Study of Methods of Removal of Colour from Agro-Based Pulp and Paper Industries.

Transcription

1 Study of Methods of Removal of Colour from Agro-Based Pulp and Paper Industries. Amandeep Kaur # and Sangeeta Sharma # # Department of Applied Sciences, Shaheed Bhagat Singh State Technical Campus, Ferozepur, India Abstract- Pulp and paper industries discharge colour effluents which disturb the aesthetics of quality of water. The effluent colour is mainly derived from lignin and its derivatives. This discharge of strongly coloured water can be carcinogenic, mutagenic and very harmful for the environment so it is very necessary to reduce the concentration of colour from the effluents. Many methods have been tried out for the removal of colour in recent years, but promising results have not been formed. In this paper we have studied various methods for the removal of colour from agro-based pulp and paper industries specially advanced oxidation methods, using adsorbents, electro-coagulation and using surfactants. Key words- electro coagulation, surfactants, adsorbent, advanced oxidation. Introduction Paper and pulp industry is one of the major industrial area that utilizes a very large amount of ligno-cellulosic materials and water during manufacturing process associated with the release of chlorinated ligno sulphonic acid, chlorinated resin acids, chlorinated phenols and chlorinated hydrocarbons, synthetic dyes etc. in the effluents which are carcinogenic, mutagenic and is of serious threat to human health. The major source of colour is mainly from pulp mill process and from bleaching section. [1] The manufacturing process of paper is shortly discussed here These color imparting highly toxic compounds are generated unknowingly in the effluents but this degrade the water quality on discharging them into water bodies. It has been reported from various studies that waste water stream of pulp and paper industry drastically affects the aquatic animals that receive the effluents in form of damaging of liver, respiratory problems and geno-toxicity. Many health issues like vomiting, headache, nausea and diarrhoea and eye irritation has also been noticed in workers as plenty of organic chemicals are present in the effluents. 210 Amandeep Kaur and Sangeeta Sharma

2 So, these effluents of paper and pulp industry have become threatening to the environment as they persist for long duration in the environment that do not degraded easily. Lignin and its derivatives which are mainly responsible for the brown colour over there, can not be degraded naturally. [2] Even degradation is not completely achieved by flocculation and precipitation. In addition to this, it is also responsible for rising temperature of water and retarding photosynthesis phenomena that leads to decreasing concentration of dissolved oxygen. [3] Hence, decolourization of these effluents and treatment of waste water streams should be taken on priority basis. There are several techniques that have been employed by pulp and paper industry to treat the effluent. Some of these are adsorption, advanced oxidation process, electro-coagulation, solvent extraction, membrane separation, biological treatments etc. All the above said processes are capable enough to remove the colour of effluents to some extent but till date, no promising method has been developed to achieve adequate colour removal. Some of these methods have been discussed here. 1. Surfactant modified adsorbents- It has been reported by Fungaro et.al. (2000) that zeolite materials are low cost media for the removal of colour from waste water. [4] Zeolites were synthesized from cyclone ash and were modified with a cationic surfactant hexadecyl trimethyl ammonium bromide. [5] Surfactant modified zeolite shows upto 100% of colour removal from waste water. Complete adsorption occurs because of increase in surface area of the adsorbent modified with surfactant. Further, Zeolites have almost no affinity for anionic or non-polar organics. By treating the Zeolite with cationic surfactant like HDTMA, an organic coating is made on the surface of zeolite. [6] These surfaces have hydrophobic properties. Anionic pollutants are retained at the surface because of the opposite charge whereas non-polar organic pollutants present in waste water partition into the surfactant coating. [7] The initial concentration used by Fungaro et.al. (2000) exceeds the critical micelle concentration of the surfactant. [4] It has been found that colour removal efficiency increases when the waste water samples are diluted with de-ionized water and it is maximum at 95% dilution. This fact indicated that adsorption onto modified zeolite may be included as the tertiary step of waste water treatment. [8].This technique is not very successful for removal of color at industrial level. 2. Adsorption Technology- Significant work has been reported on the problem of colour removal from pulp and paper mill wastes at global level with the help of adsorption materials. Activated carbon, silica, saw dust, fly ash and many bio-adsorbents have been used for the removal of colour but the problem of cost and handling has always been of great concern. It has been reported by Yadav et.al (2012) that out of all these, activated carbon is found to be more stable to dilute acids and bases and more over more than 95% colour removal can be done with activated carbon. The percentage removal increases with increase in adsorbent doses and with decrease in particle size of adsorbent material. [9] But, as the initial conc. of adsorbate pollutants increases, the adsorption process slows down and hence efficiency of colour removal decreases because total adsorption sites available on the adsorbent are limited. So, the process is not very suitable for removal of color at industrial level. 211 Amandeep Kaur and Sangeeta Sharma

3 The bagasse fly ash, obtained from the sugar industry has been found to be good adsorbent for removal of colour from pulp and paper mill effluent. Various variables like contact time, initial concentration, size of particles, dose of adsorbents etc affect the efficiency of colour removal. It has been reported by Jain et.al (2009) that 86% of colour removal has been done with fly ash having contact time for 60 min.,at dosage of 2g/L of bagasse fly ash. [10].This method is very effective at the bench scale but complete mixing of ash with effluent at low conc. which is must for colour removal is not possible on the industrial scale. 3. Advanced Oxidative method- No doubt decolourization can be achieved by adsorption processes but complete degradation of these coloured imparting compounds is not possible. So, chemical treatment has been investigated for these non degradable compounds which get decomposed into simpler ones. Among chemical treatment, advanced oxidation process is one of the novel method used to treat paper pulp effluents [11] where, high reaction rate of these oxidation reactions degrade complex compounds into simpler ones that can be removed afterwards in post treatment processes. Chemical oxidation method includes the application of ozone, hydrogen peroxide,tio 2,Fenton s reagent etc to remove colour from waste water stream. Ozone and H 2 O 2 combination is found to be more effective rather than when they are used alone. But, Fenton s reagent is one of the good degrading agent for pulp and paper mill effluents as it has been found that colour removal efficiency is best achieved with the use of Fenton reagent [12]. Moreover, Fenton s oxidation process is less costly as compared with ozone and H 2 O 2. The colour removal efficiency comes out to be 80% with Fenton s reagent whereas with other reagents it was found to be nearly 70%. This method is quite effective if used along with biological treatment of waste water. 4. Decolorization by electro coagulation Electro-coagulation is one of the advanced oxidation process, [13] offering high removal efficiencies of colour, chemical oxygen demand, biochemical oxygen demand. It is basically the generation of coagulants via an electrolysis process. Electric current is applied to the metal plates of the required coagulant (usually iron or aluminium electrodes), as a result metal ions are released from the anodic site into the aqueous solution and hydrogen gas is liberated at the cathodic site. [14] These hydrogen gas bubbles takes the pollutant at the top of the solution so that they can be collected and removed easily. The following chemical reactions takes place using Al electrodes. 212 Amandeep Kaur and Sangeeta Sharma

4 Anode- Al (s) Al 3+ ( aq ) + 3e - Cathode- 3H 2 O +3e /2 H 2 (g) + 3OH - Overall reaction- Al +3 (aq) + 3OH Al(OH) 3 The production of Al(OH) 3 with large surface area is helpful for adsorption of soluble organic pollutants and trapping of colloidal particles and hence colour reduction. [15] Deepak Sharma(2014) reported that decolorisation was found to be increased with increase in sodium chloride conc.,current density and impeller rotational speed. About 92% color removal takes place at initial ph of 7, current density 25mA/cm 2,rotational speed of 100 rpm, NaCl conc. of 1g/1L and electrpolysis time of 60 minutes. The main advantages of this technology over some other methods are that, there is no generation of secondary pollutants, no additional coagulants are required for the process to be carried out. Moreover, time consumption is less. [16]. Although EC is a successful method to treat wide range of waste water but its full potential as a waste water treatment is yet to be explored. It requires more fundamental knowledge of engineering design. Conclusion All the above said techniques for the removal of color from pulp and paper industry are quite effective at bench scale but at industrial level where the conc. of pollutants is high, these methods do not work well. More work is to be done to formulate a viable method to remove coloured pollutants from pulp and paper mill effluents at industrial level as tertiary treatment. References 1. T Fukuzum, Microbial decolourization and defoaming of pulping waste liquors; In: Kirk TK, Chang HM, Higuchi T, editors. Lignin biodegradation: microbiology, chemistry and potential application, vol. 2, pp , 1980.,CRC Press,USA 2. P. Bajpai, A Mehna, PK Bajpai, Decolourization of kraft bleach plant effluent with the white rot fungus Teammates versicolor Process Biochem., vol.28, pp , R. Ragunathan, K. Swaninathan, Biological treatment of pulp and paper industry effluent by Pleurotus sp,. World J of Micro and Biotech., vol. 20, pp , Fungaro, Denise Alves, Borrely, Suelilvone, Higa Marcela, Perrodico Tche Ouimica, vol. 11, no. 22, pp. 7-14, P. Cunico, D.A. Fungaro, C.P. Magdalena, Tche Quimica, vol. 8, no. 17, D.A.Fungaro, C.P. Magdalena, Environment and Ecology Research vol. 2, no. 97, S.K. Ghadiri, R. Nabizadeh, A.H. Mahvi, S. Nasseri, H. Kazemian, A.R. Mesadaghinia, Sh. Nazmara, Iranian J Environ. Health Sci. Engineer. Vol. 7, pp.241, Amandeep Kaur and Sangeeta Sharma

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