Advanced Oxidation Processes for the Treatment of Surfactant Wastes

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1 J. Chem. Eng. Chem. Res. Vol. 1, No. 3, 2014, pp Received: June 19, 2014; Published: September 25, 2014 Journal of Chemical Engineering and Chemistry Research Advanced Oxidation Processes for the Treatment of Surfactant Wastes S. Chitra, K. Paramasivan, A.G. Shanmugamani, S.V.S. Rao and Biplob Paul Centralised Waste Management Facility, Nuclear Recycle Board, Bhabha Atomic Research Centre, Kalpakkam , India Corresponding author: S. Chitra Abstract: Advanced Oxidation Processes (AOP) using ozone, H 2 O 2, ultrasound (US), ultraviolet radiation (UV), Fenton s reagent (FeII+H 2 O 2 ) alone or in combination involving hydroxyl radicals are considered as possible methods of clean and ecologically safe remedial treatment for the degradation of organics. In the present study, comparison of kinetics of photochemical, sonochemical and chemical oxidation of 1,000 mg/l of surfactant sodium dodecyl sulpahte (SDS) and a commercial detergent used for decontamination at Centralized Waste Management Facility, Kalpakkam using combination of processes viz., sunlight + FeII + H 2 O 2, UV (15W) + FeII + H 2 O 2, US (130KHz) + FeII + H 2 O 2 and FeII + H 2 O 2 at ph 3.0 was investigated and compared. The surfactant concentration during the course of the degradation was monitored by Methylene Blue Active Substance (MBAS) method. The kinetics of degradation of SDS was much faster than the commercial detergent in all the processes. The rate of degradation in all the processes followed a first order reaction. The photochemical, sonochemical and chemical oxidation yielded complete degradation of surfactant and the rate of degradation of the surfactants follow the order Sunlight + FeII + H 2 O 2 UV (15W) + FeII + H 2 O 2 US (130 KHz) + FeII + H 2 O 2 FeII + H 2 O 2. Both visible and UV light in the solar spectrum were utilized efficiently for the degradation of surfactants. From the observed ph changes during the degradation formation of acidic intermediates is suspected. Key words: Advanced Oxidation Process (AOP), Fenton s reagent, sodium dodecyl sulphate, commercial detergent. 1. Introduction At Centralized Waste Management Facility (CWMF), Kalpakkam detergent bearing wastes are generated during the decontamination of personnel protective wears and contaminated materials. These wastes are generally mixed with beta-gamma wastes and are subjected to chemical treatment process by addition of 20 ppm of Cu +2, 30 ppm of Fe(CN) 4-6, 50 ppm of Fe +3, 150 ppm Ca +2 and 260 ppm PO 3-4 at ph 9.5 for removal of activity [1]. The removal of activity is expressed as decontamination factor (DF) which is a ratio of the specific activity of the effluent before and after treatment. Many of the detergents used in the domestic and industrial laundry operations contain 5-30% of anionic-based surfactants such as sodium dodecyl sulphate (SDS) and linear alkyl benzene sulphonate (LAS) usually in mixtures consisting basically of five homologues from C 10 LAS to C 17 LAS, each one containing several phenyl positional isomers (26 in total internal and external). Besides it, 3-8% DATs (dialkyl tetralin sulphonates) and 3-6% iso-las (isomers with a methyl group branched to the linear aliphatic chain) may also be present in such a mix [2]. However, these surfactants present in these detergent bearing wastes interferes in the chemical treatment processes reducing the DF and hence it calls for a pre-treatment step of removal surfactants to render the radioactive liquid waste amenable for treatment [3]. It is not unusual then to find high concentrations of LAS in industrial wastewaters [4]. It has been reported that higher concentrations of these surfactants are not biodegradable [5]. Commonly, physico-chemical processes of treatment are considered to be less environmentally friendly,

2 164 Advanced Oxidation Processes for the Treatment of Surfactant Wastes costly, generate large volumes of chemical sludge and often requiring a pre-dilution of the detergent bearing wastewater to be treated [6]. As a consequence, techniques suitable for destruction of surfactant are needed to render the liquid waste amenable to treatment and thus protect the environment. In light of the increasing concern over the contamination of the environment by hazardous chemicals, there is a great need to develop innovative technologies for the safe destruction of toxic pollutants. The processes must be cost effective, easy to operate, and capable of achieving a total or near-total mineralization. Advanced Oxidation Processes (AOP) involving hydroxyl radicals, which are one of the strongest inorganic oxidants next to elemental fluorine, have been extremely effective in the destruction of organic pollutants. These advanced oxidation process (AOP) generally use a combination of oxidation agents (such as H 2 O 2 or O 3 ), irradiation (such as UV or ultrasound), catalysts (such as metal ions or photo catalysts) and radiolysis (such as gamma irradiation or electron beam) as a means to generate hydroxyl radicals. The reason that H 2 O 2 can be used for such diverse applications is the different ways in which its selectivity can function. H 2 O 2 has none of the problems of gaseous release or chemical residues that are associated with other chemical oxidants. By simply adjusting the conditions of the reaction (e.g., ph, temperature, dose, reaction time, and/or catalyst addition), H 2 O 2 can often be made to oxidize one pollutant over another, or even to favor different oxidation products from the same pollutant [7-9]. The degradation of surfactant has been attempted by ozonation [10], UV + Fenton s reagent (FeII + H 2 O 2 ) and UV + H 2 O 2 [11], heterogeneous and homogeneous phototchemcial reactions [12-14], ultrasonic irradiation [15, 16], combined sonochemical and photochemical techniques [17] with variable results. Extensive studies on the Photo-Fenton and TiO 2 - mediated photocatalytic degradation of several surfactants using solar energy has been reported [18-20]. Previous studies [14, 6-21] reveal information on the different advanced oxidation processes for the degradation of SDS and LAS at concentration levels of 1,000 mg/l-1,600mg/l. Most of the reports about surfactant degradation are related to pure surfactants like SDS, LAS namely Sodium Dodecyl Benzene Sulphonate (SDBS) but very few reports are available on the degradation of mixtures of surfactants present in the commercial detergent products which are discharged into wastewaters. It is a well known advantage of AOPs which has also been demonstrated that even a partial mineralization of the organic leads to organic products which enhances its biodegradability in the aqueous phase [22, 23]. Our previous studies also confirmed that there was a tremendous improvement in DF (from 5 to 40) where AOPs were used as a pre-treatment step to degrade the organic viz., EDTA followed by a chemical treatment step for a typical radioactive waste which was received at CWMF [1]. From Table 1 which depicts the studies on interference of surfactants in treatment of detergent bearing radioactive wastes carried out at CWMF it was observed that there was decrease in the removal of activity at surfactant concentration of 1,000 ppm and above and there was also increase in time of settling of the chemical precipitate during treatment. Based on the above observations the present study, without taking into consideration the formation of degradation intermediates, a comparison of kinetics of degradation of 1,000 mg/l commercial detergent used in CWMF and a pure surfactant sodium dodecyl sulphate (SDS) was carried out using stoichiometric quantities of H 2 O 2 (30% w/v) in all the experiments viz., sunlight + (FeII + H 2 O 2 ), UV (15 W) + (FeII + H 2 O 2 ), FeII + H 2 O 2, US (130 KHz) + FeII + H 2 O 2. The feasibility of application of the above mentioned AOPs was also explored. 2. Materials and Methods

3 Advanced Oxidation Processes for the Treatment of Surfactant Wastes Experimental Setup and Materials The photoreactor was a glass trough (Borosil) with inside dimensions of mm deep. A UV lamp (15W with λ max = nm) was positioned horizontally over the reactor. The distance of the UV lamp from the surface of the sample was maintained at 70 mm. The set-up was housed inside a fume hood. For the experiments carried out using UV lamp (15 W), a cover was used to house the glass trough to control the UV radiation. For the experiments on photodegradation using sunlight (λ in the range of nm), a beaker containing surfactant, FeII and H 2 O 2 was kept directly in open under sunlight. The ph value of the solution for the photo-fenton processes was adjusted using H 2 SO 4 solution. Fig. 1 depicts a typical spectrum of solar radiation. The light intensity inside the reacting medium was measured by potassium ferrioxalate actinometry. The light intensity during the experiments using solar radiation was 1.2E-2 einsteins/cm 2 and using UV (15 W λ max = nm) was 3.5E-3 einsteins/cm 2. Sonication experiments were performed in an ultrasonic cleaning bath of frequency 130 KHz ELMA Transsonic industrial table top model T1-H-20-MF of power 300 W. The reactions were carried out in a one-liter beaker which was closed during ultrasonic irradiation. The beaker was placed inside the ultrasonic bath. In addition to the above-mentioned instrumentation, a standard ph meter was used. Table 1 Interference of surfactant in the chemical treatment of radioactive waste. Specific Activity Time taken for Concentration of after chemical Sl.No. settling of surfactant (ppm) treatment precipitate (hrs) (Bq/mL) > 8 Characteristics of the radioactive waste: ph-9.04, Total Dissolved salts: 1,365 mg/l, Initial specific activity (β-γ) Bq/mL. Fig. 1 A typical solar spectrum. During the studies on interference of surfactants in treatment of detergent bearing radioactive wastes, the estimation of gross beta-gamma specific activity in the supernatant was carried using GM counter. All the chemicals viz., sodium dodecyl sulphate salt, hydrogen peroxide (30% w/v), FeSO 4, was obtained from E-Merck analytical grade of 99.9% purity. The commercial detergent used at CWMF during decontamination was taken as such. The chemical composition of the commercial detergent was viz., surfactant 20-30%, complexing agent EDTA- 20% was determined in the laboratory and the remaining constituted viz., bleaching agent, perfumes, whitening agent etc [24]. 2.2 Degradation Procedures By stoichiometric calculations, 35 moles of H 2 O 2 are required to completely oxidize 1 mol of SLS to CO 2, SO 2, and H 2 O. The balanced stoichiometric equation is as follows: C 12 H 25 OSO 3 Na + 35 H 2 O 2 12CO 2 + SO H 2 O + NaOH (1) To 95 ml of 1,000 mg/l surfactant solution taken in the photoreactor, 0.001% (w/v) of Fe +2 was added and mixed thoroughly before the addition of 5 ml H 2 O 2 (30% w/v). The concentration of Fe +2 used in these experiments was optimized during preliminary studies in the laboratory.

4 166 Advanced Oxidation Processes for the Treatment of Surfactant Wastes The time at which the UV lamp/us system was turned on was considered time zero or the beginning of the experiment. During analysis the evaporation loss was calculated by measuring the volume before and after the reaction at every time interval and was taken into consideration. 2.3 Analytical Methods The ph of the solution was measured using a calibrated pocket ph meter (HACH) at appropriate time intervals. One drop of hydrazine was also added to prevent H 2 O 2 from reacting with organic substrates during the analysis. The surfactant concentration was determined by Methylene Blue Active Substance (MBAS) method. The intensity of the blue coloured complex is measured colorimetrically at 652 nm [25]. The hydrogen peroxide was measured by the standard iodometric titration [26]. The EDTA present in the samples was analysed titrimetrically against standard Mg +2 using Eriochrome Black T as indicator. At least triplicate runs were carried out for each condition averaging the results. The variations were systematically within ±10% of the stated values Results and Discussion 3.1 Fenton and Photo-Fenton Processes Figs. 2-4 illustrate the comparison of percent degradation of 1,000 mg/l of the commercial detergent used in the CWMF and sodium dodecyl sulphate (SDS) as a function of time using FeII + H 2 O 2 alone, UV (15 W) + FeII + H 2 O 2 and sunlight + FeII + H 2 O 2. It can be observed that there was complete degradation of SDS and the commercial detergent at 23 hours and 42 hours, 1 hour and 2 hours, 0.5 hour and 1.25 hours, for the samples treated with Fenton reagent alone, UV(15 W) + Fenton s reagent, sunlight + Fenton s reagent respectively. In the case of the samples treated with Fenton s reagent alone, the reaction is mainly catalytic effect of ferrous salt. From Eq. (2) Fe 2+ + H 2 O 2 Fe +3 + OH - + OH. (2) (k 1 = 58 mol -1 dm 3 s -1 ) and Eq. (3), Fe 3+ + H 2 O 2 Fe 2+ + HO 2 +H + (3) (k 2 = 0.02 mol -1 dm 3 s -1 ) % degradation SDS Commercial detergent Fig. 2 Time (hrs) Degradation of surfactant (1,000 mg/l) using Fenton s reagent.

5 Advanced Oxidation Processes for the Treatment of Surfactant Wastes % degradation SDS Commercial detergent Fig. 3 Time (hrs) Degradation of surfactant (1,000 mg/l) using UV(15W) + Fenton s reagent % degradation SDS Commercial detergent Fig. 4 Time (hrs) Degradation of surfactant (1,000 mg/l) using sunlight + Fenton s reagent. It is apparent that the decomposition of H 2 O 2 by iron ions is through the interaction between Fe +2 and Fe +3. Because the reaction rate of Eq. (2) was faster than that of Eq. (3), Fe +2 was rapidly oxidized to Fe +3 in the reaction process. Therefore the concentration of hydroxyl radical in the solution rapidly increased and

6 168 Advanced Oxidation Processes for the Treatment of Surfactant Wastes could oxidize the surfactant. From Eq. (3) Fe 3+ + HO 2 Fe 2+ +O 2 +H + (3) It could be seen that there was slow regeneration of Fe +2 from the reduction of Fe +3. It can be due to non-chain reactions of Fenton s oxidations in which all the oxidation is affected by the hydroxyl radical and there is considerable loss of the hydroxyl radical due to the following reaction [27]. Fe 2+ + OH (Fe-OH) 2+ (4) Hence, the rate of complete degradation of surfactant using Fenton s reagent alone is much slower than the other processes. The rate of degradation of surfactant using UV (15 W) + FeII + H 2 O 2 was 23 times faster than that in the system using FeII + H 2 O 2 alone. In combination of thermal process and UV irradiation, the oxidation power of Fenton s reagent was significantly increased mainly due to photo-reduction of Fe +3 to Fe +2, which could react with H 2 O 2 establishing a cycle mechanism of generating additional hydroxyl radicals which is shown by Eq. (5) [28]. Fe +3 + H 2 O 2 + h OH + Fe +2 + H + (5) The temperature of the reaction process was found to vary from C. Furthermore, the effect of UV light also attributed to the direct hydroxyl radical formation and regeneration of Fe +2 from the photolysis of the complex Fe(OH) 2+ in solution Eq. (6). Fe(OH) +2 + h OH + Fe +2 (6) From the simultaneous application of UV and Fenton s reagent there is considerable synergistic effect on the rate of surfactant degradation. Hence, higher degradation rate of surfactant was observed in the UV (15 W) + FeII + H 2 O 2 system. The kinetics of degradation of the surfactant using sunlight + (FeII + H 2 O 2 ) was the fastest when compared to the systems viz., FeII + H 2 O 2, UV (15 W) + (FeII + H 2 O 2 ), US (130 KHz) + FeII + H 2 O 2 which is in agreement with the results obtained later [4, 2, 29]. The rate of degradation of surfactant using the system sunlight + (FeII + H 2 O 2 ) was 46 times faster than the system using FeII+H 2 O 2 alone. Both visible and UV light in the solar spectrum were utilized efficiently for the degradation of surfactants. Recently it has been proved that the irradiation of Fe(III) + H 2 O 2, also called Fenton-like reactions, enhances the rate of oxidant production through the involvement of high valence Fe intermediates responsible for direct attack to organic matter [30, 31]. Absorption of visible light upto 550 nm [31, 32] by the complex formed between Fe(III) and H 2 O 2 seems to be the cause of formation of such high valence Fe-based oxidants. Another important reason is the photoexcitation of complexes formed between Fe(III) and organic matter, in particular carboxylic acids, a functional group that is always present along mineralization processes of low oxidation state organics. The molar absorption coefficients of such complexes and the quantum yields of their reaction of photolysis are even larger than the values corresponding to the excitation and photolysis of the Fe(III) aquo complexes [30]. The Fe(III) complexes of the carboxylic acids that absorb in the UV-VIS range are through a ligand to metal charge transfer (LMCT) reaction Eq.(7) yielding Fe +2 and OH with good quantum yield even in the absence of H 2 O 2 [33]. Fe(III) (RCO 2 ) 2 + hυ Fe(II) + CO 2 + R (7) In addition to the above auto-oxidation in the presence of Fe(III) through Eqs. (8-9) or other oxidative pathways can also take place. R + O 2 ROO oxygenated products (8) Fe 2+ + OH (9) This is true with the surfactant mineralization where formation of carboxylate intermediates is there before formation of carbon-di-oxide and water [34]. The formation of acidic intermediates using HPLC techniques has been identified during the degradation of LAS with initial concentration 1,000 mg/l [6]. Hence, kinetics of degradation of surfactants using sunlight + (FeII + H 2 O 2 ) was fastest when compared to FeII+H 2 O 2 and UV (15 W) + FeII + H 2 O 2 reagent. This is in conformity with the results reported in

7 Advanced Oxidation Processes for the Treatment of Surfactant Wastes 169 literature [29, 35] which show that among a set of light sources tested for photo-fenton processes, solar light has the largest fraction of photons with the energy needed to drive the photoreactions involved in the reactive system. Owing to the above, the design and the plant treatment for large volumes of decontamination wastes containing surfactants using sunlight is easy, cost effective and safe to operate [4]. 3.2 Sono-Fenton Processes Irradiation by high power ultrasound in a liquid leads to the acoustic cavitation phenomenon, such as the formation, growth and collapse of bubbles, accompanied by the generation of local high temperature, pressure and reactive radical species. This conditions leads to some chemical reactions in three phases: internal cavity, interface boundary layer and the bulk liquid Thermal decomposition may take place in the internal parts of the cavities. The reactions with radicals occur in the interface boundary layer. In wastewater treatment a bubble of cavitation may function as a micro-reactor inside which, the volatile compounds are destroyed. During sonolysis of water and in the presence of oxygen, the cavity may also be 100 considered as source of H, OH, HOO radicals, which have been extremely effective in the destruction of organic pollutants [36]. To enhance the efficiency of degradation, a more effective utilization of OH radicals is desirable. It is expected that addition of Fe(II) + H 2 O 2 will regenerate OH, thus accelerating the rate of degradation and thereby increasing the efficiency of ultrasonic degradation [15]. The time required for complete degradation of 1,000 mg L -1 SDS and commercial detergent using US (130 KHz) + FeII + H 2 O 2 was at 3 hours and 12 hours respectively (Fig. 5). The kinetics of degradation using US (130 KHz) + FeII + H 2 O 2 was faster seven times and twice for SDS and commercial detergent when compared to degradation of SDS and commercial detergent using Fenton s reagent alone respectively. A substance with high hydrophobicity and a high boiling point will be oxidised by OH radical in the interface boundary layer region and in the surrounding bulk liquid. Substances with high hydrophobicity and a low boiling point will enter the cavity and be completely decomposed by combustion or pyrolization. Since the surfactant consists of hydrophilic and hydrophobic % degradation SDS Commercial detergent Time (hrs) Fig. 5 Degradation of surfactant (1,000 mg/l) using US(130 KHz)+Fenton s reagent.

8 170 Advanced Oxidation Processes for the Treatment of Surfactant Wastes groups, the decomposition of the groups may be caused by the oxidation by OH radicals while in the cavity they will be pyrolysed. Hence, the kinetics of degradation using US (130 KHz) + FeII + H 2 O 2 is faster than the degradation using Fenton s reagent alone. Overall it was observed that photochemical degradation favours faster degradation when compared to sonochemical degradation and chemical degradation. In the case of photochemical degradation there was direct exposure of UV radiation onto the reaction medium whereas in the case of sonodegradation there was attenuation of the sound wave by the glass medium. Due to the above the number of cavitation bubbles produced in the reaction vessel may be less. Higher frequency and power of the ultrasound may be helpful in bringing about faster kinetics of degradation [37]. However, in the single processes, the decomposition rate is still insufficient and the surfactant may not be completely mineralized. It is considered that the hydrophilic substances can be decomposed efficiently using photochemical degradation and the hydrophobic substances that are caught in the cavitation bubbles can be decomposed efficiently by ultrasonic irradiation. The synergistic effect of both sonochemical and photochemical degradation can be explored for more effective degradation of surfactants. In general, the kinetics of degradation of organics using advanced oxidation processes is related to the structure of the organic, molecular aggregation and degradation pathway i.e. reaction of OH radicals with the intermediates formed during the degradation [38]. In all the experiments viz., photochemical degradation and chemical degradation of SDS and the commercial detergent there was a change in ph from 3.0 to 2.0 and 8.0 to 4.5 for sonochemical degradation as the reaction proceeded. Since the reaction solution during the degradation processes became acidic in nature formation of acidic intermediates is possible. This observation is in agreement with the results obtained [2, 38] regarding the mechanism of degradation of surfactants that the hydrocarbon moiety in a surfactant is attacked by actively oxidative species to form a hydroxylated compound and a hydroxyperoxide derivatives which are subsequently oxidized to CO 2 via formation of aldehyde or carboxylic acid derivatives. From the above experiments it was also observed that the kinetics of degradation of SDS was much faster than the commercial detergent. In the literature it has been cited that the aromatic moiety in the alkyl benzene sulphonate structure is degraded more rapidly than the alkyl chain [38] and hence the faster kinetics of degradation of commercial detergent is expected. Whereas the results obtained in our study shows faster degradation kinetics for the pure straight chain surfactant SDS than the commercial detergent. The SDS is a linear alkyl sulphate containing only C 12 alkyl chain, whereas the commercial detergent is a linear alkyl benzene sulphonate, which contains a mixture of C 12 -C 17 alkyl groups and also each one containing several phenyl positional isomers (26 in total internal and external). Besides it, 3-8% DATs (dialkyl tetralin sulphonates) and 3-6% iso-las (isomers with a methyl group branched to the linear aliphatic chain) may also be present in such a mix. The influence of structure of the organic compound plays an important role in their mineralisation by OH radicals [39]. In the commercial detergent the different position of the aromatic ring in the isomeric structures decide the ease of oxidation by hydroxyl or hydroperoxyl radicals [2]. Also the initial concentration of the SDS is very close to that of its critical micelle concentration (cmc) i.e., 8mM and that of the commercial detergent is above its cmc values i.e., mol L -1 (554 mg/l) [37] which is another contributing factor towards slow degradation kinetics in the case of the commercial detergent than the pure surfactant. In addition to the above mentioned reasons presence of different kind of organic and inorganic species acting as scavengers can react with OH

9 Advanced Oxidation Processes for the Treatment of Surfactant Wastes 171 radicals which is the reason for the reduced kinetics of the degradation of commercial detergent than the pure surfactant SDS [2]. The presence of other additive ingredients like the optical brighteners, fragrances, bleaching agents present may also interfere with degradation process [21]. Hence, kinetics of degradation of SDS is faster than the kinetics of degradation of commercial detergent. 3.3 Kinetics of Degradation of Surfactant by Fenton, Photo-Fenton and Sono-Fenton Processes The rate of degradation of surfactant viz., SLS and LAS was investigated for the systems Sunlight + FeII + H 2 O 2, UV (15 W) + FeII + H 2 O 2, US (130 KHz) + FeII + H 2 O 2 and FeII + H 2 O 2. The degradation of surfactant was observed as a function of time and the data were fitted to a first-order rate model ln C t /C 0 = - k 0 t (10) where C 0 and C t are the concentration of surfactant at times 0, and t, k 0 is a first order rate constant (hr -1 ) and t is the time (hrs). The rate constants were determined using a first order rate model (Eq. 10). The results are listed in Table 2. The rate of degradation of the surfactants follow the order Sunlight + FeII + H 2 O 2 UV (15 W) + FeII + H 2 O 2 US (130 KHz) + FeII + H 2 O 2 FeII + H 2 O 2 which depicts the effect of UV/US in addition to Fenton s reagent on the kinetics of degradation of surfactants. 4. Conclusion The results from the comparative study on the kinetics of surfactant degradation revealed that the Table 2 Reaction rate constants for the degradation of Surfactant (1,000 mg/l) Type of oxidation process Time (hrs) k 0(hr -1 ) SLS LAS SLS LAS Sunlight+FeII+H 2 O UV(15W)+FeII+H 2 O US(130KHz)+FeII+H 2 O FeII+H 2 O reaction using Sunlight + FeII + H 2 O 2 was faster than that obtained in any of the other processes viz., UV (15 W)+ FeII + H 2 O 2, US (130 KHz) + FeII + H 2 O 2 and FeII + H 2 O 2 respectively. Hence, the design and plant treatment for large volumes of decontamination wastes containing surfactant using sunlight is easy, cost effective and safe to operate. From the ph changes during the oxidation processes, formation of acidic intermediates is suspected. Studies using UV lamp of power greater than 15 W and higher frequency of Ultrasound, might improve the kinetics of degradation of the commercial detergent. The usage of a probe type sonicator could improve the kinetics of degradation than a bath type sonicator. The synergistic effect of both sonochemical and photochemical degradation can be explored for more effective degradation of surfactants. Acknowledgment The authors express their sincere thanks to Mrs. Sharal Sarojini for having assisted in carrying out the experimental work and Sh. TSS Raghavan for technical assistance. References [1] A.G.S. Mani, K. Paramasivan, S. Chitra, P.K. Sinha, K.B. Lal, Ttratment of radioactive liquid waste containing ethylenediamine tetraacetic acid using photo-fenton oxidation as a pre-treatment step, in: Proceedings of the 3 rd Indian Environental Congress, 2004, pp [2] J. Fernandez, J. Riu, E. Garcia-Calvo, A. Rodriguez, A.R. Fernandez-Alba, D. Barcelo, Determination of photodegradation and ozonation by products of linear alkylbenzene sulphonates by liquid chromatography and ion chromatography under controlled laboratory experiments, Talanta 64 (2004) [3] S. Chitra, Sandhya Chandran, P. Sasidhar, K.B. Lal, R.V. Amalraj, Biodegradation of surfactant bearing wastes, Indian J. Environmental Protection 11 (1991) [4] T. Zhang, T. Oyama, S. Horikoshi, J. Zhao, N. Serpone, H. Hidaka, Photocatalytic decomposition of the Sodium Dodecylbenzenesulphonate surfactant in aqueous titania suspensions exposed to highly concentrated solar radiation and effects of additives, Applied Catalysis B: Environmental 42 (2003)

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