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Coagulation-Filtration - Chwirka & Thomson 1 Arsenic Removal by Coagulation & Precipitation Processes Presentation Prepared by: Joe Chwirka - Camp Dresser.

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Presentation on theme: "Coagulation-Filtration - Chwirka & Thomson 1 Arsenic Removal by Coagulation & Precipitation Processes Presentation Prepared by: Joe Chwirka - Camp Dresser."— Presentation transcript:

1 Coagulation-Filtration - Chwirka & Thomson 1 Arsenic Removal by Coagulation & Precipitation Processes Presentation Prepared by: Joe Chwirka - Camp Dresser & McKee Bruce Thomson - University of New Mexico Presented by: YuJung Chang – HDR Engineering, Inc.

2 Coagulation-Filtration - Chwirka & Thomson 2 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

3 Coagulation-Filtration - Chwirka & Thomson 3 Acid-Base Chemistry of As(V)

4 Coagulation-Filtration - Chwirka & Thomson 4 Acid-Base Chemistry of As(III)

5 Coagulation-Filtration - Chwirka & Thomson 5 Redox Chemistry of As

6 Coagulation-Filtration - Chwirka & Thomson 6 Solubility of As(III) Compounds

7 Coagulation-Filtration - Chwirka & Thomson 7 Solubility of As(V) Species

8 Coagulation-Filtration - Chwirka & Thomson 8 Important Points As has two oxidation states - As(III) & As(V) As(III) Non-ionic (H 3 AsO 3 ) at neutral pH High solubility More toxic to many organisms As(V) Ionic (H 2 AsO 4 - /HAsO 4 2- ) at neutral pH Some phases are less soluble More reactive in solution: Membranes IX Adsorption

9 Coagulation-Filtration - Chwirka & Thomson 9 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: FeCl 3 + 3H 2 O = 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

10 Coagulation-Filtration - Chwirka & Thomson 10 Solubility of Fe(OH) 3

11 Coagulation-Filtration - Chwirka & Thomson 11 Effect of pH on Surface Charge of Fe(OH) 3

12 Coagulation-Filtration - Chwirka & Thomson 12 Covalent Bond Formation (Grossl et al., 1997)

13 Coagulation-Filtration - Chwirka & Thomson 13 pH of Zero Point of Charge Electrostatic attraction is important first step in adsorption pH zpc = pH at which net surface charge = 0 Surface is positive at pH < pH zpc Most clay minerals have pH zpc < 6 Hence poor adsorption Clays dominate surface chemistry of soils Fe(OH) 3 and Al 2 O 3 have relatively high pH zpc Good adsorbents of As(V)

14 Coagulation-Filtration - Chwirka & Thomson 14 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)

15 Coagulation-Filtration - Chwirka & Thomson 15 As Removal by Conventional Trt. - 2

16 Coagulation-Filtration - Chwirka & Thomson 16 As Removal by Conventional Trt. - 3 Strong correlation to removal of Fe & use of FeCl 3 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

17 Coagulation-Filtration - Chwirka & Thomson 17 Arsenic Removal vs FeCl 3 Dose, Albuquerque NM

18 Coagulation-Filtration - Chwirka & Thomson 18 Ambient pH: FeCl 3 vs As Leakage, NAS Fallon

19 Coagulation-Filtration - Chwirka & Thomson 19 El Paso Jar Testing

20 Coagulation-Filtration - Chwirka & Thomson 20 pH Adjustment with CO2, NAS Fallon, NV

21 Coagulation-Filtration - Chwirka & Thomson 21 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

22 Coagulation-Filtration - Chwirka & Thomson 22 Silica Speciation with pH

23 Coagulation-Filtration - Chwirka & Thomson 23 Silica in US Water Supplies (NAOS) After Davis and Edwards

24 Coagulation-Filtration - Chwirka & Thomson 24 Polymeric Silica After Davis and Edwards 50 mg/L 17 mg/L 5 mg/L

25 Coagulation-Filtration - Chwirka & Thomson 25 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

26 Coagulation-Filtration - Chwirka & Thomson 26 Schematic of Coagulation/ Filtration Aeration FeCl3 Rapid Mix Solids to Dewatering Treated Water Pressure Filter Solids to Landfill Raw Water CO 2

27 Coagulation-Filtration - Chwirka & Thomson 27 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

28 Coagulation-Filtration - Chwirka & Thomson 28 Vertical Pressure Filter

29 Coagulation-Filtration - Chwirka & Thomson 29 Direct Filtration Performance (Based on 0.1 lbs Solids/sf)

30 Coagulation-Filtration - Chwirka & Thomson 30 Backwash Water as Percent of Production (Based on 250 gal/sf)

31 Coagulation-Filtration - Chwirka & Thomson 31 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.

32 Coagulation-Filtration - Chwirka & Thomson 32 Coagulation/ Pressure Filtration Particle size Particle breakthrough backwash requirements filter ripening Backup Filters

33 Coagulation-Filtration - Chwirka & Thomson 33 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

34 Coagulation-Filtration - Chwirka & Thomson 34 Microfiltration General Concepts Low Operating Pressure, 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

35 Coagulation-Filtration - Chwirka & Thomson 35 What is C/MF? Aeration FeCl3 Rapid Mix Solids to Dewatering Treated Water Microfiltration Unit Solids to Landfill Raw Water CO 2

36 Coagulation-Filtration - Chwirka & Thomson 36 Pressure Driven Membranes0.001µ0.01µ 0. 1µ 1.0µ10µ100µ1000µ Dissolved Organics Bacteria Sand Cysts Viruses SaltsColloids Media Filtration Microfiltration Ultrafiltration Nanofiltration Reverse Osmosis

37 Coagulation-Filtration - Chwirka & Thomson 37 MF Process Operates in Direct Filtration ModeFeed Filtrate Feedwater (with contaminants) Filtrate

38 Coagulation-Filtration - Chwirka & Thomson 38 Solids are Removed from Module by an Air-Water Backwash Air (100 psig) Air Feedwater 123

39 Coagulation-Filtration - Chwirka & Thomson 39 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

40 Coagulation-Filtration - Chwirka & Thomson 40 Microfiltration General Concepts Low Operating Pressure, 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

41 Coagulation-Filtration - Chwirka & Thomson 41 What is C/MF? Aeration FeCl3 Rapid Mix Solids to Dewatering Treated Water Microfiltration Unit Solids to Landfill Raw Water CO 2

42 Coagulation-Filtration - Chwirka & Thomson 42 Pressure Driven Membranes0.001µ0.01µ 0. 1µ 1.0µ10µ100µ1000µ Dissolved Organics Bacteria Sand Cysts Viruses SaltsColloids Media Filtration Microfiltration Ultrafiltration Nanofiltration Reverse Osmosis

43 Coagulation-Filtration - Chwirka & Thomson 43 MF Process Operates in Direct Filtration ModeFeed Filtrate Feedwater (with contaminants) Filtrate

44 Coagulation-Filtration - Chwirka & Thomson 44 Solids are Removed from Module by an Air-Water Backwash Air (100 psig) Air Feedwater 123

45 Coagulation-Filtration - Chwirka & Thomson 45 Pall Microfilter

46 Coagulation-Filtration - Chwirka & Thomson 46 Memcor Performance NAS Fallon, 15 mg/L FeCl3 25 GFD (No FeCl3) 27 GFD 38 GFD (No FeCl3) 32 GFD 27 GFD

47 Coagulation-Filtration - Chwirka & Thomson 47 Memcor Cleaning Efficiency NAS Fallon, Citric Acid

48 Coagulation-Filtration - Chwirka & Thomson 48 Pall Performance NAS Fallon, FeCl3 45 mg/L

49 Coagulation-Filtration - Chwirka & Thomson 49 El Paso C/MF Pilot Studies

50 Coagulation-Filtration - Chwirka & Thomson 50 El Paso Pilot Studies Only Pall MF tested Ferric dose 10 mg/L pH lowered to 6.8 with CO2

51 Coagulation-Filtration - Chwirka & Thomson 51 El Paso Pall Performance

52 Coagulation-Filtration - Chwirka & Thomson 52 Fallon Paiute Shoshone Tribe C/MF PFD

53 Coagulation-Filtration - Chwirka & Thomson 53 Fallon Paiute Shoshone Tribe C/MF

54 Coagulation-Filtration - Chwirka & Thomson 54 Fallon Paiute Shoshone Tribe As Treatment Faciliy

55 Coagulation-Filtration - Chwirka & Thomson 55 Fallon Paiute Shoshone Tribe Start-up December 2004

56 Coagulation-Filtration - Chwirka & Thomson 56 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

57 Coagulation-Filtration - Chwirka & Thomson 57 Recent Studies on Particle Size Filtration and Arsenic Removal

58 Coagulation-Filtration - Chwirka & Thomson 58 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.

59 Coagulation-Filtration - Chwirka & Thomson 59 Comparison of C/MF to Pressure Filters at the Fallon Paiute Shoshone Tribe

60 Coagulation-Filtration - Chwirka & Thomson 60 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.

61 Coagulation-Filtration - Chwirka & Thomson 61 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.

62 Coagulation-Filtration - Chwirka & Thomson 62 Concurrent Iron, Manganese, and Arsenic Drinking Water Standards Fe: Secondary Standard of 0.30 mg/L Mn: Secondary Standard of 0.05 mg/L

63 Coagulation-Filtration - Chwirka & Thomson 63 Iron and Arsenic Removal Oxidize Fe with Cl 2 or O 3 Adsorb As onto Fe(OH) 3 precipitate pH needs to be around 7.3

64 Coagulation-Filtration - Chwirka & Thomson 64 Manganese and Arsenic Removal As requires low pH for adsorption Mn requires high pH (>10) for oxidation with Cl 2 Mn oxidation by ClO 2 is rapid & appears to be independent of pH ClO 2 reported to be ineffective for As(III) oxidation. May need to add Cl 2 in addition


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