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

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

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

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

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

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

design

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

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

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

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

results

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

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

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

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

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

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