The Water Purification Plant of Karlskrona

Transcription

1 The Water Purification Plant of Karlskrona Jan Andersson, Ljungsjömåla Text, Bild & Form HB, 2001 TEKNISKA FÖRVALTNINGEN

2 The Water Purification Plant of Karlskrona Lyckebyån Lyckebyån Cleansing Fingaller Råvatten- Pumps of Råvatten- DynaSandfilter DynaSandfilter Mixing Blandnings- Chamber Oxidationsbassänger Oxidation Tanks Carbon Kolfilter Filter Purified Renvatten- Water Worm Grill pumpar Natural Water snäcka kammare snäcka Purified Renat tvättvatten Washing till Water Lyckebyån Lamella Lamellseparator Slamlager Sludge Centrifug Spin Dryer back to Lyckebyån Separator Holding tank The Water purification Plant of Karlskrona, process schedule. Illustration: Pär Samuelsson SLAM Low Lågreservoar Reservoir Dricksvatten- Pumps of Distribution pumpar Drinking Water For the populated area of Karlskrona and the areas near by, there s a shortage of groundwater. Therefor must the most of the natural water for drinking-water production be collected from the river of Lyckebyån, which unfortunately is far from being an ideal source of water supply. The small river has its sources in the regions of Kosta in the south of Småland. During its 100 kilometers of traveling down to Lyckeby, the water passes several different types of landscapes that affect the quality of the water. From forest- and agriculture regions are nutritive substances being added, and its passage through marshes and swamps ads among other things humus substances, iron and manganese. In combination with large variations of the water temperature depending on the season, this make Lyckebyån to one of the most difficult natural waters for production of drinking-water in Sweden. As a consequence the water works of Karlskrona has one of the most advanced processes for drinkingwater production in the country. The running of Lyckebyån. Illustration: Per Lewis-Jonsson

3 The Inlet of Natural Water The inlet of natural water takes place from the reservoir in Lyckeby by a natural drop via two inlet pipes. The inlets have strainers that prevent objects bigger than 30 millimeter to join the water into the pipes. To prevent the strainers from being plugged whit leaves etc., the inlet pipes is provided with floating dryers both upstream and downstream the position of the inlet. The inlet pipes has a length of 30 meters and a diameter of 50 centimeters The water level in the reservoir is continually measured with a pressure sensor, which is situated at the salmon ladder. The measured data is being registered and stored in the process computer of the water purification plant. The water purification plant also has a turbine, which is driven by the water from the reservoir. The turbine and the belonging generator produce a third of the electricity needed at the water purification plant. The plant is also provided with a diesel-driven spare power unit, which can be used in case of a power failure. The spare power unit has the capacity to manage the total electricity need for the water purification plant. The inlet of natural water from the Lyckebyån is taken place from the reservoir construction above the salmon ladder in Lyckeby. Photo: Jan Andersson

4 Cleansing Grill and Pumps of Natural Water Before the water is processed the water passes a grill with a column width of three millimeters where the bigger particles is being removed. The cleansing grill is cleaned automatically. The maximal flow of natural water to the water purification plant runs up to cubic meters per hour. From the cleansing grill the water is led to a tank for natural water. To this point the water has traveled thanks to differences in level, but from here an on the water has to be pumped mechanically. The three pumps of natural water are placed in the immediate connection to the tank of natural water and in a way that there s always a overpressure on the sucking side of the pumps. If the level in the tank of natural water getting to low the pumps is being blocked. The pumps of natural water can be maneuvered both from the control room and from the machine room. The natural water is pumped into the water purification plant by three giant pumps, all with different capacities of 1.000, 750 and 500 cubic meters per hour. Illustration: Pär Samuelsson

5 Natural Water Worm and Pumping Pit On its way to the natural water worm the water pass a measuring chamber, where different parameters are being measured and registered for example ph and temperature. The natural water is led to the bottom of the natural water worm, where the water then ascend to the outlet at the top of the tank. In the natural water worm the ph, alkalinity and hardness is adjusted through admixture of calcium oxide and carbonic acid. This measure is taken place because the following treatment with aluminum sulfate should be successful. Aluminum sulfate adds the water through the channel that led the water from the natural water worm to the pumping pit. In simple words the aluminum sulfate acts like glue between the great number of very tiny pollution particles, which is dissolved in the water. The metal ions adhere on the surface of the pollution particles. The pollution particles then lose their hydrofil character, are gathered together and become so large that they are easily removed. After admixture of aluminum sulfate the previously dissolved particles are gathered tighter and become so large that a sand filter can remove them. The method is called a chemical precipitation.illustration: Jan Andersson

6 DynaSand-Filter The most of the pollution in the natural water is separated in the sand filter. In the water purification plant there is 40 so-called DynaSand-filter with a total filter area of 200 square meter and with a filter depth of two meter. The purification process is similar to the natural purification in a gravel ridge. In other words, when the water passes the filter the pollution particles are getting stuck in the sandbed. On the contrary in the dune sand filter the separation begins at the bottom of the sandbed and the water is then being purified on its way up through the filter. The DynaSand-filter has an automatically cleaning of the sand filter and can therefor be in process continually. The most soiled sand at the bottom is pumped to the center of the container where the sand is cleaned and then allowed to fall to the top of the sandbed. The washing water, about 150 cubic meter per hour, is led away to purification before it s released to Lyckebyån. In the DynaSand-filter almost every iron, aluminum and humus is being separated together with fifty percent of the amount of manganese Inlet of natural water outlet of purified water washing water to purification cleaned filter sand soiled filter sand In the DynaSand-filter the natural water is turned to almost drinking water. Left in the purified water there is only minor rests of manganese and microorganisms together with smell and flavoring, which are separated in the following steps.

7 Wash Water Purification The main part of the pollution in the natural water is separated in 40 DynaSand-filters of the water purification plant. From here the pollution particles is transported by the wash water to a special sludge treatment in connection with the purification of the wash water. The wash water is purified by sedimentation in a lamella separator. To make the sedimentation easier polymers are being added, longish molecules with ability to tie pollution and to make this water rejected. There are many transverse plates in the lamella separator, which creates a very large sedimentation area. When the pollution s have sediment on the plates, they glide down to the bottom on the separator, where from they are pumped further to a sludge storage. In the sludge layer further thickened is taken place when the pollution sink to the bottom. The thickened sludge is pumped to a spin dryer where the water is separated by powerful rotation. The sludge is taken from the centrifuge to a container for further transportation to the deposit works in Bubbetorp. Purified Renat washing water tvättvatten Stirrer Omrörare Admixture Tillsats av of polymer polymer Inlet Inlopp of Lamella Lamellskivor sheets washing water tvättvatten To Till sludge slamlager deposit Purification of wash water from the DynaSand-filters is taken place by sedimentation in a lamella separator. Illustration: Jan Andersson

8 Mixing chamber The water is led further from the DynaSand-filter to a mixing chamber for dosage of calcium water and addition of chlorine and chlorine dioxide. Hereby a raising of the ph value is obtained (to 8,5) which is necessary to separate remaining substances of manganese through oxidization. The addition of chlorine and chlorine dioxide is done for two reasons. On one hand chlorine/chlorine dioxide is working as means of oxidization, which the dissolved manganese can be transferred through to manganese oxide which is possible to separate. On the other chlorine and chlorine dioxide have a disinfectant effect on microorganisms. The volume of the mixing chamber is only eight cubic meters. Therefor the mixing of calcium water, chlorine and chlorine dioxide is made with the help of a stirrer. After the mixing chamber is the ph value and chlorine content in the water tested. Addition of chlorine and chlorine dioxide in the mixing chamber is done in order to facilitate oxidization of manganese into manganese oxide. The addition also neutralizes microorganisms as for example bacteria and funguses. Illustration: Pär Samuelsson

9 Oxidization Tanks The three oxidization tanks of the water purification plant hold about cubic meter water in total. It takes several hours for the water to pass through these, which enables that almost all manganese has the time to oxidize into manganese oxide during this break. A side effect of the large volume is that is also gives a certain safety margins if any disturbance would occur in earlier process steps. The oxidization tanks of today have earlier served as sedimentation tanks. Therefor they are shaped with double bottoms to increase the sedimentation area. Even if it isn t the main purpose here, it still takes place sedimentation of a smaller amount of manganese oxide. Therefor the tanks must be cleaned some times per year. The majority of the manganese oxide is however separated in the following coal filters. Outlet utlopp to till Carbon kolfilter Filter Inlopp Inlet An oxidization tank in cross-section with arrows that show the flow path of the water. In the oxidization tanks dissolved manganese is transformed into large solid particles of manganese oxide, which are possible to separate. Illustration: Jan Andersson

10 Carbon Filters The water purification plant has eleven carbon filters all together with a filterbed consisting of very small granules of active coal. Purification in carbon filters is done through mechanical filtering, but mainly by adsorption on the surface of the carbon particles. The total area of seven gram filter carbon is approximately as big as a football field. While the total area of all carbon filter granules correspond to as much as a quarter of the area of the whole of Sweden. In the carbon filters is manganese oxide separated plus various smell substances and flavoring. The carbon filters are particularly important during the summer months when the natural water gets sharp taste deterioration from degradable products coming from for example algae. The carbon filters are cleaned by back flushing with clean water every tenth day. The flush time is about 20 minutes and for every back flushing it takes 150 cubic meter of drinking water. In the carbon filters are among other things smell substances and flavoring adsorbed on the surface of the carbon particles. The total surface area of the small carbon particles is very large, the area of seven gram of active carbon correspond for example a football field. Illustration: Pär Samuelsson

11 Purified Water Worm and Distribution When the water leaves the coal filter its finished drinking water, the most common and important provision of Sweden. Before it can be distributed out on the main system some adjustments must be done. The ph value of the water, alkalinity and degree of hardness are to be directed against values which among other things decreases the corrosion effect of the water in order to limit corrosion on the pipes. Furthermore, small amounts of chlorine must be added to prevent bacteria growth in the distribution pipes. For the reasons above are lye, carbonic acid and chloride amine dosed to the water on its way to or in the purified water worm. The distribution is carried out with the help of drinking water pumps from a low cistern out to the consumers. The pumps are regulated with number of revolutions and are constantly working to keep up a water pressure in the pipes. In order to manage a sufficient pressure in the whole main system, it s also necessary with water towers and pump provided pressure-increasing stations. The drinking water is supplied via a distribution net which besides pipes also consists of water towers and pressure increasing stations. There are over 500 kilometers water pipes in the municipality of Karlskrona. Illustration: Pär Samuelsson