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The Influence Of Hypolimnetic Aeration On The Spatial And Temporal Evolution Of Phosphorus And Dissolved Oxygen

Congress: 2015
Author(s): Ahmed Kettab (Alger, Algeria), Mostefa Gafsi, BEN OTHMAN Dorsaf, Djehiche Abdelkader, BENNAi‡AR Naoual
Research Laboratory of Civil Engineering: RLCE, ResearchTeam1, Ecole Nationale Polytechnique Alger (ENP),2, Centre d’Étude et de recherches sur le Droit des Activités Maritimes et de l’Environnement3

Keyword(s): Sub-theme 10: Management of water resources,
AbstractAbstract The problems of water quality are related to the decrease in the dissolved oxygen content, particularly in the lower layers. The immediate consequences are varied and can include the formation of iron and manganese solution and suspension compounds, methane, hydrogen sulfide, ammonia, phosphorus, which cause fish killing, and odor problems that are undesirable in water supplies. The main purpose of this study is to show the effect of hypolimetic aeration to improve the concentration of dissolved oxygen and level of phosphorus in the depths of the lake. The 10.3 km2 of the water of Hallwil Lake are an important tourist center for the canton of Lucerne (Switzerland). For this, EAWAG, to address the eutrophication of Hallwil lake, put into service in the winter of 1985/1986, an installation of a aeration system in two alternate modes of aeration namely by the aeration system in winter destratification and an aeration hypolimnetic in summer (air / pure oxygen). As a result, the average value of the dissolved oxygen and the amount of phosphorus is found in the range of allowed values which are: Summer Season: (30 m ≥H ≥15 m): [O2]min ≥ 4.5 g/m3 ; [P2 ]max ≤ 0. 20 g/m3 1. Introduction In order to remediate to the eutrophication of the Hallwil lake, the Department of Surface Water, Research and Management Institute for Federal Planning, Treatment and the Protection of Waters (EAWAG) in Lucerne (Switzerland), has implemented in the winter of 1985/1986, an installation of alternate aeration system in two aeration modes (Gafsi, M., and Kettab, 2009) - An aeration by a destratification system in winter period; - A hypolimnetic aeration in summer period (air/ pure oxygen). The aims of this study are as follows: - Improvement of the oxygen concentration in the deep zones of the lake in the case of the spatial variation; - Improvement of the phophorus concentration in the deep zones of the lake in the case of chorological variation 2. Materilas and methods The six (06) diffusers of figure 1, have a diameter of 6.5 m each, and are located in a circular configuration of 3.00 m diameter near the middle of the lake (Figure 1 and table 1). Every diffuser uses air or oxygen during summer season for the hypolimnetic aeration mode and air during the cold season for the destratification aeration mode. Table 1 shows the characteristics of the lake as well as the system of the diffuser which has been installed in the Hallwil lake, when the destratification and the aeration or the hypolimnic oxygenation is set. 4. Conclusions As a result, the average value of the dissolved oxygen and the amount of phosphorus is found in the range of allowed values which are: - Summer Season: (30 m ≥H ≥15 m): [O2]min ≥ 4.5 g/m3 ; [P2 ]max ≤ 0. 20 g/m3 Therefore, we can state the noticeable facts created by these two techniques: Phosphorus concentration in the lake is reduced since the middle of the 70s from 250 mg/m3 to 49 mg/m3. In the other side, the oxygen supply in summer has avoided the lack of oxygen in the depth, and its content was maintained over 4 mg/l. During the summer season, the deepest layer of the lake has known an sufficient quantity of oxygen (especially in the hottest months of the year), in order to neutralize the internal and external polluting materials. The hypolimnetic mode of aeration seems to be the most appropriated in the warm month of the year, since it allows to promote the content in dissolved oxygen in the deep layers on one hand, and to maintain a thermal stratification which entertains a suitable environment for the living of cold water fishes on the other hand. In contrast, the complete brewing of water is not permitted when the thermal stratification occurs. REFERENCES. Gafsi, M., and Kettab, A. Spatial Variation of physic-Chemical Parameters by Destratification and Hypolimnetic Aeration: Cas of Hallwill Lake (Switzerland). The 2nd International Conference Integrated Water Resources Management and Challenges of the Sustainable Development, Agadir, Maroc, March 24, 25 and 26, 2010. Abstract Volume, p 89, 2010. Gafsi, M., Kettab, A., Benmamar, S., et Benziada, S. International Journal of Food, Agriculture & Environment-JFAE., Vol 7. (2) 815-822. 2009 Gafsi, M., and Kettab, A. L'Eutrophisation dans les Eaux de Surface, Modelisation Physique. Thèse de Doctorat d'Ă©tat en Hydraulique, Ecole Nationale Polytechnique (ENP) d'Alger, AlgĂ©rie, Novembre 2009 McGinnis, D.F, A.Lorke, A.Wuest, A.Stockli, and J.C. Little. Water Resources Research, Vol.40, W10206, doi: 10.1029/2004WR003038, 2004 Stefan A. McCord, P.E., S.Geoffrey Schladow and Theron. Modelling Artificial Aeration Kinetics in Ice-Covered Lakes. Journal of Environmental Engineering, Vol.126, N°.1, January, 2000.Paper N°.17874.pp.21-31, 2000. Fast, AW. Artificial Aeration as a lake restoration technique. Proceeding of National Conf on lake restoration, 121-131 (1978). Wuest, A., Brooks, N.H.et Imboden, D.M. Bubble plume
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