overcoming the challenge of managing ion exchange residuals
TRANSCRIPT
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Ca
2+
Dis
pla
ced
(m
g/L
as
Ca
CO
3)
Regenerant Concentration Relative to IX Capacity
NaCl KCl
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0 100 200 300 400
NO
3 d
isp
lace
d (
mg
/L-N
)
Concentration of Regenerant Relative to IX capacity
KCl NaCl
Overcoming the Challenge of Managing Ion Exchange ResidualsGabe Maul, Treavor Boyer, Environmental Engineering Sciences
Conventional IX Residuals Management Experimental DesignCompare alternative regenerants KHCO3, KCl, and NaHCO3, to NaCl in regeneration and
treatment of a wide variety of contaminants using combined ion exchange.Hypothesis: Ion exchange resins will be regenerated by K+ similarly to Na+, and regenerated by HCO3
- similarly to Cl-.
Expected Contribution to Water Treatment
Improve the sustainability and viability of ion exchange process
Demonstrate synergistic advantages of alternative regeneration and combined ion exchange
Uncover operational challenges with combined ion exchange regeneration
Alternative IX Residuals Management
Remaining Questions1. Combined Ion Exchange Regeneration Pilot
2. Biodegradation with K+ and HCO3-
3. Vegetative tolerance with K+ and HCO3-
Combined Ion Exchange
Treatment Adv.
• Selectively remove
complimentary
anion & cation pairs
• Co-removal when
contaminants
interact: 70% DOC
& 55% hardness
• Easy retrofit
Regeneration Adv.
• Fully utilize
regenerant
• Generate as low
as 50% less
residuals
compared to
individual
• Easy retrofit
+
Treatment:
Ca2+ & NO3-
Na+
Ca2+
Cation IX
_ ___
__++
+
++
+
++
+
NO3-
Cl-Anion IX +++
+++
__
__
_
__ _
_
Na+
Alternative RegenerationK+
Na+ HCO3-
K+ HCO3-
Cl- Na+
Cl- 1. KCl - #1 source of potassium for agricultural crops
2. NaHCO3 – less harmful to humans and ecosystems;
reduced corrosion
3. KHCO3 – combination of benefits
Novel Approach
Results
IX Resin Resin DoseRegeneration
Capacity
Contaminant
Removal Capacity
Cation 0.45 mL/L 0.9 meq/L 45 mg/L Ca as CaCO3
Anion 1.0 mL/L 0.9 meq/L 12.6 mg/L as N
Fig. 2: Regenerant concentrations varying
1x - 300x the resin IX capacity. (For NaCl,
ranges from ~50 – ~15,000 mg/L)
Table 1: IX Dose and Removal Capacity for Regenerating Ca2+/NO3-
exhausted resin
1. Arbitrary resin dose
selected of 1.0 mL/L
3. Check: removal
capacities reasonable
Min. resin capacity
Min. resin capacity
2. Cation dose based
on equivalent
regeneration capacityFig. 1: Start with resin
exhausted with Ca2+ and NO3-
NO3-
+++
+++
NO3-
NO3-
NO3-
NO3-
NO3-
NO3-
Ca2+
_ ___
__
Ca2+
Ca2+Ca2+
Ca2+
Ca2+Ca2+
Do not
interact
Fig. 3: Regeneration Efficiency of NaCl and KCl on
Ca2+ Resin
Fig. 4: Regeneration Efficiency of NaCl and KCl on
NO3- Resin
• ↑ regenerant concentration, ↑ regeneration
• 300x was not concentrated enough to displace all Ca2+
• K+ regenerated Ca2+ resin slightly better than Na+
• Treatment efficiency of K+ expected slightly worse
• 100x was sufficient to displace most NO3-
• Cl- regenerated NO3- similarly with both regenerants
• Fully regenerated resin displaced 20% more NO3 than
minimum capacity � test capacity
• 100x regenerant (5,000 mg/L) will regenerate all NO3- resin, but only 70% of Ca2+ resin
• Can dose higher NO3- resin than Ca resin with similar regeneration
1. Compare regeneration efficiency of HCO3-
to Cl- (with Ca2+/NO3- resin pair)
Upcoming Experiments and Challenges
HCO3- Cl-
CaCO3 (or Ca(HCO3)2) precipitation
• Acidify samples before Ca titration
HCO3- Ca2++
2. Determine treatment efficiency of resin
K+ and HCO3- compared to Na+ and Cl-
_ ___
__
K+
K+
K+K+
K+
K+
K+
+++
+++HCO3
-
HCO3-
HCO3-
HCO3-
HCO3-
HCO3-
Analyzing K+ and HCO3-
• IC (K+) and either DIC or alkalinity (HCO3-)
Simulate precipitation?
3. Repeat for more contaminants:
Ions Interact: Toxic Pair:
Ca2+/NOM- Cd2+/ClO4-
Cover robustness of IX?
Base on IX functional groups?
• Anion: quaternary ammonium,
phosphonium, sulfonium
• Cation: sulfonic acid, carboxylic acid
Or on major types of contaminants?
• Oxyanions, salts, organics, metals
Experiment Challenge
4. Aquatic toxicity with K+ and HCO3-
5. HCO3 loading to wastewater treatment plant
6. Regenerant reuse after precipitation