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Arsenic Removal by Coagulation & Precipitation Processes. Presentation Prepared by: Joe Chwirka - Camp Dresser & McKee (chwirkajd@cdm.com) Bruce Thomson - University of New Mexico (bthomson@unm.edu) Presented by: YuJung Chang – HDR Engineering, Inc. Introduction.

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arsenic removal by coagulation precipitation processes

Arsenic Removal by Coagulation & Precipitation Processes

Presentation Prepared by:

Joe Chwirka - Camp Dresser & McKee (chwirkajd@cdm.com)

Bruce Thomson - University of New Mexico (bthomson@unm.edu)

Presented by: YuJung Chang – HDR Engineering, Inc.

Coagulation-Filtration - Chwirka & Thomson

introduction
Introduction
  • Arsenic removal by coagulation & filtration is effective for many applications
  • Presentation will discuss:
    • Chemistry of the process
    • Variables affecting process performance (especially pH & coagulant dose)
    • Process variations
      • Coagulation & granular media filtration
      • Coagulation & membrane filtration
    • Design considerations

Coagulation-Filtration - Chwirka & Thomson

acid base chemistry of as v
Acid-Base Chemistry of As(V)

Coagulation-Filtration - Chwirka & Thomson

acid base chemistry of as iii
Acid-Base Chemistry of As(III)

Coagulation-Filtration - Chwirka & Thomson

redox chemistry of as
Redox Chemistry of As

Coagulation-Filtration - Chwirka & Thomson

solubility of as iii compounds
Solubility of As(III) Compounds

Coagulation-Filtration - Chwirka & Thomson

solubility of as v species
Solubility of As(V) Species

Coagulation-Filtration - Chwirka & Thomson

important points
Important Points
  • As has two oxidation states - As(III) & As(V)
  • As(III)
    • Non-ionic (H3AsO3) at neutral pH
    • High solubility
    • More toxic to many organisms
  • As(V)
    • Ionic (H2AsO4-/HAsO42-) at neutral pH
    • Some phases are less soluble
    • More reactive in solution:
      • Membranes
      • IX
      • Adsorption

Coagulation-Filtration - Chwirka & Thomson

coprecipitation
Coprecipitation
  • Coprecipitation involves removal of two or more constituents by a precipitation reaction. Coprecipitation of As with Fe(OH)3 is an effective treatment process:

FeCl3 + 3H2O = Fe(OH)3(s) + 3H+ + 3Cl-

Points:

    • Produces HCl which will lower pH
    • Typical Fe dose ~10-4 M, whereas As conc. ~10-7 M, hence As is minor component within precipitate
    • As likely removed by adsorption onto Fe(OH)3 surface with subsequent enmeshment as floc particle grows
    • Al(OH)3 also effective

Coagulation-Filtration - Chwirka & Thomson

solubility of fe oh 3
Solubility of Fe(OH)3

Coagulation-Filtration - Chwirka & Thomson

effect of ph on surface charge of fe oh 3
Effect of pH on Surface Charge of Fe(OH)3

Coagulation-Filtration - Chwirka & Thomson

covalent bond formation grossl et al 1997
Covalent Bond Formation(Grossl et al., 1997)

Coagulation-Filtration - Chwirka & Thomson

ph of zero point of charge
pH of Zero Point of Charge
  • Electrostatic attraction is important first step in adsorption
  • pHzpc = pH at which net surface charge = 0
    • Surface is positive at pH < pHzpc
  • Most clay minerals have pHzpc < 6
    • Hence poor adsorption
    • Clays dominate surface chemistry of soils
  • Fe(OH)3 and Al2O3 have relatively high pHzpc
    • Good adsorbents of As(V)

Coagulation-Filtration - Chwirka & Thomson

as removal by conventional treatment mcneill edwards 1997
As Removal by Conventional Treatment (McNeill & Edwards 1997)
  • Survey of conventional coagulation-flocculation water treatment plants
  • Correlate As removal to removal of Fe, Mn, & Al
    • [Fe] = Iron Precip. Formed (mM)

Coagulation-Filtration - Chwirka & Thomson

as removal by conventional trt 2
As Removal by Conventional Trt. - 2

Coagulation-Filtration - Chwirka & Thomson

as removal by conventional trt 3
As Removal by Conventional Trt. - 3
  • Strong correlation to removal of Fe & use of FeCl3 as coagulant
  • Weaker correlation to removal of Al & use of Alum
    • Possible sorption onto colloidal Al(OH)3 which passes through granular media filters
    • Improved As removal achieved by minimizing effluent total Al concentration
  • Note the importance of particulate As

Coagulation-Filtration - Chwirka & Thomson

arsenic removal vs fecl 3 dose albuquerque nm
Arsenic Removal vs FeCl3 Dose, Albuquerque NM

Coagulation-Filtration - Chwirka & Thomson

ambient ph fecl 3 vs as leakage nas fallon
Ambient pH: FeCl3 vs As Leakage, NAS Fallon

Coagulation-Filtration - Chwirka & Thomson

el paso jar testing
El Paso Jar Testing

Coagulation-Filtration - Chwirka & Thomson

ph adjustment with co2 nas fallon nv
pH Adjustment with CO2, NAS Fallon, NV

Coagulation-Filtration - Chwirka & Thomson

silica impacts arsenic removal at ph 7 0 and above
Silica Impacts Arsenic Removal at pH 7.0 and Above

pH 8.5

pH 7.5

pH 6.5

FeCl3 Dose: 4 mg/L

After Clifford and Ghurye

Coagulation-Filtration - Chwirka & Thomson

silica speciation with ph
Silica Speciation with pH

Coagulation-Filtration - Chwirka & Thomson

silica in us water supplies naos
Silica in US Water Supplies (NAOS)

After Davis and Edwards

Coagulation-Filtration - Chwirka & Thomson

polymeric silica
Polymeric Silica

50 mg/L

17 mg/L

5 mg/L

After Davis and Edwards

Coagulation-Filtration - Chwirka & Thomson

coagulation filtration
Coagulation/ Filtration
  • Use pressure filters
  • Direct Filtration frequently used for iron and manganese removal.
  • Limited to low ferric dose applications.
  • High coagulant dose will result in frequent backwash requirements
    • Increased residuals production & handling costs
    • Increased production of wastewater

Coagulation-Filtration - Chwirka & Thomson

schematic of coagulation filtration
Schematic of Coagulation/ Filtration

FeCl3

Pressure Filter

CO2

CO2

Treated Water

Raw Water

Aeration

Rapid Mix

Solids to Dewatering

Solids to Landfill

Coagulation-Filtration - Chwirka & Thomson

calculation of filter loading limitation
Calculation of Filter Loading Limitation
  • Rule of Thumb, no more than 10 mg/L of FeCl3
  • Limit Solids Loading to 0.1 lbs/SF
  • May need to add sedimentation

Coagulation-Filtration - Chwirka & Thomson

vertical pressure filter
Vertical Pressure Filter

Coagulation-Filtration - Chwirka & Thomson

direct filtration performance based on 0 1 lbs solids sf
Direct Filtration Performance(Based on 0.1 lbs Solids/sf)

Coagulation-Filtration - Chwirka & Thomson

backwash water as percent of production based on 250 gal sf
Backwash Water as Percent of Production(Based on 250 gal/sf)

Coagulation-Filtration - Chwirka & Thomson

c f o m issues
C/F O&M Issues
  • Large backwash volume (20 gpm/sf for 10 minutes)
  • Tanks may need internal painting, 10 yr intervals. Use 316 SST.
  • Standby filters, typically provided, but need to evaluate.
  • Pneumatic or electric valve operators.

Coagulation-Filtration - Chwirka & Thomson

coagulation pressure filtration
Coagulation/ Pressure Filtration
  • Particle size
  • Particle breakthrough
  • backwash requirements
  • filter ripening
  • Backup Filters

Coagulation-Filtration - Chwirka & Thomson

coagulation microfiltration
Coagulation/ Microfiltration
  • Pilot tested in Albuquerque, 1998
  • Pilot tested in NAS Fallon, NV, 2001
  • Pilot tested in El Paso, TX, 2001/2002
  • Fallon Paiute Shoshone Tribe: 0.5 mgd
  • City of Albuquerque: 2.3 mgd

Coagulation-Filtration - Chwirka & Thomson

microfiltration general concepts
Microfiltration General Concepts
  • Low Operating Pressure, 5 - 30 psi
  • 0.1 to 0.2 micron pore size
  • Water flow from Outside to the Inside
  • Air-Water Backwash
  • Backwash Every 25 to 30 minutes (95% recovery)
  • Flux rate defined as Gallons/SF/Day (GFD)
  • Chemical Cleaning Frequency > 30 days

Coagulation-Filtration - Chwirka & Thomson

what is c mf
What is C/MF?

FeCl3

CO2

Microfiltration Unit

CO2

Treated Water

Raw Water

Aeration

Rapid Mix

Solids to Dewatering

Solids to Landfill

Coagulation-Filtration - Chwirka & Thomson

pressure driven membranes
Pressure Driven Membranes

0.001µ

0.01µ

0. 1µ

1.0µ

10µ

100µ

1000µ

Sand

Dissolved Organics

Bacteria

Viruses

Cysts

Salts

Colloids

Media Filtration

Microfiltration

Ultrafiltration

Nanofiltration

Reverse Osmosis

Coagulation-Filtration - Chwirka & Thomson

mf process operates in direct filtration mode
MF Process Operates in Direct Filtration Mode

Filtrate

Feed

Feedwater (with contaminants)

Filtrate

Coagulation-Filtration - Chwirka & Thomson

solids are removed from module by an air water backwash
Solids are Removed from Module by an Air-Water Backwash

Air

Feedwater

Air (100 psig)

1

2

3

Coagulation-Filtration - Chwirka & Thomson

coagulation microfiltration39
Coagulation/ Microfiltration
  • Pilot tested in Albuquerque, 1998
  • Pilot tested in NAS Fallon, NV, 2001
  • Pilot tested in El Paso, TX, 2001/2002
  • Fallon Paiute Shoshone Tribe: 0.5 mgd
  • City of Albuquerque: 2.3 mgd

Coagulation-Filtration - Chwirka & Thomson

what is c mf40
What is C/MF?

FeCl3

CO2

Microfiltration Unit

CO2

Treated Water

Raw Water

Aeration

Rapid Mix

Solids to Dewatering

Solids to Landfill

Coagulation-Filtration - Chwirka & Thomson

pressure driven membranes41
Pressure Driven Membranes

0.001µ

0.01µ

0. 1µ

1.0µ

10µ

100µ

1000µ

Sand

Dissolved Organics

Bacteria

Viruses

Cysts

Salts

Colloids

Media Filtration

Microfiltration

Ultrafiltration

Nanofiltration

Reverse Osmosis

Coagulation-Filtration - Chwirka & Thomson

mf process operates in direct filtration mode42
MF Process Operates in Direct Filtration Mode

Filtrate

Feed

Feedwater (with contaminants)

Filtrate

Coagulation-Filtration - Chwirka & Thomson

solids are removed from module by an air water backwash43
Solids are Removed from Module by an Air-Water Backwash

Air

Feedwater

Air (100 psig)

1

2

3

Coagulation-Filtration - Chwirka & Thomson

pall microfilter
Pall Microfilter

Coagulation-Filtration - Chwirka & Thomson

memcor performance nas fallon 15 mg l fecl3
Memcor PerformanceNAS Fallon, 15 mg/L FeCl3

32 GFD

27 GFD

27 GFD

38 GFD

(No FeCl3)

25 GFD (No FeCl3)

Coagulation-Filtration - Chwirka & Thomson

memcor cleaning efficiency nas fallon citric acid
Memcor Cleaning EfficiencyNAS Fallon, Citric Acid

Coagulation-Filtration - Chwirka & Thomson

pall performance nas fallon fecl3 45 mg l
Pall PerformanceNAS Fallon, FeCl3 45 mg/L

Coagulation-Filtration - Chwirka & Thomson

slide48

El Paso C/MF Pilot Studies

Coagulation-Filtration - Chwirka & Thomson

el paso pilot studies
El Paso Pilot Studies
  • Only Pall MF tested
  • Ferric dose 10 mg/L
  • pH lowered to 6.8 with CO2

Coagulation-Filtration - Chwirka & Thomson

el paso pall performance
El Paso Pall Performance

Coagulation-Filtration - Chwirka & Thomson

fallon paiute shoshone tribe c mf pfd
Fallon Paiute Shoshone Tribe C/MF PFD

Coagulation-Filtration - Chwirka & Thomson

fallon paiute shoshone tribe c mf
Fallon Paiute Shoshone Tribe C/MF

Coagulation-Filtration - Chwirka & Thomson

fallon paiute shoshone tribe as treatment faciliy
Fallon Paiute Shoshone Tribe As Treatment Faciliy

Coagulation-Filtration - Chwirka & Thomson

fallon paiute shoshone tribe start up december 2004
Fallon Paiute Shoshone Tribe Start-upDecember 2004

Coagulation-Filtration - Chwirka & Thomson

c mf summary
C/MF Summary
  • Emerging Technology for Arsenic Treatment
  • Can be designed for high flux rates with Low TOC groundwater
  • Optimize solids loading by pH pre-treatment
  • Cost competitive with other technologies

Coagulation-Filtration - Chwirka & Thomson

recent studies on particle size filtration and arsenic removal
Recent Studies on Particle Size Filtration and Arsenic Removal

Coagulation-Filtration - Chwirka & Thomson

c mf o m issues
C/MF O&M Issues
  • Membrane Replacement: Pall warrantees membranes for 10 years, prorated.
  • Chemical cleaning with citric acid, can not be recycled, must be disposed of.
  • Provide sufficient replacement parts, not system redundancy.

Coagulation-Filtration - Chwirka & Thomson

comparison of c mf to pressure filters at the fallon paiute shoshone tribe
Comparison of C/MF to Pressure Filters at the Fallon Paiute Shoshone Tribe

Coagulation-Filtration - Chwirka & Thomson

residuals characteristics for c mf and c f
Residuals Characteristics for C/MF and C/F
  • C/MF around 4% to 5 % Backwash.
  • C/F around 5% to 10% Backwash.
  • Recycle the backwash water to minimize wastewater.
  • Ferric residuals will pass TCLP, however, may not pass the Cal WET.

Coagulation-Filtration - Chwirka & Thomson

residuals handling
Residuals Handling
  • Mechanical dewatering will be complicated: Ferric sludge is difficult to dewater
  • Need body additives, Diatomaceous Earth
  • Filter Bottom Dumpsters and polymer for small applications.
  • Solids drying ponds:
    • Ponds need to be lined.
    • Anaerobic conditions may release the As.
    • Provide access for sludge removal equipment.

Coagulation-Filtration - Chwirka & Thomson

concurrent iron manganese and arsenic drinking water standards
Concurrent Iron, Manganese, and ArsenicDrinking Water Standards
  • Fe: Secondary Standard of 0.30 mg/L
  • Mn: Secondary Standard of 0.05 mg/L

Coagulation-Filtration - Chwirka & Thomson

iron and arsenic removal
Iron and Arsenic Removal
  • Oxidize Fe with Cl2 or O3
  • Adsorb As onto Fe(OH)3 precipitate
  • pH needs to be around 7.3

Coagulation-Filtration - Chwirka & Thomson

manganese and arsenic removal
Manganese and Arsenic Removal
  • As requires low pH for adsorption
  • Mn requires high pH (>10) for oxidation with Cl2
  • Mn oxidation by ClO2 is rapid & appears to be independent of pH
    • ClO2 reported to be ineffective for As(III) oxidation.
    • May need to add Cl2 in addition

Coagulation-Filtration - Chwirka & Thomson