Part 1: Single choice question (points" 15=15 points. only one choice is the correct answer, please select) 1. According to chemical properties, water pollutants can be classified into A organic pollutant and inorganic pollutant 8. domestic pollutant and industrial pollutant c refractory pollutant and removable pollutant o degradable pollutant and undegradable pollutant 2. When design a screen, the flow velocity of wastewater should be less than m/s. A 10 B! c0.1 D 0.01 3. In the mixing step, the velocity gradient should be S1-1. A 200-500 11 300-500 c: 500-1000 D 1000-1500 4. Suspended solids are removed from water through sedimentation by gravity, according to their difference to the water's A density B. mass C. volume D. Buoyancy Particles whose velocity is critical settling velocity can be totally removed in ideal settling tank. A more than Bless than cequal to D. no demanding & Surface load and have the same value, though represent different meaning, A remaining time a critical settling velocity ceflect depth D effect length 7. Particle's settling efficiency is related to in ideal settling tank A water depth Bank length C. surface load Dhorizontal flow velocity * The major mechanism of the migration of impurity particles in fast filtration is: A interception i sedimentation cinertial Diffusion