| Summary: | The purpose of this report is to present a study on the water quality of the Drinking water-treatment plant of Luleå (Sweden): to give an explanation to the observed difference in temperature, using both sampling period data and historical data found: finally some alternatives will be suggested to try to improve this quality. With respect to the water quality, three aspects have been differentiated, studying them separately with the purpose of locating the points to improve: • Turbidity and conductivity: Generally the quality of the water sent to the distribution system is within Swedish standards (0.5NTU for the turbidity and conductivity < μs/cm), but in some points these values are surpassed. • Particle size distribution: it has been drawn up a map of the particle distribution, classified by large vs. number, done to the three wells with more turbidity of the system. Approximately the 91% of particles are less than 5μm of equivalent diameter. • Organic matter: a study was made for three wells with a high turbidity, where the organic matter relatively the inorganic one –as volatile carbon (loss)- was under (approx.) to 30% in the considered cases. In order to explain the observed temperature differences throughout the years, three hypotheses have been studied: • Different retention times: from the time the water enters the infiltration ponds until it leaves by the wells, an average of two months passes. • Soil as a heat exchanger: by means of an energy balance it has been seen that the Earth absorbs energy from the water when it’s warms, cooling it and vice versa. • Inner heat of the Earth: it has been obtained an approximate temperature gradient of the deepest point of the wells using the thermal gradient. Last, some tests were carried out to see the viability of introducing a chemical precipitation in the process to decrease the turbidity, but there was no perceivable coagulation in any studied cases. With respect to the possibility of introducing membrane filtration technology, the most viable filtration ...
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