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Method of regeneration:
Regeneration in Aqueous media:
Waste treatment:
Arsenic removal: Design guidelines
Fluoride removal: design guidelines
- Alumina has a neutral surface at pH 9
- At lower pH, it is positively charged - An ion
adsorption: AlOH + Lz----> AlL(z-1) + OH-
- Below pH 3, alumina starts to be soluble
- Capacity is a function of:
- ion polarity
- ion equilibrium solubility
- competitive adsorption from other ions
- pH of the solution
- Non-aqueous media: heat or pressure
swing regeneration
- Aqueous media: chemical regeneration
(pH adjustment)
- Backwash with raw water: Upflow - 10 min
- removal of solids accumulated in the bed
- expansion of the bed
- Regeneration: 2 steps - 1 % NaOH solution
- Upflow
- Rinsing with raw water
- Downflow
- Neutralization: H2SO4 solution - pH: 2.5
When the fluoride or arsenic level drops below the limit, the water becomes
usable.
The pH at the inlet is adjusted to 5.5 when the outlet pH gets below 7.5.
Waste water: 4% of the total throughput
- from backwash: only raw water - discharged to existing storm
water disposal systems
- from regeneration and neutralization: water with high
levels of fluoride or arsenic ions - must comply with local wastewater
discharge standards - Concentrate waste in lined evaporation ponds
and further dispose of it.
- pH: for Arsenate (As(V)): about 6 - 6.2
for Arsenite (As(III)): 8-9
Arsenate adsorbes better than arsenite
Arsenite should be first oxidized into arsenate then be treated
- Bed size: minimum of 1 ft3 per gpm of water;
minimum depth: 3 ft
- Flowrate: minimum 2.5 to 3 gpm/ft2
- Temperature: 40oC rather than 25oC
Capacity for As (V): Capacity is reduced in
presence of chloride and sulfate
at pH 6, 25oC, SO42-=7.5 meq/l, Cl-=7.5 meq/l:
q=16.2 C0.43
q and C in mg/g
As (V) outlet content: down to 0.02 ppm
- Flowrate: 12 bed volume/hr to obtain low levels
(down to 0.2 ppm)
- Capacity for Fluoride: Capacity is reduced in
presence of bicarbonate ions.
Typical capacity is 1.2-1.5% Wt.
- Fluoride outlet content: typically 1 ppm
down to 0.2 ppm
For further information, please contact: Tramfloc, Inc., 480-491-6895 or water@tramfloc.com.