The main drawback of drinking water chlorination involves the formation of quite hazardous disinfection by-products (DBPs), represented mainly by halogenated species. Based on the authors’ monitoring data since 2002, the prevalence of chlorine over bromine in the composition of volatile DBPs was shown for the drinking water in Ufa (Russia). However, the situation was completely reversed in the case of semi-volatile DBPs. The principal goal of the present study involved rationalization of the results of the long-term monitoring. Gas chromatography–mass spectrometry (GC-MS) was used for the qualitative and quantitative analysis of volatile DBPs. Identification of semi-volatile compounds was carried out with GC-MS, while gas chromatography with an atomic emission detector (GC-AED) was used for their quantification. A significant contribution of oxygen to the composition of semi-volatile compounds proves the decisive role of the dissolved organic matter oxidative destructive processes. Statistical analysis revealed notable linear correlations for trihalomethane and haloacetic acid formation vs. chlorine dose. On the contrary, halogenated semi-volatile products do not demonstrate any correlations with the water quality parameters or chlorine dose. Principal component analysis (PCA) placed them into separate groups. The results allow for proposing that formation of the organohalogenated species involved the fast penetration of bromine into the humic matter molecules and, further, their oxidative destruction by active chlorine.

Introduction. To conduct a total assessment of carcinogenic, non-carcinogenic, and organoleptic risks to public health and cover both normalized and non-normalized pollutants of potable water, based on the results of long-term monitoring studies, it is possible using an integral indicator of chemical harmlessness of water. Material and methods. Authors studied potable water of water intakes of surface and infiltration types from potable water reservoirs and remote zones of Ufa water distribution networks. Impurities were determined by chromatography, inductively coupled plasma mass spectrometry, photometric, nephelometric, and titrimetric methods. Results. The main effect on the amount of carcinogenic risk in potable water of the surface water intake are chloroform, bromodichlethane, dichloroacetic acid, in the infiltration water intake - in addition to these compounds zinc, lead and chromium are in addition influenced. Organic compounds (phthalates, benz(a)pyrene, volatile aromatic compounds, etc.) have no effect on this type of risk due to the presence in water in low background concentrations. The identified number of individual carcinogenic risks for bromodichloroacetic acid and dichloroacetic acid according to the WHO classification corresponds to the second range. As the surface type water intake is removed from the potable water reservoir, the total carcinogenic risk of water decreases by 13-30%, and the infiltration type increases by 41-84%. Values of noncancerogenic and organoleptic risks are constant for potable water of different water intakes and correspond to recommended limit values. The excess of the maximum permissible concentrations (SanPin 1.2.3685-21) of individual substances in the potable water of the city has not been detected for the whole period of observation. In terms of the integral indicator of chemical harmlessness, the most favorable is the po-table water of the infiltration water intake, in the technology of which is mainly used the UV for decontamination of water. Conclusion. Using a risk assessment methodology complements the traditional approach to assessing water quality under modern hygiene standards. It becomes possible to evaluate the effect of pollutants of various classes on water quality when they are present together.

Regression and neural network model for predicting the required dose of coagulant, depending on the quality of river water supplied for water treatment, are considered, their comparative analysis is carried out. For modelling and forecasting, statistical data collected for the period from 2005 to nowadays. Regression models were built on the true values of the factors (water quality indicators) and on their first differences to eliminate the trend in the series. For the models built on the true values, the statistical significance, was confirmed, high values of the coefficient of the determination were obtained, the values of the approximation errors were 22–25 %. In neural network modelling, networks of the multilayer perception were used. Generalization error on the test set when using other type of networks (RBF-networks, Elman networks), was significant above. Computational experiments have shown that, in general, the accuracy of neural network models is higher than regression ones. The average learning error was 7–9 %, the error on the test set increases to 12–16 %. The reliability of the forecast is increased by training the network on more recent data and using a larger set of facts. An increase in the influence of indicators of permanganate oxidability and colour of the initial river water on the dose of reagents with a simultaneous decrease in the degree of influence of alkalinity over the last five-year period was revealed. This confirms the need to periodically update data for building models. Selected models recommended for implementation in industrial monitoring of water treatment technology at the enterprise.

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The integral indicators for assessment of total concentration of chlorine and bromine in semi-volatile organic substances (SVOS) of water are presented. The method is based on liquid/liquid extraction of SVOS from a sample of water (natural, potable, industrial, purified sewage water etc.), concentrating the extract and without derivatization or conversion analyzed by the method of gas chromatography, coupled with atomic emission detecting (GC-AED). In this case the AED operates in two modes: the chlorine selective channel with detection at a wavelength of 479 nm and the bromine selective channel – at 478 nm. Under the given conditions of sample preparation and the chromatographic procedure the components are registered with Kovats retention index on non-polar phases from 900 to 3200. The range of the analytical procedure covers classes of SVOS, such as halogen-containing pesticides, aromatic and aliphatic hydrocarbons, fatty acids, ethers, polyaromatic hydrocarbons, phenols and their halogen derivatives. The total concentration of chlorine and bromine is calculated by component-independent calibration which is available by using an AED. The indexes are named Technogenic Organic Chlorine and Technogenic Organic Bromine, because analyzed compounds have technogenic or secondary technogenic origin. The sensitivity of determination is 1×10−6 mg/dm3 for the specified elements.