Study On The Mechanism Of The Light-shading Method

The algal bloom caused by the eutrophication is at present one of the most serious calamities which influence the safety of drinking water source,so study on the control measure of algal bloom became a significant problem to be solved. And, light-shading method was advanced to be a lash-up control measure to protect drinking water source. The effect on algal control of light-shading method had been approved well. But , the mechanism of light-shading method and the feasibility of project need further study. This article focused on the effect of light intensity on the the algal growth and vertical distribution in the water column, which because the light intensity was asymmetric distributed in lake. According the characteristic of algal growth and vertical distribution under low light intensity, the measure combined by the light-shading and aeration was explore to accelerate the algal contabescence, shorten the algal control period, improve the DO of water. The main content and conclusion was followed:1) The light intensity is asymmetric distributed in lake. In order to investigate the effect of the light intensity on the algae growth, the experiment of the light intensity on the biomass of Scenedesmus obliquus was conducted in the water column. In the water column, on the continuous flow which lose rate is 10%, the biomass of Scenedesmus obliquus trended to decrease, when the incident light intensity was about 10000lux(the available average light intensity was ablut 2000lux). But, Scenedesmus obliquus trended to increase in the flask when the incident light intensity was 500lux. It was showed that the available average light intensity well represented the light resource acquired by alga, the steady-state biomass of Scenedesmus obliquus and the available average light intensity showed the remarkable positive correlativity (R=0.93).2) Besides the growth, the algal vertical distribution was also effected by the light intensity. Firstly, the experiment of the effect of the light intensity on the algal carbohydrate content was conducted in the flask. Furthermore, the experiment of the effect of light intensity on algal vertical distribution and algal carbohydrate content was conducted in the water column. The result showed: Microcystis trended to assemble in the surface when the incident lgiht intensity was 0lux, after 24h, the algal density ascended to be 4.85×106 cells/ mL when the algal density was 3.6×105 cells/mL at the beginning. However, the algal density in the bottom trended to increase when the light intensity was enough. The flask experiment showed: the algal carbohydrate content had a good answer to the change of the light intensity. And, the water column experiment showed: the algal carbohydrate content in different depth under different light intensity trended to increase with the increase of the depth.3) According the characteristic of algal growth and vertical distribution under low light intensity, the measure combined by the light-shading and aeration was designed to control the algae growth. The continous flow experiement in the combined system showed that the average romove efficiency of Chla was above 75%, the DO of effluent was above 4mg/L when the HRT is 4 days.