An Excellent Water Quality Is Not Only Crucial For The .

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16 Cape Town drinking water monitoring solution from MetrohmOn 28 July 2010, the General Assembly of the UnitedNations declared clean water and sanitation as afundamental human right! This underlines the importanceof water and hygienic standards that have to be checkedby national and regional water and sanitation departments.An excellent water quality is not only crucial for thelocal population of the City of Cape Town and the touristindustry, it was also highly important for a successfulhosting of the 2010 Soccer World Championship!ProcessLab water analysis systems from Metrohm are usedto monitor the drinking water quality.Cape Town drinking waterThe drinking water of the City of Cape Town largely originatesfrom unpolluted mountain catchments and is treated accordingto national and international drinking water standards in the city'swater treatment facilities. There are nine main water treatment plants and some smaller ones within a distance of up to 80 km offfrom the city center. Cape Town's water treatment and distributionsystem is currently supplying more than 3.5 Million residents spreadover almost 2500 km2.Customer application report

17The operators of Cape Town drinking water treatment plants benefit from the easy operation of ProcessLab: analysis are performed fully automatically.One of the most important tasks is to maintain a good waterquality throughout the whole distribution system up to the customers tap. This can be assured by adding chlorine gas to the waterto obtain an adequate amount of free residual chlorine at all pointsin the network. The modular ProcessLab analyzer platform fromMetrohm is used to analyze the Cape Town water quality. Usingbuilt-in data network functionality, all analytical data are availableimmediately to all authorized managers.Requirements for a new analyzer systemPlant operators in all water treatment plants ensure a safe andreliable drinking water production around the clock. They draw samples from the water processing stream at various sampling points thathave to be analyzed quickly and therefore on-site. A suitable analyzerhas to determine Free Active Chlorine (FAC; consists of dissolvedchlorine and hypochlorite), pH value, temperature, P alkalinity*, Malkalinity**, and total water hardness fully automatically.*P alkalinity: phenolphthalein alkalinity obtained by titrating to pH 8.2**M alkalinity: methyl orange alkalinity obtained by titrating to pH 4.3In the past, titrimetric methods with visual endpoint determi nation using color indicators have been used. Therefore, the resultsdepended on the operator’s perception. Results were written downin a paper logbook in each plant and had to be collected by callingthe plant operators. This procedure was labor-intensive and errorprone.It takes a few minutes to two hours for the water from thedifferent treatment plants to reach the City of Cape Town. It is inevitable to centrally monitor, store, and manage the analysis results ofall water treatment plants and to make them immediately availableto all area and plant managers. With proper water and sanitationmanagement in place, in case of issues, there will be sufficient timeto take countermeasures.A new, easy-to-use analyzer had to be free from all these drawbacks, enabling Cape Town a secure and reliable water treatmentplant operation.INFORMATION 1 2011

18Unpolluted mountain catchments and reservoirs provide the water treatment plants with high-quality raw water.Metrohm solution: networked ProcessLab analyzer systemMetrohm's automated water analyzers MATi (Metrohm Automated Titration System) for laboratory analysis and the atline analyzerProcessLab fulfill Cape Town's requests. In 2007, the authoritiescontacted Metrohm and had several MATis installed in the ScientificServices' laboratories of the Water and Sanitation Department ofCape Town. Very positive experiences led to the implementation ofa ProcessLab demo system. Fully satisfied, the City of Cape Towndecided to buy additional eight ProcessLab systems in 2009. Theywere installed at the water treatment plants in early 2010.Easy operation and reliable resultsProcessLab is a modular and fully-customizable analyzer forautomated process analysis (atline analysis). Its operation is basedon the same tiamo methods that are already used for severalMATi systems in the Scientific Services main laboratory. The methodsnow feature fully automated electrode calibration as well as recordkeeping of calibration data. ProcessLab analyzes samples within minutes with a much higher repeatability and accuracy compared tothe old manual determination methods. Working with ProcessLab isso easy: After collecting water samples from various sampling pointsat d ifferent stages of the water treatment process, the operator directly brings them to the analyzer. There he enters his user nameand password, simply selects the method, and starts the determination.Excellent data availability and safetyThe nine ProcessLab analyzers installed in the water treatmentplants are the clients of a tiamo client-server network. The centraltiamo server is securely located within the IT Department ofdowntown Cape Town civic centre. The client-server database ensures that new results from the clients are immediately transferred tothe central server. Trouble-free operation of any client connected isalso supported by storing all their methods on this server. All systemsare equipped with uninterruptible power supplies (UPS) to guaranteeall-time availability of the analyzers. On the clients, the access tosensitive functions and methods is protected from alteration by theplant operators – to ensure consistent data.All analytical data, including curves (especially titration curves),are immediately available to all area and plant managers, the qualitymonitoring department, and management. They now have sufficienttime to take countermeasures right from their office desks, if necessary. Data transmission over distances of up to 80 km from the clientsto the server is achieved via the technical network of the City ofCape Town using Ethernet connections and wireless point-to-point connections.Customer application report

19DPD is used to detect free active chlorine.Training and maintenance by Metrohm Service EngineersMore than 100 Cape Town plant operators received trainingby Metrohm Service Engineers on topics like general use, care, andmaintenance of ProcessLab. The accurate determination of the different sum and individual parameters as well as electrode calibration was discussed too. Metrohm also optimized and adapted theapplications to local conditions (e.g., hard or soft water). A serviceand maintenance contract for the next two years makes sure that thesystems keep running smoothly.Method and parameters measured by ProcessLabIn Cape Town, the nine ProcessLab analyzers determine thefollowing parameters of various process water samples fully automatically: Free Active Chlorine (FAC) P and M alkalinity pH value and temperature (pH can also be determined underN2 atmosphere) Total water hardness (only if necessary at specific plants)Prior to each analysis, the 100 mL overflow pipette and thet itration vessel are cleaned by rinsing with sample to be analyzed. Therunoff is collected in a waste container. This is followed by a threecycle rinsing step with deionized water using four spray nozzles.The sample is then aspirated into the overflow pipette usingperistaltic pumps. A solenoid valve is opened to transfer the sampleby means of a transfer pump from the overflow pipette into the titration vessel. After all auxiliary agents have been added via additionalperistaltic pumps, the analyses are performed. In the end, the spentsolution is disposed of in the waste container and the titration vessel,sensors, magnetic stirring bar, tubing, and burette tips are rinsedwith deionized water.Free Active Chlorine (FAC)Chlorine gas is used for the chlorination of drinking water. Freeactive chlorine destroys disease causing bacteria contained in thewater. To ensure safe drinking water, after final chlorination in thewater treatment plant, chlorine has to be topped up at several placesthroughout the whole water distribution system network.DPD (N,N-diethyl-p-phenylenediamine) is used to detect freea ctive chlorine in the ProcessLab DPD titration method. DPD isoxidized by chlorine to form a magenta-colored, mesomericallystabilized, semiquinoid salt (Wurster Dye) as the primary oxidationproduct. The magenta-colored species is then titrated (reduced) in aphosphate buffered medium with ferrous ammonium sulfate to thecolorless endpoint using a separate gold electrode.INFORMATION 1 2011

20Map with the Cape Town main water distribution system and the mainwater treatment plants located up to 80 km off from the city center.pH value & alkalinitypH value and alkalinity serve as typical sum parameters andare required to be within certain limits. The alkalinity is determinedby titration using hydrochloric acid as titrant with an Aquatrodeplus sensor. The P alkalinity (acid capacity up to pH 8.2, KA 8.2) is determined by titrating to pH 8.2 and the M alkalinity (acid capacityup to pH 4.3, KA 4.3) by titrating to pH 4.3. Various process watersamples are collected on an hourly basis; the analyses are performedautomatically including calibration.Soft water needs to be stabilized to protect the distributions ystem network as well as the consumers’ plumbing and appliancefrom corrosion. This is done by first adding lime to an alkalinity of 30mg/L as CaCO3 and then CO2 to correct the resulting water pH of9.2. It is very important that pH value and alkalinity are monitoredregularly.pH measurement under nitrogen atmosphereMeasuring the pH value of the very soft, ion deficient, lowalkalinity water of treatment plants Voelvlei and Brooklands poseda special challenge. During pH measurement, the slightest exposureof the water sample to atmospheric CO2 caused an immediatepH drop (formation of carbonic acid). To ensure accurate results,nitrogen from a connected cylinder is used to transfer the aspiratedsample from the overflow pipette into the titration vessel and, atthe same time, to purge the titration vessel prior to sample introduction, and to cover the water sample with nitrogen before andduring pH measurements. This process is automatically controlled byProcessLab.Total water hardnessTotal water hardness – the sum of calcium and magnesiumhardness – is determined according to Metrohm Application BulletinAB-033 (see www.metrohm.com/com/Applications) by photometrictitration with EDTA using Eriochrome Black T indicator. Raw boreholewater (abstracted groundwater from a borehole) used by the Atlantiswater treatment plant has a very high calcium content and needssoftening by means of an ion-exchange resin. Hardness determination on the raw borehole and the final softened water is importantfor operating cost effectively. The ProcessLab now accurately determines the total hardness and facilitates the water softening process.SummaryThe Water and Sanitation Department of Cape Town can obtainand guarantee an excellent drinking water quality by operating aMetrohm drinking water monitoring system. Plant operators caneasily determine Free Active Chlorine (FAC), pH value, temperature,alkalinity, and total water hardness of various water samples fullyautomatically and with high precision using ProcessLab. A clientserver database ensures that new analysis results from the watertreatment plants are immediately transferred to the central serverfor monitoring purposes and data storage. Results are fully traceableand countermeasures can be taken early, if necessary. ProcessLabprovides the information to optimally and cost-efficiently softenhard water or stabilize soft water. Comprehensive Metrohm support,including user training and maintenance, assures a smooth operationof the monitoring system.Customer application report

ProcessLab water analysis systems from Metrohm are used to monitor the drinking water quality. Cape Town drinking water The drinking water of the City of Cape Town largely originates from unpolluted mountain catchments and is treated according to national and international drinking water standards in the city's water treatment facilities.

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