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Kavita Mahulikar and Taylor Reiss Cornell University 10 December 2005

The use of a conical lime reactor to control the pH of drinking water in small scale water treatment systems. Kavita Mahulikar and Taylor Reiss Cornell University 10 December 2005. objective.

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Kavita Mahulikar and Taylor Reiss Cornell University 10 December 2005

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  1. The use of a conical lime reactor to control the pH of drinking water in small scale water treatment systems Kavita Mahulikar and Taylor Reiss Cornell University 10 December 2005

  2. objective Counteract the pH lowering effects of alum through the addition of lime in a small scale water treatment plant

  3. objective Why? • Honduras Water Supply Project uses alum during flocculation • Alum lowers the pH of the water • Want to deliver clean, safe water of pH > 6

  4. objective How? • Calcium Oxide (CaO) “lime” • Saturation pH ≈ 12.4 • High acid neutralizing capacity (ANC) • Readily available in Honduras • Conical Reactor • Direct part of plant flow into reactor • Maintain consistent effluent pH around 12

  5. design From Schult, Christopher R., and Okun, Daniel A. Surface Water Treatment for Communities in Developing Countries.” Great Britain: Intermediate Technology Publications, 1984.

  6. design • Reactor 1 • Diameter ≈ 7 cm • Bottom was too flat, not ideal cone shape • Difficult to keep particles in suspension • Reactor 2 • Diameter ≈ 3 cm • Closer to ideal cone shape • Easier to maintain lime “blanket” D

  7. Flow Accumulator pH Probe Pressure Sensor Solenoid Valve Tap Water Metal Influent Tube Lab Bench Collection Tank CaCO3 Waste To Plant design effluent

  8. design

  9. results Experiment 1 • Q = 350 mL/min • CaO dose = 178 g

  10. results Experiment 1 • Q = 350 mL/min • CaO dose = 178 g

  11. results Experiment 2 • Q = 200 mL/min • CaO dose = 178 g

  12. results Experiment 2 • Q = 200 mL/min • CaO dose = 178 g

  13. results

  14. results Why? • ↓ flow rate = ↓ exit velocity • Difficult to keep particles in suspension over time • Lime has low solubility, thus, ANC is directly related to concentration of particles • As particles settle out, ANC goes down • At 200 mL/min, there was a lot of lime that never left the reactor

  15. analysis ANC Calculations

  16. analysis Feasibility Assuming: • Alum dose = 40 mg/L • Average reactor effluent ANC = 0.035 eq/L • Q = 350 mL/min Then: • Max. Plant Flow Rate = 30.5 L/min

  17. analysis Feasibility Potential Problems: • Unstable System • Calcium Carbonate (CaCO3) Removal

  18. conclusion Our experimental design is not feasible for small scale water supply in Honduras But maybe someday…

  19. conclusion Possible Alternatives • Use a base with a higher solubility • Larger Reactor, higher residence time

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