PARTICLE DYNAMICS IN THE DRINKING WATER DISTRIBUTION NETWORK OF LULEÅ / Partikeldynamik i Luleas dricksvattennät

An investigation of the particle quantity and size distribution, along with the turbidity pattern, has been used to study particle behaviour within the municipal water distribution system of the city of Luleå, Sweden (65 000 consumers). The water source is the Lule River, which has a soft water with a hardness of 20-30 mg/L as CaCO3 and can be characterized by low alkalinity, pH and mineral content. During the treatment process the
surface water undergoes rapid filtration, induced infiltration, lime-CO2-conditioning and disinfection with chlorine.

The sampling program included control or the water quality after the treatment plant and at three locations within the water distribution system with different average water residence times in the network. The frequency of sampling was based on continuous monitoring of turbidity during a one-week period. Twelve discrete, sequential samples at a time interval of 2 hours were taken by an automatic sampler at each location to moni-
tor the particle count and size distribution in a range between 1.3 and 28 pm. To obtain a representative insight into particle composition, 3 different samples per location were taken for screening on an electron microscope. The results indicated that the majority of particles monitored at the sampling locations were smaller than 10 μm in diameter. A predominance of Ca-rich particles was noticeable immediately after the treatment works.
Dissolution of these particles occurred in the transmission pipes in the steady flow direction, while further in-crease in the water detention time in the network led to a growth of the daily average particle count, representing mainly Si-, 0-,and Al-rich particles.