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ADVANCED CHEMICAL OXIDATION AND TOXICITY REDUCTION OF 2,4,6-TRICHLOROPHENOL BY USING FENTON'S REAGENT - PART II

Somnath Basu''21 Venkat Sreenivasan2, and Irvine w. Wei2

L Deer Island Treatment Plant, Massachusetts Water Resources Aut�ority, Winthrop, MA 02152 2' Department of Civil and Environmental Engineering,

Northeastern University, Boston, MA 02115

Abstract

Laboratory investigation has shown that Fenton's Reagent is a very effective oxidant for 2,4,6-Trichlorophenol (TCP). The authors reported the first phase of this research, consisting of five different reactions of Fenton's Reagent on TCP, at the 1995 AIChE Summer National Meeting in Boston as Part I of this paper. The results demonstrated total removal of TCP, with almost complete release of aromatic ring bound chlorine atoms into chloride ions, significant reduction of TOC, and very importantly, significant toxicity reduction compared to the original substrate. These results suggested that Fenton's Reaction can be considered as a candidate process for treatment of actual wastewaters or groundwater contaminated with TCP. However, a thorough knowledge of the reaction chemistry and mechanism is essential prior to any such field scale application.

The present paper will report the second phase of this research, consisting of a study of the reaction kinetics. The rate of reaction is a function of several parameters. Qualitatively, the results indicate that the reaction rate is greatly enhanced by increasing the ratio of hydrogen peroxide to TCP. There is an optimum molar ratio for ferrous ions to TCP, beyond which the TOC reductions, at the end of the reaction, drop off.

Reaction is fastest between pH 2. 5 and 3. 5. The rate drops dramatically at pH values above 4. o. If the pH is not adjusted externally, the reaction automatically drives the pH down to approximately 2.0. Rate of reaction increases with temperature in the range of 15 to 3 soc. Also, incremental addition of hydrogen peroxide, instead of a single batch, significantly enhances the reaction. Ferric ions also catalyze the oxidation reaction, but slow down the reaction significantly compared to the ferrous ions.

All reactions were conducted with 500 ml batches of 1 mM TCP solutions in deionized water, in continuously agitated laboratory reactors.

I

Introduction

Fenton's Reagent has been rejuvenated to solve the problems of environmental pollution control after it remained in relative obscurity for about a hundred years. Reported first by H. J. H. Fenton in 1894 for its ability to oxidize various organic compounds dissolved in water, Fenton's Reagent is an aqueous solution of hydrogen peroxide and ferrous ions. The ferrous ion act as a homogeneous catalyst; while the hydrogen peroxide serves the role of the oxidant.

In an attempt to describe the interaction between hydrogen peroxide and ferrous ions in aqueous phase, Haber and Weiss (1934) proposed:

Fe2+ + HO - OH Fe3+ + (OH)- + OH* (eqn.l)

The free hydroxyl radical (OH*) is an unstable highly active species. In absence of other· reactants, it further reacts with ferrous ions to produce more ferric ions and hydroxyl ions:

Fe2+ + OH* --- Fe3+ + OH- (eqn.2)

Merz and Waters (1947) showed that in presence of various organic substances, the hydroxyl radicals abstract hydrogen atoms from the organic compounds and organic free radicals (R*) by the following mechanism:

OH* + Organic Compound --- R* + H20 R* + HO - OH --- R -OH + OH*

(eqn.3) (eqn.4)

Simultaneous generation of hydroxyl and organic radicals initiate chain reactions leading to oxidation of the organic substrates in aqueous phase.

The model of Merz and waters has been significantly improved by others, most notably by Walling and Kato (1971).

The ability of the highly energized hydroxyl radicals to oxidize organic substrates in water, as explained above, can be effectively utilized in the treatment of certain industrial wasewaters that are recalcitrant or toxic to biological treatment. Application of Fenton's Reagent to such wastes subject the organic molecules to oxidative degradation, leading to the formation of total or partial oxidation products. Even if the pollutants are partially oxidized the products, e.g. alcohols, acids, etc., are generally less toxic and more biodegradable, compared to the original organic substrates. This renders the wastewaters, containing such pollutants, acceptable to the municipal sewer systems (Bowers, et. al, 1987). A successful field scale application of Fenton's Reagent to solve the problems of toxicity and poor biotreatability of a Qhemical manufacturing plant wastewater has been reported for the first time by Fagan (1994).

2

Potter and Roth (1993) extensively investigated the kinetics of oxidation of several mono- and di-chlorinated phenolic isomers by Fenton's Reagent. For the three monochlorophenols the original substrates disappeared more than 90% in about an hour.

The present research forms a part of an ongoing study of the effect of Fenton's Reagent on 2, 4, 6 Trichlorophenol ( TCP) in aqueous phase. TCP is believed to represent a group of organic chemicals that contain high level of toxicity. It is a priority pollutant, used as a biocide, and is a designated RCRA Hazardous Waste. It is a common industrial chemical, primarily used as a wood preservative agent. These characteristics form a good basis for selection of TCP as a model compound for this research.

Part I of this paper (Chen, Basu, and Wei, 1995) reported the findings of the screening tests. The important conclusions derived from those tests were as follows:

- The reaction involves continuous release of organically bound chlorine atoms to chloride ions with simultaneous drop of pH, as well as oxidation of the organic structure.

- Rate of reaction increases with increase of the ratio of hydrogen peroxide (oxidant) to TCP (substrate).

- Under the reaction conditions for the reported set of reactions TCP disappeared almost completely within 1. 5 hours, with simultaneous appearence and disappearence of unidentified intermediate organics.

Fenton's Reaction results in significant reduction of toxicity of TCP in water, as expressed by the EC 50 value.

The present paper reports the results of twenty two experiments to demonstrate the effects of several important parameters, including oxidant to substrate ratio, catalyst to oxidant ratio, reaction temperature, and pH, on the rate and extent of reaction. A set of optimum conditions have also been presented.

Experimental Section

1. Reagents

a) TCP stock solution (1mM) in deionized water was prepared in the laboratory from 98% pure 2,4,6-Trichlorophenol in solid form, manufactured by Aldrich Chemical Inc.

b) 3% stock solution of Hydrogen Peroxide was prepared by diluting a 30% reagent grade solution manufactured by Fisher Chemical.

c) The Ferrous ions, which act as catalyst in the Fenton's Reactions, were supplied in the form of Ferrous Sulfate crystals (FeS0,,7H,O), manufactured by J.T.Baker.

3

d) The Ferric ions, which were also used as catalyst in one reaction, were supplied in the form of 20% (wjv) Ferric Nitrate with 3% (wjv) nitric acid solution, purchased from VWR.

e) eerie Sulfate solution (0.1 N in Sulfuric Acid), used as a titrant for the determination of Hydrogen Peroxide concentrations, was purchased from VWR .

f) Deionized (DI) Water was used to fulfill all the needs of water to carry out the experiments, e. g. for preparation of solutions, cleaning of glasswares, etc. DI Water was prepared in the laboratory from distilled water with the help of a Millipore Milli-Q water purification system.

2. Experiments

Twenty two experiments were conducted under various conditions as clearly outlined in Table I. The oxidant to substrate ratios and the catalyst to oxidant ratios indicated in the table, represent the starting molar ratios. In the course of reactions those ratios keep changing.

For all reactions, except those maintained at constant pH (Expt. Nos.15, 16, 17, and 18), no attempt was made to adjust the pH. The pH was allowed to float freely. As already reported in the Part I of this paper, the natural tendency of pH is to continuously drop as the reactions proceed. For experiments 15, 16, 17, and 18, constancy of the respective pH values were maintained within the variations indicated in the table by addition of o. 5 (N) NaOH solution or 0.5 (N) H2S04 solution externally.

Throughout the course of reaction, all reactions were maintained at constant temperatures as indicated in the table. It can be observed from the table that except for experiment nos. 19 and 20, all reations were carried out 25°C. The purpose of conducting reactions 19 and 20 was to examine the effect of temperature on the reaction rate. Constant temperatures throught the reaction were maintained by carrying out the reactions in a constant temperature laboratory.

Experiment no. 21 was conducted in order to compare the effectiveness of ferric ions as catalyst with respect to ferrous ions. All the conditions of this reaction were maintained identical to experiment no. 4, except for the oxidation state of the catalyst.

Finally, the effect of addition of the oxidant (hydrogen peroxide) in increments has been examined by conducting experiment no. 22. This reaction is identical to experiment no. 4 with the exception that the same total amount of hydrogen peroxide was added in five equal increments at times o, 10, 20, 30, and 50 minutes, respectively. In case of experiment no. 4 all the hydrogen peroxide was added to the reaction system at the start ( 0 min. ) of the reaction.

4

In the course of all the reactions samples were collected at regular intervals of time and preserved in the refrigerator at 4°C after immediately quenching them by sodium sulfite (Na2S03) crystals.

3. Analytical Methods

The analytical methods used for this research are listed below. These have been described in detail in Part I of this paper.

a) Chloride Ion Concentration and pH measurement

These were continuously analyzer (Orion Model combination electrode) electrode Model 9617BN). the reaction system.

monitored with the help of a pH/ISE 720A) with a pH probe (Orion pH and a chloride electrode (Orion The probes were dipped directly into

b) TCP and Reaction Product Analyses

The samples preserved from the experiments were analyzed later for identification and quantification of the various chemical species involved in the reactions, by High Performance Liquid Chromatography. A Hewlett-Packard HP 1050 HPLC system with an auto sampling device, a reversed phase Hypersil ODS packed column (particle size 5 micron, column size 10 em L x 2.1 mm ID), and a UV absorbance detector was used as the analytical instrument. The detector was set at an wavelength of 295 nm.

The samples were directly injected into the column. The mobile phase consisted of an acidic solution of KH2PO, as solvent A, and acetonitrile as solvent B. Gradient elution technique was used.

c) Total Organic Carbon Analyses

The substrate ( 1 mM pure TCP solution) and the reaction products after completion of every reaction was analyzed for Total Organic Carbon (TOC) with the help of a Dohrmann DC-80 Carbon Analyzer.

Results and Discussion

The twenty two experiments were organized in two major parts. The first part was devoted to the examination of the effects of oxidant to substrate ratio and the catalyst to oxidant ratio on the reaction kinetics and the ultimate decomposition of TCP. Based on the results of this an optimum combination of TCP:H202:Fe2. has been established.

The experiments in the second part were conducted using certain fixed ratios of reactants and catalyst,•under the various reaction conditions. The results of this part indicate the effects of temperature, pH, oxidation state of catalyst, and mode of addition

5

of the oxidant on the rates of oxidation reaction.

The results are discussed in detail as follows . •

Effect of Oxidant to Substrate Ratio and catalyst to Oxidant Ratio:

As has been already reported in the Part I of this paper, the rate of reaction is directly a function of the oxidant to substrate ratio. The rates and the extents of oxidation have been based upon the increase of concentration of free chloride ions in the reaction systems.

In this part of the paper, the extent of each reaction has been expressed in terms of the percentage of the chloride ions released at the end of the reaction with respect to the theoretically maximum possible release of chloride ions (which is 106. 5 mg/L for the starting substrate concentration of 1mM TCP). This is represented in Fig.1, in the form of a bar graph, as functions of H202: TCP molar ratios and Fe2•: H202 molar ratios. Four molar ratios of Fe2•:H,02 - 0.05, 0.10, 0. 25, and 0.50, as shown on the X-axis of Fig . 1, have been considered. The three bars for a single Fe2+:H,02 molar ratio represent the percentages of organic bonded chlorine atoms in TCP released as chloride ions, each representing a H202:TCP ratio in ascending order from the left to the right. Thus, in each group of three bars the left bar represents the result for a H20,:TCP molar ratio of 2. 75:1, the middle one for 5. 5:1, and the right bar for 11:1, for each Fe2•:H202 molar ratio. For the Fe2•:H202 ratio of 0. 05:1, the three individual H202 to TCP ratios are shown on the top of the respective bars. Although not shown on the top of the bars for the other Fe2•:H,:O, ratios, the same order for H202:TCP has been maintained for all four sets in Fig.1 ..

Fig.1 demonstrates that the extent of reaction is a weak function of Fe2•: H,02 molar ratio. In general, the reaction takes place to the maximum extent for a Fe2+: H202 ratio between o .10 and 0. 25: 1. At a ratio lower than this the conversion of TCP decreases because of catalyst limitation. At a higher ratio also the conversion decreases, probably because of the fact that, at high catalyst concentration a lot of active hydroxyl radicals are generated from the hydrogen peroxide very rapidly, at the start of the reaction. The second step, reaction of the hydroxyl radicals with TCP is not as fast, resulting in accumulation of unconsumed, free hydroxyl radicals in the system. These free radicals react with each other by a parallel, undesirable path to produce water as follows, leading to wasteful consumption of a part of the originally supplied hydroxyl radicals.

OH" + OW --- H20 + 1/2 02 (eqn.5)

It is also observed that, for any given catalyst to oxidant ratio, the extent of reaction is directly a function of the oxidant to substrate ratio (only with one exception at Fe2•: H202 o. 25:1). Obviously, this indicates that maximum oxidation takes place at H20,:TCP of 11:1. However, within the optimum range of catalyst to

6

oxidant ratio, the extents of reactions for H,02:TCP ratios of 5.5:1 and 11:1 are both above 90%. Because hydrogen peroxide is an expensive chemical, for practical application, a good optimum ratio for H,O,:TCP is 5.5:1, which will achieve more than 90% conversion (dechlorination) of TCP while reducing the cost due to hydrgen peroxide by half.

A similar bar graph has been produced based on TOC destruction as a function of Fe2•: H20;, ratio and H202: TCP ratio, as shown in Fig. 2. The results do not show any clear trend with respect to Fe2•: H,O, ratio. However, TOC destruction is a direct function of H,O,:TCP ratio, with only one exception at Fe2•:H,02 ratio of 0.25:1. From TOC destruction point of view the Fe2•: H202 ratio of 0.10:1 is better than 0. 25: 1. Therefore, considering the dechlorination and TOC removal aspects, the optimum oxidant to substrate and catalyst (Fe2• :H,O,) molar ratios for oxidation of 2, 4, 6-Trichlorophenol (TCP) by Fenton's Reagent are 0. 10:1 and 5.5:1, respectively.

The reaction kinetics for dechlorination of TCP as a result of oxidation by Fenton's Reagent is presented in Figure 3. All four reactions (Expt. No. 4, 5, 61 and 7) were conducted at the optimum catalyst to oxidant ( Fe2•: H,O,) ratio of o. 10: 1, and a constant temperature of 25°C. No attempt was made to adjust pH by adding chemicals from outside, and the pH was allowed to float freely during the course of each reaction. The variation of pH during each reaction is shown in Fig.4. The only variable in the four reactions· is the oxidant to substrate (H,O,:TCP) ratio, as shown in the legend. As already discussed, the reaction kinetics is a direct function of oxidant to substrate molar ratio, for a given catalyst to oxidant molar ratio. The two reactions at oxidant to substrate ratios of 8.25:1 and 11:1 are very fast, and almost indistinguishable from one another. At the oxidant to substrate ratio of 5.5:1, the rate is reasonably fast as conversion in excess of 90% can be accomplished in 30 minutes. At the lowest ratio of 2.75:1 the reaction is much slower and continues beyond 90 minutes, by which time the conversion is even less than 80%. Therefore, from reaction kinetics point of view also, the optimum oxidant to substrate ratio and catalyst to oxidant ratios, selected above, are reasonably good. Reaction 14 was conducted as a blank run, with only hydrogen peroxide and no ferrous ions. The results indicate almost no reaction take place in absence of ferrous ions.

In this present work, the discussion on reaction kinetics is limited only to qualitative analyses of the results.

Effect of pH:

Each of the reactions 15, 16, 17, and 18 was conducted under constant values of pH during the course of reaction, but the pH values of the four reactions were different from one another, at 2 .,0, 3. 5, 5. o, and 6. 5, respectively. For these reactions, pH values were kept constant by adding appropriate amounts of 0.5 (N) sodium hydroxide solution, or 0. 5 (N) sulfuric acid solutions, from outside. Even with the best attempts the variations, as indicated

7

..

in the legends of Fig. 5, could not be avoided. Other reaction parameters, e.g. starting oxidant to substrate ratio, starting catalyst to oxidant ratio, and temperature were the same (H202: TCP=5. 5: 1, Fe»: H202=0.251 and Temp.=25°C).

It is very clear from Fig. 5 that the rates and extents of the reactions at pH values 2.0 and 3.5 are the fastest, and very close to each other. Both of these parameters drop dramatically as the (constant) pH of the reaction is elevated. Accordingly, the minimum dechlorination of TCP was observed at a reaction pH of 6.5. The reaction rate levelled off within 15 minutes of the start of reaction, while the reaction proceeded less than 9%. Therefore, the optimum range of pH for carrying out advanced oxidation of TCP using Fenton' reagent is between 2.0 and 3.5.

From Fig.3 it can be observed that if pH is not externally adjusted the reaction ( Expt. No. 5) is fast, and comparable. with those conducted at constant pH levels (Expt. Nos. 15 and 16) between 2.0 and 3. 5. This is true because, in case of TCP, as soon as the reaction starts various organic acids are formed as intermediate products, which depress the system pH down. This process continues leading the pH to the optimum range, which supports progress of the reaction at a rapid pace. This trend can be observed from pH profiles for experiments 4, 5, 6, and 7 (Fig. 4). Thus, for the case of treatment of water containing TCP by Fenton's Reagent, it is not necessary to add chemicals from any external source to maintain the pH within the optimum range, since the reaction spontaneously drives itself to that range.

Effect of Temperature:

The rate of any chemical reaction is a direct function of temperature. The reaction under the constant conditions of oxidant to substrate ratio ( H202: TCP=2. 75: 1) , catalyst to oxidant ratio ( Fe2•: H202=0. 1: 1) , and a temperature of 25°C ( Expt. No. 4) , was repeated at two other temperatures - 15°1 and 25°C (Expt. 19, and 20, respectively) to examine the effect of temperature on the rate of oxidation of TCP by Fenton's Reagent. The reaction temperatures were maintained constant by conducting the reactions in a constant temperature laboratory, equipped with the mechanism to adjust the temperature as desired. The total experimental set up, necessary chemicals, and glasswaare were preserved in the constant temperature laboratory at the desired temperature 24 hours ahead of the experiment to allow for the necessary temperature equilibration. All reaction conditions, except the temperature, were identical for these three reactions. Fig.6 demonstrates that the rate of oxidation of TCP by Fenton's Reagent increases significantly with increase of the reaction temperature.

Effect of oxidation State of Catalyst:

Walling and Weil (1974) proposed a series of redox chain reactions for the ferric ion catalyzed decomposition of hydrogen peroxide.

8

'•·

Fe3• + H202 --- Fe2+ + HO; + H+ (eqn.6)

The chain is initiated by the above reaction. According to this mechanism ferric ions can also generate hydroxyl radicals by the reaction represented by equation 1 via the generation of ferrous ions as the first step.

The effect of substituting ferric ions for ferrous ions as catalyst has been examined by conducting experiment 21. Ferric ions were supplied in the form of ferric nitrate solution. Originally the reaction was started with an oxidant to substrate ratio of 2.75: 1, and catalyst to oxidant ratio of 0.1: 1. Under these conditions the reaction was observed very slow. To boost up the rate, at 10 minutes after th� start, more hydrogen peroxide solution was added to the system to make starting oxidant to substrate ratio of 11: 1. Even this did not improve the rate and more ferric solution was added to the system at 30 minutes after start of the reaction, to make the starting catalyst to oxidant ratio of 0. 5: 1. At this point the reaction rate was found to be picking up. The results are presented in the form of Fig. 7.

From the results it appears that higher quantities of both the oxidant and catalyst are required to carry out oxidation reaction by using ferric ions as catalyst.

Effect of Mode of Addition of Oxidant:

In experiment 22 the oxidant (-3% H202 solution) was added to the reaction system in five equal increments, at 0 (start of the reaction), 10, 20, 30, and 50 minutes, respectively. The total hydrogen peroxide added was equal to that added in experiment 4. All the other reaction conditions of these two reactions were identical. The results, as shown in Fig. 8, indicate that initially reaction 4 proceeds a little faster because of the availability of much larger concentration of hydroxyl radicals, but after about 40 minutes the rate of reaction 22 picks up and overtakes the reaction 4. The result also show that the rate of reaction 22 continuously increases as the oxidant addition is continued, as opposed to the rate of reaction 4, which gradually starts decreasing after 40 minutes from the start of reaction.

The above results confirm that the first step of the reaction, represented by equation 1, is very fast and almost instantaneously produces stoichiometric amounts of hydroxyl radicals. The subsequent step( s) of the oxidation of the substrate by the hydroxyl radicals is(are) the rate limiting step(s) for the overall reaction. In the case of reaction 4, the rate of generation of hydroxyl radicals is much greater than the rate of consumption, resulting in accumulation and self-destruction as suggested by equation 5. This leads to the waste of a part of hydrogen peroxide used at the start of the reaction. In the case of reactioo 22, hydroxyl radicals do not get such an opportunity to accumulate and involve in alternate unproductive reactions.

9

Kinetics and Reaction Mechanism:

The study reported in this paper is a part of an ongoing comprehensive research on this subject. The reaction pathway for oxidation of the organic substrate, TCP, involving identification of intermediate and final products by HPLC and mass spectroscopy (MS), is currently in progress. The results of this investigation will be reported elsewhere. A quantitative relationship for the reaction rate also will be presented.

Toxicity Reduction:

Toxicity determinations of the original substrates (TCP) and the products after treatment by Fenton's Reagent were conducted with the help of a Microtox test instrument. The results indicate significant toxicity reduction. Details of these experiments have been reported by Chen, Basu, and Wei in the Part I of this paper. currently biotreatability of the reaction products is under investigation. The results will be reported elsewhere.

Conclusions

Above results can be summarized in the form of the conclusions listed below:

1. The optimum oxidant to substrate ratio and catalyst to oxidant ratio for oxidation of TCP with Fenton's Reagent is 5. 5: 1, and 0.1:1, respectively.

2. For oxidation of TCP, the optimum range of pH is 2 to 3. 5. However, no attempt needs to be made to maintain the pH as the reaction drives itself to the optimum pH range.

3. The rate of reaction increases significantly with the increase of temperature. In the case of a real industrial discharge, decision needs to be made, based upon the temperature of the effluent, whether preheating of the effluent will be necessary or not.

4. Ferric ions can also act as catalyst for oxidation of TCP by hydrogen peroxide, but are not practical because of the requirement of large amounts of both oxidant and the catalyst.

5. Utilization of hydrogen peroxide as the oxidant can be enhanced by addition in smaller increments rather than a single addition at the start of the reaction. This is an important consideration for practical application, which can reduce the application of hydrogen peroxide for the same level of treatment, leading to more economic operation.

6. The above findings for TCP can at best be used as a set of general guidelines. For other compounds, tests should be performed on individual substrates to optimize the treatment parameters on a

10

case by case basis.

References

1. Fenton, H. J. H., J. Chem. Soc. (Lond.), 65, 899 (1894) 2. Haber, F., and Weiss, J., Proc. Royal Soc. (Lond.), A147, 332-351 (1934) 3. Merz, J. H., and �aters, w. A., Faraday Soc. Disc. (Lond), 2, 179 (1947) 4. Walling, C., and Kato, s., J. Am. Chem. Soc., 93(17), 4275-4281 ( 1971) 5. Bowers, A. R., et. al, Water Sci. Tech., Vol. 21, 477-486 (1989) 6. Fagan, M. R., Env. Protection, 45-52, Sept. 1994 7. Potter, F. J., and Roth, J. A., Haz. Was. & Haz. Mat., 10(2), 151-170 (1993)

..

8 . Chen, K. , Basu, S. , and Wei, I . , W. , 11 Adv. Chem. Oxid. and Tox. Red. of 2, 4, 6-TCP by Using Fen. Reagent - Part I 11, Presented at AIChE Summer National Conference, Aug. 95, Boston 9. Walling, c., and Weil, Weil, T., Int. Jour. of Chem. Kinetics, Vol. VI, 507-516 (1974).

II

TABLE I

Exoerimental Conditions for Oxidation of TCP with Fenton's Reagent

Expt. No. Starting Starting pH Temp.(oC) Catalyst Mode of addn. Fe(II):H202 H202:TCP Condition Oxdn.State of Oxidant

1 0.05:1 2.75:1.0 Floating 25 II Single Batch 2 0.05:1 5.50:1.0 Floating 25 II Single Batch 3 0.05:1 11.0:1.0 Floating 25 II Single Batch 4 0.10:1 2.75:1.0 Floating- 25 II Single Batch 5 0.10:1 5.50:1.0 Floating 25 II Single Batch 6 0.10:1 8.75:1.0 Floating 25 II Single Batch 7 0.10:1 11.0:1.0 Floating 25 II Single Batch 8 0.25:1 2.75:1.0 Floating 25 II Single Batch 9 0.25:1 5.50:1.0 Floating 25 II Single Batch

10 0.25:1 11.0:1.0 Floating 25 II Single Batch 11 0.50:1 2.75:1.0 Floating 25 II Single Batch 12 0.50:1 5.50:1.0 Floating 25 II Single Batch 13 0.50:1 11.0:1.0 Floating 25 II Single Batch 14 - 11.0:1.0 Floating 25 II Single Batch 15 0.10:1 5.50:1.0 Const.@2.0 25 II Single Batch 16 0.10:1 5.50:1.0 Const.@3.5 25 II Single Batch 17 0.10:1 5.50:1.0 Corist.@5.0 25 II Single Batch 18 0.10:1 5.50:1.0 Const.@6.5 25 II Single Batch 19 0.10:1 2.75:1.0 Floating 15 II Single Batch 20 0.10:1 2.75:1.0 Floating 35 II Single Batch 21 0.10:1 2.75:1.0 Floating 25 Ill Single Batch 22 0.10:1 2.75:1.0 Floatina 25 II Incremental

12

100

90

80

70

'C "' en 60 "' "' a; It: "' 50

-w 'C

·;: 0

:2 40 0 '$.

30

20

10

0

Fig.1 EFFECTS OF OXIDANT TO SUBSTRATE RATIO AND CATALYST TO OXIDANT RATIO

ON ULTIMATE CHLORIDE RELEASE

0.05:1 0.10:1 0.25:1 0.50:1

Fe(ll} : H202 Ratio

•- Expt. No.

70

60

50

c 0

:;:: 40 "

:I ... -"'

- .. .... 0

u 30 0

1-� •

20

10

0

Fig. 2 EFFECTS OF OXIDANT TO SUBSTRATE RATIO AND CATALYST TO OXIDANT RATIO

ON TOC DESTRUCTION

,,...""""" ,., .. ,,,)\,,., ,_.,.,., .. ,,.,.,,,,.,.,. '"'""""'' '""""'·""'"' """''·' """""""" "'""'''"''''·'"""'·"'"'"'" .,,., . .,.,.,.,, ., , . .,,,.,, """"

mMI!�ffimiii!l!lili��mmimMimmmrnJ!ffiliffimlm]mmmm!liillmlwMm:: . !liltlmmmmmmm :imm�JIJ�ii!Baii�mml ru 1 ! II

0.05:1 0.10:1 0.25:1 0.50:1

Fe(ll) : H202 Ratio

•- Expt.No.

� V>

, "' (/) "' "' a; 0:: "' , ·;:: 0 :;: 0 ';!.

100

90

80

70

60

50

40

30

20

10

0

0

Fig. 3 RATE OF REACTION AS A FUNCTION OF OXIDANT TO SUBSTRATE MOLAR RATIOS

1 2 3 5 7 9 10 11 15 20 25 30 40 45 50 60 75 90

Time in Minutes

H202:TCP

--.-2.75:1.0

--11-5.50:1.0

�8.25:1.0

�11.0:1.0

-"'

J: <l.

5

4.5

4

3.5

3

2.5

2

1.5

1

0.5

0

0

Fig. 4 pH PROFILE AS A FUNCTION OF OXIDANT TO SUBSTRATE RATIO

H202:TCP

--2.75:1.0

-- 5.50:1.0

-.k- 8.25:1.0

--*-11.0:1.0

1 2 3 5 7 9 10 11 15 20 25 30 40 45 50 60 75 90

Time in Minutes

Fig. 5 EFFECT OF pH ON THE RATE OF REACTION

90

80

70

60 "" Q) "' .. -+-pH 2.0+/-0.05 Q)

50 a; - 0::: _,

Q)

--pH 3.5.0+/-0.15

--pH 5.0+/-0.5 "C ·;:: 40 0 �pH 6.5+/-0.15 .<: 0 ';fl.

30

20

10

0-

0 1 5 10 15 20 30 45 60

Time in Minutes

-00

, Q) "' "' Q)

&! Q) , ·;:: 0 :2 0 *'

Fig. 6 EFFECT OF TEMPERATURE ON THE RATE OF REACTION

100

90

80

70

60

--+-Temp.=15 C

50 --Temp.=25 c

--Temp.=35 c

40

30

20

10

0

0 1 2 3 5 8 10 12 15 20 25 30 40 45 50 60 75 90 120 150 180 210

Time in Minutes

"C "' "' "' "' Qj 0:: ..... "' "' "C ·;:: 0

:2 u "" 0

Fig. 7 EFFECT OF OXIDATION STATE OF CATALYST ON THE RATE OF REACTION

80

70

60

50

40

30

20

10

0 ll"i?Z:··"'�'"'"''"

0 2 5

H202:TCP=2.75:1

"Fe(III):H202=0.1 :1

10 15 20 25 30 40 45 50 60 75 90 120 150 180 210

Time in Minutes

�--With Fe(ll)

--With Fe(lll)

Fig. 8 RATE OF REACTION AS A FUNCTION OF MODE OF ADDN. OF H202

100

90

80

70

"t:l .,

60 Ul "' ., a;

,_, a:: 0 ., 50

"t:l

--+--With Single Addn. of H202

--With I ncr. Addn. of H202 ·;: .2 .c

40 u ;fl. •- Time of Addn. of Equal

30 Increments of H202

20

10

0

0 2 5 10 15 20 25 30 40 50 60 75 90 ;/(,

Time in Minutes