Lime Softening Philippe ppt

EWB-UCB lime softening research group
Basic process of lime softening
 1. Rapid Mixing of Lime.
 2. Flocculation of Solids.
 Solid colloids agglomerate into larger particles.
 3. Sedimentation.
 Solids settle out.
Basic Chemistry
 Lime provides OH- which increases the pH of water.
 Dissolved CO2 is changed to Bicarbonate (HCO-1) then
to carbonate (CO3-2) as pH increases.
 CaCO3 first precipitates.
 Then at higher pH, Mg(OH)2 precipitates.
Arsenic removal is dependent on
 Coprecipitates with magnesium hydroxide
 Less than 10% precipitates at pH 9.6
 Removal of As(V) approaches 100% and As(III) 75% at
pH 10.5
Choice of Lime: Lime or LimeSoda?
 Lime: Only Carbonate hardness
 Lime and Lime-Soda: A lot of non-carbonate
 Other variations?
Obstacles to arsenic removal
 Trace amounts of orthophosphate and Carbonate
reduces coprecipitation with magnesium hydroxide
 Other problems?
Future Steps
 Look into quality of hardness
 Is it carbonate or noncarbonate?
 What are the variations of lime based on the quality of the
 Lime, soda, other additives and grades of Lime
 What are possible obstacles to precipitation
 How to deal with pH>11
 Leave it as is, stabilize it, reduce it?
 What is to be done with the sludge
 Use in gardens as fertilizer? Other outcomes?
 Anything Else?
Sorry I Can’t Be here, I am teaching
People how to sail.
 EPA Wastewater Technology Fact Sheet Chemical Precipitation
 Fields, K. A., Chen, A. S. C., Wang, L., Supply, N. R. M. R. L. (US) W., &
Division, W. R. (2000). Arsenic removal from drinking water by
coagulation/filtration and lime softening plants. Contract. National
Risk Management Research Laboratory, Office of Research and
Development, US Environmental Protection Agency. Retrieved from
 Wikipedia

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