A Study for Chloroform Formation in Chlorination of Resorcinol

Turk J Engin Environ Sci 25 (2001) , 289 – 298. c TUB¨ ITAK˙ A Study for Chloroform Formation in Chlorination of Resorcinol Tülay A. OZBELGE¨ Middle East Technical University, Department of Chemical Engineering, 06531 Ankara-TURKEY Received 27.07.1999 Abstract In this study, resorcinol, chosen as a model humic acid, is chlorinated with sodium hypochlorite in aqueous medium. The effects of some factors, such as initial concentrations of resorcinol and chlorine, as well as their ratios, temperature, time and pH on chloroform formation, are investigated and discussed. Correlations with accuracies of 10% are obtained to predict the formed chloroform concentration in terms of time, initial total organic carbon (TOC), initial chlorine to initial TOC ratio, reaction temperature and reaction pH. In the chlorination of water containing total organic carbon due to the presence of humic acids at a certain concentration, the necessary optimum chlorination time for each applied chlorine dosage, ensuring the maximum permissible chloroform concentration in the drinking water, can be determined from these correlations. Key Words: Chlorination, humic acid, resorcinol, haloform reaction, trihalomethane, chloroform, disinfec- tion, drinking water. Resorsinolun Klorlanmasında Olu¸san Kloroformun Formasyonuuzerine ¨ bir Çalı¸sma Ozet¨ Bu ¸calı¸smada model hümik asit olarak se¸cilen resorsinol, sulu ortamda sodyum hipoklorit ile klor- lanmı¸stır. Resorsinol ve klorun ba¸slangı¸cderi¸simleri ve bunların oranları, sıcaklık, zaman ve pH gibi bazı faktörlerin kloroform olu¸sumuna etkileri incelenmi¸svetartı¸sılmı¸stır. Olu¸san kloroformun deri¸simini zaman, ba¸slangı¸c toplam organik karbon deri¸simi, ba¸slangı¸cklorderi¸siminin ba¸slangı¸c toplam organik karbon deri¸simine oranı, reaksiyon sıcaklı˘gı ve reaksiyon pH’sı cinsinden önsezinleyen %10 hassasiyette korelas- yonlar elde edilmi¸stir. Hümik asitlerin varlı˘gı nedeniyle belli bir deri¸simde toplam organik karbon i¸ceren suyun klorlanmasıyla olu¸sacak kloroformun tolere edilebilir en yüksek deri¸simi a¸smamasını garanti eden gerekli optimum klorlama süresi, uygulanacak herbir klor dozu i¸cin, bu korelasyonlardan saptanabilir. Anahtar Sözcükler: Klorlama, hümik asit, resorsinol, haloform reaksiyonu, trihalometan, kloroform, dezenfeksiyon, i¸cme suyu. 289 OZBELGE¨ Introduction centages of chlorination: 2-chloro- ; 4-chloro- ; 2,4- dichloro-; 4,6-dichloro- and 2,4,6-trichloro-resorcinol. The formation of chlorinated organics and espe- They identified the intermediates in the absence of cially of trihalomethanes (THMs) during the disin- phosphate buffer which might participate in the re- fection of water with chlorine is emerging as a per- action and alter the structure of the products. Only sistent problem associated with the maintenance of the relative rates of chlorination were determined for potable water quality due to the fact that high con- resorcinol and several of the chlorinated resorcinols. centrations of THMs in drinking water may have car- Based on the above-given information from the cinogenic effects in the long-term, according to the literature, resorcinol was chosen as a model humic information published by the National Cancer In- substance and its chlorination in aqueous medium stitute of the U.S.A. (1976). Therefore, the water deprived of any halogen ions, ammonia and addi- industry now faces a regulation proposed by the En- tional organic substances is investigated in this work. vironmental Protection Agency (EPA) to limit the The effects of some factors such as initial concentra- long-term average exposure of the public to THMs tions of resorcinol and chlorine as well as their ratios, up to 100 µg/l via the drinking water supply. temperature, time and pH are studied and discussed. The humic substances naturally present in water Developing equations for predicting the chloroform constitute the dominant precursors of THMs among formation rate and kinetics as a function of these which chloroform is known to be the by-product oc- factors is considered to be advantageous, because curring at the highest concentrations. Therefore, they will allow more adequate design formulations the conditions controlling the formation of chloro- of treatment plants that minimize the formation of form have to be optimized to keep the THM con- THMs and better prediction of the influence of envi- centrations within the permissible ranges, while effi- ronmental parameters on the plant performance. ciently disinfecting water by chlorination. Also, to establish a reaction pathway for the formation of chloroform and the chlorinated acids, knowledge of Experimental the structure of humic material is necessary. Leer Reagents: Resorcinol, 4-chloro-resorcinol and et al. (1985) reported that the possibility of 1,3- 4,6-dichloro-resorcinol were obtained in high purity dihydroxybenzene structures as the precursor frag- from Aldrich Chemical Company. Sodium hypochlo- ment for chloroform formation from humic material rite (NaOCl) solution (5% by wt) was directly used remained to be proven, although Rook (1977, 1980) as a stock solution during the experiments. The proposed a mechanism for the reaction between chlo- solutions of resorcinol, 4-chloro-resorcinol and 4,6- rine and resorcinol (1,3-dihydroxybenzene). Leer et dichloro-resorcinol were prepared by weighing appro- al. (1985) also emphasized the necessity for the iden- priate amounts of each and diluting them with ultra- tification of reaction intermediates to understand the pure water to the desired molarities. Ultrapure water mechanism of the chlorination reaction between chlo- of 18 MΩ-cm resistivity was used for all stock solu- rine and resorcinol, being a model precursor frag- tion preparations and also for cleaning and rinsing ment for chloroform formation. all the glassware during the experiments. Boyce and Hornig (1983) conducted a series of ex- Reaction vessel: In order to reduce any pho- periments showing that the derivatives of resorcinol tolytically induced reactions, 50 ml-amber glass bot- were highly effective precursors of THMs at neutral tles covered with teflon-septum headings were used and alkaline pH. They identified and reported the without stirring. chlorination intermediates of resorcinol at different Residual chlorine analysis: Based on the lit- conditions. The distribution of products was found erature survey, the DPD (diethyl-p-phenyl-diamine) to be strongly dependent on both the pH and the rel- method was chosen for the residual chlorine analy- ative initial concentrations of chlorine and resorcinol sis as the most appropriate technique (Wilde, 1991) in solution. They used phosphate buffer for adjust- giving very quick and reproducible results. ing the desired pH in the solution and their study Haloform analysis: The reaction was quenched was directed to elucidate the mechanism rather than by the addition of excess sodium thiosulfate to the the kinetics. An investigation of the aqueous chlo- solution, before the analysis of the unreacted reac- rination of resorcinol was also reported by Heasley tants and the formed products. The analyses were et al. (1989) at different pH values and varying per- carried out by direct aqueous injections of 0.1 µlsam- 290 OZBELGE¨ ples to a Hewlett-Packard 5890 Gas Chromatograph constant temperature of 120◦C. 0.1 µlsampleswere (GC) with a flame ionization detector (FID). Pre- injected to the GS using 1 µl gas-tight Hamilton sy- liminary runs were performed to choose the most ringes with sensitivities of 0.001 µl and at least suitable column and the detector in the present ex- three injections of this volume were repeated for each perimental work. A high performance, cross-linked specific measurement. Each experimental run was methyl silicone gum capillary column (called HP-1 also repeated three times to check the accuracy and after its trade name) with a length of 25 m and an the reproducibility of the results. The syringes were outside diameter (OD) of 0.32 mm was decided to be cleaned after each experiment with detergents and used at a constant temperature of 120◦C throughout ultrapure water, rinsed with pure alcohol and dried the analyses. The electron capture detector (ECD) in an oven at 100◦C. was best in the detection of chloroform after its ex- Standard solutions: The standard solutions of traction from the aqueous medium into an organic resorcinol and chloro-resorcinols were prepared at solvent, namely, n-pentane with an extraction effi- different concentrations in ultrapure water. Only ciency of 99% , whereas extracted resorcinol samples chloroform was injected in its pure form as a 0.1 µl gave unsatisfactory results due to the low extraction standard sample into the GC. The internal standard efficiency of resorcinol in n-pentane (about 1% ). In chosen to be para-chlorophenol, as it did not inter- the present study, a common organic solvent for ex- fere with the products of analysis, could be easily tracting both the reactants and the by-products from detected and its retention time as well as its position the aqueous medium with high extraction efficiencies with respect to the intermediate products was found could not be found either at the end of a thorough in the literature (Heasley et al., 1989). literature survey, or after a tedious trial and error procedure involving preliminary laboratory work. It Experimental set-up and procedure: The was found by Mukhopadhyay and Sohani (1989) that experimental set-up as well as the sequential flow 99% recovery of resorcinol from the aqueous phase of the

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