水污染

ISSN 1063�455X, Journal of Water Chemistry and Technology, 2012, Vol. 34, No. 2, pp. 117–123. © Allerton Press, Inc., 2012. Original Russian Text © N.A. Klimenko, E.A. Samsoni�Todorova, L.A. Savchina, T.P. Chekhovskaya, I.N. Lavrenchuk, T.N. Zasyad’ko, 2012, published in Khimiya i Tekh� nologiya Vody, 2012, Vol. 34, No. 2, pp. 195–205. Seasonal Fluctuations in the Content of Different Forms of Organic Carbon and Their Changes in Water Treatment Processes N. A. Klimenko, E. A. Samsoni�Todorova, L. A. Savchina, T. P. Chekhovskaya, I. N. Lavrenchuk, and T. N. Zasyad’ko Dumanskii Institute of Colloid Chemistry and Water Chemistry, NAS of Ukraine, Kiev Received June 23, 2011 Abstract—We have assessed the content of different forms of organic carbon (total, bioaccessible, and assimilated) in the water of the Dnieper river in the area of the water intake of the Dnieper water station and in the water after all treatment stages used. The article has investigated seasonal changes in the content of different forms of organic carbon and the impact of water treatment on these indicators. DOI: 10.3103/S1063455X12020087 Keywords: assimilated organic carbon, bioaccessible organic carbon, total organic carbon, natural organic compounds. INTRODUCTION Natural water in the basin of the Dnieper River is characterized by a high content of natural organic com� pounds (NOC) substantially affecting, in water treatment, the quality of drinking water obtained. Since NOC are a substrate ensuring vital activities of microorganisms, their presence in definite concentrations deter� mines biological stability or instability of drinking water. Water biological stability is a state whereby there are no conditions for reproduction of coliform and heterotrophic bacteria [1] and, accordingly, secondary water pollution. In transportation and storage of water the repeated growth of microorganisms may result in the deterioration of bacterial qualities, taste, and gust of the water, increases corrosion and promotes the growth of invertebrate hydrobionts in the system [2]. The main factor determining biological stability of the water is the presence in it of biologically accessible organic carbon (BAOC). BAOC is identified as a fraction of soluble organic carbon, which may be mineralized by heterotrophic microorganisms. Apart from BAOC an important indicator of water biological stability is the presence in it of an assimilated organic carbon (AOC) [3–4]. Some researchers believe that it is the content of AOC in he water that correlates with the secondary bacterial growth and is a measure of bacterial mass [5]. Papers [3, 6, 7] consider AOC as part of BAOC. The presence of BAOC and AOC in the water is determined by the process of AOC oxidizing processes both due to natural reactions in the water ecosystem and as a result of using oxidants when preparing and disinfecting water. According to the data of [5, 8, 9] the reaction activity of different oxidants with respect to AOC is mani� fested in a different way. Thus, ozone is known as the most reactive oxidant [10]; chlorine dioxide and ferrate react mainly with phenol compounds: chlorine or hypochlorite react fast only with amines; permanganate slowly interacts with organic compounds, mainly with olefins. In the case of AOC generation when the water is treated by different oxidants there are not enough data for the comparison [11, 12]. However, paper [13] found that simple carboxylic acids in oxidation treatment of water with ozone constitute a substantial part of AOC [10, 13]. The potential of the formation of organic acids in ozonization is in series 10.8–62.8 μg/mg of total organic carbon (TOC) [10]. A relatively high potential of formation can also be observed for chlorine dioxide—5.3–17.9 μg TOC. In the case of chlorination the capacity of the formation of organic acids was low and did not exceed 3.4 μg/mg TOC. The authors of [10] proposed to use the potential for the formation of organic acids as a measure characterizing the formation of BAOC and AOC. However, as was shown in [14] main ozonization by�products—aldehydes and carboxylic acids account only for 37% of BAOC. Meantime, it is BAOC that is the main precursor for the formation of trihalomethanes and halogenacidic acids in decon� tamination of the water with chlorine [2]. Determination of BAOC [15] showed that NOC of the neutral hydrophilic nature possess the highest biodegradability. Then follows fractions of charged hydrophilic com� pounds, weakly hydrophobic and strongly hydrophobic acids. NATURAL WATERS 117 In the water of the Dnieper reservoirs prevailing components of NOC are humic compounds, which con� stitute or Kiev, Kremenchug, and Kakhovka reservoirs respectively 77.5; 66.9 and 5.4 [16]. In its turn, humic 118 KLIMENKO et al. JOURNAL OF WATER CHEMISTRY AND TECHNOLOGY Vol. 34 No. 2 2012 compounds have prevailing amount of fulvic acids (FA) whose content is 20–40 higher than that of humic acids [16]. In this case the A molecular weight in the Kiev and Kremenchug reservoirs is mainly in the range 200–1000 amu. One may expect that the natural background of the BAOC content in the water of the Dnieper River will be relatively small and water chlorination will slightly affect its changes. However, the data on the determination of BAOC and AOC in the Dnieper River water are absent. Meantime, drinking water is considered biologically stable if the AOC level is less than 10–20 μg acetate� C/dm3 without disinfection and less than 50–100 μg of acetate�C/dm3 if the water is disinfected [1, 17]. Thus, the data on the content of TOC, BAOC, and AOC in the initial water and after its treatment for obtaining dinking water is a basis for assessing the efficiency of water�treatment processes, necessary correc� tion of the technology and the use of new processes especially with the account of ensuring water biological stability in distribution systems. The objective of the present paper is to assess the content of TOC, BAOC, and AOC in the Dnieper River in the area of the Dnieper Water Station (DWS), its seasonal changes and the impact of water treatment on these indicators. EXPERIMENTAL The Dnieper River water in the spot of DWS water intake at the 1st lift (herewith this water is designated as W1) and the water after all treatment stages provided for at the DWS from the tank of clean water (hereinafter W2) were chosen as objects of research. The content of total organic carbon (mC/dm3) was found by the method of catalytic burning at 800°C on a Shimadzu TOC�V CSN device (Japan). Determination of UV 254 was carried out on a two�beam spectrophotometer Unico 4802 at the wavelength λ = 254 nm using a quartz laboratory dish with l = 1 cm. When investigating BAOC the technique was used presented in [4, 18–20]. These papers show that when determining BAOC the best thing is to use microorganisms from the drinking�water conditioning station and distribution systems and fix them on inorganic carriers. However, in our experiments biologically active sand taken from DWS fast filters was used. Directly before the research the sand was repeatedly washed with distilled water until the achievement of a constant value of the TOC content in washing water (not more than 0.5 mg C/dm3). After washing 100 g of wet biologically active sand were placed into five incubation flasks then each was topped up with 300 cm3 of the water studied. The experiment was carried out in a thermal room (20 ± 2°C) at constant aeration of a water sample at an intensity of 4 dm3/h. The air from the aerator passed through a drexel filled with distilled water. The incubation period constituted 7 days. Every day a water sample was taken from incubation flasks and the TOC content was determined. Foe determination of BAOC (mg/dm3) the ratio proposed in [18–21] was used: BAOC = TOCini – TOCmin – TOCwash, where TOCini is the TOC content in the solution before the incubation, TOCmin is a minimal content of TOC over the incubation period, TOCwash is the TOC content in the washing water after final washing of the sand, mg C/dm3. DETERMNATION OF ASSIMILATED ORGANIC CARBON A standard indicator strain of assimilated carbon in the water Pseudomonas fluorescens P 17 was used. The indicator strain was obtained from the National Collection of Industrial and Marine Bacteria (NCIMB, Great Britain). The strain was stored in a lyophilic state at 8°C and on a plain agar at room temperature. The culture was sowed again once a month. The preparation of experiments was carried out according to standard methods of research of water and waste water [22] with some modifications. The microbiological determination of AOC in water samples is recommended to be carried out by means of the strain P. fluorescens P 17, which was grown on tap water since it is believed that it is limited by carbon. In Ukraine tap water often contains great amount of carbon therefore it is not suitable for preparing sowing material. In this connection sowing material was prepared on the medium of the following composition (in g/dm3): K2HPO4—0.17; NH4Cl—0.767; KNO3—1.444; NaCl—0.1; MgSO4—0.1. For preparing the solution deionized water was used. SEASONAL FLUCTUATIONS IN THE CONTENT OF DIFFERENT FORMS 119 JOURNAL OF WATER CHEMISTRY AND TECHNOLOGY Vol. 34 No. 2 2012 The experiment was conducted in vesses treated in such a way as to minimize the content of carbon on its surface. For this purpose glassware was used with thin sections, test tubes were closed with special metal plugs, vials of dark glass of 50 cm3 were closed by screwing in aluminum plugs. The vessels were treated with deter� gents, washed with hot water and a 0.1 M solution of hydraulic acid. After that the vessels were rinsed thrice at first with distilled and then with dionized water and sterilized. The vials, pipettes, and test tubes with metal covers additionally were held in a drying cabinet for 180 min at 350°C. The following reagents were used in the research: the solution of sodium acetate—400 mgC/dm3; the solu� tion of sodium thiosulfate—13.2 mg/dm3; the physiological solution—8.5 g/dm3. All reagents were prepared on deionized water and sterilized. As a result of specially conducted experiments it was found that the indica� tor strain P. fuorescens P 17 grows uniformly both on medium R2A proposed in [22] and on the meat�peptone agar medium (MPA). Therefore, all investigations were conducted on the latter. To each of four vials a 50 cm3 solution of salts were introduced and sterilized. A solution of sodium acetate was added to two vials so that the final AOC concentration of acetate constituted 100 μg/cm3. A day’s culture of the strain P. fluorescens P 17 was grown; from it a suspension was prepared on a sterile physiological solution containing 500 million of cells in 1 cm3 according to the McFerline standard. By doing consecutive dissolu� tions 250000 cells/cm3 were obtained. Such suspension, 100 μl, were introduced into every vial. The vials were incubated for 10 days at 20°C. Then from the content of each vial tenfold dissolutions were prepared. Samples by dissolving 10–3 and 10–4 in the amount of 0.1 cm3 were plated on MPA on Petri dishes. Each sample was plated on 35 dishes, which were incubated at 20°C for three days; after that the amount of colonies that grew up was counted in colony�forming units (CFU). The culture grown on a salt medium with acetate was stored at 8°C and was used as a sowing material for determination of AOC periodically checking the titer of the cul� ture in the vial. The increment of the strain P. fluorescens P 17 on acetate and the AOC content were calculated by formulas given in [22]. Then 50 cm3 of freshly sampled filtered water were introduced to the vials. The solution of sodium thiosul� fate of 0.1 cm3 each were introduced to the same vials for neutralization of disinfectants, which may be in the water. The vials were closed with plugs and were pasteurized on a water bath at 70°C for 30 min. The samples were cooled and inoculated with sowing material of the strain P. fluorescens P 17 until the concentration 500 CFU/cm3. The inoculum was held at 20°C for 10 days. The samples from each vial were dissolved tenfold. From dissolutions 10–3; 10–4 and 10–5 were sowed by 0.1 cm3 into Petri dishes. The sowings were held in a thermostat at 20°C for three days. After that the amount of grown�up colonies was calculated and determined the AOC content in the selected samples of the water in the following way: AOC = × 1000, where N is the amount of P. fluorescens P 17, which grew on a water sample being investigated, CFU/cm3; n is an increment of P. fluorescens P 17 on acetate calculated per 1 μg of acetate carbon, μg acetate�C/dm3 RESULTS AND DISCUSSION The determination of TOC, BAOC, and AOC was carried out from January 2010 till March 2011 in the initial water sampled at the water intake place on the 1st lift and the water that has passed all stages of treatment provided for at DWS. Figures 1 and 2 show histograms of variations of the values TOC and BAOC in the waters under study over the period in question. The data on the change of the UV254 values over the same period are shown in Fig. 3. Table 1 shows the variation of the TOC content in waters W1 and W2 from January 2010 till March 2011. As can be seen from Figs. 1, 2, and Table 1 the highest value of the TOC magnitude was observed in January 2010 and is determined by specific climatic conditions in this period. In this case rather high were the UV254 values and the relative fraction of BAOC as part of TOC. This is related to an increase in the water of com� pounds with aromatic and chromophore groups, which are effectively removed in the coagulation–settle� ment–filtration processes. In February 2010 the TOC value and the BAOC value decreased, while the UV254 vale remain effectively unchanged, however the degree of TOC removal changed insufficiently. From April till June one could observe a gradual increase of the TOC content and an increase of the UV254 value. In accor� N n ��� 120 KLIMENKO et al. JOURNAL OF WATER CHEMISTRY AND TECHNOLOGY Vol. 34 No. 2 2012 dance with it the degree of the TOC removal from 43.7 to 50.3% increased. A BAOC fraction in this case was within the range 18.5–23.0%. Fig. 1. Variation of the TOC (�) and BAOC (�) values in water samples W1 from January 2010 until March 2011. 0 2 4 6 8 10 12 TOC, mg C/dm 3 J an ua ry 2 01 0 Month F eb ru ar y 20 10 M ar ch 2 01 0 A pr il 20 10 J un e 20 10 J ul y 20 10 A ug us t 2 01 0 S ep te m be r 20 10 M ay 2 01 0 M ar ch 2 01 1 F eb ru ar y 20 11 J an ua ry 2 01 1 D ec em be r 20 10 N ov em be r 20 10 O ct ob er 2 01 0 Fig. 2. Variation of the TOC (�) and BAOC (�) values in water samples W2 from January 2010 until March 2011. 0 5 10 15 20 25 J an ua ry 2 01 0 Month TOC, mg C/dm 3 F eb ru ar y 20 10 M ar ch 2 01 0 A pr il 20 10 J un e 20 10 J ul y 20 10 A ug us t 2 01 0 S ep te m be r 20 10 M ay 2 01 0 M ar ch 2 01 1 F eb ru ar y 20 11 J an ua ry 2 01 1 D ec em be r 20 10 N ov em be r 20 10 O ct ob er 2 01 0 SEASONAL FLUCTUATIONS IN THE CONTENT OF DIFFERENT FORMS 121 JOURNAL OF WATER CHEMISTRY AND TECHNOLOGY Vol. 34 No. 2 2012 A decrease of the TOC content, the values UV254, and fractions of BAOC in August and September 2010 was conducive to substantial decrease of the TOC removal degree. Thus, the analysis of the quoted data makes it possible to suppose that the TOC removal degree in the coagulation–settlement–filtration processes best of Table 1. Efficiency of removing total organic carbon from the Dnieper River water after all stages of treatment Sampling time TOC, mg C/dm3 TOC decrease degree, % W1 W2 January 2010 19.2 9.2 52.1 February 2010 16.0 9.0 43.8 March 2010 14.4 7.9 45.1 April 2010 16.1 9.2 42.9 May 2010 18.1 10.0 44.7 June 2010 18.0 9.4 47.8 July 2010 18.0 9.2 48.9 August 2010 16.0 9.4 41.2 September 2010 14.4 9.2 36.1 October 2010 12.4 7.0 43.6 November 2010 10.1 7.5 25.7 December 2010 9.1 8.4 7.7 January 2011 13.2 8.9 32.6 February 2011 14.3 9.8 31.5 March 2011 16.2 10.6 34.6 0 20 40 60 80 100 120 UV 254 J an ua ry 2 01 0 Month F eb ru ar y 20 10 M ar ch 2 01 0 A pr il 20 10 J un e 20 10 J ul y 20 10 A ug us t 2 01 0 S ep te m be r 20 10 M ay 2 01 0 M ar ch 2 01 1 F eb ru ar y 20 11 J an ua ry 2 01 1 D ec em be r 20 10 N ov em be r 20 10 O ct ob er 2 01 0 Fig. 3. Variation of the UV254 value in the Dnieper River water from January 2010 until March 2011: �—W1; �—W2. 122 KLIMENKO et al. JOURNAL OF WATER CHEMISTRY AND TECHNOLOGY Vol. 34 No. 2 2012 all correlate with the change of the UV254 value, i.e. the greater it, the higher the TOC removal degree. One could not observe a sharply pronounced correlation between the BAOC fraction and the TOC removal degree. Table 2 gives the data on a decrease of the BAOC fraction in the Dnieper Rive water and after its treatment. As can be seen, the degree of a decrease of the BAOC content after water treatment the lower, the higher BAOC fraction as part of TOC. The presence of such differences between different water samples may be referred to the changes in the quality composition of NOC in different periods of the year determined by the variations in the distribution in terms of the molecular weight, the degree of hydrophilicity–hydrophobicity, density, and the composition of functional groups. As is known, coagulants most effectively remove hydrophobic components of NOC and worse hydrophilic ones. No doubt, biologically accessible organic carbon is a more hydrophilic fraction of TOC with a smaller molecular weight than other fractions. Therefore, the relationship being observed between the efficiency of reducing the TOC content and the BAOC fraction (see Table 2) is quite valid. The absence of such a relation� ship is, perhaps, related to the fact that the removal of NOC (in units of TOC) is determined by several mech� anisms: neutralization of the charge of colloid particles, complexation–precipitation of a dissoluble fraction and its adsorption on the floccules being precipitated and aluminum hydroxide [23]. The correlation being observed between the UV254 and the degree of TOC removal makes it possible to assume that a decisive in the given process of coagulation is also adsorption of aromatic compounds of the fraction of fulvic acids prevailing in the Dnieper River water. They determine the bulk of the NOC charge, which greatly affects the coagulation process. For ensuring biological stability of the water it is very important to assess the level of AOC content in the Dnieper River water before and after its treatment. Table 3 provides data on measuring the change of the AOC content in the samples of waters W1 and W2 from January 2010 till March 2011. As can be seen from the data of Table 3 the content of AOC in the untreated water of the Dnieper River is rather high and its state is far from biologically stable. It may determine the fouling of water treatment facilities at the stage of coagulation. After all stages of treatment provided for at DWS the degree of reducing the content of AOC is rather high and the state of the water in some cases may be assessed as biologically stable or approaching it. Table 2. Efficiency of a decrease of the content of biologically accessible organic carbon in water treatment processes of the Dnieper River