Experimental Studies on Saline Waste Water Treatment Using Electrochemical Catalytic Reactors

8/3/2019 Experimental Studies on Saline Waste Water Treatment Using Electrochemical Catalytic Reactors

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EXPERIMENTAL STUDIES ON SALINE WASTE

WATER TREATMENT USING

ELECTROCHEMICAL CATALYTIC REACTORS

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ABSTRACT

Leather tanning industry is highly polluting as it produces large amount of organic

and inorganic pollutants. With high saline content, the wastewater invariably has a rather

high conductivity because of the presence of anions and cations in the aqueous solution.

Soak liquor was treated through Advanced Oxidation Process, comprising of

Electrochemical catalytic oxidation (ECO) and Fentons activated carbon catalyticoxidation system (FACCO). Alum was used to coagulate the suspended particles and the

supernatant was sand filtered. It was further treated in ECO reactor consisting of graphite

anode, stainless steel cathode and packed with activated carbon catalyst. Electrical current

supplied was 13.0A/m 2 and potential applied was 8.0V. The percentage removal of COD,

TOC, BOD and Protein in ECO reactor of residence time 1 hour was studied. To optimize

the reactor, its various parameters such as the hydrogen peroxide concentration, ferrous

sulphate concentration, voltage, current and anode to cathode surface area ratio wasstudied. The ECO reactor designed after optimizing the appropriate operating conditions

such as current, potential difference, residence time, chemical dosing of the samples

before the oxidation reactions, which can effectively reduce the organic pollutants in the

soak liquor.

Keywords : Soak liquor- electrochemical catalytic oxidation reactor-chemical oxygen

demand-biological oxygen demand
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1. INTRODUCTION

Leather tanning industry is highly polluting as it produces large amount of organic and

inorganic pollutants. It has a strong potential to cause land and water pollution due to the

disposal of untreated effluent. In the tanneries the hides are washed with water to removethe salt and other particles. After washing, a large quantity of water is let out as

wastewater. This wastewater consisting 24% sodium chloride, traces of calcium chloride

along with bio-particles like blood, flesh, skin and other suspended particles is called

soak liquor. The results from the previous investigations revealed that the biological

methods may not be a good choice, primarily because of the inhibitory effect of high

salinity on the microbial growth. With high saline content, the wastewater invariably has

a rather high conductivity because of the presence of anions and cations in the aqueous

solution. To take advantage of this characteristic a plausible alternative for dealing with

saline wastewater is to use the electro catalytic method. In our study, we conducted the

experiments to examine the effects of various operating conditions on the efficiency of

the electro catalytic method of treating highly saline wastewater and its followed by

Fentons Activated Carbon Catalytic Oxidation (FACCO) for the removal of residual

organics from the soak liquor.

2. AIM OF THE STUDY:

To conduct the experiments on the ECO reactor and to optimize its various parameters

such as the hydrogen peroxide concentration, ferrous sulphate concentration, voltage,

current, anode to cathode surface area ratio, duration. Based on the optimized values,

ECO reactor of the following capacities 50m 3 per day, 100 m 3 per day, 150 m 3 per day

and 200 m 3 per day is to be designed.

3. MATERIALS AND METHODS

3.1 Experimental ProcedureThe soak liquor is generated from tanneries; waste pieces of salted hide (trimmings) were

soaked in water overnight. 4 liters of water was added for every 1 kg of salted hide. The

soak liquor was then cloth filtered to remove sand particles and hair. A part of this filtered

soak liquor is collected as the initial sample for analysis.

3.1.1 Primary clarification

The filtered soak liquor is coagulated to settle the suspended particles using a 2% alum

solution. After the addition of alum the solution is allowed to stand for two hours. After 2hours the supernatant is siphoned out.

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3.1.2 Sand filter

A sand filter was used with diameter of 6 cm and height 30cm. It

consisted of 2.5 cm layer of gravel (diameter 3 mm). This was followed

by a 10 cm layer of coarse sand ( diameter 1mm). The supernatantliquid was poured into the sand filter through the top and drained at

the base through a hole about 2mm in diameter.

3.1.3 Batch studies on electro catalytic oxidation

reactor

The coagulated and sand filtered soak liquor was used for electro

catalytic oxidation. The oxidation reaction was carried out with

initiators H2O2 and FeSO4 and mesoporous activated carbon as theheterogeneous catalyst with a set potential difference and current.

The experiment was carried out with different operating

conditions. The various operating conditions that had to be studied

were H 2O2 concentration,FeSO 4 concentration, Potential difference,

Current, Number of anodes, Distance between electrodes and time

3.2 Electro catalytic reactor

The electro catalytic reactor has a fiber glass body. It has a

capacity of 0.006525m 3 . Dimensions being 0.15mX 0.15mX0.29m. The

thickness of the fiber glass being 0.005m. The reactor is packed with

pebbles in the bottom (diameter 5mm) for a height of 0.05m followed

by gravel (diameter 1.5 to 2mm). It is then packed with activated

carbon for a height of 0.15m. The cathode is made of stainless steel

and it is placed close to the walls of the reactor on all 4 sides. The

anode used is made of graphite. The anode is placed in the center; ithas a diameter of 0.025m and a length of 0.21m. Air is supplied using

air diffusers placed in the carbon bed and air is sent at a rate of

0.5cfm. An outlet is placed in the bottom its diameter being 0.4mm

through which a tube is attached. The working capacity of the reactor

is 1250ml. The reactor is used as a batch reactor.

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Fig-1: Diagram of electro catalytic reactor

3.3 FACCO reactor

The FACCO reactor is cylindrical with a diameter of 9.5cm with a

height of 50cm. The reactor is packed with pebbles in the bottom

(diameter 5mm) for a height of 8cm followed by gravel (diameter 1.5 to

2mm) to a height of 2cm. It is then packed with activated carbon for aheight of 20cm. The carbon bed is provided with air distributors

through which air is sent at a rate of 0.5cfm. On the top the reactor has

a revolving distributor through which the sample is sprayed into the

reactor. An outlet is placed at a height of 5cm from the base.

Before putting the soak liquor which was treated using the

electro catalytic reactor into the FACCO reactor the pH is adjusted to

3.5 and 0.1ml of H2O2 per litre and 0.1g of FeSO4 per litre is addedand mixed thoroughly. The mixture is fed to the FACCO reactor using a

peristaltic pump. The retention time of the soak liquor in the FACCO

reactor is 1 hour.

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Fig-2: Diagram of FACCO reactor

3.4 Analysis of soak liquorT he various factors that must be analyzed in the soak liquor are chemical oxygen demand,

total organic carbon, protein estimated by Lowrys method, microbial activity, biological

oxygen demand, total solids and dissolved salts.

4. RESULTS AND DISCUSSION

4.1 Effect of H 2O 2

In the study of the effect of H 2O2 concentration, the potential difference

was maintained at 8V and current maintained at 0.8A, with theconcentration of FeSO 4 being 100mg/L. One anode was used and the

distance between the electrodes is 0.065m. The residence time was

one hour. And the different amounts of H 2O2 concentrations used were

0.025; 0.05; 0.075 and 0.1ml/L.It is observed that the maximum

percentage reduction occurs when a concentration of 0.1ml/L of

hydrogen peroxide is used. 0.1ml It is clearly seen that better degradation of the

parameters studied occurs when a concentration /L of hydrogen peroxide is used. Thushydrogen peroxide is optimized to 0.1ml/L.

4.2 Effect of FESO 4

For the study of the effect of FeSO 4 concentration, the

potential difference was maintained at 8V and current maintained at

0.8A, with the concentration of H 2O2 being 0.1ml/L. One anode was

used and the distance between the electrodes is 0.065m. The

residence time was one hour. And the different amounts of FeSO 4concentrations used were 0; 25; 50; 75 and 100mg/L.The optimum

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concentration of Ferrous sulphate has been fixed at 75 mg/L since

there is no considerable change in the degradation COD, TOC and BOD

when 75 mg/L or 100 mg/L of ferrous sulphate is used.

4.3 Effect of Potential DifferenceFor the study of the effect of potential difference, the current is

maintained at 0.8A, with the concentration of H 2O2 being 0.1ml/L and

concentration of FeSO 4 being 100mg/L. One anode is used and the

distance between the electrodes is 0.065m. The residence time is one

hour. And the potential difference is maintained varied using a rectifier

as 2V, 4V, 6V and 8V. It has been observed that the organic depletion

was maximum when the potential difference in the electro catalyticoxidation reactor is maintained at 8 V and it was noted that the further

increase in the potential didnt affect the values considerably.

4.4 Effect of current

For the study of the effect of current, the potential

difference was maintained at 8V, with the concentration of H 2O2 being

0.1ml/L and concentration of FeSO 4 being 100mg/L. One anode was

used and the distance between the electrodes is 0.065m. Theresidence time was one hour. And the current was maintained at

different values, which are 0.5A, 0.6A, 0.7A and 0.8A.

4.5 Effect of Anode/Cathode surface area ratio

For the study of the effect of number of anode/cathode surface

area ratio, the potential difference was maintained at 8V and current

maintained at 0.8A, with the concentration of H 2O2 being 0.1ml/L and

that of FeSO 4 being 100mg/L. Distance between the electrodes was0.065m. The residence time was one hour. The experiment was carried

out by first running the reactor with one anode and then with two and

finally with three anodes. It was observed that the more the anode to

cathode surface area better was the oxidation of the organics in the

soak liquor though there was some loss in the net effective anodic

surface area. From the observation, the surface area of the anode

increases the oxidation of the organics also increase considerably.

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4.6 Effect of distance between electrodes

Long gap between the electrodes may prove to be ineffective for

the actual design the electrodes are spaced out at a distance of

approximately 0.142 m. The following tables and graphs provide abetter insight.

4.7 Effect of Duration

It was observed that as the residence time increases, there is

increased oxidation of the organics in the soak liquor due to increased

generation of hydroxyl radicals and hence improved reduction in the

physico-chemical characteristics. It is noticed that the best results

were obtained as the residence time was increased but since there wasno considerable increase in reduction of the organics the residence

time was optimized at 1 hr. 5. UV SPECTROSCOPY FOR THE SAMPLE:

Further a UV absorption spectroscopy was conducted to verify the

degradation of the complex organic molecules to simpler organic

structures. The following graphs were obtained.

Fig-3: UV absorption spectra for initial

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Fig-4: UV absorption spectra for sample treated by ECO reactor .

.

Fig-5: UV absorption spectra for sample treated by FACCO react

6. CONCLUSION

An ECO reactor was designed after optimizing the appropriate operating conditions

such as current, potential difference, residence time, chemical dosing of the samples

before the oxidation reactions which can effectively reduce the organic pollutants in the

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soak liquor which is one of the main effluents discharged from the leather industries

evidently observed by the reduction of COD, BOD, Protein, TOC values. Moreover, the

quality of the dissolved salts, after comparing the color and the odor of the dissolved salts

obtained after treating the ECO treated soak liquor sample in the FACCO reactor met the

standards for reuse. No sludge is generated after treating the sample in the ECO and

hence poses no problem of sludge disposal. Hence the ECO reactor can be concluded as

a feasible technology for treatment of saline waste water with high organic load and

especially for leather industries.

REFERENCE

[1] Marcel Dekker (1989) Chemistry and physics of carbon, vol. 21, pp.147 386

[2] Butterworth (1989) Introduction to carbon science vol19, pp.107-51

[3] Bio resource Technology (2002), vol. 81, pp 45-52.

[4] Chemosphere 45, (2001), pp85-90.

[5] Ellis Harwood (1987) Chemical Processes in wastewater treatment, pp185-215

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Documents

Experimental Studies on Saline Waste Water Treatment Using Electrochemical Catalytic Reactors