AP1_03.vp 1 Introduction In recent years attention has been drawn to understand- ing, characterising and predicting water quality behaviour in drinking water distribution systems. These systems act as large-scale chemical and biological reactors with a consider- able residence time. Improper design and operation may result in water of diminished quality in terms of increased water age, reduced disinfectant residual, increased growth of disinfectant by-products and bacterial levels, and may impact the level of compliance with current and impending wa- ter-quality regulations [1]. In the past, several authors have proposed algorithms for use in simulating the spatial and temporal variations in distribution system water quality. 2 Experimental part This study concentrates on changes in water quality trans- port in the pipelines that take drinking water from WTP Plav to the town of Tábor and to the towns and villages that lie on this route [2]. The length of these pipelines is about 80 km. The material of the pipelines is steel without any type of coat- ing. They carry about 285 l�s�1 from WTP Plav. There are six reservoirs along the pipelines, at various intervals, with a total capacity of about 48000 m3. The samples for this study were taken from six locations along the pipelines travelling towards Tábor (Fig. 1). Two methods were used to predict the decrease in residual chlorine in the distributed water. 3 Modeling of chlorine decay The first method for the decrease in chlorine in the bulk flow is based on first order kinetics [3]: c c k tt e� � � 0 1 where ct is the chlorine concentration in time t, in mg�l ��, c0 chlorine concentration in time t = 0, in mg�l ��, t time in days, k1 first order decay coefficient in d �1. The chlorine decay coefficient k1 calculated from the values of chlorine concentrations measured in the period 1997–2000 ranged from 0.252 d�1 to 1.336 d�1 and their coefficient of correlation varied from 0.637 to 0.999. A value lower than 0.9 was stated only 5 times. The second method for modelling possible chlorine loss in a pipe [4] combines the effect of bulk reaction, wall reaction and mass transfer. The overall rate of chlorine decay can be expressed as follows: � ��c b f H w� � � �k k R c c where � is the rate of chlorine decay in mg�l�1�d��, kb first order decay coefficient in d ��, c chlorine concentration in bulk flow in mg�l�1, kf mass transfer coefficient in m�d �1, RH hydraulic radius in m, cw chlorine concentration at the pipe wall in mg�l �1. The coefficient of chlorine uptake calculated by the second method includes two factors – chlorine uptake in bulk flow, and chlorine transfer from the bulk liquid to the wall with the subsequent reaction with biofilm and consumption of chlorine in the corrosion process. The calculated values of kb for the whole period 1997–2000 ranged from 0.00 to 1.336 (d�1) and for the constants kw1 (constant of chlorine uptake on the wall) from 0.828 to 1.000 (m�d�1). A coefficient of correlation lower than 0.9 was stated only in one case. This © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 3 Acta Polytechnica Vol. 41 No. 3/2001 Effect of the Distribution System on Drinking Water Quality A. Grünwald, B. Št’astný, K. Slavíčková, M. Slavíček The overall objective of this paper is to characterise the main aspects of water quality deterioration in a distribution system. The effect of residence time on chlorine uptake and the formation and evolution of disinfection by–products in distributed drinking water are discussed. Keywords: drinking water, distribution system, chlorine uptake, THM and HAA formation. Fig. 1: The samples for this study were taken from six locations along the pipelines travelling to the town of Tábor model demonstrated higher similarity to the measured values than the previous model. It was shown that the piping procedure has an important effect on the residence time in different parts of the distribu- tion system. Piping from WR Hosín II into WR Chotýčany take place during the night and is complete by 5 o’clock in the morning. The residence time difference between the samples taken from WR Chotýčany and WR Hosín II is about 5 hours. The decay of active chlorine with increasing residence time in the distribution system is given in Fig. 2. The concentration of chlorine active in the effluent from WTP Plav or WR Hosín II ranged during the whole period between 0.15 and 0.85 mg�l�1. In the influent to WR Sv. Anna and Veselí n/L the concentration of active chlorine was zero. The residence time at the end of the pipeline (WR Sv. Anna) was between 4.56 and 7.26 days. The average retention time was 5.85 days. 4 Deposition formation Previous research on the south Bohemian transport pipe- line has shown that deposits formed from particles of various origins and size can under specific conditions deteriorate the quality of distributed drinking water [5]. As a consequence of the resuspension of these deposits there is a rise in the consumption of active chlorine and in the formation of disin- fection by-products in the bulk flow. In our research a number of deposits were sampled from different sampling points along the transport pipeline. Sam- ple 1 comes from the shaft behind WR Hosín, Sample 2 from the shaft behind WR Chotýčany, Sample 3 from the shaft before WR Zlukov and Sample 4 from the shaft before WR Sv. Anna. The characteristics of these samples are given in Table 1. The characteristics of the deposits given in Table 1 show no dependency on sampling point. The content of suspended solids varied between 353 and 892 mg�l�1, an the content of volatile solids was rather low (1.3–3.1 % of suspended solids). The main part of the sus- pended solids consisted of iron. Its content ranged between 84.5 and 215 mg�g�1 (8.45–21.5 % of total suspended solids). The highest values were found in Samples 1 and 2. The content of other metals, e.g., manganese (0.28–0.67 %), nickel (0.01–0.04 %) and zinc (0.05–0.007 %) was much lower. Sedimentation analysis was used to analyse the charac- teristics of deposit suspension. From the measured values the sedimentation rates of particles and their proportion in the suspension were calculated. The comparison of the sedimen- tation curves is given in Fig. 3. The results of the sedimentation show that the biggest proportion of the particles deposited at higher rates were in Sample 1, sampled from the shaft near WTP Plav. The reason for this could be the high iron content. The sedimentation curves of Samples 2, 3 and 4 were similar, but a larger propor- tion with good sedimentation was found in Sample 4. This sample contained the highest content of suspended solids and the highest content of TOC. Fig. 2 shows that the deposits consisted mainly of particles that sediment at low rates and are able to pass from the de- posits into the bulk flow when there are changes in hydraulic conditions in the distribution system. These particles can deteriorate the quality of transported drinking water. 4 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ Acta Polytechnica Vol. 41 No. 3/2001 Fig. 2: Decay of active chlorine residual as a function of residence time Sample No. 1 2 3 4 Total solids [mg�l��] 1103 535 630 833 Volatile solids [mg�l��] 84 35 81 119 Nonvolatile solids [mg�l��] 1019 500 549 714 Suspended solids [mg�l��] 892 353 439 627 Volatile solids [mg�l��] 65 11 31 71 Nonvolatile solids [mg�l��] 827 342 408 556 CODMn [mg�l ��] 21.0 5.8 7.4 19.0 usp. s. [mg�l��] 16.1 1.4 3.0 7.0 Fe [mg�l��] 215.4 214.1 153.0 84.5 [%] 21.5 21.4 15.3 8.45 Mn [mg�l��] 3.0 2.8 4.2 6.70 [%] 0.3 0.28 0.42 0.67 Ni [mg�l��] 0.16 0.10 0.18 0.39 [%] 0.016 0.01 0.02 0.04 TC [%] 4.81 7.85 8.50 7.02 IC [%] 1.72 7.77 7.62 3.81 TOC [%] 3.09 0.08 0.88 3.21 Table 1: Characteristics of deposits from the pipeline WTP Plav – town of Tábor Fig. 3: Sedimentation curves 5 Formation of disinfection by-products The possible formation of disinfection by-products by reacting with chlorine was studied in the laboratory experi- ments under controlled conditions (temperature 20 °C, re- sidence time 72 hours, chlorine doses 0.5–4.0 mg�l�1, by chloramination constant addition of NH4 � 0.5 mg�l�1). De- posits from the shaft before WR Sv. Anna were used. Their characteristics were as follows: Content of suspended solids 346 mg�l�1, TOC 7.46 mg�l�1, pH 7.6. The experimental results are given in Fig. 4. It was shown that the concentration of chloroform in- creased with increasing doses of chlorine from 15.4 �g�l�1 (at Cl2 dose 0.5 mg�l �1) to 77.7 �g�l�1 (at Cl2 dose 4.0 mg�l �1) whereas during chloramination with the same chlorine doses the THM content ranged from 11.5 �g�l�1 to 14.1 �g�l�1. This means that the increase in THM concentration was negligible. 6 Conclusions The research has shown that the particles of deposits re- suspended into the bulk flow during changes in hydraulic conditions in the distribution system can be a real source of THM and HAA. Formation of these compounds depends mainly on the concentration of resuspended particles in wa- ter, doses of chlorine, and reaction time. Acknowledgements This research has been supported by GAČR grant No. 103/99/0659 and by Research program CEZ: J04/98211100002. The authors would like to thank prof. V. Janda, doc. N. Strnadová and MSc P. Fišar from the Department of Water Technology and Environmental Engi- neering VŠCHT Prague for their assistance. References [1] Kiéné, L., Lu, W., Lévi, Y.: Relative Importance of the Phenomena Responsible for Chlorine Decay in Drinking Wa- ter Distribution Systems. Wat. Sci. Tech., Vol. 38, 1998, pp. 219–272 [2] El-Shafy, M. A., Grünwald, A.: THM Formation in Wa- ter Supply in South Bohemia, Czech Republic. Water Res., Vol. 34, No. 13/2000, pp. 3453–3459 [3] Vasconcelos, J. J. et al: Kinetics of Chlorine Decay. Journal AWWA, Vol. 89, No. 7/1997, pp. 54–65 [4] Ozdemir, O. N. et al: Realistic Numerical Simulation of Chlorine Decay in Pipes. Water Res., Vol. 32, No. 11/1998, pp. 3307–3312 [5] Grünwald A. et al: Effect of Deposits on Water Quality in Distribution System (2000). CTU Reports, Proceedings of WORKSHOP 2000, Part B, Vol. 4, No. 7/2000, p. 568 Prof. Ing. Alexander Grünwald, CSc. grunwald@fsv.cvut.cz Ing. Bohumil Št’astný stastny@fsv.cvut.cz Ing. Kateřina Slavíčková slavickova@fsv.cvut.cz Ing. Marek Slavíček slavicek@fsv.cvut.cz Department of Sanitary Enginee ringCzech Technical University in Prague Faculty of Civil Engineering Thákurova 7, 166 29 Praha 6, Czech Republic © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 5 Acta Polytechnica Vol. 41 No. 3/2001 � � Fig. 4: Formation of THM in suspension with various doses of chlorine or chloramine << /ASCII85EncodePages false /AllowTransparency false /AutoPositionEPSFiles true /AutoRotatePages /None /Binding /Left /CalGrayProfile (Dot Gain 20%) /CalRGBProfile (sRGB IEC61966-2.1) /CalCMYKProfile (U.S. Web Coated \050SWOP\051 v2) /sRGBProfile (sRGB IEC61966-2.1) /CannotEmbedFontPolicy /Error /CompatibilityLevel 1.4 /CompressObjects /Tags /CompressPages true /ConvertImagesToIndexed true /PassThroughJPEGImages true /CreateJobTicket false /DefaultRenderingIntent /Default /DetectBlends false /DetectCurves 0.0000 /ColorConversionStrategy /CMYK /DoThumbnails false /EmbedAllFonts true /EmbedOpenType false /ParseICCProfilesInComments true /EmbedJobOptions true /DSCReportingLevel 0 /EmitDSCWarnings false /EndPage -1 /ImageMemory 1048576 /LockDistillerParams false /MaxSubsetPct 100 /Optimize true /OPM 1 /ParseDSCComments true /ParseDSCCommentsForDocInfo true /PreserveCopyPage true /PreserveDICMYKValues true /PreserveEPSInfo true /PreserveFlatness true /PreserveHalftoneInfo false /PreserveOPIComments true /PreserveOverprintSettings true /StartPage 1 /SubsetFonts true /TransferFunctionInfo /Apply /UCRandBGInfo /Preserve /UsePrologue false /ColorSettingsFile () /AlwaysEmbed [ true ] /NeverEmbed [ true ] /AntiAliasColorImages false /CropColorImages true /ColorImageMinResolution 300 /ColorImageMinResolutionPolicy /OK /DownsampleColorImages true /ColorImageDownsampleType /Bicubic /ColorImageResolution 300 /ColorImageDepth -1 /ColorImageMinDownsampleDepth 1 /ColorImageDownsampleThreshold 1.50000 /EncodeColorImages true /ColorImageFilter /DCTEncode /AutoFilterColorImages true /ColorImageAutoFilterStrategy /JPEG /ColorACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000ColorACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000ColorImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 300 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /GrayImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000GrayACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000GrayImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 1200 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict << /K -1 >> /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile (None) /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False /CreateJDFFile false /Description << /ARA /BGR /CHS /CHT /DAN /DEU /ESP /ETI /FRA /GRE /HEB /HRV (Za stvaranje Adobe PDF dokumenata najpogodnijih za visokokvalitetni ispis prije tiskanja koristite ove postavke. Stvoreni PDF dokumenti mogu se otvoriti Acrobat i Adobe Reader 5.0 i kasnijim verzijama.) /HUN /ITA /JPN /KOR /LTH /LVI /NLD (Gebruik deze instellingen om Adobe PDF-documenten te maken die zijn geoptimaliseerd voor prepress-afdrukken van hoge kwaliteit. De gemaakte PDF-documenten kunnen worden geopend met Acrobat en Adobe Reader 5.0 en hoger.) /NOR /POL /PTB /RUM /RUS /SKY /SLV /SUO /SVE /TUR /UKR /ENU (Use these settings to create Adobe PDF documents best suited for high-quality prepress printing. Created PDF documents can be opened with Acrobat and Adobe Reader 5.0 and later.) /CZE >> /Namespace [ (Adobe) (Common) (1.0) ] /OtherNamespaces [ << /AsReaderSpreads false /CropImagesToFrames true /ErrorControl /WarnAndContinue /FlattenerIgnoreSpreadOverrides false /IncludeGuidesGrids false /IncludeNonPrinting false /IncludeSlug false /Namespace [ (Adobe) (InDesign) (4.0) ] /OmitPlacedBitmaps false /OmitPlacedEPS false /OmitPlacedPDF false /SimulateOverprint /Legacy >> << /AddBleedMarks false /AddColorBars false /AddCropMarks false /AddPageInfo false /AddRegMarks false /ConvertColors /ConvertToCMYK /DestinationProfileName () /DestinationProfileSelector /DocumentCMYK /Downsample16BitImages true /FlattenerPreset << /PresetSelector /MediumResolution >> /FormElements false /GenerateStructure false /IncludeBookmarks false /IncludeHyperlinks false /IncludeInteractive false /IncludeLayers false /IncludeProfiles false /MultimediaHandling /UseObjectSettings /Namespace [ (Adobe) (CreativeSuite) (2.0) ] /PDFXOutputIntentProfileSelector /DocumentCMYK /PreserveEditing true /UntaggedCMYKHandling /LeaveUntagged /UntaggedRGBHandling /UseDocumentProfile /UseDocumentBleed false >> ] >> setdistillerparams << /HWResolution [2400 2400] /PageSize [612.000 792.000] >> setpagedevice