DETERMINATION OF PURIFICATION RATIO OF WEST LAKE IN HANOI

Abstract

West Lake is a natural lake located in the Northwest of Hanoi with an area of more than 500 hectares with a circumference of 18 km. Like other water bodies, West Lake water is still capable of self-cleaning with conditions related to a number of factors including the dissolved oxygen (DO) value of lake water. When the amount of waste increases, the self-cleaning capacity of the lake does not respond, leading to a decrease in DO in the water, thereby leading to adverse changes to aquatic life. DO is used as a parameter to assess the level of organic pollution of water sources. DO also has great significance for the self-cleaning process of the lake. When DO drops low (< 4 mg/l) fish and other aquatic animals die, the water becomes black and has a foul odor. The main source of oxygen is from the atmosphere and from photosynthesis by aquatic plants. Oxygen depletion is caused by many factors, the most important of which is Biological Oxygen Demand (BOD). The results indicated that if the condition of excess nutrients in the lake is prolonged, it can affect the anoxic thickness of the lake bottom layer and will continue to move upward in the surface water of the lake. This situation can lead to a decrease in the self-cleaning capacity of the tank. The self-cleaning capacity of the tank is evaluated based on the ratio of the value of the air intake rate constant (K2) and the oxygen reduction rate constant (K1). The value of self-cleaning rate (K2/K1) on West Lake in dry season is 1.6 and in rainy season is 2.24 which belongs to the self-cleaning range (>1).