![Page 1: Kavita Mahulikar and Taylor Reiss Cornell University 10 December 2005](https://reader035.vdocuments.mx/reader035/viewer/2022062805/56814ce9550346895db9e740/html5/thumbnails/1.jpg)
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
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objective
Counteract the pH lowering effects of alum through the addition of lime in a small
scale water treatment plant
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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
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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
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design
From Schult, Christopher R., and Okun, Daniel A. Surface Water Treatment for Communities in Developing Countries.” Great Britain: Intermediate Technology Publications, 1984.
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designReactor 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
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design
effluent
Tap Water
Lab Bench
CaCO3 Waste
To Plant
CollectionTank
Metal Influent Tube
Solenoid Valve
Pressure Sensor
Flow AccumulatorpH
Probe
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design
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resultsExperiment 1• Q = 350 mL/min• CaO dose = 178 g
pH as a function of time
8
9
10
11
12
13
0 3 6 9 12
Time (hr)
pH
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resultspH and ANC as a function of time
0.00000
0.01000
0.02000
0.03000
0.04000
0.05000
0.06000
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00
Time (hr)
AN
C (
eq
/L)
12.15
12.20
12.25
12.30
12.35
12.40
12.45
12.50
12.55
12.60
pH
ANC pH
Experiment 1• Q = 350 mL/min• CaO dose = 178 g
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results
pH as a function of time
8
9
10
11
12
13
0 3 6 9 12Time (Hr)
pH Series1
Experiment 2• Q = 200 mL/min• CaO dose = 178 g
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resultspH and ANC as a function of time
0.00000
0.00500
0.01000
0.01500
0.02000
0.02500
0.03000
0.03500
0.04000
0.04500
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (hr)
AN
C (
eq/L
)
10.00
10.50
11.00
11.50
12.00
12.50
13.00
pH
Initial ANC After Mixing ANC pH
Experiment 2• Q = 200 mL/min• CaO dose = 178 g
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results
ANC as a function of time
0.00000
0.01000
0.02000
0.03000
0.04000
0.05000
0.06000
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00
Time (hr)
AN
C (
eq
/L)
Q = 350 mL/min Q = 200 mL/min
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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
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analysisANC Calculations
HOHCOHCOANC 233 2
)(34.6)(1
)(2
1
)(1
56.1gCao
1CaO178
2
2
OHmolesOHmoleCa
OHmoles
moleCaO
OHmoleCamoleCaOg
Experiment OH- Initial
OH- after 7 hours
OH- after 4 days
1 Q = 350 mL/min 6.34 moles 2.78 moles N/A
2 Q = 200 mL/min 6.34 moles 4.4 moles 2.54 moles
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analysis
FeasibilityAssuming: 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
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analysis
Feasibility
Potential Problems: Unstable System Calcium Carbonate
(CaCO3) Removal
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conclusion
Our experimental design is not feasible for small scale water supply in Honduras
But maybe someday…
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conclusion
Possible Alternatives
Use a base with a higher solubility Larger Reactor, higher residence time
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