KEYExam3 - University of Wyoming College of Engineering and...

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University of Wyoming College of Engineering and Applied Science CE 3400 – Introduction to Environmental Engineering KEY TO EXAM – Chapters 10-13 22 November 2010 1. THIS QUESTION IS WORTH 12 POINTS. The diagram shown below is the one we used during our water treatment lectures. Add labels to the shaded boxes that are numbered 1-4 and briefly describe what happens in each of these four stages of the water treatment process. What occurs in Stage 1? Chemicals are added and mixed very rapidly: (1) for softening (to reduce harness) and/or (2) for coagulation to destabilize particles and dissolved solids so as to facilitate their removal What occurs in Stage 2? Aggregation of destabilized/flocculated particles is achieved through very slow mixing What occurs in Stage 3? Type II Settling/sedimentation/clarification is achieved which involves physical separation to remove flocs formed during flocculation. Materials that are denser than water settle from suspension via gravity. What occurs in Stage 4? Particles that escaped flocculation and/or settling (Stages 2/3) are caught on the sand filter
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CE 3400/Dr. Colberg Key to Exam 3 22 November 2010 2 2. THIS QUESTION IS WORTH 4 POINTS. List two ions (cations or anions) that are responsible for “hardness” in water. Fe 2+ , Fe 3+ , Mg 2+ , Ca 2+ , HCO 3 - , CO 3 2- 3. THIS QUESTION IS WORTH 6 POINTS. What is the purpose of running a ‘jar test’? Please be specific. Hint: there are two pieces of information that are gained from running a jar test. Please describe both. (1) To determine which coagulant will work best for a given raw water source (2) To estimate the minimum dose that is required to achieve the desired reduction in turbidity 4. THIS QUESTION IS WORTH 6 POINTS. What is the difference between particles that settle by ‘Type I/Discrete Particle Settling’ and particles that settle by ‘Type II/Flocculent Settling’? Please be specific. Discrete Particle Settling (aka Type I Settling) Particles have little or no tendency to flocculate Particles readily settle out at a constant velocity due to gravity Examples: settling of sand particles during cleaning of rapid sand filters in water treatment plants; grit/sand removal in wastewater treatment Flocculent settling (aka Type II Settling) Particle sizes tend to increase as particles settle so that settling velocity increases with time No general formula for determining settling velocities
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