Research On The Optimization Model Of Water-lifting Aeration Control Cyanobacteria In Reservoir

In order to get the most economical layout spacing, mixing depth and diameter of the water-lifting aerator, the floating and subsiding velocity of Cyanobacteria was measured under different conditions such as different illumination, temperature, pressure, the density of Cyanobacteria with different motion velocity was calculated by Stokes formula and simulated by Fluent simulation software. Established a method to simulate the distribution of Cyanobacteria in the peripheral flow field by using Fluent simulation software. Using Fluent simulation software to simulate the distribution of Cyanobacteria in the peripheral flow field of water-lifting aerator under different conditions, such as the depth of water, mixing depth and diameter of water-lifting aerator, calculating the average net productivity of Cyanobacteria in the water and the annual cost of per unit control area, access to the optimized layout spacing, mixing depth and diameter of water-lifting aerator. The main conclusions are as follows:(1) The Cyanobacteria showed strong propensity of floating under the illuminance from15001x to60001x, and they floated fastest under the illuminance of1500lx, the Cyanobacteria particle with floating velocity of more than1.2cm·min-1accounted for46%under the illuminance of15001x. The floating velocity slowed down when the illuminance was lower than15001x or higher than60001x. In the temperature range of8to25Celsius degree, the Cyanobacteria floated and the floating velocity increased with temperature. The Cyanobacteria floated under the pressure of0-0.1MPa and the floating velocity slowed down as the pressure increased. Most Cyanobacteria were suspended in the water when the pressure reached0.2-0.3MPa and only a small part of the Cyanobacteria floated or settled. When the pressure reached0.4-0.6MPa, the Cyanobacteria notably settled and the subsiding velocity increased with the increase of pressure. The Cyanobacteria particle with subsiding velocity of more than0.5cm·min-1accounted for64.5%when the pressure was0.6MPa. Integrated illuminance, pressure and temperature, the Cyanobacteria floated under the depth of water of0-30m and the floating velocity slowed down as the depth of water increased. Most Cyanobacteria were suspended in the water when the depth of water reached40m and only a small part of the Cyanobacteria floated or settled. When the depth of water reached50-60m, the Cyanobacteria notably settled and the subsiding velocity increased with the increase of the depth of water.Gas vesicles bursted when the gas vesicles of the Cyanobacteria could not bear the external pressure. The buoyancy of the Cyanobacteria diminished until the floating force became smaller than its weight, causing the particles of the Cyanobacteria to settle. Under normal atmospheric pressure, the particle diameter was positively correlated to the floating velocity, while negatively correlated to the density. Under high pressure, the particle diameter was positively correlated to the subsiding velocity and the density.(2) Established a method to simulate the distribution of Cyanobacteria in the water by using Fluent simulation software, verifying the result with the pilot experiment, the simulation results were similar to the experimental results. The mixture multiphase flow model was applied to simulate the distribution of Cyanobacteria in the peripheral flow field, choosing the unsteady formulation and k-ε turbulence model, refer to the productivity of Cyanobacteria in different depth of water, the net productivity of Cyanobacteria in the peripheral flow field could be calculated, the efficacy of the water-lifting aerator control algae could be evaluated. Simulation results showed that, the water-lifting aerator mixing intensity larger, the flow velocity in the peripheral flow field was greater than the Cyanobacteria floating velocity, algae suspended in the water were carried to the lower level of the water, and distribution of Cyanobacteria in the peripheral flow field was even. The water-lifting aerator mixing intensity smaller, the flow velocity in the peripheral flow field was smaller than the Cyanobacteria floating velocity, only a small part of the Cyanobacteria were carried to the lower level of the water, the volume fraction of the Cyanobacteria in the top water was larger than bottom water.(3) Fluent simulation software was applied to simulate the water flow velocity and the distribution of Cyanobacteria in the peripheral flow field under different conditions such as the depth of water, mixing depth and diameter of water-lifting aerator. During the operation, there was a vortex in the peripheral flow field, Cyanobacteria suspended in the water were carried to the lower level of the water, and gathered in the center of the vortex, the volume fraction of Cyanobacteria was the largest in the center of the vortex. When the aeroelastic intervals were constant, water-lifting aerator control scope increased with the increase of the water depth. When the depth of water was certain, water-lifting aerator mixing depth and diameter had little impact on the control scope, while the efficacy of the water-lifting aerator was better. Within the radius of water-lifting aerator control algae, the average net productivity was negative, Cyanobacteria showed a decline trend. When calculating radius exceeds the radius of water-lifting aerator control algae, the average net productivity was increased rapidly.(4) The total cost model of the water-lifting aeration technology was established to calculate the annual cost of per unit control area. In total cost per unit area, the particle of annual operation cost was far greater than the investment. With the increase of water depth, annual cost of per unit control area decreased. When the depth of water was certain, the annual cost of per unit control area increased rapidly with the increase of mixing depth and diameter of the water-lifting aerator. When the water depth was60m, the economic water-lifting aerator mixing depth was17m and algae suspended in the water could be carried to the water depth of40m and settled. The diameter of water-lifting aerator was500mm, layout spacing was180m.