1. 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

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” Conical Reactor
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. design Tap Water Lab Bench CaCO3 Waste To Plant Collection Tank
Metal Influent Tube
Solenoid Valve
Pressure Sensor
Flow Accumulator pH
Probe
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 Experiment OH- Initial after 7 hours
after 4 days
1 Q = 350 mL/min
6.34 moles
2.78 moles
N/A
2 Q = 200 mL/min
4.4 moles
2.54 moles

16. analysis Feasibility Assuming: Alum dose = 40 mg/L
Average reactor effluent ANC = 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. Possible Alternatives
conclusion
Possible Alternatives
Use a base with a higher solubility
Larger Reactor, higher residence time