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EFFECTIVENESS OF SNAIL SHELL AS AN ADSORBENT FOR THE TREATMENT OF WASTE WATER

ADIOTOMRE, K.O.

Department of Chemical Engineering, Delta State University, Abraka, Nigeria

E-mail: oadiosking@yahoo.com ABSTRACT The Effectiveness of snail shell as an adsorbent for the treatment of waste water was studied. Carbonized carbon was produced from snail shell. This project reports on the characterization of carbonized carbon produced from snail shell. After the snail was carefully removed from the shell, it was washed and dried and was then carbonized at various temperatures with a range of 100

0C starting from 300

0C to 1000

0C.

The parameters used for the characterization of the carbonized snail shell adsorbent are pH, % moisture content, % carbon yield, Iodine values, % ash content, bulk density, porosity, bulk volume, mean particle size and adsorptive capacity. The results of the experiment that was performed on the carbon adsorbent obtained from the snail shell showed that the best form that can be used as an adsorbent was obtained at a temperature of 800

0C because it possess the highest porosity value. Porosity determines how effective

liquids can be adsorbed by the adsorbent. The result showed that the treatment of waste water with snail shell activated carbon improved for all the parameters tested and varied with time as compared with that of the raw water before treatment. Keyword: Snail shell, activating agent, characterization, waste water INTRODUCTION Carbon is an industrial adsorbent both in the carbonized and the activated form. Snail shell is one of the raw materials which carbon can be produced from. Carbon gotten from snail shell is cheap to obtain due to the ease of availability in this part of the country and also since the shell is a waste. Several organic materials have been used for the production of carbon, some of which include coconut shell, rice husk, banana peels, orange peels etc. Out of all this materials that have been mentioned snail shell and coconut shell possess the advantage of withstanding a very high temperature up to like 1000

0C

without it been converted totally to ash. Carbon Adsorbent has a lot of importance in our day to day life, even in the industries such as the sugar and starch industry it is used to remove the colored matter in the syrup. In water purifications it is also used as a decolorizer, which also removes odor and taste from the underground water being treated. It is used for treating industrial waste effluent both for primary and tertiary treatment. The importance of carbon cannot be over emphasized. The purpose of this present study is to investigate the adsorptive properties of carbon gotten from snail shell and to provide the favourable conditions that will give the optimal performance.

Objectives of the Study i. Production of low cost adsorbent (carbon) from snail shell ii. Determination of the optimum temperature for carbonization of the snail shell. iii. Characterization of the carbonized snail shell to determine such parameters as pH, % moisture content, % carbon yield. Iodine values, % ash content, bulk density, porosity, bulk volume, mean particle size and adsorptive capacity

Relevance of Study

International Journal of Innovative Environmental Studies Research 3(3):1-12, July-Sept. 2015

© SEAHI PUBLICATIONS, 2015 www.seahipaj.org ISSN: 2354-2918

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The shell is of great economic importance due to the carbon adsorbent which can be produced from it. Presently, organic contaminants removal from industrial waste makes use of expensive adsorbents. The use of modified snail shell as an adsorbent will to a large extent reduce cost of treatment. Activation of carbonized snail shell is a method used to modify the carbon adsorbent. It helps to displace the pore making it more porous so that adsorbate can adhere to it more easily. A well prepared adsorbent increases the effectiveness and quality of adsorption.

MATERIALS AND METHOD

Preparation of sample Some quantity of snail was bought from Mcciver market in Warri. After removing the snail, the shells were washed intensely with detergent and distilled water and sun dried at room temperature for one week, the dried shells were then broken into smaller size. Carbonization: The prepared sample was placed in a steel crucible furnace which was set at a temperature of 300

0C and

left for one hour after which the carbonized sample at this temperature was retrieved from the furnace. Same was repeated for temperatures up to 1000

0C at an interval of 100

0C

Characterization The carbon samples at each of the various temperatures of carbonization i.e. 300

0C to 900

0C at an interval

of 1000C were characterized based on the following parameters:

Bulk Volume

5g of the carbonized sample was weighed and transferred into a clean measuring cylinder. The volume is then read and recorded against the carbonization temperature This is the bulk volume at this temperature. Bulk Density The bulk volume obtain above was used to divide the mass of carbonized sample i.e. 5g. This gives the bulk density which was recorded against the carbonization temperature. Bulk density = mass of carbonized sample/bulk volume pH 3g of samples was weighed and added to 20ml of distilled water and left for 30 minutes. The pH was taken The pH meter was calibrated and the pH of the samples was read.

Porosity

10g of sample was weighed using an electron weighing balance into a graduated cylinder and was then tapped until there was no change in volume.

The weighed sample in the measuring cylinder was then immersed into water in a beaker and brought to boil.

After the pore has been displaced, the sample was superficially dried and weighed again. The weight divided by the density of water gives the pore volume, porosity was therefore

calculated from pore volume by dividing the pore volume of the particle with the total volume of the particle.

Porosity (φ) = (Ws – Wd)/ ( vs Vp ) Wd = Weight of dried sample Ws = Weight of superficially dried wet sample

vs = density of water Vp = total volume of particle Ash Content Determination Two grams of dry sample was placed into a porcelain crucible and transferred into a preheat muffle furnace set at the various temperature ranging from 300 to 900 degree Celsius at an interval of 100

0C. The

furnace was left for one hour after which the crucible and content was reweighted and the weight noted. If Wo is the dry weight of the sample and Wash is the constant weight after drying, The percent ash content (dry basis) is given by

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Determination of Moisture Content 5g of the carbonized snail shell was weighed and dried in a drier continuously. The dried sample was constantly reweighed at 10min Interval until a constant weight was obtained. The ratio of the change in weight to the original weight expressed in percentage Gives the moisture content given as

Determination of Carbon Yield In determining carbon yield, the dried weight Wo of each carbon sample was determined and the carbon yield Ych was determined by

Where: Wch is the weight of carbon retrieved from the furnace Wo is the dried weight of the carbon sample.

Iodine value (i) Preparation of 0.05M of Iodine

To prepare 0.05M of Iodine, 20g of iodide free potassium iodide was dissolved in 40ml of water in a glass stopper 1 liter flask.12.7g of iodide was weighed out on watch glass using a weighing balance and it was then transferred by means of a small glass funnel into the concentrated potassium iodide solution. A glass stopper was inserted into the flask and it was shaken in the cold until all the iodide dissolves. The solution is allowed to attain room temperature and the mark is made up with distilled water. (ii) Preparation 0.1M of Sodium Thiosulphate

25g of sodium thiosulphate (Na2SO3.5H2O) crystals was weighed out dissolved in boiled out distilled water and was made up to one liters in a volumetric flask with boiled out distilled water. (iii) Determination of Iodine Value 3g of the sample was transferred into a conical flask and 25cm

3 of 0.05M iodide solution was added to

each of the flask. The flask were agitated for 30 minutes, after which the sample (carbonized snail shell) free aliquot were decanted into a beaker, 20ml of the aliquot was pipetted into a conical flask for titration.0.1M sodium thiosulphate solution was titrated against the 20ml aliquot of each

at this point 5cm3 of starch indicator was added to the analyze

and the titration was continued until a drop of the thiosulphate made the dark blue coloration colorless. The quantity of the thiosulphate needed to titrate 20ml of the blank iodide solution was also determined the iodide value was calculated as follows

Iodine value=( – )

X= Volume of thiosulphate used for sample free aliquot Y= Volume of thiosulphate used for blank W= Weight of sample V= Volume of iodine solution used M=molarity of the iodine solution used

Mean Particle Size The weight average mean particle size was determined as follows: 5g of the carbonized snail shell at the different temperatures was weighed out with an electric weighing device. The weighed sample was placed in the standard Taylor screen which was arranged according to the sizes of the screens. The amount retained on each screen was noted and weighed and this was done for

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each screen I the set up until the final screen. The total weight was cumulated and was used to calculate the weight average mean particle size.

∑

Where Dpi =the size of the particle retained on the screen Xi =the weight fraction of the particles retained on the screen

Analysis of Waste water The waste water was analyzed before and after treatment with chemically activated sample produced. The idea was to make comparison between the two samples. These analyses involve the change in the physiochemical parameter of the waste water.

RESULTS AND DISCUSSION

Characterization of the carbonized snail shell adsorbent at various temperatures

Variation of temperature with amount of Iodine adsorbed From the result in Table 1 and Fig .1 it is seen that the amount of iodine adsorbed (iodine values) decreased with increase in temperature values this is due to the fact that at 300

0C much carbon adsorbent

is formed which provides the available site for the adherence of the iodine. When the temperature of carbonization rises the carbon production drops due to the formation of ash as bye product.

Table 1: Amount of iodine adsorbed at various temperature

Figure 1: Graph of Amount of Iodine adsorbed (g/g) against Temperature (0C)

Variation of carbonization temperature with ash produced From the table and the graph, it is clearly seen that as the carbonization temperature of the snail shell was increased, the ash content also increased; this was due to the fact that amorphous carbon was unstable at

Temperature (

0c)

Amount of iodine adsorbed (g/g)

300 1.31

400 1.30

500 1.32 600 1.31

700 1.33

800 1.35

900 0.92

1000 0.86

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 200 400 600 800 1000 1200

Am

ou

nt

of

Iod

ine

ad

sorb

ed

(g

/g)

Temperature OC

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high temperature. And when it is formed in the carbonization process, ash is also formed as bye product. Thus an increase in the carbonization temperature increased the ash content.

Table 2: % Ash Content at various carbonization temperatures Temperature (

0c) % Ash Content

300 6.8

400 7.7 500 9.0

600 10.0 700 11.0

800 16.0 900 26.0

1000 31.0

Figure 2: Graph of % Ash content against Temperature (0C)

Variation of carbonization temperature with porosity The porosity of the carbon adsorbent obtained increased gradually with increase in carbonization temperature. This is due to the fact that as the temperature increased the pore volume of the carbon adsorbent formed opens up. At 800

0C, the curve showed a sharp point which indicated the optimum

obtainable value of the porosity. Since porosity is responsible for the quantity of materials adsorbed it can be said that 800

0C is the best temperature of carbonization.

0

5

10

15

20

25

30

35

0 200 400 600 800 1000 1200

% A

sh c

on

ten

t

Temperature OC

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Table 3: Porosity of adsorbent at different carbonization temperature

Temperature (0c) Porosity

300 0.09 400 0.07

500 0.08

600 0.13 700 0.28

800 0.44 900 0.33

1000 0.31

Figure 3: Graph of Porosity against Carbonization Temperature (0C)

Variation of Carbonization Temperature with Carbon Yield The percentage carbon yield reduces as the carbonization temperature increases this is as a result of the increase in the bye product (ash) formed as the temperature of carbonization increases. The active carbon formed is what is responsible for adsorption. the decrease in the carbon yield result from the fact that amorphous carbon does not withstand too much a temperature instead it disintegrate into ash the bye product which does not possess any adsorption property (Table 4 and Fig. 4).

Table 4: % Carbon yield at different carbonization temperature

Temperature (0c) % Carbon Yield

300 93.0

400 92.3 500 91.0

600 90.0 700 89.0

800 84.0

900 74.0

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 200 400 600 800 1000 1200

Po

rosi

ty

Temperature OC

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Figure: 4 Graph of % Carbon yield against Temperature (

0C)

Variation of Carbonization Temperature with Moisture content Moisture is the amount of moisture i.e. water content of the carbon produced. From the obtained result (Table 5 and Fig 5) it is seen that the moisture content dropped with an increase in the carbonization temperature. This could be as a result of an increase in the temperature of the environment which could cause the water contained in the environment to evaporate. This could also cause an escape of carbon produced.

Table 5: % Moisture content at different carbonization temperature Temperature (

0c) % Moisture Content

300 0.006 400 0.002

500 0.001 600 0.000

700 0.000

800 0.000 900 0.000

1000 0.000

Figure 5: Graph of moisture content (%) against Temperature (

0C)

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700 800 900 1000

% C

arb

on

yie

ld

Temperature OC

-0.001

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0 200 400 600 800 1000 1200

% M

ois

ture

co

nte

nt

Temperature OC

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Variation of Carbonization temperature with pH The pH result obtained above showed that with increase in carbonization temperature pH also increased as shown in Table 6 and Fig 6. This is as a result of modification caused on the carbon due to temperature rise. The capacity of an adsorbent to adsorb is less when the adsorbent is acidic this is a clear indication as to why the pH is slightly alkaline (Petterson 2002).

Table 6: pH value of adsorbent at different carbonization temperature

Temperature (0c) pH

300 8.0

400 8.3 500 8.5

600 8.5 700 8.6

800 8.5 900 8.6

1000 8.5

Figure 6: Graph of pH against carbonization temperature (

0C)

Variation of Carbonization temperature with bulk density The bulk volume is almost constant as the temperature of carbonization increases (Table 7 and Fig 7. This is due to the homogeneity of the size of the snail shell that was carbonized. It shows that increasing carbonization temperature of the snail shell has no effect on the bulk physical property of the adsorbent (2006 Cameron Carbon Incorporated www.cameroncarbon.com).

Table 7: Bulk density at different carbonization temperature

Temperature (0C) Bulk Density (kg/m

3)

300 1.3500

400 1.3500 500 1.4000

600 1.3890 700 1.3500

800 1.3890

900 1.3500 1000 1.3160

7.9

8

8.1

8.2

8.3

8.4

8.5

8.6

8.7

0 200 400 600 800 1000 1200

pH

Temperature OC

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Variation of carbonization temperature with Bulk volume /specific volume

The specific volume which is the volume per mass of the carbon adsorbent produced is derived from the bulk volume which is the volume of a known mass of the adsorbent. It is a bulk property of the adsorbent. The result in table 8 and fig.8 showed the specific volume to be constant with increased carbonization temperature. The significance of the bulk volume is that it is to a large extent an indication of the average particle size of the adsorbent.

Table 8: Bulk volume at different carbonization temperature

Temperature (0C) Bulk Volume (m

3/kg)

300 0.74

400 0.74 500 0.71

600 0.72 700 0.74

800 0.72

900 0.74 1000 0.76

Variation of carbonization temperature with the mean particle size of adsorbent The mean particle size which is another bulk property of the adsorbent was between 1.1165 to 1.196 which approximate to 1mm was constant as a result of the bulk reduction of the snail shell in a rolling mill. The mean particle size plays a very important role in that the size is responsible for how large the surface area of the adsorbent is. The larger the size of the particles the smaller the surface area available for materials to be adsorbed. In other words the finer the particles the larger the area available for adsorption. Since reaction rate increases with surface area and chemisorption is a chemical type of adsorption process it is seen that the optimum is 800

0C since it has the smallest particle size and largest

surface area.

Table 9: Mean particle size at different carbonization temperature

In the carbonization of the snail shell, grounded unmodified snail shell was burnt in a furnace for 60minutes at 300°C, 400°C,500°C, 600°C, 700°C, 800°C,900

0C and 1000

0C. 800°C was taken as the

optimum temperature for carbonization because it possess the highest porosity value, Adsorbs the highest amount of iodine and possess the lowest mean particle size. The porosity is responsible for how a compound can adhere to the carbon which is seen on the iodine value of the adsorbent, at 800°C it was 1.35g/g of iodine that was adsorbed by the carbonized snail shell. The mean particle size 1.1128mm was smallest at 800°C which is an indication that at that carbonization temperature the adsorbent possess the largest surface area. Since larger surface area is provided by smaller particle sizes The increase in ash content as temperature rises is as a result of the formation of lesser amount of carbon as temperature increases. The bye product (ash) to an extent reduces the adsorption capacity after the

Temperature (0C) Mean particle size (mm)

300 1.1365

400 1.1165 500 1.1180

600 1.1261 700 1.1170

800 1.1128

900 1.1242

1000 1.1958

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optimum temperature is attained above that temperature the micro pore structure collapses which leads to decrease in the amount of iodine adsorbed

Water Analysis Table 10 (Analysis of water treated with adsorbent) represents data showing how efficient the adsorbent

is in treating wastewater. As already pointed out under pH analysis discussion above, the pH is seen to

increase with increase in carbonization temperature. But at an optimum temperature (temperature

producing a more active carbon), the pH at this temperature indicates an adsorbent produced having the

optimum capacity to adsorb or to remove organic contaminants from waste water thus increasing the

clarity of the water from a brownish color. The Biological Oxygen Demand (BOD) which tells how much

oxygen is consumed by bacterial in the decomposition of organic material decreased from 48mg/l to

22mg/l after treatment with the adsorbent. Treatment of the waste water with the adsorbent also had such

effect on the Chemical Oxygen Demand (COD) which is a measure of the organic matter content of a

sample that is susceptible to oxidation by a strong chemical oxidant. The analysis also showed a decrease

in the conductivity from 342µs/cm to 164µs/cm. And since conductivity is a measure of how well water

can pass an electrical current and also an indirect measure of the presence of inorganic dissolved solids

such as chloride, magnesium etc. A high concentration of dissolved solids although increases the

conductivity of a body of water, it can cause decrease in dissolved oxygen levels (Streamkeeper’s Field

Guide, 1991). All these established the fact that the adsorbent is very suitable for treating wastewater.

Table 10: Water analysis Water sample Units Before Treatment After treatment

pH Nil 10.6 7.1 Colour Nil Brown Clear

Temperature 0C 30.3 29.7

BOD mg/l 48 22

COD mg/l 146 90 Conductivity µs/cm 342 164

CONCLUSION The snail shell which is a common waste was converted by carbonization to a useful and effective adsorbent material. The snail shell was carbonized at varying temperatures ranging from 300

0C to 1000

0C at 100

0C interval.

The carbon adsorbent produced at the different carbonization temperature was characterized with the following parameters pH, % moisture content, and % carbon yield. Iodine values, % ash content, bulk density, porosity, bulk volume, mean particle size Judging with the porosity, Iodine value and the mean particle size the optimum carbonization temperature was found to be 800

0C with a porosity of 0.44, iodine adsorption of 1.35 and a mean particle size of

1.126mm. Also, the result of the treated waste water with snail shell activated carbon improved the parameter with time comparing the raw water before it was treated.

NOMENCLATURE X= volume of thiosulphate used for sample free aliquot Y= volume of thiosulphate used for blank W= weight of sample V= volume of iodine solution used M= molarity of the iodine solution used Dpi =the size of the particle retained on the screen

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Xi =the weight fraction of the particles retained on the screen Dw= weight average mean particle size Wch =the weight of carbon retrieved from the furnace Wo= the dried weight of the carbon sample. Ych=% carbon yield WSh= weight of sample after removal from oven Wd = Weight of dried sample Ws = Weight of superficially dried wet sample

vs = density of water X/M = amount adsorbed per unit weight of adsorbent Qo= empirical constants b = empirical constants Ce= equilibrium concentration of adsorb ate in solution Vp = total volume of particle

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