Removal of Arsenic from Drinking Water

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Removal of Arsenic from Drinking Water by
Nanofiltration

Zdravka Lazarova Austrian Research Centers GmbH
ARC Department WATER
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• Outline
• Pressure-Driven Membrane Processes
• Nanofiltration Main Characteristics
• Experimental Results on NF of As(III) and
  As(V)
• Comparison NF90, NF200, NF270
• Effect of Process Parameters
• pressure difference
• arsenic concentration
• pH value of feed
• Conclusions

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• Arsenic Removal Technologies for Drinking Water
  Treatment
• VIABLE TREATMENT TECHNOLOGIES
• Coagulation Precipitation
• Adsorption
• Ion Exchange
• Oxidation
• Biological Techniques
• MEMBRANE SEPARATIONS

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• Arsenic Removal Technologies for Drinking Water
  Treatment
• Best Available Technologies (BAT) for Arsenic
  removal ?
• USEPA suggested for As(V)
• Ion exchange
• Activated alumina
• Reverse osmosis
• Coagulation/filtration
• Lime softening

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• Arsenic Removal Technologies for Drinking Water
  Treatment
• Technologies with increasing importance !
• Granular Ferric Hydroxide (GFH)
• Iron-based Coagulation/Microfiltration
• Iron Oxide-Coated Sand
• NANOFILTRATION

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Pressure-Driven Membrane Processes

COMPARISON MF - UF NF- RO
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Source adapted from http//www.kochmembrane.com
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NF - Process Characteristics

• Performance characteristics between RO and UF
• Essentially lower pressure than RO (P 0.5-6
  MPa)
• Removes molecules in the 0.001 µm range (MWCO
  0.2 to 200)
• Applications water softening, removing of
  organic matter, desalting of organic reaction
  products, removal of nitrates, removal of metal
  ions

Source adapter from http//www.kochmembrane.com
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Membrane Process Applied for Large-Scale
Cross-Flow Membrane Filtration
R(C)
RETENTATE (As-Concentrate)
Feed
?p
PERMEATE (pure water)
P
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• SOLUTION CHEMISTRY
• pH
• As-concentration
• As-species
• Ionic strength
• Co-solutes

• FUNCTIONAL PHYSICAL PARAMETERS
• Pressure
• Temperature
• Flow Rate (cross-flow velocity)
• Recovery

• MEMBRANE CHARACTERISTICS
• Porosity/MWCO
• Charge
• Salt separation ability
• Hydrophilicity
• Fouling

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EXPERIMENTS

COMPARISON performance of NF90, NF200, NF270 for
removal of As(III) and As(V) from drinking water

• Effect of pressure difference
• Effect of pH
• Effect of As-concentration

FilmTec TM NF Membranes, Dow, USA
Membrane name Description Salt Rejection Permeability (Lmh/bar) Zeta Potential (mV)
NF270 loose NF 40-60 13 -5 to -16
NF90 tight NF 85-95 6.7 -15 to -30
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Membrane Test Unit AMAFILTER
Flow Rate 100- 1000 L/h Pressure 0-60
bar Membrane contact surface 63,5 cm2
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Comparison NF270-NF200-NF90 permeate flux as a
function of pressure difference
As(V)- As(III) at 400 L/h pH 8
As100µg/LT25C
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Comparison NF270-NF200-NF90 As-retention as a
function of pressure difference
As(V)- As(III) at 400 L/h pH8
As100µg/LT25C
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As(V) -retention as a function of
As-concentration in feedMEMBRANES NF-90
NF-270 (T)
Q 400 L/h pH 8 pressure 5 bar T25C
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As(III) -retention as a function of
As-concentration in feedMEMBRANES NF-90
NF-270 (T)
Q 400 L/h pH 8 pressure 5 bar T25C
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As- Retention/Flux as a function of pH-value
MEMBRANES NF-90
Q 400 L/h pH 8 pressure 5 bar T25C
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COMPARISON As(V)- Sb(V)

20 bar
15 bar
20 bar
10 bar
15 bar
5 bar
10 bar
5 bar
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CONCLUSIONS

• COMPARISON NF-MEMBRANES NF-90, NF-200, NF270
• Membrane performance depends on arsenic forms
  (As(III) As(V)) and experimental conditions
  (feed concentration, pH, ionic strength?, feed
  matrix (co-ions )?
• Arsenic retention efficiency follows the order
  NF90gtNF200gtNF270
• Removal of As(V) is substantially higher not
  sensitive to pressure changes (96-99 at 5-20
  bar)
• Effect of feed concentration on As- rejection
  depends on the membrane type
• As(III) treatment is more sensitive to the
  pH-value of the feed
• Pilot experiments are needed for process
  optimisation

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Electrochemical Oxidation of As-containing waters
FLOW SHEET DIAGRAMM
H2O
-e-
H OH-

• ORGANIK

As(III)
mobile electrochemical plant
As(V)
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Austrian Research Centers GmbH -ARC

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