THE WATER PRODUCTION SUBSYSTEM FAILURES AFFECTS OF KRAKW’S WATER SUPPLY SYSTEM

Izabela Zimoch Silesian University of Technology, Institute of Water and Wastewater Engineering Gliwice,

Abstract Krakow, the oldest capital of Poland is the town situated on the river. The population of Krakow is 770 thousands of inhabitants. It is one of the most important cultural and scientific centres in Poland. There are a lot of industrial branches such as metallurgical), pharmaceutical, machine- building industry), food industry and others. Such strongly developed city requires large amount of water to meet needs of its inhabitants and industry. Taking into consideration the abovementioned factors, the function of the water supply system (WSS) is to supply to people and other users water of proper quality according to the rules and in a quantity resulting from the users needs, in the existing service conditions and in the definite part of time, or in any moment. This paper contains the preliminary reliability analysis of the water supply system (WSS) of Krakow city. It regards the influence of the failures of the water production subsystem elements on the whole system usage. The water-supply subsystem operations in the damage conditions computer simulation results, regarding current exploitation parameters, are presented. Individual scenarios, reflecting hypothetical situations of interference for correct water supply system operating, cover random event, i.e. water source contamination, lack of electricity, technological errors influencing water treatment effects, failures of transit water-pipe networks and others. That allowed pointing out critical points in water production and distribution subsystem. Their failures would cause the biggest threat to fail to comply with the basic system task, that is to provide consumers with continuous supply of suitable quality and quantity water. Presented study were done as a part of research project KBN 5T07E 044 25 „Determination of reliability operation model of water supply system (WSS) in the aspect of secondary water contamination in a water pipe network”.

Keywords: water supply system (WSS), water production subsystem (WPS), water distribution subsystem (WDS), failure, reliability, computer simulation

The current exploitation conditions of Water Supply System in Poland The increase of legal requirements concerning water quality supplied to buyers makes new tasks for managers of water-pipe systems. Activities taken for purpose of improving water quality and supply reliability, cannot only be restricted to water production subsystem. In the Poland, the law regulations including in the Act of Water Supply and Sewage Disposal 2001(DzU nr 72 poz. 747) impose on subjects exploiting water-pipe responsibility of quality not only of produced water but first of all of water supplied to consumers. Nowadays, the level of technology development of water conditioning allows obtaining very high quality of water, much higher than formal requirements. However, state of majority of water distribution subsystems does not satisfy conditions, which allows keeping level of water quality during transporting to a consumer. Such situation increase risk of water buyer and water supplier. Polish water supply systems (WSS) of big urban and rural agglomeration actually have excess of productivity. Above state comes from political and economical situation of Poland in many years of last century. Low price was causing incessant increase of water requirement for existential and economical aims of society, as well as using water from WSS for production process in many industrial plants. Consequences of that was permanent lack of enough amount of water, it resulted many restrictions on water usage: prohibition of watering home gardens or urban greens, no water supply to inhabitants from higher zones of supply and supplying water during drought period with water carts. That events forced water supply enterprises to seek new sources of water to satisfy requirements of inhabitants as well as of industry. Social and economical changes that took place at the beginning of 90’s of the last century, putting in order water price resulting from cost of production and distribution has changed rapidly conditions of WSS operating. In addition many years of Poland tries to integrate with EU countries have contributed to legal changes containing also water supply sector. Nowadays water supply enterprises do not struggle with problem of water amount or

production them with respect to present quality standards, but with problem of keeping such parameters during transporting to consumers. During a few last years, wide choices of variety and professional computer programs were arisen. They are very supportive and useful for design and management of urban water supply system and sewage system. Present level of computer techniques allows using them in estimation of water-pipe systems operating and in analysis of their critical elements, as aspect of technological process and engineer solutions (Bush, Uber, 1998; Kennedy and others, 1991; Lee and others, 1991; Milkiewicz and others, 1999; Siwoń, 1997, 1998; Ulanicka and others, 2000). They allow simulating different variants of random events of different probability of occurrence. More often they are using to hydraulic analysis of designed and actual operating water distribution subsystem and frequency determine of taking water sample for quality analysis. It has made a possibility of determining critical points in the production subsystem as well as in the distribution subsystem, which failure states may be the highest risk of not fulfilling basic tasks of the system, which is ensuring a continuous water supply to buyers. Making use of computer analysis of results gives opportunity of taking steps that minimize effects of that events, and what is more, minimizing risk taken by water-pipe enterprises and increasing consumer safety.

Water supply system of Krakow

The characteristic of Krakow’s water supply system The actual water supply system of Krakow city has came into being as a result of contracting a water- pipe plants, modernization and as well as develop of main network, resulting from new housing estate on the suburb. The beginning of Krakow system comes most probably on XIII century, when Krakow get a licence of building of aqueducts, what is said in documents done by Leszek Czarny. However, the beginning of the present city WSS is 1898, when City Council decided to build new water-pipe. It was a pumping water-pipe fed with surface water from Bielan with the highest daily capacity of 16,000 m3. The official start of operating that water-pipe took place 14 February 1901 and was beginning of consequent development of today’s city WSS. The present WSS of Krakow city consists of two extended subsystems: water treatment subsystem (WTS) and water distribution subsystem (WDS). The water treatment subsystem consist of feed systems, creating separated technological lines operating with respect to water from Raba, , Dłubna, Sanka and underground water from intake in Mistrzejowice. Water sources as well as range of water supply regions from separate intakes are presented in the figure 1.

ZUW ZUW D DŁUBNIA RUDAWA Uj. łu DŁUBNIA 3 b 33 R 3 Mis t rz . n 25 200 m /d ud 5555 200200 mm /d /d i 25 200 m /d awa a

Wisła Sanka ZUW BIELANY 21 000 m33 /d KRAKÓW φ 1000 ZUW φ 1400 RABA ZBIORNIKI S IERC ZA 33 3 207 000 m /d Zapas ok 170 000 m 207 000 m /d ZBIORNIKI GORZKÓW Raba Zapas ok 30 000 m3

e ki Uj.Wież c zy bc ezioro Do J

Key: ZUW – Water Treatment Plant Uj. Mistrz. – Water Intake Mistrzejowice Zbiornik Siercza, Zapas ok. 170 000m3 – Water Tank Siercza, Volume 170 000m3 Zbiornik Gorzków, Zapas ok. 30 000m3 – Water Tank Gorzków, Volume 30 000m3 Jezioro Dobczyckie – Dobczyce Reservoir Figure 1. Water supply regions of Krakow WSS ( Archival materials, 2004)

The greatest part of urban water supply is the Raba intake in Dobczyce supplying about 48% of actual water requirements (table 1).

Table 1. The production of Krakow water supply arrangement (Archives materials, 2004) Supply arrengement Mean production [m3/d] Productivity [m3/d] WTP Raba 77 768 207 000 WTP Bielany 13 476 21 000 WTP Rudawa 29 441 55 200 WTP Dłubnia 22 433 25 200 WTP Mistrzejowice 5 141 6 000

Actual productivities of water conditioning plants cause that the present urban water supply system of Krakow is classified as system with excess that is to say it has reserve of productivity on the level 112% of mean daily urban requirement.

Water supply arrangement of Raba Raw water is uptake from tower-type water intake from reservoir Dobczyce, witch has possibility of water intake from a level of the best quality parameters. Then water is pressed inside two pipelines (∅1000 and ∅1400) to the water conditioning plant (fig.2). Untreated coming water is oxidizing in the process of preliminary ozonization in contact tank with two chambers. Mean dose of ozone during process is in the range 0 – 2 g/m3. Ozone produced on the spot by system of PCI Ozone, of capacity 30 kgO3/h. After process of preliminary ozonization water flow to the separation chamber where is added active carbon in dose 0 –2 g/m3 of water and coagulant (PAX or aluminum sulfate) in dose 0 – 40 g/m3. To water is added also periodically flocculent Magnaflok in dose 0 – 0.5 g/m3 of water. In the next chamber separation of water jet is made into higher and lower (Archives materials, 2004; Zimoch, 1999)

Ozone Al2(SO4) Active carbon 1 2 3 4 5 6

Cl2

ZB.DOBCZYCKI

Key: 1 – preliminary ozonization, 2- coagulation, 3- sorption, 4- sedimentation, 5- rapid filtration 6 - disinfection

Figure 2. The technological scheme of water treatment plant Raba

The higher jet is conveyed water to the technological string of Raba I containing a system of classic coagulation. The jet in pipeline ∅1000 flows to coagulation building into fast mixers. They are round chambers, where water is bottom let in and top let out. The holdup time in mixers is about 1 minute. Next, water flows through flocculation chambers (12 pieces), with holdup time 6 – 10 minutes. From swirl chambers it flows to 12 after coagulation horizontal settling tanks of capacity 8,000 m3. Holdup time in settling tanks is about 2.5 h. Then water is steered to rapid filters. In the technological process of water conditioning there are 12 sand-gravel filters of area 44 m2 each and capacity 6.5-8 m3/h. Sludge from filters washing is disposal to sludge thickeners, from where is pumped over to sludge drying bed. To minimize aggressiveness of water it is added lime milk in numbers of 0 – 20 g/m3. This way treated water goes to reservoir of pure water Raba I (2x3 thousand m3), where is in the process of disinfection using gas chlorine. Treated water is pressed with pumping engine 30B52 type (6 pieces) of capacity 0.25 m3/s to reservoirs in Gorzków, and then to the urban water distribution subsystem. The low jet is steered to the technological string of Raba II that means to system of multifunctional devices: accelerators (4 pieces). Nominal capacity of accelerator with 2.5 hour of water holdup is 2,160 m3/h. After the accelerator water is steered to 16 fast sand-gravel filters of area 85 m2 each and capacity 5.5 – 7.5 m3/h. The next stage of water treatment is disinfection, which is executed in the pure water reservoir Raba II (2x8.5 thousand m3). After disinfection process water is pressed with pumps (8 pieces) of capacity 0.56 m3/s to reservoirs in Gorzków. Along water flow route from WTP Raba (Water Treatment Plant Raba) to Krakow there are localized pure water reservoirs in Gorzków of capacity 22.5 thousand m3, from where water gravitationally flows to a pure water reservoirs complex in Siercza (4 x 34 thousands m3 and 3 x 7.5 thousands m3). Water reservoirs in Siercza operate as straightway and are of reserve-balance type. From the reservoirs

water gravitationally flows inside pipelines ∅1000 and ∅1400 to Krakow, where in the control station in Piaski Wielkie regulation of flow and pressure parameters and steering of water distribution to the urban water – pipe network take place (Zimoch, 1999).

Water supply arrangement of Bielany The Bielany plant (fig.3) as the oldest water production object in Krakow had in over 100-year exploitation numerous modernizations. Initially it produced water from water-bearing deposits Bielany and Przygorzały regions. After few years of exploitation it appears that increasing water requirements exceeded efficiency of water-bearing terrain and forced to redeveloping intake and to base production on artificial supplies, feeding initially by water from the Wisła River and next also from the Sanka River. Nowadays the plant is basing mainly on water from the Sanki River, what is caused among others by low level of water purity from the Wisła River. High quality of produced water comes among others from used technological treatment based on natural water purification in slow filters. Filtered water taken by 100 of wells is in the process of disinfection with chlorine. After treating water if pressed to the Kościuszko reservoirs and then to the urban network (Archives materials, 2004).

1 2 3 Chlorine SANKA

Key: 1-sedimentation, 2 – slow filtration, 3 - disinfection

Figure 3. The technological scheme of water treatment plant Bielany

Water supply arrangement of Rudawa In 1955 it begun being exploiting the next water supply arrangement (fig.4) basing on water from the Rudawa River. Actually operating technological system is an effect of many modernizations. Nowadays, water from the intake is steered to two impounding reservoirs. They are devices of preliminary water treating, ensuring narrower range of variability of water quality parameters coming to the water purification plant as well as raw water reservoirs, which keep water reserve for 3-7 days for maintaining plant exploitation in case of occurrence of random events that is source contamination or rapid increase of turbidity. Water quality in the intake is continuously monitored by measuring pH- value, turbidity, concentration of ammonia nitrogen, phosphates and oil-derivative. Monitoring usage increases operating reliability of the supply arrangement. In the plant water is treated in process of classic coagulation. The most common coagulant is polyaluminium chloride of mean dose 30 g/m3. Then water is filtrated by sand bed (12 pieces). Area of a single filter is 29.5 m2, velocity is in the range of 6 – 8 m/h. Next treatment stage is a sorption process in six carbonaceous filters (granulated carbon F300-Chemviron Carbon), and area also about 29.5 m2. Operating parameters of the filters system ensure 11-15 minutes of contact time of water with the deposit. The last element of technological string of water treatment is disinfection with chlorine dioxide. Water treated in this way is steered to the urban water - pipe network (Archives materials, 2004).

Aluminium sulfate ClO 1 2 4 5 6 2 3 RUDAWA

Key: 1- row water basins, 2- coagulation, 3– sedimentation, 4- rapid filtration, 5- sorption on active carbon filter bed, 6- disinfection

Figure 4. The technological scheme of water treatment plant Rudawa

Water supply arrangement of Dłubnia The development of Krakow WSS was containing among others adding to the system in 1960 new supply arrangement (fig. 5), operating on the base of water from the Dłubnia River. In 1993 it has started complex plant modernization containing coagulation and disinfection. Now raw water from the intake in Zesławice is pressed to a building of classic coagulation devices. Coagulation process is done with aluminium salts, which average dose is in the range 12-35 g/m3, and in thawing snow periods or intensive rainfalls in the river basin of Dłubnia it increases to 50 g/m3. When quality of raw water in the intake decreases to parameters of class A3, then process of water treatment is helped with sorption on dusty activated carbon (dose 1-5 g/m3). Next stage of water treatment is filtration on opened fast filters. The filtration system contains 10 beds of area 31.2 m2 each, process velocity is in the range of 4.7 – 5.3 m/h. After filtration and disinfection (chlorine dioxide) water gravitationally flows to the Krzesławice reservoirs, supplying inhabitants of Nowa Huta (Archives materials, 2004).

Powdered active carbon ClO2 1 Al2(SO4) 2 3 4 5 DŁUBNIA

Key: 1- coagulation, 2- sedimentation, 3- sorption on active carbon, 4 – rapid filtration, 5-disinfection

Figure 5. The technological scheme of water treatment plant Dłubnia

Water supply arrangement of Mistrzejowice That supply system is very important for supplying water for buyers in Nowa Huta. It is an underground intake localized in northern-western area of old airplane in Czyżyny. The system from coming into existence in 1953 was successively developed. At the present rate of production of intake with operating 8 deep-well pumps is 6,000 m3. High quality of water means it does not required any water treatment except preventing disinfection with minimal dose of sodium hypochlorite, having in view non-fulfillment of secondary bacteriological contamination of water pressed to the urban pipe network (Archives materials, 2004).

The characteristic of Water distribution subsystem Water in Krakow is supplied to consumers by a complex system of transit, main and distributing pipelines. Total length of water-pipe network together with home water attachment on the area serviced by City of Krakow Water and Sewage Utility Company is over 1,840 km. Because of formation during the last hundred years, its age as well as material of separate elements of the network is different. Material structure of the network is shown in figure 6.

400

300

200

100 Length [km] Length

0 Grey Steel Asbestos PVC PE iron-cast cement

transit and main pipes distributing pipes w ater-pipe terminals

Figure 6. Material structure of water-pipe network in Krakow city

The main part of age structure is water-pipes made after 1980. Majority of such water-pipes are ones made in 90’s, with application of new technologies and materials. Owing to it its technical value is very high (Wierzbicki, 2001). Inseparable element of the water distribution subsystem is reserve and level tanks (table 2). At present in the water supply system of Krakow is operating 10 water tanks systems of total length over 270,000 m3, what is 162% of the actual urban water demand. Mainly they are made as reinforced concrete constructions of round shape and with one or more chambers. An exception is a tank in Zwierzyniec of rectangular shape. It is the oldest tank in Krakow coming into existence in 1900. Apart from the terrain tanks City of Krakow Water and Sewage Utility Company is now exploiting an elevated tank Las Wolski. The greatest set of water tanks set of total volume 158,500 m3 is placed in Sieracza along the transit route from WTP Raba to Krakow (Archives materials, 2004).

Table 2. List of drinking water tank in WDS of Krakow city (Archives materials, 2004) Tank Establish year Bottom elevation Depth Total [m above sea [cm] capacity level] [m3] Kościuszko 1900 / 1987 258,2 / 256,2 400 / 600 25 000 Las Wolski 1964 366,00 600 120 Kosocice 1966 / 1976 / 1997 287,0 / 284,4 500 / 720 14 500 Krzemionki 1958 / 1973 247,2 400 / 400 20 400 Rajsko 1999 337,0 500 1000 Krzesłąwice “bottom” 1972 256,7 / 252,7 400 / 800 8 000 Krzesłąwice “top” 1952-1960 271,0 500 10 000 Mistrzejowice 1968 / 1987 270,4 / 267,4 500 / 800 16 000 Wola Justowska 1930 274,0 250 150 Gorzlów 1974 / 1988 376,000 800 22 500 Siercza 1974 / 1990-1998 333,5 /333,3 800 158 500

Modeling of operating parameters for Krakow’s WDS Simulation of operating parameters of WDS was made using computer program EPANET 2. Inside the program was created a simplified model of the urban water-pipe network of Krakow using data gained form Water Company. The model consists of 446 junctions, representing fundamental water distribution points on the supply area. Each junctions was described by basic data like: three- dimensional coordinates (x, y, z), daily water demand (rate of withdrawal from the network) and category of demand. Integral impute data elements of hydraulic model are characteristic parameters of water – pipe like: start and end nodes, diameter, length, roughness coefficient and working status (open, closed, or contains a check valve) In the analysis was taken into consideration 625 sections of pipelines of transit, main and distributing networks in the range of diameter over 150 mm. In the considered simplification of the water distribution subsystem was considered main storage tanks i.e.: Kościuszko, Krzemionki, Kosocice, Krzesławice, Gorzków and Siercza. The primary input properties for tanks are: bottom elevation (where water level is zero), diameter or shape, initial, minimum and maximum water level. Considered in model Krakow’s tanks collect 90% of water stored in the subsystem and are stabilized elements of the system during periods of variable water demand (table 2). As it is shown in data table, the most important for the system regular operation is a tank system Siercza – Gorzków, which are able to store 100% of daily water demands. With respect to the performed analysis of hour flows it was created proximate distribution of water demand in the course of the day (fig. 7). To estimate an operation of WSS of Krakow it was simulated a system behavior in the case of failure and necessity of disable particular supply arrangements. The above analysis was performed with assumption of keeping continues and full water supply for consumers to buyers covered by unused productivity of the rest of operating plants, as well as stored in the water storage tanks. Simulation contained 4 scenarios, showing disabled water treatment plants by random events, excluding their further exploitation, e.g. contamination of source water, no current supply: scenario 1 – the Bielany WTP disable, scenario 2 – the Rudawa WTP disable, scenario 3 – the Dłubnia WTP disable, scenario 4 – the Raba WTP and the storage network tanks system Siercza disable. Obtained results were compared with operation parameters of the water distribution subsystem in normal exploitation conditions of WSS (scenario 5).

1,4

1,2

1

0,8

0,6 Nh parameter Nh 0,4

0,2

0 123456789101112131415161718192021222324 hour

Figure 7. Hour water demand curve in the city

Because performed simulations are preliminary stage of the WSS operating estimation in aspect of changing of water quality during transporting to consumer, as a primary comparative criterions were taken hydraulic parameters, which determine processes of secondary contamination: direction and velocity of water flow in water-pipes. Analysis of those parameters allows estimating a range of supply zones for particular water treatment plants with respect to random system exploitation conditions. In figure 8 was shown distribution function of percentage water flow velocity for particular scenarios of the WSS operation. From presented diagrams follows that change of supply structure of WSS with constant demand level does not effect essential variation of water flow velocity inside taken into consideration water-pipes. Disable a particular plants results at most 10% increase of distribution function of velocity distribution, without any essential variation of pressure in the subsystem. Probably it was caused by little absolute variation of flow. For the assumed constant of distribution function 90% variation of velocity in the computation scenarios does not exceed 0.14 m/s.

100 90 80 70

60 50 the Rudawa WTP disable 40 the Dłubnia WTP disable 30 the Raba WTP disable

Distribution function 20 the Bielany WTP disable normal exploitation of WSS 10

0 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 flow velocity [m/s]

Figure 8. Velocity distribution function – scenarios 1-5

Conclusions 1. Present level of computer techniques allows using them in operating estimation of water-pipe networks and particularly estimation of hydraulic operation parameters of a water distribution subsystem. Programs consider parameters as time horizon of simulation and steps allowing testing WDS in dynamic conditions most similar to real ones. They allow simulating different variants of random events of different probability of occurrence during different exploitation conditions. 2. Using results of computer analyses of WDS operation gives possibility of taking steps that minimize results of unexpected random events, and minimizing risk taken by water-pipe enterprises resulting from area of their activity and increase safety of consumers. Moreover, they are useful in taking decisions considering modernization and development of WSS. 3. The simulation performed for actual operation parameters of the urban water supply system of Krakow has shown that failure of a single supply system should not result in a lack of required amount of water. Nevertheless obtained results from particular scenarios shown essential variation of supply zone areas with variation of water flow direction in the network. Variation of stable supply directions may be reason of secondary water contamination in the water-pipe network.

Acknowledgements This study was supported by KBN – State Committee for Scientific Research under the contract No. 5T07E 044 25

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