CHLORINE CONSUMPTION MODELING AND TRIHALOMETHANE FORMATION POTENTIAL: KODIAT MDAOUAR DAM (BATNA, ALGERIA)

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1 Proceedings of the 3 th International Conference of Environmental Science and Technology Athens, Greece, 5-7 September 23 CHLORINE CONSUMPTION MODELING AND TRIHALOMETHANE FORMATION POTENTIAL: KODIAT MDAOUAR DAM (BATNA, ALGERIA) MELLAHI DHAOUADI, ABDOU IMEN, BAASSOU. ZOHRA, GHEID ABDELHAK 2 : Laboratory of Chemistry and Environmental Chemistry (LCEC), Department of Chemistry, Hadj Lakhdar University, Batna, Algeria. 2 : Laboratory of Water and Environmental Sciences, Messadia M ed Cherif University, Souk-Ahras, Algeria address: mellahipg@yahoo.fr ABSTRACT Humic substances are the most widely distributed organic products of surface water, they are known by their strong reactivity with chlorine, producing trihalomethanes (THM). THM are classified as carcinogenic compounds that are regulated by the world health organization and other government organizations (CEE, US EPA). After a succession of operations: filtration, softening and concentration with reverse osmosis, Hydrophobic and transphilic fractions of natural organic matter (NOM), were isolated from water supplies (Koudiat Medaour dam Batna), using no-polar XAD-7HP and XAD-4 resin. Under standard conditions (ph = 7. ±.2, 25 C), hydrophobic (HPO) and transphilic (TRS) fractions, are chlorinated with an excess of sodium hypochlorite, then chlorine consumption and UV254 variation are followed. The obtained results were modeled by nonlinear regression using XLStat-pro-7.5 software. After seven days of chlorination, the trihalomethanes formation potential (THMFP) was analyzed using gas chromatography LLE-GC-ECD. The results show that the chlorine consumption of HPO and TRS fractions are practically similar and their values are.6 and.235 mg-cl 2/mg-C respectively. On the other hand, the formation of THMFP of TRS fraction (59.62 µg-thm/mg-c) was more important than that of HPO fraction (32.87µg-THM/mg-C). The chlorine consumption model confirms the first order with two speeds, the fast speed from to 2 hours and the slow speed from 2 to 68 hours. The characterization of functional groups by infrared (FTIR) shows more important carboxylic and phenolic functions in the transphilic fraction than in hydrophobic fraction, this is in correlation with the strong reactivity of the transphilic fraction compared to that of hydrophobic fraction. Keywords: humic substances, no-polar XAD-7HP and XAD-4 resin, chlorine consumption, THMFP.. Introduction Surface waters, compared to deep waters, are more vulnerable and susceptible to various origins of natural contamination and/or anthropic. The natural organic matter (humic and fulvic acids), is one of the fractions present in surface waters (Thurman, 985).This fractions of organic matter are the main precursor of THM formation and other disinfection by-products (DBPs) such as haloacetic acids and halogenated acetonitriles. These DBPs are formed, by reactions between disinfectants (ozone, chlorine dioxide, chloramines, etc.) and natural organic matter, and in the presence of bromide ions (Rook, 974).Chlorine is the most commonly disinfectant used in Algeria. Its use as a disinfectant has been very useful, especially in the fight against water-borne diseases. Johannes Rook (974) indicates the presence of chloroform and other THMs in water

2 surfaces treated with chlorine. He also confirmed the exact conditions that govern THMs formation, attributed mainly to humic substances (Rook, 975). A few years later, the International Agency for Research on Cancer (IARC) has classified chloroform and bromodichloromethane as possible human carcinogens (Group 2B) (ATDS, 997). This study deals with the identification of THM formation after the isolation of humic substances from the water of Koudiat Medaouar dam (Timgad, Batna), as hydrophobic and transphilic fractions (Malcolm and MacCarthy, 992). In the aim to follow the kinetics of chlorine decay and the THM formation potential, the obtained fractions are then chlorinated with a sodium hypochlorite solution (APHA, 25a). 2. Materials and methods 2.. Study site The studied samples are taken from Koudiet-Medouar Dam in Timgad (Batna) on May 2 st, 22. The dam is located 7 km north-east of Timgad (Batna - Algeria). It ensures water supply for cities Concentration and fractionation of humic substances on XAD resins Figure explains the main steps of humic substances fractionation on XAD-4 and XAD-7 HP resins (Acros organics New Jersey, USA). First step: after sampling, the raw water is directly filtered through 5 μm, μm and.45 μm filters respectively (water quality polymer filter member, and THOMAPOR USA). Second step: softening of sulfonic resin R-SO 3Na (amberlite IR-2(Na) BDH chemicals ltd Poole England). Samples are concentrated times on reverse osmosis pilot (Film TEC Model N TW USA). The retained organic matter from the reverse osmosis membrane has been desorbed by.5m NaOH solution, and then the solution is mixed with the retentate. We obtain a solution mixture of concentrate and sodium Eluate. Third step: the resulting mixture was acidified with a concentrated HCl solution to ph=2 (Redel de Haën 37% Germany). Then, the mixture is eluted successively through two columns of macroporous resin XAD-7HP and XAD-4. Both columns were packed according to the protocol of Standard Methods (APHA, 25a). After elution, the columns are rinsed with a formic acid solution of ph = 2 (HCOOH, Paneac Spain). The hydrophobic and transphilic fractions were obtained by desorption with a mixture of acetonitrile 75% water 25% (acetonitrile SIGM-ALDRICH). The retained fraction from XAD-7HP was the hydrophobic fraction (HPO).The retained fraction from XAD-4 was the transphilic fraction (TRS). The obtained fractions are then purified in a rotavap to remove the eluting solvent and the formic acid traces. Figure. Extraction and fractionation of NOM

3 2.3. Chlorine demand Chlorine demand was determined by the method 57 B of Standard Methods (APHA, 25b). Preparing a series of samples with the same concentration of DOC and increasing chlorine concentrations with the ratios R (mg-cl 2/mg-C) =.53;.7;.6; 2.4. After adding the chlorine-dosing solution, samples were transferred to the incubator and maintained in darkness at 25 C for 7 days. After a 7-day incubation period, the test samples were removed from the incubator, and an aliquot of the sample was collected for residual chlorine analysis. The ratio R is selected to perform the kinetics of chlorine decay and for the determination of THMFP that gives residual chlorine greater than mg/l Kinetics modeling of chlorine decay In this work, We have considered that the reaction of chlorine consumption has two speeds the rapid one and the slow one (Gallard and von Gunten, 22): MON R + Cl 2 MON S + Cl 2 K R K S Integration of the equations: R-X (rapid) R-X (slow) C t t dcr n R C CR R R dcr K R. C dt dcs n K S. CS dt K dt and - m + - n + n R S C t t dcs m S C CS S - n + - m + R S K dt C t = C.f - - n +.K.t + - f.c - - m +.K.t (n and m ) The first-order model for the kinetics of chlorine decay has been proposed by (Gang et al., 23a; Gang et al., 23b; Chang et al., 26). C t = C. f.exp K.t f.exp K.t When n = m =, we can write: R S The Factors K R, K S, and f were determined by nonlinear regression method using XLStatpro-7.5 software. C R: is the initial chlorine concentration participating in the rapid reaction; C S: is the initial chlorine concentration participating in the slow reaction; K R: is the first-order rate constant for rapid reactions (h - ); K S: is the first-order rate constant for slow reactions (h - ); C : the initial chlorine concentration (C = C R + C S); C R (t): the Residual chlorine concentration hypothetical separate rapid reaction; C S (t): the Residual chlorine concentration hypothetical separate slow reaction; C(t): the residual chlorine concentration at any time t. C(t) = C R(t) + C S(t); n, m: the order of the rapid and the slow reaction, respectively; f: the fraction of chlorine demand attributed to rapid reactions. C f C 2.5. Kinetics of chlorine decay and UV 254 degradation A 7-day incubation period of chlorine decay was carried out using a dose of initial chlorine (7.45 mg-cl 2 / L). Both samples were chlorinated with 8 ml of a solution of 86 mg-cl 2 / L (sodium hypochlorite) and buffered at ph = 7.±.2 with 2 ml of phosphate buffer solution (KH 2PO 4 68g, NaOH g/l), then the volume was completed to 2 ml with distilled water. The samples maintained in darkness at 25 C in amber glass bottles of liter sealed with TFE-lined caps. Residual chlorine and UV 254 absorption were measured at different time intervals:,.5,, 2, 4, 6.8, 24, 52, 96, 22, 68 hours Analysis methods THM Analysis: THM were analyzed using LLE- GC-ECD method (Shimadzu GC-7A equipped with Selective electron capture detector ECD 63 Ni). After a 7-day incubation period, samples were extracted with n-pentane (MERCK Class GC, Germany) and the R

4 extract is injected into a capillary column (25 m X.25 mm fused-silica id,.25 µm film thickness, OV7, Split ratio :5, velocity 2 cm/sec, Qcol =,8 ml/min). The used analysis method is in accordance with the EPA Method 55.(USEPA, 995) modified by (Nikolaou et al., 22; Nikolaou et al., 25; Leivadara et al., 28). Standard solutions were treated in the same conditions as the samples. UV 254 : The absorbance was performed using a Shimadzu Pharmaspec 7 UV-Vis Spectrometer. The absorbance at 254 nm was measured in a rectangular quartz cell having an optical path length of cm. FTIR Characterization The analyses were carried out using a FTIR spectrometer JASCO FTIR- 4. The HPO and TRS fractions were analyzed in solid form after a vacuum vaporization in a rotavap. Residual free chlorine analysis: the concentration of free chlorine was measured using spectrophotometer (HI 967, Hanna Instruments Deutschland GmbH), and recommended reagents DPD (N,N-diethyl-p-phenylenediamine). 3. Results and Discussion 3.. Water quality study The important water quality parameters, of Koudiat Mdaouar dam are summarized in the Table : Table. Important water quality parameters Hardness TH F Alkalinity TAC F Turbidity NTU UV254 Raw water DOC mg-c/l cm - % Fraction SUVA L.mg-C -.m - HPO TRS Raw water HPO TRS 3.2. FTIR spectra The FTIR spectra of HPO and TRS fractions are shown in Figure The results are perfectly correlated with literature (Leenheer, 29; Platikanov et al., 2; Matilainen et al., 2). - The broad band at about cm is generally assigned to OH stretching groups. - The band usually appearing at cm - is attributed to C-H stretching vibrations, asymmetric and symmetric methyl and methylene groups. - The strong adsorption in the region cm - is assigned to carbonyl C=O combination of carboxyl, ester, and ketone groups. - The weak peak appearing between 4 and 383 cm - is associated to C-H bending vibrations for methyl and methylene groups. - The peak at cm - is attributed to C O stretch (carboxylic groups, phenols, aromatic/unsaturated ethers)

5 Figure 2. FTIR spectra of hydrophobic (right) and transphilic (left) fractions 3.3. Kinetics modeling of chlorine decay 3.3. Chlorine demand R is defined as the ratio of the initial concentration of active chlorine over concentration of DOC (mg-cl 2 / mg-c). Plotting the curve R = f ([Cl 2] residual) we can determine the ratio R for that the residual chlorine after a 7-day incubation period will be greater than mg- Cl 2/L. The results are shown in the Table 2: Table 2. Determining the chlorine demand: R (mg-cl 2 / mg-c) = f ([Cl 2] residual) R (mg-cl 2/mg-C) R 2 Residual chlorine mg/l (HPO) Residual chlorine mg/l (TRS) According to Table 2, the chlorine demand varied linearly with the initial chlorine concentration (DOC concentration was remain constant). The specific demand of chlorine for hydrophobic and transphilic fractions is:.6,.235 mg-cl 2/mg-C, respectively Modeling of the chlorine decay kinetics After chlorination of HPO and TRS fractions with a solution of sodium hypochlorite at 85 mg/l, we followed the chlorine decay kinetics measuring the concentration of residual chlorine and UV 254. The modeling of chlorine decay kinetics of the rapid and the slow speed in first order (Gallard and von Gunten, 22) is presented in Figure 4 below:

6 C (t) mg/l C(t) mg/l TRS fraction HPO fraction Time (hours) Time (hours) Figure 4. Modeling of the chlorine decay kinetics for HPO and TRS fractions. These results confirm that the chlorine consumption was very rapid during the first two hours, and the speed was gradually decreased for both fractions. After 2 hours, the residual chlorine was 8.8 and 9.8%, After hours, it was reduced to 5. and 6.74% for TRS and HPO fractions respectively. The model parameters, f, K S and K R are grouped in Table 3. Table 3.The three parameters of the chlorine decay kinetics model. Fraction f K R (h - ) K S (h - ) R 2 HPO TRS The ratio f, that expresses the fraction of the initial chlorine attributed to the rapid reaction, was 34.7% for HPO fraction and 35.4% for TRS fraction. the rapid speed can be attributed to the reactivity of resorcinol organic matter and other compounds of the β- diketones family or/and β-ketoacides, while the slow speed is attributed to phenolic compounds (Marhaba and Van, 2) Kinetics of matter organic degradation (UV254) Figure 5 illustrates the variation of UV254 as a function of time, after chlorination of both fractions, under the same conditions of chlorine decay kinetics. UV 254 cm -,8 HPO TRS,72,64,56,48,4,32,24,6,8, Time (hours) Figure 5. The UV254 changes with time for HPO and TRS fractions

7 UV254 decreased rapidly during the rapid phase (2 hours), thus, only a small change in UV254 was seen during the slow phase. This slow variation of UV254 is attributed to the stability of the benzyl or phenyl rings. The UV expresses the existence of the double bonds, especially aromatic rings. The chlorination reaction causes aromatic ring opening. In addition, the variation of the UV254, can be attributed not only to the aromatic ring opening, but also change/removal of functional groups of the aromatic rings (Gang et al., 23b). 3.4 Trihalomethane Formation Potential (THMFP) Under standard conditions, HPO and TRS are stored in darkness at 25 C in amber glass bottles. After a 7-day incubation period, THM were analyzed. The obtained results are shown in Table 4. Table 4. THMFP and Specific THMFP for HPO and TRS fractions. Fractions DOC [THMFP] Specific THMFP Specific THMFP/specific chlorine mg-c/l µg/l µg THM/mg-C demand µg-thm/mg-cl 2 HPO TRS To give a more general expression we calculated specific THMFP and specific chlorine demand (expressed in μg-thm/mg-c and mg-cl 2/mg-C). The ratio between the two parameters allows us to determine another very interesting parameter that expresses the THMFP formed per mg of consumed chlorine (μg-thm/mg-cl 2). The three parameters are summarized in Table 4 that allow us to compare between the reactivity of chlorine and THM formation. The results show that the chlorine decay of HPO and TRS fractions are practically similar their values are.6 and.235 mg-cl 2/mg-C respectively. On the other hand, the formation of the specific THMFP of TRS fraction (59.62 µg-thm/mg-c) was more important than that of HPO fraction (32.87 µg-thm/mg-c). In the absence of bromide, transphilique fraction give more THMFP in the HPO fraction, this can be interpreted by the effect of several factors: In FTIR spectrum of TRS fraction, the absorbance of alcoholic and carboxylic functions are greater than that of carbonyl function, the case is reversed in the hydrophobic fraction spectrum. Therefore the transphilic fraction is richer in oxygen than HPO fraction, so this can provide more active sites. 4. Conclusions - The transphilic fraction is more reactive with chlorine than the hydrophobic fraction, FTIR spectra confirmed this result, since the transphilic fraction is richer in active functional groups than the hydrophobic fraction. - Modeling of chlorine decay kinetics confirmed the first order for the rapid and slow speeds (resolution>.99). - The combination of the concentration and fractionation of humic substances using reverse osmosis technology with macroporous resins was very important, since the consumption of chlorine in the case of direct chlorination of raw water can be attributed to other compounds such as Fe 2 +, Mn 2 +, sulfides, ammonium... - The non-aromatic raw water study (SUVA =.88), was confirmed by the low rate of the hydrophobic fraction (58%).

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