Performance of a novel vertical-flow settler: a comparative study.
By increasing particle concentration and G value (root-mean-square velocity gradient) to enhance flocculation, a novel vertical-flow settler was designed to increase sedimentation effectiveness, and to simultaneously improve operational stabilization. Due to the gradual decrease in upward flow-rate of raw water, a flocs blanket would form and suspend in the middle section of the settler, not at the bottom as in a conventional clarifier. Enough large flocs, resulted from flocculation or filtration, would continuously settle out of the flocs blanket, and simultaneously, the flocs in raw water or those forming above the blanket would ceaselessly enter the flocs blanket. As a result, the flocs concentration in the blanket could keep a dynamic balance. The hydrodynamic shear in the blanket was improved by flow separation, which was induced by the abrupt change in flow channel. Due to the floes blanket and improved hydrodynamic shear, flocculation would be enhanced, which was helpful for removing fine particles in raw water. A comparative study showed that the novel vertical-flow settler had a much better performance in the removal of the particles in raw water than a conventional one, when they treated kaolin suspensions of different concentrations (500, 100 and 50 mg/L, respectively) coagulated by polyaluminum chloride(PAC1) at the up-flow rates of I and 2 mm/s, respectively.
Influence of Alum Coagulant Dose and Influent Turbidity on Floc Blanket Growth Rate, Steady-State Suspended Solids Concentration, and Turbidity Removal
AbstractFloc blankets are concentrated, fluidized beds of particles utilized in some water treatment plants. Floc blankets occur in vertical-upflow sedimentation tank configurations and are reported to enhance removal of suspended solids. In this research, floc blankets were formed in the laboratory at an upflow velocity of 1.2  mm/s and at varying alum coagulant dosages with influent turbidities of 10 nephelometric turbidity units (NTU), 100 NTU, and 500 NTU. Image analysis was utilized to quantify floc blanket suspended solids concentration and floc-water interface height over time. Blankets formed with higher influent turbidities required a lower ratio of coagulant dose to influent turbidity, formed more quickly, had higher steady-state suspended solids concentrations, and achieved better suspended solids removal efficiency. Increasing alum coagulant dose decreased steady-state floc blanket suspended solids concentration and resulted in lower effluent turbidities. At an influent turbidity of 100 NTU, e...
Assessing student learning in higher education
Chapter 1. Introduction to the Text, Chapter 2. What is Assessment?, Chapter 3. Student Learning, Chapter 4. Methods and Strategies: An Overview, Chapter 5. Assessing Essays, Chapter 6. Multiple Choice Questions, Chapter 7. Assessing Practical Work, Chapter 8. Assessing Projects, Chapter 9. Assessing Problems, Chapter 10. Assessing Oral Communication, Chapter 11. Self and Peer Assessment, Chapter 12. Self Assessment: Related Approaches, Chapter 13. Using Computers in Assessment, Chapter 14. Changing Assessment, Chapter 15. Reliability, Validity and Examining, Chapter 16. Quality, Standards and Underlying Issues, Bibliography Notes and comments on activities Some further reading Appendix One: Examples of examination questions in Arts, Law and Social Sciences