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Feasibility studies on solar photo degradation of phenol.

Introduction

The world's ever increasing population and progressive adoption of an industrial based lifestyle led to an increased anthropogenic impact to the environment. (Asamudo et al., 2005).The enigma for the public, scientists and academicians is how to tackle the contaminants that jeopardize the environment. Thus, the quality as well as the quantity of clean water supply is of vital significance for the welfare of mankind (S.S.Dara, 2001).

Phenols are considered toxic for some aquatic life forms in concentrations superior to 50 ppb and the ingestion of one gram of phenol can have fatal consequences in humans. Its dangerousness lies in the effect that it has on the nervous system of living beings. In addition, they have a high oxygen demand, 2.4 mg O2 per mg of phenol. Another additional effect is the capacity of phenols to combine with existing chlorine in drinking water, giving rise to chlorophenols, compounds that are even more toxic and difficult to eliminate. So an effective and economic treatment for eliminating phenols in water has been in urgent demand. (Mohamed Ksibi et al, 2003).

The concentration of phenol from different industrial wastewater is shown in table 1.

Traditional wastewater treatment techniques include activated carbon adsorption, chemical oxidation, biological digestion, etc. Nevertheless, these methods transfer the pollutant from water to another phase and hence produce secondary wastes. Phenol, is also a concern in the biological stage of wastewater treatment, due to its bio resistance and toxicity to microbial population. (S.G.Poulopoulos, et.al, 2006). An ideal treatment can neutralize all contaminant and no leaving behind any hazardous residues. Currently, the existing treatment process generally cannot remove phenol completely. Photocatalytic process is one alternative that is expected to be able to solve the problem.(Kuo-Hua Wang et.al,1999).

The researchers reported, phenol could be removed by photocatalytic process with the following advantages namely,

(i) Complete oxidation of organic pollutants in a few hours.

(ii) High active catalyst adaptable to specially designed reactor system

(iii) Oxidation of pollutant in ppb range

Solar Ultraviolet Radiation potential in India

In a tropical country like India (8[degrees]4'-37[degrees]6' N latitude), highest level of global solar UV radiation is received. Adequate amount of Solar UV radiation is received for almost 10 months a year. Average mean peak irradiance of Solar UV-A is 47 W/[m.sup.2] -66 W/[m.sup.2] and average mean peak irradiance of Solar UV-B is 0.195 W/[m.sup.2]-0.3384 W/[m.sup.2] corresponding to Tiruchirappalli field conditions (P.Balasaraswathy, 2004). Nearly, 95-98% of the sun ultraviolet radiation reaching the earth's surface is UV-A. Only 2-5% of UV light at the earth surface is solar UV-B. Practically all of UV-C and much of UV-B is absorbed the ozone and the atmosphere.

According to Blanco (2001) UV radiation represents between 3.5 and 8% of the solar spectrum, fluctuating with the presence of clouds and increasing with altitude. The percentage of global UV radiation (direct + diffuse), with regard to the global, generally increases when the atmospheric transmitivity decreases, mainly due to clouds, but also to aerosols and dust (Mehos and Turchi, 1992). In fact, the average percentage of UV with respect to total radiation on cloudy days is up to two percent higher than values on clear days. Since the UV radiation is not absorbed by water vapour, as much as 50 percent of this, or more in very humid locations or during cloudy or partly cloudy periods, can be diffuse. The diffuse component can make up to 50% of the total available UV light even on a clear day because the shorter wavelengths UV photons are more readily scattered within the atmosphere. Solar energy available in various regions is typically 8.3% ultra-violet (200 nm -400 nm), 38.2% visible (400 nm-700 nm), 28.1% near infra-red (700 nm-1100 nm) and 25.4% infrared/far-infrared portion.

[FIGURE 1 OMITTED]

Inorder to utilize the solar energy for treatment of industrial effluents the semiconductor band gap wavelength has been matched with solar spectrum as shown in table 2:

Titanium dioxide is biologically and chemically inert; it is stable to photo and chemical corrosion, and inexpensive. TiO2 can use natural (solar) UV radiation and has an appropriate energetic separation between its valence and conduction bands, which can be surpassed by the energy of a solar photon and therefore absorbs in the near UV light i.e. <387 nm. (S.Malato Rodriguez et.al.. 2004).

Other semiconductor particles (e.g., CdS or GaP) absorb larger fractions of the solar spectrum than Ti[O.sub.2] and can form chemically activated surface-bond intermediates, but unfortunately, such catalysts are degraded during the repeated catalytic cycles usually involved in heterogeneous photocatalysis. The energy needed to activate the semiconductor catalyst recommended for the solar detoxification process corresponds to UV component of the solar radiation. Selection of catalyst must be in such a way that it uses maximum fraction of solar energy. (S.Malato Rodriguez et.al.. 2004).

So this experimental study aims at degrading simulated phenol effluent and actual industrial effluent by using 15W UV lamp. The phenol concentration considered for the study includes 20, 50,100, 150,200 and 250 ppm.

Experimental setup & Procedure

The experimentation were carried out using tubular photo reactor with 15W UV lamp fitted with quartz sleeve and enclosed in a stainless steel reactor.

The experimentation was conducted in batch mode and as well as in circulation mode. The reactor inner diameter with 15W UV lamp is 35.2 mm and enclosing a quartz tube of diameter 33 mm and height of the stainless steel reactor is 445 mm for 15W reactor.

The specifications of the UV lamp used are given in Table 3.

The experimentation was carried out using a flow rate of 60 ml/min of phenol in circulation mode inside the photoreactor. The effluent was circulated using a peristaltic pump of 110 rpm. The catalyst employed is titanium dioxide of 0.2 g./L. The experiments were conducted in two methods either in presence or absence of catalyst. A magnetic stirrer was used to stir the contents in mixing tank for uniform distribution of catalyst in the effluent. The contents in mixing tank are pumped using peristaltic pump to the photoreactor. The effluent is circulated once again to the mixing tank to avoid any heat accumulation and evaporation losses of the effluent. The resultant effluent sample is collected from the outlet and analysed using COD thermo reactor using closed reflux method.

The experimental setup for continuous mode is shown in Figure 2.

[FIGURE 2 OMITTED]

The samples were analysed in COD analyser to determine the effect of treatment of phenol.

Results and Discussions

The graph is plotted for time versus COD (mg/L) for different concentration of phenol.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

The actual time taken for degradation of phenol effluent for different concentration is determined. The resultant ultraviolet light intensity used is calculated. The influence of effect of catalyst on phenol degradation is studied. The time taken for degradation with catalyst is 6.5 hrs and 8.0 hrs for degrading 250 ppm of phenol effluent with and without TiO2 catalyst respectively.

Design of Solar Collector

The solar collector is designed to treat 1000 lt of phenolic wastewater. It is found that 1 [m.sup.2] of area of solar collector treats 1 lt of effluent. So 10 x 10 [m.sup.2] area is required for treating 1000 lt of phenol. The solar collector is designed using stainless steel as material of construction with UV transparent fluoropolymers covering. Two reflector type arrangements made up of aluminium are kept on either sides of flat plate collector to reflect the incoming solar radiation more effectively over entire UV spectrum thus increasing the performance of flat plate collector. The thickness of stainless steel plate employed is 2 mm and density of stainless steel is 7.9 g/[cm.sup.3]. The capacity of solar collector for treatment of phenolic wastewater is 0.2 [m.sup.3].

The average solar ultraviolet radiation available per day is 20W. So if solar radiation is used the output is 100W considering average solar ultraviolet as 20W and if it is utilizing 6 hrs of sunlight for wastewater treatment. So fabrication of collector requires 1580 kg of stainless steel material. Cost of stainless steel per kg is Rs 30. The fabrication cost is around Rs 47,400 using stainless steel material. The reflector material is made up of aluminium on both sides. The total cost inclusive of fabrication of stainless steel reactor, reflector and catalyst is approximately Rs 53,000. Therefore the payback period is approximately 265 days.

The UV lamp utilizes electrical energy for its operation. To get the same electricity from solar PV power, assuming 15% efficiency of PV panel and radiation intensity as 800W/m2 and operating time as 6 hrs, the actual energy output is 720 W/[m.sup.2]. Considering the average peak UV as 20W/[m.sup.2] for Tiruchirappalli field conditions.The watts of energy required for treatment of effluent in 6 hrs operating time is shown in shown in Table 4 & Table 5 with and without catalyst.

Conclusion

Solar UV C radiation alone can degrade phenol effluent since it has lesser wavelength and hence more energy content. Usage of PV panel for supply of electricity of UV lamp is considered economically viable for operation. So the time required for complete degradation is found out using laboratory UV photo reactor so as to test the feasibility of using actual solar radiation.

It is technically feasible to remove a wide range of organic and inorganic compounds from contaminated water using a photocatalytic process. However, at the current state of development only a few applications are near to being commercially viable. This number could be expanded with significant progress by the improvement of the photo-efficiency of the process. In order for a solar process to compete with comparable systems using electric lamps, significant progress must be made in reducing the cost of solar collectors. Suitable catalyst could be employed to utilize the maximum amount of solar UV radiation. To make the process more effective solar UV and solar visible could be coupled in such a way that initial treatment by solar UV radiation and then utilizing solar visible light using suitable catalyst.

Acknowledgement

The authors wish to express their gratitude to National Institute of Technology, Tiruchirappalli for providing us all the facilities to carry out this work.

References

[1] Mohamed Ksibi, Asma Zemzemi, Rachid Boukchina, 2003, "Photocatalytic degradability of substituted phenols over UV irradiated Ti[O.sub.2]", Journal of Photochemistry and Photobiology A: Chemistry 159, pp. 61-70.

[2] Kuo-Hua Wang et.al, 1999, "Photocatalytic degradation of 2-chloro and 2-nitrophenol by titanium dioxide suspensions in aqueous solution", Applied Catalysis B : Environmental 21, pp. 1-8.

[3] Garcia, J., Diez, F. and Coca, J., 1989, Ingenieria Quimica, 238, pp. 151-158.

[4] Nelson Saksono, Slamet "Phenol Degradation by photocatalytic process on Titanium dioxide catalyst", North American Catalysis Society Newsletter http://www.che.ui.edu

[5] S.G. Poulopoulos, et.al, 2006, "Photochemical treatment of phenol aqueous solutions using ultraviolet radiation and hydrogen peroxide", Journal of Hazardous Materials, B129, pp. 64-68.

[6] S. Malato Rodriguez et.al., 2004, "Engineering of solar photo catalytic collectors", Solar Energy, 77, pp. 513-524.

[7] P. Balasaraswathy, 2004, Paper presented in National Conference of Indian Association of Dermatology "Sunlight in India"

[8] Blanco, J. and Malato, S., 2001, "Solar detoxification", UNESCO. Natural Sciences, World Solar Programme.

[9] Mehos, M. and Turchi, C, 1992, "Measurement and analysis of near ultraviolet solar radiation", Solar Eng., 1, pp. 51-55.

[10] Duffie JA, Beckman WA, 1991, In: Solar engineering of thermal processes, 2nd ed. New York: Wiley, pp. 263.

S. Shanmuga Priya (1) *, M. Premalatha (2) and N. Anantharaman (3)

(1) Research Scholar, Chemical

(2) Assistant Professor

(3) Professor & Head, Chemical Engineering/Centre for Energy & Environmental Science And Technology National Institute of Technology, Tiruchirappalli-620015

* Corresponding author

E-mail: shanpriyanitt@yahoo.co.in, latha@nitt.edu
Table 1: Concentration of phenol in Industrial wastewater
(Garcia, J et.al, 1989)

Industry           Concentration of
                   phenol (mg/L)

Coal mining        1000-2000
Lignite            10000-15000
  transformation
Gas production     4000
Petrochemicals     50-700
Pharmaceuticals    1000
Oil refining       2000-20000

Table 2: Matching solar energy wavelength with band gap
wavelength of semiconductor

Semiconductor   Band Gap   Band Gap     Solar
                Energy     wavelength   energy
                (eV)       (nm)         wavelength

Ti[O.sub.2]     3.0        390          UV - A
ZnO             3.2        387          UV - A
ZnS             3.7        336          UV - A
BaTi[O.sub.3]   3.3        375          UV- A
Sn[O.sub.2]     3.9        318          UV - A
SrTi[O.sub.3]   3.4        365          UV - A

Table 3: Specification of UV lamp

Lamp    Lamp              Lamp           Lamp
Input   Current           Length         Diameter
Watts   (Amps)            (nm)           (mm)

15      0.340             440            26

Lamp    Radiation         Lamp
Input   Output in Watts   Temperature
Watts   @250 - 280 nm     ([degrees]C)

15      4.0               40

Table 4: Time for degradation of effluent in presence of catalyst

Concentration       Time for complete   UV light
of phenol (ppm)     degradation (hrs)   used (W-hr)

20                  0.7                 2.33
50                  1.0                 3.33
100                 5.0                 16.67
150                 5.0                 16.67
200                 5.5                 18.33
250                 6.5                 21.67

Table 5: Time for degradation of effluent without catalyst

Concentration      Time for complete   UV light
of phenol (ppm)    degradation (hrs)   used (W-hr)

20                 1.0                 3.33
50                 1.5                 5.00
100                6.0                 20.00
150                6.8                 22.67
200                7.0                 23.33
250                8.0                 26.67
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Author:Priya, S. Shanmuga; Premalatha, M.; Anantharaman, N.
Publication:International Journal of Applied Engineering Research
Article Type:Report
Date:Oct 1, 2008
Words:2262
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