N. Kulikov et al./Chem.J.Mold. 2008, 3 (1), 67-69correspondingly. Besides, BC modification led to certain compacting <strong>of</strong> catalyst granules: it is confirmed by bulkdensity growth, which is 986 and 1037 g\dm 3 for GFG and GFG-M correspondingly.The specific surface <strong>of</strong> GFG-M sample is greater by 24 m 2 \g than that <strong>of</strong> GFG. From the other hand, as the data<strong>of</strong> table 1 show, the difference between mesopores <strong>of</strong> mentioned samples is 13.9 m 2 \g. However taking into account thefact that there is a certain error at S spdetermination and adsorption measurements, we have reasons to establish rathersatisfactory coincidence <strong>of</strong> both calculation results and those received by the instrumental method. Hence, we candraw a conclusion about the correctness <strong>of</strong> application <strong>of</strong> chosen models for the description <strong>of</strong> equilibrium adsorptionprocesses in the system “hopcalite – water”. If initial hopcalite GFG is characterized with rather equal mesopore volumedistribution according to their size, GFG-M is characterized with narrow distribution with maximum at 3.8 nm.Thus, bentonitic clay modification allows to construct hopcalite porous structure purposively, to be exact: t<strong>of</strong>orm mesoporous structure with narrow distribution <strong>of</strong> pore volume on sizes by means <strong>of</strong> variation <strong>of</strong> binding materialparticle size.References[1] Golbraih Z.E. Manganese dioxide as an adsorbent // In the book: Active manganese dioxide.-L.:ONTI-Himteoret.1937.-p.124-162.[2] Rode E.Y. Manganese oxygen compounds.-M.: PH AN SSSR. 1953.-478 p.[3] Kireev S.G., Mukhin V.M., Kireev A.S. and others. Theoretical problems <strong>of</strong> <strong>chemistry</strong> <strong>of</strong> surface, adsorption andchromatography: Thesis <strong>of</strong> rep. to X International conference. April, 24-28, 2006, Moscow-Klyazma.-M.: IFHRAN, 2006.-p.175.[4] Keltsev N.V. Principles <strong>of</strong> adsorption technique. 2 edition, revised and complem.- M.:Chemistry. 1984.-592 p.nd[5] Kireev S.G., Mukhin V.M., Tchebykin V.V. Modern state and development perspectives <strong>of</strong> adsorption theory: Coll.<strong>of</strong> mater. <strong>of</strong> IX International conference on theoretical questions <strong>of</strong> adsorption and adsorption chromatography-Moscow, 2001, April,24-26.- M.: IFH RAN. 2001.-p. 225-228.[6] Greg S., Sing K. Adsorption, specific surface, porosity: Transl. from Engl. 2 edition-M.: Mir. 1984.-306 p.nd[7] Komarov V.S. Adsorbents and their properties.-Minsk: Science and technique. 1977.-248 p.69
Chemistry Journal <strong>of</strong> Moldova. V. Gladchi General, et al./Chem.J.Mold. Industrial and 2008, Ecological 3 (1), 70-76 Chemistry. 2008, 3 (1), 70-76THE STUDY OF REDOX CONDITIONS IN THE DNIESTER RIVERViorica Gladchi a *, Nelli Goreaceva a , Gheorghe Duca b , Elena Bunduchi a , Lidia Romanciuc a ,Igor Mardari a , Ruslan Borodaev aaMoldova State Univeristy, 60 A.Mateevici str. MD 2009, MoldovabAcademy <strong>of</strong> Sciences <strong>of</strong> Moldova, tefan cel Mare 1, Moldova*E-mail: ggladchi@yahoo.com, phone: 577538, fax: 577557Abstract: The work presented in the paper discusses the contribution <strong>of</strong> the Novodnestrovsc water system to theformation <strong>of</strong> redox conditions in the lower Dniester. The conclusions were drawn on the basis <strong>of</strong> a long-term protocol<strong>of</strong> analyses that included the analysis <strong>of</strong> the oxygen regime, evaluation <strong>of</strong> the content <strong>of</strong> hydrogen peroxide, rH 2,biological oxygen demand as well as other additional parameters.Keywords: kinetic indicators, hydrogen peroxide, redox state, free radicals, inhibition capacity.IntroductionThe Dniester is a trans-boundary river crossing the countries <strong>of</strong> Moldova and Ukraine, discharging into theBlack Sea. Its total length is 1352 km, with 636 km flowing through Moldova. The river is the largest one in Moldovaand the chief source <strong>of</strong> drinking water for more than a million people. The Dniester River basin occupies 57% <strong>of</strong> thearea <strong>of</strong> the Republic <strong>of</strong> Moldova, and run-<strong>of</strong>f water, municipal effluents and industrial discharges contribute to thedegradation in water quality [1-5].In 1981 in the middle part <strong>of</strong> the river on the territory <strong>of</strong> Ukraine a barrage was constructed, creating theHydropower Station. The newly formed storage pond is 194 km long; the capacity <strong>of</strong> the reservoir is 3.0 km 3 . The mainpurpose <strong>of</strong> the reservoir construction was for power supply and flood control. In 1985 another dam was constructeddownstream <strong>of</strong> the Novodnestrovsc barrage in order to create a 20-km buffer reservoir. The second barrage also servesas a frontier between Moldova and Ukraine. The main purpose <strong>of</strong> the second barrage construction was to regulate thewater discharge from the first barrage and also to generate electric power.The Dniester reservoir is a canyon-type, deep-water lake with a 54 m maximum depth near the dam. Low watertemperature, a deficiency in dissolved oxygen, and the presence <strong>of</strong> hydrogen sulfide and ammonium are typical for thehypolimnion <strong>of</strong> such reservoirs [6]. Once the reservoir was filled with water, organic-rich sediments have accumulated,and the decomposition <strong>of</strong> this organic material creates low red-ox conditions. In other similar reservoirs, elevatedphosphate and transition metal concentrations have been measured that can be attributed to the reductive-dissolution <strong>of</strong>iron- and manganese- oxides, and the release <strong>of</strong> adsorbed phosphate [7]. All these chemical species can have an adverseimpact on down-stream aquatic life [8].Since the beginning <strong>of</strong> full-capacity operation <strong>of</strong> the Hydroelectric Power Plant, dramatic changes in the waterquality occurred in the river emerging from the buffer reservoir. The temperature regime <strong>of</strong> the river has been changedas follows: the mean temperature value decreased by 8-10 0 C in summer time; when the average air temperature reached30-32 0 C, the water temperature in the lower reach was 16-18 0 C. Severe changes in the aquatic ecosystem occurred: thediversity <strong>of</strong> hydrobiont species was decreased, fish stocks also decreased, and mass fish kills were <strong>of</strong>ten observed [9].Ichthyologists have pointed out the negative effects <strong>of</strong> the dam on the ichthyo-fauna. Some fish species have stoppedspawning, and fish stocks have been 18-fold reduced. Reproduction <strong>of</strong> some species has decreased 30-fold. Certainstudies revealed that 80% <strong>of</strong> the sturgeon sampled showed signs <strong>of</strong> spawn reabsorption. The presence <strong>of</strong> reducingsubstances in the amounts exceeding quite <strong>of</strong>ten the contents in oxidizers (hydrogen peroxide), provoke the unbalance<strong>of</strong> these processes in water environment. It is known that the reductive, quasi-reducing and super oxidative conditions<strong>of</strong> natural waters are destructive for the development <strong>of</strong> hydro-bionts, including fish [10-12; 13-32]. Quasi-reducingconditions is toxic for certain bacteria, and fish larvae [13]. The red-ox state <strong>of</strong> surface natural waters is a parameter thatcharacterizes the ecological state <strong>of</strong> the water body and its auto-purification capacity [8; 15-17; 30-32]. Biologicallyhealthy fresh water is determined by the presence in it <strong>of</strong> hydrogen peroxide within the limits <strong>of</strong> 10 -6 mol/l [15-16].In sea water the amount <strong>of</strong> hydrogen peroxide is substantially lower then in fresh waters [7,11,12; 22-25]. In thebiogeochemical cycle <strong>of</strong> oxygen in fresh water ecosystems the stationary concentrations <strong>of</strong> oxidative equivalents suchas OH radicals constitute 3-5 . 10 -16 mol/l. The range <strong>of</strong> variation <strong>of</strong> their concentration should not vary by more than afactor <strong>of</strong> 10 [23]. Redox processes in surface natural waters containing dissolved oxygen occur with the formation <strong>of</strong>intermediate active forms, namely, hydrogen peroxide, and hydroxide - and super-oxide radicals. Chemical processes<strong>of</strong> oxidation, which change the redox state <strong>of</strong> metal ions, depend on the rates <strong>of</strong> free radical formation and destruction,and their steady-state concentrations.In order to perform investigations <strong>of</strong> the river there were selected 6 permanent sites located as follows:Site 1 – v.70
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