Ion Exchange for Drinking Water Treatment

1
Ion Exchangefor Drinking Water Treatment

• Wolfgang H. Höll
• Forschungszentrum Karlsruhe
• Institute of Technical Chemistry / WGT
• Santander Spain, February 8, 2008

2
Application of Ion Exchangers
First documentation Mose Exodus, 15.
chapter First technical application Gans,
1903, K removal from sugar juice
3
Species to be Removed by IEX

• a) Bulk Components
• Ca2, Mg2, Na, K
• SO42-, NO3-, Cl-
• CO2, HCO3-, CO32-, SiO2
• Natural organic Matter (NOM)
• b) Trace components
• Heavy metals (e.g. (Fe, Mn), Pb2, Ni2, ...)
• As species, Cr(VI) species, F-, Borate, ClO4-,
  Se, Sb species, ...

4
Actual Applications of Ion Exchange in Drinking
Water Treatment

• Elimination of
• Hardness ( alkalinity)
• Nitrate ( sulphate)
• Arsenic
• NOM
• Uranium radio isotopes
• Heavy metal cations (Ni, Hg, ...)
• Chromate
• Perchlorate
• Boron

5
Existing Ion Exchangers

• Zeolites
• Polymeric exchange resins (strongly and weakly
  acidic / basic)
• Metal (hydr-) oxides
• Mixed polymeric / inorganic materials
• A manifold of other materials

6
Inorganic Ion Exchangers

• Sodalite cage Combination of
  cages around a-cage

7
Inorganic Ion Exchangers

• Zeolite A Zeolite ZSM-5
• Replaces/replaced phosphates in detergents

8
Inorganic Ion Exchangers

• Zeolite A Crystals

9
Polymeric Exchangers Matrix

• Crosslinked polystyrene
• Polyacrylic or polyacrylic amine structure
• Phenol formaldehyde copolymer
• Poly alkyl amine (polyamines epichlorhydrine)

10
Polymeric Exchangers Functional Groups
11
Designations

• Weakly acidic exchangers (WAC)
• Strongly acidic exchangers (SAC)
• Strongly basic exchangers (SBA)
• Weakly basic exchangers (WBA)
• Chelating exchangers (IDA)

12
Designations

• Exchange processes are written in terms of
  formal chemical equations
• Overbarred symbols refer to the exchanger
  phase
• R- symbolises the hydrocarbon structure to
  which the functional groups are attached

13
Particle Size
Conventional Resin Monosphere Resin
particle diameter
Approximately 0.3 dP 1.2 mm uniform
particle size
14
pH Range of Application

• Cation Exchangers Anion Exchangers
• pKC lt 1 (strongly acidic) pKA gt 13 (strongly
  basic)
• 4 6 (weakly acidic) 5
  8 (weakly basic)
• Application above pKC Application below pKA

15
Series of Selectivity
Series of Selectivity

• SAC Ca2 gt Mg2 gt Na gt H
• WAC H gtgt Ca2 gt Mg2 gt Na
• SBA SO42- gt NO3- gt Cl- gt HCO3-
• WBA OH- gtgt SO42- gt NO3- gt Cl-
• IDA H gt Cu2 gt Ni2 gt Ca2 gt Mg2

16
General About Application of Ion Exchangers for
Food Treatment
Ion exchangers are technical polymeric products
which may contain impurities from manufacturing.
- Strongly acidic exchangers release
oligomeric compounds. - weakly acidic
exchangers may release acrylic or methacrylic
acid, acryl nitrile or acrylamide. - Anion
exchangers may release amines. For treatment of
drinking water only ion exchangers can be applied
which correspond to the regulations of each
individual country.
17
Regulations in Germany Until 2003 (1)

• - All chemicals used for synthesis have to be
  mentioned in a positive list Ion exchangers
  which are synthesised with further chemicals are
  not allowed.
• Ion exchangers must not increase the content of
  bacteria of the water to be treated.
• - The exchangers must not release substances,
  (i) which present health risks, (ii) which are
  undesirable with respect to taste and odour,
  (iii) which can be avoided by technical measures
  or, (iv) which cause changes of water quality
  beyond the purpose of application of the
  exchange resin.

18
Regulations in Germany Until 2003 (2)

• The exchange resins have to undergo a pumping
  test with recycling of the liquid phase for 168
  hours (DIN 54 411) in which the change of water
  quality and the release of organic compounds are
  measured. ?DOC lt 1 mg/L (measured as
  KMnO4 consumption)
• Acryl nitrile is individually analysed. It has a
  recommended value of 0.02 mg/L for the pumping
  test. For a one-time flow across the test filter
  this corresponds to 0.36 µg/L. All other
  substances are measured through TOC.
• Release of organic substances during regular
  service operation by ion exchangers which fulfil
  the above conditions is normally very small and,
  therefore, negligible.

19
Regulations Now

• In exchangers have to demonstrate their
  applicability in pilot scale experiments
• A so-called Extensive Demonstration of
  Efficiency has to be made during application in
  full scale with supply of population. Several
  parameters are controlled by public health
  authorities
• Successful demonstration leads to general
  permission

20
Technical Ion Exchange Processes
Technical ion exchange processes consists of a
service cycle to remove the undesirable ions,
followed by a regeneration cycle, in which the
ions adsorbed before are removed from the
exchanger to allow its re-use. Then the
exchanger can be re-used in the next service
cycle.
21
Possible Regeneration Chemicals (D)

• H2SO4 (DIN 19618)
• CO2
• Ca(OH)2
• NaHCO3
• Na2CO3
• CaCO3

• MgCl2
• NaCl (DIN 19604)
• NaOH (DIN 19616)
• CaCl2
• HCl (DIN 19610)
• NH3
• (NH4)2CO3

22
Softening Principle

• Service Cycle
• Regeneration
• General Feature
• Sorption of preferred species during service
  cycle,
• Loading with non-preferred species during
  regeneration

23
Softening

• Development in Equilibrium Diagram

a equilibrium at tap water concentration, e
equilibrium at 2 mol/L total concentration
24
Home Softening
Softener in a dish washer
25
Public Water Supply Softening
26
Softening / Dealkalisation

• a) Strongly acidic exchangers
• Service Cycle
• Regeneration
• Application of HCl (or H2SO4), loading with
  non-preferred species

27
Softening / DealkalisationPublic Water Supply
28
Softening / Dealkalisation Technology
FLUICON continuous Process
29
Softening / Dealkalisation

• b) Weakly acidic exchangers
• Service Cycle (until all HCO3- is converted to
  CO2)
• Regeneration
• Application of HCl (or H2SO4), loading with a
  preferred species !

30
Public Softening / Dealkalisation
31
Home Softening/ Dealkalisation
Water for preparation of coffee and tea
32
Nitrate Removal

• Service Cycle
• Regeneration Application of NaCl
• Service Cycle Sorption of preferred ions,
  Regeneration Sorption of non-preferred ions

33
Nitrate Removal

• Problem
• Conventional SBA exchangers prefer sulphate over
  nitrate, therefore, nitrate occurs first in the
  filter effluent.
• Solution
• Synthesis of so-called nitrate-specific
  exchangers by replacing methyl groups by ethyl,
  propyl or butyl groups

34
Nitrate Removal

• Service Cycle, conventional Type 2 resin

35
Nitrate Removal

• Service Cycle, nitrate-selective resins

36
Nitrate Removal

• Concepts
• Application of almost completely regenerated
  exchangers, blending with untreated water
• Application of partly regenerated exchangers to
  treat the complete water
• Numerous plants exist in the US, UK and France.

37
Nitrate Removal

• Application of almost completely regenerated
  exchangers,
• product water blended with untreated raw water

38
First Nitrate Elimination Plant in USA
HIGGINS pseudo-continuous Process
39
Nitrate Removal

• Application of partly regenerated exchangers,
  treatment of the full throughput, cyclic switch
  of service/regeneration cycles

40
Nitrate Removal

• Application in Germany
• Discharge of large volumes of spent NaCl-bearing
  regenerant solutions is highly unwanted.
• Only one small plant at Hemeln (10 m³/h) went
  into service (decommissioned).

41
Nitrate Removal

• Modification
• Electrolytic decomposition of nitrate in the
  spent regenerant (NITROUT Process)

42
Nitrate Removal NITROUT Process

• b) Electrolytic decomposition of nitrate
• Anodic reactions
• Cathodic reactions (subsequent)
• total

43
NITROUT Process Principle
44
NITROUT Process Performance
Application Hackpüffel / Sangershausen Resin IM
AC HP 555 (nitrate-selective) Raw water
Nitrate 85.9 mg/L (51.1 mg/L)
Sulfate 370 mg/L (107 mg/L) Product
water 10 mg/L (before blending) Regenerant 9
NaCl Nitrate in spent regenerant 4,500 30,900
mg/L
45
Nitrate Elimination in Households
Application Filter cartridges for installation
under kitchen sink Nitrate Eater
46
Conventional Partial Demineralisation
Principle Step 1 Cation exchange for H using a
SAC exchanger Step 2 Anion exchange of effluent
of step 1 using a WBA exchanger, sorption of
acids Concept Treatment of bypass water,
blending with untreated raw water So far No
application
47
Problem of Demineralisation
Service Cycle Regeneration (real) Waste
salt 250 NaCl
48
Attempts between 1963 - 1980

• Application of carbonic acid for regeneration
• Conversion of weakly acidic cation exchangers
  to the free acid form
• Conversion of anion exchangers to the
  bicarbonate form

49
Basic Considerations
Regeneration of Cation Exchanger Regeneration
of Anion Exchanger
50
Key to CARIX Process
Production of Regenerant for Anion
Exchanger Production of Regenerant for Cation
Exchanger Solution Mixed Bed Which Remains
Mixed During Service and Regeneration
51
CARIX Process Principle, Service cycle
Service cycle A elimination of neutral
salts Service cycle B additional
softening/dealkalisation
52
CARIX Process Principle, Regeneration
Regeneration with CO2 (at a pressure of 6
bar) Further regeneration of cation
exchanger Waste salt 100 Excess carbon
dioxide is no salt and can be recovered
53
CARIX Process Technical Realisation
54
Breakthrough PerformanceTotal Hardness and
Alkalinity
55
Breakthrough PerformanceAnions of Strong Acids
56
Properties of the CARIX Process

• Available effective capacities
• 50 of total capacity for weakly acidic
  exchanger
• 20 of total capacity for strongly basic
  exchanger
• Therefore
• No far-reaching demineralisation, only partial
  demineralisation possible
• Large exchanger volumes needed

57
Properties of the CARIX Process

• Further Properties
• Disinfection because of high concentration of CO2
  in the regeneration step
• No product water for regeneration and rinsing
• Only pH adjustment by degassing as post-treatment

58
CARIX Process Plant at Bad Rappenau
59
Existing CARIX Plants
Objective Max. Throughput Reduction of
hardness 170 m³/h, 120 m³/h, sulfate,
nitrate (4) 100 m³/h, 160 m³/h Reduction of
hardness, 260 m³/h, 600 m³/h, sulfate
(4) 250 m³/h, 120 m³/h Reduction of hardness,
160 m³/h nitrate
(1) Reduction of hardness (2) 50 m³/h, 20
m³/h
60
Performance of Mixed Bed Plants
61
Performance of Softening Plants
62
Selective Removal of Heavy Metals Reason

• Application of N-bearing fertilizers in
  agriculture,
• Nitrate penetrates into the underground
• Nitrate oxidises sulphidic inorganic compounds
  (FeS, NiS, ZnS)
• Therefore Occurrence of Ni2, Fe2, Zn2, SO42-
  in groundwater

63
Selective Removal of Heavy Metals Principle 1

• Application of chelating ion exchangers
• Service cycle
• Regeneration

64
Selective Removal of Heavy Metals Scheme
Feed
Indiviual
Column
Column
(Drinking water)
1
2
Dosage
(z.B. Ca
2
,
pH

7
,8
Zn
2
, H

)
c(Ni)
21
µg
/l
c(Ca) 70 mg
/l
Nickel
Resin
Dosage
c(Ni) 100 µg/l
Raw water
Tank
Columns
3
(40 m
)
3 - 22
c(Ni) lt 5 µg/l
Effluent
Courtesy of IWW Mülheim
65
Selective Removal of Nickel Results
Feed
50
Composition
c(Ni) 100 µg/l
45
c(Zn) 30 µg/l
40
c(Ca) 70 mg/l
pH 7,8
35
30
c(Ni) gt 5 µg/L
c(Ni) gt 5 µg/L
c(Ni) gt 5 µg/L
in µg/l
Nickel concentration
25
after 120.000 BV
after 150.000 BV
after 215.000 BV
20
(10 weeks)
(16 weeks)
(35 weeks)
15
10
Criterion of
5
Breakthrough
5 µg/l Ni
0
0
50.000
100.000
150.000
200.000
Throughput, Bed Volumes (BV)
70 BV/h
56 BV/h
36 BV/h
Courtesy of IWW Mülheim
66
Selective Removal of Nickel Commercial Plant
Throughput up to 40 m³/h In service since
9/2004 Regeneration not on site
Courtesy of IWW Mülheim
67
Selective Removal of Heavy Metals Principle 2

• Application of weakly basic anion exchangers
• Me Hg, Cu, Pb, Cd, Zn, Ni, no Ca, Mg
• Regeneration

68
Removal of Heavy Metals, PR ChinaView of Pilot
Plant
Two Filters, 75 L resin each, Vessels for
H2SO4, NaOH Sand filter
69
Selective Removal of Mercury Results of Pilot
Scale Experiments in Haikou / China
Resin Purolite A 947
70
Weakly basic anion exchangers for chromate
removal Principle

• Service cycle
• Regeneration (if needed)

71
Chromate removal Results

• Results of Pilot Scale Experiments in Shenyang /
  PR China

72
Weakly basic anion exchangers for Uranium complex
species Principles

• Application of weakly basic exchangers
• Application of strongly basic exchangers
• No regeneration intended!

73
Weakly basic anion exchangers for Uranium complex
species Pilot test results
74
Removal of Natural Organic Matter (NOM)
Principle Application of SBA resins
(Hannover Fuhrberg, decommisioned)
Application of magnetic micro ion exchangers
75
Application of magnetic micro resins Idea
Problem Often slow exchange kinetics Possible
solution Use of small sorbent particles to
increase the specific contact surface Resulting
Problem No application in conventional
filters Solid-liquid separation
difficult Solution Magnetic micro resins
obtained by adding magnetite or maghemite
during synthesis
76
Magnetic micro resins Properties, handling

• Solid-Liquid Separation

77
Magnetic micro resins Applications

• Removal of NOM from raw waters of the drinking
  water supply by means of strongly basic MIEX
  exchangers (commercialised)
• Removal of heavy metals by means of weakly basic
  MIEX exchangers (pilot scale tests)

78
Magnetic Micro Resins

79
Magnetic micro resins NOM sorption
Courtesy of ORICA Comp.
80
Magnetic micro resins Technical principle
81
Magnetic micro resins Performance
NOM Elimination, Danville, Kentucky, USA

Courtesy of ORICA Comp.
82
Magnetic micro resins Full-Scale Plant
NOM Elimination Plant, 110 m³/h

Courtesy of ORICA Comp.
83
Magnetic micro resins Problems
Problem so far Discharge of NaCl-bearing
wastewater Possible solution Removal of NOM
from spent regenerant by means of
micro/ultrafiltration, under development

84
Arsenic Removal A Worldwide Problem
85
Arsenic Removal A Worldwide Problem
86
Arsenic Removal A Worldwide Problem
Arsenic Situation in Bangladesh
87
Arsenic Removal A Worldwide Problem
88
Arsenic Health Problems Hyperkeratosis

89
Arsenic Removal by Means of Granular Iron
(Hydr)Oxides Products
Available suitable sorbents GFH Granular
Ferric Hydroxide Bayoxide E 33 Granular Ferric
Oxide further products inorganic
(amphoteric) ion exchangers
90
Granular Ferric Hydroxide
91
Granular Iron (hydr)oxides Sorption
Mechanism of elimination Protonation of surface
(below point of zero charge!) Sorption of As
species No Regeneration !
92
Granular Ferric Hydroxide Plants in Germany
Large Plant, 110 m³/h
Small Plant, 14 m³/h
93
Granular Ferric Hydroxide Performance
Treatment capacities as a function of feed pH and
background composition. Limit 10 µg/L
94
GFH Plant in Dare County, North Carolina, USA
95
GFH 10 000 Houshold Devices in West Bengal
GFH
96
Novel Exchanger DevelopmentSOLMETEX-Ion Exchange
Resin
Ion Exchangers Polymeric network (macroporous
polystyrene) with incorporated ferric hydroxide
nanoparticles
97
SOLMETEX-Ion Exchange Resin As Removal
Courtesy of SOLMETEX Comp.
98
SOLMETEX-Ion Exchange Resin As Removal
Courtesy of SOLMETEX
99
Fluoride Problems
100
Fluoride Health Problems Fluorosis
dental Skeletal fluorosis

101
Activated Alumina for Fluoride Elimination
?
Al2O3 3 H2O
2 Al(OH)3
300 to 800 C
102
Mechanism of Fluoride Elimination
Protonation of surface (below point of zero
charge!) S-OH H ?
S-OH2 Sorption of F- ions S-OH2 F-
? S-OH2F-
103
Results of Fluoride Elimination
Main problem Efficient elimination only at pH
6.2
104
Boron Problems
Boron presents health problems at elevated
concentrations. The problems mainly occurs during
seawater desalination for drinking water
production because boric acid partly passes the
reverse osmosis membranes. Solution Application
of boron-specific ion exchangers
105
Mechanism of Borate Removal
Functional groups of resin Methyl
glucamine Application Plant in Israel
Regeneration in two steps i) sulfuric acid, ii)
NaOH
106
Ion Exchange Technology
HIGGINS pseudo-continuous Process
107
Muchas Gracias!Thank you very much for your
attention !