Removal of Phenol from Refinery Wastewater - Literature review Example

Removal of Phenol from Refinery Wastewater Name Institution Date Table of Contents Removal of Phenol from Refinery Wastewater 2 Introduction 2 Literature Review 3 Methods used to remove phenol from wastewater 4 Adsorption on granulated activated carbon 4 Solvent Extraction 5 Chemical Oxidation 6 Electrooxidation 6 Advantages and disadvantages of the methods 8 Conclusion 10 Appendix 1: Levels of phenol in Industrial waste waters 11 References 12 Removal of Phenol from Refinery Wastewater Introduction Organic compounds discharged into water contaminate the environment. Wastewater that contains phenol and its compounds is discharged from phenolic resin plants, oil refineries and coke plants. Phenol and its compounds usually impart some problems in the taste and odour of drinking water even when taken in very small levels. It is said to be a protoplasmic poison and damages all types of cells. This therefore calls for the need to remove phenolic waste from wastewater before it is discharged into natural streams of water (Rengaraj et al. 2001). It is important to remove the phenols from wastewater before discharging it to natural water bodies. Conventional processes used for the removal of phenol from waste water include adsorption on activated carbon, solvent extraction, electrochemical techniques, chemical and bacterial oxidation, and irradiation among others. Despite their existence, they have not been considered sustainable in phenol removal because of some of their shortcomings. Use of enzyme peroxidase from horseradish has been discovered as an alternative method of phenol removal. This paper will review the literature on removal of phenol from refinery wastewater. Literature Review The primary way of reducing the amount of hazardous substances in wastewater would be to prevent entry of the substances into sewer systems. Wastewater removal of these substances is a secondary way and it involves use of different technologies of wastewater treatment that are advanced. Such additional treatment techniques are needed for removal of suspended components from the wastewater. The use of these advanced waste water treatment techniques has to achieve the removal of organic matter and suspended solids efficiently. It also has to remove nutrients that are found in the waste efficiently so as to limit eutrophication of waters. Toxic and other harmful organic and inorganic substances have to be removed too so as to meet the requirements set for wastewater treatment. At times, the inorganic or heavy metals found in wastewater are removed for reuse in industries. Phenol is a hydrocarbon that has a boiling point of 182 ºC. It is therefore categorized as being non-volatile since its b.p. is above 100 ºC and it has a vapor pressure of 0.41 mm Hg at room temperature (this is less than 1 mm Hg). This means that it cannot be removed from wastewater by the air-stripping method. Phenol has been known to be soluble in water as well as being flammable. A particular choice of method for the removal of phenol should therefore be done in consideration of the properties of phenol. Methods used to remove phenol from wastewater Water treatment technologies are used in removal of phenol from wastewater. Successful removal has been achieved through use of both biological and physicochemical techniques, and these have been used industrially at large scale, removing phenol at high efficiencies. For instance, organic pollutants from petroleum industry wastewaters are removed using chemical oxidation and biological treatment. The choice of a suitable technique for removal usually depends on the economic factors and special characteristics of wastewater. Some of the commonly used techniques for treatment will be discussed below (Metcalf and Eddy, 2003). Adsorption on granulated activated carbon Adsorption on activated carbon has been most commonly used to remove dissolved organic material. Activated carbon is a product of various carbonaceous materials like wood, peat and lignite. These materials are effective because they have a large surface area. Carbon is obtained by anaerobically charring the raw materials below 600 ºC and then activating it through partial oxidation. Oxidation can be done using carbon dioxide at 600 – 700 ºC or by use of water at 800 – 900 ºC. The oxidation process is as shown below: CO2 + C 2CO (1) H2O + C H2O + CO (2) The processes will develop porosity hence increasing the surface area and leaving the atoms of carbon in arrangements that comprise affinities for the organic compounds. Two types of activated carbon may be used: powdered activated carbon with particles of about 50 – 100 µm diameter and granular activated carbon whose particles have a diameter of about 0.1 – 1 mm. For water treatment, granular carbon is mostly used (Roostai N. and Tezel F.H, 2004). Solvent Extraction Solvent extraction is also referred to as liquid extraction or liquid-liquid extraction. The method involves selective removal of the waste constituent, like phenol, from wastewater by contacting it with an organic solvent; hence it becomes more soluble in the solvent than in the wastewater. The solvent is mixed with the waste stream so as to allow for mass transfer of phenol (the contaminant) from the wastewater to the solvent. Since the solvent is immiscible in water, it will separate from water by gravity. The solvent solution which contains the extracted phenol is referred to as the extract. The waste stream which has had contaminants removed from it referred to as the raffinate. Sometimes the extract is usually sufficiently enriched and the useful material may be recovered. In order to recover the solvent and the organic chemicals that are reusable, distillation is done. This solvent extraction process is often used in food processing, or processing and the petroleum industry (Shen Y., 2002). Chemical Oxidation Removal of toxic organics like phenol by chemical oxidation has proved effective. Ozone and chlorine are used as the oxidants. Use of ozone as the oxidant has been to remove phenol at pH 7 and an initial concentration of 1000 mg/ L at 48 % efficiency of removal. The effectiveness of this oxidation process is influenced by several factors like the reactivity of ozone with the compound that is targeted; its rate of reactivity, the degree of incidental stripping that is associated with dispersion of ozone, the pH and temperature of reaction. For instance, during the treatment of phenol, the rate of treatment proceeds at twice the speed when the pH of phenol is 11 as compared to when it is at pH 7. Electrooxidation This process occurs by two mechanisms: indirect and direct oxidation. Direct oxidation involves degradation of compounds at the anode surface. First, the compounds shift from the solution to the surface of the anode by diffusion, and are then oxidized. Electrooxidation efficiency is affected by mass transfer of the waste compounds and the electron transfer at the surface of the electrode. At the anode, adsorbed hydroxyl radicals are generated. It is these radicals that cause the degradation of the organic compounds. The compounds get degraded into other inorganic compounds, water and carbon dioxide. R + MOx (OH)z = CO2 + zH+ + ze + MOx Indirect oxidation involves generation of strong oxidizing agents at the surface of the anode and then the oxidizing agents oxidize organic compounds from wastewater, like phenol. Chlorine gas is an example of an electrochemical oxidant. Oxidation of a chloride at the anode generates chlorine gas (Anglada et al. 2009). Biological treatment: Use of enzyme peroxidase from horseradish According to Stanisavljević and Nedić (2004), enzyme peroxidase has been found to have the ability to catalyze oxidation of many aromatic compounds. The enzyme is obtained from horseradish roots (Cochlearia armoracia L.). An example of such a catalyzation process is shown below where an aromatic substrate (AH2) is catalyzed by enzyme peroxidase. E + H2O2 Ei + H2O (1) Ei + AH2 Eii + AHx (2) Eii + AH2 E + AHx + H2O (3) Chemicals used include phenol, polyethylene glycol, hydrogen peroxide and 4-aminoantipyrene. Horseradish roots should be washed and passed in a commercial juicer to obtain horseradish peroxidase at low purity. Peroxide (H2O2) oxidizes enzyme (E) into compound I (Ei), which is an intermediate enzyme. The compound allows an aromatic compound (AH2) to its active site and oxidizes it. This leads to production of a free radical (AHx) which is released to the solution and the enzyme is left in compound II state (Eii). Another aromatic molecule is oxidized by Eii and a free radical is produced as the enzyme is returned to its original state. By this, the cycle is completed. The free radicals produced from the reaction diffuse into the solution where a reaction occurs and polyaromatic products are formed. The polymers formed are insoluble in water and can therefore be removed using solid-liquid operations. Consideration has to be given to the composition of wastewater that leaves this treatment unit. This is because the process entails addition of preparation of crude enzyme and polyethylene glycol (PEG) which are organic compounds that have high contents of carbon. A combination of these compounds with excess organic reagents can affect the aquatic environment since they demand high oxygen. When PEG is used at minimum levels, it is removed completely together with phenol (Wilberg et al, 2000). Advantages and disadvantages of the methods At low concentrations (below 0.1 mol/L), biological treatment can be used for removal of phenol through digestion. Higher concentrations; above 20 mol/L, require the use of solvent extraction. On the other hand, adsorption can be applied for treating phenols at intermediate concentrations. In adsorption, chemical and physical bonding is used to hold the molecules of the adsorbate to the surface of the adsorbent. This process has a good capacity as it can be used in adsorbing many organic molecules. However, use of the adsorbent such as activated carbon is expensive and during its regeneration, additional effluent is produced resulting in a 10-15 % loss of the adsorbent. In addition, heating of carbon to high temperatures requires high amounts of energy. There is also a requirement of periodic backwashing when particulate matter accumulates in the system. Solvent extraction has the advantage of low operating temperatures. In addition, less volatile components can be used to analyze the reaction. However, it is disadvantaged by the incompleteness of its purification process. Besides, hazardous products may be formed from the reaction (Jadhav and Vanjara, 2004). Use of chemical oxidation may at times be considered because it takes a relatively short time and there is no production of sludge. Besides, it leads to improvement of biodegradability of wastewater compounds an also reduces the toxicity of wastewater. In spite of this, knowledge of the wastewater composition has to be known before deploying the method. It also involves additional costs in terms of acquiring reagents and the potential by-products may be toxic or non-bio-degradable. Electro-oxidation my thus be preferred in place of chemical oxidation. It does not involve addition if chemicals and it is a versatile method since it can be used to remove many contaminants. In addition, it operates under low pressure and temperature and there is no accumulation of oxidation-refractory organics. It also has its disadvantages in high power consumption during the electrolysis process. Its operational costs are high and during the process, there is a risk of formation of chlorinated organic or other compounds. Further, regular replacement of electrodes is required (Wilberg et al, 2000). The use of the biological method might provide a more convincing method. It is Effective over a broad range of conditions of operation as well as temperature and pH. In addition, it has a broader specificity for the substrate. This means that it has a wide application. In addition, it achieves an almost perfect removal of phenol. But this method too has its downside. While using the method, care has to be taken in the proportions of the reagents, otherwise some compounds (like PEG) which are hazardous to aquatic creatures will not be removed. Conclusion The problem of water pollution has continued to be addressed in recent times so as to rescue the aquatic organisms. Conventional methods of removal of phenol from wastewater have not achieved high efficiency levels of removal. They have the disadvantages of high costs, low efficiency and their applicability is limited to some concentration range, their reactions lead to formation of by-products that are hazardous and the purification process is not complete. This presents use of biological digestion using enzyme peroxidase as the better alternative for phenol removal. Its advantages include its effectiveness over a broad range of conditions of operation as well as temperature and PH. It also has a broad specificity of the substrate. In addition, the conversion of phenol in wastewaters is nearly complete. Use of enzyme peroxidase method has an overall advantage over the other methods due to its reliability and should therefore be the preferred method. Appendix 1: Levels of phenol in Industrial waste waters Source (Industrial) Concentration of phenol (mg/ L) Petroleum refineries 40 - 185 Coal conversion 1700 – 7000 Rubber industry 3 – 10 Leather 4.4 – 5.5 Textile 100 – 150 Petrochemical 200 – 1220 Coke ovens 600 – 3900 Phenolic resin production 1600 Phenolic resin 1270 – 1345 Paint manufacturing 1.1 Wood preserving industry 50 – 953 Fiber glass manufacturing 40 – 2564 Pulp and paper industry 22 Ferrous industry 5.6 - 9.1 (Metcalf and Eddy, 2003) References Anglada et al, 2009. Contributions of electrochemical oxidation to waste-water treatment: fundamentals and review of applications. Journal of Chemical Technology and Biotechnology, 84 (12), pp. 1747–1755. Environmental Protection Agency (EPA), 2002. Manual Report for List of Chemical Priority. USA. Jadhav D. N. and Vanjara A. K., 2004. Removal of Phenol from Wastewater Using Sawdust Polymerized Sawdust and Sawdust carbon. Indian Journal of Chemical Technology. Vol. 11, pp 35-41. Mumbai, India. Metcalf and Eddy, 2003. “Wastewater Engineering: Treatment and Reuse” (McGraw Hill International Edition, Newyork. Rengaraj S. et al. 2002. Agricultural solid waste for the removal of organics: adsorption of phenol from water and wastewater by palm seed coat activated carbon, Waste Manegement 22, 543. Roostai N. and Tezel F.H, 2004. Removal of phenol from aqueous solution by adsorption, Journal of Environmental Management 70, 157. Shen Y., 2002. Phenol sorption by organoclays having different charge characterisrics, Colloid and Surfaces. Stanisavljević Miodrag and Nedić Lidija, 2004. Removal of Phenol from Industrial Wastewaters by Horseradish (Cochlearia Armoracia L) Peroxidase. Bujanovac. Wilberg et al, 2000. "Removal of phenol by Enzymatic Oxidation and Flotation, Brazilian Journal of Chemical Engineering. Volume 17, (4-7). Sao Paolo. Read More

Phenol has been known to be soluble in water as well as being flammable. A particular choice of method for the removal of phenol should therefore be done in consideration of the properties of phenol. Methods used to remove phenol from wastewater Water treatment technologies are used in removal of phenol from wastewater. Successful removal has been achieved through use of both biological and physicochemical techniques, and these have been used industrially at large scale, removing phenol at high efficiencies.

For instance, organic pollutants from petroleum industry wastewaters are removed using chemical oxidation and biological treatment. The choice of a suitable technique for removal usually depends on the economic factors and special characteristics of wastewater. Some of the commonly used techniques for treatment will be discussed below (Metcalf and Eddy, 2003). Adsorption on granulated activated carbon Adsorption on activated carbon has been most commonly used to remove dissolved organic material.

Activated carbon is a product of various carbonaceous materials like wood, peat and lignite. These materials are effective because they have a large surface area. Carbon is obtained by anaerobically charring the raw materials below 600 ºC and then activating it through partial oxidation. Oxidation can be done using carbon dioxide at 600 – 700 ºC or by use of water at 800 – 900 ºC. The oxidation process is as shown below: CO2 + C 2CO (1) H2O + C H2O + CO (2) The processes will develop porosity hence increasing the surface area and leaving the atoms of carbon in arrangements that comprise affinities for the organic compounds.

Two types of activated carbon may be used: powdered activated carbon with particles of about 50 – 100 µm diameter and granular activated carbon whose particles have a diameter of about 0.1 – 1 mm. For water treatment, granular carbon is mostly used (Roostai N. and Tezel F.H, 2004). Solvent Extraction Solvent extraction is also referred to as liquid extraction or liquid-liquid extraction. The method involves selective removal of the waste constituent, like phenol, from wastewater by contacting it with an organic solvent; hence it becomes more soluble in the solvent than in the wastewater.

The solvent is mixed with the waste stream so as to allow for mass transfer of phenol (the contaminant) from the wastewater to the solvent. Since the solvent is immiscible in water, it will separate from water by gravity. The solvent solution which contains the extracted phenol is referred to as the extract. The waste stream which has had contaminants removed from it referred to as the raffinate. Sometimes the extract is usually sufficiently enriched and the useful material may be recovered. In order to recover the solvent and the organic chemicals that are reusable, distillation is done.

This solvent extraction process is often used in food processing, or processing and the petroleum industry (Shen Y., 2002). Chemical Oxidation Removal of toxic organics like phenol by chemical oxidation has proved effective. Ozone and chlorine are used as the oxidants. Use of ozone as the oxidant has been to remove phenol at pH 7 and an initial concentration of 1000 mg/ L at 48 % efficiency of removal. The effectiveness of this oxidation process is influenced by several factors like the reactivity of ozone with the compound that is targeted; its rate of reactivity, the degree of incidental stripping that is associated with dispersion of ozone, the pH and temperature of reaction.

For instance, during the treatment of phenol, the rate of treatment proceeds at twice the speed when the pH of phenol is 11 as compared to when it is at pH 7. Electrooxidation This process occurs by two mechanisms: indirect and direct oxidation. Direct oxidation involves degradation of compounds at the anode surface. First, the compounds shift from the solution to the surface of the anode by diffusion, and are then oxidized. Electrooxidation efficiency is affected by mass transfer of the waste compounds and the electron transfer at the surface of the electrode.

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