Sukanchan Palit1,2
1Consultant, 43, Judges Bagan, Post-office-Haridevpur, Kolkata-700082, India
2Associate Professor, Chemical Engineering, Rural Engineering College, Bhalki, Bidar District, Karnataka, India
Corresponding author: sukanchan68@gmail.com, sukanchan07@yahoo.com
ABSTRACT:
Conventional and traditional textile wastewater treatment processes is a challenge to environmental engineers and environmental scientists because of the restrictions on effluent quality by the environmental pollution authorities. Conventional degradation techniques have a disadvantage since 53% of 87 colours are identified as non-biodegradable. Besides dyes cannot be degraded by primary and secondary treatments. Primary treatment involves coagulation and flocculation while secondary treatment involves activated sludge process. Both of these treatments do not successfully degrade textile dyes. So the need for tertiary treatment process-advanced oxidation process such as ozonation. Bubble column reactor is an effective alternative to the environmental pollution problem. The present vision is to present effectively the importance of bubble column reactor and ozonation of dyes as the reaction medium in it.
KEY WORDS: bubble, reaction, dyes, ozonation, ph
The effluent from textile industries is a serious concern to the human being particularly to the environmentalist. The effluent contains a large variety of dyes and chemicals which is non degradable and a challenge for the textile industry. The major pollution in textile wastewater comes from dyeing and finishing processes. These processes involve the input and application of complex organic compounds. So their degradation is very difficult. So the scientific endeavour towards advanced oxidation processes which includes ozonation, H2O2/UV, O3/UV, O3/ H2O2, O3/ H2O2/UV. The major concern is that only 47% of 87 of dyestuff are biodegradable. From literature it has been seen that the residual colour is usually due to insoluble dyes which have low biodegradability as reactive blue 21, direct blue 80 and vat violet with COD/ BOD ratio of 59.0,17.7 and 10.8 respectively. These are the difficulties in the conventional oxidation treatments of dyestuffs used in textile industry. In order to ease the concept, advanced oxidation processes(AOP’s) have been developed to generate hydroxyl free radicals by different techniques. AOP’s are combination of ozone (O3), hydrogen peroxide (H2O2) and UV irradiation which showed the greatest potential to treat and degrade textile wastewaters.
2.0 ADVANCED OXIDATION PROCESS (AOP’s):
The goal and purpose of any AOP’s design is to generate and apply hydroxyl free radical (HO’) as strong oxidant to destroy compound that cannot be oxidized by conventional oxidant. The goal and vision of advanced oxidation processes is radicals and the effectivity-selectivity of attack which is a useful positive side for an oxidant. AOP is very much versatile and intensive scientific endeavour since they provide possible and different ways for OH’ radicals. Generation and production of HO’ is commonly accelerated by combining O3, H2O2, TiO2, UV radiation, electron-beam irradiation and ultrasound. Of these avenues, O3/ H2O2, O3/UV and H2O2/UV hold the greatest potential to oxidize textile wastewater.
3.0 Bubble column reactors and its efficacy:
Bubble column reactors belong to the general class of multiphase reactors which consist of three main categories namely, the trickle bed reactor (fixed or packed bed), fluidized bed reactor and the bubble column reactor. A bubble column reactor is basically and primarily a cylindrical vessel with a gas distributor at the bottom. The gas is sparged in the form of bubbles into either a liquid phase or a liquid-solid suspension. When a solid phase exists, these reactors are generally referred to as slurry bubble column reactors. Bubble column reactors are primarily used in chemical processes involving reactions such as oxidation, chlorination, alkylation, polymerization and hydrogenation, in the manufacture of synthetic fuels by gas conversion processes and in biochemical processes such as fermentation and biological effluent treatment. Bubble column reactors have excellent heat and mass transfer characteristics, meaning high heat and mass transfer coefficients. Other characteristics are little maintenance and low operating costs due to lack of moving parts and compactness.
Table 1:Composite textile industry wastewater characteristics:
|
Parameters |
Values |
|
pH |
7.0-9.0 |
|
Biochemical Oxygen Demand(mg/L) |
80-6000 |
|
Chemical Oxygen Demand(mg/L) |
150-12,000 |
|
Total Suspended Solids(mg/L) |
15-8000 |
|
Total Dissolved Solids(mg/L) |
2900-3100 |
|
Chloride(mg/L) |
1000-1600 |
|
Total Kjeldahl Nitrogen(mg/L) |
70-80 |
|
Colour(Pt-Co) |
50-2500 |
The major concern is that BOD/COD ratio of the composite textile wastewater is around 0.25 which implies that the wastewater contains large amount of non-biodegradable organic matter.
4.0 Advanced Oxidation Technologies and its importance:
The appearance of compounds that are difficult to degrade by conventional chemical and/or biological methods (toxic, mutagenic, carcinogenic pollutants) in natural waters recently created a pressing need for the development of efficient water treatment processes. The search for a solution to this problem has involved extensive examinations in the field of advanced oxidation (AOP’s). In chemical oxidation processes, reaction mechanisms change structure, and chemical properties of the organic substances. Molecules break in smaller fragments; higher percent of oxygen appears in these molecules in form of alcohols, carboxylic acids etc. Oxidation of organic compounds with oxidation such as ozone or OH’ radicals usually yields more oxidized ones which are in most cases more easily biodegradable than the former ones. This is the general idea that yields to the combination of a chemical oxidation processes. Oxidation with ozone or hydrogen peroxide has been found to be an alternative to chlorination, because the oxidation does not result in toxic chlorinated organic compounds. Advanced Oxidation Technologies (AOTs) including Advanced Oxidation Process (AOPs) and other physicochemical methods which are:
1) Advanced Oxidation Process (AOP’s)
2) Non-thermal Plasmas (NTP) for air and wastewater treatment
3) Electrohydraulic cavitation and sonolysis.
5.0 Review of research work done in the domain of ozonation (advanced oxidation processes) of dye:
Sarasa et al (1998)1 delineated the treatment of a wastewater resulting from dyes manufacturing with ozone and chemical coagulation. The degradation of the compounds present in a previously chlorinated wastewater resulting from the production of azoic dyes has been studied in this project. Towards this end, the first step developed was the characterization of the spillage water by GC/MS and GC/FID. Secondly, a combined ozone+Ca(OH)2 treatment was carried out, determining its efficiency on this wastewater. Chu et al (2000)2 dealt with the advanced oxidation process of ozonation of dye and its kinetics. A quantitative estimation of direct ozonation and indirect free radical oxidation of dyes with assorted chromophores was studied through the examination of reaction kinetics in the ozonation procedure. The reaction kinetics of dye ozonation under different conditions was determined by adjusting the ozone doses, dye concentration and reaction pH. According to their research, the ozonation of dyes was found dominant by pseudo-first order reaction and the rate constants decreased as the dye/ozone ratio increased. They made a quantitative prediction of direct and indirect dye ozonation kinetics. In 2001 Ciardelli et al (2001)3 studied on the treatment and reuse of wastewater in the textile industry by means of ozonation and electroflocculation. Two different oxidation treatments,ozonation and electroflocculation ,were experimented on a pilot scale to test their efficiency in removing polluting substances from wastewaters of textile industries. Both pilot plants used reproduced very closely a full –scale treatment in order to obtain indications about the feasibility of a transfer on industrial scale.By means of ozone treatment very high colour removal (95-99%) was achieved and treated waters were reused satisfactorily in dyeing even with light colours. Talarposhti et al (2001)4 delineated on the topic of colour removal from a simulated dye wastewater using a two-phase anaerobic packed bed reactor. According to them, the treatment alternatives applicable for the removal of colour vary, depending upon the type of dye wastewater. A synthetic ,simulated mixed dye waste(Basuc Yellow 28,Basic Yellow 21,Basic Red 18.1, Basic Violet Red 16,Basic Red 46,Basic Blue 16, Basic Blue 41) representing a known waste from a fibre production factory, was investigated. The biological process of anaerobic digestion has been recognised as a simple and energy-efficient means of treating and stabilising a wide range of organic industrial wastewaters. Their study sets out to demonstrate the effect of different loading rates, dye concentrations and hydraulic retention times (HRTs) on colour removal efficiency under mesophilic anaerobic conditions. Wu et al (2001)5 studied the ozonation of aqueous azo dye in a semi-batch reactor. Results showed that the rate of ozone transfer increased with increases in the initial dye concentration, the applied ozone dose and temperature. A model was developed to predict the enhancement factor of ozone mass transfer. This model which they developed enables the prediction of mass transfer coefficient of ozone from the following parameters: initial dye concentration, applied ozone dose, temperature and concentration of dissolved in the organic-free water. The present model was also valid for reactors of larger sizes. The results of kinetic studies showed that ozonation of the azo dye was a pseudo-first-order reaction with respect of dye. The apparent rate constant increased with the applied ozone dose and temperature. In addition, ozonation reduced chemical oxygen demand and enhanced the biodegradability of the wastewater. In 2002, Chen6 et al devised a dynamic model of ozone contacting process with oxygen mass transfer in bubble columns. The dynamic process of the dissolution of ozone in a counter current bubble column is studied for model establishment. Sevimli et al (2002)7 studied the ozone treatment of textile effluents and dyes projecting the effect of applied ozone dose, pH and dye concentration. The ozonation of wastewater supplied from a treatment plant(Samples A and B) and dye-bath effluent (Sample C) from a dyeing and finishing mill and acid dye solutions in a semi-batch reactor has been examined to explore the impact of ozone dose ,pH and initial dye concentration. Results revealed that the apparent rate constants were raised with increases in applied ozone dose and pH, and decreases in initial dye concentration. While the colour removal efficiencies of both wastewater Samples A and C for 15 min ozonation at high ozone dosage were 95 and 97 % respectively, these were 81 and 87% respectively at low ozone dosage. n 2002,Koch8 et al delineated the ozonation of hydrolyzed azo dye reactive yellow 84(CI).The combination of chemical and biological water treatment processes is a promising technique to reduce recalcitrant wastewater loads. The yardsticks to the efficiency of such a system is a better understanding of the mechanisms involved during the degradation process. According to a conclusion of their research, for textile mill effluents, ozonation can achieve high colour removal, enhance biodegradability, destroy phenols and reduce the chemical oxygen demand(COD).Their work deals with the degradation of hydrolyzed Reactive Yellow 84(colour index),a widely used azo dye in textile finishing processes with two monochlorotriazine anchor groups. The ozonation of the hydrolyzed dye in ultra pure water was performed in a laboratory scale cylindrical batch reactor. Rittman et al(2002)9 did pilot studies and interpreted models from the treatment of a coloured groundwater by ozone-biofiltration. Pilot studies investigated the fates of colour, dissolved organic carbon (DOC), and biodegradable organic matter(BOM) by the tandem of ozone plus bio filtration for treating a source water having significant colour(50 cu) and DOC93.2mg/l).Transferred ozone doses were from 1.0 to 1.8 g O3/g C. Rapid bio filters used sand, anthracite or granular activated carbon as media with empty-bed contact time(EBCT) up to 9 minutes. The pilot studies demonstrated that ozonation plus bio filtration removed most colour and substantial DOC and increasing the transferred ozone dose enhanced the removals. A. H. Konsowa (2003)10 investigated the decolorization of wastewater containing direct dye by ozonation in a batch bubble column reactor. Their study comprises decolorization of wastewater containing direct dye (Isma Fast Red 8B) by ozonation and envisioned in an attempt to abate pollution caused by textile dyeing houses and dye-producing plants. The decolorization process of the direct dye was carried out by bubbling ozone at the bottom of a bubble column reactor containing the dye solution. The effect of dye concentration, ozone dose, ozone air flow rate and solution pH on the rate of decolorization was studied11,12,13.
6.0 Vision of ozonation and advanced oxidation process:
Both ozonation and advanced oxidation processes are path breaking domains of environmental engineering and environmental science. It can create wonders in the field of environmental chemistry. Man’s as well a scientist’s vision is expanded and widened with continuous research pursuits. This branch of environmental science will open up new frontiers of innovation and research.
7.0 ACKNOWLEDGEMENT:
I acknowledge Principal of Rural Engineering College, Bhalki, Dr. B.B. Lal and is indebted to his help. I am also grateful to Dr. Bhaskar Sengupta, Faculty, Queen’s University, Belfast, United Kingdom under whose guidance I did research work in the field of ozonation of dye.
8.0 REFERENCE:
1. Sarasa .J., Roche .M.P., Ormad. M.P., Gimeno. E., Puig A., Ovelleiro. J.L.,(1998)Treatment of a wastewater resulting from dyes manufacturing with ozone and chemical coagulation, Water Research, Vol. 32, No.9
2. Chu. W., Ma. C.W. (2000) Quantitative prediction of direct and indirect dye ozonation kinetics, Water Research,Vol.34,No.12
3. Ciardelli. G., Ranieri. N., (2001) The treatment and reuse of wastewater in the textile industry by means of ozonation and electroflocculation, Water Research,Vol.35,No.2
4. Talarposhti A., Donnelly. T., Anderson. G.K.,(2001)Colour removal from a simulated dye wastewater using a two-phase anaerobic packed bed reactor, Water Research,Vol.35,No.2
5. Wu.J., Wang .T.,(2001) Ozonation of aqueous azo dye in a semi-batch reactor, Water Research , Vol.35,No.4
6. Chen. Y.H., Chang C.Y., Chiu C.Y., Huang W.H., Yu.Y.H., Chiang P.C.,Ku .Y., Chen .J.N.,(2002)Dynamic model of ozone contacting process with oxygen mass transfer in bubble columns, Journal of Environmental Engineering,Vol.128,No.11
7. Sevimli.M.F., Hasan. Z.S.,(2002)Ozone treatment of textile effluents and dyes: effect of applied ozone dose, pH and dye concentration, Journal of Chemical Technology & Biotechnology,Vol.77,Issue 7
8. Koch. M., Yediler.A., Lienert. D., Insel G., Kettrup. A.,(2002) Ozonation of hydrolyzed azo dye reactive yellow 84(CI),Chemosphere,46
9. Rittman. B.R., Stilwell D., Garside .J.C., Amy .G.L., Spagenberg, Kalinsky. A., Akiyoshi, E. (2002)Treatment of a colored groundwater by ozone-biofiltration: pilot studies and modelling interpretation., Water Research,Vol.36
10. Konsowa.A.H.(2003) Decolorization of wastewater containing direct dye by ozonation in a batch bubble column reactor,Desalination,Vol.158
11. Palit Sukanchan,(2010) Studies on Ozone-oxidation of Dye in a bubble column reactor at different pH and different oxidation-reduction potential, International Journal of Environmental Science and Development, Vol. 1, No.4, October,2010
12. Palit Sukanchan(2009) Ozonation of Direct Red – 23 dye in a fixed bed batch bubble column reactor, Indian Journal of Science and Technology, Vol.2 , No.10,Oct,2009.
13. Palit Sukanchan(2011)Ozonation associated with nanofiltration as an effective procedure in treating dye effluents from textile industries with the help of a bubble column: A review, International Journal of Chemistry and Chemical Engineering, Vol 1, Number 1(2011) pp 53-60
Received on 31.12.2011 Modified on 06.01.2012
Accepted on 12.01.2012 © AJRC All right reserved
Asian J. Research Chem. 5(2): February 2012; Page 161-163