Study On Hydrodynamic Algae Control Mechanism And Applicable Conditions In Surface Water Environment

Eutrophication and algal blooms are the main problems in the surface water environment,and the nutrient salt,light and hydrodynamic state of water bodies are important influencing factors and causes.Technical measures to cut off the exogenous input of nutrients and control the internal release can fundamentally solve the eutrophication of water bodies and the high incidence of algae.Segregate water from light can effectively inhibit algal blooms.The hydrodynamic control measures of algal blooms are affected by nutrient concentration,N/P ratios and light intensity.But the control conditions are different and the mechanism is not clear.This study established an algae growth simulation reactor in a flowing water environment.The Chlorella vulgaris was used as the experimental research object to test the growth state of algae under different vertical flow conditions.Exploring and analyzing the mechanism of vertical hydrodynamic state inhibiting algae growth.Through path analysis and the results of previous experiment,the application condition of algae control has been put forward.This application condition of hydrodynamic algae control was carried out under different nutritional levels and illumination conditions.The research results will provide theoretical and technical support for controlling the surface water environment to inhibit algal blooms.The main conclusions are as follows:The algae control experiment of vertical circulation movement of water body in the light zone showed that low vertical flow rates could promote algae growth,and algae inhibition was more evident as the vertical flow rate increased.Compared with control group,when the flow rate was 0.05m/s,the OD value of algae became higher,the specific growth rate reached the maximum,and the synthesis of chlorophyll-a was the most.The flow rate of 0.05m/s could promote the growth of Chlorella vulgaris.The reason might be that the flow rate enhanced the electron transport activity of PSII.And less light energy transformed into thermal energy,the actual photosynthetic efficiency of the cells was increased.When the flow rate reached 0.10m/s and 0.15m/s,the OD value,specific growth rate and chlorophyll-a concentration of Chlorella vulgaris decreased with the increased of flow velocity.The growth of Chlorella vulgaris was inhibited.The reason might be that the electron transfer activity of the PSII was supressed,more light energy transformed into thermal energy,and the actual photosynthetic efficiency of the cells was lowered.The SOD activity analysis of algae cells showed that the SOD of algae cells was positively correlated with the flow velocity.The higher the flow rate,the greater the hydrodynamic stress.The algae control experiment of vertical circulation movement between the light zone and the non-light zone showed that higher velocity could inhibit algae growth and low velocity could promote algae growth,though the comparison of the vertical circulation movement in the light zone.The vertical flow rate could promote the growth of Chlorella vulgaris at 0.05m/s and 0.10m/s.The promotion of 0.10m/s was greater,probably because this flow rate accelerated the circulation of algae and maked Chlorella vulgaris circulated to the upper water body with better illumination conditions.Therefore,the algae cells received more light,it could enhance the electron transport activity of the PSII,and the actual photosynthetic efficiency of the cells was increased.When the flow rate reached 0.15m/s,the OD value and chlorophyll-a concentration of Chlorella vulgaris increased most slowly,and It could inhibit the proliferation of algae cells.In this velocity,the algae cells received the highest vertical hydrodynamic stress and the actual cell photosynthetic activity was low.Based on the preliminary test results of horizontal flow control of algae in water bodies,statistical methods such as path analysis and decision tree analysis were used to analyze and determine the applicable conditions for horizontal motion inhibiting algae growth.Within the experimental setting conditions,the path analysis results showed that the importance of the three environmental factors affecting the growth of Chlorella vulgaris was in order of light intensity,N/P ratio and flow rate.The decision tree analysis showed that in the medium light intensity,regardless of the ratio of N/P,algae could be inhibited by increasing the horizontal flow rate(greater than 0.3 m/s).While at high light intensity,the shading method was an effective method for inhibiting algae.Therefore,the horizontal motion algae control method should select the appropriate algae control technology according to the nutrient status of the water body and the light intensity of the environment.Compared vertical circulation flow algae control with the horizontal flow algae control,the algae control effect was different.The flow rate required for the vertical circulation movement was lower,and the higher horizontal flow rate could achieve a good algae control effect.For deep water bodies,it could choose to control algal blooms in vertical circulation motion between the light zone and the non-light zone.For shallow surface water,the combination of horizontal and vertical hydrodynamics was more conducive to controlling algal blooms.