Remediation Strategies for Phenolic Compounds Toxicity

V. Srihari¹* and Ashutosh Das²

¹National Institute of Construction Management and Research-Construction Industry Staff College (NICMAR-CISC), Kondapur, Hyderabad,Telangana-500 084.

²PRIST University, Vallam, Thanjavur, Tamil Nadu-613402(INDIA).

*Corresponding Author E-mail: vsrihari2005@gmail.com; acadas@gmail.com

ABSTRACT:

Phenol, although used as an essential ingredient for pharmaceutical and cosmetic applications, yet can lead to severe toxicity on improper handling. Several industrial wastewater (especially, from coke-oven plants, pharmaceuticals, textile and chemical industries) pose serious threat to living organisms. The present paper provides an outline of the physico-chemical characteristics, usages and hazards and remediation measures for control of phenol toxicity. The various analytic methods of attempts for dephenolation of wastewater include steam stripping, solvent extraction, oxidation (O₃, H₂O₂, and ClO₂), ion exchange, biodegradation and adsorption methods were discussed.

KEYWORDS: phenol, hazardous compounds, toxicity, adsorption, dephenolation.

INTRODUCTION:

Phenol (C₆H₅OH) is the monohydroxy derivative of Benzene and is a clear, colorless-to-white solid, hygroscopic in nature. It was first isolated from coal tar in 1834 and was named carbolic acid. It is also called as Benzenol, hydroxybenzene, monophenol, oxybenzene, phenyl alchohol, phenyl hydrate, phenyl hydroxide, phenylic acid, phenylic alcohol¹. Phenol has a distinct odor that is sweet and tarry. Most people begin to smell phenol in air at about 40 parts of phenol/ billion parts of air (ppb), and begin to smell phenol in water at about 1-8 parts of phenol / million parts of water (ppm). The classification of various phenol compounds is shown in Figure 1.

Phenols are stronger acids than alcohols, because the oxygen atom acquires a positive charge by resonance and, thus, proton release is facilitated. Phenol is a weak acid (pKa = 9.98) and the effect of a ring substituent on the acid strength depends on whether the group is electron withdrawing or releasing, its position, and its ability to give resonating structures (i.e., the methyl group is electron releasing and decreases the acid strength from all ring positions).

The phenolic group occurs in a large number of natural and industrial products, extending from phenolic resins, herbicides, surfactants, alkaloids, steroids, and glycosides to numerous other groups. Unlike alcohols (which also contain an -OH group) phenol is a weak acid. A hydrogen ion can break away from the -OH group and transfer to a base. The physico chemical characteristics and various forms of phenol are given in the table 1^{2, 3}.

Phenolic Compounds Usage Patterns

The main use of phenol is as an intermediate in the production of phenolic resins. However, it is also used in the production of caprolactam, which is mainly used in the manufacture of nylon 6 and other synthetic fibers and bisphenol A, which is widely used to produce polycarbonate plastics, dyes, epoxy coatings and flame retardants ⁴

Phenol can have beneficial effects which include ointments, ear and nose drops, cold sore lotions, mouthwashes, gargles, toothache drops, analgesic rubs, throat lozenges and antiseptic lotions⁵. The other derivatives of Phenol (o-cresol, m-cresol, p-cresol and Pentachlorophenol) are also used as a slimicide, which is a chemical toxic to bacteria and fungi characteristic of aqueous slimes and as a wood preservative⁶ The main anthropogenic sources of phenol in natural water include coal tar and wastewater from manufacturing industries such as resins, plastics, fibres, adhesives, iron, steel, aluminum, leather, rubber, effluents from synthetic fuel manufacturing, paper and pulp mills and wood treatment facilities⁷. Other releases of phenol result from pharmaceuticals, disinfectants⁸. In 1996 the total release of 414.7 tonnes of phenolics were reported in Canada and its world production reached 7.8 million tones in 2001⁹. Phenol ranks in the top 50 in production volumes for chemicals produced in the United States. Phenol has been widely produced mainly by two processes, oxidation of Cumene or toluene or by vapour phase hydrolysis of Chlorobenzene¹⁰.

Table 1: Physico-chemical characteristics of phenol

SNo	Property	Description
1	Chemical formula	C6H5OH
2	Molecular Weight	94.11
3	Melting point	43^0C
4	Boiling point	181.8^0C
	Auto ignitation	715^0C
	Flash point open cup Closed cup	85^0C 79^0C
5	Density @20^0C	1.0545g/cm^3(@20^0C) 1.132g/cm^3(@25^0C)
6	Solubility in water	8.7 g/100ml (20^0C) 6.7 g/100ml )16^0C) >63.5^0C, all proportion soluble
7	Solubility In organic solvents	Highly soluble in alcohols, chloroforms, ether, benzene, acetone
8	Henry’s law constant	4X10^7m^3/mol
9	Viscosity	2.47mPa.s(60^0C)
10	pH in water	6.0
11	pka	9.99

Phenol Induced Toxicity:

There is a long history of human exposure to phenol. Effects in humans attributed to chronic phenol exposure include anorexia, progressive weight loss, diarrhea, headache, vertigo, salivation, and a dark coloration of the urine. Methemoglobinemia and hemolytic anemia, as well as liver damage, have also been reported following human exposure to phenol¹¹. The odour threshold has been reported to range from 0.021 to 20 mg/m³ in air, while the threshold for odour in water has been reported to be 7.9 ppm. A taste threshold value of 0.3 ppm water has been suggested¹².

The effect of phenol on fish and other aquatic organisms has been reported in several studies. Fishes are sensitive to phenol at concentrations ranging from 5 ppm for rainbow trout (Oncorhynchus my kiss) to 85 ppm for gold fish (Carassius auratus). The tainting of fish occurs at levels of 15-23 ppm, toxicity to fresh water invertebrate species occurs in a range from 2 ppm for Caddisfly to 2000ppm for the flower fly¹³.

Studies in humans and animals indicate that most of the phenol that enters the body through skin contact, breathing contaminated air, eating food or drinking water, or using products containing phenol, leaves the body in the urine within 24 hours. The normal range of phenol in the urine of unexposed individuals is 0.5-80 milligrams of phenol per liter of urine.

Dephenolation of Aqueous Media

Removal of phenol mainly depends on two principles i.e. first is, recovery of phenol from wastewater for reuse and second is, to make the wastewater harmless. The following methods are most popular for the removal of phenol are Stem stripping, biological processes, reverse osmosis, solvent extraction, enzymatic oxidations, catalytic oxidation, H₂O₂ oxidation, ionizing radiation and ozonation, adsorption/ion exchange.

.

Steam Stripping:

In Kopper’s method of steam stripping, dephenolation takes place at 100⁰C and stripped phenol absorbed by 15% sodium hydroxide solution. It is estimated that 1000m³ of wastewater would require 200 tonnes of steam and 2 tonnes of sodium hydroxide⁸. Ansari, 1996¹⁴ compared different processes and suggested that this method was a fast, efficient and economical approach to treat phenolated wastewaters. This method is useful for concentrations above 100ppm of phenolated wastewaters, but the capital cost of this method is high⁸.

Biological Methods:

The microorganisms capable of degrading phenol are highly specialized and require a controlled, stable environment. Under ideal conditions several weeks are required to develop the proper biological sludge. The efficiency of an acclimated biological system treating phenolic wastes depends strongly on temperature, pH, nutrients (nitrogen, phosphorus, and minerals), oxygen concentration, phenol concentration, and other organics concentrations in the wastewater. To degrade phenol, the microorganism population must be stable. Fluctuation in any of the preceding variables shifts the balance of this population, reducing system efficiency and possibly killing the biological organisms. Optimum phenol removal occurs at neutral pH (7.0), 70°F and constant phenol concentration. The main advantage of this method is reduced capital and operational costs Proper acclimatization, toxic limit of phenol, removal of oil and tar, provision of supplements such as nitrogen, phosphates, potassium and other salts are essential features of biological treatment⁸. Although aerobic biological treatment predominant one, anaerobic method finding an ever increasing application due to low energy consumption and sludge production¹⁵. Hickman and Novak, 1984¹⁶ studied the ability of activated sludge reactor to with stand the shock loads of phenol by achieving 95% removal. The bacteria (Pseudomonas putida) are able to degrade phenol into methane and CO₂. Ehrhardt and Rehm, 1989¹⁷ immobilized the bacteria onto activated carbon, depending on the adsorption capacity this type of system degrade upto 17g/l in batch culture in 218 hours.

Reverse osmosis:

Yanic et al., 1996¹⁸ studied the phenol removal by using a permeable polyamide membrane and reported the removal efficiency of 78% of phenol for the optimum phenol concentration was < 3 ppm, operating pressure was 2 atmospheres.

Solvent Extraction:

For wastewaters containing high phenol concentrations, solvent extraction reduces the phenol to acceptable levels. In solvent extraction, two immiscible or partially soluble liquids are brought into contact for transfer of one or more components. The extraction of phenols by using solvents is the best method when concentration of phenol is high in the solution⁸. The most popular solvents are Benzene, light tar oil, hydrogenated tar oils ester groups, phenosolvan (higher Partition coefficient than benzene) etc. The extracted phenol is then washed out with caustic to form the sodium salt and the benzene is reused. In the petroleum industry, light catalytic cracking oils are used as extractors, and in the coking industry, coke oven light oils are used as extractors. Process efficiency depends on solvent choice and system design. The extraction methods are uneconomical if the flow rates are at least 200m³/day and 350 m³/day in benzene–NaOH method and phenosolvan method respectively for a minimum phenol concentration of 2000 ppm⁸.

Enzymatic oxidations:

Enzymes are proteins and are found in all types of cells. Enzymes are biological catalysts; the reactions speeded up one million times faster than the rate in the absence of enzymes¹⁹. Peroxidases are enzymes that catalyze the oxidation of organic and inorganic compounds. The enzyme catalyzed reaction for Phenolic wastes may be as follows

H₂O₂ + 2ArOH 2ArO- + 2 H₂O -----[1]

Where ArOH is the Phenolic waste and ArO ia a phenoxy radical, which is highly reactive and develops insoluble polymer, that can be removed by filtration. High strength phenol wastes are treated by the enzyme Caprius Macrorhizus Peroxidase by an extra cellular peroxidase developed from common dung and fungus. The soybean hull peroxidase is capable of oxidizing aromatic hydrocarbons in the presence of hydrogen peroxide²⁰.

Carbon Adsorption:

Activated carbon in the powdered and granular forms is used to remove phenolic tastes and odors from drinking water supplies. In wastewater treatment applications, where phenol content is considerably greater than in potable water applications and the flow is continuous, granular carbon systems are more economical. Depending on the concentration of phenol and other organic compounds in the wastewater, activated carbon will adsorb from 10 to 25 gm of phenol per 1000 gm of carbon. This capacity can be determined from isotherm and column test data. In general, phenol adsorption improves as the pH decreases. Adsorption at high pH is poor, since phenolate salt forms and is difficult to adsorb. This is an advantage in applications where phenol recovery is worthwhile. The phenol is adsorbed at the low pH and reclaimed as sodium salt by chemical regeneration, using hot caustic. If the phenolate cannot be reused, regenerant disposal is a problem. Also, if quantities of other organic substances are present in the waste stream, they too will be adsorbed. These organic compounds may not be desorbed during caustic regeneration, which will decrease the phenol capacity of the carbon upon subsequent regeneration. If chemical regeneration does not sufficiently recover the phenol capacity of the carbon, thermal reactivation will be required. Adsorption of phenol by the activated carbon has been widely employed method, however, its high initial cost and difficulty in regeneration made researchers to look for other alternatives. Many investigators have attempted agricultural wastes^21-25, soils²⁶, and polymers²⁷.

Chemical Oxidation:

Air, chlorine, ozone, and other chemical oxidizing agents are used to destroy phenol, which is first converted to hydroquinone and then to quinone. Additional oxidation destroys the aromatic ring, forming organic acids and eventually carbon dioxide and water. Air is an inexpensive oxidizing agent but reactions are slow. Phenol can be completely decomposed by chlorination at pH 7.7, provided that the stoichiometric amount of chlorine is added. This is accomplished in water treatment plants by superchlorination. The major portion of the chlorine applied consumes other organic compounds and destroys ammonia. Approximately 42 parts of chlorine per part of phenol are required. Ozonation effectively oxidizes phenol. However, the initial cost of producing ozone is high. Ammonia does not interfere in ozonation, and approximately 5.8 parts of ozone are required per part of phenol.

CONCLUSIONS:

Phenol, being a basic byproduct for many industries viz., coke-oven, paint, pesticides, petrochemicals, plastics, pharmaceutical and cosmetic applications, find a wide spread concentration in industrial effluents, leading to severe toxicity to living organisms. The present paper reviews the physico-chemical characteristics, industrial applications, toxic effects on human and aquatic life. It also highlights the remedial measures for control of phenol toxicity.

REFERENCES:

1. Lewis RJ, Sax’s dangerous properties of industrial materials 9th ed. Volumes 1-3, New York, NY: Van Nostrand Reinhold, 1996: 2630-2631.

2. Lide DR, CRC Handbook of chemistry and physics Boca Raton, FL: CRC Press, 1993.

3. Kirk Othmer, Encyclopidia of chemical Technology, John Wiley and Sons Inc., NewYork, NY, 1982.

4. Sawer CN, McCarty PL and Parkin GF, Chemistry for Environmental Engineering, 5th Edn, Tata McGraw-Hill Publishing Company Ltd., New Delhi, 2003.

5. EPA. Ambient water quality criteria document for phenol. Prepared by the U.S. Environmental Protection Agency, Office of Health and Environmental Assessment, Environmental Criteria and Assessment Office, Cincinnati, OH for the Office of Water Regulations and Standards, Washington, DC. EPA 440/5-80- 001A. NTIS PB81-117772, 1980.

6. Erickson BE, Alkylphenols in sewage sludge applied to land, Environmental Science and technology, 36(1); 2002: 10A-11A.

7. EPA. Treatability manual. The U.S. Environmental Protection Agency, Washington, DC: Office of Research and Development. EPA 600/2-82-001A, I.8. 1-1 TO 1-5, 1981.

8. Mahajan SP, Pollution control in Process industries, TaTa McGraw Hill, NewDelhi, 1994: 115-125.

9. Phenol, Chemical Week, 164; 2002: 31.

10. Beszedits S and. Silbert MD, Treatment of Phenolic wastewaters, B and L information services, Toronto. 1990.

11. ACGIH. Documentation of the threshold limit values and biological exposure indices. 6th edition. American Conference of Governmental Industrial Hygienists. Cincinnati, OH. 1204-1208, BEI155-BE1158. 1991.

12. IPCS, Health and Safety Guide No.88, PHENOL, World Health Organization, Geneva 1994.

13. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological profile for phenol, Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service. 1998.

14. Ansari MA, Strip and Destroy, Industrial Wastewater, 4(3); 1996: 39-43.

15. Ross WR, Anaerobic treatment of industrial effluents in South Africa, Water SA, 15(4); 1989: 231-246.

16. Hickman GT and Novak JT Acclimation of activated sludge to pentachlorophenol. Journal of Water Pollution Control Federation, 56(4); 1984: 364-369.

17. Ehrhardt HM and Rehm HJ, Semicontineous and continuous degradation of phenol by Pseudomonas putidaP8 adsorbed on activated carbon, Applied Microbiology Biotechnology, 30; 1989: 312-317.

18. Yanic C, Tor L and Afsar H, Optimum Conditions for removal of phenol by reverse osmosis. Chimica Acta Turcica, 24: 1996: 67-70.

19. Bailey JE and Ollis DF, Biochemical Engineering fundamentals, 2^nd edition, McGraw-Hill, New York. 1986.

20. Colin Flock, Bioremediation of phenols and chlorophenols with soybean peroxidase (SBP) and crude soyabean seed hulls: modeling and experimental studies, MS thesis submitted to The University of Western Ontario, London. 1998.

21. Keirse H, Van Hoof F, Jansens J, Buekens A, Water treatment by means of activated carbon prepared from locally available waste materials (II), Water Science and Technology. 18; 1986: 55–56.

22. Srihari V, and Das Ashutosh, Study on Adsorption of Phenol from Aqueous Media Using Extracted Residue of Hemidesmus Indicus, Asian Journal of Microbiology Biotechnology and Environmental Science 7 (3); 2005: 469-472.

23. Srihari V, Madhan Babu S, and Das Ashutosh, Kinetics of Phenol-Sorption by Raw Agro –Wastes, Journal of Applied Sciences, Asian Network for Scientific Information 6(1); 2006: 47-50.

24. Srihari V, and Das Ashutosh, Comparative Studies on Adsorptive Removal of Phenol by Three Agro-based Carbons: Equilibrium and Isotherm Studies, Ecotoxicology and Environmental Safety, 71; 2008: 274-283.

25. Srihari V, and Das Ashutosh, The Kinetic and Thermodynamic Studies of Phenol- Sorption onto Three Agro-based Carbons, Desalination, 225; 2008: .220–234.

26. Viraraghavan T and Alfaro FM, Adsorption of phenol from wastewater by peat, fly ash and bentonite, Journal of Hazardous. Materials. 57; 1998: 59–70.

27. Juang R and Shiau J, Adsorption isotherms of phenols from water onto macroreticular resins, Journal of Hazardous. Materials. B 70; 1999: 171–183.

Received on 25.11.2014 Accepted on 29.11.2014

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Asian J. Pharm. Tech. 2014; Vol. 4: Issue 4, Oct.-Dec., Pg 179-183