS and SSCScanning electron microscopy of RSS and SSC are

shown in Figs. 3 and 4, respectively. A comparison of the results of the two samples shows that the morphol-ogy of RSS is coarser. The morphology of SSC sample appears more pronounced and refined. This is an indi-cation of the surface modifications that occurred in the course of processing the shell into a coagulant. This

can be attributed to the removal of constituent minerals and other materials that contaminated the shell. Fig. 4 shows a well-developed active site, typical of a good coagulating agent for SSC sample.

Effects of the Operating Parameters on the Removal EfficiencyEffect of pH and coagulant dosage

The effect of pH on the removal efficiency at varying coagulant dosages is presented in Fig. 5. It can be seen that the removal efficiency increased by decreasing the pH. This depicts better performance of the treatment process at an acidic pH medium than in an alkaline pH medium. Acidic pH medium represents the presence of higher positive ions in the solution which enhances the charge neutralization capability of the coagulant. In contrast, in alkaline pH medium, more of negative ions are present in the solution, reducing the positivity of the surface electrical potential. This will result in weaker charge neutralization. In a related work [8] an optimum pH was also reported to be in the acidic pH medium when aluminum sulphate coagulant was used.

On the other hand, the effect of coagulant dosage on the removal efficiency was studied at coagulant

Fig. 4. SEM result of SSC sample at 1500x magnification

Fig. 3. SEM result of RSS sample at 1500x magnification.

Fig. 5. Effect of pH on the removal efficiency at varying coagulant dosage.

Fig. 6. Effect of settling time on the removal efficiency at varying coagulant dosage.

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dosage range of 200 - 2000 mg L-1. It can be seen (Fig. 5) that the increase in coagulant dosage up to 1500 mg L-1 resulted in an increase in removal efficiency, but a further increase to 2000 mg L-1 brought about decrease in the removal efficiency. This can be attributed to an effect of overdosing of the coagulants. 1500 mg L-1 coagulant dosage can be considered to be the point of equilibrium between the surface charge of the pollut-ants in the wastewater and the opposite charge of the coagulant. Beyond this equilibrium concentration, a charge imbalance is created in the wastewater solution and will result in the re-stabilization of the colloidal particles in the wastewater.

Effect of settling time Time for the settling of the coagulated flocs, termed

‘settling time’, was analyzed at the optimum pH and the results are presented in Fig. 6. Turbidity removal effi-ciency was found to increase with settling time for all the coagulant dosage values considered. More settling time represents more privilege for settleable particles with low settling speeds to settle. It can be observed that the first 30 minutes represents the highest degree of flocculation. This is in agreement with Smoluchowski’s theory of rapid coagulation [31].

Effect of TemperatureThe results from the investigation of the effect of

solution temperature in the range of 30oC to 60oC on the removal efficiency are presented in Fig. 7. They re-vealed that the increase in temperature resulted in higher removal efficiency. The temperature of 60oC gave the best result. This is because, at an increased temperature, the molecules of the wastewater solution gain more ki-netic energy. This will result in an increase in the rate at

which collision between the colloidal particles and the coagulating agent occurs. These will positively impact on the coagulation reaction rate. Also, increasing the solution temperature will enhance the settling kinetics of the colloidal particles.

Pseudo-second order coagulation kineticsThe second order reaction kinetics for the removal

of particles from wastewater which results in turbidity depletion can generally be expressed as Eq. 2. Upon separation and integration of eq. 2, eq. 3 was obtained according to [18, 21, 32].

2dC KCdt−

= (2)

0

1 1 KtC C= + (3)

The pseudo-second order reaction kinetics was evaluated using eq. 3. A plot of 1/C as a function of time gave a straight line graph with slope K, and intercept 1/Co as shown in Fig. 8, where K is the reaction rate constant, Co and C are initial concentration and concentration of total dissolved and suspended solids (TDSS) (mg L-1) at any time t, respectively.

The kinetics parameters obtained are presented in Table 4. It can be seen that reaction rate constant K in-creased with increase in coagulant dosage. A maximum K value was obtained at a coagulant dosage of 1500 mg L-1, the optimum coagulant dosage. At 1500 mg L-1 coagulant dosage, the highest aggregation rate was obtained, while at 200 mg L-1 the lowest aggregation rate was obtained as represented by the values of the rate constant.

The fitness of the experimental data to the kinetic

Fig. 7. Effect of solution temperature on removal efficiency.Fig. 8. Second order kinetics plots for SSC coagulation treatment of AWW.

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Table 4. Kinetics parameters for second order reaction kinetics of SSC coagulation.

Parameter 200mg l-1 400mgl-1 600mgl-1 800mgl-1 1000mgl-1 1500mgl-1 2000mgl-1

K2, mg/m 1.10E-05 1.60E-05 1.70E-05 2.20E-05 2.20E-05 2.80E-05 2.70E-05

Co , mg/l 2469.136 2610.966 2610.966 2770.083 2564.103 2645.503 2673.797

R2 0.9817 0.9892 0.9896 0.9936 0.9925 0.9958 0.9935

Rate Equation (mg/lmin)

1.10E-05C2

1.60E-05C2

1.70E-05C2

2.20E-05C2

2.20E-05C2

2.80E-05C2

-2.70E-05C2

model was assessed using linear regression coefficient R2. The R2 values > 0.98 suggest that the coagulation treatment of AWW using SSC followed the pseudo-second order kinetic model.

Modeling and Optimization StudyCCD was used to examine the combined effects of

the process variables on turbidity removal efficiency. The experimental and predicted results of the combined effect of the four process variables on the response (% Removal) are presented in Table 5.

Table 6 presents the result of the Analysis of Variance (ANOVA). ANOVA is a statistical tool used to check the significance of the fitness of a selected model as well as the significance of individual terms and their interaction on the dependent variable. The P-value (Probability of error value) is used to check the significance of each regression coefficient and the interactions between the test variables [33]. The model obtained for the response is represented by Eq. 4.Removal (%) = 77.39–14.36A+0.71B+2.86C+5.17D-0.11AB+0.38AC+1.44AD–0.13BC–0.52BD-1.21CD–3.04A2-0.026B2+0.29C2+0.60D2 (4)

P-values less than 0.05 indicate that model terms are significant. In this case, A, B, C, D, AD, BD, CD, A2, D2 are significant model terms (Table 6). Therefore, eliminating the insignificant terms, the final model for abattoir wastewater treatment using SSC is presented as Eq. 5.Removal (%) = 77.39 – 14.36A + 0.71B + 2.86C + 5.17D + 1.44AD – 0.52BD --1.21CD – 3.04A2 + 0.60D2 (5)

Test of Adequacy of the ModelThe model summary statistics (Table 7) indicates

that a quadratic model fitted the ANOVA analysis and

hence it was suggested. The coefficient of regression R2 was used to validate the fitness of the chosen model. From Table 7, it can be seen that R2 for the quadratic model has a high value of 0.9985 showing that 99.85 % of the variability in the response can be explained by the model.

Predicted versus Actual ResponseThe predicted versus actual plot (Fig. 9) shows the

correlation between the actual experimental response and the predicted response. It can be observed in the plot that the points were linearly distributed to the straight line of the plot, this depicts a close correlation between the experimental response and the predicted response. The plot has also shown that the selected model is ad-equate in predicting the response variables.

3D Response Surface Plots for the Treatment ProcessThe 3-D response surface plots are presented in

Figs. 10 - 14. The response surface curves were plotted

Fig. 9. Predicted versus Actual response plot.

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Std A:pH B:Coag dosage C:Settling time D:Temp Actual Predicted Value Value 1 2 1000 40 40 80.25 80.69 2 4 1000 40 40 48.13 48.55 3 2 1500 40 40 83.82 83.62 4 4 1500 40 40 50.77 51.03 5 2 1000 50 40 88.05 88.32 6 4 1000 50 40 56.98 57.70 7 2 1500 50 40 90.36 90.75 8 4 1500 50 40 59.09 59.68 9 2 1000 40 50 91.66 91.58 10 4 1000 40 50 64.70 65.21 11 2 1500 40 50 92.28 92.46 12 4 1500 40 50 65.39 65.63 13 2 1000 50 50 93.75 94.39 14 4 1000 50 50 68.82 69.53 15 2 1500 50 50 94.66 94.75 16 4 1500 50 50 68.98 69.44 17 1 1250 45 45 94.11 93.95 18 5 1250 45 45 37.75 36.50 19 3 750 45 45 76.97 75.86 20 3 1750 45 45 79.01 78.71 21 3 1250 35 45 73.00 72.82 22 3 1250 55 45 85.49 84.26 23 3 1250 45 35 70.18 69.44 24 3 1250 45 55 90.77 90.10 25 3 1250 45 45 78.05 77.39 26 3 1250 45 45 77.12 77.39 27 3 1250 45 45 77.50 77.39 28 3 1250 45 45 77.45 77.39 29 3 1250 45 45 76.98 77.39 30 3 1250 45 45 77.25 77.39

Table 5. Experimental and Predicted response of the four process variables in terms of real values.

to understand the interaction of the test variables and to determine the optimum level of each variable for maximum response. Fig. 10 gives the interactive effect of coagulant dosage and temperature. It can be deduced that a significant decrease in pH and a slight increase in coagulant dosage increased the removal efficiency. Simi-

lar shapes were obtained in Figs. 11 and 12 for settling time versus pH and temperature versus pH, respectively. Fig. 11 shows that removal efficiency increased with an increase in settling time and a decrease in pH, while Fig. 12 revealed that increase in both pH and temperature resulted in an increase in removal efficiency. The interac-

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Source Squares df Sum of Square F Value

p-value Prob > F

Model 6157.74 14 439.84 719.77 < 0.0001 significant A-pH 4950.47 1 4950.47 8101.14 < 0.0001 B-Coag. Dosage 12.17 1 12.17 19.91 0.0005 C-Settling time 196.48 1 196.48 321.53 < 0.0001 D-Temperature 640.36 1 640.36 1047.91 < 0.0001 AB 0.20 1 0.20 0.34 0.5713 AC 2.30 1 2.30 3.77 0.0713 AD 33.21 1 33.21 54.34 < 0.0001 BC 0.26 1 0.26 0.42 0.5260 BD 4.25 1 4.25 6.96 0.0186 CD 23.35 1 23.35 38.22 < 0.0001 A2 253.68 1 253.68 415.12 < 0.0001 B2 0.019 1 0.019 0.031 0.8633 C2 2.27 1 2.27 3.71 0.0732 D2 9.71 1 9.71 15.90 0.0012 Residual 9.17 15 0.61 Lack of Fit 8.45 10 0.85 5.94 0.0314 Pure Error 0.71 5 0.14 Cor Total 6166.90 29

Table 6. ANOVA for Response Surface Quadratic model.

Fig. 10. 3D surface plot of coagulant dosage versus pH. Fig. 11. 3D surface plot of settling time versus pH.

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tion between temperature and coagulant dosage in Fig. 13 showed that at a fairly constant coagulant dosage the removal efficiency increased slightly with temperature. The interaction between settling time and temperature in Fig. 14 indicated a poor interactive influence on the yield. This is because a combination of variables like time, temperature, and pH without dosing in a coagulant is not expected to produce any reasonable yield in a coagulation process.

Validation of Optimization Result The Optimal condition for optimum performance

of the treatment process was determined and validated experimentally. A combination of the experimental and predicted optimum efficiencies of the coagulation treatment of AWW using SSC is presented in Table 8. The experimental efficiency obtained is close to the predicted value at the optimal condition. This confirms the effectiveness of the developed model.

Fig. 12. 3D surface plot of temperature versus pH.

Fig. 13. 3D surface plot of temperature versus coagulant dosage.

Fig. 14. 3D surface plot of temperature versus settling time.

Std. Adjusted Predicted

Source Dev. R-Squared R-Squared R-Squared PRESS Linear 3.83 0.9404 0.9309 0.9084 564.73 2FI 4.00 0.9507 0.9248 0.9174 509.11 Quadratic 0.78 0.9985 0.9971 0.9919 49.72 Suggested Cubic 0.98 0.9989 0.9954 0.8579 876.44 Aliased

Table 7. Model Summary Statistics.

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CONCLUSIONS

The effectiveness of snail shell coagulant in the coagulation treatment of abattoir wastewater was suc-cessfully examined in this work. The results presented showed that the performance of coagulation treatment of abattoir wastewater using snail shell coagulant is de-pendent on initial solution pH, coagulant dosage, settling time and operating temperature. The reaction kinetics study showed that the reactions conformed to a pseudo second order kinetic model.

Process modeling and optimization was carried out using central composite design (CCD). The study has shown that a removal efficiency of 94.39 % can be achieved at the following optimum conditions: pH of 2; coagulant dosage of 1000 mg L-1; settling time of 50 min-utes and operating temperature of 50oC. The findings of this work has shown that snail shell that is considered as a domestic waste in this part of the world can successfully be used as a coagulant in the primary decontamination of abattoir wastewater by coagulation technique.

AcknowledgementsWe wish to acknowledge in appreciation, the De-

partment of Chemical Engineering, Nnamdi Azikiwe University Awka, Nigeria, for making their laboratory facilities available for the conduct of the experiments. Chinedu Umembamalu, the laboratory technologist of the Department of Chemical Engineering, Nnamdi Azikiwe University Awka, is specially acknowledged for the technical assistance offered during the labora-tory works.

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Table 8. Replicate experiments at the optimum conditions for SSC coagulation process.

pH Coag. Dosage (mg L-1)

Settling time (Min)

Temp. (oC)

Predicted Removal

Eff.(%)

Exp. Removal

Eff. (%)

2 1000 50 50 94.39 93.33

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