Modernizacja stacji uzdatniania wód podziemnych "Letniki" koło Elbląga

The object under study was retrofitted in the late 1990s with the aim to upgrade the quality of the water sent to the distribution system in general, and the removal efficiency for iron, manganese and ammonia nitrogen in particular. The taken-in water, which comes predominantly from the Quaternary aquifer, is classified as "hard water" because of the high concentrations of iron, manganese and ammonium nitrogen (5.0 gFe/m[3], 1.5 gMn/m[3] and 2.0 gN/m[3]). The water treatment train made use of prior to the retrofit (which included aeration and single-stage filtration) yielded only iron removal to the level of about 0.3 gFe/m[3]; the concentrations of the other investigated compounds still exceeded considerably the admissible values, as they ranged from 0.5 to 1.0 gMn/m[3] and from 0.9 to 2.0 gN/m[3]. Following analysis of the pilot-plant results, an additional filtration stage, which involved a mature high-silica sand bed, was proposed. The retrofit of the treatment plant brought about a noticeable improvement of water quality. The concentrations of iron, manganese and ammonia nitrogen in the treated water amounted to 0.2 gFe/m[3], 0.05 gMn/m[3] and 0.2 gN/m[3], respectively. However owing to the incomplete separation of the tanks and to the distribution of mixed water (after the first and second stage of filtration), the concentration of manganese in the tap water slightly exceeds the admissible values.