WTP Březová is the biggest water treatment plant in the area of Karlovy Vary. The plant is the main source for the Water Supply System of the Karlovy Vary Region, which delivers water to more than a third of the region´s population. The water treatment plant was constructed in years 1972 – 1982 and put into operation in 1984. The raw water is taken from Stanovice Reservoir, a high quality natural source located in the source water protection area without any risk of industrial, agricultural or urban pollution. The plant produces about 250 liters of drinking water per second; however it´s capacity is designed for more than double (650 l/s). Traditional two-step technology was originally used at this plant – coagulation and filtration, completed with hardening. The plant was modernized in years 2011 – 2016 and a third step has been added to the water treatment process: ultrafiltration. The plant is today fully automated and computer controlled with a nonstop service.
Water treatment technology
Raw water intake
The capacity of the Stanovice Reservoir is 24.2 million cubic meters of water. The outlet tower enables to take water from six profiles, depending on the water level and it´s quality in different layers. Raw water is transported to the water treatment plant by gravity through a 3.56 km long steel pipe one meter in diameter. The average daily raw water inflow is about 22,000 m3.
Before treatment the raw water is used as an energy source. A small hydropower plant and a heat pump system have been installed at the raw water inlet. The hydropower takes advantage of the altitude difference between the reservoir and the water treatment plant to generate electricity for use at the treatment plant. The heat pump benefits from the thermal energy of the raw water and delivers heat to the administrative building.
First step of treatment process
In this step the particles of dirt in raw water stick together (coagulate) by using chemicals and are then removed by settling. The coagulation has two phases – rapid and slow mixing.
Raw water first goes to the rapid mixing chamber, where it is mixed with the coagulant (Aluminium sulphate). Under an intensive and rapid mixing by vertical agitators the particles are destabilized and they start to form micro-flocs.
Water then flows to three flocculation tanks; each of them is eight meters deep and divided into two parts by a partition. Here the water is gently stirred during ten to thirty minutes with paddle agitators, in order not to break the created flocs. Due to electrochemical reactions flocs grow in size.
After coagulation the water enters three double–deck settling tanks, where the flocs of optimum size created in previous stages settle out. Each tank is divided by perforated walls into four parts; the total volume of tanks is 9,000 m3. The water spends about nine hours here, most of impurities settle out in the first two parts of the tank, equipped with circular sludge scrapers.
Second step of treatment process
Overflow water from the last part of settling tanks is directed via troughs and pipes to eight open rapid filters. The water passes here through the fine sand where unsettled impurities are trapped. The total filter surface is 518m2. Water stays here one hour on average. Regular cleaning of the filter media is necessary to ensure proper function of filters. After four days of operation of each filter, the filter cycle changes to the backwash cycle. During backwashing the backwash water together with the air are forced upwards through the filter in order to raise and rinse the sand grains. The backwash water is taken from a storage tank, the air is provided by blowers. The backwash cycle is fully automated. The sand in filters is regularly changed.
Third step of treatment process
Filtered water from the sand filters is directed into the last step of treatment – ultrafiltration unit, where it is finally cleaned by using fiber membranes.
The ultrafiltration fiber membranes are thin plastic tubes with the diameter of four millimeters and seven capillaries inside. The water is forced through the capillaries and disperses laterally through the pores of the membrane, which are 20 nanometers in diameter. Particles that cannot pass through the capillary walls are retained inside. Thus remaining suspended solids or pathogenic organisms are removed from water, up to the size of viruses. However the membrane allows the passage of calcium and magnesium, which are necessary for the human body.
Fiber membranes are placed in the ultrafiltration modules, which are organized in four blocks. The single module consists of 2,600 fibers, each block contains 72 modules. Water is pumped into the ultrafiltration blocks by using inlet pump station with pre-filtration.
Thorough backwashing of the membranes is crucial for proper function of the ultrafiltration unit. This is carried out by using the backwash pump station. Approximately once per hour the filtration stops and the membranes are backwashed. Furthermore, the chemical cleaning, disinfection and integrity tests of membranes are carried out periodically. Backwash water storage tank, storage tank for chemicals, chemical dosing equipment, neutralizing tank, connecting pipes, valves and sensors are parts of ultrafiltration unit as well. The ultrafiltration unit is operated by an automated control system, which ensures the proper functioning of the entire device, based on measuring operating conditions (pressure, flow, PH).
Backwash wastewater from sand filters or ultrafiltration and sludge from settling tanks or lime saturator are discharged to the sludge treatment, located at 400 meters from the water treatment plant. The sludge treatment consists of sixteen sedimentation tanks. The sludge settled at the bottom of the tanks is then discharged to the municipal wastewater treatment plant of Karlovy Vary.
Final treatment of the drinking water quality and disinfection
After the ultrafiltration is finished, the lime is dosed for pH adjustment. The raw water is in fact naturally slightly acidic; it´s pH is decreased by applying coagulant as well. Therefore the lime water, prepared in lime saturator, is added to the treated water in order to increase pH. The water from the Stanovice Reservoir contains only small amounts of minerals, so carbon dioxide together with lime are added to the treated water to reach the optimal water hardness.
A phosphate corrosion inhibitor is further added to the water. Phosphates are commonly used as an additive in the food industry. The inhibitor forms a protective layer on the inner surface of the pipe, which is considerably reducing the corrosion rate of steel pipe (including internal plumbing system) in order to prevent the release of iron from the pipe into the drinking water.
Finally, the water is disinfected by dosing chlorine together with ammonium chloride, which prevent the microorganisms from growing in water distribution network and maintain the water safe to the consumers’ taps.
The treated water flows then to the water tank with a storage volume of 5,000 m3 of drinking water. The tank can ensure the water supply in case of the disruption of water treatment for nearly two days. The water is then distributed to consumers via distribution network.
Treatment process diagram